A Perspective on Ethernet TCP/IP as a Fieldbus Outline - CERN
A Perspective on Ethernet TCP/IP as a Fieldbus Outline - CERN
A Perspective on Ethernet TCP/IP as a Fieldbus Outline - CERN
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A <str<strong>on</strong>g>Perspective</str<strong>on</strong>g> <strong>on</strong> <strong>Ethernet</strong> <strong>TCP</strong>/<strong>IP</strong><strong>as</strong> a <strong>Fieldbus</strong>Prof. J.-D. DecotignieCSEM Centre Suisse d’Electr<strong>on</strong>ique et de Microtechnique SAJaquet-Droz 1, 2007 Neuchâteljean-dominique.decotignie@csem.ch<strong>Outline</strong>‰ introducti<strong>on</strong>‰ early attempts‰ what is new ?‰ 7 re<strong>as</strong><strong>on</strong>s to adopt <strong>Ethernet</strong>‰ requirements and how <strong>Ethernet</strong> can fulfil them ?‰ standardisati<strong>on</strong> effort‰ c<strong>on</strong>clusi<strong>on</strong><strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 2© J.-D. Decotignie, 2001
Some Years Ago ...<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 3© J.-D. Decotignie, 2001Why <strong>Fieldbus</strong>ses ?‰ we mean here a link with sensors and actuators‰ process9 e<strong>as</strong>e c<strong>on</strong>figurati<strong>on</strong> (auto c<strong>on</strong>figurati<strong>on</strong> ?)9 e<strong>as</strong>e redundancy‰ manufacturing9 reduce cabling costs (planning, installati<strong>on</strong>, maintenance,etc.)9 allow to test sub-<strong>as</strong>semblies separately<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 4© J.-D. Decotignie, 2001
Today ...<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 5© J.-D. Decotignie, 2001Early Attempts with <strong>Ethernet</strong>‰ in the early 80’s9 FACTOR, Sinec H1, LAC, ARLIC‰ late 80’s9 a number of proposals to improve predictability‰ MAP¾ CSMA/DCR, DOD-CSMA¾ some were available in silic<strong>on</strong>‰ randomness w<strong>as</strong> a problem for the users<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 6© J.-D. Decotignie, 2001
Why <strong>Ethernet</strong> and <strong>TCP</strong>/<strong>IP</strong> ?‰ attachment costs have dropped‰ switches and full duplex‰ cheap cable and c<strong>on</strong>nector‰ higher signalling rates‰ priorities‰ <strong>TCP</strong>/<strong>IP</strong> is the "lingua franca"<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 7© J.-D. Decotignie, 20017 re<strong>as</strong><strong>on</strong>s to adopt <strong>Ethernet</strong>‰ lot of cheap and integrated silic<strong>on</strong>‰ integrati<strong>on</strong> with the Internet is straightforward‰ with <strong>TCP</strong>/<strong>IP</strong> all c<strong>on</strong>venti<strong>on</strong>al protocols can be used‰ there is a clear path to future incre<strong>as</strong>e of bandwidth‰ a single soluti<strong>on</strong> is now possible‰ existing fieldbusses have reached their limits‰ the market is <strong>as</strong>king for it<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 8© J.-D. Decotignie, 2001
Tomorrow ... or w<strong>as</strong> it 20 yearsago ?<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 9© J.-D. Decotignie, 2001Requirements‰ traffic (mostly small packets with low latency9 type¾ sporadic (<strong>on</strong> request)¾ periodic or cyclic (more than a single period)9 relati<strong>on</strong>ships¾ client-server , producer c<strong>on</strong>sumer‰ data c<strong>on</strong>sistency9 simultaneous sampling and indicati<strong>on</strong> of c<strong>on</strong>sistency9 timestamps (or precedence relati<strong>on</strong>ship) <strong>on</strong> data‰ rugged and low cost soluti<strong>on</strong><strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 10© J.-D. Decotignie, 2001
Bounded Latency‰ CSMA/CD with random backoff9 many nodes, l<strong>on</strong>g packets ⇒ 100% use9 small packet ⇒ 37% worst c<strong>as</strong>e use9 no guarantee9 capture effect‰ <strong>TCP</strong>‰ CPU + OS performance<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 11© J.-D. Decotignie, 2001Efficiency‰ to transmit 16 bits9 PROFIBUS FMS ~451 bits + 2 switch times (max. large)9 F<strong>IP</strong> ~ 122 bits + 1 switch time (max 90 bits)9 CAN ~200 bits (request and resp<strong>on</strong>se)9 ethernet ~1000 bits (request and resp<strong>on</strong>se)<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 12© J.-D. Decotignie, 2001
How to Improve ?‰ switched full duplex <strong>Ethernet</strong>‰ admissi<strong>on</strong> c<strong>on</strong>trol / traffic smoothing [Kwe00]‰ priorities (IEEE 802.12)9 too few levels to be used efficiently‰ use m<strong>as</strong>ter slave‰ use tokens [Ven94]‰ CSMA/DCR<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 13© J.-D. Decotignie, 2001Some Words about Switches‰ add latency in absence of collisi<strong>on</strong>s‰ predictable in absence of overloads9 need to know the working principle of the switch (notstandard)‰ can in principle limit the impact of externallygenerated traffic‰ may be used to add redundancy<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 14© J.-D. Decotignie, 2001
Data C<strong>on</strong>sistency‰ sampling9 periodicity cannot be achieved¾ except with synchr<strong>on</strong>ised clocks‰ temporal c<strong>on</strong>sistency‰ event relati<strong>on</strong>ship9 no guaranty¾ except with synchr<strong>on</strong>ised clocksthere exists adequate clock synchr<strong>on</strong>isati<strong>on</strong>algorithms but it is difficult to get goodresoluti<strong>on</strong>s<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 15© J.-D. Decotignie, 2001Relati<strong>on</strong>ships‰ client server9 <strong>TCP</strong> is OK‰ producer c<strong>on</strong>sumer9 no for <strong>TCP</strong>9 there exists <strong>IP</strong> address ranges for multic<strong>as</strong>t and broadc<strong>as</strong>t9 requires the use of UDP¾ but no acknowledgement<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 16© J.-D. Decotignie, 2001
Rugged and Low Cost‰ resistance to industrial use9 cables9 c<strong>on</strong>nectors‰ low cost9 tree topology9 additi<strong>on</strong>al devices9 more CPU power9 remote powering absent<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 17© J.-D. Decotignie, 2001Standardisati<strong>on</strong> Efforts‰ <strong>Fieldbus</strong> Foundati<strong>on</strong> HSE (High Speed <strong>Ethernet</strong>)‰ Profibus ProfiNet‰ EtherNet/<strong>IP</strong> supported by ODVA (Open DeviceNetVendor Assoc.), CI (C<strong>on</strong>trolNet Intl) and IEA(Industrial <strong>Ethernet</strong> Associati<strong>on</strong>)‰ IAONA (Industrial Automati<strong>on</strong> Open NetworkingAlliance)‰ MODBUS <strong>TCP</strong>‰ IDA (Interface for Distributed Automati<strong>on</strong>)<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 18© J.-D. Decotignie, 2001
Some Advises [bog88]‰ cables should be too l<strong>on</strong>g and of good quality‰ not too many nodes in a single collisi<strong>on</strong> domain‰ check the interface performance9 generates a lot of losses‰ chech the correct implementati<strong>on</strong> of the protocols9 ex. random backoff<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 19© J.-D. Decotignie, 2001Other Advises‰ study the architecture carefully in order to avoidoverloads‰ isolate externally generated traffic9 gateways‰ switches are not always necessary [Lan98]clients hubs 10M switch 10/100 switch 1001 230 247 1344 582 257 14716 2035 402 331<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 20© J.-D. Decotignie, 2001
7 re<strong>as</strong><strong>on</strong>s to avoid <strong>Ethernet</strong>‰ cabling is more complicated and more expensive‰ security in not guaranteed‰ the protocols do not make the job‰ there exist better and cheaper performing soluti<strong>on</strong>s‰ it is unlikely that a universal soluti<strong>on</strong> will exist‰ remote powering is absent‰ <strong>Ethernet</strong> does not guarantee the temporal c<strong>on</strong>straints(even with switches)<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 21© J.-D. Decotignie, 2001C<strong>on</strong>clusi<strong>on</strong>‰ <strong>Ethernet</strong> and <strong>TCP</strong>/<strong>IP</strong> can be used <strong>as</strong> a fieldbus9 need additi<strong>on</strong>al protocols9 protecti<strong>on</strong> against externally generated traffic9 careful use‰ it is also possible to use a gateway between <strong>Ethernet</strong>and an existing fieldbus9 gateway role9 other transmissi<strong>on</strong> media can be used (wireless, mains, etc.)<strong>CERN</strong> <strong>Ethernet</strong> <strong>as</strong> a <strong>Fieldbus</strong> 22© J.-D. Decotignie, 2001
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