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Industrial Ethernet Network

Waskita Indrasutanta, ir.Wifgasindo Dinamika Instrument Engineering, PT.

Revised August 4, 2003

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Why Ethernetfor Industrial Automation?

International standard market dominance Low cost Ease of equipment and accessories availabilityHigh performance on different speeds: 10, 100, 1000 Mbps and faster with auto adjustable speed and packet bufferingIP is a routable protocol connects to LAN and WAN: Connects to subsystems for APC (Advanced Process Control), Critical Control, ease of integration for business functions like Online PIMS (Plant Information Management System), Remote Monitoring and Control, ERP (Enterprise Resource Planning).Continuous developmentMulti-protocol carrierCan use different physical media: Fiber optics, IP Radio, etc.But needs standard application layer to be interoperable

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Is Industrial Ethernet different than standard Ethernet?

It is the same Ethernet that works based on CD/CSMAEthernet is initially designed for IT network that is not time criticalIndustrial applications are very time critical PCN (Plant Control Network) must be ‘deterministic’networkHarsh industrial environment (extreme temperatures, high humidity, high vibrations, dust and corrosive gases, etc.) requires high ratings of equipments including network accessoriesExtra precautions of disturbance, DOS (Denial-Of-Service) attacks, hacking of the network, or unawareness of risk in Industrial applications

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Can we make Ethernet ‘deterministic’ / ‘real-time’?

Dedicated Control NetworkAvoid collisions by Industrial SwitchesIndustrial ProtocolUDP Real-time SecretDeterministic Software

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Dedicated Control NetworkUtilize Dedicated PCN (Plant Control Network) LAN that is isolated from IT and other Network by means of Router and FirewallLimit the number of IP Nodes make multiple LAN segments when there are to many IP NodesGenerally, limiting network traffic for industrial control only. This lightly loaded PCN will give you real-time performance because it is free and often unpredictable traffic on the plant-wide networkPCN shall only carry small I/O packets and is therefore lightly loaded. By only using fraction of network bandwidth we are assured that data will always arrive quicklyFull-Duplex network ports simply doubling the throughput bandwidth

Control Network

FF-H1

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Avoid ‘collisions’ by Industrial Switch

Hub: Simply broadcast each message to all ports. When there is more than one Node (Device) communicating there will be ‘collision’ and data have to be re-transmitted randomly only One transmission at a time. Other Nodes have to wait until ongoing communication is completed. Though wiring looks to be in Star topology, but communication still work like in Bus topology

Switch: Will connect Sender port to Recipient port (can be multiple if Publisher –Subscriber relationship protocol being used). Ethernet Switch can make multiple connections at a time (depending on the Switch throughput bandwidth) just like the way DPBX worksUse of Industrial Switch that can do fast switching such as ‘cut-through’ or slower ‘store and forward’ technique with large message buffers will certainly improve the speed of transmissionUtilizing Industrial Switch avoid ‘collision’, because the networks is not shared and therefore multiple communications are possible, i.e. one communication does not collide with another; Message queue management and performing automatic speed changes on the appropriate ports. Industrial Switch has better rating to be able to work in industrial environment (extreme temperatures, high humidity, high vibration and shocks, etc.)

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Industrial ProtocolTypes of Communication

Client-Server (Master-Slave)Report Distribution (Source-Sink)Publisher-Subscriber

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Client-Server (Master-Slave) Relationship

A Client polls the Server which responds to the requestPoint-to-Point communicationAlso used by Profibus, HART and ModbusCentral control on Master-Slave: only one Master on a single network; Multiple (limited) concurrent Client on Client-Server

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Report Distribution / Report by ExceptionSource-Sink Relationship

Source sends out a message to one or more Receivers (Sinks) acting as temporary Master

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Publisher-Subscriber Relationship

A Publisher sends a message to one or more Receivers (Subscriber).Highly efficient as one communication reaches several destinations.Data reaches all subscribers at the same time, enabling synchronized action, eliminating jitter.Used to link function blocks over the Fieldbus (FF-H1 & FF-HSE)

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Industrial ProtocolWhat is TCP/IP?

TCP/IPIP = Internet ProtocolTCP = Transmission Control Protocol

Defines how message is sent Guarantees message delivery It takes large messages that have to be broken up for transmission and reassembles at the receiving end (even if packets arrive out of order) Smart enough to reduce traffic if network is getting busy (delaytransmission) Handles the entire delivery process in reliable mannerUnfortunately, its priority is simplicity for the user and reliability, but not timelines of the delivery

TCP/IP is great, but it was not designed for real-time systemsTCP/IP is still widely used in most Industrial Systems that do not require milisecond response

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Industrial ProtocolUDP Real-time Secret

UDP = User Datagram ProtocolUDP is the actual data packet of TCP delivery system; TCP managethe delivery of UDP packets; Each UDP packet have an IP Address and travel on the same network and have the same inner content as TCP messages UDP is the heart of TCP messagesWhen we use UDP messaging directly, we have control when to send each packet. Since operating variables (PV, SP, MV, Status,Tag, etc) are basically short messages, TCP capabilities of reassembling large messages is not required. Even if there is a large amount of data to move, the OPC Server can break it up to manageable pieces as it does for every other communication mediaUDP packets do not carry the overhead of TCP stack (memory usage and firmware complexity); UDP do not require explicit sessions to be established between sending and receiving stationand they do not have long timeouts associated with TCP sessions and delivery mechanismIndustrial Switch will respond to UDP in a much faster manner making up a real-time networkFF-HSE uses UDP/IP for time critical operating variables and TCP/IPfor other non-time-critical parameters

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Deterministic SoftwareFastest network in the world won’t give deterministic performance unless the application software that is sending messages is structured for real-time results. Most HMI and similar industrial application software use deterministic I/O polling and utilize real-time task scheduling techniquesBasic schemes used by I/O Drivers, DDE Servers, OPC Servers in industrial software is to poll I/O in a deterministic fixed sequence to ensure repeatable and ‘deterministic’ results. This fixed polling guarantees that collisions will not occur is we use ‘deterministic control network’Depending on the communication type being used, i.e. Client-Server (Master-Slave), Report Distribution / Report by Exception / Source-Sink or Publisher-Subscriber, determinism varies (the latter the more deterministic / real-time)

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Network Security

In Industrial Ethernet application

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System Administration Authority

It is known that IT Engineers are more competent about computers and network; I&C Engineers are not as expert as IT Engineers about computers and networks

tendency that IT Department will take over PCS system administrationHowever, IT Engineers have limited expertise about PCS mistakes will be very dangerous for the PlantAdministration Rights have to be divided into different areas:

IT Department shall administer from Router WAN leg to the entire IT WANI&C Department shall administer from Router PCN leg to the entire Plant Control SystemAdministration Rights exchange shall be coordinated between the administration areas to make entire system to work as designed

PCN

OWS EWSSupervisory

ControlOPAMServer

IndustrialPortal

SIS FGDS OtherSubsystems

PIMSServer

Enterprise Intranet / WAN

Router/Firewall

PCS

WorkstationWorkstation

Workstation

Workstation Workstation

Workstation

LINE OF ADMINISTRATION AUTHORITY

AdministeredBy IT

AdministeredBy I&C

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High Availability Fault Tolerant

In Industrial Ethernet applications

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Dual Network set

Workstationswith Dual NIC

Redundantdual portLinking device

Redundantsingle port

Linking device

Primary Switch Secondary Switch

Singledual port

Linking device

Device and Switch failures can also be tolerated

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Loop / Ring Topology

Hub Hub

Hub

Ring-topology fault-tolerantProprietary hubs/switchesStandard wire or fiberHirschmann Rail-familyWorks with and Ethernet device and protocolHub works as “splitter”Much faster than “spanning tree”One wire failure can be toleratedHub failure cannot be tolerated

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Combo / Redundant-Ring

Primary Secondary

Media duplication and complete redundancy in one.

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Thank YouIndustrial Ethernet Network

Waskita Indrasutanta, ir.Wifgasindo Dinamika Instrument Engineering, PT.Revised August 4, 2003