1、1Asynchronous Traffic Shaper(802.1Qcr)and its applicability to Automotive use-cases Alon RegevSeptember 20232 802.1Qcr ATS(Asynchronous Traffic Shaper)introduction Differences between talkers and switches Comparison between ATS vs.other TSN schedulers Interactions of ATS with other shapers Applicabi

2、lity to automotive applications Testing ATS for conformance and performance Summary and recommendationsAgenda3Defined in IEEE 802.1Qcr-2020Enables maximum latency guaranteesDoes not require time synchronizationProvides per-stream egress metering of trafficProvides fault isolationNodes and/or streams

3、 can be dynamically added,changed,or removed at runtimeEfficient use of Ethernet bandwidthAsynchronous Traffic Shaper-Introduction4For a single streamBased on the Token Bucket Algorithm with some tweaks to minimize hardware complexityApplied on each egress portPseudo-code on right is generalized mod

4、el*802.1Q defines this procedure in clause 8.6.11.3 for bridges and 49.1.2 for endstationsDetails:The scheduler algorithmdef ProcessFrame(frame):lengthRecoveryDuration=length(frame)/CommittedInformationRate emptyToFullDuration=CommittedBurstSize/CommittedInformationRate schedulerEligibilityTime=Buck

5、etEmptyTime+lengthRecoveryDuration bucketFullTime=BucketEmptyTime+emptyToFullDuration eligibilityTime=max(arrivalTime(frame),schedulerEligibilityTime)if not bridge or(eligibilityTime=(arrivalTime(frame)+MaxResidenceTimeInS):#The frame is valid if(eligibilityTime bucketFullTime)?BucketEmptyTime=sched

6、ulerEligibilityTime:BucketEmptyTime=schedulerEligibilityTime+eligibilityTime bucketFullTime Send(frame)at time(eligibilityTime)Else:#The frame is invalid Discard(frame)*Scheduler groups are not modeled in this single stream code for simplicity;see following slides for discussion of scheduler groupsP

7、arameters(set during configuration):CommittedInformationRate:the“bandwidth”allocated to the steamCommittedBurstSize:the maximum amount of data to hold in the bucket Data egress can exceed the CommittedInformationRate only for CommittedBurstSize amount of data MaxResidenceTime:(for bridges)the maximu

8、m time between ingress and egress of a frame(in bridge)If the eligibilityTime for a frame would exceed the MaxResidenceTime,the frame is droppedVariables(maintain the state while running):eligibilityTime:the earliest time the frame is allowed to egressBucketEmptyTime:the“state”of the scheduler;indic

9、ates a point in time when the bucket would be empty if the packet were transmitted at the eligibilityTime.May be in the past,present,or future.5for a single stream,when the stream ingress rate equals the CommittedInformationRate Ingress rate=200 bits/s(frame length=200 bits,frame rate=1/sec)Line rat

10、e=1000 bits/s CommittedInformationRate=200 bits/s CommittedBurstSize=400 bits MaxResidenceTimeinS=10“tokens”is the time delta between arrivalTime and BucketEmptyList(to show tokens available)The algorithm:example6for a single stream,when the stream ingress rate is higher than the CommittedInformatio

11、nRate Ingress rate=300 bits/s(frame length=300 bits,frame rate=1/sec)Line rate=1000 bits/s CommittedInformationRate=200 bits/s CommittedBurstSize=400 bits MaxResidenceTimeinS=10“tokens”is the time delta between arrivalTime and BucketEmptyList(to show tokens available)The algorithm:example“Down Payme

12、nt”“layaway payment plan”7for a single stream,when the stream ingress rate is lower than the CommittedInformationRate Ingress rate=200 bits/s(frame length=200 bits,frame rate=1/sec)Line rate=1000 bits/s CommittedInformationRate=300 bits/s CommittedBurstSize=400 bits MaxResidenceTimeinS=10“tokens”is

13、the time delta between arrivalTime and BucketEmptyList(to show tokens available)The algorithm:example8ATS scheduler(per stream)End stations have a simplified ATS implementation defines in 802.1Q clause 49A single local clock is usedOne ATS scheduler is assigned per streamFrames output by multiple AT

14、S schedulers need to be sorted by eligibility time to determine transmit orderFrames are never dropped due to the ATS algorithm in end stationsIn reality there are likely limits,but not specified in 802.1QCan be implemented fully in software(no special NIC functionality is required)ATS in end statio

15、ns(socket writes frame)localsystemclock(to MAC/PHY)sort frames byeligibility timetransmit head at time49.18.6.8.5calculate arrivalTimecalculate arrivalTimelookup stream configATS scheduler(per stream)lookup stream configcalculate arrivalTimelookup stream configATS scheduler(per stream)9Defined in 80

16、2.1Q clause 8.6One ATS scheduler instance per scheduler groupA scheduler group is shared by all streams from a single ingress port,optionally per stream classReduces the sorting complexity for ATS outputs(from an ATS scheduler per stream to an ATS scheduler per group)Supports priority reassignment b

17、ased on streamAllows the same stream to be given different priorities in different bridges providing more fine-grained controlMaximumSDU filtering drops frames greater than per-stream limitATS scheduler drops frames that would not meet MaximumResidenceTimeMaximumResidenceTime is configured per sched

18、uler groupAllows separate scheduler and transmission selection clocks with device-specified maximum offset and frequency deviationsATS in bridgesStream FiltersPriority assignment(to MAC/PHY)ATS schedulersort queue inputs byeligibility timetransmit head at no earlier than eligibilityTime8.6.5.48.6.8.

19、5Input per scheduler group(1 group for each traffic class for each Ingress port,Stream FiltersPriority assignmentATS schedulerQueueQueue8.6.5.38.6.5.68.6.6ATSSchedulerclockTxSelectionClock10In bridges,a scheduler group is shared by all streams from a single ingress port,optionally per stream classFr

20、ames are not reordered within a stream groupif a frame from stream A is received and has an eligibilityTime assigned,subsequent received frames from all other streams will have elibilityTimes set no earlier than thisA MaximumResidenceTime value is shared by all streams in the stream groupEffectively

21、 limits the maximum among of time that the eligibilityTime of one stream can delay frames from other streams in the same scheduler groupExample:Stream A is configured for 1 frame/s;stream B is configured for 100 frames/secMaximumResidenceTime is set to 100msWhat happens if a frame from Stream A arri

22、ves early?If the frame arrives more than 100ms before its schedulerEligibilityTime it is droppedIf the frame arrives within 100ms from its schedulerEligibilityTime,it is queued Frames from stream B will be queues behind it(until the stream A frames eligibilityTime is reached;up to 100ms)Frames queue

23、d for from stream B for the up to 100ms will then be burst after the frame from Stream AImplications of Scheduler Groups11Comparing ATS to other Schedulers802.1Qcr Asynchronous Traffic Shaper802.1Qav Credit Based Shaper802.1Qbv Ehnancements for Scheduled TrafficRequires 802.1AS time syncNo,but devic

24、es need to specify maximum frequency deviation(i.e.,100ppm)Yes,but only frequency syntonization is really requiredYes-gate time accuracy depends on time sync accuracyShaping unitShaping per stream;scheduler groups affect shapingShaping per stream(at talker)and per classShaping per gateBurst Accumula

25、tiononly within stream groupyesBursts are allowed only when gate open,protecting other traffic classesMaximum latency guaranteesYesNo-failure cases have been demonstratedYesTraffic typesPeriodic,periodic burst,random with bandwidth limitOnly fixed periodic trafficPeriodic,periodic burst,random with

26、bandwidth limitRelative Max LatencyMediumHighLowRelative complexity of ImplementationMediumLowHighRelative complexty of configurationMediumLowHigh12ATS scheduled based on receive time;not based on transmit statusIf ATS traffic egress is blocked(by higher priority queues,gates,etc.)transmit may be de

27、layed(while scheduling is not)Interactions with 802.1Qbv Enhancements for Scheduled TrafficATS will keep on scheduling frames(based on eligibilityTime)while the gate associated with the ATS queue is closedWhen the gate is opened,ATS traffic can send a burstInteractions with 80.1Qav Credit Based Shap

28、erCBS is intended to use the highest priority queues(but will only transmit if credits are available)ATS in intended to use the highest N queues(for N priorities)Each can block the other if given higher priority(leading to a potential burst from frames scheduled by the other algorithmInteractions of

29、 ATS with other schedulers13ATS applicability to AutomotiveTwo distinct types of systemsIn-car,engineered networks with(mostly)predetermined latency/bandwidth requirementsChangeable control applications such as assembly linesATS for in-vehicle networksLow-cost to implementGuaranteed worst case laten

30、cy(better than 802.1Qav)Better utilization of available bandwidth than 802.1QbvBetter performance for the next-to-highest priority traffic classesDoes not require time synchronization or hardware timestampingUnlike 802.1Qbv that only supports periodic traffic,ATS can be used for periodic,event-based

31、,and rate-constrained trafficATS for control applicationsLow planning/implementation effortEasier to modify than 802.1Qbv Only need to add new stream to tableBetter utilization of available bandwidth than 802.1QbvSupports many types of traffic/streams with different constraints on each streamDoes no

32、t require time synchronization or hardware timestampingBetter performance for the next-to-highest priority traffic classes14Device-level conformance Testing for ATS should includeStream Filtering:correctly identifying the Stream Gate,scheduler ID,and Max SDU;maximum SDU filteringStream Gating:correc

33、tly updating(or not updating)the priorityProper handling of multiple prioritiesATS scheduler:eligibilityTime assignment,MaxResidenceTime enforcement,GroupEligibilityTime enforcementClock offsets are within the ClockOffsetMin to ClockOffsetMax rangeClock rates are within the ClockRateDeviationMaxassi

34、gnedEligibilityTime:property compensating for clock offset and processing delayDynamic changes to configuration parametersSystem and Interoperability tests should be run to validate interactions between ECUsWhat needs to be tested in ATS15To fully test 802.1Qcr,both the traffic to the 802.1Qcr compo

35、nent and the traffic transmitted from the 802.1Qcr component need to be controlled and monitored by external test stationTo test multiple scheduler groups,multiple talker ports need to be connected to the DUTTraffic needs to be sent to the 802.1Qcr implementation with controlled times of arrival at

36、the 802.1Qcr implementation.To validate frequency deviation,the test station must use an accurate reference time sourceAll test stations/test ports must be time synchronizedValidating an ATS bridge16To fully test 802.1Qcr,both the traffic to the 802.1Qcr component and the traffic transmitted from th

37、e 802.1Qcr component need to be controlled and monitored.Traffic from the 802.1Qcr engine is typically analyzed by an external test stationTraffic needs to be sent to the 802.1Qcr implementation with controlled times of arrival at the 802.1Qcr implementation.A standardized software traffic generator

38、 that can be externally controlled is proposed to accomplish thisTo validate frequency deviation,the test station must use an accurate reference time sourceValidating an ATS end station implementationTest Station TS1DUT/SUTSoftware Test TrafficGenerator SW-TG1802.1Qcrimplementation17While 802.1Qcr h

39、as been published in 2020,commercial implementations are only starting to become availableThere is limited ATS knowledge/experience in automotiveThis presentation attempts to take a step is resolving thisATS has potential benefits and limitations vs.other schedulersIt is recommended thatATS be evalu

40、ated for applicability to any automotive applicationSystem simulations should be used to model traffic behavior under both ideal and unexpected conditions(i.e.,blabbing idiot or out-of-spec oscillator)Any ATS implementation should be tested to validate its conformance,performance and interoperabilitySummary and Recommendations18Questions?Alon R