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Achieving Realtime Capabilities in Ethernet Networks by Edge-Coloring of Communication Conflict-Multigraphs. Frank Dopatka [email protected] 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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Achieving realtime capabilities in ethernet networks by edge coloring

Achieving Realtime Capabilities

in Ethernet Networks

by Edge-Coloring

of Communication Conflict-Multigraphs

Frank Dopatka

[email protected]

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


Achieving realtime capabilities in ethernet networks by edge coloring

  • Aim: merge demands of Automation Technologywith 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


Achieving realtime capabilities in ethernet networks by edge coloring

  • 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


Achieving realtime capabilities in ethernet networks by edge coloring

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 ?


Achieving realtime capabilities in ethernet networks by edge coloring

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!


Achieving realtime capabilities in ethernet networks by edge coloring

slide 6

Survey of our Approach


Achieving realtime capabilities in ethernet networks by edge coloring

slide 7

I: Generate Communication Lines

Given networking infrastructure with tree-topology...


Achieving realtime capabilities in ethernet networks by edge coloring

slide 8

I: Generate Communication Lines

...with switches, their ports, and devices.


Achieving realtime capabilities in ethernet networks by edge coloring

slide 9

I: Generate Communication Lines

Line-topology emulated: 3-port-hubs → minimize packet delays


Achieving realtime capabilities in ethernet networks by edge coloring

slide 10

I: Generate Communication Lines

R1b

R1a

Given requirement R1: dev12 sends to dev17


Achieving realtime capabilities in ethernet networks by edge coloring

slide 11

I: Generate Communication Lines

R1b

R1a

Choosing 1 root-distributor at first for all requirements...


Achieving realtime capabilities in ethernet networks by edge coloring

slide 12

I: Generate Communication Lines

R1b

R1a

R1b

R1a

and acquire uplinks from each device to the root-distributor...


Achieving realtime capabilities in ethernet networks by edge coloring

slide 13

I: Generate Communication Lines

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concatenation of 2 uplinks → CL 1


Achieving realtime capabilities in ethernet networks by edge coloring

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slide 14

I: Generate Communication Lines

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Each CL is stored by using an attribution-technique.

The root-node is not needed any more.


Achieving realtime capabilities in ethernet networks by edge coloring

slide 15

I: Generate Communication Lines

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conflict:at least 2 CL share 1 port → common resource

our aim:schedule the conflicts → temporal separation:TDMA


Achieving realtime capabilities in ethernet networks by edge coloring

slide 16

II: Build Conflict Multigraph for each Switch

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Why is each switch independent ? → Tree topology !

→ Schedules can be synchronized after generation :-)


Achieving realtime capabilities in ethernet networks by edge coloring

slide 17

II: Build Conflict Multigraph for each Switch

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Independency of the switches:

2 CL in 1 switch have a conflict, or they never have !


Achieving realtime capabilities in ethernet networks by edge coloring

slide 18

II: Build Conflict Multigraph for each Switch

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Independency of the switches:

A conflict raises never or in exactly one order in the network !


Achieving realtime capabilities in ethernet networks by edge coloring

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ports → nodes of the graph

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CLs→ edges of the graph

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slide 19

II: Build Conflict Multigraph for each Switch

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Achieving realtime capabilities in ethernet networks by edge coloring

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Color 1:

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Color 2:

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Color 3:

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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


Achieving realtime capabilities in ethernet networks by edge coloring

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slide 21

IV: Calculate the Schedule

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Achieving realtime capabilities in ethernet networks by edge coloring

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


Achieving realtime capabilities in ethernet networks by edge coloring

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!


Achieving realtime capabilities in ethernet networks by edge coloring

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 resultsif no odd amount of ports are used

  • non-realtime traffic options can be added by additional time-slots


Achieving realtime capabilities in ethernet networks by edge coloring

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


Achieving realtime capabilities in ethernet networks by edge coloring

Thank you for your Attention!

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