Industrial Ethernet Technologies, August 2011 - IEA

Industrial Ethernet Technologies, August 2011 - IEA
Industrial Ethernet Technologies
Page 1
© EtherCAT Technology Group, August 2011
Industrial Ethernet Technologies: Overview
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Editorial Preface:
This presentation intends to provide an overview over the most important
Industrial Ethernet Technologies. Based on published material it shows
the technical principles of the various approaches and tries to put these
into perspective.
The content given represents my best knowledge of the systems
introduced. Since the company I work for is member of all relevant
fieldbus organizations and supports all important open fieldbus and
Ethernet standards, you can assume a certain level of background
information, too.
The slides were shown on ETG Industrial Ethernet Seminar Series in
Europe, Asia and North America as well as on several other occasions,
altogether attended by several thousand people. Among those were
project engineers and developers that have implemented and/or applied
Industrial Ethernet technologies as well as key representatives of some of
the supporting vendor organizations. All of them have been encouraged
and invited to provide feedback in case they disagree with statements
given or have better, newer or more precise information about the
systems introduced. All the feedback received so far was included in the
slides.
You are invited to do the same: provide feedback and – if necessary –
correction. Please help to serve the purpose of this slide set: a fair and
technology driven comparison of Industrial Ethernet Technologies.
Nuremberg, August 2011
Martin Rostan, [email protected]
Industrial Ethernet Technologies
Page 2
© EtherCAT Technology Group, August 2011
Industrial Ethernet Technologies: Overview
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
All Industrial Ethernet Technologies introduced in this presentation are
supported by user and vendor organizations. EPSG and ETG are pure
Industrial Ethernet organizations, whilst the others have a fieldbus
background and thus members primarily interested in the respective
fieldbus technology.
All technology names as well as the names of the organizations promoting
and supporting those are trademarked. The trademarks are honored.
Page 3
© EtherCAT Technology Group, August 2011
Basic Slave Device Approaches
Classification
Profinet
ITApplics
Principle applied by:
Ethernet/IP
• SNMP
(CbA)
Sercos III
• DHCP
Layer 5..7
•…
Hardware
Modbus/TCP
and Real-Time Data
Automation API
TCP/UDP
Layer 4
Powerlink
Application
Parameter-Data
• HTTP
Software
CC-Link IE
A
• Completely TCP/UDP/IP based
• Ordinary Ethernet Controllers and Switches
Layer 3
IP
Layer 1+2
Ordinary Ethernet Controller
Slave Device Architecture
Industrial Ethernet Technologies
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Depending on the real time and cost requirements, the technologies follow
different principles or approaches. This comparison tries to group those
approaches in three different classes by looking at the slave device
implementations:
Class A uses standard, unmodified Ethernet hardware as well as standard
TCP/IP software stacks for process communication. Of course some
implementations may have modified „tuned“ TCP/IP stacks, which provide
better performance.
Class A approaches are also referred to as „best effort“ approaches. The
real time performance is limited by unpredictable delays in infrastructure
components like switches – no just due to other traffic on the network. The
by far largest obstacle to better real time performance however is provided
by the software stacks (TCP/UDP/IP).
Page 4
© EtherCAT Technology Group, August 2011
Basic Slave Device Approaches
Classification
Profinet
• Process Data: Parallel Channel to TCP/UDP/IP
• TCP/UDP/IP Timing Controlled by Process Data Driver
• Ordinary Ethernet Controllers and Switches (or Hubs)
ITApplics
CC-Link IE
(RT)
Software
Ethernet/IP
Sercos III
Application
• HTTP
Parameter
Process
• SNMP
Data
Data
• DHCP
Layer 5..7
Layer 4
Automation API
•…
TCP/UDP
IP
Powerlink
Hardware
Layer 3
Modbus/TCP
Layer 1+2
B
Process Data
Protocol
Timing-Layer
Ordinary Ethernet Controller
Slave Device Architecture
Industrial Ethernet Technologies
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Class B approaches still use standard, unmodified hardware, but do not
use TCP/IP for process data communication. A dedicated process data
protocol is introduced, which is transported directly in the Ethernet frame.
TCP/IP stacks may still exist, but typically their access to the Ethernet
network is controlled and limited by what can be considered a timing layer.
Of course this description is pretty generic – but more details are given in
the technology specific sections.
Page 5
© EtherCAT Technology Group, August 2011
Basic Slave Device Approaches
Classification
Profinet
• Process Data: Parallel Channel to TCP/UDP/IP
• TCP/UDP/IP Timing Controlled by Process Data Driver
• Special Realtime Ethernet Controllers or Switches
ITApplics
CC-Link IE
(IRT)
Software
Ethernet/IP
Sercos III
Application
• HTTP
Parameter
Process
• SNMP
Data
Data
• DHCP
Layer 5..7
Layer 4
Automation API
•…
TCP/UDP
IP
Powerlink
Hardware
Layer 3
Modbus/TCP
Layer 1+2
C
Process Data
Protocol
Timing-Layer
Special Realtime Ethernet
Controller
Slave Device Architecture
Industrial Ethernet Technologies
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Class C approaches aim even higher with regard to performance. In order
to achieve these goals, dedicated hardware has to be used (at least on
the slave device side).
In case of Profinet IRT, the Special Real-time Ethernet Controller is more
a Special Switch Device – but the result is the same: better performance
due to better hardware integration.
This does not exclude the use of TCP/IP and the Internet Technologies.
Industrial Ethernet Technologies
Page 6
© EtherCAT Technology Group, August 2011
PROFINET Overview
Classification
Profinet
PROFINET – PI / Siemens Ethernet Solution
Three different varieties:
Version 1 (2001)
CbA:
Ethernet/IP
A
„Component based
Automation“
Version 2 (2004)
RT:
Version 3 (2005)
B
Soft Real Time
(Software Based)
CC-Link IE
IRT:
C
Isochronous Real
Time
(Hardware Based)
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
Pictures sourced from PTO/PNO website
© EtherCAT Technology Group
There are 3 PROFINET-Versions:
Version 1 („Component Based Automation“), a Class A approach
Version 2 ((Soft) Real Time“), a Class B approach
Version 3: („Isochronous Real Time“), a Class C approach
Profibus International (PI) tries to move away from the terms RT/IRT and
introduced the term Profinet IO for both RT and IRT…
Industrial Ethernet Technologies
Page 7
© EtherCAT Technology Group, August 2011
PROFINET Performance
Classification
Profinet
Communication cycle time + Jitter
PROFInet PROFInet
V3.0 (IRT) V2.0 (SRT)
PROFInet
V1.2 (TCP/ IP)
Ethernet/IP
CC-Link IE
C
B
A
Sercos III
Powerlink
15%
Modbus/TCP
EtherCAT
0,25...1,0
msec
10
msec*
100%
t
100
msec
* Depending on configuration, 1 ms has been demonstrated
Summary
Pictures sourced from PI website
© EtherCAT Technology Group
Not all IRT devices support cycle times < 0.5 ms, e.g. Siemens Sinamics
Controller.
Industrial Ethernet Technologies
Page 8
© EtherCAT Technology Group, August 2011
PROFINET V1 (CbA)
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
• Initial Profibus Answer to the Ethernet Hype: Profinet V1
• Remote Procedure Calls on TCP/IP originally
using DCOM
• Access to Profibus Networks via Proxy Devices
• For Parameter Data only, not for Process Data
• since DCOM will not be advanced by Microsoft any more,
Profinet CbA V2 has SRT Protocol Adaptation
• few known Products.
Engineering,
HMI
Internet
Powerlink
Modbus/TCP
EtherCAT
A
Automation
device
Engineering,
HMI
TCP/IP- Ethernet
Intelligent
field device
Proxy
PROFIBUS
Intelligent
drive
Summary
Pictures sourced from PI website
Automation
device
Field device
Drive
© EtherCAT Technology Group
Initially the PNO/PTO message was: protect your investment and continue
using Profibus, for Ethernet connectivity we provide a transparent
gateway.
Work on the gateway (proxy) concept was started as early as 1999. First
spec (V0.9) published in March 2001 (Ethernet/IP was first introduced in
2000).
Industrial Ethernet Technologies
Page 9
© EtherCAT Technology Group, August 2011
Component Based Programming Approach
Engineering Interface
Classification
Data Interface
Profinet
Information
Ethernet/IP
Vendor A
Bottle Cleaning
Vendor B
Filling
CC-Link IE
PROFIBUS
• PROFINET CbA
comprises more than just
the communication
• Approach may be fine for
50 variables, but how do
you handle 500 variables
this way?
PROFIBUS
PROFInet Connection Editor
Sercos III
Powerlink
Modbus/TCP
Bottle Cleaning
Filling
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Pictures sourced from PI website
Profinet CbA (Component Based Automation) comprises more than just a
communication protocol: the CbA programming approach with graphical
mapping of variables to establish communication links.
Industrial Ethernet Technologies
Page 10
© EtherCAT Technology Group, August 2011
PROFINET V2 (RT)
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Originally named „Soft Realtime“ (SRT)
B
„Best Effort“ Protocol with 5 .. 10 ms typical cycle time and 15% jitter
Modified Stack bypasses TCP and IP for Realtime-(process)data
Aimed at and suited for PLC type applications (including drive
control, but not motion control)
• Requires substantial amount of software (Field device: ~ 1MByte)
Limitations:
• Soft Realtime Solution
with
•
•
•
•
– Influence by TCP traffic
– Inpredictable Queue
delays in switches
– Stack delays
• Standard Controllers are
sensitive for IP Multicast
Traffic
Summary
Pictures sourced from PI website
© EtherCAT Technology Group
Industrial Ethernet Technologies
Profinet V2 was initially called SRT (Soft Real-time). The term „soft“ was
later dropped for marketing reasons.
Profinet RT is also addressed as Profinet I/O (together with IRT).
Siemens has started to communicate that Profinet RT will provide similar
performance as Profibus. Even though this is optimistic (typically Profibus
is faster and provides better node synchronization), one can read this
statement as follows:
If Profibus performance is sufficient, but Profibus is not expensive enough,
Profinet RT is an alternative ;-)
Industrial Ethernet Technologies
Page 11
© EtherCAT Technology Group, August 2011
PROFINET V2 (RT) and V3 (IRT)
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
V2 Real-Time (RT)
• Software Solution with Standard Controller
• Usage of Standard Network Components
• Real-Time as good as provided by
– Switching Technology
– VLAN-Tagging (Prioritization, IEEE802.1q)
V3 Isochronous Real-Time (IRT)
• Synchronization of all nodes
• Bandwidth reservation for
isochronous Data
• Requires Special Hardware ASIC
B
C
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Profinet IRT is a class C approach which introduces special hardware in
order to achieve sufficient performance and synchronicity for motion
control applications.
Industrial Ethernet Technologies
Page 12
© EtherCAT Technology Group, August 2011
PROFINET V3 (IRT) Features
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
•
•
•
•
Timeslicing Approach by special Switch ASICs
C
Switches can be integrated into devices
Topologies: Line (up to 25 nodes), Branch, Tree supported
Cycle Time 250 µs to 4 ms, 1 µs jitter
IRTchannel
(TCP/IP)
Cycle 1
IRTchannel
(TCP/IP)
Cycle 2
Cycle n
Powerlink
e.g. 1 ms position control loop
Modbus/TCP
EtherCAT
Synchronization
Deterministic communication
IRT- Data
Summary
open communication
TCP/IP- Data
Pictures sourced from PI website
© EtherCAT Technology Group
Industrial Ethernet Technologies
The minimum cycle time is determined by the approach to include generic
TCP/IP traffic in a gap wide enough for the largest Ethernet frame.
This approach leads to limited bandwidth utilization, since even though
most applications only have sporadic TCP/IP communication, the
bandwidth remains reserved for this kind of traffic.
Even though the specification allows for cycle times starting from 250µs,
some Siemens IRT master devices only support cycle times starting from
500 µs.
Industrial Ethernet Technologies
Page 13
© EtherCAT Technology Group, August 2011
PROFINET V2 (RT) and V3 (IRT)
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Both versions can be mixed, if
• supported by master
• only IRT switches are used
• enough bandwidth available
IRT
channel
Standard
channel
Cycle 1
IRT
channel
Standard
channel
IRT
channel
Cycle 2
= time window
Cycle 1
e.g. 2 ms position control loop
Powerlink
isochronous
communication
Modbus/TCP
RT
communication
Standard
communication
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
In principle both varieties (RT+IRT) can be mixed. Since IRT switches
have to be used then, one can say:
RT devices can be integrated in IRT networks, if there is sufficient
bandwidth and if the master supports this.
Siemens recommends in the current System Manual* to position the RT
devices at the end of the Profinet system, outside of the IRT sync domain.
Synchronization between the RT and IRT devices is not possible (“if you
want to synchronize with IRT, the respective Profinet devices must
support IRT communication”).
* Source: Siemens Profinet System Description, page 153, “Setting up Profinet with IRT”, 07/2010, A5E00298288-05
Industrial Ethernet Technologies
Page 14
© EtherCAT Technology Group, August 2011
PROFINET IRT System Planning (I)
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Input for planning/configuration of the network:
• the topology of the network
• For every connected port of every device in the IRT network
the partner port has to be configured – configuring the cable
length or signal delay time is also recommended for better
results
• and for every transmission the optimization algorithm needs:
• the source- and the target node,
• the amount of transmission data,
• projected features of the connection path (e.g. Redundancy)
Output of the projection for every transmission and device
respective switch:
• Ports and exact transfer time timing for each frame
Summary
© EtherCAT Technology Group
Besides hardware costs, the crucial issue of Profinet IRT is the complex
system planning.
Industrial Ethernet Technologies
Page 15
© EtherCAT Technology Group, August 2011
PROFINET IRT System Planning (II)
Classification
Profinet
Ethernet/IP
CC-Link IE
• Complex recursive optimization problem
• Configuration and System Planning is a process
executed by a central Algorithm in the Engineering
System.
• Small change in input (e.g. one more node) may lead to
big change in output (cycle time and thus performance),
due to unpredictable behavior of optimization algorithm
Sercos III
Powerlink
Modbus/TCP
Strong interdependency between topology and
performance
EtherCAT
Summary
© EtherCAT Technology Group
For each node all communication relationships have to be known and
scheduled. Of course there are strong interdependencies between the
schedules. Therefore the system planning is a complex recursive
optimization problem without a straightforward solution – even with fairly
simple topologies.
Due to the complex nature of this problem the optimization algorithm may
come up and be satisfied with a relative rather than the absolute optimum
– which means, that a small change in the configuration (e.g. adding just
one more node) may result in large changes in the network performance.
The algorithm was developed by Prof. Dr. Ulrich Lauther and has 23.000
lines of code, according to Siemens. A license for the planning algorithm
(in dll format) can meanwhile be obtained by PI members – it remains a
black box algorithm, however.
Industrial Ethernet Technologies
Page 16
© EtherCAT Technology Group, August 2011
PROFINET IRT Performance
Classification
Published…
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
but…
Modbus/TCP
EtherCAT
Valid for a network CLUSTER
(4 networks) only, not for a single network…
Summary
Pictures sourced from PI website
© EtherCAT Technology Group
For several years, this was the performance data table published for
Profinet IRT. However, the table is valid only for a cluster of networks: 150
nodes sharing 50% bandwidth at 1ms cycle time means 500 µs / 150 =
3,33 µs per node. The shortest Ethernet frame takes 7µs to transmit.
This is not to state that Profinet IRT was not fast enough for most
applications...
Industrial Ethernet Technologies
Page 17
© EtherCAT Technology Group, August 2011
IRT Topology – and some conclusions
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
• Line, Branch, Tree
Topology is supported
• Cascading of switches in a line has limit of 20 - 25 devices
• → this means: branch/star topology is the common design,
whether desired or not
• For any installation with more than 20 - 25 devices, network
branches are required
• The network topology layout requires a top-down approach
• The planning process will mandate the layout and wiring of a
configuration
• performance data is true for a specific topology ONLY
• Topology restrictions apply when designing a network
with a required performance
Summary
Pictures sourced from PI website
© EtherCAT Technology Group
The non-linear and even unpredictable interdependency between topology
and performance may require several iterations (or „try and error“ steps)
when designing a network layout for a required performance.
Industrial Ethernet Technologies
Page 18
© EtherCAT Technology Group, August 2011
Profinet IRT, RT, IO + RT Classes
B
Classification
Profinet
Ethernet/IP
Software based Profinet
(Profinet RT)
Sercos III
Powerlink
Soft Real Time
Modbus/TCP
Hardware assisted Profinet
(Profinet IRT)
RT Class 1
Best effort approach
based on
standard network
components:
CC-Link IE
C
RT Class 2
RT Class 3
time slicing without
topology planning:
Soft Real Time with
Hardware Support
PLC Type Applications
with topology oriented
network planning +
defined timing for
each connection path:
Hard Real Time
Motion Applications
All variants are called
EtherCAT
Profinet IO
Summary
© EtherCAT Technology Group
In order to avoid the complex topology network planning process, an
intermediate approach had been introduced: RT Class 2 (within Siemens
also called IRT “Flex” or “IRT with high flexibility”) using Profinet chips
(e.g. ERTEC). High priority network traffic is sent in the IRT time slice, but
without predefined timing for each connection. Low priority communication
is handled in the NRT time slice. Profinet chips have to be used
throughout. Cyclic behavior can be achieved if the network load is low and
the application tasks are synchronized with the communication cycle. The
downside is that there is unused bandwidth that is exclusively reserved
and cannot be used for other communication.
IRT Flex was intended as a simplified Profinet IRT variety for PLC type
applications that utilize ERTEC profinet chips (Siemens Simatic S7).
However, due to incompatibility issues, IRT Flex is not promoted or
recommended by Siemens any more.
RT Class 3 (also called IRT “TOP” or “IRT with high performance”) is the
variant formerly referred to as Profinet IRT. This approach provides hard
real time behavior but requires the detailed network planning (topology
editor) and the optimization algorithm: the topological information from the
configuration is used for planning the communication. Siemens is adopting
this variant for PLCs as well.
PTO/PNO generally downplays the differences between the Profinet
variants, summarizing all of them with the term “Profinet IO”.
Industrial Ethernet Technologies
Page 19
© EtherCAT Technology Group, August 2011
Profinet Conformance Classes
Classification
B Software based Profinet
(Profinet RT)
Profinet
Ethernet/IP
CC-Link IE
RT Class 1
Best effort approach
based on
standard network
components:
Soft Real Time
C Hardware assisted Profinet
(Profinet IRT)
RT Class 2
time slicing without
topology planning:
RT Class 3
with topology oriented
network planning +
defined timing for
Soft Real Time with each connection path:
Hardware Support
Hard Real Time
Sercos III
Conformance
Class A
Conformance
Class B
Conformance
Class C
Powerlink
with Topology
Recognition
with LLDP
(no SNMP)
MRP optional
with
Topology
Recognition
(SNMP, LLDP-MIB)
MRRT optional
with Topology Recognition
(SNMP, LLDP-MIB)
CutThrough Switch Behavior Mandatory
4 Priorities Mandatory
MRPD mandatory
Modbus/TCP
EtherCAT
PLC Type Applications
All variants are called Profinet
Summary
Motion Applications
IO
© EtherCAT Technology Group
In addition to the RT classes, Profinet has introduced (see IEC 61784-2)
Application Classes (Isochronous for motion control, Non-isochronous
for factory process + building automation),
Redundancy Classes (MRP: Media redundancy protocol; MRRT: Media
redundancy for real-time (dropped in Profinet V2.3); MRPD: media
redundancy for planned duplication) and
Conformance Classes. The Conformance Classes predominantly define
the support for the topology recognition features. Redundancy Classes
and Conformance Classes are interlinked.
Topology Recognition originally was required for Conformance Class B +
C, only; meanwhile this is required for Conformance Class A (but without
LLDP-MIB).
It was found that there are issues when using unmanaged switches with
Profinet Class A (in B managed switches are mandatory): common COTS
switch chips forward LLDP (Link Layer Discovery Protocol) frames to all
ports, which leads to substantial additional network traffic (the frames are
handled like broadcast frames).
Conclusion: even for Conformance Class A Profinet networks, in
reality managed switches have to be used (for LLDP) - and they have
to be selected very carefully (IT support required).
see also EFTA 2007 Conference Paper by Iwan Schafer + Max Felser, Berne University
of Applied Sciences: “Topology Discovery in PROFINET”:
http://www.felser.ch/download/ETFA-01-2007.pdf
Industrial Ethernet Technologies
Page 20
© EtherCAT Technology Group, August 2011
Profinet Robustness (I)
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
• Profinet can be vulnerable if certain non-Profinet network
traffic occurs, such as high density of (short) ARP requests
• This applies to RT as well as to IRT, since in IRT the NRT
channel is used for supporting services, such as:
• Synchronization (IEEE1588)
• All acyclic services
(which are used by some masters in a cyclic way).
• Discovery protocol (LLDP)
Short Frames
Bus
Powerlink
Modbus/TCP
EtherCAT
Summary
Isochronous Real-Time
CPU
Non Real-Time
Synchro
nization
IRT
CPU busy
• Therefore Profibus International has published a
spec/guideline called „PROFINET IO Net load“
• Thus the Profinet user is now responsible to ensure
that certain network load limits are not exceeded.
© EtherCAT Technology Group
Profinet marketing has always claimed that Profinet provides (quote from PI “Profinet
Benefits” presentation):
• “Unlimited IT communications parallel to real-time communications
• Easy use and integration of standard Ethernet applications”
However, since the Profinet technology itself (unlike e.g. EtherCAT) has no means to
control or restrict incoming “unlimited IT communications”, there can be rare overload
situations that cause the network to fail. If the communication processor of a drive is
too busy to handle e.g. an occasional burst of broadcasted ARP frames and therefore
cannot keep up with executing the IEEE1588 services, the synchronization fails (of
this drive, and all nodes further downstream) and the master will consider these
nodes to have an error – the system stops.
One could consider this an implementation problem that can be avoided by providing
sufficient processing resources throughout – but it is a problem that occurs in reality,
especially in large networks.
It can be challenging to ensure that certain network load limits are not exceeded. If
e.g. a service notebook starts to scan the network for IP addresses at high pace, who
knows what kind of load condition this generates?
By the way: Industrial Ethernet technologies that tunnel other Ethernet traffic - such
as EtherCAT – remain in control of the additional network load and avoid such
situations by design.
Industrial Ethernet Technologies
Page 21
© EtherCAT Technology Group, August 2011
Profinet Robustness (II)
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
Screenshot from Profibus International website : http://www.profibus.com/nc/downloads/downloads/profinet-io-net-load-1/display/
© EtherCAT Technology Group
There are reports suggesting that exceeding 5% ARP load for 1 ms can
already be an issue.
Industrial Ethernet Technologies
Page 22
© EtherCAT Technology Group, August 2011
Profinet / EtherCAT Comparison
by Profibus International (PI)
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
• On press conferences in Nov 2007, PNO/PI published
performance comparsions with EtherCAT
• It was found that in typical application scenarios (line
structure, 50 nodes, < 60Bytes cyclic data per node)
EtherCAT is substantially faster than Profinet IRT
• According to the PNO,
Profinet IRT is faster if
the average payload per
node exceeds 60 Bytes
• However, some features
of EtherCAT (such as
full-duplex frame usage
and pipelining of frames)
were not considered
Summary
Picture sourced from PNO press kit
© EtherCAT Technology Group
Within the research project “ESANA”, funded by the German Federal Ministry of
Education and Research, Siemens, Phoenix Contact and some other parties
were looking for performance enhancement possibilities for Profinet. This is
remarkable, since it documents that in PNO/Siemens/Phoenix view the current
Profinet IRT is not fast enough to succeed.
The performance comparison shown on this slide is at least questionable: even
with very favorable assumptions for Profinet it was not possible to reproduce the
results. EtherCAT is substantially faster than shown, since several EtherCAT
features were not taken into account:
- EtherCAT can use the same bandwidth for input and output data (full-duplex
usage of the frame).
- EtherCAT can send the next frame before the first one has returned (pipelining
of frames).
One of the authors of the study has meanwhile admitted this shortfall.
So in fact EtherCAT is faster than Profinet IRT, regardless of the payload
per node.
Furthermore, all the Profinet calculations do not include the local stack
performance in the slave devices. Unlike with EtherCAT, in a Profinet IRT slave
device a communication µC (ERTEC: ARM) is taking the data from the MAC
interface and makes it available to the application. With EtherCAT, this is done
on the fly in hardware, the data is made available in the DPRAM or Input/Output
of the EtherCAT Slave Controller without further delay.
Industrial Ethernet Technologies
Page 23
© EtherCAT Technology Group, August 2011
Profinet / EtherCAT Comparison
by Profibus International (PI)
Classification
• When taking all EtherCAT Features into account, the
performance comparison looks different:
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
• EtherCAT is faster, regardless of the payload per node
Summary
© EtherCAT Technology Group
This slide shows the relative performance comparison if all the EtherCAT Features are
taken into account (purple line). This calculation was confirmed by a conference paper of
Dr. Gunnar Prytz, ABB Research Center, at ETFA 2008 („A performance analysis of
EtherCAT and Profinet IRT“), which can be downloaded from the ETG website:
http://www.ethercat.org/pdf/english/ETFA_2008_EtherCAT_vs_PROFINET_IRT.pdf
The blue line shows the comparison according to the PNO paper.
ETG was asked to provide a statement regarding the PNO press conference. Here it is:
•We are pleased that the PNO has chosen EtherCAT as performance benchmark and
thank for the associated publicity.
•The PNO acknowledges our statement, that high-end performance with cycle times
significantly below 1 ms is a relevant selection criteria for an Industrial Ethernet solution.
•The PNO analysis shows clearly, that in typical application scenarios EtherCAT is much
faster than the fastest Profinet variant IRT class 3.
•We congratulate the PNO on having found a special scenario (comb structure, in which
the nodes in the branch lines are not updated in each cycle), in which a future version of
Profinet IRT seemingly matches or exceeds EtherCATs performance.
•This comb structure was compared with an EtherCAT line structure – and not with an
EtherCAT comb structure, in which the nodes in the branch lines can be updated in each
cycle.
•EtherCAT is and remains the fastest Industrial Ethernet solution.
•EtherCAT does not need and will not need the complex network planing and
optimization that current and future Profinet IRT variants require.
Industrial Ethernet Technologies
Page 24
© EtherCAT Technology Group, August 2011
Next Generation Profinet IRT
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
• In November 2007 also a new Profinet IRT Version was
announced: originally named IRT+, this version can be
considered Profinet V4
• In the new version intends to improve the performance in line
topologies by
– Shortening the frames as they pass through subsequent
nodes (Dynamic Frame Packing DFP), which requires
new datagram structure with multiple CRCs
– Changed interpretation of the Ethernet MAC address
(Destination address contains Frame ID) to reduce
forwarding time in IRT ASICs (“Fast Forwarding“)
• This new Version requires new Profinet ASICs
• In Oct 07 the price for the old ASICs was reduced by 40%
EtherCAT
Summary
© EtherCAT Technology Group
Profibus organization PNO showed a Profinet V4 demonstrator in April
2008 at Hannover Fair. According to a PNO press release of Nov 26,
2008, “The specifications will be finished in the second half of 2009“.
Similar to RT and IRT version that are summarized as “Profinet IO” in
order to play down the many varieties of the technology, the Profinet
organization does not use the term IRT+ (or Profinet V4) any more. The
features of the new version which requires new chips are contained in the
Profinet specification V2.3, which was published in October 2010.
Since EtherCAT achieves a better bandwidth utilization (less overhead
per node), it will remain the fastest Industrial Ethernet technology, even
though there may be scenarios with just a few nodes where a carefully
optimized network consisting of Profinet V4 nodes may come close to the
performance of an EtherCAT with default settings.
Industrial Ethernet Technologies
Page 25
© EtherCAT Technology Group, August 2011
IRT+: Dynamic Frame Packing (DFP)
Classification
DFP aims to enhances Profinet IRT Performance in Line Topologies
–
Frame Efficiency will be improved by shortening frames
dynamically in node (only in line topology)
–
In DFP-Lines, IP-Frames (other Ethernet Traffic) will be
fragmented – just as with EtherCAT
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
Picture: Phoenix Contact @ SPS/IPC/Drives Congress 2009
© EtherCAT Technology Group
DFP will work in line topologies, only.
With DFP Profinet introduces the layer 2 fragmentation of IP-Frames –
another feature that EtherCAT has introduced and which Profinet
marketing used to condemn…
Industrial Ethernet Technologies
Page 26
© EtherCAT Technology Group, August 2011
IRT+: Fast Forwarding (FF)
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
•
Fast Forwarding (FF) will reduce Cut-Through Forwarding Time
by introducing Multicast MAC Adresses with integrated Profinet
Address
– Cut Through Switch can decide („forward to which port?“)
after reception of Profinet destination address (FID, frame ID)
DA
Header
SA
VLAN
ET FID
Datagram
FCS
Datagram
FCS
Decision Time without FF
FID DA
Header
SA
VLAN
ET FID
Decision Time with FF
EtherCAT
Summary
© EtherCAT Technology Group
For introducing Fast Forwarding the address usage had to be modified.
The goal is to reduce the „per-node-delay“ of Profinet. Since Profinet
Version 2.3 the FrameID is part of the OUI (Organizationally Unique
Identifier) in the MAC address, with the first two bits set to “1” (= Locally
Administered Group Address).
Industrial Ethernet Technologies
Page 27
© EtherCAT Technology Group, August 2011
Profinet V2.3 – and IRT+ Timeline
Classification
Profinet
•
Next Generation Profinet (IRT+) was announced in 2007
•
End of 2010, Profinet IRT V 2.3 Specification was released
•
V2.3 contains the IRT+ Features DFP + FF,
plus more changes such as
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
•
•
Fragmentation of NRT Frames
(Profinet now also makes use of Tunneling)
•
Configuration in Run Mode
•
Network Scan and Parameter Upload
•
Media Redundancy added
•
Boot-Up for IRT (Class 3) modified
However, Devices supporting Dynamic Frame Packing and
Fast Forwarding (IRT+) are not expected before 2013
EtherCAT
Summary
© EtherCAT Technology Group
As of August 2011, the conformance test cases for IRT+ are scheduled for
mid of 2013. So far there is not even Profinet Master ASIC officially
announced that will support DFP and FF – it is understood, though, that
Siemens is working on a next generation ERTEC chips, which will most
likely support these features. These nextGen ERTECs are not expected
before 2013 either, so the Profinet community will have to wait some more
years for IRT+.
Industrial Ethernet Technologies
Page 28
© EtherCAT Technology Group, August 2011
New Profinet Chip TPS1 “Tiger”
Classification
Profinet
Ethernet/IP
•
Developed by Phoenix Contact (+ inIT),
distributed by Renesas, marketed by
KW Software
•
Goal: Simpler to integrate than Siemens
ERTEC200
•
DFP - Dynamic Frame Packing +
FF - Fast Forwarding not (yet) supported
•
PHYs + Protocol CPU integrated,
but no Application µC
•
Aimed at I/O and Drives
•
Initially announced for 2009, first samples
mid of 2011, series production expected
for Q1/2012
•
Marketing: “Joint Development of Phoenix
and Siemens” in order to stress
compatibility with ERTEC
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
Picture sourced from KW Software Website
© EtherCAT Technology Group
TPS1 is also called “Tiger” chip, since it was planned to be released in the Year of the Tiger
(2/2010 – 2/2011). Even though it will now be released in the Year of the Rabbit (or Hare), no
plans are known to officially rename it the “Rabbit” chip.
The Tiger aka TPS1 (aka Rabbit) chip is a Phoenix Contact development (subcontracted to the
Institut Industrial IT (inIT) of the University of Applied Science Westfalen Lippe) – and Phoenix
Contact (not Siemens) also was the driving force behind Profinet V4 (IRT+). So the TPS1 was
intended to be the first chip supporting the new Profinet version.
But end of 2009 it looked that Siemens was unhappy about Phoenix trying to take the lead in
Profinet advancement and therefore forced Phoenix into a lengthy consensus building process
within PNO in order to delay the availability of Profinet V4. Meanwhile Siemens seems to have
recognized that this strategy backfired on Profinet in general.
So in March 2010 PNO held a press conference where in total contrast to the statements of Nov
2009, where Siemens had denied any involvement in the TPS1 development, Siemens and
Phoenix Contact called the TPS1 a joint development of both companies which they plan to use
also in the future in devices of their own product portfolio.
Nevertheless, PNO committees changed the Fast Forwarding technology again in fall 2010 and
thus too late for the first version of the TPS1 chip. So the TPS1 chip will initially not support the
DFP and FF – which is not such a big problem, since there is no master in sight supporting these
features anyhow. As mentioned before, Siemens is believed to be also working on a next
generation Profinet chip, which is not expected before 2013 – and it seems that Phoenix accepts
that this chip will be the first one to support DFP and FF.
The TPS1 is for slave devices only. The integrated “Profinet CPU” is an ARM core and executes
the time critical parts of the Profinet protocol. Digital I/O can be connected directly to the chip. For
communication with the application (host) CPU the chip contains internal DPRAM, which can be
accessed via serial or parallel interface. Since its cyclic process data image is limited to 340 bytes,
it is hardly suitable for bus couplers of modular I/O devices or other more complex devices. KW
Software claims that with this chip the interface hw costs can be reduced to 13€ (~19$).
Industrial Ethernet Technologies
Page 29
© EtherCAT Technology Group, August 2011
PROFINET ASIC Pricing
Siemens/NEC
ERTEC 200
ERTEC 400
Functionality
PROFInet RT + IRT
IEEE 1588
ARM 9 Processor
2 Port Switch with PHY
PROFInet RT + IRT
IEEE 1588
ARM 9 Processor
4 Port Switch, no PHY
PCI Interface
RMII Interface (4port)
CC-Link IE
Application field
Single drives
Comparable field devices
High-end Motion Controller
Network components
Sercos III
ASIC Technology
0.15 µm Technology
304pin BGA 19 x 19 mm
0.15 µm Technology
304pin BGA 19 x 19 mm
Powerlink
Pricing
(since Oct 2007)
12.57 €
@ order size 350 units
30.00 €
@ order size 350 units
Classification
Profinet
Ethernet/IP
Modbus/TCP
EtherCAT
Pricing shows that PROFInet is more on the „complex“ field
device network side than on the cost efficient I/O system side.
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
First samples of the ERTEC 400 were shipped in May 2005, first samples
of the ERTEC 200 were shipped in May 2006.
Initially, the ERTEC 400 was sold for 38€ and the ERTEC 200 for 19 € per
chip (@ 10.000 units/year). As of Oct 1st, 2007, Siemens lowered the
prices substantially, presumably since the next generation IRT which
requires new ASICs is under development.
12.57€ respective 30€ per chip still exceeds fieldbus cost levels not only
for simple devices, in particular if one considered the amount of memory
needed:
A Profinet slave device needs about 1 MByte of Code for the
communication part. For implementation with ERTEC chips, a VxWorks
license is required: the stack is provided as object code for this RTOS.
Industrial Ethernet Technologies
Page 30
© EtherCAT Technology Group, August 2011
PROFINET and INTERBUS
Classification
Profinet
the Interbus View…
Management
Level
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
Control
Level
Ethernet
TCP/IP
Complex
field devices
Simple
field devices
EtherCAT
…there is life below PROFINET…
Summary
Picture sourced from Interbus Club website
© EtherCAT Technology Group
Due to system complexity and costs Interbus as well as Profibus expect
life below Profinet.
Industrial Ethernet Technologies
Page 31
© EtherCAT Technology Group, August 2011
IRT and Siemens Motion Control
Classification
For closed loop motion control Siemens
is using Drive-CLiQ, not Profinet IRT…
Profinet
Drive-CLiQ:
Siemens Motion Control
Network based on 100
Mbit Ethernet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
Pictures sourced from Siemens website
© EtherCAT Technology Group
Interesting enough, Siemens has also developed another Ethernet based
motion control network: Drive-CLiQ.
Drive-CLiQ is used to connect the Sinamics motion controller containing
the path planning algorithm (trajectory controller) with the drives, the
position sensors (encoders, tachometers, resolver) and also with terminal
modules (HMI).
Profinet IRT and Profibus are used to network and synchronize several
such motion controllers – so primarily for controller/controller
communication.
End of November 2010 Siemens announced that they are is now even
opening Drive-CLiQ to feedback sensor manufacturers who are invited to
implement this interface in their encoders, resolvers, tachometers and
linear position sensors. Siemens also provides a special chip for that
purpose.
Industrial Ethernet Technologies
Page 32
© EtherCAT Technology Group, August 2011
PROFINET Adoption Rate
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
• As of July 2011, Profibus
International claimed that the
online product guide meanwhile
contains 500 Profinet devices.
• However, as of August 15, 2011,
there were 428 entries, out of
which 170 are cables and
connectors, 41 are services and
tools, 46 are interface boards,
chips and switches, and 25 are
fieldbus-independent I/O
terminals – and 70% of the
remaining devices are Siemens…
• Also, the product guide lists only
3 Profinet drive vendors besides
Siemens – and none of them supports IRT (RT Class 3)
Summary
© EtherCAT Technology Group
Given that the first version of Profinet was introduced 10 years ago, and
that it is promoted by the market leading automation giant, the adoption
rate of Profinet is poor.
As of August 2011, there are very few non-Siemens Profinet masters – in
particular non-Siemens IRT-masters are difficult to find. Also, there are no
known non-Siemens IRT drives.
Industrial Ethernet Technologies
Page 33
© EtherCAT Technology Group, August 2011
PROFINET Summary
Classification
• 3 different Versions:
Proxy Approach, Soft Real Time, Isochronous Real Time
Profinet
• Proxy Approach: vaporware
Ethernet/IP
• RT: rather complex Profibus replacement, but will have
market share due to support by Siemens
CC-Link IE
• There will be underlying networks (for cost reasons)
Sercos III
• IRT for motion control: meets motion control requirements
but very complex and expensive
Powerlink
• IRT expected to be predominantly Siemens only
(like Profibus DPV2 for Motion Control)
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Profinet RT is not low cost, requires a lot of code and is not high
performance, but in the long run it will be a success – regardless of the
technology, simply due to the Siemens (+ PNO/PTO) market position, just
like Profibus.
The German car makers have announced to use Profinet in car assembly
lines „if it provides technological and economical advantages“ (quote).
Daimler, e.g., has clearly stated that this announcement does not cover
the power train business, where CNC and other motion control
applications are in place. Furthermore, there will be underlying fieldbus
systems in the car assembly line, too. But certainly the auto makers
announcement gave Profinet (RT) a marketing push.
The situation is different for Profinet IRT: A solution with sufficient
performance, but with rather expensive chips and a very complex network
planning and configuration tool where the key algorithms are not open.
IRT is positioned at servo motion control applications and will therefore be
– just like Profibus MC – a Siemens motion control solution with limited
support from third party vendors (just like Profinet MC).
Plus, Siemens latest Motion Control product line prefers a different
communication link for closed loop control: DriveCliq, which uses Ethernet
physical layer, only.
Industrial Ethernet Technologies
Page 34
© EtherCAT Technology Group, August 2011
Ethernet/IP: Overview
Classification
Profinet
Ethernet/IP
• ODVA (Rockwell) Approach: „IP“ stands for Industrial Protocol
• CIP (Common Industrial Protocol): common object library for
Ethernet/IP, ControlNet, DeviceNet, CompoNet
• Follows Approach A.
Device Profiles CIP Motion
Valves
CIP
CIP Message Routing, Connection Management
Transport
EtherCAT
Other
CIP Data Management Services
Explicit Messages, I/O Messages
Application
Powerlink
Modbus/TCP
Robots
CIP Application Layer
Application Object Library
CC-Link IE
Sercos III
I/O
A
Encapsulation
TCP
UDP
ControlNet
Transport
DeviceNet
Transport
CompoNet
Transport
Network
IP
Data Link
EtherNet
CSMA/CD
ControlNet
CTDMA
CAN
CSMA/NBA
CompoNet
Time Slot
Physical
EtherNet
Physical Layer
ControlNet
Phys. Layer
DeviceNet
Phys. Layer
CompoNet
Phys. Layer
Summary
© EtherCAT Technology Group
Ethernet/IP claims to use the same application layer as Devicenet,
Controlnet and CompoNet. This may be beneficial for those that are
familiar with those fieldbus networks. However, taken from the experience
when implementing Devicenet and Controlnet, the synergy effects are
expected to be somehow limited, since the communication technologies
and even the protocols differ substantially.
Industrial Ethernet Technologies
Page 35
© EtherCAT Technology Group, August 2011
Ethernet/IP Functional Principle
Classification
Profinet
Consumer / Producer Model
• Advantage: very efficient for slave-to-slave Communication
• Disadvantage: requires Broadcast communication and thus
filtering in each device
Ethernet/IP
CC-Link IE
producer
consumer
consumer
accept
consumer
accept
Sercos III
prepare
filter
filter
filter
send
receive
receive
receive
Powerlink
Modbus/TCP
broadcast communication
EtherCAT
Summary
© EtherCAT Technology Group
By applying broadcast or multicast communication, the switches cannot
forward incoming frames to a single destination port only - so they act like
(full-duplex) Hubs, but with larger delay.
Industrial Ethernet Technologies
Page 36
© EtherCAT Technology Group, August 2011
Ethernet/IP Switch + Router Issues
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
from a technical paper found on the ODVA website
Summary
http://www.odva.org/Portals/0/Library/Publications_NotNumbered/Utilization_of_Modern_Switching_Technology_in_EtherNetIP_Networks.pdf
© EtherCAT Technology Group
This paper by Anatoly Moldovansky, a senior engineer from Rockwell
Automation (and a nice guy!), highlights some of the issues with
Ethernet/IP: there is a need for routers with multicast/broadcast control
features, and there is no standard way to implement or configure these.
IGMP snooping constrains the flooding of multicast traffic by dynamically
configuring switch ports so that multicast traffic is forwarded only to ports
associated with a particular IP multicast group.
Furthermore, high-end switches typically have high-end prices. Rockwells
documentation states that switches for Ethernet/IP have to support IGMP
snooping as well as port mirroring (for troubleshooting). They should also
support VLAN and SNMP – so manageable switches are required.
Industrial Ethernet Technologies
Page 37
© EtherCAT Technology Group, August 2011
Ethernet/IP Topology
Classification
Profinet
Ethernet/IP
CC-Link IE
• Standard Switched Ethernet Topology
• By nature: unpredictable
Switch + Stack Delays
• Network separation by
Router with IGMP snooping
• Limited Real Time
Capabilities
Router
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Even though the switch delays are unpredictable by nature, the delays
introduced by the software stacks are much more significant.
Industrial Ethernet Technologies
Page 38
© EtherCAT Technology Group, August 2011
Ethernet/IP Device Level Ring (DLR)
Classification
Profinet
Ethernet/IP
CC-Link IE
• Cable Redundancy Technology based on Ring topology
• Dedicated Ring Supervisor Node and DLR protocol for
network management
• Devices with special embedded switches
• Introduced in 2008, first DLR products in 2009
• DLR unaware nodes should be connected through 3-port
protocol aware switches
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
Picture: Rockwell Automation Press Release, Oct. 2009
© EtherCAT Technology Group
DLR technology first published in Nov 2008 version of Ethernet/IP spec.
First products in Q3 2009.
Requires special nodes who support the DLR protocols
Ring supervisor node monitors network status with “Beacon frames”, per
default every 400µs. In case of failure, ring supervisor actively
reconfigures the network (e.g. by remotely opening or closing ports)
ODVA recommends to connect “DLR unaware nodes” through 3-port
protocol aware switches.
Fault recovery time for a 50-node network: about 3 ms.
Enhances the Ethernet/IP topology options, also supports combinations of
several rings and combinations of redundant rings with classical Ethernet
star topologies – at the price of special nodes.
Industrial Ethernet Technologies
Page 39
© EtherCAT Technology Group, August 2011
Ethernet/IP Performance
Classification
Profinet
• Minimum Cycle Time (RPI; Requested Packet Interval)
is dependent on number of CIP connections
• Each Device can have multiple CIP Connections
min_RPI = (number of connections x 2) / (no. of frames/second)*
* (assumed all connections request same “RPI” scan time).
Ethernet/IP
CC-Link IE
No. of
Min_RPI (ms)
Connections
with 5000
Frames/sec
Min_RPI (ms)
with 10000
Frames/sec
Min_RPI (ms)
with 25000
Frames/sec
(standard
scanners)
(high performance
scanners)
(ultra high performance
scanners)
4
1,6
0,8
0,32
8
3,2
1,6
0,64
16
6,4
3,2
1,28
32
12,8
6,4
2,56
64
25,6
12,8
5,12
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
These theoretical cycle times do not take switch and remote stack delays into
account; Rockwell quantifies the switch delay at 0,1 ms per switch.
© EtherCAT Technology Group
Industrial Ethernet Technologies
Ethernet/IP distinguishes CIP and TCP Connections. A CIP connection transfers data from an
application running on one end-node to an application running on another end-node. A CIP connection is
established over a TCP connection. A single TCP connection can support multiple CIP connections.
Most Rockwell Ethernet/IP devices support up to 64 TCP connections, the number of CIP connections
differs from device to device (e.g. 1756-ENBT: 128 CIP connections, 1756-EN2T and later: 256 CIP
connections). All Rockwell scanners support a maximum of 32 multicast tags (producer/consumer I/O
connections).
For communication with an I/O device, typically more than one CIP connection is used (e.g. one for
implicit messaging, one for explicit messaging).
The Rockwell Automation (RA) publication “Ethernet Design Considerations” (ENET-RM002A-EN-P,
July 2011) shows the complex process of how to predict the network performance. There is also an
“EtherNet/IP Capacity Tool“ available.
Rockwell also recommends to add scanner cards to the controller and divide the scanning function
between the cards if the throughput is not sufficient.
The Packet Rate Capacity (packets/second) of most Rockwell Ethernet/IP scanners is 5000 Frames/sec
– with the exception of the ControlLogix series, where Rockwell is constantly increasing the scanner card
performance. As of August 2011, the latest generation (firmware >3.6) scanners support up to 25.000
frames/second (see Table 9 of Rockwell Automation Publication ENET-RM002A-EN-P, July 2011). With
these new high end scanners (1756-EN2xx, 1756-EN3xx) the right hand column of the cycle time table
applies – and it is obvious that the system real time performance remains comparatively poor.
The standard ControlLogix Ethernet IP Bridge (1756-ENBT) still supports 5000 Frames/sec. The release
notes (Publication 1756-RN591Q-EN-P - January 2008) of this device contain the following passage:
Performance Considerations: In general, the 1756-ENBT module is capable of supporting 5,000
packets/seconds. However, it is possible in some applications, depending on the combination of
connection count, RPI settings, and communication formats, that the product may be able to achieve
only 4,000 packets/seconds.
See also: Rockwell Automation (RA) publication “Ethernet/IP Performance” (ENET-AP001D-EN-P,
released October 2004, according to RA website still valid in Aug 2011)
Industrial Ethernet Technologies
Page 40
© EtherCAT Technology Group, August 2011
Ethernet/IP + CIP Sync
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
• Ethernet/IP has limited Real Time Capabilities:
– limited Cycle Time Performance, limited Determinism
– acceptable Throughput (for large Data Units)
• CIP Sync adds Time Synchronization, but does not reduce
cycle time or process data performance
• Distributed Clock Protocol: IEEE 1588
• CIP Sync: announced April 2003, added to CIP spec in May
2006 (Version 3.0). First products shipping since 2009.
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
CIP sync was introduced to improve the real time behavior of the system.
The marketing message given by ODVA tries to tell that by adding
synchronization the real time capability is achieved – but time
synchronization does not improve cycle time, throughout or performance.
CIP sync was announced in April 2003, and included in Version 3.0 of the
CIP spec in May 2006.
First CIP sync products from Rockwell Automation are the sequence of
events (SOE) data capture modules that support timestamps. The version
with CIP sync support is shipping since mid of 2009.
Industrial Ethernet Technologies
Page 41
© EtherCAT Technology Group, August 2011
What is IEEE 1588?
Classification
Profinet
Ethernet/IP
• A method for precision time synchronisation tailored to
requirements of distributed measurement and control
systems. Widely independent of transport protocol.
• 1588 on Ethernet: Version 1 (2002) based on UDP/IP,
Version 2 (2008) also with direct Ethernet (Layer2) option
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
Source: introduction_to_1588.pdf by IEEE
© EtherCAT Technology Group
IEEE 1588, officially entitled "Standard for a Precision Clock Synchronization
Protocol for Networked Measurement and Control Systems" , is a technology for
time synchronization that is or will be used by a variety of systems: Ethernet/IP,
Profinet, Powerlink,... EtherCAT also supports gateways to IEEE 1588 systems for
external time synchronization.
The first version of IEEE1588 was published in November 2002. Version 2 (IEEE
1588-2008) followed in March 2008 and added various features, including the layer
2 transport option (embedded in the Ethernet frame without UPD/IP) and the
“transparent clock” approach which improves the accuracy for linear systems (line
topology) since it eliminates cascaded clocks.
V2 of the standard is not directly interoperable with V1.
IEEE supports an annual international symposium on 1588 technology. In
conjunction with this symposium a plug fests for improving interoperability is held.
Industrial Ethernet Technologies
Page 42
© EtherCAT Technology Group, August 2011
IEEE 1588 Hardware Support
Classification
Profinet
• In order to achieve good results hardware timestamping is
required
• This functionality can be implemented in MACs, PHYs or
integrated solutions.
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
Source: Dirk Mohl, www.ieee1588.com
© EtherCAT Technology Group
In general the stack processing times limit the accuracy in case of pure
software implementations. For good results hardware with built in
IEEE1588 timestamp support has to be used – and the corresponding
switches. First silicon was introduced by Intel and Hyperstone, meanwhile
National Semiconductor, Freescale, Zarlink and others provide
processors, MACs and PHYs with such features. FPGA-IP with IEEE1588
timestamp functionality is also available.
Industrial Ethernet Technologies
Page 43
© EtherCAT Technology Group, August 2011
CIP Sync in ISO/OSI Model
Classification
Profinet
Ethernet/IP
Layer
5...7
Layer
4
CIP
Synchronized
Clock Value
TCP
1588Extension
UDP
(User Datagram Protocol)
CC-Link IE
Sercos III
Layer
3
„explicit
Messages“
Powerlink
Modbus/TCP
Layer
1 and 2
EtherCAT
IP
„Real-TimeI/O-Data“
n
oC
OTS H
(Internet
Protocol)
W
any m
o
re
optional Hardware
Support for
better Accuracy
Ethernet according to IEEE 802.3
C
A
?
CIP...Common Industrial Protocol
Summary
© EtherCAT Technology Group
In order to make the time synchronization independent from software
jitters and stack performance, at least the time stamp functionality had to
be implemented in hardware (directly in or at the Ethernet MAC).
This turns the class A approach “Ethernet/IP” into the class C approach
“Ethernet/IP with CIP Sync”, even though silicon with direct timestamp
support may be considered COTS technology at some stage.
Industrial Ethernet Technologies
Page 44
© EtherCAT Technology Group, August 2011
Ethernet/IP + CIP Sync
I/O
Drive
I/O
Controller
I/O
Drive
I/O
Drive
Controller
Drive
Powerlink
I/O
Controller
Sercos III
Drive
CC-Link IE
Limited No. of Connections
Bus cycle time is typically 5 .. 10 ms
Reaction time is typically 15 .. 30 ms
Determinism is added via system-time-synchronized actions and
timely non-deterministic communication.
Drive
Ethernet/IP
•
•
•
•
I/O
Profinet
Best suited and typically used
as Controller to Controller network
Drive
Classification
Modbus/TCP
EtherCAT
Summary
Example Ethernet/IP Network
© EtherCAT Technology Group
Even though it is more and more used for I/O communication as well, the
nature of Ethernet/IP clearly shows that this technology is aimed at the
controller to controller level. The synchronization capabilities of CIP Sync
are suitable for synchronizing motion controllers, but the communication
performance is not sufficient for closed loop servo drive communication.
Industrial Ethernet Technologies
Page 45
© EtherCAT Technology Group, August 2011
CIP Motion + CIP Sync
Classification
Enhances CIP networks for motion control
Profinet
• Ethernet/IP Premise: Full duplex, switched Ethernet with QoS
Prioritization, IEEE 1588 Synchronization and time stamped data
transmission is deterministic enough for motion control
Ethernet/IP
• Motion Control Device Profile included in CIP Spec since 2006
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
• First products shown in fall 2009, started shipping in 2010
• Performance limitation
of Ethernet/IP
leads to trajectory
generator in drive
• Same approach as
with legacy non-motion
fieldbus systems
EtherCAT
Summary
© EtherCAT Technology Group
Beginning of 2006, ODVA announced an initiative to enhance the CIP
protocols by CIP Motion for motion control over Ethernet/IP.
ODVA acknowledges that three main ingredients are required:
Synchronization services: for this purpose IEEE1588 time synchronization (CIP
Sync) will be employed
Timely Data Transfer: The goal is to use standard Mechanisms to ensure this:
- Full-Duplex 100-BaseT or 100BaseF “Fast” Ethernet.
- Ethernet switches to eliminate collisions.
- QoS frame prioritization to eliminate queuing delays
Motion Control Device Profiles: have been added in V3 of the CIP spec.
The goal is to achieve high-performance motion control over standard, unmodified,
Ethernet.
Even though ODVA aims to achieve timely data transfer in the sub-millisecond cycle
time range, this is in total contradiction to the “real life” Ethernet/IP performance. It
may be possible to achieve sufficient results in very small, isolated and well
engineered networks with carefully selected components. But real life applications
will almost certainly be limited to open loop motion control with the trajectory
generator in the drive – which is also possible with legacy fieldbus systems like
DeviceNet. Whilst the CIP Motion Device Profile is mapped to Ethernet/IP only (and
not to DeviceNet, ControlNet), most parameters and mechanisms of the profile
clearly have been included to compensate for lack of short cycle times: they describe
local trajectory generation. Compared to other drive profiles of IEC 61800-7, the
profile is therefore rather complex.
Introducing CIP Motion products implies that Rockwell – a Sercos vendor in the past
– has turned down Sercos-III and tries to push an own motion bus approach.
Industrial Ethernet Technologies
Page 46
© EtherCAT Technology Group, August 2011
CIP Motion + CIP Sync
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
CIP Motion Profile: ongoing project
C
• At the ODVA general assembly in 2009, major changes in the CIP
Motion Profile were announced, since the requested performance
could not be achieved with the original version of the spec
• Among other changes,
Host CPU
CIP Motion Object
CIP
the Startup Procedure
was modified
TCP
UDP
1588
• The Drive-to-Controller
IP
Process Data assembly
was reduced from 120(!)
Ethernet MAC
Bytes to 36 Bytes
• It is now recommended
CIP Motion Hardware Assist FPGA
to use a „CIP Motion
BRP
Ring
CIP Motion Assist
Hardware Assist FPGA“
Support Support
(Packet Extraction / Insertion)
for implementing a CIP
Motion drive
Embedded
1588 Assist
• Thus CIP Motion now
(Time Stamping)
Switch Support
a Class C approach
PHY
Summary
PHY
© EtherCAT Technology Group
It is interesting that ODVA now recommends to use an FPGA for implementing the
protocol: at the 2007 ODVA general assembly the presentation “Why CIP Motion,
Why Now?” claimed that CIP Motion – unlike its competitors – was using “COTS
Ethernet hardware, no proprietary ASICs or processors”.
First CIP Motion products were previewed at the Rockwell Automation Fair in
November 2009 and became available in 2010. In September 2010, RA published a
comprehensive CIP Motion Reference Manual (286 pages) and a CIP Motion
Configuration and Startup user manual (298 pages).
See also:
http://www.odva.org/Portals/0/Library/CIPConf_AGM2009/2009_CIP_Networks_Conference_Technical_Track_CIP_
Motion_Implementation.pdf
Industrial Ethernet Technologies
Page 47
© EtherCAT Technology Group, August 2011
Ethernet/IP Complexity
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
• In July 2011, Cisco and
Rockwell Automation
published a Design and
Implementation Guide for
Plantwide Ethernet/IP Networks.
• The document has 548 (!)
pages and specifically
addresses Plant Managers
and Control Engineers as
well as IT Managers.
• One can either consider this guide
• a pretty voluminous manual, or
• an indicator for the complexity of implementing
Ethernet/IP in manufacturing environments
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
The guideline (ENET-TD001D-EN-P) can be found here:
http://literature.rockwellautomation.com/idc/groups/literature/documents/td
/enet-td001_-en-p.pdf
Or here:
http://www.cisco.com/en/US/docs/solutions/Verticals/CPwE/CPwE_DIG.p
df
Industrial Ethernet Technologies
Page 48
© EtherCAT Technology Group, August 2011
Ethernet/IP Summary
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Conclusions:
• Network made for many Bytes of information per connection
• Initially not intended for Drives and I/O (Bit-sized connections)
Technical Issues:
• Performance not convincing („use ControlNet“)
• Ethernet/IP uses broadcast telegrams
• requires complex router configuration (e.g. IGMP snooping)
to avoid frame flooding of connected manufacturing and
corporate networks
• Filter algorithm implementations differ within switches,
therefore IT specialist may be needed in real life situations
Strategic Issues:
• Relatively slow adoption rate outside Rockwell world
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
A quote from a Rockwell employee: if you need more performance, use
Controlnet...
Adoption rate: as of August 2011, about 12 years after publication of the
spec, the ODVA website listed 100 “non Rockwell”- product guide entries
(141 altogether), out of which 27 are switches, cables and connectors.
For comparison: 6 ½ years after publication of the spec, the EtherCAT
(ETG) website lists 272 “non-Beckhoff” product guide entries (308
altogether, 14 switch, media converter, cable and connector entries).
Industrial Ethernet Technologies
Page 49
© EtherCAT Technology Group, August 2011
CC-Link IE: Overview
Classification
Profinet
Ethernet/IP
• CC-Link is the legacy Fieldbus developed by
Mitsubishi in 1997 and since 2000 promoted by
CC-Link Partner Association (CLPA)
• CC-Link IE: „IE“ stands for Industrial Ethernet
• Follows Approach C – needs special interface chips.
C
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Source: CLPA Brochure Nov 2010, www.cc-link.org
CC-Link is an RS485 based fieldbus technology introduced by Mitsubishi Electric
in 1997. In 2000, the CC-Link Partner Association (CLPA) was founded, and since
then CC-Link is promoted as an open technology. CC-Link is intended for I/O type
communication – not for motion control (for this purpose Mitsubishi uses
SSCNET).
CC-Link LT is the CLPA technology focusing on simplified wiring and intended for
simple I/O devices; it competes with Componet and AS-Interface.
CC-Link Safety is the CLPA network for functional safety. Unlike other functional
safety protocols, CC-Link Safety is not making use of the “black-channelapproach” but requires a separate network: CC-Link Safety cannot be transported
via CC-Link or CC-Link LT.
CC-Link IE is the Industrial Ethernet technology of CLPA.
There are two versions:
1.CC-Link IE Control (also named CC-Link IE Controller) is intended for
controller/controller communication
2.CC-Link IE Field is intended for I/O type communication (similar to CC-Link).
The 3rd CC-Link IE version, CC-Link IE Motion, is on the roadmap.
In July 2011 a Functional Safety Protocol for integration into CC-Link IE Field was
announced by CLPA.
Industrial Ethernet Technologies
Page 50
© EtherCAT Technology Group, August 2011
CC-Link IE Control: Overview
Classification
Profinet
Ethernet/IP
• CC-Link IE Control: for Controller/Controller communication
(CLPA: „in-factory backbone“)
• Media Access Control: Token Passing
• One Control Station, up to 119 Slave Stations
• Process Images exchanged by Shared Memory Approach
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Source: CLPA Brochure Nov 2010, www.cc-link.org
Token Passing Approach:
A CC-Link IE network consists of a single control station and multiple
slave stations. As in standard token passing networks, the control station
manages the network and starts the token passing sequence by sending
the token to the first slave station on the network.
The slave station that receives the token performs its cyclic transmission,
and then passes the token to the next station in the sequence.
After the last slave station completes the process, it passes the token
back to the CC-Link IE control station where the entire sequence is started
again.
A general problem of Token Passing is the error recovery: if the token
frame is lost for any reason, the entire token passing system has to be
reconfigured – of course the real time behavior is then gone temporarily.
Industrial Ethernet Technologies
Page 51
© EtherCAT Technology Group, August 2011
CC-Link IE Control: Protocol
¾Classification
• CC-Link IE Frame is embedded in Ethernet Frame
¾Profinet
• Frame layout is configured at boot up and fixed at run-time
¾Ethernet/IP
• Token holder writes to pre-assigned area of the frame
• Frame Format is not published
¾CC-Link IE
¾Sercos III
¾Powerlink
¾Modbus/TCP
¾EtherCAT
¾Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Source: CLPA Brochure 2009, www.cc-link.org
The CC-Link IE Control frame is directly embedded in the Ethernet frame.
In addition to the MAC address there is a node number and a network (in
the CC-Link IE Header), which are primarily used for addressing.
Unfortunately the CLPA CC-Link IE Control specification does not cover
the transport layer and the network layer, protocol details are not
published.
According to an article published by CLPA Europe (IEB Issue 49, November 2008),
“TCP/IP communications is supported by way of the transient/acyclic communication
function.” However, the specs do not mention this option – it seems that the authors refer
to the SLMP over TCP/IP option (see below).
Industrial Ethernet Technologies
Page 52
© EtherCAT Technology Group, August 2011
CC-Link IE Control: Topology
Classification
Profinet
Ethernet/IP
• Topology: Ring
• Ring Topology provides Cable Redundancy
• Physical Layer: 1000BASE-SX Multimode
Optical Fiber 50/125µm (IEEE 802.3)
• Connectors: LC Connectors (Duplex)
LC Duplex Connector
CC-Link IE
Sercos III
• Max Distance between nodes: 550m
• Up to 120 nodes per network, multiple networks can be coupled
Master
Slave
Slave
Slave
Slave
Slave
Slave
Slave
Powerlink
Modbus/TCP
CC-Link IE Control cannot make use of existing
Ethernet Backbone: requires separate Network
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Picture: Wikimedia Commons
Unlike most other Industrial Ethernet technologies, which use a standard
Ethernet network (which is in place in many factory automation
environments already), CC-Link IE Control needs a dedicated and
separate network of its own.
Only ring topology is supported – switches cannot (and need not) be used.
CC-Link IE Control products may limit the max. no of nodes. Example: as
of 8/2011, only one Mitsubishi CC-Link IE Control Interface supports 120
nodes, the others support 64 nodes.
Industrial Ethernet Technologies
Page 53
© EtherCAT Technology Group, August 2011
CC-Link IE Control: Implementation
Classification
• CC-Link IE Control requires special interface ASIC by Mitsubishi,
standard Ethernet MACs cannot be used.
Profinet
• ASIC is not mentioned on CLPA or Mitsubishi
Ethernet/IP
Websites and Brochures
• CC-Link IE Control Specification is available for CLPA Members
CC-Link IE
on request:
Sercos III
• Spec is very „lean“, data link layer is missing, interface
Powerlink
ASIC not mentioned
For third parties, implementation of
CC-Link IE Control obviously is
not enouraged
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
The information about the special ASIC is difficult to find: neither the CC-Link IE
website, nor the brochures nor the spec provide any information about this fact. Also,
detailed information regarding the CC-Link IE Control chip – which is not the same as
the CC-Link IE Field chip CP220 - itself is not available.
„Lean“ Specification
(as of August 2011, CLPA distributes the first version of the spec, dated Dec 2007):
•Device Profile Spec:
1 page
•Implementation Rules Spec:
3 pages
•Application Layer Service Definition:
41 pages
•Application Layer Protocol Definition:
115 pages
•Communication Profile Specification:
2 pages
The application layer specs are relatively comprensive as they have been prepared for
inclusion in IEC61158 – CC-Link IE is going to be type 23. Publication of the edition of
this standard containing CC-Link IE is expected for end of 2013.
Data link layer/transport layer/network layer with key features such as boot-up, network
management and error control are not specified. The Implementation Rules Spec, the
Device Profile Spec and the Communication Profile Specs are not sufficient for
implementing the technology, the chip seems not to be available outside Mitsubishi.
The 2011 presentation „How to Develop CC-Link Compatible Products – Overview“ of
CLPA Europe does not mention CC-Link IE at all.
Thus the conclusion is that, four years after the introduction of CC-Link IE Control as
open network technology, the implementation of CC-Link IE Control is not encouraged
– if not impossible – for third parties, at least not outside Japan.
CC-Link IE Control thus cannot be considered an open technology.
Industrial Ethernet Technologies
Page 54
© EtherCAT Technology Group, August 2011
CC-Link IE Control: Performance
Classification
Performance Examples:
Profinet
Ethernet/IP
CC-Link IE
Sercos III
100 MBit
No of
Nodes
Size of exchanged
I/O process image
per node [Bytes]
No of Devices with
asynchronous
Communication
Link Scan Time
(=Cycle Time)
[ms]
EtherCAT
[ms]
8
128
0
1,6
0,1
16
256
0
2,0
0,37
16
256
16
3,0
0,42
32
32
32
4,8
0,14
50
64
50
7,9
0,34
256
50
8,0
1,25
50
Powerlink
Gbit
Cycle Time
Computed with Formulas from Mitsubishi Reference Manual CC-Link IE Controller Network
Modbus/TCP
EtherCAT
•
CC-Link IE Control Cycle Time is sensitive to number of nodes,
but hardly influenced by amount of data exchanged.
•
Link Refresh Times αT+ αR (Σ typically 1..2ms) and
Line Control Time Nc (50…100ms) were not considered.
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Due to using Gigabit Ethernet physical layer, CC-Link IE Control cycle
time is hardly influenced by the amount of data exchanged. In contrast,
due to its functional principle, EtherCAT is hardly influenced by the
number of nodes – and is much faster anyhow, in spite of using 100Mbit
technology.
In order to have a fair comparison, the dedicated and separated CC-Link
IE Control network was compared with a dedicated and separated
EtherCAT (Device Protocol) network, which can also be used for
controller/controller communication. However, in many cases the
EtherCAT Automation Protocol (EAP) will be used for that purpose, since
EAP can be transmitted via an already existing Ethernet backbone (which
is of course not limited to 100Mbit/s). Since EAP is making use of
standard Ethernet switch technology, the EtherCAT cycle times listed
above are not achieved with this approach.
The Link Scan Time (=Cycle Time) formula used was taken from Chapter 7.1 (Link Scan
Time) of the “MELSEC Q series/Programmable Controller/Reference Manual (CC-Link IE
Controller Network)” SH(NA)-080668ENG Version E of 01.10.2008. We used formula (1)
with LY=0, T=2 (default value) and the Line Control Time Nc (Time required for
reconfiguring the data link when network is disconnected and reconnected) =0. Usual
values for Nc given in that manual are 50ms (Normal) and 100ms (Worst). For error case
considerations this time has to be added. For Cyclic Transmission Delay Time the Link
Refresh Times have to be taken into account as well.
Industrial Ethernet Technologies
Page 55
© EtherCAT Technology Group, August 2011
CC-Link IE Field: Overview
Classification
Profinet
•
•
•
•
CC-Link IE Field: for I/O type communication
Media Access Control: Token Passing
All Frames are broadcasted (Switches act like Hubs)
One Control Station, up to 120 Slave Stations
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Source: CLPA Brochure Nov 2010, www.cc-link.org
CC-Link IE Field is the adaptation of CC-Link IE Control to the field level.
The functional principle – token passing - is shared by both variants. CCLink IE Field uses copper based Gigabit Ethernet, and supports non-ring
topologies such as star and line.
120 Slave stations: the specification allows for up to 253 slave devices;
however, current implementations only support 120 slave devices.
Industrial Ethernet Technologies
Page 56
© EtherCAT Technology Group, August 2011
CC-Link IE Field: Frame Types
Classification
• CC-Link IE Frames are directly embedded in Ethernet Frame
• There are three basic frame types
Profinet
Transient Transmission Frame,
for acyclic Parameter Communication
Ethernet/IP
CC-Link IE
Cyclic Transmission Frame,
for process data exchange
Sercos III
Powerlink
Transmission Control Frame, for
Token Passing and Network Management
EtherCAT
Ethernet
Header
890F
Modbus/TCP
CC-Link IE Field Network Frame
(46..1500 Bytes)
CRC
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
CC-Link IE Field uses Ethernet frames according to IEEE 803.2 and the
Ethertype 0x890F.
As of August 2011, the CC-Link IE Field Data Link Layer specification
contains no further information than this. The format of the transmission
control frame, of the transient transmission control frame and the cyclic
transmission control frame are not published.
Industrial Ethernet Technologies
Page 57
© EtherCAT Technology Group, August 2011
CC-Link IE Field: Phases
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
CC-Link IE Field has three communication phases
a)Initialization Phase: Master establishes Token Passing Route
1. Master finds Slave Devices
2. Master collects information about Slaves
3. Master distributes Token Passing Route
4. Master distributes Parameters
5. Master instructs Slaves to reflect the Parameters
6. Master verifies Slave Parameter Reflection Status
b)Refresh Phase: Cyclic and Acyclic Data Exchange
1. Each node, after receiving Token, first sends Status Frame
2. Then sends Cyclic Data Frame(s)
3. Then sends Acyclic Data Frame(s)
4. Then sends Token frame to next Token holder
c)Return Phase: New nodes are detected and included in Token
Passing Scheme. Master decides when to start Return Phase.
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
The CC-Link IE Field specification describes the phases in general and
also shows the sequence of frames that are exchanged – but it does not
contain the frame formats itself.
Industrial Ethernet Technologies
Page 58
© EtherCAT Technology Group, August 2011
CC-Link IE Field: Refresh Phase
Classification
Profinet
• Process Data Exchange takes place during Refresh Phase.
• Cyclic Transmission size of each node is fixed during runtime.
• Upper limit of acyclic frames per node is fixed during runtime.
Ethernet/IP
CC-Link IE
Status Frame
Cyclic Transmission Frame
Acyclic („Transient“) Transmission Frame
Token Frame
Cycle („Link Scan“)
Master
Sercos III
Slave 1
Powerlink
Slave 2
Token Passing
Modbus/TCP
Slave 3
EtherCAT
Slave 4
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
After receiving the token, the slave device first sends its status frame,
then one or more cyclic transmission frames, optionally followed by acyclic
frames (for the so called transient communication). The number of acyclic
frames per node and cycle can be limited in order to avoid cycle time
violations. Lastly, the node sends the Token Frame to the next token
holder.
All Frames are broadcasted: nodes with two ports send all frames to both
ports, and switches are used like hubs (making use of broadcast MAC
addresses).
CC-Link IE distinguishes different node types, which differ by maximum
process data size as well as features such as support of acyclic
communication:
e.g.:
•“Remote Device Stations” are limited to 128 bits of cyclic I/O data (+
register data) and do not support client functionality in acyclic
communication.
•“Remote I/O stations” are limited to 64 bits of cyclic I/O data (no register
data) and do not support acyclic communication at all.
Industrial Ethernet Technologies
Page 59
© EtherCAT Technology Group, August 2011
CC-Link IE Field: Topology
Classification
Profinet
Ethernet/IP
•
•
•
•
•
Topology: Combination of Line and Star Topology, or Ring
Physical Layer: 1000BASE-T (IEEE 802.3)
Connectors: Shielded RJ-45
Max Distance between nodes: 100m
Up to 120 nodes per network, multiple networks can be coupled
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Source: CLPA Brochure Nov 2009, www.cc-link.org
The topology of CC-Link IE Field is more flexible than the CC-Link IE
Control topology.
As of August 2011, ring topology is not supported by (Mitsubishi) CC-Link
IE Field products yet.
Industrial Ethernet Technologies
Page 60
© EtherCAT Technology Group, August 2011
CC-Link IE Field: Implementation
Classification
• CC-Link IE Field also requires special interface
ASIC by Mitsubishi: CP220 (BGA256, 17x17mm)
Profinet
Standard Ethernet MACs cannot be used.
Device-side Hard- and Software
• CC-Link IE Field Specification is
available for CLPA Members on
request:
Reception Buffer
CC-Link IE Field Communication Control
Ethernet MAC interface
PHY
RJ45
• Spec is pretty „lean“, but more
Trafo
Powerlink
Transmission Buffer
Trafo
Sercos III
Cyclic Communication Buffer and
Transient Communication Buffer
RJ45
CC-Link IE
CC-Link IE
Field Controller
• ASIC is not (yet) available in Europe
PHY
Ethernet/IP
comprehensive than CC-Link
Modbus/TCP
IE Control spec.
EtherCAT
For third parties, implementation of
CC-Link IE Field looks challening
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
CP220 Picture: Mitsubishi Japan Website
According to Mitsubishi Electric Germany, the CC-Link IE Field chip CP220 is not
(yet) available in Europe.
„Lean“ Specification
(as of August 2011, CLPA distributes the version BAP 1605 of May 2010):
•Device Profile Spec:
8 pages
•Implementation Rules Spec:
7 pages
•Data Link Layer Spec:
2 lines (not pages)
•Application Layer Service Definition:
56 pages
•Application Layer Protocol Definition:
153 pages
•Communication Profile Specification:
15 pages
The application layer specs are relatively comprensive as they have been prepared
for inclusion in IEC61158 – CC-Link IE is going to be type 23. Publication of the
edition of this standard containing CC-Link IE is expected for end of 2013.
With the CP220 manual it may be possible to implement a slave device, but since
there is no information about the Data Link Layer a master device cannot be
implemented by third parties as of now.
Thus the conclusion is that as of August 2011 the implementation of a CC-Link IE
Field slave device by third parties is very challenging, at least outside Japan.
Industrial Ethernet Technologies
Page 61
© EtherCAT Technology Group, August 2011
CC-Link IE: SLMP
FTP
Profinet
• SLMP stands for Seamless Message Protocol
HTTP
Classification
Common Application Protocol, SLMP
TCP/UD
P
IP
Ethernet/IP
CC-Link
Ethernet
RS-485
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
• SLMP is independent of the data link layer and can be
implemented on CC-Link IE and TCP(UDP)/IP
• According to CPLA, legacy CC-Link also supports a similar
protocol
• SLMP supports
• Client/Server communication:
for remote access to parameters or status information
• Remote Control of Devices
• Event driven communication („on-demand communication“)
© EtherCAT Technology Group
Industrial Ethernet Technologies
By introducing SLMP aims to install a common protocol layer and thus a
“cross-media” communication option for all CC-Link technologies. This
can be seen as the attempt to provide an approach similar to CIP (ODVA)
– however, SLMP does not contain device profiles. Thus, it may provide a
common “how to communicate” protocol, but lacks a “what to
communicate” definition.
Industrial Ethernet Technologies
Page 62
© EtherCAT Technology Group, August 2011
CC-Link IE Field: SLMP
Classification
Profinet
• For devices that do not support a dedicated CC-Link IE Field
chip, CLPA suggests using SLMP protocol through TCP/IP
SLMP
SLMP
Ethernet
Ethernet
TCP
IP
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Master
Switch
Slave
Slave
Ethernet
Device
Gate
way
Switch
Gbit
Slave
Slave
SLMP
Ethernet
Device
Modbus/TCP
Ethernet
Device
10/100MBit Ethernet
or Gbit
Device
Ethernet
Device
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
CLPA suggests to use the SLMP via TCP/IP approach for devices such
as RFID controllers, HMI, Barcode readers or Vision Sensors. Of course
this approach is non-real time.
To make this very clear: According to the available specifications, CC-Link
IE Field cannot transport other Ethernet traffic such as TCP/IP. The SLMP
via TCP/IP approach simply means that the SLMP protocol of CC-Link IE
can also be transported via TCP/IP, and Ethernet TCP/IP devices also
supporting the SLMP protocol can exchange information with a CC-Link IE
network via a gateway.
Industrial Ethernet Technologies
Page 63
© EtherCAT Technology Group, August 2011
CC-Link IE Field: Performance
Gbit
100 MBit
Classification
Performance Examples:
Profinet
No of
Nodes
Size of exchanged
I/O process image
per node [Bytes]
No of Devices with
asynchronous
Communication
Link Scan Time
(=Cycle Time)
Normal | High
Speed Mode [ms]
EtherCAT
[ms]
8
16
0
0,9 | 0,3
0,03
16
16
0
1,1 | 0,5
0,05
16
16
16
2,2 | 0,6
0,05
32
16
32
3,6 | 0,9
0,09
64
8
64
6,4 | 1,5
0,14
64
16
64
6,5 | 1,6
0,18
64
32
64
6,6 | 1,8
0,26
120
16
120
11,4 | 2,8
0,33
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
Cycle Time
Computed with Formulas from Mitsubishi CC-Link IE Field Network Master/Local Module User‘s Manual
•
CC-Link IE Field Cycle Time is sensitive to number of nodes,
but hardly influenced by amount of data exchanged.
•
EtherCAT is about 10 x faster than CC-Link IE Field in High Speed Mode
© EtherCAT Technology Group
Industrial Ethernet Technologies
The Mitsubishi CC-Link IE Field Master supports two modes: Normal
Mode – which is the default - performs both cyclic and acyclic (transient)
transmission without losing their inherent speed performance, while High
Speed Mode preferentially performs cyclic transmission for high-speed
communications and reduces processing speed for transient
transmissions. In High Speed Mode the maximum data size for register
communication is reduced.
Similar to CC-Link IE Control, the cycle time of CC-Link IE Field is hardly
influenced by the amount of data exchanged. In contrast, due to its
functional principle, EtherCAT is hardly influenced by the number of nodes
– and is much faster anyhow, in spite of using 100Mbit technology.
The Link Scan Time (=Cycle Time) formula used was taken from Appendix 5.2
(Link Scan Time) of the “MELSEC Q CC-Link IE Field Network Master/Local
Module User’s Manual” SH(NA)-080917ENG-E(1107)MEE of July 2011, found
on www.meau.com (Mitsubishi Electric Automation Inc, USA). Please note that it
is not (yet) possible to download this manual from within Europe – it looks like
you have to have an American IP Address to access it. We used the link scan
time formula with Ka=25,8 (Normal Mode)|18,5 (High Speed), Kb=655
(NM)|168(HS), Kc=160+60*(no_of_nodes_with_acyclic_comm)(NM)|80(HS),
Ni=0 and Kd (Maximum data link processing time when the station is
disconnected from or returned to the network) =0. Using recommended values
for Kd leads to additional ~20ms cycle time. For error case considerations this
time has to be added. For Cyclic Transmission Delay Time the Link Refresh
Times have to be taken into account as well.
Industrial Ethernet Technologies
Page 64
© EtherCAT Technology Group, August 2011
CC-Link IE: Adoption Rate
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
CC-Link IE Control:
Four years after its introduction, there is no visible adoption of CCLink IE Control outside Mitsubishi:
•As of August 2011, the CLPA product guide only lists 2 nonMitsubishi products: both are fibre optic cable.
Since the interface ASIC seems not to be available for third parties,
the hw costs of a CC-Link IE Control interface cannot be determined.
CC-Link IE Field:
About one year after its introduction, there is no visible adoption of
CC-Link IE Field outside Mitsubishi:
•As of August 2011, the CLPA product guide only lists 3 nonMitsubishi products: two cables, one switch.
Since the interface ASIC CP220 is not (yet) available in Europe, the
hw costs of a CC-Link IE Field interface could not be determined.
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
HMS Anybus shows a CC-Link IE Field Interface card on its website.
According to HMS, it is released for samples.
Industrial Ethernet Technologies
Page 65
© EtherCAT Technology Group, August 2011
CC-Link IE: Summary
¾Classification
¾Profinet
¾Ethernet/IP
¾CC-Link IE
¾Sercos III
¾Powerlink
¾Modbus/TCP
¾EtherCAT
CC-Link IE Control:
• Non-open, Mitsubishi-only fiber optic ring network making use of
Gigabit Ethernet physical layer.
• Requires separate network, transport of TCP/IP and other
Ethernet traffic is not specified.
• Intended and suitable for shared memory communication between
Mitsubishi PLCs.
CC-Link IE Field:
• Semi-open, so far de-facto Mitsubishi-only Gigabit Ethernet based
communication technology.
• Rather poor utilization of Gigabit transmission speed, less
performance than competing 100Mbit/s technologies such as
Profinet.
• According to the Spec, other Ethernet traffic (including TCP/IP)
cannot be transported trough a CC-Link IE field network
¾Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Seems difficult to find a convincing reason why an automation vendor
should adopt any CC-Link IE variant – it will be challenging to position CCLink IE as an alternative to existing Industrial Ethernet Technologies.
Industrial Ethernet Technologies
Page 66
© EtherCAT Technology Group, August 2011
SERCOS III Features
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
•
•
•
•
•
•
•
•
•
•
•
•
Combining Sercos mechanism with EtherNet Physics
100 MBit network transmission rate
Hardware based synchronization and ring topology
Integration of NRT channel, e.g. for TCP/IP
Cyclic and acyclic communication
Cross-communication between slaves
Media redundancy support
Control recognizes the physical order of devices
100BASE-TX or Fibre Optics based physical layer
Hard Real Time Requires Special Master Card
maximum of 511 slave nodes per network (since V1.1)
Line + Ring Topology, only.
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
The list of features of SERCOS-III reads like the list of features of
EtherCAT – except the last three items.
C
Industrial Ethernet Technologies
Page 67
© EtherCAT Technology Group, August 2011
SERCOS III Functional Principle
AT: Drive
Telegram
Classification
NRT: Non Real
Time Frames
MDT: Master
Data Telegram
C
Profinet
AT
MDT
NRT
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
Master
•
•
•
•
•
Slave
Slave
Slave
Slave
Slave
Slave
Slaves extract and insert data on the fly
Master sends frames – 2 or more per cycle
Slaves process frames twice
NRT data is inserted in gaps (NRT channel)
Telegram structure fixed at run time.
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
SERCOS-III has adopted the EtherCAT functional principle: processing Ethernet
frames on the fly. There are some main differences, though:
1. SERCOS-III separates input and output data in two frames – so there are at minimum
two frames per cycle
2. The slaves process the data twice: on the way out and on the way back
3. Very rigid frame layout – no changes at runtime, no bit-wise mapping.
4. Non Realtime Data (such as TCP/IP) is inserted in gaps between the frames.
These differences have the following impact – compared with EtherCAT:
1. Bandwidth utilization is lower. Dual processing in the slave devices. Therefore in
average 2-3 times slower than EtherCAT.
2. Separating input and output data and processing twice allows for topology independent
slave-to-slave communication within the same cycle. For topology independent slaveto-slave communication, EtherCAT has to relay the data through the master
(performance implementation dependent, can also be done with 2nd frame within in
the same cycle). However, since Servos III overall cycle time is higher, slave-to-slave
performance is not better than with EtherCAT.
3. Due to the „processing twice“ principle, only line topology (+ ring for redundancy) are
possible: no drop lines, tree configuration etc.
4. No flexibility in process data communication: same update rate for all nodes and data.
5. If the IP gap is shorter than the maximum Ethernet frame length (< 122 µs), the MTU
(Ethernet Maximum Transmission Unit) has to be adapted accordingly: the device
interfacing Ethernet to Sercos III has to handle the fragmentation, similar to an
EtherCAT switchport.
Industrial Ethernet Technologies
Page 68
© EtherCAT Technology Group, August 2011
SERCOS III Topology
Classification
Master
Master
... SERCOS-IIIInterface
Profinet
S ... Slave
... Primary Ring
Ethernet/IP
CC-Link IE
... redundant
secondary
Ring
...
...
S1
S1
Sercos III
S2
S2
Sn
Sn
Powerlink
Modbus/TCP
EtherCAT
Summary
Line structure (single ring)
© EtherCAT Technology Group
Ring structure (double ring)
Industrial Ethernet Technologies
SERCOS-III supports line and ring topology, only.
Ring structure: Recovery time in case of cable failure < 25µs.
No star or tree topology, thus no hot-connect of branches.
Industrial Ethernet Technologies
Page 69
© EtherCAT Technology Group, August 2011
SERCOS III Communication Cycle
Classification
MDT: Master
Data Telegram
AT: Drive
Telegram
typically: 1 MDT + 1 AT
Telegram per Cycle
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
If IP Channel used:
gap needed
Summary
Source: Presentation at Real Time Ethernet Seminar, Reutlingen, March 2005
© EtherCAT Technology Group
Industrial Ethernet Technologies
IP data is inserted in a gap („IP channel“).The gap can either be after the
input and output frames (method 1) or in between (method 2).
Industrial Ethernet Technologies
Page 70
© EtherCAT Technology Group, August 2011
SERCOS III Telegram Structure
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
Source: Presentation at Real Time Ethernet Seminar, Reutlingen, March 2005
© EtherCAT Technology Group
Industrial Ethernet Technologies
Once in real time mode, Sercos-III uses the same frame structure in every
cycle. Therefore there is no flexibility in process data communication: each
node and each process data part is updated at the same rate.
It is thus not possible to e.g. cyclically read a status bit of a device and
request data only if this status bit indicates new data.
Furthermore, since the process data length per node is fixed to either 2,4
or 8 bytes (+ 4 bytes status per device), this approach is not ideal for
devices with very small process data images (like digital I/O).
Industrial Ethernet Technologies
Page 71
© EtherCAT Technology Group, August 2011
SERCOS III Synchronization
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Synchronization Accuracy depends on Master Accuracy: hardware support required
Summary
Source: Presentation at Automation Summit, Beijing, June 2007
Source: Prof. Schwager, FH Reutlingen
© EtherCAT Technology Group
Industrial Ethernet Technologies
Just like with SERCOS-II, synchronization in SERCOS-III is based on
cyclic, deterministic and jitter-free communication. This requires special
hardware support in the master: a special dedicated SERCOS master
card.
IEEE1588 support may be added later, but will as well need hw support
for accuracy.
Industrial Ethernet Technologies
Page 72
© EtherCAT Technology Group, August 2011
SERCOS III Synchronization
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Announced in April 2007:
Soft-Master, suitable if RTOS-Jitter is sufficient for Node Synchronization
Summary
Source: Presentation at Automation Summit, Beijing, June 2007
© EtherCAT Technology Group
Industrial Ethernet Technologies
In April 2007, Sercos International announced the development of a
Sercos-III “Soft-Master”, implementing the master functionality using
software (+ a standard Ethernet Port). According to the press release
(quote), ”The achievable synchronization accuracy of a SERCOS III realtime network using a soft master is depending on the performance of the
hardware and the characteristic of the used operating system”.
Sercos International:
• special hardware support for 1µs jitter
• soft master for up to 50µs jitter
Industrial Ethernet Technologies
Page 73
© EtherCAT Technology Group, August 2011
SERCOS III Implementation
Classification
1. FPGA solution
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
2. Integrating SERCOS III interface into
universal communication controllers
Cost effective
Makes “single-chip devices” possible
Multi-Protocol capability
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
SERCOS-III Controllers are FPGA based. Later a hardcopy version may
be added.
Alternatively the Hilscher netX chip family can be used, which also
supports EtherCAT + Profinet
In order to push the adoption of the SERCOS I/O profile (which was
published in Nov 2006), Sercos launched Easy-I/O in April 2007), a free IP
Core for the Xilinx Spartan-3 XC3S250E FPGA. This code is limited to 64
Byte I/O data, and targeted at encoders, measuring sensors, valve
clusters, 24V digital I/O and analog I/O. It is not suitable for Sercos-III
drive implementation.
As of 1/2011, no product using this free IP-core is listed in the Sercos
product guide.
For Sercos International (SI) members, a commercial IP core for SercosIII is available for a one time fee. For non members of Sercos International
an annual license fee for this IP core applies. Alternatively, run-time
licenses are available (non members pay double runtime fees).
In April 2009, Sercos International announced to publish a Sercos-III
master API under GPL license. The API only supports the SERCON100M
Master IP Core (no generic Ethernet MAC). As of Aug 2011,
documentation is in German language, only (English version announced).
Industrial Ethernet Technologies
Page 74
© EtherCAT Technology Group, August 2011
SERCOS III Performance Overview
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Cyclic
data
8
12
16
12
32
12
50
32
12
Byte
Byte
Byte
Byte
Byte
Byte
Byte
Byte
Byte
Cycle
time
No. of
slaves (1)
31,25 us
62,5 us
125 us
250 us
250 us
500 us
1 ms
1 ms
1 ms
7
14
26
61
33
122
97
137
251
No. of
slaves (2)
No. of
slaves (3)
No. of
MDT / AT
30
17
94
85
120
220
2
8
21
57
31
120
95
134
245
1/1
1/1
1/1
1/1
1/1
2/2
4/4
4/4
4/4
1) without NRT channel
Modbus/TCP
2) with NRT channel: 1500 bytes = 125 µs
3) with NRT channel: 250 bytes = 20µs
EtherCAT
Summary
Source: Peter Lutz, Sercos International, 29.09.2008
© EtherCAT Technology Group
Industrial Ethernet Technologies
This performance data was provided by Sercos International in September
2008. At cycle times below 250µs the IP channel is shorter than a
maximum frame length, and thus IP traffic is fragmented: MTU (Ethernet
Maximum Transmission Unit) has to be adapted accordingly by the
gateway.
This MTU adaptation is not supported by all gateways – in fact, the only
gateway listed in the Sercos product guide as of Aug 2011 does not
support this functionality.
Industrial Ethernet Technologies
Page 75
© EtherCAT Technology Group, August 2011
SERCOS III Performance Comparison
Classification
Profinet
No. of Nodes with
given Cycle Time
Sercos III
Powerlink
Modbus/TCP
EtherCAT
EtherCAT
Application
Example
Cyclic
Data
(I+O)
Cycle
Time
No. of
Devices
without IP
channel
with IP
Channel
(20µs
|125µs)
No. of
Devices
with IP
remaining
Bandwidth
for IP
1
8 Byte
31,25 µs
7
2|-
20
48,1%
2
12 Byte
62,5 µs
14
8|-
40
32,3%
3
16 Byte
125 µs
26
21 | -
72
22,3%
4
12 Byte
250 µs
61
57 | 30
180
25,8%
5
32 Byte
250 µs
33
31 | 17
80
12,2%
6
12 Byte
500 µs
122
120 | 94
400
20,6%
7
50 Byte
1 ms
97
95 | 85
225
6,4%
8
32 Byte
1 ms
137
134 | 120
340
9,1%
9
12 Byte
1 ms
251
245 | 220
800
19,8%
Ethernet/IP
CC-Link IE
SERCOS-III
Summary
Same Sercos data as previous slide, now in comparison with EtherCAT.
© EtherCAT Technology Group
Industrial Ethernet Technologies
Comparing SERCOS-III and EtherCAT performance: at given cycle times
and amount of data per slave, the maximum number of nodes is given for
both technologies.
Please note that as of Aug 2011, there is no gateway available supporting
the shortened IP channel (which would lead to the values marked in
green)
Industrial Ethernet Technologies
Page 76
© EtherCAT Technology Group, August 2011
SERCOS III Performance Comparison
Classification
Profinet
Cycle Time with
given No. of Nodes
SERCOS-III
EtherCAT
Cyclic
Data
(I+O)
Cycle
Time
No. of
Devices
without IP
channel
No. of
Devices
with IP
Channel
No. of
Devices
with IP
Resulting
Cycle Time
Ethernet/IP
Application
Example
CC-Link IE
1
8 Byte
31,25 µs
7
2|-
2
10 µs
2
12 Byte
62,5 µs
14
8|-
8
23 µs
3
16 Byte
125 µs
26
21 | -
21
47 µs
4
12 Byte
250 µs
61
57 | 30
57
95 µs
5
32 Byte
250 µs
33
31 | 17
31
106 µs
6
12 Byte
500 µs
122
120 | 94
120
203 µs
7
50 Byte
1 ms
97
95 | 85
95
446 µs
8
32 Byte
1 ms
137
134 | 120
134
435 µs
9
12 Byte
1 ms
251
245 | 220
245
350 µs
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Another view for the comparison: now the number of nodes and the
amount of data per slave is fixed, and the resulting cycle time is
compared.
Industrial Ethernet Technologies
Page 77
© EtherCAT Technology Group, August 2011
SERCOS III Performance Comparison
Cycle Time Comparison
Classification
1000
Profinet
900
SERCOS-III
800
Ethernet/IP
Sercos III
Powerlink
Cycle Time [µs]
CC-Link IE
EtherCAT
700
600
500
400
300
200
Modbus/TCP
100
0
EtherCAT
1
2
3
4
5
6
7
8
9
Application Examples
Summary
© EtherCAT Technology Group
A graphical view for the previous table.
In average (over 9 different application scenarios), EtherCAT is 2,7 times
faster.
Industrial Ethernet Technologies
Page 78
© EtherCAT Technology Group, August 2011
SERCOS III IP-Handling (I)
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
• At Boot-Up, Slaves are in NRT
Slave
(Non Real Time) Mode until they
see first RT Frame
• In NRT Mode, Slave Chips
Protocol
behave like 3-port Switches
Handler
• Each node needs a MAC Address
• The internal Switches are
3 Port
implemented with “Store and
Switch
Forward” or with “Cut Through”
methodology
• Forwarding Delay depends on
No. of Nodes, size of IP or NRT slot, frame size and switch
methodology (may differ from node to node)
• Typical Store and Forward Delay per Node and Direction:
10…125µs, depending on Frame Length
EtherCAT
Summary
© EtherCAT Technology Group
Sercos-III implementations either follow the “store and forward” approach
for the switch (NRT) mode, which in case of Sercos-III means that the
NRT frame is only forwarded in the next cycle, or the follow the “cut
through” methodology, which means that they forward the frame only
within the same cycle if after the analysis of the destination address the
remaining IP-Slot is able to carry the maximum frame length.
It will be interesting to see how the IP communication over a large number
of cascaded switches behaves.
Industrial Ethernet Technologies
Page 79
© EtherCAT Technology Group, August 2011
SERCOS III IP-Handling (II)
Classification
Profinet
for IP Access to Slave Devices via TCP/IP:
• Gateway Device or Master with Gateway Functionality Required
• or access through open port @ last node in line
Ethernet/IP
CC-Link IE
Gateway
Device
Sercos III
AT
Powerlink
Modbus/TCP
MDT
Master
IP
Slave
Slave
Slave
Slave
Slave
EtherCAT
Summary
© EtherCAT Technology Group
In order to allow for IP access to slave devices at run-time, either routing
through the master or a special gateway device have to be used.
This is the same if IP access (e.g. for remote diagnosis) shall be
supported without the need to physically connect the link first.
If an unused port is available, this can be used alternatively. Since
Sercos-III Devices have two ports, in line topology there is one unused
port at the last node in the line (no unused port in ring topology)
Industrial Ethernet Technologies
Page 80
© EtherCAT Technology Group, August 2011
SERCOS III IP-Handling (III)
Classification
• In RT Mode, IP Traffic is inserted in IP Channel
• During IP Channel, Slave is in Switch Mode
Profinet
AT
MDT
IP
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Master
Slave
Slave
Slave
Slave
Slave
Slave
• If IP slot is short or slave controller chip works with store and
forward methodology, forwarding of larger frames is delayed to
the next cycle – in this case sending a frame e.g. to node 50
takes 50 cycles, response frame accordingly (TCP/IP
handshake).
• IP channel performance strongly depends on No. of Nodes
• As of August 2010, Multi IP-Frame Operation not implemented:
Within one cycle only one frame can be handled, regardless of
IP-channel size
Summary
© EtherCAT Technology Group
In each RT cycle, the slave controllers switch between “processing on the
fly-mode” for process data and “switch-mode” for IP data.
The forwarding behavior of IP frames in the IP slot depends on the slave
device capabilities and on the network configuration
Industrial Ethernet Technologies
Page 81
© EtherCAT Technology Group, August 2011
Sercos III IP-Channel, Store + Forward
Classification
Profinet
• In NRT Mode, incoming frames are buffered (Collision buffer)
• Store + Forward:
Frame is buffered until next IP-Channel is active (next cycle)
Ethernet/IP
Local Application
CC-Link IE
Sercos III
Internal
Rx Port 1
Internal
Tx Port 1
Internal
Rx Port 2
Internal
Tx Port 2
Collision Buffer 2
Powerlink
Collision Buffer 1
MUX
Modbus/TCP
EtherCAT
Rx Port 1
Tx Port 1
MUX
Rx Port 2
Tx Port 2
Example for Sercos-III Chip with Store + Forward Switch: Hilscher NETX Family
Summary
© EtherCAT Technology Group
Current Sercos-III implementations support Store and Forward, which
means that in NRT mode within one cycle an IP frame moves from node n
to node n+1
Industrial Ethernet Technologies
Page 82
© EtherCAT Technology Group, August 2011
Sercos III IP-Channel, Cut-Through
Classification
• In NRT Mode, incoming frames are buffered (Collision buffer)
• Cut Through: Once destination address is received:
Profinet
• If Tx-Port is not allocated by internal Tx-Port and remaining
IP-Slot is > 122µs (max. frame length), frame is forwarded
Ethernet/IP
• Otherwise: frame is buffered until next IP-Channel is active
Local Application
CC-Link IE
Internal
Rx Port 1
Sercos III
Internal
Tx Port 1
Internal
Rx Port 2
Internal
Tx Port 2
Collision Buffer 2
Powerlink
Collision Buffer 1
MUX
Modbus/TCP
EtherCAT
Rx Port 1
Rx Port 2
Tx Port 2
• If IP slot is ≤125µs, Cut-through also forwards in next cycle, only
•
Summary
Tx Port 1
MUX
Example for Sercos-III Chip with Cut-Through Switch: SERCON100 IP Core, for
which, as of August 2010, the IP-Channel frame forwarding has not yet been tested.
© EtherCAT Technology Group
Future Sercos-III implementations plan to support Cut-Through behavior
in NRT mode, which means that an IP frame can move several nodes
before it is stored for the next cycle. However, if the IP slot is shorter than
125µs, Cut-Through Sercos-III slave controllers will also have to behave
like Store-and-Forward implementations and buffer the frame for the next
cycle.
Industrial Ethernet Technologies
Page 83
© EtherCAT Technology Group, August 2011
SERCOS III IP-Performance (I)
Classification
Profinet
Ethernet/IP
IP Channel Performance Considerations
Best Case Scenario:
• All nodes support „Cut Through“-Switch behavior*
• IP channel slot longer than:
max frame length (122µs) + (No of Nodes x delay per switch)
• Then IP frame gets forwarded within one cycle
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
Example:
• Network with 100 Nodes, IP communication with last node (100)
• Cycle Time 1 ms, IP Slot 500µs, 12 Bytes I/O data per device
• Propagation Delay Master → Node 100: 1 Cycle
• Response Time IP Communication (if TCP Connection already
established): 2 ms + Stack delay
EtherCAT
* As of August 2010, Cut Through IP forwarding not yet implemented
Summary
© EtherCAT Technology Group
If IP channel slot is long enough (>>125µs) and cut-through is supported,
the performance of the IP communication may be sufficient. However, as of
August 2010, according to information on the Sercos Website, the “Cut
Through” Switch behavior was not yet implemented.
In August 2011 the North American Sercos website claims that there are
sercos III products currently on the market that support “Cut Through”. The
same website, however, states that the latest release of the Sercos IP Core
documentation is from 2009, when this functionality was not implemented
yet.
Industrial Ethernet Technologies
Page 84
© EtherCAT Technology Group, August 2011
SERCOS III IP-Performance (II)
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
IP Channel Performance Considerations
Worst Case Scenario:
• All nodes support „Store and Forward“-Switch behavior
• IP channel slot is 125µs
• Large IP frames are forwarded in next cycle only
Example:
• Network with 220 Nodes, IP communication with last node (220)
• Cycle Time 1 ms, IP Slot 125µs, 12 Bytes I/O data per device
• Propagation Delay Master → Node 220: 220 Cycles
• Response Time IP Communication (if TCP Connection already
established): 440ms + Stack delay
• If node implementation only supports forwarding in next cycle,
then even establishing a TCP/IP connection takes >660ms
(Three Way Handshake)
Summary
© EtherCAT Technology Group
If IP channel slot is short IP communication performance may deteriorate
substantially – especially in larger networks.
This can be avoided by smart configuration tools, which take the node
behavior and network size into account and adjust the IP slot time
accordingly.
It is obvious, though, that the IP handling mechanism of SERCOS III
works best in small networks.
Industrial Ethernet Technologies
Page 85
© EtherCAT Technology Group, August 2011
SERCOS III V1.1
Classification
• In July 2007, SERCOS International released the 1.1 version
of the SERCOS-III specification
Profinet
• Main changes are:
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
- Device addressing changed, now topology dependent
- Parameter addressing changed from 16-bit IDN to 32-bit structured EIDN
- status + control word format and content changed
- Redundancy and hot-plug features introduced
- Communication model changed from master/slave to connection oriented - 511 instead of 254 slave devices supported
- Mandatory IP channel introduced
- Interrupt handling changed, now one Sync-IRQ
• The specification changes require hardware adaptations
(Sercos controllers) and also major software changes.
• Version 1.0 and Version 1.1 devices are not interoperable
• First SERCOS-III V1.1 drives were shipped in Dec 2007.
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
This means that, as of beginning of 2008, Sercos-III field deployment and
application experience started all over again.
On the other hand, since hardly any Sercos-III devices were shipped
before 2008, this does not seem to be a major problem.
By introducing 32bit IDNs and thus enhancing the IDN address space,
Sercos-III device profiling differs from the profiles used in Sercos-I and –II.
Current Sercos III version is V1.1.2, which introduced hotplug capabilities
and the support of software implemented masters.
Industrial Ethernet Technologies
Page 86
© EtherCAT Technology Group, August 2011
SERCOS III V1.3
Classification
• In Q3 2011, SERCOS International plans to release the 1.3
version of the SERCOS-III specification
Profinet
• Main changes to V1.1.2 are:
Ethernet/IP
• Support of different producer cycle times (multiplexing of I/O data): not
necessary any more to update all nodes in the network with the same
cycle
CC-Link IE
• Introduction of an application timestamp: resolution 1 ms, for
establishing a system wide application time, not for synchronization
Sercos III
• 3-buffer mechanism for process data
• Introduction of oversampling data types
Powerlink
• It is intended to maintain downwards compatibility: masters
supporting V1.3 should also be able to run V1.1.2 slaves.
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
It seems that Sercos-III is not stable yet.
Industrial Ethernet Technologies
Industrial Ethernet Technologies
Page 87
© EtherCAT Technology Group, August 2011
SERCOS III Summary
Classification
Profinet
Ethernet/IP
CC-Link IE
• High Performance Industrial Ethernet Approach
• Focus on drives, so far very limited I/O, sensor, valve etc. support
• Topology: line and ring only, no branches, no drop lines,
no hot connect of segments.
• Not more than 511 nodes per network, therefore modular I/O with
bus couplers (and associated delays).
• Requires dedicated master-card for hard real time
Sercos III
Powerlink
Modbus/TCP
EtherCAT
• Soft-Master implementation for jitter up to 50µs
• Depending on configuration IP traffic can be slow
• Has been the approach that is the latest on the market
• Slow adoption rate (few Sercos I/II vendors move to Sercos III)
• EtherCAT supports the same device profile + application layer
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
SERCOS-III achieves a performance comparable with Profinet IRT – and
thus sufficient for most applications.
Whilst the SERCOS technology has a good reputation for servo drive
control, support for I/O, sensors, or other devices is not yet established.
Slow adoption rate: So far few support Sercos-III in Servo Drives. And
almost all these vendors have EtherCAT drives available.
In Nov. 2007, Elau announced support of Sercos-III as system bus. In Nov
2008, Keba did the same.
By the way: out of the 34 Sercos-I/II servo drive suppliers, 29 are ETG members. Out of
the missing 5 vendors, two discontinued their Sercos business.
Out of the 29 ETG members also supporting Sercos I/II, 23 have already shown or
announced EtherCAT drives (as of August 2011)
Industrial Ethernet Technologies
Page 88
© EtherCAT Technology Group, August 2011
Powerlink: Overview
Classification
Profinet
Ethernet/IP
CC-Link IE
•
•
•
•
•
•
Ethernet Approach originally introduced by B+R
Medium Access Control by Polling (similar to Profibus)
TCP/IP for Parameters, seperate Process Data Protocol
uses Hubs
active Master Plug-in-Card required, no Standard NICs
soft realtime („open“) mode initially announced for 2005
B
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Powerlink replaces the Ethernet CSMA/CD Media Access Control Method
by Polling: The master (called managing node) sends a poll request to
each slave (called controlled node) which then answers with a response.
Hubs (no switches): the Powerlink Spec states: „To fit EPL jitter
requirements it is recommended to use hubs“*.
Protected real time mode: Since the Powerlink topology (up to 10 nodes in
line configuration) violates IEEE802.3 roundtrip delay rules, CSMA/CD
does not work in this configuration – so a network designed for protected
mode cannot be accessed with standard Ethernet interfaces (not even in
non-realtime mode).
* In theory switches can be used, but due to the additional latency the network
performance would be unacceptable. All performance calculations in the Powerlink spec
assume a Hub Delay Time of 500ns – „store and forward“-switches have a delay time of
>10µs (for short frames), „cut through“-switches have a delay time (according to Intel) of
~7,5µs. If hubs were replaced by switches with 10µs delay, the cycle time of example 4 in
the Powerlink Spec would be increased from 2,34 ms to 19,44 ms.
In September 2005, EPSG announced that Micrels new 3-Port switch chip is endorsed for
Ethernet Powerlink implementations. However, in Powerlink applications this switch chip
is operated in half duplex repeater mode, only. Thus it is a switch chip that supports a hub
mode, too.
Industrial Ethernet Technologies
Page 89
© EtherCAT Technology Group, August 2011
Powerlink: Functional Principle
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Master
Slave
1
HUB
3
HUB
HUB
7
Modbus/TCP
2
HUB
HUB
Profinet
• Polling
(Marketing: Time Slice…)
• Hubs only, half duplex
• Broadcast: every node
receives every frame
• Thus high Interrupt load
and processing
requirements
• Limited Line Topology
(Hub Delays)
Slave
4
Slave
HUB
Classification
5
EtherCAT
6
Slave
Slave
Slave
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Powerlink Marketing calls the Media Access Method „Time Slicing“ or „Slot
Communication Network Management“. The principle nevertheless is
polling – the controlled device only „speaks“ after it was „asked“.
Due to the broadcast nature of hubs, all nodes receive all frames.
Therefore the nodes have to filter each frame.
The broadcast mechanism can be used for slave to slave communication
(consumer/producer principle). However, performance of slave to slave
communication cannot be better than the cycle time...
The accumulation of the hub delays limits the number of nodes in a line
topology.
Industrial Ethernet Technologies
Page 90
© EtherCAT Technology Group, August 2011
Powerlink Timing
• Overall Network Performance depends on Slave Implementation + Topology:
Classification
• Fast response time requires powerful processors on the slave (controller) side –
or implementation in Hardware (FPGA)
Profinet
• A lot of „idle time“ on the media, caused by stack delays plus cascaded hubs
Ethernet/IP
Cycle Time
CC-Link IE
Start of
Cyclic
(SoC)
Sercos
III
Poll
Request
(PReq)
Tstart = 26…45µs
Powerlink
~7µs
Propagation Delay
(Hubs + Cable)
Depends on
Topology
Poll
Response
(PReq)
for 1…43 Bytes
of Process Data
Poll
Request
(PReq)
Master
Response Time,
Depends on
Implementation
Start of
Async
(SoA)
Async
Send
(ASnd)
TAsyncMax = 152…200µs
Modbus/TCP
EtherCAT
Slave
Response Time,
Depends on
Implementation
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
The timing (and thus the performance) of a Powerlink network is mainly
determined by the topology and the node response times: each poll
request first has to get from the master through all hubs (both the external
ones and the integrated ones in a daisy chain or line topology) to the
destination node, then the node has to process the request, send the
response, which then again goes through all hubs back to the master.
Only after the master has received the response, he can issue the next
poll request.
At the end of the cycle there is the asynchronous phase.
Industrial Ethernet Technologies
Page 91
© EtherCAT Technology Group, August 2011
Powerlink Synchronization
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
• Powerlink Spec (2.0) says:
• At the beginning of each isochronous phase, the
Master Node transmits the multicast SoC message
very precisely to synchronize all nodes in the network.
• Propagation Delay compensation is not available
• Thus the synchronization accuracy depends on
• Ability of the Master (M) to transmit SoC equidistantly
• Ability of the Slave (S) to timestamp SoC precisely
• Accumulated Jitter of all hubs between M and S
This means:
• Powerlink Implementations without special hardware
support (such as “openPowerlink”) cannot provide
accurate synchronization by design.
• Synchronization accuracy is always topology dependent.
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Furthermore, the cycle time setting must provide sufficient leeway for accumulated response jitter
of all nodes and for repeating corrupt messages.
EPSG announced several times (also in the V2.0 spec of 2006) that precise synchronization
using IEEE1588 time precision protocol will be added in V 3.0 – however, as of August 2011, there
is no such V 3.0 in sight.
Industrial Ethernet Technologies
Page 92
© EtherCAT Technology Group, August 2011
Ethernet/IP
Drive
Drive
Drive
Profinet
Master
Drive
Application Example:
• 6 Drives
• 2 I/O Nodes
• 400 m Cable Length
• Cycle Time: 291 µs
Drive
Classification
Drive
Powerlink Performance (I)
HUB
HUB
HUB
HUB
HUB
HUB
I/O
I/O
HUB
HUB
CC-Link IE
Sercos III
Powerlink
For Comparison:
• Sercos II (16 Mbaud): < 250 µs
Modbus/TCP
• EtherCAT: 17 µs.
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
This performance example is taken from the Powerlink V 2.0 specification, Version 0.1.0. In this
version of the spec, the
-slave response time = 8µs
-master response time = 1µs (!)
-TAsyncMax = 90µs
-TStart = 45µs
-THubDelay = 0,5µs
and the resulting Cycle Time is 291 µs.
In Powerlink V 2.0 specification Version 1.0.0, (which is the current one), this performance example
is not available any more. However, the performance examples in this version assume
-slave response time = 1µs (!)
-master response time = 1µs (!)
-TAsyncMax = 120+32 (=152)µs + maximum signal propagation
-TStart = 26µs
-THubDelay = 0,5µs
Applying these values to the performance example shown above leads to a Cycle Time of 281 µs.
However, the Powerlink Spec does not demand any specific slave response time, and manuals or
data sheets of Powerlink products typically do not provide that value. Meanwhile most B&R
Powerlink products are FPGA based and thus provide a short response time – since there are few
“non-B&R” Powerlink products, such a short response time may be assumed. However, we have
seen Powerlink drives in a multivendor motion control demonstrator (equipped with a network
analyzer tool) on an EPSG booth with a response time of 10..20µs.
Industrial Ethernet Technologies
Page 93
© EtherCAT Technology Group, August 2011
Powerlink Performance (II)
Classification
Master
Profinet
Drive
Drive
Drive
Drive
Drive
Drive
Drive
Drive
HUB
HUB
HUB
HUB
HUB
HUB
HUB
HUB
Drive
Drive
HUB
HUB
Drive
Drive
Drive
Drive
Drive
Drive
Drive
Drive
HUB
HUB
HUB
HUB
HUB
HUB
HUB
HUB
…
Total of 500 m Cable
40
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
HUB
HUB
HUB
HUB
HUB
HUB
HUB
HUB
I/O
I/O
HUB
HUB
…
50
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
HUB
HUB
HUB
HUB
HUB
HUB
HUB
HUB
Cycle Time with 8 µs Slave Response: 2347 µs
Cycle Time with 1 µs Slave Response: 1767 µs
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
This performance example is referenced in the EtherCAT introductory presentation, it is
taken from the Powerlink V 2.0 specification, Version 0.1.0.
In this version of the spec, the
-slave response time = 8µs
-master response time = 1µs (!)
-TAsyncMax = 90µs
-TStart = 45µs
-THubDelay = 0,5µs
and the resulting Cycle Time is 2347 µs.
In Powerlink V 2.0 specification Version 1.0.0, this performance example is not available
any more. However, the performance examples in this version assume
-slave response time = 1µs (!)
-master response time = 1µs (!)
-TAsyncMax = 120+32 (=152)µs + maximum signal propagation
-TStart = 26µs
-THubDelay = 0,5µs
Applying these values to the performance example shown above leads to a Cycle Time of
1767 µs.
EtherCAT cycle time for this setup would be 276µs if one waits for the frame to return
before the next one is sent out, or 125µs if one does not wait (unlike Powerlink, EtherCAT
is full-duplex)
Industrial Ethernet Technologies
Page 94
© EtherCAT Technology Group, August 2011
Powerlink Performance (III)
Classification
Profinet
Topology Dependency of Powerlink Performance
Performance Example 2 in the current Powerlink Spec
comes in two topology options: star and daisy chain
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
Star Topology,
53 nodes:
Cycle Time 999 µs
Daisy Chain Topology,
53 nodes:
Cycle Time 1967 µs
EtherCAT
Summary
Source: ETHERNET Powerlink V2.0 Communication Profile Specification Version 1.0.0
© EtherCAT Technology Group
Industrial Ethernet Technologies
This performance example assumes a slave response time of 1µs (!) and a master
response time of 1µs (!)
With EtherCAT the topology influence on the cycle time is negligible, the cycle time
for separate 53 nodes with the same amount of data is 149µs (@50% bus load).
Industrial Ethernet Technologies
Page 95
© EtherCAT Technology Group, August 2011
Powerlink Interface Costs (I)
Classification
• Originally, Powerlink claimed to use
„standard Ethernet chips only“
Profinet
Ethernet/IP
CC-Link IE
• But: Performance of
Software implemented
Protocol-Stack
unsatisfactory
e.g.
Net+50
XScale425
Hyperstone
Host
2 k DPRAM
128 kB
SRAM
32 bit CPU,
e.g. ARM7, NIOS
512 kB
Flash
Ethernet
MAC
Sercos III
• Nodes need a 32 bit
CPU and infrastructure
Hub Chip / FPGA
Powerlink
Modbus/TCP
• Furthermore, Hub Chips
became bsolete ->
ASIC or FPGA required
PHY
PHY
Trafo
Trafo
RJ45
RJ45
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
This hardware block diagram was drawn by an EPSG member company
and shows the hardware effort for a Powerlink interface based on
standard chips. The discrete design of a Powerlink slave interface is not a
very cost efficient approach.
Industrial Ethernet Technologies
Page 96
© EtherCAT Technology Group, August 2011
Powerlink Interface Costs (II)
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
• Since discrete Interface is
– too slow
– too unpredictable
– way too expensive
• Powerlink moved to
FPGA implementation
• so: now HW-Situation
similar to PROFINET,
SERCOS III and EtherCAT
Host
2 k DPRAM
z.B.
128 kB
SRAM
Net+50
32 bit CPU,
z.B. ARM7
512 kB
Flash
FPGA
Ethernet
MAC
Hub Chip / FPGA
Powerlink
Modbus/TCP
B
C
PHY
PHY
Trafo
Trafo
RJ45
RJ45
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
EPSG is now supporting different implementation possibilities – the most
cost effective is the FPGA solution. It uses the same Altera FPGA that is
used for EtherCAT as well, but requires additional 10ns 256k x 16 SRAM.
In November 2007, IXXAT, B&R + Lenze announced that the master
(managing node) is now also implemented in an FPGA.
The rationale is, according to a press statement*: “Until now on the control
side there were only solutions which had limited performance and which
were not suitable or too expensive for extremely demanding applications
such as highly dynamic motion systems, since very powerful CPUs are
used.”
* Translated from the Article “Master-FPGA für Powerlink”, Computer&Automation Magazine 12/2007, p.17
Industrial Ethernet Technologies
Page 97
© EtherCAT Technology Group, August 2011
Powerlink: Versions
Classification
Network
Version
Feature
Availability
Profinet
Powerlink
Version 1
• Protected mode only
• Half Duplex Polling (Hubs)
Available by B&R
only
Ethernet/IP
Powerlink
Version 2
•
•
•
•
•
•
•
Spec: 2003
• Devices
Shipping: 2007
Powerlink
Version 3
• New protocol principle:
Burst Polling
• Switched Gbit Ethernet
Based
• IEEE1588 synchronization
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Network Management
New Frame Structure
MAC-Addressing
Asynchronous Channel
TCP/IP Support
Bridge / Router Support
Profile Support (CANopen)
Announced 2006
First outline 2009
Spec: ???
• Devices
Shipping: ???
Industrial Ethernet Technologies
Powerlink Version 1 products are available from B&R only.
Powerlink Version 2: Lenze Drives (founding member of Ethernet
Powerlink Standardization Group and driving force behind V2) started
shipping first Powerlink Products End of 2006. Lenze has meanwhile
moved to EtherCAT as system bus (Powerlink may remain in use for
applications in which there is no controller, just networked drives)
Powerlink Version 3 (Gigabit Powerlink) was announced in November
2006. Lenze is not contributing to Powerlink V3, which seems to be B&R
driven. In 2009 B&R published an article describing the functional principle
(see next slides) and announced products for 2011. As of August 2011, no
Gigabit Powerlink specification has been published (neither within EPSG
nor externally), and the most recent publication mentioning Gigabit
Powerlink on the EPSG Website is from 2008.
Industrial Ethernet Technologies
Page 98
© EtherCAT Technology Group, August 2011
Powerlink V3: Gigabit Powerlink (I)
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
• In November 2006, EPSG announced the next version of the
technology: Gigabit Powerlink
• Initially EPSG publications suggested that they would not risk
another version issue and move the existing technology to
Gigabit Ethernet
• However, in 2/2009 B&R published the new functional
principle of Powerlink V3 (Gigabit Powerlink):
• Switches instead of Hubs
Powerlink
• New Process Data Protocol Principle:
Poll Request Bursting
Modbus/TCP
• New Asynchronous Protocol Handling
EtherCAT
Summary
• Synchronization with IEEE 1588
• As of August 2011, there is no Gigabit Powerlink Spec
available.
© EtherCAT Technology Group
In November 2006, EPSG announced Gbit Powerlink as a simple
hardware modification (Quote from Powerlink “Facts” 1/2007:
“POWERLINK users can easily boost network performance by a factor of
10. Changing the hardware platform to include 1 Gigabit hardware instead
of 100 Mbit components is all any developer must do, resulting only in a
somewhat different list of components to be fitted onto an otherwise
identical PCB.”)
However, this approach was later abandoned: Doing the math's shows
that the performance gain would have been minimal. Depending on the
configuration, a factor of 1.38…2 was to be expected, since most of the
Powerlink cycle time is made up by stack delays which are not influenced
by bandwidth increase. Furthermore, moving on to switches increases the
forwarding delay within the infrastructure substantially, which would have
over-compensated the bandwidth increase.
So in 2/2009 it was announced that Powerlink V3 will be based on a new
functional principle (see next slide).
Many device vendors postponed their Powerlink implementation plans
since V2 was already outdated in 2006/2007, and Gigabit Powerlink not
yet specified.
Industrial Ethernet Technologies
Page 99
© EtherCAT Technology Group, August 2011
Powerlink V3: Gigabit Powerlink (II)
Classification
Profinet
Powerlink V2: Polling (Half Duplex)
SoC
PReq
S1
PRes
S1
Ethernet/IP
CC-Link IE
Sercos III
PReq
S2
PRes
S2
PRes
M
PRes
S3
SoA
100 MBit/s
ASnd
Sn
Powerlink V3: Burst Polling (Full Duplex)
SoP
PReq
S1
PReq
S2
PReq
S3
PRes
M
PRes PRes PRes
S1
S3
S2
Powerlink
Modbus/TCP
PReq
S3
1 GBit/s
ASnd
Sn
• In Powerlink V3 all Poll Requests will be sent immediately (Burst)
EtherCAT
• The slave devices will answer as quickly as possible – collisions
are avoided by the switches, who sort the responses in queues.
Summary
• The asynchronous bandwidth will be allocated with the help of the
Start of Cycle frame – the Start of Asynchronous Frame is omitted.
© EtherCAT Technology Group
As with the change from Powerlink V1 to V2, the announced version V3 will change both
the protocol and the cyclic behavior of the network. Hence downwards compatibility
cannot be expected.
Hubs will be replaced by switches, and instead of individual polling a “burst polling”
approach will be introduced.
The “Start of Asynchronous” Frame will be abandoned, its functionality will be included in
the “Start of Protocol” (SoP) Frame, which replaces the “Start of Cycle” frame of Powerlink
V2. A node that wants to send an asynchronous frame informs the master by flagging this
in its poll response frame. With the next SoP frame the master then allows the node to
send such a frame. Other than with Powerlink V2, asynchronous frames are thus
postponed to the next cycle.
The “poll response” frames are going to be sent with broadcast MAC addresses –this
preserves the slave-to-slave communication but puts substantial load on all devices,
which have to filter all poll responses. Furthermore, this means that for half of the traffic
the switches sacrifice their routing capabilities and become “slower hubs”.
For synchronization with IEEE 1588, the sync frame of the 1588 protocol is included in the
SoP frame. All switches have to support the IEEE 1588 peer-to-peer, one-step
transparent clocks in hardware. Thus special switches are required.
The shortest cycle time is either determined by the sum of frames sent by the master, or
by the sum of frames sent by the slaves, or by response time and the overall propagation
delay of the farthest slave device (including the switch delays). It is thus still difficult to
predict and influenced by protocol stack performances, topology and the performance of
the infrastructure components.
Industrial Ethernet Technologies
Page 100
© EtherCAT Technology Group, August 2011
Powerlink V3: Gigabit Powerlink (III)
Classification
• Another incompatible Powerlink Version
Profinet
• Resulting Cycle Time difficult to determine - depends on topology,
switch performance and slave implementation
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
• Synchronization requires Switches with 1588 Support
• Gigabit issues remain:
• 8 instead of 4 Wires (Field Mounting?)
• Power consumption significantly higher (PHY + MAC)
• Hardly any experience with Gbit inside machine control
environments
Modbus/TCP
• First products originally announced by B&R for 2011, but as of
August 2011, no products have been shown.
EtherCAT
• Functional Principle was introduced in 2001 by Beckhoff
(„RT-Ethernet“ – a predecessor of EtherCAT)
Summary
© EtherCAT Technology Group
According to a B&R customer presentation (July 2008), the R&D phase for
Powerlink V3 (Gigabit Powerlink) products is scheduled for 2009/2010,
and first products are planned for 2011. However, according to the slides
of the May 2011 B&R Powerlink Day, Gigabit Powerlink was not even
mentioned any more.
In Gigabit mode, MACs and PHYs consumer about 6 times as much
power as in 100 Mbit mode – a challenge for small field devices.
Industrial Ethernet Technologies
Page 101
© EtherCAT Technology Group, August 2011
Ethernet Powerlink Standardization Group
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
• EPSG originally hosted by Institute of Embedded Systems, Zurich
University Winterthur (Switzerland)
• In 2006, EPSG Office moved to
marketing agency in Aachen, Germany
• In 2007, EPSG Office moved to
advertising agency in Berlin, Germany
• 2007: New Logo and CI
• Recent Membership
74
Development: from
72
69 members in 5/2006 to
70
71 members in 11/2006 to
68
71 members in 4/2007 to
66
EPSG
65 members in 11/2007*
64
Modbus/TCP
62
Membership
Development
60
EtherCAT
Mai 06 Aug 06 Nov 06 Feb 07 Mai 07 Aug 07 Nov 07
Summary
* Source: Powerlink Facts May/Nov 2006/April/Nov 2007, published by EPSG; EPSG website
© EtherCAT Technology Group
Industrial Ethernet Technologies
Ethernet Powerlink Standardization Group is managed and hosted by an
advertising agency. Technical and implementation support is available by
the advertising agency and by technology providers, who charge for these
services.
Obviously membership figures of EPSG and ETG cannot be compared
directly: EPSG charges between 500€ and 5000€ per annum for
membership, whilst ETG has adopted the philosophy that charging for
access to a technology is not a sign of openness.
Therefore in small print: (Between 5/2006 and 11/2007, ETG grew from 315 to 634
members, exceeding 1750 members in Aug 2011).
The figures discussed above were taken from the EPSG publication
“Powerlink Facts”, which is available for download from the EPSG
website. Until end of 2007, there all members were listed; the June 2008
and all later editions do not list members any more.
According to EPSG website, one company (Yacoub Automation) joined
EPSG in Nov 2007, another one (Kalycito) in April 2008, Yaskawa joined
in July 2009 and Xilinx in Oct 2010. The website does not list those
companies that have left EPSG since 2007, such as e.g. Wago.
Please note that EPSG typically uses the term “members, supporters and
users” when referring to membership levels, and accumulates those to
over 400* (as of 5/2007). As of 01/2011, the website lists 144 “members
and users”.
* The EPSG website e.g. lists Tetra Pak in the members and users list. According to a Tetra Pak R&D
manager, they used Powerlink in one R&D project which was later cancelled, never delivered a Powerlink
equipped system and also terminated their EPSG membership.
Industrial Ethernet Technologies
Page 102
© EtherCAT Technology Group, August 2011
Future of EPSG?
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink Future beyond B&R looks uncertain:
• Lenze, driving force behind Powerlink V2, moved to
EtherCAT as main system bus
• Hardly any new Powerlink products since 2007
• HMS Anybus, supplier of fieldbus interface modules
(HMS website: “Anybus products support all major Fieldbus and Ethernet networks“)
discontinued their support of Powerlink
• Wago, supplier of Powerlink I/O modules, decided to
– discontinue its Powerlink products and
– quit Ethernet Powerlink Standardization Group
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
The Wago Powerlink Bus Coupler was featured in the “product news”
section of the “Powerlink Facts” brochure 1/2006 (May 2006), 2/2006 (Nov
2006) and 1/2007 (April 2007).
For most of the few new Powerlink Products introduced since 2007, B&R
either implemented the Powerlink interface or paid for the implementation.
At SPS/IPC/Drives Show in November 2009, B&R introduced EtherCAT
products.
Industrial Ethernet Technologies
Page 103
© EtherCAT Technology Group, August 2011
Powerlink Safety: History
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
• Development of Powerlink Safety was started in 2003
• In 2004 EPSG denied to make available the Powerlink Safety
Protocol for other Ethernet Technologies
• Availability of Powerlink Safety Products was announced in 2007
• First Certified Powerlink Safety Products by B&R in 2009
• IXXAT/B&R publish BSD-licensed Powerlink Safety stack in 2009
– As of 6/2010, documentation available in German, only
– IXXAT offers technical support within the scope of an extra
charged maintenance contract
• In April 2010, EPSG turns
Powerlink Safety into
“openSAFETY”, claiming it
to be “The first open and
bus-independent safety
standard for all Industrial
Ethernet solutions”.
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
• In 2004 IAONA asked EPSG to make available Powerlink Safety for
other Ethernet Technologies; this was turned down by EPSG.
• Also in 2004, innotec GmbH (a German Safety Consultancy company)
filed several patents regarding Powerlink Safety / openSAFETY. These
were granted in 2006.
• If the BSD-licensed safety stack is modified, the certification has to be
started from scratch.
Industrial Ethernet Technologies
Page 104
© EtherCAT Technology Group, August 2011
Powerlink Safety / openSAFETY
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
• Announcement of Powerlink Safety (openSAFETY) as Safety
Protocol for Ethernet/IP and SERCOS-III takes ODVA and
Sercos International by surprise:
– Neither Sercos International nor ODVA have authorised the
use of their intellectual property in conjunction with openSafety
• According to the Powerlink Safety Standard*,
– the permissible payload data range is 9–25 Bytes
– and 9 Bytes payload data require a minimum Safety Container
of 31 Bytes
• Or, in other words, communicating a single safety bit (such as the
input of a safety light curtain) requires a 31 (!) Byte Protocol to be
sent and processed
• The resulting limitations are obvious: Powerlink Safety needs
bandwidth, requires substantial processing power and cannot be
transferred over classical fieldbus systems such as CAN
Summary
* IEC 61784-3-13, A3.2 “Constraints”
© EtherCAT Technology Group
Industrial Ethernet Technologies
Statement# of Katherine Voss, Executive Director ODVA: “ODVA and Sercos
International are cooperating on the adaptation of CIP Safety to their respective industrial
Ethernet networks, EtherNet/IP and Sercos III. At this time, ODVA does not have a similar
cooperation arrangement with any other organization. … CIP Safety on EtherNet/IP is
the only network configuration for functional safety that is authorized by ODVA to run on
EtherNet/IP. “
Statement# of Peter Lutz, Managing Director Sercos International: “We were
surprised by the unauthorized usage of our registered Sercos trademark in publications
and displays on the Ethernet Powerlink Standardization Group (EPSG) booth at
Hannover fair. This might imply that the announced concept and the combination of
"openSafety" (Powerlink Safety) and Sercos III is approved and supported by Sercos
International. We would like to clearly state that no discussions have been held and that
no formal agreements are in place between SERCOS International (SI) and either EPSG
or B&R. … The introduction of an additional – incompatible – safety protocol is not
helpful as the complexity for manufacturers and users is significantly increased and the
acceptance is diminished to the same degree.”
In Nov 2010, EPSG announced an openSAFETY solution for Profinet.
Powerlink Safety, as do most safety protocols, uses the “black channel
approach”, which means that the transporting communication channel
does not have to be included in the safety considerations. The “black
channel approach” is the pre-requisite for bus independence of the safety
technology. However, with Powerlink Safety the black channel approach is
only valid within the constraints listed above which lead to a minimum
safety container of 31 Bytes.
For comparison: the minimum safety container of Safety over EtherCAT
(FSoE) is 6 bytes (for 1 Byte payload), thus FSoE is suitable e.g. for CAN
as well.
#
Statements quoted from: Industrial Ethernet Book Issue 58
Industrial Ethernet Technologies
Page 105
© EtherCAT Technology Group, August 2011
Powerlink Safety / openSAFETY
I
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OIOIIOOOIOIOOIOI
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IIIIIOOIIIOIIIIO
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IOOOOIOOIIIOIOIO
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IOIOIOIO
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Safety Input
Safety Input in minimum
openSAFETY
container
Safety Input in minimum
Safety over EtherCAT
container
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
A Safety Input device often has only a few Bit of SafeData. For a safe light
curtain for example only 1 Bit SafeData can be sufficient.
Container length for 1 Bit SafeData
Powerlink Safety:
31 Bytes
Safety over EtherCAT:
6 Byte
Industrial Ethernet Technologies
Page 106
© EtherCAT Technology Group, August 2011
Powerlink Safety / openSAFETY
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
• In “Powerlink Facts” 01/10 EPSG
compares openSAFETY with
Safety over EtherCAT and
concludes that openSAFETY
is 4 x faster.
This comparison is misleading, since
• In most safety architectures the
safe PLC is not bypassed (as shown in the openSAFETY
example)
• If such an architecture is chosen, the network management
configuration effort and the resulting traffic is enormous, since
the actuators and the safe PLC have to independently
monitor all safety communication links with cyclic frames
• The safety stack performance (31 byte minimum container
size!) is not taken into account
• EtherCAT cycles are much faster than Powerlink cycles
• Last but not least: decentralized safe PLC is optional
© EtherCAT Technology Group
Industrial Ethernet Technologies
Time synchronization in Powerlink Safety:
In order to avoid a delay of data the Consumer must query all connected
Producer for their relative time. That means each Producer/Consumer
connection needs a bidirectional communication channel on the underlying
fieldbus to synchronize the time information.
Configuration effort:
Within a Producer/Consumer network such as Powerlink the number of
communication relations is a multiplication of the number of Producer (n)
and the number of Consumer (m). In a Master/Slave network such as
EtherCAT the number is a summation.
Example: 10 Emergency stop buttons acting on 10 drives
Powerlink Safety
10 * 10 = 100 communication relations
Safety over EtherCAT
10 + 10 = 20 communication relations
Complexity of each device:
For Powerlink Safety each Consumer device (e.g. Safety related Drive)
must provide several safe connections if it supports several Producer
Inputs. The Input information must be combined within the device (Safe
Logic functionality).
With Safety over EtherCAT a single connection per FSoE Slave device to
the FSoE Master is sufficient. The logical combination of Safety Inputs is
done in the FSoE Master device.
Industrial Ethernet Technologies
Page 107
© EtherCAT Technology Group, August 2011
Powerlink Summary
Classification
Profinet
Ethernet/IP
CC-Link IE
•
•
•
•
Polling over Ethernet
All Frames are broadcasted
Cycle times similar to SERCOS-II
Performance difficult to predict: depends on selected
devices and on topology.
• Requires protected network segment
• Requires substantial processing power (master + slave) or
implementation in hardware (e.g. FPGA)
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
• V2: Based on (outdated) half duplex Hub technology
• Limited no. of nodes can be connected in line topology
• Requires Master with dedicated Communication processor:
no Commercially of the Shelf (COTS) Network interface
card (NIC)
• Versions are not downwards compatible
• Powerlink V3 announced, but no visible activities any more
© EtherCAT Technology Group
Industrial Ethernet Technologies
Due to the polling principle, the master has to wait for the response of
each slave before he can send the next request – or has to wait for the
timeout.
The response time of each slave device depends
• on its individual implementation:
- if implemented with standard components: processor
performance, software stack implementation quality, varying local
CPU load due to application etc.
- or: implemented with FPGAs
• and on the topology (number and performance of the hubs in between).
Thus it is difficult to determine the performance of the network without
measuring it.
Performance limitations require complex bandwidth optimization in more
demanding applications.
Industrial Ethernet Technologies
Page 108
© EtherCAT Technology Group, August 2011
Modbus/TCP: Overview
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
• Schneider Electric Approach: serial Modbus on TCP/IP
• Follows Approach A
• Few Services,
simple to
Request from Master
Ethernet Header
implement
Ethernet Header
IP Header
IP Header
TCP Header
• Widely used
TCP Header
Transaction ID
Transaction ID
Protocol ID
• Many Products
Protocol ID
Length
available
Length
Unit ID
Unit ID
• Non-Real-Time
Modbus fct code
Modbus fct code
Approach.
A
Data
Data
Modbus/TCP
Response from Slave
EtherCAT
Summary
© EtherCAT Technology Group
Modbus/TCP is very widely used, since it is simple to implement.
Non-real-time approach: Due to its operating principle, Modbus/TCP
cannot guarantee delivery times or cycle times or provide precise
synchronization. Strongly depending on the stack implementation,
response times of a few milliseconds can be achieved, which may be
sufficient for certain applications.
Apart from the basic data exchange mechanisms, there is hardly any
additional feature. Network management, device profiles, etc. have to be
handled by the application program, the network layer does not provide
solutions.
Industrial Ethernet Technologies
Page 109
© EtherCAT Technology Group, August 2011
Modbus/TCP: Functional Principle
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
• Polling
• Each Request/Response
Cycle passes TCP/IP
Stack 4 Times
• plus Switch Delays
• Depending on Master,
Poll Request can be
issued before the
corresponding response
has returned.
Master
Slave
Modbus
1
TCP
IP
Modbus
4
2
TCP
IP
3
1
2
Slave
5
Modbus/TCP
Slave
4
3
EtherCAT
Slave
Slave
Summary
© EtherCAT Technology Group
Modbus/TCP master implementations can either wait for each response to
return before the next request is issued, or send several requests at once
in order to allow for parallel processing in the slave devices. In the later
case the overall performance is improved.
Since the performance is primarily determined by the stack performances,
it very much depends on the implementation of the master and slave
devices – which is difficult to assess.
If a master is implemented on a standard socket interface of a Windows
OS, typical response times (per slave) are in the order of 10-20ms with a
worst case (e.g. moving a Window) of well over 250ms (We have tested
this. The reason is that the OS processes the TCP/IP stack with low
priority). Of course it is possible to implement a master with an RTOS
and/or using a dedicated communication CPU and achieve better results.
A slave device with sufficient processing power and an optimized
(=functionally reduced) TCP/IP stack may typically reply within 1-4 ms
(and in worst case, depending on the load, within 10-15ms). Standard
TCP/IP stacks on µC may have typical response times of >5ms.
Critical can be the retry times of the TCP/IP stacks – in case a frame was
lost. These retry times can be in the order of seconds – and typically are
not user definable nor mentioned in the product manuals.
Industrial Ethernet Technologies
Page 110
© EtherCAT Technology Group, August 2011
Modbus/TCP: Future?
Classification
• In April 2007, Schneider Electric joined ODVA as principal
member and announced Ethernet/IP products for 2008.
Profinet
• ODVA announced „to provide compatibility of
Modbus®/TCP devices with networks built on CIP”
Ethernet/IP
CC-Link IE
Sercos III
• A “Modbus Integration SIG” was established to specify the
“CIP to Modbus Translator”
• Modbus Translation Services for Modbus TCP devices
were added to the CIP Specifications in Nov 2007
Powerlink
Modbus/TCP
EtherCAT
• Future of Modbus/TCP looks uncertain, since driving force
seems to walk away
Summary
© EtherCAT Technology Group
Modbus/TCP will certainly not vanish any time soon, but this move of
Schneider indicates that there will not be enhancements or maintenance
of the protocol.
The most recent technical document found on the Modbus website in Aug
2011 is the MODBUS MESSAGING ON TCP/IP IMPLEMENTATION
GUIDE V1.0b from October 2006.
Schneider replaces one non-real-time protocol by another one.
Details regarding the integration of Modbus TCP into CIP can be found
here:
http://www.modbus.org/docs/CIP%20Modbus%20Integration%20Hanover%20Fair_0408.pdf
Industrial Ethernet Technologies
Page 111
© EtherCAT Technology Group, August 2011
EtherCAT Overview
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
C
• EtherCAT is:
– Industrial Ethernet down to the I/O Level
– Flexible Wiring and simple Configuration
– lower cost
– well proven
– an open technology
• Key Principle: Frame Processing on the Fly
• Master uses Standard Ethernet Controllers
A
EtherCAT
Ethernet HDR
FH
EH
Data
WC
CRC
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
The Slave implementation of EtherCAT is a class C approach: the
„processing on the fly“ technology requires dedicated slave controllers.
The slave controllers can be implemented as FPGA or ASIC – both
solutions undercut the cost levels of the other technologies discussed in
this presentation. It is not required to buy an ASIC, and there will be
several sources both for FPGA and ASIC implementations.
On the master side, EtherCAT does not require a dedicated master card:
any standard Ethernet Controller is sufficient, the master functionality is
implemented in software running on the host CPU that also runs the
application program. It was found that the master code adds less load on
the host CPU than servicing the DPRAM of an intelligent plug in card.
Industrial Ethernet Technologies
Page 112
© EtherCAT Technology Group, August 2011
EtherCAT: Ethernet “on the Fly“
Classification
Minimal protocol overhead via implicit addressing
Profinet
IPC
Ethernet/IP
..
..
DVI
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
Data
WKC
EH
Data
WKC
EH
Data
WKC
Ethernet HDR FH
EH
CC-Link IE
CRC
• Optimized telegram structure for decentralized I/O
• Communication completely in hardware: maximum
performance
• no switches needed if only EtherCAT devices in the
network
• Outstanding diagnostic features
• Ethernet-compatibility maintained
© EtherCAT Technology Group
Industrial Ethernet Technologies
EtherCAT is very effective even with small amounts of data per slave
device, since it is not necessary to send an individual Ethernet frame for
each data unit.
Since process data communication is handled completely in hardware
(EtherCAT Slave Controller), the network performance does not depend
on the µC performance of the slave devices – and is thus predictable. This
is not necessarily the case with Profinet, Ethernet/IP, Modbus/TCP and
Powerlink.
Switches are optional. Thus there are no costs related to switches, their
power supply, mounting, wiring, configuration and so on.
Since the CRC is checked by each device - regardless if the frame is
intended for this node – bit errors are not only detected immediately, but
can be also located exactly by checking the error counters.
The EtherCAT approach is still Ethernet compatible: in the master
commercially off the shelf Ethernet MACs are sufficient, since only
standard Ethernet frames are used.
Industrial Ethernet Technologies
Page 113
© EtherCAT Technology Group, August 2011
EtherCAT Performance Example
Classification
Profinet
Ethernet/IP
CC-Link IE
•
•
•
•
40 Axis (each 20 Byte Input- and Output-Data)
50 I/O Station with a total of 560 EtherCAT Bus Terminals
2000 Digital + 200 Analog I/O, Bus Length 500 m
Performance EtherCAT: Cycle Time 276µs
at 44% Bus Load, Telegram Length 122µs
• For comparison:
Sercos III 479 µs, Profinet IRT 763 µs, Powerlink V2 2347µs, Profinet RT 6355 µs
in spite of this cycle time still 56%
bandwidth remaining, e.g. for TCP/IP
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
The cycle time figures of the competing technologies were determined as
follows:
Profinet: Computations based on the specification (done by a well known
Profinet expert). The configurable cycle time for this example would be
1ms (IRT) resp. 8ms (RT).
Powerlink: see Powerlink section of this presentation. With Powerlink at
this cycle time there is no remaining bandwidth for asynchronous
communication.
For EtherCAT the Update Time (276 µs) is given: after this period of time
all output data and all input data was transferred from or to the master –
an entire cycle was finished. The telegram time is only 122µs – thus one
could communicate even faster (e.g. new data every 125µs).
Industrial Ethernet Technologies
Page 114
© EtherCAT Technology Group, August 2011
EtherCAT Synchronization
Classification
Profinet
Ethernet/IP
Precise Synchronization (<< 1 µs!) by exact
adjustment of distributed clocks.
Advantage: Accuracy does not depend on master precision, small
communication jitter and thus implementation in software only is
acceptable and does not deteriorate synchronization
S
M
CC-Link IE
∆t
IP
C
Sercos III
S
..
..
S
DVI
Powerlink
Modbus/TCP
S
S
S
S
S
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Since EtherCAT used precisely adjusted distributed clocks (a feature of
the EtherCAT Slave Controller chips), the communication cycle itself does
not have to be absolutely equidistant – a small jitter is allowed. Therefore
EtherCAT masters do not need a special hardware (like a communication
co-processor) and can be implemented in software, only – all that is
needed is an Ethernet MAC, like the one that comes with most PC
motherboards anyhow.
Measurements showed a synchronization accuracy of ~20ns with 300
distributed nodes and 120m (350 ft) cable length. Since the maximum jitter
depends on many boundary conditions (e.g. no. of nodes, network length,
temperature changes etc.), its value is given conservatively with << 1µs.
Industrial Ethernet Technologies
Page 115
© EtherCAT Technology Group, August 2011
EtherCAT is Industrial Ethernet
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
•
•
•
•
EtherCAT: only Standard Ethernet Frames (IEEE 802.3)
Master: Ethernet MAC without co-processor or special HW
Fully transparent for other Ethernet protocols
Internet Technologies (TCP/IP, FTP, Web server etc.)
without restricting the real time capabilities, even with 100µs
cycle time – no large time gaps for rare traffic needed
• Full Tool-Access to devices at real time operation –
with and without TCP/IP
48 Bit
48 Bit
16 Bit
16 Bit
Destination
Source
EtherType
Header
Embedded in Standard Ethernet
Frame, EtherType 0x88A4
EtherCAT
11 Bit
Summary
© EtherCAT Technology Group
CRC
1..n EtherCAT Datagrams
Length
0
32 Bit
…
1 Bit
4 Bit
Res.
11
Type
12
15
Industrial Ethernet Technologies
EtherCAT used only standard frames. Any other Ethernet Protocols are
tunneled fully transparently – EtherCAT thus uses a method that is
common with Ethernet itself and with many Internet technologies: every
modem tunnels Ethernet frames as does WLAN. VPN uses this approach
as does TCP/IP itself.
By using this approach EtherCAT can transport any Ethernet protocol (not
ony TCP/IP) at shortest cycle times (even if they are shorter than the
longest possible Ethernet frame).
In addition, it is not necessary to keep a large gap in the data stream – like
other approaches have to.
The protocol used is named “Ethernet over EtherCAT”.
Many EtherCAT masters support tool access from outside: a tool can
communicate via Ethernet e.g. by UDP/IP with the master, who inserts
this data into the EtherCAT communication in such a way, that a fully
transparent access to EtherCAT devices is possible without restricting the
real time capabilities.
Industrial Ethernet Technologies
Page 116
© EtherCAT Technology Group, August 2011
EtherCAT is Industrial Ethernet
Classification
Profinet
Ethernet/IP
• Connection to any Ethernet device via Switchport
• Access to web server with standard browser
• Switchport can be implemented as device feature, seperate
device or software functionality in master
• Switchport allows for hard real time capability with parallel
Ethernet communication of any kind
CC-Link IE
Sercos III
IP
C
Powerlink
Modbus/TCP
..
..
DVI
Switchport
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
The “tunnel entrance” (Switchport) for any Ethernet protocol can be
implemented in a variety of ways: as separate device, as feature of a
slave device or as software feature of the EtherCAT master.
Industrial Ethernet Technologies
Page 117
© EtherCAT Technology Group, August 2011
EtherCAT: Most flexible Topology
Classification
Profinet
Ethernet/IP
•
•
•
•
•
Flexible tree structures – arbitrarily extendable
Line without limitations through cascaded switches or hubs
100 m between two nodes, up to 65535 nodes in one segment
branches can be connected/removed at run time (“Hot Connect”)
Straight or crossed cables – automatic detection
CC-Link IE
Sercos III
I
P
C
.. DVI
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
With EtherCAT almost any number of devices (up to 65535) can be wired
in a line structure – there are no restrictions due to cascaded switches or
hubs. Any number of drop lines or branches are possible, too, providing
the most flexible topology.
Industrial Ethernet Technologies
Page 118
© EtherCAT Technology Group, August 2011
EtherCAT Gateways
Classification
Profinet
Ethernet/IP
•
•
•
•
•
EtherCAT Performance allows for: EtherCAT instead of PCI
no card slots required any more
maximum system expandability with low cost fieldbus gateways
seamless integration of fieldbus devices protects your investment
smooth migration path from fieldbus to EtherCAT
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
EtherCAT is so fast that it can replace the PCI bus (and thus the PCI
slots) in almost all applications. Fieldbus master and slave card can be
moved into the EtherCAT network. EtherCAT control computers can thus
be very compact, without restricting the expandability.
In addition, this feature provides a very elegant and smooth migration
path: Devices which are not (yet) available with EtherCAT interface, can
be integrated via underlying fieldbus systems – typically without restricting
the performance compared with the PCI solution.
Industrial Ethernet Technologies
Page 119
© EtherCAT Technology Group, August 2011
Safety over EtherCAT: Features
Classification
• TÜV certified technology
Profinet
• Developed according to IEC 61508
Ethernet/IP
• Protocol meets Safety Integrated Level (SIL) 4
• Device implementations typically SIL 3
CC-Link IE
Sercos III
Powerlink
• Suitable for functional safe I/O as well as for
functional safe motion control
• Variable CRC size for minimal overhead
Modbus/TCP
• Safe Parameter Download at boot-up: most
simple device exchange possible
EtherCAT
• Safety devices available since end of 2005
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
The error probability of the Safety over EtherCAT protocol is low enough,
that the protocol itself meets SIL 4 requirements. However, devices
implementing this protocol typically meet SIL 3 – and thus KAT 4 of EN
954-1.
Industrial Ethernet Technologies
Page 120
© EtherCAT Technology Group, August 2011
Safety over EtherCAT: Technology Approach
Classification
Profinet
Standard
application
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Safety
application
Safety
application
Safety
protocol
EtherCAT
protocol
Standard
application
Safety
Protocol
EtherCAT
protocol
Safety
over
EtherCAT
EtherCAT
Modbus/TCP
EtherCAT
EtherCAT acts as a real ‚black channel‘
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
With Safety over EtherCAT the communication channel is really “black” (or
irrelevant for the safety analysis), and not “grey”. Therefore e.g. no SIL
monitor is required to check the current error rate on the network.
Industrial Ethernet Technologies
Page 121
© EtherCAT Technology Group, August 2011
Without Redundancy: Cable Failure
Master
Classification
Profinet
RX Unit
TX Unit
RX
TX
Ethernet/IP
MAC 1
RX TX
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
☺
☺
Slave 1
Slave M-1
Slave M+1
RX
TX
RX
TX
TX
RX
TX
RX
RX
TX
TX
RX
...
© EtherCAT Technology Group
Slave N
...
RX
TX
TX
RX
Industrial Ethernet Technologies
EtherCAT is – even when wired in line topology – a ring structure, with two
channels in one cable (Ethernet full duplex feature). Whilst device located
before a cable or device failure can continue to operate (the EtherCAT
Slave Controller closes the ring automatically), devices behind the cable
failure are naturally not accessible any more.
Industrial Ethernet Technologies
Page 122
© EtherCAT Technology Group, August 2011
With Redundancy: Cable Failure
Master
Classification
Profinet
Ethernet/IP
Reco
5µs!
e: < 1
m
i
T
very
CC-Link IE
RX Unit
TX Unit
RX
TX
MAC 1
RX TX
MAC 2
RX TX
Only 2nd
Ethernet Port
required – no
special
Interface Card
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
☺
☺
☺
☺
Slave 1
Slave M-1
Slave M+1
Slave N
RX
TX
RX
TX
TX
RX
TX
RX
RX
TX
TX
RX
...
© EtherCAT Technology Group
...
RX
TX
TX
RX
Industrial Ethernet Technologies
If the line is turned into a ring, there are two communication paths to each
device: redundancy.
With EtherCAT even without special hardware in the master: a second
Ethernet port is sufficient. All slave device with two (or more) EtherCAT
ports support the cable redundancy feature anyhow.
The recovery time in case of cable failure is shorter than 15µs. The initial
switchover to the redundant line does not require any reconfiguration by
the master.
By using this device exchange at run time (hot swap) is feasible as well.
Industrial Ethernet Technologies
Page 123
© EtherCAT Technology Group, August 2011
EtherCAT is simpler to configure
Classification
Addressing:
• No manual address setting required
Profinet
• Addresses can be kept – no new addressing
if nodes are added
Ethernet/IP
Topology:
• Automatic topology target/actual comparison possible
CC-Link IE
Sercos III
Diagnosis:
• Diagnosis information with exact localization
Network planning:
Powerlink
• Performance independent of slave implementation
(e.g. stack features, µC performance)
Modbus/TCP
• Performance widely independent from topology (no switches/hubs)
EtherCAT
• Performance more than sufficient - therefore no „tuning“ required
any more, default settings do the job
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
The configuration of an EtherCAT network is very simple.
This is in particular the case for the network planning: since the process
data performance does not depend on the devices that were selected (and
their µC and stack performance) and since the topology has almost no
influence at all, hardly anything has to be considered.
Also the network tuning, which has been necessary with many fieldbus
and industrial Ethernet solutions, is hardly needed at all: even with default
settings Ethernet is more than fast enough.
Industrial Ethernet Technologies
Page 124
© EtherCAT Technology Group, August 2011
EtherCAT Implementation
Classification
Beckhoff ®
ET1100
Profinet
Hilscher
Ethernet/IP
netX® 100/500
TI's Sitara™ and
other µC + µP families
Hilscher
netX® 50
Beckhoff ®
ET1200
CC-Link IE
Sercos III
2005
Powerlink
4
0
20
Modbus/TCP
EtherCAT
ESC10/20:
Altera® Cyclone™-I
2006
2007
IP-Core
Xilinx®
Spartan™-3
IP-Core for
Altera®
Cyclone™-II
2008
2009
2011
2010
2012
IP-Core for FPGA of
Intel® Atom™ E6x5C
IP-Core for
IP-Core for
Xilinx®
Altera® Spartan™-6
Stratix™-IV
IP-Core for
Altera®
Cyclone™-III
IP-Core for
Altera®
Cyclone™-IV
IP-Core for
Xilinx® Kintex™-7
IP-Core for
Altera® Stratix™-V
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
At Hannover Fair 2011, Texas Instruments announced the EtherCAT
Slave Controller integration in its ARM® -based embedded processors.
This is the first time ever that a dedicated Industrial Ethernet hardware
interface is integrated in standard microprocessor product lines.
The TI chip turns EtherCAT into a mainstream technology also beyond the
automation world, will help EtherCAT to establish a strong position in a
wide range of embedded applications and further accelerate the adoption
of EtherCAT in the automation market,
Like all Industrial Ethernet technologies that support hard real time,
EtherCAT requires a dedicated hardware interface – unlike its competition
EtherCAT requires such hardware only on the slave side. This provides
both maximum and predictable performance of the network, since
software stack delays do not have any influence any more. In addition this
leads to lower costs. The first EtherCAT Slave Controller (ESC) back in
2004 was FPGA based, released by the originator of the technology, the
German company Beckhoff Automation. In 2005 – 2007 EtherCAT ASICs
were introduced by Beckhoff and Hilscher. Many EtherCAT device
vendors also make use of the configurable EtherCAT IP-Cores for Altera
and Xilinx FPGAs. The Texas Instruments microcontroller and
microprocessor families will complement the offering of EtherCAT chips by
the end of 2011.
Industrial Ethernet Technologies
Page 125
© EtherCAT Technology Group, August 2011
EtherCAT is lower costs
Classification
Profinet
Ethernet/IP
Master:
no dedicated plug in card (co-processor),
on-board Ethernet Port is fine
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Slave:
- low cost Slave Controller
- FPGA or ASIC
- no powerful µC needed
Infrastructure:
- no Switches/Hubs required
- Standard Ethernet Cabling
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
EtherCAT intends to even undercut the fieldbus cost levels – in spite of a
performance, that is much better and many additional features.
Industrial Ethernet Technologies
Page 126
© EtherCAT Technology Group, August 2011
EtherCAT: open technology
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
• Protocol is published completely:
• EtherCAT is IEC standard (IEC 61158, IEC 61784-2, IEC 61800-7,
ISO standard (ISO 15745-4) and SEMI standard (E54.20)
• Slave Controllers from several suppliers
• Master Stacks from several suppliers (also open source)
• Supported by the EtherCAT
Technology Group
• Foundation: November 2003
• Tasks: Support, Advancement and Promotion of EtherCAT
• Already more than1750* member companies from
52 countries in 6 Continents:
–Device Manufacturers
–End Users
–Technology-Provider
• ETG Offices in Germany, USA, China, Japan and Korea
• Membership is open to everybody
* as of Aug 2011
© EtherCAT Technology Group
Industrial Ethernet Technologies
The EtherCAT Technology Group is official standardization partner of the
IEC: the ETG nominates experts for the international standardization
committees and may submit standard proposals.
Since beginning of 2005 EtherCAT is an official IEC specification:
IEC/PAS 62407. Since Oct. 2007 EtherCAT is part of the standards IEC
61158 (Digital data communication for measurement and control –
Fieldbus for use in industrial control systems), IEC 61784-2 (Digital data
communication for measurement and control –Part 2: Additional profiles
for ISO/IEC 8802-3-based communication networks in real-time
applications) and IEC 61800-7 (Profiles for motion control systems). The
latter is particularly important for motion control applications, since it
makes EtherCAT a standardized communication technology for the
SERCOS and CANopen drive profiles, on an equal footing with SERCOS
I-III and CANopen respectively. The drive parameters and state machines
as well as the process data layout of the device profiles remain untouched
when mapped to EtherCAT. Hence the user interface does not change
when moving from SERCOS and CANopen to EtherCAT, and device
manufacturers can re-use major parts of their firmware.
EtherCAT is also part of ISO 15745-4 (device description profiles)
The EtherCAT Technology Group (ETG) is an organization in which key
user companies from various industries and leading automation suppliers
join forces to support, promote and advance the EtherCAT technology.
With over 1750 members, the EtherCAT Technology Group has become
the largest fieldbus organization in the world. Founded in November 2003,
it is also the fastest growing fieldbus organization.
Industrial Ethernet Technologies
Page 127
© EtherCAT Technology Group, August 2011
EtherCAT: versatile System
Classification
Profinet
Ethernet/IP
CC-Link IE
• Master to Slave, Slave to Slave, Master to Master
• Transparent tool access to all nodes
• open interfaces
Master
M/S
IPC
M/S
Sercos III
Switch
..
..
DVI
M/M
Powerlink
Master
IPC
Modbus/TCP
EtherCAT
M/S
..
..
DVI
S/S
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Besides the master/slave communication EtherCAT provides further
possibilities: masters can communicate among each other as well as slave
devices.
For slave to slave communication there are two varieties:
Topology dependent slaves can insert data “upstream” which can be read
“downstream” by all other slaves. In many applications that require slave
to slave communication these relationships are known at network planning
stage and thus can be handled with accordingly. Wherever this is not
possible, the second variant can be applied:
Topology independent two cycles are used for slave to slave
communication. In most cases the corresponding delay time is not critical
at all – in particular if one considers that EtherCAT is even at twice the
cycle time still faster than any other solution….
Industrial Ethernet Technologies
Page 128
© EtherCAT Technology Group, August 2011
EtherCAT also for Factory Networking
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
The EtherCAT protocol portfolio was enhanced by the EtherCAT
Automation Protocol (EAP). As a result, EtherCAT now also comprises the
Ethernet communication between control systems, as well as to the
supervisory systems. EAP simplifies the direct access of process data
from field devices at the sensor / actuator level and also supports the
integration of wireless devices.
For the factory level, the base protocols for process data communication
have been part of the EtherCAT specification from the very beginning.
Now the ETG has enhanced those with services for the parameter
communication between control systems and for routing across system
boundaries. Uniform diagnostic and configuration interfaces are also part
of the EAP. It can be used in switch-based Ethernet topologies as well as
via wireless Ethernet. Process data is communicated like network
variables, either cyclically or event-driven. Both the classic EtherCAT
Device Protocol, which utilizes the special EtherCAT functional principle of
"processing on the fly," and the new EAP make use of the same data
structures and facilitate vertical integration to supervisory control systems
and networked controllers.
While EAP handles the communication in the millisecond range on the
process control level and between control systems, the EtherCAT Device
Protocol handles I/O and motion control communication in the field level in
the microsecond range.
Industrial Ethernet Technologies
Page 129
© EtherCAT Technology Group, August 2011
EtherCAT Performance
Classification
EtherCAT is the fastest Industrial Ethernet Technology:
Profinet
Transmission Rate: 2 x 100 Mbaud (Voll-Duplex)
Ethernet/IP
Update Times:
• 256 digital I/O in 11 µs
• 1000 digital I/O distributed to 100 nodes in 30 µs = 0.03 ms
• 200 analog I/O (16 bit) in 50 µs, 20 kHz Sampling Rate
• 100 Servo-Axis (each 8 Byte I+O) every 100 µs = 0.1 ms
• 12000 digital I/O in 350 µs
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
More details ?
….. see EtherCAT Presentation
or EtherCAT website
www.ethercat.org
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
The performance figures have been determined with a mix of physical
layers, thus representing typical installations.
A comprehensive EtherCAT introduction can be found at the EtherCAT
website.
Industrial Ethernet Technologies
Page 130
© EtherCAT Technology Group, August 2011
EtherCAT Summary
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
• EtherCAT provides:
– Superior Performance
– Line, Ring, Tree, Drop Line, Star Topology
– Master/Slave, Master/Master and Slave/Slave
communication
– Integrated Functional Safety: Safety over EtherCAT
– TCP/IP without cycle time limitations
– Simple configuration – no manual address setting
– Comprehensive diagnosis functionality
– Redundancy
– Support of CANopen* and SERCOS* Drive Profiles
• EtherCAT is:
– Open technology, worldwide supported, IEC standard
– Low cost and simple to implement
Summary
*CANopen is a trademark of CiA e.V.; SERCOS interface™ is a trademark of SI e.V.
© EtherCAT Technology Group
Industrial Ethernet Technologies
EtherCAT typically is chosen for one or more of these three reasons:
- superior performance
- flexible topology – even at large distances
- low costs
For more information regarding EtherCAT please go to
www.ethercat.org
Industrial Ethernet Technologies
Page 131
© EtherCAT Technology Group, August 2011
Stack Performance Comparison (I)
Classification
Profinet
Ethernet/IP
• Stack performances of the Ethernet technologies differ
substantially, due to the different complexity of the stacks
• Softing, a German specialist for field bus technology
published* the following comparison of the stack delay
times:
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Stack Time
Profinet IO
Ethernet/IP
EtherCAT
Average
0.5788 ms
1.8873 ms
0.1143 ms
Max:
0.7391 ms
2.9571 ms
0.1821 ms
Min:
0.5394 ms
1.2332 ms
0.0474 ms
• All three protocols were implemented on the same
hardware (interface board with FPGA + Softcore CPU) and
by the same team, so they are indeed comparable
* Source: „Einer für alle; Flexible Real-Time-Ethernet Anschaltung mit FPGA“,
messtec drives Automation Real-Time Ethernet Sonderheft 2010, by Frank Iwanitz,
Business Development Manager Real-Time Ethernet at Softing GmbH, Munich, Germany
Summary
© EtherCAT Technology Group
•
•
•
•
Industrial Ethernet Technologies
Most performance comparisons only look at the network itself up to
the slave controller chips, and neglect the stack performances.
However, the stack performance is crucial when looking at the overall
network system performance
Softing is using the eCos RTOS on the Softcore CPU that runs the
stacks
The stack times were measured from the interrupt that is generated
at the reception of the Ethernet frame at the IP core until the data is
made available to the application at the application interface (stack
API).
Industrial Ethernet Technologies
Page 132
© EtherCAT Technology Group, August 2011
Stack Performance Comparison (II)
Classification
• Softing stack performance data shown in a diagram,
+ Beckhoff EtherCAT Slave Sample Code (SSC*)
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
* SSC Stack Delay time measured on EL9800 EtherCAT Evaluation Kit
using the 10 Mhz Serial Process Data Interface and a 40 MHz
16 Bit PIC CPU; 2 Byte Output Data, min 15µs, max 20µs
Summary
© EtherCAT Technology Group
•
•
Industrial Ethernet Technologies
Most performance comparisons only look at the network itself up to
the slave controller chips, and neglect the stack performances.
However, the stack performance is crucial when looking at the overall
network system performance
Industrial Ethernet Technologies
Page 133
© EtherCAT Technology Group, August 2011
RTE Technology Comparison: Summary
Classification
Performance
Profinet
Ethernet/IP
Cycle Time
Modbus
/TCP
Ethernet
/IP
ProfiNet
RT
Powerlink
ProfiNet
IRT
CC-Link
IE
Sercos III
EtherCAT
--
--
-
o
+
o
+
++
--
--
--
-
+
+
+
++
+
--
-
o
CC-Link IE
Sercos III
Synchronicity
Powerlink
Modbus/TCP
Throughput of
IP Data
+
o
(CIP sync)
(with special
interface hw)
++ ++ ++
o
(half
duplex)
EtherCAT
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
In principle, one should not compare technologies in such an overview table: since
the ratings are based on figures, assumptions and assessments that cannot be given
in full detail, one may come to a different conclusion. However, some like this and
ask for these tables.
In order to provide a better transparency, comments for each row are provided.
Cycle Time: EtherCAT is about 3 times faster than Profinet IRT and Sercos-III, and
about 10-15 times faster than Powerlink or CC-Link IE. Due to TCP/IP usage for
process data communication and the related stack delays, the Modbus cycle time in
principle is longer than with Profinet I/O – but this is widely implementation
dependent.
Synchronicity: The EtherCAT distributed clock mechanism provides jitter-values of
<<1µs. With Sercos-III, Powerlink and CC-Link IE the jitter depends on the
communication jitter of the master, with Profinet-IRT (and Powerlink and CC-Link IE
Field) it (also) depends on the number of cascaded switches resp. hubs. All four
technologies claim a jitter of <1µs – as does CIPsync.
Throughput of IP data: with the „best effort“ approaches Modbus, Ethernet/IP and
Profinet RT the throughput of IP data is basically limited by the stack performance.
Since Profinet IRT and EtherCAT reserve bandwidth for Real-time communication,
the remaining throughput for IP data is reduced by the protocol – but typically it
remains higher than the stack performance of an embedded TCP/IP stack. With IRT
the user has to ensure that certain load limits are not exceeded. Powerlink suffers
from half duplex communication and overall poor bandwidth utilization due to polling.
CC-Link IE does not transport other Ethernet traffic (the SLMP option is the other
way round: SLMP via TCP/IP in external Ethernet networks). Sercos-III suffers from
the delay introduced by large no. of cascaded switches (in Realtime Mode).
Industrial Ethernet Technologies
Page 134
© EtherCAT Technology Group, August 2011
RTE Technology Comparison: Summary
Classification
Wiring
Profinet
Modbus
/TCP
Ethernet
/IP
ProfiNet
RT
Powerlink
ProfiNet
IRT
CC-Link IE
Sercos III
EtherCAT
-
++
--
Ethernet/IP
Topology
Flexibility
CC-Link
IE
--
--
--
+
+
(Control)
+
(Field)
Sercos III
Line Structure
Powerlink
--
--
--
o
o
(10)
(~25)
--
(Control)
+
+
++
(511)
(65535)
-
+
(Field)
COTS
Modbus/TCP
Infrastructure
Components
++
+
o
o
(no
Switch)
EtherCAT
(Switch, Router,
Connector etc.)
--
--
(Control)
+
(Field)
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Topology Flexibility: EtherCAT supports line, tree, star, ring, drop lines without
practical limitations on number of nodes and hardly any influence on performance.
Profinet IRT: line, tree, star, drop lines, but limited no. of nodes and strong
interdependency between topology and performance. CC-Link IE Control: ring
only; CC-Link IE Field: star + line, ring announced. Powerlink: line, tree, star, drop
lines, but strong limitation due to hub delays. Sercos-III: line and ring only.
Line Structure: ModbusTCP, Ethernet/IP + Profinet RT only support line
topology with device integrated switches – and of course, the switch delays
accumulate. With Powerlink, only few nodes in line, due to hub delays. According
to B&R user manual, a maximum of 10 hubs is allowed between master and slave
– so only 10 nodes in line. With Profinet IRT, accumulated jitter due to cascaded
switches limits the no. of nodes in line topology. CC-Link IE Field: up to 121 nodes
in line, Sercos-III specifies up to 511 nodes in line, EtherCAT supports up to
65535.
Commercially Off The Shelf (COTS) Infrastructure Components: Ethernet/IP
asks for manageable switches with IGMP support. Hubs with 100 MBit/s
(Powerlink) cannot be considered COTS technology, since the chips are obsolete.
Profinet RT requires a careful switch selection. Profinet IRT requires special
switches throughout, Sercos-III does not allow switches, EtherCAT can be used
with switches (between masters and EtherCAT segments). If required, EtherCAT
networks can be further extended e.g. by inserting fiber optic segments using
standard infrastructure devices. CC-link IE Control: no COTS devices possible;
CC-Link IE Field: Switches can be used.
Industrial Ethernet Technologies
Page 135
© EtherCAT Technology Group, August 2011
RTE Technology Comparison: Summary
Classification
Features
Profinet
Ethernet/IP
Slave to Slave
Communication
Modbus
/TCP
Ethernet
/IP
ProfiNet
RT
Powerlink
ProfiNet
IRT
CC-Link
IE
Sercos III
EtherCAT
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
✔
-/✔
✔
✔
(switches
with
spanning
tree)
✔
✔
✔
o*
✔
✔
✔
-
✔
✔
✔
✔
-
✔
✔
CC-Link IE
TCP/IP & other
Internet
Sercos
III
Technologies
supported
Powerlink
Cable
Redundancy
Modbus/TCP
Safety
EtherCAT
Summary
#
* planning algorithm extremely complex, no known implementation
#
CC-Link Safety is separate bus system, Safety Protocol for CC-Link IE Field announced in July 2011
© EtherCAT Technology Group
Industrial Ethernet Technologies
Slave to Slave Communication: supported by all technologies. Via Master only:
Modbus/TCP. Directly between slaves, but initiated by master: all others
(EtherCAT: depending on topology). Topology independent slave-to-slave
communication with EtherCAT requires 2 frames (which can be sent within the
same cycle), so performance of this communication type may be degraded to
Sercos-III or Profinet IRT levels.
TCP/IP & other Internet Technologies supported: almost all technologies allow
for TCP/IP communication and Internet Technologies. Modbus/TCP, Ethernet/IP
and Profinet I/O have no scheduling for this communication, all others do.
Powerlink, Profinet-IRT, Sercos-III and EtherCAT connect generic Ethernet devices
(e.g. Service notebooks) via Gateways or special switchports. CC-Link IE Field can
connect external SLMP/TCP/IP devices via Gateway, but cannot transport generic
TCP/IP or Ethernet traffic.
Cable Redundancy: For Modbus/TCP switches with spanning tree protocol can be
used to establish cable redundancy (between the switches only). Ethernet/IP has
introduced the DLR protocol (and the corresponding devices). For Profinet RT there
is the Media Redundancy Protocol (MRP). For Powerlink, redundancy requires
doubling of all infrastructure components plus additional redundancy interface
devices (or special redundancy slaves). Profinet IRT aims for redundancy (MRP is
not suitable for IRT), but the planning algorithm for a redundant IRT topology is so
complex that its implementation is questionable. Sercos-III and EtherCAT support
cabling redundancy, for EtherCAT with very little additional hw effort (only a 2nd
Ethernet port in the master, no special card).
Safety: There is no Modbus/TCP safety protocol. The safety approaches of the
other technologies differ regarding availability: Safety over EtherCAT products are
shipping since end of 2005.
Industrial Ethernet Technologies
Page 136
© EtherCAT Technology Group, August 2011
RTE Technology Comparison: Summary
Classification
Costs
Profinet
Modbus
/TCP
Ethernet
/IP
ProfiNet
RT
Ethernet/IP
Node Interface
Costs
CC-Link IE
Sercos
III
Development
Effort
Powerlink
Master Costs
Modbus/TCP
Infrastructure
Costs
EtherCAT
o
-
++
+
-
+
--
(Switch)
(Switch)
-+
-o
(Switch)
Powerlink
ProfiNet
IRT
+
ERTEC400
CC-Link
IE
?
(w. FPGA)
o
ERTEC200
o
-*
o
--*
o
?
-*
o
(Hubs
integr.)
(Switch
integr.)
(Switch
integr.)
Sercos III
EtherCAT
+
++
+
(w. FPGA)
(w. FPGA)
+ +
-* ++
++ ++
(no
Switch)
(no
Switch)
(Switch
integrated)
Summary
© EtherCAT Technology Group
* Requires Special Master Card with Co-Processor
Node Costs: Whilst Modbus/TCP – due to limited real time claims – can be implemented on
16bit µC, Ethernet/IP, Profinet I/O and Powerlink require substantial processing power and
memory. Using FPGAs, Powerlink, Sercos and EtherCAT achieve comparable cost levels,
the ASIC implementation of EtherCAT reaches or undercuts fieldbus cost levels. Node costs
for CC-Link IE Field are difficult to determine, since the ASICs are not available (at least not
in Europe). CC-Link IE Control ASICs are not available at all.
Development effort: Assuming the TCP/IP stack is present, Modbus/TCP can be
implemented with very low effort. Profinet I/O requires about 1 MByte (!) of code. Profinet
IRT is very complex – not only but in particular the master. EtherCAT slaves can be
implemented with very little effort, since all time critical functions are provided in hardware.
EtherCAT masters range from very simple (e.g. with one process image) or more complex
(e.g. with dynamic scheduling). Sercos development effort for slave devices is assumed to
be similar to EtherCAT, since real time part is handled in hw, too. Development Effort for
CC-Link IE Field are difficult to determine, since the ASIC manuals are not available (at
least not in Europe).
Master Costs: Modbus/TCP, Ethernet/IP, Profinet I/O and EtherCAT masters do not require
a dedicated plug in card. Since EtherCAT masters typically only send one frame per cycle,
the additional CPU load on the master is much lower than with the others in this group. For
hard real time applications, Profinet IRT, CC-Link IE, Powerlink and Sercos-III require
special dedicated master cards with communication co-processors. For soft realtime
requirements, Powerlink and Sercos-III can also be implemented with SoftMaster.
Infrastructure Costs: Whilst Modbus uses switches (but no special ones), Ethernet/IP (+
typically Profinet RT) require manageable switches (Ethernet/IP with IGMP support).
Depending on the topology, the integrated hubs (Powerlink) or switches (Profinet-RT) or
special switches (Profinet-IRT, CC-Link IE) are sufficient - if not, external hubs or special
switches are required. Sercos-III and EtherCAT do not require switches or any other active
infrastructure components.
Industrial Ethernet Technologies
Page 137
© EtherCAT Technology Group, August 2011
RTE Technology Comparison: Summary
Classification
Strategic
Topics (I)
Profinet
Modbus
/TCP
Ethernet
/IP
ProfiNet
RT
Powerlink
ProfiNet
IRT
CC-Link
IE
Sercos III
EtherCAT
+*
o
+*
+*
+
++
++ ++ ++
o
++ ++
+
++
++ ++ ++
o
+
++
Ethernet/IP
Size of
supporting
organization
CC-Link
IE
++ +*
Sercos III
Worldwide
User Group?
Powerlink
Modbus/TCP
Time to Market
EtherCAT
Summary
(V3/Gbit?)
o
(new IRT
Version in
2011)
o
* Not all ODVA or PTO/PNO or CLPA members support Ethernet
© EtherCAT Technology Group
Industrial Ethernet Technologies
User Group Size: No. of members in the user group is not crucial, but may serve as
an indicator for the acceptance. As of August 2011, the EtherCAT Technology Group
has 1750 member companies (membership free of charge*), Sercos International has
49 member companies**. EPSG (Powerlink) has 66 member companies***. ODVA has
277 member companies****. Profibus International (PI) consists of 25 regional
organizations with a total of over 1400 members (Siemens is 25 x member), and
CLPA***** has 1548 members, but their membership is predominantly fieldbus
(Profibus, CC-Link) related. ModbusTCP is so widely used that the Modbus IDA
membership of 69 members****** only does not reflect its acceptance.
Worldwide User Group: ODVA and PI are present worldwide – as is ETG, with
offices in Europe, North America, China, Korea and Japan. CLPA and Sercos have
offices in Europe, North America and Japan.
Time to Market: Modbus/TCP is available since 1999. Ethernet/IP since 2001. Profinet
RT has entered the market in 2005. Powerlink V3 is expected for 2011, Powerlink V2 is
available since 2007, the B&R proprietary version 1 is shipping since end of 2002. The
next generation Profinet IRT is expected for 2013. CC-Link IE Control is not available
for 3rd parties, CC-Link IE Field was introduced in 2010. First Sercos-III V1.1 devices
were shipped end of 2007. EtherCAT is used in series applications since end of 2003.
* since ETG membership is free of charge, membership figures should not be compared 1:1 with the other organizations.
** according to website www.sercos.de/www.sercos.com as of Aug 2011.
***according to EPSG Publication “PowerlinkFACTS” published in November 2007. In April 2007, there were 71 member
companies. Since then now new membership figures published.
**** according to www.odva.org as of Aug 2011
***** CLPA website claims 1548 members as of July 2011, but lists only about 200. There used to be a free of charge
membership option – maybe this is the reason for the difference.
***** according to www.modbus-ida.org as of Aug 2011
Industrial Ethernet Technologies
Page 138
© EtherCAT Technology Group, August 2011
RTE Technology Comparison: Summary
Classification
Strategic
Topics (II)
Profinet
Ethernet/IP
Special
Hardware
used? IE
CC-Link
Modbus
/TCP
Rate?
(CIP
Sync)
++
International
+
-
+
(CIP
Sync)
Modbus/TCP
EtherCAT
Standardization
ProfiNet
RT
++ ++ ++
-
Sercos III
Powerlink
Adoption
Ethernet
/IP
+
+
Powerlink
CC-Link
IE
Sercos III
EtherCAT
o
-
-
-
o
(S: HUB
FPGA)
(M+S)
(M+S)
(M+S)
(S)
o
--
--
o
++
+
(+)
+
+
o
-
(2003-2006)
(since 2006)
+
ProfiNet
IRT
+
(IRT)
(IRT+)
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
Special Hardware Used: Modbus/TCP, Ethernet/IP (not: CIPsync) + Profinet
RT can be implemented with standard hardware chips. For Powerlink, the
integrated hub is implemented as FPGA, since 100MBit/s hub chips are
obsolete. Profinet IRT, CC-Link and Sercos-III require special chips in master
and slave, EtherCAT requires an EtherCAT Slave Controller (FPGA or ASIC)
but no special chips, cards or co-processors in the master.
Adoption Rate: Modbus TCP has been used for many years. Ethernet/IP,
Profinet RT are spreading. Since 2007: hardly any new Powerlink products.
Potential Profinet IRT vendors wait for technology stability (IRT+). CC-Link IE
Control: only Mitsubishi products (except cable + connectors), CC-Link IE Field:
very few non-Mitsubishi products so far. Sercos-III 1.1 started shipping in
December 2007. EtherCAT: large selection of master and slave devices from
large variety of vendors (e.g. over 90 different servo drive vendors, 60 I/O
device vendors, over 120 master vendors); more than 1200 implementation kits
sold, many more devices expected soon.
International Standardization: As far as international standardization is
concerned, all are part of IEC 61158 and IEC 61784-2 since Oct 2007 – the only
exception is CC-Link IE, which is expected to become an IEC standard in 2013
(only the application layer, though)
Modbus-TCP: Communication Profile Family (CPF) 15, IEC 61158 Type 15
Ethernet/IP: CPF 2, IEC 61158 Type 2
Profinet: CPF 3, IEC 61158 Type 10
Powerlink: CPF 13, IEC 61158 Type 13
CC-Link IE: CPF 8, IEC 61158 Type 23 (NWP submitted)
Sercos-III: CPF 16, IEC 61158 Type 19
EtherCAT: CPF 12, IEC 61158 Type 12
Industrial Ethernet Technologies
Page 139
© EtherCAT Technology Group, August 2011
Classification
Profinet
Ethernet/IP
CC-Link IE
Sercos III
Powerlink
Modbus/TCP
EtherCAT
Thank
you!
Summary
© EtherCAT Technology Group
Industrial Ethernet Technologies
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