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Achieving Realtime Capabilities in Ethernet Networks by Edge-Coloring

Achieving Realtime Capabilities in Ethernet Networks by Edge-Coloring of Communication Conflict-Multigraphs. Frank Dopatka Frank.Dopatka@uni-siegen.de http://www.bs.informatik.uni-siegen.de/. Institute of Operating Systems and Distributed Systems University of Siegen, Germany.

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Achieving Realtime Capabilities in Ethernet Networks by Edge-Coloring

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  1. Achieving Realtime Capabilities in Ethernet Networks by Edge-Coloring of Communication Conflict-Multigraphs Frank Dopatka Frank.Dopatka@uni-siegen.de http://www.bs.informatik.uni-siegen.de/ Institute of Operating Systems and Distributed Systems University of Siegen, Germany PDCN 2006: Parallel and Distributed Computing and Networks, 15.02.2006

  2. Aim: merge demands of Automation Technology with the trend towards Ethernet • TDMA instead of CSMA/CD: • industrial-realtime & asynchronous time-slots • compatibility vs. speed... slide 2 Ethernet in Automation Technology ? • Idea: one network from ERP- & office-area (SAP) to the field-devices (sensors, actuators) • Ethernet: widely-used, easy to use & low cost; • CSMA/CD → non-deterministic behaviour • Automation Technology: determinism, cyclic communication, min. cycle-time, less payload, min. delay & jitter, decentral periphery

  3. SIEMENS • in-house realtime 4-port switch ASICs • → in-house; 4-ports; packet delays • Beckhoff Automation • standard Ethernet NICs with special • HW-connectors • data transmitted like shifting register • → no real Ethernet any more slide 3 Existing Solutions • Bernecker+Rainer (B&R) • standard Ethernet hubs & central manager → no concurrent communication; only RT-members

  4. slide 4 Aim of our Work • develop an approach, independent from existing hardware • support: switches and/or hubs → distributors, half- & full-duplex transmission, decentral periphery → concurrent communication • using a top-down strategy: • - tree-based infrastructure is given • - requirements of the devices (QoS-requests) are given • previously well-known requirements of the devices are e.g.: • - Who sends how many data to whom and when ? • - What is maximum delay and jitter ?

  5. slide 5 Aim of our Work • first results for a restricted problem-class: • - unicast-addressing → Communication Line (CL): sender → receiver • - uniform packet-size (Ethmin: less payload) • - transmission at each production cycle: no priorization • - neither delay, nor jitter in distributors, devices & cables our scientific contribution: We designed a 4-step-approach for this restricted problem-class by using known algorithms!

  6. slide 6 Survey of our Approach

  7. slide 7 I: Generate Communication Lines Given networking infrastructure with tree-topology...

  8. slide 8 I: Generate Communication Lines ...with switches, their ports, and devices.

  9. slide 9 I: Generate Communication Lines Line-topology emulated: 3-port-hubs → minimize packet delays

  10. slide 10 I: Generate Communication Lines R1b R1a Given requirement R1: dev12 sends to dev17

  11. slide 11 I: Generate Communication Lines R1b R1a Choosing 1 root-distributor at first for all requirements...

  12. slide 12 I: Generate Communication Lines R1b R1a R1b R1a and acquire uplinks from each device to the root-distributor...

  13. slide 13 I: Generate Communication Lines 1 1 1 1 1 1 concatenation of 2 uplinks → CL 1

  14. 2 4 2 3 4 3 5 2 8 7 7 9 6 9 8 5 6 4 6 5 5 4 5 5 slide 14 I: Generate Communication Lines 1 1 1 1 1 1 Each CL is stored by using an attribution-technique. The root-node is not needed any more.

  15. slide 15 I: Generate Communication Lines 1 2 4 3 4 2 3 5 2 8 7 7 9 6 1 9 8 5 1 6 4 6 1 5 1 1 5 4 5 5 conflict : at least 2 CL share 1 port → common resource our aim : schedule the conflicts → temporal separation:TDMA

  16. slide 16 II: Build Conflict Multigraph for each Switch 1 2 4 3 4 2 3 5 2 8 7 7 9 6 1 9 8 5 1 6 4 6 1 5 1 1 5 4 5 5 Why is each switch independent ? → Tree topology ! → Schedules can be synchronized after generation :-)

  17. slide 17 II: Build Conflict Multigraph for each Switch 1 2 4 3 4 2 3 5 2 8 7 7 9 6 1 9 8 5 1 6 4 6 1 5 1 1 5 4 5 5 Independency of the switches: 2 CL in 1 switch have a conflict, or they never have !

  18. slide 18 II: Build Conflict Multigraph for each Switch 1 2 4 3 4 2 3 5 2 8 7 7 9 6 1 9 8 5 1 6 4 6 1 5 1 1 5 4 5 5 Independency of the switches: A conflict raises never or in exactly one order in the network !

  19. 6 1 5 3 2 ports → nodes of the graph 4 CLs → edges of the graph 9 8 7 slide 19 II: Build Conflict Multigraph for each Switch 4 2 1 3 4 2 3 5 8 7 7 9 6 1 9 8 5 6

  20. 6 1 5 3 Color 1: 2 4 Color 2: 9 Color 3: 8 7 slide 20 III: Greedy-Edge-Coloring Heuristics WHILE (not all edges colored) x := any non-colored edge M := set of neighbor-edges from x color(x) := lowest color not present in M END WHILE

  21. 6 1 5 3 2 1 3 2 4 9 8 7 slide 21 IV: Calculate the Schedule 1 3 7 2 5 8 4 6 9

  22. slide 22 First Results • We generated 32 random conflict-graphs each with • - 4 / 5 / 6 / 8 / 12 / 16 / 24 / 32 ports • - 2000 / 4000 / 8000 / 16000 randomized CLs • →greedy-coloring on 2.4Ghz Intel P4-Laptop • 4000 CLs in a switch can be calculated in 3 sec.: O(n2) • Time complexity with constant amount of CLs reduces logarithmical with the amount of ports ! • → lower „density“ of the graph • → easier to find next free color for greedy

  23. slide 23 First Results Problems with odd amount of nodes/ports & circles in graph: 12% more colors than theoretical lower bound on average... otherwise 0.1% more colors on average But: - cyclic transmission unusual in Automation Technology - 5-port-switch: only 2 CLs at the same time anyway!

  24. slide 24 Conclusion • We found a method for a restricted problem-class: • - unicast-addressing • - uniform packet-size - sending at each cycle • - neither delay, nor jitter • schedules nearby theoretically best-case results if no odd amount of ports are used • non-realtime traffic options can be added by additional time-slots

  25. slide 25 Conclusion & Future Work • include more common cases → relax restrictions • - multicasting & multiple packet sizes • - sending at each 2nd, 3rd,... cycle • - handle delay & jitter • improve the coloring by usage of known additional heuristics • → only necessary for distributers with most colors • consider, where the schedule is enforced • - inside the switches & dev-polling („Laptops allowed“) • - using external arbiters & dev-polling („standard hardware“) - enforcing inside the devices („fast“) • → consequences for the generation of the schedules • simulate industrial case scenarios with own framework

  26. Thank you for your Attention! Any Questions?

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