5.1
Industrial Data Communication
WestermoHandbook
Industrial Ethernet
First edition published december 1994. © Westermo, Sweden 1994.
Second edition published 1996. © Westermo, Sweden 1996.
Edition 2.1 published 1997. © Westermo, Sweden 1997.
Edition 3.0 published 1998. © Westermo, Sweden 1998.
Edition 4.0 published 2001. © Westermo, Sweden 2001.
Edition 5.0 published 2004. © Westermo, Sweden 2004
Edition 5.1 published 2006. © Westermo, Sweden 2006
Production: Westermo Teleindustri AB, Sweden.
Illustrations:Visual Information Sweden AB, Eskilstuna, Sweden.
Photo: bildN,Västerås.
Repro: Ågerups Repro AB, Eskilstuna, Sweden.
Printing: Eskilstuna Offset AB, Eskilstuna Sweden.
All information in this handbook can be changed without prior notice.
Contact Westermo for latest information.
www.westermo.com2 Industrial Ethernet
Industrial Ethernet 3www.westermo.com
Dear Reader
You are holding in your hand the fifth edition of the Westermo Handbook.The first
edition of the Handbook was printed 11 years ago in 1994 and has over the years
become a tool used by engineers and others who have an interest in data commu-
nication.
As in the previous editions our goal has been to give not only an in-depth presen-
tation of the Westermo product range but also a comprehensive overview of the
most common theoretical aspects of data communication.The theoretical and gen-
eral application section has been increased in every new edition of the handbook
and this 5th edition is no exception.
This edition of the handbook differs from the previous editions. Due to the huge
increase in our product range we have divided the handbook into sections to be
easier to use.
The different sections are:
… Theoretical and general applications
… Modems & Remote Access
… Industrial Ethernet
… Local Data Communications
Our hope is that the Westermo Handbook will become a useful tool to help
you in your everyday work and a supplement to the service provided by all
the dedicated people we have round the world.
Contents
Industrial Ethernet ............................................................................................................................................................................................... 6–11
Ethernet – Where did the name originate? ........................................................................................................................ 6
What is Ethernet? ............................................................................................................................................................................................... 6–7
Why use Ethernet on industrial systems? .............................................................................................................................. 8
Is Ethernet Deterministic? .............................................................................................................................................................................. 8
How to make Ethernet Industrial! ......................................................................................................................................... 9–11
Westermo Ethernet Products ...................................................................................................................................................... 12–19
Ethernet adapters ................................................................................................................................................................................................... 12
What is an Ethernet adapter ........................................................................................................................................................ 12
Protocols .................................................................................................................................................................................................................. 13–14
User Datagram Protocol (UDP) ............................................................................................................................................. 13
Transmission Control Protocol (TCP) ............................................................................................................................ 13
Point to Point Protocol (PPP) ...................................................................................................................................................... 14
Routers ................................................................................................................................................................................................................................... 15
Switches ................................................................................................................................................................................................................................. 15
Managed switch ......................................................................................................................................................................................................... 16
Ring switch ........................................................................................................................................................................................................................ 17
Time synchronization in switched Ethernet ..........................................................................................................18–19
Ethernet Fibre Optic Connection .......................................................................................................................................... 20–21
Fibre Optic Cable Construction ...................................................................................................................................................... 21
Selection Guide .................................................................................................................................................................................................... 22–25
General Technical Information ...................................................................................................................................................... 26–33
DIN-rail products .................................................................................................................................................................................................... 26
Environmental and mechanical conditions ........................................................................................................................ 26
Electrical conditions ............................................................................................................................................................................................. 27
Safety conditions ...................................................................................................................................................................................................... 28
Installation conditions ........................................................................................................................................................................................ 28
DIN-rail versions / Enclosure .................................................................................................................................................... 29–33
Applications ................................................................................................................................................................................................................ 34–57
Bottle filling machine ........................................................................................................................................................................................... 34
Flatbed printer ............................................................................................................................................................................................................. 35
City-wide fire reporting system over WAN ................................................................................................................... 36
Multi-site access control system ....................................................................................................................................................... 37
Connecting legacy equipment to SCADA network .......................................................................................... 38
Oil pipeline monitoring & control ................................................................................................................................................. 39
Water treatment plant .................................................................................................................................................................................... 40
Station signalling system ................................................................................................................................................................................ 41
www.westermo.com4 Industrial Ethernet
Drug manufacturing ............................................................................................................................................................................................. 42
Substation automation .................................................................................................................................................................................... 43
Substation automation .................................................................................................................................................................................... 44
Triplicated safety shutdown system ............................................................................................................................................. 45
Pumping safety system .................................................................................................................................................................................... 46
Robot application .................................................................................................................................................................................................... 47
Barrier controls ........................................................................................................................................................................................................... 48
Ethernet within road tunnel .................................................................................................................................................................... 49
Ethernet communications in wind power generator ........................................................................................ 50
Fibre optic Ethernet back bone with remote access and SMS alarms .................................. 51
Redundant fibre optic ring ........................................................................................................................................................................ 52
Time synchronization for off-shore platforms ............................................................................................................. 53
Supervision and traffic control ............................................................................................................................................................ 54
Unmanaged switch, outdoor in harsh environment ........................................................................................... 55
Multi- vendor network redundancy ............................................................................................................................................ 56
Ethernet extender over twisted pair ......................................................................................................................................... 57
Products.............................................................................................................................................................................................................................. 58–93
ED-10 UDP, serial adapter ............................................................................................................................................................ 58–59
ED-10 TCP, serial adapter ............................................................................................................................................................... 60–61
ED-12 TCP, serial adapter ............................................................................................................................................................... 62–63
EDW-100, serial adapter .................................................................................................................................................................. 64–65
EDW-120, serial adapter .................................................................................................................................................................. 66–67
MCW-211, media converter ...................................................................................................................................................... 68–69
ED-20, router .................................................................................................................................................................................................... 70–71
SDW-550, 5 port switch .................................................................................................................................................................. 72–73
SDW-541, 5 port switch .................................................................................................................................................................. 74–75
SDW-532, 5 port switch .................................................................................................................................................................. 76–77
DDW-100, Ethernet SHDSL extender ...................................................................................................................... 78–79
U200, 8 port switch ................................................................................................................................................................................ 80–81
R200, 8 port ring switch ........................................................................................................................................... 82–83
T200, 8 port real-time switch .................................................................................................................................................. 84–85
Lynx 100 / 1100, 8 port switch ............................................................................................................................................ 86–87
Lynx 300 / 1300, 8 port switch ............................................................................................................................................ 88–89
Lynx 400 / 1400, 8 port switch ............................................................................................................................................ 90–91
Lynx 045, 5 port switch .................................................................................................................................................................... 92–93
Glossary ........................................................................................................................................................................................................................... 94–99
Industrial Ethernet 5www.westermo.com
Industrial Ethernet
Ethernet as a data communications standard has been with us for many years and is
the basis for the vast majority of office networks around the world today. Despite
many claims over the years that it will be superseded it continues to evolve and offer
the features that the users require and hence will be used for many years to come.
In recent years Ethernet has also gained acceptance in the industrial market.
Ethernet – Where did the name originate?
In 1972, Robert Metcalfe and his team at Xerox developed the first experimental
Ethernet system to interconnect the Xerox Alto, a personal workstation with a
graphical user interface.The experimental
Ethernet network was used to link Altos to
each other, to servers and to laser printers.
The signal clock for the experimental
Ethernet interface was derived from the
Alto’s system clock, which resulted in a data
transmission rate on the experimental
Ethernet of 2.94 Mbit/s. Robert Metcalfe’s first experimental network was called the
Alto Aloha Network.
In 1973, Metcalfe changed the name to “Ethernet,” to make it clear that the system
could support any type of computer- not just the Xerox Alto.To illustrate that his
new network mechanisms had evolved well beyond the basic system he chose to
base the name on the word “ether” as a way of describing an essential feature of the
system.The physical medium (i.e., a cable) carries data to all stations, much the same
way that the old “luminiferous ether” was once thought to propagate electromagnet-
ic waves through space.Thus, Ethernet was born.
What is Ethernet?
The basic principle of Ethernet communication is called CSMA/CD (Carrier Sense
Multiple Access/Collision Detection). Put simply if a device wishes to communicate
then it checks the line to see if it is clear, if it is, then the data is transmitted else it
waits for a clear line. Collision detection is important as it is possible that two or
more devices may transmit simultaneously and the data will collide. By detecting that
a collision has occurred and retransmitting later, no data is lost.
www.westermo.com6 Industrial Ethernet
Station
I
Transeiver
Interface
Controller
The Ether
Tap
Interface CableCX
Terminator
The first true Ethernet standard was called
10Base5.The network was based around a
single length of thick coaxial cable up to
500 m (1666 ft) long with transceivers tap-
ping into the cable at points along its length.
The data rate was fixed at 10 Mbit/s. If a
larger network was required then repeaters
could be used.
The next important standard was 10Base2,
again running at 10 Mbit/s, but using a lower
cost thin coaxial cable connected to net-
work interface cards by T pieces.This solu-
tion was much cheaper and became popular
for small networks.
The next big step for the Ethernet network was the introduction of structured
cabling.The 10BaseT standard was developed that relied on using hubs and kept the
cable distance below 100 m (333 ft).
Another step up was the evolution of faster
networks and the use of fibre optic cables
for long distance data transmission. Hence
more standards arose including 100BaseT,
100BaseFX etc.
With mixed standards, higher numbers of
connected devices and now two data rates
to consider, connecting the networks together became more complicated, hence the
development of the Ethernet switch.
Industrial Ethernet 7www.westermo.com
10Base5 Coax Cable
Tranceiver Tranceiver Tranceiver TranceiverTransceiver Transceiver
500 metres (1666 ft)
Transceiver Transceiver
10Base5 Coax Cable
10Base2 Coax Cable
Tranceiver Tranceiver Tranceiver TranceiverTransceiver Transceiver
185 metres (616 ft)
Transceiver Transceiver
10Base2 Coax Cable
100 metres (333 ft)UTP cables
Hub
www.westermo.com8 Industrial Ethernet
Ethernet Adapter
Networking Device
Ethernet/Serial
Interface
Network Enabling
Serial Devices
Device Server
Serial Server
Network Adapter
ComPort Server
Terminal SServer
Serial Device Server
IP Converter
Why use Ethernet for Industrial Systems?
Fieldbuses have been the traditional way for data communications in industry.
There are many different types and standards meaning interoperability is difficult
and expensive and is the main reason Ethernet started to be considered for
industrial applications. Other benefits include:
Reliability Ethernet is a well defined open standard meaning that interop-
erability is simplified and components are available from multi-
ple sources. Ethernet is open and transparent. Many different
protocols can run simultaneously on the same network.
Speed Data rates of 10 Mbit/s and 100 Mbit/s are common place
with Gigabit solutions also now available – the fastest field-
bus protocols run at 12 Mbit/s and most operate at less
than 2 Mbit/s.
Determinism Protocols already exist to prioritise data and hence make
Ethernet virtually deterministic, the ultimate goal of the
industrial user.
Is Ethernet Deterministic?
Determinism is the key word in many industrial networks – with a deterministic net-
work it is possible to say with complete certainty that an event occurred within a
particular time window.
With the CSMA/CD technique employed in the original Ethernet systems deter-
minism was impossible however with the advent of the Ethernet switch things have
changed. Collisions in the cabling infrastructure no longer occur.The twisted pair or
fibre optic links are point to point and can be full duplex. A packet sent to a switch is
stored and retransmitted to the correct destination port. If that port is busy, the
switch can wait hence no collisions and no retransmissions.The problem is now the
potential wait in the queue.
Modern switches have features that can guarantee that this queue is never a prob-
lem. Ethernet packets can be configured to carry a priority tag. If a switch supports
prioritisation then that packet jumps to the start of the queue. Another useful fea-
ture in dataflow control is head of line blocking prevention – head of line blocking is
a problem in some switches because they use a FIFO buffering system, meaning that
if a packet is being held up at the front of the queue then the entire queue is
blocked. Some switches have a method of preventing this problem.
How to make Ethernet Industrial!
When designing equipment for industrial environments there are certain features
and functions that are more important than others.Westermo have always designed
equipment for industrial applications so we understand what the market requires
and we know that quality and functionality are important factors when looking at the
total cost of a project.
Important aspects of industrial data communication equipment design include:
The unit must be constructed to eliminate communica-
tion disturbances and downtime.We achieve this by
using high quality components such as long life capaci-
tors and verify the design in harsh environments.
Industrial communication devices are often installed
near equipment like a welder or heavy machinery that
generates electromagnetic noise.We have more than
30 years of experience in designing and manufacturing
data communication equipment for industry and we
use all this knowledge when designing Industrial
Ethernet equipment.
There is often a requirement for extended tempera-
ture ranges in industrial applications.We guarantee this
functionality by using high quality components that
have an extended working temperature range for both
hardware and connectors.
In industrial applications the method of installation is
always important as units can be mounted into
machinery that has to move or is prone to vibration.
All our products are designed for high mechanical per-
formance with DIN-rail mounting.When designing the
products we always look into problems related to
vibration, mechanical connection and security.
Industrial Ethernet 9www.westermo.com
Downtime elimination
Industrial EMC design
Extended temperature
range
Mechanical performance
One of the most common causes of data communica-
tion errors is different earth potentials between con-
nected units.This is eliminated with galvanic isolation of
all the interfaces; this is one of the standard features in
all Westermo products.
Industrial equipment is also often exposed to high cur-
rent power lines, reactive loads or high voltage switch-
gear, this kind of equipment often generates transients
that cause communication errors. One way to elimi-
nate this problem is to design products with enhanced
surge/transient protection.
It is important to have a reliable power supply for
industrial equipment, often DC power is used together
with batteries.When charging a battery a higher volt-
age is used and all connected units must be designed
for this circumstance. In some cases it is also important
to use redundant power inputs for extended security.
www.westermo.com10 Industrial Ethernet
Galvanic Isolation
Transient suppression
Power
When using equipment in real-time applications it is
important to have different levels of prioritisation. In
the fast, ring and time switches there are built in func-
tions and queues guaranteeing transmission of priori-
tised data.
Our units are installed in many different applications all
over the world.To meet local demands for safety, elec-
trical immunity, ESD and vibration we have designed
the units to meet international standards.
Industrial Ethernet 11www.westermo.com
Determinism
Approvals
Westermo Ethernet Products
www.westermo.com12 Industrial Ethernet
Serial Ethernet Adaptors
What is a Serial Ethernet Adapter?
A Serial Ethernet Adapter might take many different forms and will be able to
perform any of the functions below. It will not only provide remote connection
to serial devices. It will also give the user the possibility to:
… Extend the life of existing serial equipment.
… Simplify equipment diagnostics and maintenance.
… Save pathway and line usage costs for long-distance communication.
… Integrate peripherals into an existing overall infrastructure.
Each connected device can be accessed directly over the local network, via router,
a WAN or (if enabled) through the Internet.
… Use the same error correction mechanisms linking millions of PCs world-wide.
… Share data with any number of computers and other resources on your network.
… Replace limited distance serial connections.
… Use a high number of long distance, virtual COM ports without the need for
bulky cabling.
Industrial Ethernet 13www.westermo.com
Protocols
User Datagram Protocol (UDP)
UDP provides a connectionless datagram service.This means that
the arrival of datagrams or data packets is not controlled and the
reliability of the communication is the responsibility of the applica-
tion. In this way UDP is a simpler method of communication than
TCP. As data is sent and received without any established connec-
tion the data transfer is more efficient and often faster. UDP is
therefore used in applications that require efficient use of the
bandwidth and also have higher level protocols to handle lost
data.
Available products
EDW-100
EDW-120
ED-10 UDP
Transmission Control Protocol (TCP)
TCP is a connection-oriented delivery service. Connection-
oriented means that a session must be established before hosts
can exchange data. An acknowledgement is used to verify that
the data was received by the other host. For each data segment
sent, the receiving host must return an acknowledgement (ACK).
If an ACK is not received, the data is retransmitted. Flow-control
between the hosts is managed by TCP. For larger amounts of data
that have to be split between packets TCP provides a method for
reliably reassembling the data in the correct order. Because of the
requirement to establish a session and acknowledge transmissions
TCP takes longer to transmit data than UDP and uses more
bandwidth.
Available products
EDW-100
EDW-120
ED-10 TCP
ED-12 TCP
Serial/IP
TCP
UDP / User Datagram Protocol
Connectionless
… No sessions are established
… No Server/Client needed
Reliability is the responsibility of the application
Applications
Does not guarantee delivery
… No sequence numbers
… No acknowledgements
… Point to point
… One to Many
TCP
Application
Internet
Network
Transport
Data
Data
Ack
Application
Internet
Network
… Point to point … Server/Client
Transport
Point to Point Protocol (PPP)
The Point to Point Protocol (PPP) originally emerged as an encapsulation protocol
for transporting IP traffic over point to point links, typically over PSTN lines between
modems. PPP established a standard for assigning and managing IP addresses, asyn-
chronous and bit-oriented synchronous encapsulation, network protocol multiplexing,
link configuration, link quality testing, error detection and option negotiation for
added networking capabilities. PPP provides a method for transmitting datagrams
over serial point to point links, which include the following three components:
… PPP uses the High-Level Data Link Control (HDLC) protocol as a basis for
encapsulating datagrams over point to point links.
… An extensive Link Control Protocol (LCP) to establish, configure and test the
connection.
… A family of Network Control Protocols (NCP) for establishing and configuring
different network layer protocols.
PPP is capable of operating across any DTE/DCE interface and does not impose any
restriction regarding transmission rate other than those imposed by the particular
DTE/DCE interface in use.
COM port redirector software
COM port redirector software is used to create a virtual COM
port within a PC, with these ports applications can immediately
use a serial server’s serial ports as if they were local serial ports.
The software will redirect data, originally sent to a local COM
port using TCP/IP to the remote serial server. No change of
computer application software is then necessary.
Available products
COM port redirector software,Viritual IP and Serial IP.
www.westermo.com14 Industrial Ethernet
Application software
Application software
Data to / from COM3
Data to / from COM4
Data to / from COM5
Data to / from COM256
COM port
redirector software
Routers
In a network, a router is a device or, in some cases, software in a computer,
that determines the next network point to which a packet should
be forwarded toward its final destination.The router is connected
to at least two networks and decides which way to send each
information packet based on its current understanding of the
state of the networks it is connected to.
IP routers provide a connection between subnets.When a
host wishes to send data to a host in another IP subnet the host
sends the data to its gateway or router address which then knows how to forward
that data packet to the correct network.
Available products
ED-20
Ethernet Switches
A switch is a device used to construct Ethernet networks and control the data flow
and bandwidth of the network.
A switch stores incoming packets and then tests the packet for check sum errors,
if an error is found the packet is discarded. After that a decision is made as to which
port or ports the packet should be forwarded to.This decision is made based on
tables of Media Access Control (MAC) addresses. All MAC tables are created and
maintained automatically from the received packets.When the switch receives a
packet on a port it stores the source MAC address in the MAC table that corre-
sponds to that port. If a node is silent for a long time the MAC address will “age
out” and be removed from the table.
A switch can operate in full duplex mode, this ensures that an Ethernet controller
will never see any collisions occurring when operated in such a manner.
A switch can be either managed or unmanaged, an unmanaged switch can not be
reconfigured using external software tools.
Available products
Unmanaged switches see page 17
Industrial Ethernet 15www.westermo.com
Router
Subnet A
B C
Subnet B
Host A Host D
Managed Ethernet Switches
A switch can be managed or unmanaged. A managed switch allows access to its
functions to allow it to be reconfigured or monitored.This management can be
inband- using protocols on the network or outband via a local management port or
fault contacts. A managed switch often uses SNMP (Simple Network Management
Protocol) for inband management. SNMP is the Internet standard protocol devel-
oped to manage nodes (servers, workstations, routers, switches and hubs etc.) on an
IP network. SNMP enables network administrators to manage network performance,
find and solve network problems, and plan for network growth.
Network Redundancy
Network redundancy means that alternative network paths exist in the network, and
that alternative paths are activated when a network topology change is detected.
Many different concepts and protocols are available on the market. Non industrial
networks are often based on the well established IEEE standard Spanning Tree
Protocol (STP). A new improved version of STP has recently been released. This
protocol is called Rapid Spanning Tree Protocol (RSTP). RSTP can reconfigure the
network topology faster than STP. The network topology reconfiguration time is a
critical factor for some network applications. Some applications can tolerate minutes
and some only milliseconds of downtime. Fast reconfiguration is required in most
cases for industrial networks. Data is often sent cyclically with short intervals on such
networks.The system operation might be badly affected if too many packets of data
are lost during reconfiguration of the network topology.
Traditional protocols such as STP and RSTP are in many cases not fast enough for
industrial networks.Therefore, special protocols have been developed for this market
in order to offer faster reconfiguration times. Most of these protocols only support a
simple ring topology, while STP and RSTP support mesh structured networks. It
should however be noted that all network redundancy protocols have topology
rules. Some of the special network redundancy protocols are able to cope with
more complex network topologies.Two or more redundant rings can be connected
together in a redundant manner. Such a redundant topology is referred to as
Redundant Bridged Rings.The R200 uses a Fast Re-configuration of Network
Topology (FRNT) (patent pending) protocol.The pictures on the next page
shows a comparison of network redundancy.
Each switch has knowledge of the network topology, not only its neighbouring
switches as in the case for STP. An FRNT topology change event packet will be sent
directly to the focal point switch in case of a topology change (e.g. a link loss or a link
www.westermo.com16 Industrial Ethernet
establishment), while an STP implementation will only send STP control packets one
network hop. The focal point switch will then based on the received topology
change event packet, generate a topology change command. This packet is sent to
each member switch in the ring.
Ring Switch
A ring switch is a switch with redundant ring technology.The switch can be used in a
single ring network or in a multiple ring network with bridge link redundancy.This
eliminates network failure caused by fibre or copper failures.The speed of ring recov-
ery is an essential part of designing your network.The R200 can recover from a fail-
ure in only 30mS if such a failure does occur.When used in conjunction with redun-
dant power supplies a very reliable system can be designed.
The switch also incorporates two priority queues, which are designed to ensure
that the network data is deterministic.This is achieved by implementation of Layer 2
and Layer 3 priority. In addition, head of line blocking prevention ensures that the
switch does not become congested by low priority data.This allows engineers to
design a reliable, deterministic and redundant network, while prioritising data into
low and high priority queues.
Industrial Ethernet 17www.westermo.com
Single ring
Multiple ring with bridge link
redundancy
Unmanaged switches:
SDW-550 5 TX ports.
SDW-541 4 TX and 1 FX port.
SDW-532 3 TX and 2 FX.
Lynx 045 5 TX ports M12 connectors.
U200 8 port fast switch with connectivity options from 8 TX to 8 FX ports.
Managed switches:
R200 8 port ring switch with R200 8 port ring switch with connectivity options from 8 TX to 8 FX ports.
Lynx 100 8 port switch with 6 TX and connectivity options from 2 FX ports.
Lynx 300 8 port ring switch with 6 TX and connectivity options from 2 FX ports.
Lynx 400 8 port VLAN ring switch with 6 TX and connectivity options from 2 FX ports.
Lynx 1100 8 port Gigabit switch with 6 TX and connectivity options from 2 FX ports.
Lynx 1300 8 port Gigabit ring switch with 6 TX and connectivity options from 2 FX ports.
Lynx 1400 8 port Gigabit VLAN ring switch with 6 TX and connectivity options from 2 FX ports.
Available products
Time synchronization in switched Ethernet
Distributed systems with real time requirements have often been based on fieldbuses
as the communication solution, but switched Ethernet is now a preferred alternative
for many applications due to the never ending price decrease driven by the office
Ethernet market, high bandwidth, priority features (e.g.VoIP) and the availability of
Ethernet switches and Ethernet enabled products fulfilling industrial environmental
requirements. However, the switch latency will vary depending on the switch load.
Variable switch latency means that raw data sent from two different data acquisition
nodes to the same receiving node may be delayed differently. This is a problem, but
can be solved if the packets of data are time stamped. The receiving node can
resample the incoming raw data based on the time stamps, and raw data from
several sources can be correctly compared. This requires time synchronization.
The timing accuracy that can be achieved in a LAN, based on switched Ethernet,
where time synchronization data is distributed via this infrastructure, depends on two
factors:
1. Time stamping of incoming and outgoing time packets. Time stamping should
preferably be performed at the lowest possible level in the OSI protocol stack
in order to avoid variable latency through the stack.
2. Variable network latency.The switch latency depends on the network load,
drop link speed, packet sizes and the switch architecture.
Which protocol is used for time synchronization is of less importance as
long as the issues above are handled properly.We do, however, recom-
mend SNTP/NTP as the time synchronization protocol since this is an
open internet standard with few limitations. Source code for this proto-
col is also available.
Time stamping
The timing accuracy depends on where the time stamping of incoming
and outgoing time packets was performed, and the variation in the net-
work latency.Time stamping can be performed in the SNTP/NTP appli-
cation layer, Ethernet driver level (software) or Ethernet data link/physi-
cal layer (hardware).
Why is switch latency a problem?
The figure shows a traditional time synchronization implementation,
where time packets are sent through a switched Ethernet infrastructure.
The network latency depends on the network load, drop link speed, packet sizes, the
www.westermo.com18 Industrial Ethernet
Time client
Time delay
Time delayTime server
switch architecture and the number of switches between the
server and the client. The switch latency may vary from a
few tens of microseconds up to several milliseconds.
The packet may be further delayed if other packets are
queued for transmission on the same output port.
Protecting the time packets by using prioritization does not
improve the situation, because the transmission of another
packet may already be started when the time packet arrives
at the output port.
Time server in the Ethernet switch
The switch latency problem can be removed if the time server is integrated in to the
Ethernet switch. There will only be one drop link (direct wire) between the server
and the client if this implementation is used, and the timing accuracy will be inde-
pendent of the network load if the time packets are time stamped in hardware.
An accuracy of better than one microsecond can be achieved at the time client if
the time client also performs time stamping in hardware.The figure above shows
this implementation, where an integrated GPS receiver is used as the time base.
Available products
T200 8 port time switch with connectivity options from 8 TX to 8 FX ports
Industrial Ethernet 19www.westermo.com
TCP UDP
MAC
802.3
IP
TCP UDP
MAC
802.3
IP
T2
T0
T0 T0 T0
SNTP*
HW**
SNTP*
HW**
Ethernet switch withSNTP time server
End node with SNTP time client
Ethernet Fibre Optic Connection
Historically the standard medium for factory networking has been copper cable
because in the past fibre optic cables were expensive and difficult to terminate.
Instead of conducting electrical signals as in the case of the copper cable, fibre
optic cable propagates light waves.A fibre optic cable is made up of core and
cladding layers of glass.The difference in the refractive index of the two types of
glass cause total internal reflection of the light within the core to occur and hence
propagation of that light. Surrounding the fibre there is a protective layer which
acts as a buffer. Electrical signals are converted to light using LEDs or lasers and
photodiodes are used to receive the light and convert back to the electrical sig-
nals.
Typically in Ethernet systems there are two types of fibre optic cable used; single-
mode and multimode.
Singlemode fibre typically has a core diameter of 9 microns and when used in con-
junction with light of 1300 nm allows the propagation of only a singlemode
of light.The advantage of this is that the pulses of light can not be distorted
by waves taking different paths through the core.This means that single-
mode systems can be used over much greater distances and with higher bandwidths
than multimode cable.
Multimode fibre tends to have core diameters of 50 or 62.5 microns. More distor-
tion of the light pulses mean that transmission distances are much lower
than for singlemode fibres. Components for multimode systems tend to be
much cheaper than those for singlemode thus compensating for the lower
transmission ranges.
The greatest advantage of the fibre optic cable is that it is immune to electrical and
magnetic interference. Consequently, it is highly suitable for harsh industrial environ-
ments, guarantees secure transmission and has a very high transmission capacity.
www.westermo.com20 Fibre optic
Fibre Optic Cable Construction
Fibre optic cable is composed of:
Core The centre of the fibre and the medium for the transmission of
optical (light) signals. It ranges in diameter from 5 to 200 microns.
Cladding The optical material which surrounds the core and causes the light
from the core that strikes it to be reflected keeping the optical
information in the core.The cladding increases the diameter of the
glass fibre to the range of 125 to 230 microns.
Connectors There are many connectors on the market for fibre cables, but
there are four main connectors used for professional Ethernet
installations and they are:
SC simplex connector used for
multi- or singlemode.
LC duplex connector used for
singlemode.
MTRJ duplex connector used for
multi- or singlemode.
ST simplex connector used for
multimode.
Core
Cladding
Fibre optic 21www.westermo.com
ED-10UDP ED-10TCP ED-12TCP EDW-100
Application
Serial to Ethernet … … … …
Switch
Router
Media converter
SHDSL Ethernet Extender
Interface
RS-232 or RS-422/485 … … … …
10 Mbit TX (copper) … … … …
100 Mbit TX (copper) …
100 Mbit FX (fibre)
Flexible combination copper/fibre
Number of Ethernet ports 1 1 1 1
Number of serial ports 1+1* 1+1* 2 1
DSL
Functionality
Managed ICMP/SNMP … / – … / – … / – … / –
VLAN Transparent
Ethernet Bridge
Isolation between interfaces … … … ** …
Extended temperature range …***
DIN-mounted … … … …
Rack or wall mountable
Designed to industrial standards … … … …
Product guide
www.westermo.com22 Industrial Ethernet
* Used for local configuration/Status only ** Not between RS-232 *** Relesed Q1-2006
EDW-120 MCW-211 ED-20 SDW-550 SDW-541 SDW-532 DDW-100
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…
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…
… …
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1 2 1 5 5 5 1
2 1+1*
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…
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Industrial Ethernet 23www.westermo.com
Ethernet U200 R200 T200 Lynx 045
Application
Switch … … … …
Media converter … … …
Interface
10/100 Mbit TX (copper) … … … …
10/100 Mbit M12 connector …
100 Mbit FX (fibre) … … …
1 Gbit TX (copper)
1 Gbit FX (fibre)
Flexible combination copper/fibre … … …
Number of Ethernet ports 8 8 8 5
Functionality
Managed ICMP/SNMP … / – … / … … / …
Prioritization … … …
Redundant ring … …
Time synchronization …
VLAN … …
IGMP Snooping … …
Isolation between interfaces … … … …
Extended temperature range … … … …
DIN-mounted … … … …
Rack or wall mountable … … … …
Designed to industrial standards … … … …
www.westermo.com24 Ethernet
Product guide
Lynx 100 Lynx 300 Lynx 400 Lynx 1100 Lynx 1300 Lynx 1400
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8 8 8 8 8 8
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Ethernet 25www.westermo.com