YOKOGAWA Vnet/IP Manual

Technical
Information
Vnet/IP Network
Construction Guide
TI 30A10A05-01E
TI30A10A05-01E
©Copyright Aug. 2011 (YK)
5th Edition Mar. 2019 (YK)
Yokogawa Electric Corporation
2-9-32, Nakacho, Musashino-shi, Tokyo, 180-8750 Japan

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Introduction
The purpose of this document is to ensure that users who use a Vnet/IP control bus understand
the Vnet/IP system conguration, necessary precautions to set up the system, and the settings
required to create a control network system before they set up a Vnet/IP system.
Chapter 1 describes Vnet/IP. Chapters 2 and 3 provide the information required to congure a
Vnet/IP system. Ensure that you read Chapter 1 rst if you are not familiar with the background of
Vnet/IP.
Chapter 1 provides an overview of the Vnet/IP system conguration when it is used as a control
network, and the devices required for the system.
Chapter 2 describes the Vnet/IP network settings based on system conguration examples.
It provides examples of the basic system conguration, multiple domain conguration, and
connection with existing systems. These examples describe the required devices, settings, and
information when setting up the network. We recommend that you evaluate the general Vnet/IP
system conguration by following these examples. You must read Chapter 1 rst to understand
Chapter 2.
Chapter 3 describes the Vnet/IP network settings in a system conguration that does not use
information network but uses Vnet/IP to perform communication that is normally done on an
information network. It provides examples of the basic system conguration and multiple domain
conguration. These examples also describe the required devices, settings, and information
when setting up the network. To set up a system without using information network, you have to
fully understand the conditions described in Chapter 1.6 of this document, and then congure
and run the system appropriately. You must read Chapter 1 rst to understand Chapter 3.
Chapter 4 describes the layer 2 switches, layer 3 switches, cable for Vnet/IP, time
synchronization in the Vnet/IP system, and necessary precautions when installing network
devices. Time synchronization is important for the electronic records; electronic signatures (21
CFR Part 11) compliant system of Food and Drug Administration (FDA) or for the Sequence of
Event (SOE) system.
This document addresses the Vnet/IP network conguration as a control network. When Vnet/
IP is connected to an external network, it is necessary to take security issues into consideration.
Therefore, this document does not provide complete information on the required network
conguration or settings. When connecting to an external network, contact the network
administrator to determine the appropriate network conguration.
With the release of CENTUM VP R5.01 and ProSafe-RS R3.01, the guidelines are changed so
that Vnet/IP is used as a network for control communications, and other communications are
performed on an information network other than Vnet/IP. This document is customized to address
this change. Refer to “TI 30A10A10-01 Vnet/IP Network Construction Guide (Legacy Edition)” for
the legacy guide.
nRelated documents
TI 30A10A10-01E Vnet/IP Network Instruction Guide (Legacy Edition)
TI 30A10A20-01E Vnet/IP Built-In security Features
TI 30A10A30-01E Network Switch for Vnet/IP
All Rights Reserved Copyright © 2011, Yokogawa Electric Corporation Mar.19,2012-00

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nGlossary
The following table describes the terms commonly used in this document.
Table Glossary terms (1/2)
Term Description
1000BASE-LX A gigabit Ethernet optical interface standard specied in IEEE 802.3 with a
transmission rate of 1 Gbps.
1000BASE-T A gigabit Ethernet UTP interface standard specied in IEEE 802.3 with a transmission
rate of 1 Gbps.
100BASE-TX A Fast Ethernet UTP interface standard specied in IEEE 802 with a transmission rate
of 100 Mbps.
APCS An Advanced Process Control Station (APCS) performs control functions with a station
to improve advanced control and plant e󰀩ciency.
BCV A generic name for Bus Converter. It connects V net stations to V net or HF Bus
stations in other domains.
BCV-H A Bus Converter for HF Bus. It connects V net stations to HF Bus stations in other
domains.
BCV-L A Bus Converter for RL Bus. It connects V net stations to RL Bus stations in other
domains.
BCV-V A Bus Converter for V net. It connects V net stations to V net stations in other domains.
CENTUM A generic name for Integrated Production Control System CENTUM VP and CENTUM
CS 3000.
CENTUM system A system that consists of CENTUM components.
Control bus TCP/IP
communications
The TCP/IP protocol communications on the control bus V net.
Control Communications A generic name for the control data communication between CENTUM or ProSafe-RS
stations.
Control network The transmission path for control communication between CENTUM and ProSafe-RS
systems.
DCOM A Microsoft-dened specication for distributed object technology. It enables software
components referred to as COM objects to communicate and exchange data and
processing requests on a network.
ENG A station with engineering functions that performs CENTUM system conguration and
maintenance management. It can be the same station as the HIS.
Exaopc A station on which Exaopc OPC Interface Package is installed.
Exapilot A station on which Exapilot Operation E󰀩ciency Improvement Package is installed.
Exaquantum A station on which Exaquantum Plant Information Management System is installed.
FCS A Field Control Station (FCS) is a component of the CENTUM system that performs
process control and manages communications with subsystems such as PLCs.
Firewall A generic name for functions and devices that protect the local network against
unauthorized access from an external network.
Gigabit Ethernet An Ethernet standard for 1 Gbps transmission rate, as dened by IEEE802.3.
GSGW A Generic Subsystem Gateway Station (GSGW) collects and congures data of
various subsystem types through OPC DA servers. It is a station with the Generic
Subsystem Gateway Package.
HIS A Human Interface Station (HIS) serves as a human machine interface of the
CENTUM system. It is used for operation and monitoring.
HUB A device that connects network devices on an Ethernet network.
Information network The transmission path for le transfer and data communication between CENTUM
or ProSafe-RS stations and generic Ethernet devices. The information network uses
Ethernet standard protocols.
IP address An Internet Protocol (IP) address is a logical address that identies network devices.
Layer 2 switch (L2SW) A network device that relays packets at Layer 2 (Data Link Layer) of the OSI reference
model.
Layer 3 switch (L3SW) A network device that relays packets at Layer 3 (Network Layer) of the OSI reference
model.
MAC address Abbreviation of Media Access Control address which is a unique address that is
assigned to each Ethernet interface for identication.
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Table Glossary terms (2/2)
Term Description
OPC A standard interface that supports the development of measurement control system
using COM or DCOM of Microsoft.
OPC DA Refers to OPC Data Access, which is an OPC based real-time data access.
Open Communications The communications with Ethernet-based standard protocols on a Vnet/IP network.
Optical Fiber cable A cable used for optical communication. It is required for extending transmission
cables and cables between buildings or noisy locations because it has low attenuation
and immunity from electromagnetic interference. The two types of optical ber cable
are single-mode and multi-mode.
PCS Process Control System (PCS) is a generic name for systems that perform process
control such as CENTUM and its subsystems or PLC instrumented systems.
PLC Programmable Logic Controller (PLC) is a generic name for controllers that perform
sequence control.
PRM A station on which Plant Resource Manager (PRM) is installed.
ProSafe-RS A generic name for Safety Instrumented System ProSafe-RS R3, ProSafe-RS R2, and
ProSafe-RS R1.
ProSafe-RS system A system that consists of ProSafe-RS components.
SCS A Safety Control Station (SCS) is a safety controller of ProSafe-RS that performs logic
functions such as interlock, emergency shutdown, and re and gas protection.
SENG A station of ProSafe-RS that performs engineering functions such as application
conguration, downloading, application testing, and carrying out of maintenance
tasks on SCSs. You can install the SENG functions on a station that has HIS or ENG
functions.
SFP A Small Form-factor Pluggable (SFP) is an MSA-compliant detachable optical
transceiver for network communication devices.
SIOS A System Integration OPC Station (SIOS) integrates third party process control
systems (PCSs) with the CENTUM system.
SNTP server A station that provides time in response to client requests by using the Simple Network
Time Protocol (SNTP), which is a standard protocol for synchronizing time on the
network.
UGS A Unied Gateway Station (UGS) is a Vnet/IP dedicated station that integrates
subsystem controllers such as STARDOM controllers (FCN/FCJ) or third party PLCs
with the CENTUM VP system.
UTP cable The most commonly used Unshielded Twisted Pair (UTP) cable. 100BASE-T uses
Enhanced Category 5 (CAT5e) UTP cables or higher. UTP cables usually use RJ45
plugs as connectors.
V net A process automation control network that uses the token passing method. It has a
transmission rate of 10 Mbps.
V net router A device that connects a Vnet/IP domain to a V net or VL net domain. It is used to relay
control communications.
VL net A control network for CENTUM CS 1000.
Vnet/IP A process automation control network based on gigabit Ethernet that complies with the
international standard (IEC 61784-2 Ed.2.0).
Vnet/IP domain A region in which devices are connected without using L3SW or V net router in a Vnet/
IP network.
Vnet/IP protocol A control communication protocol on Vnet/IP that conforms to IEEE 802.3 and UDP/IP.
Vnet/IP stations A generic name for devices such as FCS and SCS for Vnet/IP, V net router, and
stations in which a Vnet/IP interface card is installed.
WAC router A device used for connecting two Vnet/IP domains via wide area network (WAN)
through a public network or a dedicated network.
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nSymbol Marks
Throughout this Technical Information, you will nd several di󰀨erent types of symbols are used to
identify di󰀨erent sections of text. This section describes these icons.
WARNING
Indicates precautions to avoid a danger that may lead to death or severe injury.
CAUTION
Indicates precautions to avoid a danger that may lead to minor or moderate injury or
property damage.
IMPORTANT
Identies important information required to understand operations or functions.
TIP
Identies additional information.
SEE
ALSO
Identies a source to be referred to.
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Trademark
nTrademark
• Vnet/IP, CENTUM, ProSafe, Exaopc, Exapilot and Exaquantum are either registered
trademarks or trademarks of Yokogawa Electric Corporation.
• PRM is registered trademarks of YOKOGAWA in the United States and/or Japan.
• Windows is registered trademarks or trademarks of Microsoft Corporation in the United
States and/or other countries.
• Ethernet is a registered trademark of XEROX Corporation.
• Other company and product names appearing in this document are trademarks or
registered trademarks of their respective holders.
• TM or ® mark are not used to indicate trademarks or registered trademarks in this
document.
• Logos and logo marks are not used in this document.
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Vnet/IP Network
Construction Guide
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CONTENTS
TI 30A10A05-01E 5th Edition
1. Overview of Vnet/IP.................................................................................. 1-1
1.1 Vnet/IP Features ................................................................................................ 1-2
1.2 Vnet/IP System Components........................................................................... 1-3
1.2.1 Vnet/IP Stations ................................................................................. 1-5
1.2.2 Vnet/IP Network Devices ................................................................... 1-7
1.2.3 Cable for Vnet/IP................................................................................ 1-7
1.2.4 Ethernet Communication Devices .................................................... 1-7
1.3 Vnet/IPMainSpecications ............................................................................. 1-8
1.3.1 Communications Specications ........................................................ 1-8
1.3.2 Achieving high reliability with Redundancy........................................ 1-9
1.3.3 Achieving high reliability with Ring Conguration............................ 1-11
1.4 Vnet/IP System Structure ............................................................................... 1-13
1.5 Information Network Communication .......................................................... 1-20
1.6 Conditions without an Information Network................................................ 1-21
2. Vnet/IPNetworkConguration ............................................................... 2-1
2.1 IPAddressSetting ........................................................................................... 2-2
2.2 NetworkCongurationExample..................................................................... 2-6
2.2.1 Connection within a Domain.............................................................. 2-6
2.2.2 Connecting Multiple Domains............................................................ 2-7
2.2.3 Connection with Existing Systems................................................... 2-10
2.2.4 Connecting network switches by Ring Topology ............................. 2-14
2.3 ConnectionwithExternalNetwork ............................................................... 2-15
3. Vnet/IPNetworkCongurationwithoutusingInformation
Network ..................................................................................................... 3-1
3.1 Bandwidth used for Open Communications ................................................. 3-2
3.2 IPAddressSetting ........................................................................................... 3-3
3.3 NetworkCongurationExample..................................................................... 3-6
3.3.1 Connection within a Domain.............................................................. 3-6
3.3.2 Connecting Multiple Domains............................................................ 3-7

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4. Appendix ................................................................................................... 4-1
4.1 Layer 2 Switch (L2SW) ..................................................................................... 4-1
4.2 Layer 3 Switch (L3SW) ..................................................................................... 4-1
4.3 Cable for Vnet/IP ............................................................................................... 4-2
4.4 Time Synchronization ...................................................................................... 4-4
4.5 PrecautionswhenInstallingNetworkDevices.............................................. 4-9
4.6 Notes on System Power-on ........................................................................... 4-10
4.7 Ringnetworkconguration........................................................................... 4-11
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1. Overview of Vnet/IP
Vnet/IPisahighlyreliableandresponsivecontrolnetworkthatisdevelopedby
YOKOGAWA.
ThissectionprovidesanoverviewofVnet/IPbydescribingitsfunctionsand
specications.
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1. Overview of Vnet/IP 1-2
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1.1 Vnet/IP Features
Vnet/IPisaprocessautomationcontrolnetworkthatisbasedongigabitEthernet.Ithas
thefeaturesthatareimportantforastableplantoperation,namelyhighreliability,and
real-timeresponse.Italsoprovidessecurityagainstthreatsfromanexternalnetwork,
such as cyber attacks.
Vnet/IP connects the devices that make up the CENTUM and ProSafe-RS systems. It
allowstheexchangeofcontroldataamongthesedevices.Vnet/IPcanalsoconnectto
othersystemsthatuseVnetorVLnetastheircontrolnetworkbyusingaVnetrouter.
You can use network devices such as Layer 2 Switch (L2SW) or Layer 3 Switch (L3SW),
andtransmissionmediasuchasUTPcablesoropticalbercablestosetupVnet/IP.
Vnet/IP is a control network that complies with the international standard (IEC 61784-2
Ed.2.0) and conforms to IEEE 802.3 and UDP/IP.
n Highreliability
Vnet/IP is a control network with dual redundant buses and consists of independent subnets, bus
1 and bus 2. The control communication is usually performed by using bus 1. However, when
a problem occurs in bus 1, the path switches immediately and automatically so that the control
communication is performed by using bus 2.
nReal-time response
Vnet/IP implements a dedicated protocol for performing high-quality communication on UDP/IP,
which is a protocol that is suitable for real-time communication.
The transmission scheduling function prevents transmission delays and packet loss by stopping
packets from being accumulated. Real-time response is achieved by prioritizing among the
di󰀨erent communication types.
nSecurity
Vnet/IP takes security into account. It performs authentication by using a shared secret key that
is updated periodically to prevent cyber attacks such as data eavesdropping, falsication, and
spoong.
SEE
ALSO
For more information about Vnet/IP security features, refer to the following.
“Security Standard of System Product” (TI 30A10A20-01E)
In this document, we recommend that you perform non-control communication, which is
information communication, on an information network other than Vnet/IP. If the information
network is not used but Vnet/IP is used for both control communication and information
communication, refer to the conditions described in Chapter 1.6 of this document
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1.2 Vnet/IP System Components
ThefollowinggureshowsanexampleofaVnet/IPsystemconguration.
Bus1
L2SW L2SW
Bus2
L3SW (*1)
Other
Vnet/IP
Domain
FCS
SIOS
L2SW
SCS V net router
UGS/
GSGW
APCS
HIS Exaopc ENG SENGPRM
PCS
Subsystem
Node Unit
ESB bus
Information Network (Ethernet)
Network
Printer
File Server
010201E.ai
Business Network
OPC ClientsPRM Clients
Firewall
SNTP Server
V net
Domain
L3SW: Layer 3 switch
L2SW: Layer 2 switch
*1: WAC router is used for connecting to other Vnet/IP domain via WAN.
(Refer to GS 33J01A10-01EN for an example of system conguration including WAC router.)
FigureSystemCongurationExample
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In this document, devices such as stations in which a Vnet/IP interface card is installed, FCS and
SCS for Vnet/IP, and V net router are all referred to as Vnet/IP stations. Vnet/IP stations support
Vnet/IP protocols.
Vnet/IP stations:
• HIS
• ENG
• FCS
• APCS
• UGS
• SIOS
• GSGW
• Exaopc
• PRM (Field Communications Server)
• SENG
• SCS
• V net router
• WAC router
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1.2.1 Vnet/IP Stations
nHIS
An HIS serves as a human machine interface of the CENTUM system that is used for operation
and monitoring. Software packages installed on a computer or on a console HIS, consisting of a
computer and Open Display Console Assembly. You can install and run operation and monitoring
functions, and/or engineering functions on an HIS as necessary.
A Vnet/IP interface card is required to connect to Vnet/IP.
nENG
An ENG is a station with engineering functions that performs CENTUM system conguration and
maintenance management. It can be the same station as the HIS.
A Vnet/IP interface card is required to connect to Vnet/IP.
nFCS
An FCS performs process control and manages communications with subsystems such as
PLCs.
The following types of FCS are available for Vnet/IP and FIO:
AFV30S: Field Control Unit (for Vnet/IP and FIO, 19-inch Rack Mountable)
AFV30D: Duplexed Field Control Unit (for Vnet/IP and FIO, 19-inch Rack Mountable)
AFV40S: Field Control Unit (for Vnet/IP and FIO, with Cabinet)
AFV40D: Duplexed Field Control Unit (for Vnet/IP and FIO, with Cabinet)
AFV10S: Field Control Unit (for Vnet/IP, 19-inch Rack Mountable)
AFV10D: Duplexed Field Control Unit (for Vnet/IP, 19-inch Rack Mountable)
nAPCS
An APCS performs control functions with a station to improve advanced control and plant
e󰀩ciency.
The APCS requires installation of the “LFS1200 APCS Control Functions.” A Vnet/IP interface
card is required to connect to Vnet/IP.
nUGS
A UGS is a station that integrates subsystem controllers such as STARDOM controllers (FCN/
FCJ) or third party PLCs with the CENTUM VP system. It is connected by subsystem controllers
and various communication protocols such as Modbus, EtherNet/IP, and OPC DA. Similar to the
FCS, you can operate and monitor UGS from the HIS.
The UGS requires installation of the “LBC1500 Unied Gateway Station Standard Function
(UGS).” A Vnet/IP interface card is required to connect to Vnet/IP.
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1. Overview of Vnet/IP 1-6
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nSIOS
An SIOS integrates third party process control systems (PCSs) with the CENTUM system.
The SIOS is a station on which the “LBC2100 System Integration OPC Client Package” is
installed. A Vnet/IP interface card is required to connect to Vnet/IP.
nGSGW
A GSGW collects and congures data of various subsystem types through OPC DA servers.
Subsystem data is assigned to GSGW function blocks. Similar to the FCS, you can operate and
monitor function blocks from the HIS.
The GSGW is a station on which the “LFS1250 Generic Subsystem Gateway Package” is
installed. A Vnet/IP interface card is required to connect to Vnet/IP.
n Exaopc
Exaopc provides an open OLE for Process Control (OPC) interface. The Exaopc station works as
an OPC server on which the “NTPF100 Exaopc OPC Interface Package” is installed. A Vnet/IP
interface card is required to connect to Vnet/IP.
nPRM (Field communications Server)
The Field Communications Server of PRM is a station that collects and congures eld device
information online.
A Vnet/IP interface card is required to connect to Vnet/IP.
nSENG
A SENG is a station of ProSafe-RS that performs engineering functions such as application
conguration, downloading, application testing, and carrying out of maintenance tasks on SCSs.
You can install the SENG functions on a station that has HIS or ENG functions. A Vnet/IP
interface card is required to connect to Vnet/IP.
nSCS
An SCS is a safety controller of ProSafe-RS that performs logic functions such as interlock,
emergency shutdown, and re and gas protection.
The following types of SCS are available for Vnet/IP:
SSC60S: Safety Control Units (Rack Mountable Type, for Vnet/IP)
SSC60D: Duplexed Safety Control Units (Rack Mountable Type, for Vnet/IP)
SSC50S: Safety Control Units (Rack Mountable Type, for Vnet/IP)
SSC50D: Duplexed Safety Control Units (Rack Mountable Type, for Vnet/IP)
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nV net router
A V net router is a device that connects a Vnet/IP domain to a V net or VL net domain. It relays
communication between Vnet/IP stations and V net or VL net stations.
The following V net router is available:
AVR10D: Duplexed V net Router (redundant use of communications modules and power
supply modules)
nWide Area Communication Router (WAC router)
A WAC router is the hardware used for connecting two Vnet/IP domains via a wide area network
(WAN) through a public network or a dedicated network. It enables the operation and monitoring
of FCS/SCS distributed in a remote Vnet/IP domain. Satellite communications can also be used
as a WAN.
AW810D: Wide Area Communication Router
1.2.2 Vnet/IP Network Devices
nLayer 2 Switch (L2SW)
Layer 2 switches connect devices in a Vnet/IP domain. Vnet/IP uses the recommended layer 2
switches that support a transmission rate of 1 Gbps.
nLayer 3 Switch (L3SW)
Layer 3 switches are network switches with routing functions that connect Vnet/IP domains
to each other. If a Vnet/IP system consists of multiple domains, the routing function of layer 3
switches relays communications among the domains. Vnet/IP uses the recommended layer 3
switches that support a transmission rate of 1 Gbps.
nSNTP server
An SNTP server synchronizes the Vnet/IP station time with the Coordinated Universal Time
(UTC). It synchronizes the time of all the stations through Vnet/IP by generating highly accurate
time information from GPS signals.
1.2.3 Cable for Vnet/IP
Vnet/IP uses cables, such as Enhanced Category 5 (CAT5e) UTP cables or optical ber cables,
to connect devices in the system.
For optical ber cables, we recommend that you use the single-mode type.
1.2.4 Ethernet Communication Devices
Peripherals such as network printers, le servers, or rewalls are connected to the information
network. They are not connected to the Vnet/IP network and are not protected by the Vnet/IP
security. Therefore, ensure that they do not become a vulnerability to security during operation.
nPeripherals
You can use Windows-compatible peripherals such as printers because an HIS, ENG, and
SENG support Microsoft Windows.
Contact YOKOGAWA for more information on the peripherals that you can use with the system.
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1.3 Vnet/IPMainSpecications
ThissectiondescribesthemainspecicationsofVnet/IP.
1.3.1 CommunicationsSpecications
nControl communications
Communication method: Read/write communications, message communications, and link
transmission
Link transmission period: 100 msec
nTransmission path
Network topology: Star topology
(tree or ring topology for multiple connection)
Transmission path redundancy: Dual redundant paths (control communications only)
Transmission rate: 1 Gbps
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1.3.2 AchievinghighreliabilitywithRedundancy
Vnet/IP is a control network with dual-redundant buses. Statuses of both Vnet/IP stations and
communication paths are constantly monitored. The most suitable control communication path is
always selected to ensure stable plant operations.
nStatus of Vnet/IP stations and communication paths
Vnet/IP stations can exchange their statuses and the statuses of communication paths with each
other. Therefore, the statuses of Vnet/IP stations and communication paths on Vnet/IP are stored
and updated periodically in Vnet/IP stations.
nCommunication path selection
A Vnet/IP station comprehends the path status for a communication destination from its own
communication path information, and chooses a normal bus to transmit the control data required.
Vnet/IP usually uses bus 1 for the control communication path. It does not use bus 1 and bus
2 alternately. When a problem occurs in bus 1, the communication path switches to bus 2.
However, after bus 1 recovers, the communication path reverts to bus 1. The switching of buses
is performed on the respective communication paths that lead to the destination.
On the left side of the following gure, a communication error occurs in the cables between
station C and layer 2 switch for bus 1. In this case, bus 1 is used between stations A and B, while
bus 2 is used between stations A and C. On the right side of the same gure, the layer 2 switch
for bus 1 is not working. In this case, bus 2 is used between stations A and B, and between
stations A and C.
010301E.ai
L2SW
BA C
Bus 1 side
Bus 2 side
BA C
Bus 1 side
Bus 2 side
In cases where a failure occurs between
station C and L2SW cable on bus 1 side
In cases where L2SW
on bus 1 side is defective
L2SW
L2SW L2SW
Figure SelectionofTransmissionPath
Dec. 26, 2016-00

1. Overview of Vnet/IP 1-10
TI 30A10A05-01E
nRedundant CPUs in Vnet/IP stations
The duplexed FCSs, duplexed SCSs, and duplexed V net routers have two CPUs. Each of the
two CPUs is connected to layer 2 switches in a dual-redundant Vnet/IP.
As mentioned earlier, a Vnet/IP station stores information of other stations that are on
Vnet/IP. This includes information about CPU control rights. The sending station uses the control
rights information of the receiving station to determine the path to take for sending the control
information, and the CPU module to which the information is sent.
In the following gure, station A determines that CPU2 has the control rights for station B, and
therefore communicates with station B CPU2 through the layer 2 switch for bus 1. On the other
hand, CPU1 has the control rights for station C. However, a communication error occurs in the
path between station C CPU1 and layer 2 switch for bus 1. Therefore, station A CPU1 and station
B CPU2 communicate with station C CPU1 through the layer 2 switch for bus 2.
010302E.ai
L2SW
CPU1
(Stand-by)
Bus 1 side
Bus 2 side
CPU2
(Control)
CPU1
(Control)
CPU2
(Stand-by)
CPU1
(Control)
CPU2
(Stand-by)
Station A Station B Station C
L2SW
Figure TransmissionPathforRedundantCPUs
Aug.19,2011-00