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Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks

Florian Heilmann, Gerhard Fohler

Chair of Real-Time Systems TU Kaiserslautern RTN 2017 Dubrovnik

Contents of this presentation Time-Triggered schedule affects Rate-Constrained transmission time and jitter TT scheduler can reduce this impact Proof-of-concept Simulation results

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks 1

Outline TTEthernet primer

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks

Based on Switched Ethernet Special nodes and switches

Global synchronization Link schedules

Virtual links Four traffic types (highest to lowest priority) PCF: Process Control frames TT: Time-Triggered traffic RC: Rate-Constrained traffic BE: Best-Effort traffic TT: Time-Triggered traffic

TTEthernet primer

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks 2

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks

Co-Existence of TT and RC traffic

RCin Output time TT schedule time

TT window

RC-1 RC-2 RC-3

TT window TT window

BAGvl time time RC traffic shaping BAGvl Timely Block

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Outline Problem description and motivation TTEthernet primer

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks

Goals during scheduling/routing

Accommodate all functionality Meet deadlines Lowest possible transmission time Lowest possible jitter For both RC and TT

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Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks 5

Problem: RC and TT schedule interdependency

TT transmission time and jitter depends on : TT routing & scheduling (TT RC integration strategy) RC transmission time and jitter depends on: RC routing (TT RC integration strategy) TT routing & scheduling

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks 6

RC routing TT scheduling RC transmission time RC transmission time dependencies TT/

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks 7

Motivation: Improve RC transmission time using the TTScheduler

What can be done in the TTScheduler? Change integration strategy: Infeasible to change to help individual RC virtual links Adjust the TT schedule We can change the TT transmission window placement! Question: Is there a “better way”? In some (all) cases: YES!

Outline TTEthernet primer Problem description and motivation

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks

Window placement strategies

Pipelined ASAP (PA)

TT scheduled ASAP “Pipelined” across consecutive links to minimize TT transmission time

TT- window

RC-1

TT- window TT- window

RC-1

TT- window

RC-1

TT- window TT- window

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks

Window placement strategies

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li li+1 RCin time

Aligned Distributed (AD):

Increase porosity (Steiner’09) to fix issues of Pipelined ASAP Vacant intervals for RC Resulting RC transmission time still very high

RC-1 RC-1 RC-1

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks

Window placement strategies

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TT- window TT- window TT- window TT- window TT- window TT- window

time li li+1 RCin

Outline TTEthernet primer Problem description and motivation Our solution: Link-Based Offsets

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks

Window placement strategies

TT-window TT-window TT-window RC-1

li li+1

Issues with Aligned Distributed

RC-1 TT-window RC-1 TT-window TT-window

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks 10

RCin time Repeated delaying on consecutive links Caused by alignment of TT windows

TT-window TT-window TT-window RC-1

li li+1

Our solution: Link-Based Offsets

RC-1 TT-window RC-1 TT-window TT-window

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks 11

RCin time Define offset: Integer values oi for each link li Shift TT transmission windows on li by oi * len(w)

• i+1 =0
• i =0

Our solution: Link-Based Offsets

RC-1

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks 12

time Shifting according to offsets … … breaks alignment of Aligned Distributed … allows RC message to transmit sooner on li+1 1 * len(w) li li+1 RCin

TT-window TT-window TT-window RC-1 TT-window RC-1 TT-window TT-window

• i+1 =1
• i =0

Conditions for offsets oi

RC-1

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks 13

time Difference between offsets of consecutive links matters Even difference re-establishes alignment  RC transmission time increases In this (simple) example: Difference must be odd 2 * len(w) li li+1 RCin

TT-window TT-window RC-1 TT-window RC-1 TT-window TT-window

• i+1 =2
• i =0

Link-Based Offsets as scheduler extension

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks 14

Procedure: Schedule network with vacant intervals Determine offsets oi Apply offsets oi to link schedules Assumptions/limitations: Timely Block integration strategy Starting point: Aligned Distributed schedule Equal size of TT transmission windows

Outline TTEthernet primer Simulation results Problem description and motivation Window placement strategies Our solution: Link-Based Offsets

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks

OMNET++ with CoRE4INET 2 nodes, 3 switches 5 TT Virtual links, 1 RC Virtual link Equal period(TT)/BAG(RC), equal window size (TT), same path (TT/RC) RC transmission time: Point in time before send/after reception

Simulation parameters

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks

l1 l2 l3 l4

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1000 900 800 700 600 500 400 300 PA AD LBO

strategy delay (µs)

Observations:

Best case transmission time:

Pipelined ASAP lowest Link-Based Offsets almost as low Aligned-Distributed highest

Worst case delay transmission time:

Pipelined ASAP highest Aligned Distributed almost as high Link-Based Offsets lowest

Jitter:

Pipelined ASAP highest Aligned Distributed and Link-Based Offsets low

Simulation results

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks 16

• Trans. time: Lower is better

Jitter: Low deviation is better

RC delay by strategy

Outline TTEthernet primer Simulation results Conclusion and future work Problem description and motivation Window placement strategies Our solution: Link-Based Offsets

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks

Conclusion and future work

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks 17

TT Transmission window placement affects RC transmission time and jitter TT scheduler can (in some cases) reduce this impact Link-Based Offsets is a solution for simple cases

Complex topologies & routes Relax parameter limitations Multiple RC virtual links Impact on TT traffic

Conclusion and future work

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks 18

This work Future work

Thank you for your attention!

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks

Questions?

Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks