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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 1 Rate-Constrained Traffic in TTEthernet Networks

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

TTEthernet primer 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 TT: Time-Triggered traffic RC: Rate-Constrained traffic BE: Best-Effort traffic Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on 2 Rate-Constrained Traffic in TTEthernet Networks

Co-Existence of TT and RC traffic RC-1 RC-2 RC-3 RC in time RC traffic shaping time BAG vl BAG vl TT TT TT TT schedule window window window time Output time Timely Block Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on 3 Rate-Constrained Traffic in TTEthernet Networks

Outline TTEthernet primer Problem description and motivation 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 Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on 4 Rate-Constrained Traffic in TTEthernet Networks

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 5 Rate-Constrained Traffic in TTEthernet Networks

RC transmission time dependencies TT/ RC transmission RC routing time TT scheduling Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on 6 Rate-Constrained Traffic in TTEthernet Networks

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

Outline TTEthernet primer Problem description and motivation Window placement strategies 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 RC-1 RC in TT- TT- TT- RC-1 l i window window window TT- TT- TT- RC-1 l i+1 window window window time Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on 8 Rate-Constrained Traffic in TTEthernet Networks

Window placement strategies 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 in RC-1 TT- TT- TT- RC-1 l i window window window TT- TT- TT- l i+1 RC-1 window window window time Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on 9 Rate-Constrained Traffic in TTEthernet Networks

Outline TTEthernet primer 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

Issues with Aligned Distributed Repeated delaying on consecutive links Caused by alignment of TT windows RC in RC-1 l i TT-window RC-1 TT-window TT-window l i+1 TT-window TT-window RC-1 TT-window time Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on 10 Rate-Constrained Traffic in TTEthernet Networks

Our solution: Link-Based Offsets Define offset: Integer values o i for each link l i Shift TT transmission windows on l i by o i * len(w) RC in RC-1 o i =0 l i TT-window RC-1 TT-window TT-window o i+1 =0 l i+1 TT-window TT-window RC-1 TT-window time Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on 11 Rate-Constrained Traffic in TTEthernet Networks

Our solution: Link-Based Offsets Shifting according to offsets … … breaks alignment of Aligned Distributed … allows RC message to transmit sooner on l i+1 RC in RC-1 o i =0 l i TT-window RC-1 TT-window TT-window o i+1 =1 l i+1 TT-window TT-window TT-window time RC-1 1 * len(w) Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on 12 Rate-Constrained Traffic in TTEthernet Networks

Conditions for offsets o i Difference between offsets of consecutive links matters Even difference re-establishes alignment  RC transmission time increases In this (simple) example: Difference must be odd RC-1 RC in o i =0 l i TT-window RC-1 TT-window TT-window o i+1 =2 l i+1 TT-window TT-window time RC-1 2 * len(w) Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on 13 Rate-Constrained Traffic in TTEthernet Networks

Link-Based Offsets as scheduler extension Procedure: Schedule network with vacant intervals Determine offsets o i Apply offsets o i to link schedules Assumptions/limitations: Timely Block integration strategy Starting point: Aligned Distributed schedule Equal size of TT transmission windows Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on 14 Rate-Constrained Traffic in TTEthernet Networks

Outline TTEthernet primer Problem description and motivation Window placement strategies Our solution: Link-Based Offsets Simulation results Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks

Simulation parameters 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 l 1 l 2 l 3 l 4 Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on 15 Rate-Constrained Traffic in TTEthernet Networks

Simulation results delay (µs) RC delay by strategy 1000 Trans. time: Lower is better Observations: Jitter: Low deviation is better 900 Best case transmission time: 800 Pipelined ASAP lowest Link-Based Offsets almost as low 700 Aligned-Distributed highest Worst case delay transmission time: 600 Pipelined ASAP highest Aligned Distributed almost as high 500 Link-Based Offsets lowest 400 Jitter: Pipelined ASAP highest Aligned Distributed and 300 strategy Link-Based Offsets low PA AD LBO Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on 16 Rate-Constrained Traffic in TTEthernet Networks

Outline TTEthernet primer Problem description and motivation Window placement strategies Our solution: Link-Based Offsets Simulation results Conclusion and future work Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on Rate-Constrained Traffic in TTEthernet Networks

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

Conclusion and future work This work Future work Complex topologies & routes Relax parameter limitations Multiple RC virtual links Impact on TT traffic Heilmann, Fohler - Impact of Time-Triggered Transmission Window Placement on 18 Rate-Constrained Traffic in TTEthernet Networks

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