Ten questions to ask before implementing Circuit Emulation

Ten questions to ask before
implementing Circuit Emulation Services
over Packet Switched Networks
A White Paper from Telco Systems
Contents
What is CESoPSN? ................................................................................................................................................. 3
Is CES over PSN technology relevant only when a packet switched technology is implemented over the
carriers’ network? .................................................................................................................................................... 3
What is TDMoIP and how is it different from CESoPSN? ....................................................................................... 4
What are the advantages of using pseudowire (PW) to transport CES? ................................................................. 4
How is QoS ensured for PWs over Ethernet networks? ......................................................................................... 4
How is the PDH timing distributed in pseudowire deployments? ........................................................................... 4
What type of OAM features does the CES device support in the access network to the customer? ..................... 4
How does the number of hops affect the end-to-end clock accuracy? .................................................................. 6
How does circuit emulation behave in the presence of packet loss? ..................................................................... 6
What industry standards apply to CES devices? .................................................................................................... 6
AccessTDM™: Circuit Emulation Services over Packet ......................................................................................... 7
Telco Systems’ CES over PSN product offering ..................................................................................................... 8
T-Marc™ 254 ........................................................................................................................................................... 8
T-Metro™ ................................................................................................................................................................. 9
Ten questions to ask
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Circuit emulation technology enables TDM traffic to be transported transparently over modern packet switched
networks (PSN), including Ethernet, IP, MPLS and PBT.
Circuit Emulation Services over Packet-Switched Network offers a different approach to transport TDM traffic over
IP, Ethernet or MPLS networks. One main benefit of the technology is its ability to transport many TDM trunks from
one location to another over a packet network.
Before implementing this bridging technology between your existing TDM infrastructure and pcket-switched
networks, there are some questions you should ask.
This paper will try to answer the top ten questions about CES over PSN.
What is CESoPSN?
Circuit Emulation Services over Packet-Switched Network
(CES over PSN) is basically a method by which a TDM circuit
(such as T1 or E1) is “tunneled” transparently through a
packet-switched network (PSN). An interworking function
(IWF) on each end of the PSN transforms
TDM data into packets on ingress and reverses this process
on egress. As a result, the TDM equipment on either end
of the PSN (Figure 1) perceives a direct connection to the
opposite end and is unaware of the intermediary network that
is used to emulate the behavior of a TDM circuit.
Is CES over PSN technology relevant only
when a packet switched technology is
implemented over the carriers’ network?
In todays’ deployments it is typical to find both legacy SDH/
SONET and new PSN infrastructures coexist at the point
of presence (POP). Many customers wish to receive legacy
TDM services in parallel to new Ethernet based ones.
In the Figure 3 scenario CES circuits can run over the first
mile and handed off at the point of presence (POP) of the
PSTN while Ethernet traffic is transported natively, without
any unnecessary encapsulation over the first mile and than
switched to its destination over the PSN.
Figure 1: Circuit Emulation Service over Packet
TDM data may be transported over the IP, MPLS, or Ethernet
networks, by simply choosing the right encapsulation method
and assigning the address of the target device. Figure 2
illustrates a point to multipoint CES over PSN scenario.
Figure 3: CES Transport to Destination over the PSN
Figure 2: Schematic View of the CES Concept
Ten questions to ask
What is TDMoIP and how is it different from
CESoPSN?
TDMoIP technology is also a method for transporting TDM
traffic over packet networks. However, TDMoIP is using the
technology developed for ATM networks, but instead of
transporting the ATM cells over ATM it multiplexes multiple
ATM cell payloads in common frames and transports them
over a packet-switched network.
CES over PSN, on the other hand, maps DS0 timeslots
over PSN frames. Although TDMoIP and CESoPSN supply
similar functionality, CESoPSN has been implemented by
more vendors since its implementation is simpler and straight
forward. Today CESoPSN has become the defacto standard.
What are the advantages of using
pseudowire (PW) to transport CES?
Pseudowire emulation technology has been designed to
provide a transparent tunnel over the packet switched
network. Running circuit emulation services (CES) over
pseudowire enables the migration of legacy TDM-based
services to modern packet switched networks which are
optimized for offering new revenue generating services. The
customers enjoy the benefit of continuous support in the
currently used services alongside the option to use new
revenue-generating services.
When scaling of the network is required, hierarchical VPLS
(H-VPLS) is critical. H-VPLS eases provisioning and simplify
the packet network. With VPLS, end-to-end provisioning
becomes intuitive and straight forward. H-VPLS helps
reducing the overall number of pseudowires and relieves the
replication and signaling burdens of the provider equipment
by using MTU switching to aggregate customer VPLS traffic
before sending it to the provider edge. The MTU and PE
devices connect via a single pseudowire per VPLS instance.
How is QoS ensured for PWs over Ethernet
networks?
Having guaranteed QoS is crucial for CES PWs to become
a valid replacement for the traditional TDM circuits. TDM
networks are connection-oriented, and network resources
are allocated along the transmission path for the sole use of
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the provisioned circuit. Modern carrier Ethernet networks are
equipped with prioritization mechanisms that can ensure top
priority for the transmitted data flow across the network. But
Ethernet networks are connectionless and shared by multiple
traffic flows. Attributes such as guaranteed bandwidth and
constant bit rate do not exist, unless more sophisticated
mechanisms such as MPLS traffic engineering are used.
How is the PDH timing distributed in
pseudowire deployments?
Pseudowires use multiple methods to distribute PDH timing.
The most common method today the adaptive method in
which the PDH clock is regenerated at the far end of the PSN
using a sophisticated adaptive mechanism. Other methods
are now under development such as differential timing,
out-of-band timing-over-packet (based on IEEE1588), and
synchronous Ethernet.
What type of OAM features does the CES
device support in the access network to the
customer?
Protection measures such as dual homing, link aggregation or
Carrier-class Ethernet-based ring should be taken to protect
the first mile segment and in-service tools for advanced OAM
(Operation, Administration and Management) and service
assurance should be integrated (Figure 4) in order to manage,
control and monitor the customer equipment and the
delivered services remotely.
Figure 4: OAM features of CES over PSN
Ten questions to ask
Fast reroute
Fast Reroute (FRR) is a mechanism that facilitates fast
local repair of protected Label Switched Paths (LSP) in
case of link or node failures. FRR redirects user traffic
onto backup LSP tunnels in 10s of milliseconds, a
failover time that matches the capability of SONET link
restoration. While the speed of repair is the primary
advantage of FRR, the feature has two noticeable
benefits – increased reliability and high scalability.
Scalability is achieved by supporting the mapping of all
primary tunnels that traverse a link onto a single backup
tunnel, limiting the growth of backup tunnels to the
number of links in the backbone.
End-to-end service assurance
End-to-end service assurance provides an Service Level
Agreement (SLA) measurement tool for Ethernet services
and integrates with the IP/MPLS core. External and
internal test heads can be used for service turn-up, fault
isolation, and on-going customer SLAs.
Link oam (IEEE 802.3ah)
The IEEE 802.3ah Ethernet in the First Mile (EFM)
standard defines the operations, administration and
maintenance (OAM) mechanism needed for the
advanced monitoring and maintenance of Ethernet
links in the first mile for both network operation
and troubleshooting. The IEEE 802.3ah OAM-EFM
standard covers discovery, link monitoring, remote fault
detection, remote loopback, MIB variable retrieval and
vendor-specific enhancements. This was the first step
toward including inherent management capabilities in
Ethernet equipment for public network deployment and
transforming it into a highly reliable technology.
| 5
Connectivity fault management (IEEE
802.1ag)
IEEE 802.1ag Connectivity Fault Management (CFM)
refers to the ability of a network to monitor the health
of a service delivered to customers as opposed to just
links or individual bridges. The standard defines proactive
and diagnostic fault localization procedures for pointto-point and multipoint Ethernet Virtual Connections
(EVC) that span one or more links. It is end-to-end within
an Ethernet network. IEEE 802.1ah provides improved
troubleshooting tools at Layer 2 between multiple
vendors and multiple providers. This Layer 2 ping and
traceroute features will provide capabilities for detecting,
verifying and isolating connectivity failures in these
networks.
MEF services OAM
The Metro Ethernet Forum Operation, Administration
and Maintenance (MEF OAM) is defining a standard
which describes the implementation of bridged-Ethernet
per- VLAN network-wide for estimating service
assurance metrics and specific connectivity tests.
By using an MEF OAM network, operators gain the
ability to monitor the activity of the single-link/entire
bridged Ethernet network by using a built-in mechanism
that enables real-time testing of connectivity, latency,
jitter and frame-loss parameters on the bridged network
without need for higher-layer implementations. MEF
OAM also offers the ability to perform automatic periodic
network-wide service assurance and quality verifications.
Ten questions to ask
How does the number of hops affect the
end-to-end clock accuracy?
The number of hops will increase the packet delay variation
(PDV). In practice the effect of the increase in the PDV in high
performance Ethernet networks would not affect the clock
accuracy, but it may affect the clock acquisition durations,
which becomes longer as the end to end delay and jitter
become bigger.
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• CESoPSN (Circuit Emulation Services over
Packet-Switched Network)
• A method to encapsulate structured (N x DS0) TDM
signals over Packet Switched Networks (PSN).
• Emulation of NxDS0 circuits saves PSN bandwidth
when non-active timeslots are not transported or for
dynamic timeslot allocation.
• Supports DS0-level grooming and distributed
crossconnect applications
How does circuit emulation behave in the
presence of packet loss?
• Conforms with ITU-T Y.1413, MEF 8, MFA 8.0.0 and
IETF PWE3 CESoPSN draft
CES is not sensitive to reasonable packet loss rate (below
1%). The clock can still be recovered but CES has no
means to recover the lost data. This is the reason why most
users of CES technology choose to implement it over high
performance PSN with almost no packet loss when high
priority is given to the CES flow across the network.
• TDMoIP (TDM over IP)
What industry standards apply to CES
devices?
Intensive work has been done in multiple standardization
bodies:
• IETF PWE3 (Pseudo-Wire Emulation Edge–to-Edge)
working group
• MEF (Metro Ethernet Forum)
•ITU-T
• MPLS Frame-Relay Alliance
The result is the following set of TDM over PSN protocols:
• SAToP (Structure-agnostic transport over packet)
• Simply encapsulates N consecutive bytes into a IP,
MPLS or Ethernet
• Encapsulates structured (NxDS0) TDM signals and voice
with/without CAS signaling using 8-bit timeslot
resolution
• Static timeslot allocation according to ITU-T Y.1413,
MEF 8, MFA 4.1 and IETF PWE3 TDMoIP draft
• Dynamic timeslot allocation according to ITU-T Y.1414
(clause 10), MFA 5.1 and the IETF PWE3 TDMoIP draft.
• MEF-defined CES Services
Metro Ethernet Forum (MEF) has defined four general CES
service types for the Metro Ethernet Network (MEN) provider.
The services are defined for Ethernet networks but may be
provided over all types of packet networks:
•
TDM Access Line Service (TALS) – in which the MEN
provider provisions and manages TDM leased lines via
CESoE, and at least one endpoint terminates at the
PSTN (Public Switched Telephone Network).
• TDM Line Service (T-Line) – in which MEN provider
provisions and manages TDM private lines via CESoE
between enterprise endpoints.
• Supports unstructured TDM (if there is a structure, it is
ignored)
•
Customer operated CESoE, in which enterprises or
cellular providers manage TDM private lines via CESoE
over point-to-point Ethernet (E-Line) service from MEN
provider.
• IETF Standards track (RFC 4553), ITU-T Y.1413, MEF 8,
MFA 8.0.0
• Mixed service, which is combination of any of the three
services above.
Ten questions to ask
Telco Systems’ Carrier Ethernet product line implements the
following industry standards:
Standardization
Body
Target
Network
CES
Standard
Notes &
Standards
Names
IETF
IP
SAToP
CESoPSN
ITU
MPLS
SAToP
CESoPSN
Rec. Y.1413
Metro
Ethernet
MPLS
SAToP
CESoPSN
Rec. Y.1413
Forum
Carrier
Ethernet
SAToP
CESoPSN
MEF-8
MPLS
Forum
MPLS
SAToP
CESoPSN
MFA 8.0.0
MPLS
Forum
MPLS
SAToP
CESoPSN
MFA 8.0.0
AccessTDM™: Circuit Emulation Services
over Packet
AccessTDM™ enables service providers to extend their reach
and addressable customer base to include both voice and
data without sacrificing revenues from existing TDM services.
AccessTDM conforms to IETF, MFA, and MEF standards for
flexible deployment, provisioning, and delivery of TDM/PDH
services over Ethernet. Based on Circuit Emulation Services
over Packet (CESoP) standards for T-Line (T1/E1) services,
AccessTDM protects users’ legacy equipment investments
(i.e.: PBX’s and routers with T1/E1 interfaces) while cost
effectively enabling Ethernet service providers the ability to
offer revenue generating services over dedicated, managed
next-generation packet networks for end-to-end service
assurance.
| 7
Service providers can increase enterprise cost-efficiency and
productivity by offering a combined voice and data network
to business users who want to protect their investments in
robust, fully-featured TDM equipment yet enjoy the benefits
of a high-performance Carrier Ethernet network. Circuit
emulation technology addresses this requirement by placing
TDM interfaces side by side with high capacity Carrier
Ethernet services.
Incumbent operators can utilize their lucrative E1/T1 services
while converging their underlying transport infrastructure on
new, high performance, cost-effective Ethernet, IP and MPLS
technologies. Alternative operators, including Multi-Service
Operators (MSOs), which primarily use packet switched
infrastructure, can utilize CES to offer high value TDM
services, while leveraging their new high performance packetbased networks.
Subscribers benefit not only from additional high-speed
services but also by being able to purchase a service
package based on one cost-effective access link with
simplified billing, allowing them to achieve toll quality voice
connectivity with all the functionality developed around E1/
T1 over the last several decades. TDM services based on
CES also have advantages for the cellular backhaul market,
allowing the transport of the Radio Access Network over cost
effective and bandwidth rich Carrier Ethernet.
Ten questions to ask
Telco Systems’ CES over PSN product
offering
Telco Systems has developed a comprehensive CES over
PSN solution using TDM pseudowire technology. The Telco
Systems’ CES over PSN solution is purpose-built to address
the needs of carriers and service providers. It enables a
smooth migration to PSN and capacity upgrade, supports
multiple grades of service to address the different applications
cost-effectively, and addresses all networking needs required
to support operating in a Carrier Ethernet environment.
Telco Systems’ Carrier Ethernet family of switch-routers and
PWE3 gateways comprises of a diverse mix of devices, from
small customerlocated equipment (CLE) to higher capacity
aggregation units for the carrier’s central office or pointof-presence (POP). The Telco Systems’ family of products
facilitates a wide range of applications, including simple
end-to-end circuit extension over IP/Ethernet/VPLS/MPLS,
and guarantees the delivery of a variety of legacy services
over packet-switched networks using a set of integrated
OAM tools to assure the service integrity and delivery. When
combined with Telco Systems’ residential/SOHO ATA-CPE
and VoIP IAD product line, these solutions support a wide
range of legacy and emerging services, delivering voice, fax
and data services over IP/Ethernet/MPLS networks without
compromising traditional PSTN quality.
Telco Systems CES over PSN solution supports the following
applications:
• Cellular backhaul over a packet-based network.
• Branch and Campus PBX connectivity to the PSTN
over PSN.
• Extension of all PSTN Class 5 services over PSN
• T1/E1 leased-line services over PSN
•Broadband wireless voice/data access
| 8
T-Marc™ 254
Telco Systems’ T-Marc™ 254 is a cost-optimized, fullymanaged Ethernet and circuit-emulation (PWE3) gateway,
which performs Ethernet and TDM service demarcation
allowing carriers and service
providers to offer business customers a mix of legacy TDMbased services together with enhanced fully managed Carrier
Ethernet services.
T-Marc™ 254 supports up to four digital T1/E1 trunks and
four 10/100Mbps copper links over Ethernet/IP packetbased network. The platform supports differential grades of
service, while providing traffic isolation for multiple services
or applications using advanced QoS mechanisms.
The T-Marc-254 utilizes AccessTDM™ to deliver legacy
TDM over Ethernet enabling service providers to extend
their reach and addressable customer base to include both
voice and data without sacrificing revenues from existing
TDM services. Based on Circuit Emulation Services over
Packet (CESoP) standards for T-Line (T1/E1) services, the
T-Marc protects users legacy equipment investments (e.g.,
PBX’s, routers with T1/E1 interfaces) while cost effectively
enabling Ethernet service providers the ability to offer
revenue generating services over dedicated, managed next
generation packet networks.
Ten questions to ask
T-Metro™
Telco Systems’ T-Metro™ is an advanced Metro Ethernet
Access CPE / CLE platform that support Ethernet LAN / Line
services and TDM backhauling with Circuit Emulation (PWE3),
through the use of
advanced Hierarchical QoS (tens of thousands of queues)
as well as Hierarchical Virtual Private LAN Services (HVPLS)
hubs-and-spokes and MPLS based rings support. T-Metro is
a compact 1RU 19” enclosure that is NEBS 3 compliant.
T-Metro can host a variety of TDM CES modules to support:
• 4 T1/E1
• 8 T1/E1
• Channelized OC3/STM-1*
T-Metro platform is also equipped with fixed eight (8)
10/100BaseTX ports, twelve (12) SFP-based 100BaseFX
ports and two (2) SFP-based 1000BaseX ports.
| 9
Contact information
International Headquarters
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Tel: +972-4-993-5630
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(EMEA)
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52062 Aachen
Tel: +49 241 463 5490
Fax: +49 241 463 5491
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