Glossary of Industrial Ethernet - Industrial Ethernet University

Glossary of Industrial Ethernet - Industrial Ethernet University
The interest in Industrial Ethernet has brought about a completely
new dictionary of terms. Here are some of the most important terms
introduced to date.
Bandwidth—The maximum capacity of a network channel.
Usually expressed in bits per second (bps). Ethernet
channels have bandwidths of 10, 100, and 1000 Mbps.
4B/5B—A block encoding scheme used to send Fast
Ethernet data. In this signal encoding scheme, 4 bits of data
are turned into 5-bit code symbols for transmission over the
media system.
Baud—A unit of signaling speed representing the number of
discrete signal events per second and, depending upon the
encoding, can differ from the bit rate.
10BASE-T—10 Mbps Ethernet system based on Manchester
signal encoding transmitted over Category 3 or better
twisted-pair cable.
10BASE-FL—Popular 10 Mbps link fiber optic solution which
replaces the older FOIRL implementation utilizing 850 nm
fiber optic technology.
100BASE-FX—100 Mbps Fast Ethernet system based on
4B/5B signal encoding transmitted over fiber optic cable
utilizing 1300 nm fiber optic technology.
100BASE-SX—850 nm fiber optic technology that supports
auto-negotiation. 100BASE-SX devices can communicate
with 10BASE-FL devices at 10 Mbps and other 100BASE-SX
devices at 100 Mbps.
100BASE-TX—100 Mbps Fast Ethernet system based on
4B/5B signal encoding transmitted over two copper pairs.
100BASE-X—Term used when referring to any Fast Ethernet
media system based on 4B/5B block encoding. Includes
100BASE-TX and 100BASE-FX media systems.
802.3—IEEE Working Group for CSMA/CD LANs.
AUI—Attachment Unit Interface. The 15-pin signal interface
defined in the original Ethernet standard that carries signals
between a station and an outboard transceiver.
Auto-negotiation—A protocol defined in the Ethernet standard that allows devices at either end of a link segment to
advertise and negotiate modes of operation such as the
speed of the link, half- or full-duplex operation, and fullduplex flow control.
Auto-MDIX—A protocol which allows two Ethernet devices
to negotiate their use of the Ethernet TX and RX cable pairs.
This allows two Ethernet devices with MDI-X or MDI
connectors to connect without using a cross-over cable. This
feature is also known as Auto-crossover.
Bit—A binary digit. The smallest unit of data, either a zero
or a one.
Bit Rate—The amount of bits that can be sent per second.
Usually described in units of kbps or Mbps and frequently
referred to as the data rate.
Block Encoding—Block encoding is a system whereby a
group of data bits are encoded into a larger set of code bits.
Block encoding is used in Fast Ethernet.
Bridge—A device that connects two or more networks at
the data link layer (layer 2 of the OSI model).
Broadcast—A transmission initiated by one station and sent
to all stations on the network.
Bus—A shared connection for multiple devices over a cable
or backplane.
Category 5—Twisted-pair cable with electrical characteristics
suitable for all twisted-pair Ethernet media systems, including
10BASE-T and 100BASE-TX. Category 5 and Category 5e cable
are preferred cable types for structural cabling systems.
Category 5e—An enhanced version of Category 5 cable,
developed to improve certain cable characteristics important
to Gigabit Ethernet operation. It is recommended that all
new structured cabling systems be based on Category 5e
cable; however, this cable may not be the best for use in
industrial installations because of noise susceptibility.
Collision—The result of having two or more simultaneous
transmissions on a common signal channel such as halfduplex Ethernet or shared Ethernet.
Collision Domain—The set of all stations connected to a
network where faithful detection of a collision can occur. A
collision domain terminates at a switch port.
CRC—Cyclic Redundancy Check. An error-checking technique
used to ensure the fidelity of received data.
Crossover Cable—A twisted-pair patch cable wired in such a
way as to route the transmit signals from one piece of
equipment to the receive port or another piece of
equipment, and vice versa. This allows communication
between two peer devices. The opposite of a crossover
cable is the straight-through cable.
CSMA/CD—Carrier Sense Multiple Access/Collision Detect.
The medium access control (MAC) protocol used in Ethernet.
Forwarding—The process of moving frames from one port to
another in a switching hub.
Frame—The fundamental unit of transmission at the data
link layer of the OSI model.
Full-duplex Operation—A communications method that
allows for the simultaneous transmission and reception
of data.
Data Link Layer—Layer 2 of the OSI reference model. This
layer passes data between the network layer and the
physical layer. The data link layer is responsible for
transmitting and receiving frames. It usually includes both
the media access control (MAC) protocol and logical link
control (LLC) layers.
Gigabit Ethernet—A version of Ethernet that operates at
1000 Mbps.
DCE—Data Communications Equipment. Any equipment
that relays data between Data Terminal Equipment (DTE).
DCEs are not considered end devices or stations.
Hub—A DCE with three or more ports at the center of a
star topology network. Hubs can usually be cascaded with a
hub-to-hub connection. Frequently this name is used to
mean repeating hub.
Differentiated Services (Diff-Serv)—Diff-Serv is a Quality of
Service (QoS) method described in RFCs 2474 and 2475.
This is a layer-three method utilizing the eight-bit type-ofservice field in an IP packet.
Half-duplex Operation—A communications method in which
transmissions and receptions can occur in either direction
but not at the same time.
IEEE—Institute of Electrical & Electronics Engineers. A
professional organization and standards body.
DTE—Data Terminal Equipment. Any piece of equipment at
which a communication path begins or ends. A station
(computer or host) on the network is capable of initiating or
receiving data.
IGMP Snooping—The ability of a switch to observe Internet
Group Multicast Protocol (IGMP) traffic in order to learn
IP Multicast group membership for the purpose of restricting
multicast transmissions to only those ports which have
requested them.
Encoding—A means of combining clock and data information
into a self-synchronizing stream of signals.
Internet—Worldwide collection of networks based on the
use of TCP/IP network protocols.
Error Detection—A method that detects errors in received
data by cyclic redundancy checks (CRC) or a checksum.
Jabber—The act of continuously sending data. A jabbering
station is one whose circuitry or logic has failed, and which
has locked up a network channel with its incessant
transmissions.
Ethernet—A popular LAN technology first standardized by
DEC, Intel, and Xerox (or DIX) and subsequently
standardized by the IEEE through the 802.3 committee.
LAN—Local Area Network.
Fast Link Pulse—A link pulse that encodes information used
in the Auto-negotiation protocol. Fast link pulses consist of
bursts of the normal link pulses used in 10BASE-T.
Late Collision—A failure of the network in which the
collision indication arrives too late in the frame transmission
to be automatically dealt with by the medium access control
(MAC) protocol. The defective frame may not be detected
by all stations requiring that the application layer detect
and retransmit the lost frame, resulting in greatly reduced
throughput.
Fiber Optic Cable—A cable with a glass or plastic filament
which transmits digital signals in the form of light pulses at
wavelengths of 850 nm (10BASE-FL and 100BASE-SX) or
1300 nm (100BASE-FX).
Link Integrity Test—This test verifies that an Ethernet link is
connected correctly and that signals are being received
correctly. This is a helpful aid but does not guarantee the
link is completely functional.
Flow Control—The process of controlling data transmission
at the sender to avoid overfilling buffers and loss of data at
the receiver.
Link Layer—Short for Data Link Layer. This is layer 2 on the
OSI model.
Fast Ethernet—A version of Ethernet that operates at
100 Mbps. Although 100 Mbps is no longer the fastest data
rate, this term is still used.
FOIRL—Fiber Optic Inter-Repeater Link. An early version of
fiber optic link segment replaced by 10BASE-FL.
Link Pulse—A test pulse sent between transceivers on a
10BASE-T link segment during periods of no traffic, to test
the signal integrity of the link.
Link Segment—A point-to-point segment that connects only
two devices and is “capable” of supporting full-duplex
operation.
MAC—Medium Access Control. A protocol operating at the
data link layer used to manage a station’s access to the
communication channel.
MAC Address—A unique address assigned to a station interface, identifying that station on the network. With Ethernet,
this is the unique 48-bit station address. Same as the
physical address.
Manchester Encoding—Signal encoding method used in all
10 Mbps Ethernet media systems. Each bit of information is
converted into a “bit symbol” which is divided into two
halves. One half is high and the other is low. Manchester
encoding results in a 20 Mbaud stream although data is
only being sent at 10 Mbps.
MAU—Medium Attachment Unit. The MAU provides the
physical and electrical interface between an Ethernet device
and the media system to which it is connected. Also referred
to as a transceiver.
MDI—Medium Dependent Interface. The name for the
connector used to make a physical and electrical connection
between a transceiver and a media segment. For example,
the RJ-45-style connector is the MDI for 10BASE-T and
100BASE-TX.
MDI-X—An MDI port on a hub or media converter that
implements an internal crossover function. This means that a
“straight-through” cable can be used to connect a station to
this port, since the signal crossover is performed inside
the port.
MIB—Management Information Base. A management
information base (MIB) describes a set of managed objects.
An SNMP management console application can manipulate
the objects on a specific computer if the SNMP service has
an extension agent DLL that supports the MIB. Each
managed object in a MIB has a unique identifier. The
identifier includes the object’s type (such as counter, string,
gauge, or address), the object’s access level (such as read,
or read/write), size restrictions, and range information.
MII—Medium Independent Interface. Similar to the original
AUI function, but designed to support both 10 and 100
Mbps, an MII provides a 40-pin connection to outboard
transceivers (also called PHY devices). Used to attach
802.3 interfaces (MACs) to a variety of physical media
systems.
Media Converter—A device that converts signals from one
media type to that of another.
Multicast—A transmission initiated by one station to many
stations on the network.
NIC—Network Interface Card. Also called an adapter,
network interface module, or interface card. The set of
electronics that provides a connection between a computer
and a network.
Node—A node is where data enters and exits a network.
OPC—Originally, OLE for Process Control. A process control
communications standard for accessing process data from
multi-vendor systems.
OSI—Open Systems Interconnection. A seven-layer reference
model for networks, developed by the International
Organization for Standardization (ISO). The OSI reference
model is a formal method for describing the interlocking
sets of networking hardware and software used to deliver
network services. It is a good model, but strict compliance
to the model is seldom accomplished.
OUI—Organizationally Unique Identifier. A 24-bit value
assigned to an organization by the IEEE. Ethernet vendors
use the 24-bit OUI they receive from the IEEE in the process
of creating unique 48-bit Ethernet addresses. Contemporary
Controls has been assigned a vendor OUI.
Packet—A unit of data exchanged at the network layer. This
is a much abused definition and the terms “frame” and
“packet” are frequently interchanged.
Patch Cable—A twisted-pair or fiber optic jumper cable used
to make a connection between a network interface (on a
station or network port on a hub) and a media segment, or
to directly connect stations and hub ports together.
PAUSE—A unique frame sent by full-duplex capable stations
to indicate to the sender to slow down transmissions.
PHY—Physical Layer Device. The name used for a
transceiver in Fast Ethernet and Gigabit Ethernet systems.
Physical Layer—The bottom layer in the OSI seven-layer
reference model. This layer is responsible for physical
signaling—including connectors, timing, voltages, and
related issues. Data sent over the physical layer are termed
symbols.
Plenum Cable—A cable that is rated as having adequate fire
resistance and satisfactorily low smoke-producing characteristics
for use in plenums (air-handling spaces). Air-handling
spaces are often located below machine room floors, or
above suspended ceilings and require the use of plenumrated cable.
Point-to-Point Technology—A network system composed of
point-to-point links. Each point-to-point link connects two
and only two, devices—one at each end. Devices could be
DTEs or DCEs, but no more than two can be connected on
one link.
Port—A connection point for a cable. Repeater hubs and
switching hubs typically provide multiple ports for
connecting Ethernet devices.
Port Mirroring—Port mirroring allows a switch port to
monitor packets from any or all of its ports so that traffic
can be analyzed.
Promiscuous Mode—A mode of operation where a device is
configured to receive all frames on a network regardless of
the destination addresses. Typically used by network
analyzer tools.
Propagation Delay—The signal transit time through a cable,
network segment, or device. Important in making collision
domain calculations.
Protocol—A set of agreed-upon rules and message formats
for exchanging information among devices on a network.
Quality of Service (QoS)—Some switches support QoS (per
802.1p and 802.1Q standards) whereby tagged messages,
or messages received on a certain port, can be assigned
one of eight levels of priority. QoS can be important where
time-critical applications can be impaired by data delays.
RapidRing™—Contemporary Controls’ proprietary redundant
ring technology which provides an alternate path in the
event of a single break in the ring.
Rapid Spanning Tree—Newer version of Spanning Tree
Protocol that is backward compatible while providing a
faster recovery time.
Rate Limiting—The ability of a switch to limit the throughput
of particular ports on the switch. Used to prevent certain
ports from consuming all the bandwidth.
Repeater—A physical layer DCE used to interconnect
segments within the same network. An Ethernet repeater
can only link Ethernet segments that are all operating in
half-duplex mode and at the same speed. Some repeaters
offer media conversion as well.
Repeating Hub—A repeater with more than two ports. This
name is frequently shortened to simply “hub.”
RJ-45—An 8-pin modular connector used on twisted-pair
links.
SC—Subscriber Connector. This is a type of fiber optic
connector used in 100BASE-FX fiber optic media systems.
The connector is designed to be pushed into place,
automatically seating itself.
Segment—A cable made up of one or more cable sections
and connections joined together to produce the
equivalent of a continuous cable.
Slot Time—A unit of time used in the medium access control
(MAC) protocol for Ethernet.
SNMP—Simple Network Management Protocol. The de
facto standard for switch management. A familiarity with
MIB objects is necessary to manage a switch with an
SNMP management program. SNMP is not necessarily
limited to TCP/IP networks.
Spanning Tree Protocol—A link management protocol
providing path redundancy and preventing network loops
by defining a tree to span all switches in a network. It forces
redundant data paths into a standby (blocked) state. If a
path malfunctions, the topology is reconfigured and the link
reestablished by activating the standby path.
ST—Straight Tip. This is a type of fiber optic connector used
mostly in 10BASE-FL and FOIRL links, but also in 100BASE-TX
links. The male end of this connector has an inner sleeve
with a slot cut into it, and an outer ring with a bayonet
latch. The inner sleeve is aligned with a mating key in the
socket and the outer ring is turned to complete the
bayonet latch.
Star Topology—A network topology in which each station
on the network is connected directly to a hub.
Straight-through—Refers to a cable where cable connections
at both ends of the cable are pinned the same way. Used
to interconnect non-peer devices such as a hub to a station.
Station—A unique, addressable DTE on a network.
Sometimes referred to as a node.
Switching Hub—A switching hub is another name for a
multiport bridge; a DCE that interconnects network
segments at the data link layer. Switching hubs are typically
located in the center of a star topology, and provide
multiple ports for connections to network stations.
Frequently this name is shortened to switch.
TIA-568A, B—Two standards used to define RJ-45 pin
connectors and wire color-coding schemes.
Topology—The physical layout of a network.
Transceiver—A combination of the words transmitter and
receiver. A transceiver is the set of electronics that sends
and receives signals on a media system. Transceivers may
be internal or external. Sometimes called a MAU.
Trunking—Two or more ports grouped together as one
logical path to increase bandwidth between a switch
and a network node when a single path cannot handle the
traffic. Loops are avoided because specific paths are
designated. Often a single link is designated for flooding
broadcasts and packets of unknown destination. Trunks
can provide redundancy to critical devices.
Twisted-Pair Cable—A multiple-conductor cable whose
component wires are paired together, twisted, and enclosed
in a single jacket. A typical Category 5 twisted-pair segment
is composed of a cable with four twisted pairs contained
in a single jacket. Each pair consists of two insulated copper
wires that are twisted together.
VLAN—Virtual Local Area Network. A LAN that maps
stations on a basis other than location such as by
department, user type or application. Managing traffic,
workstations, and bandwidth can be easier with a VLAN
and improve network efficiency.
Web Server—A computer or device that serves up Web
pages. By installing server software and connecting a computer or device to the network, it can become a Web server.
Every Web server has an IP address and possibly a
domain name.
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