Timing Analysis of AVB Traffic in TSN Networks using Network Calculus

Transcription

1 Timing Analysis of AVB Traffic in TSN Networks using Network Calculus Luxi Zao, Paul Pop Tecnical University of Denmark Zong Zeng, Qiao Li Beiang University

2 Outline Introduction System Model Arcitecture Model Application Model Timing Analysis for AVB Traffic in TSN Network Performance Evaluation Conclusions & Future Work 2 /36

3 Wy Timing Analysis? A real-time network is safety-critical Failure or malfunction Meet certain timeliness requirements Guaranteed to be delivered witin teir deadlines Serious arm to umans, equipment, or environment 3 /36

4 Wy TSN Network? Eternet Pros.: excellent bandwidt, scalability, compatibility, cost properties. Cons.: not suitable for real-time and safety critical applications. Extension protocols - AFDX, TTEternet, EterCAT Pros.: satisfy te real-time requirements. IEEE Time-Sensitive Networking (TSN) A collection of sub-standards of Eternet; Inerits te Pros. of Eternet; Cons.: dedicated, incompatible wit eac oter and expensive. Overcomes te Cons. of Eternet, i.e. suitable for safety-critical and real-time applications. 4 /36

5 Outline Introduction System Model Arcitecture Model Application Model Timing Analysis for AVB Traffic in TSN Network Performance Evaluation Conclusions & Future Work 5 /36

6 Arcitecture Model End systems (ES), Switces (SW) Pysical links (Full duplex) Dataflow routing a sequence of directed links connecting a single source ES to one or more destination ESes ES1 dr 2 ES3 SW1 SW2 ES2 dr 1 ES4 SW3 6 /36

7 Application Model Time-Triggered (TT) traffic; Higest priority; Hard real-time applications tat require very low latency and jitter; Audio-Video Bridging (AVB) traffic; Lower priority tan TT traffic; Best-Effort (BE) traffic Applications tat do not require any timing guarantees. Applications tat require bounded end-to-end latencies; 7 /36

8 How TT and AVB work? Time-Aware Saper (TAS) for an output port of a node Eigt queues Gate ES/SW ES1 ES2 Open Closed Gate-Control List (GCL) SW1 SW2 ES3 ES4 TAS T T c la s s q u e u e... A V B C la ss A q u e u e A V B C la ss B q u e u e... B E c la ss q u e u e CBS CBS... GCL G a te G a te G a te... G a te TSA SW3 8 /36

9 How TT Works? Gate-Control List (GCL) TT gates open, gates of oter traffic closed Transmitted in te pre-designed time; TT accomplis low latency and jitter. TT 1 q TT ES1 q TT q A V B _ A q A V B _ B t t t t t dr 2 p TT1 p TT2 100 s 150 s yp e rp e rio d s SW1 q TT E S, S W t TT 2 q TT ES2 q A V B _ A q A V B _ B E S, S W 2 1 S W, S W 1 2 t t t t t t t t t t t t t t t t q TT q A V B _ A q A V B _ B t t t t t q TT q A V B _ A q A V B _ B t t t t dr 1 t t t a fra m e o f TT 1 2 a fra m e o f TT 2 9 /36

10 How AVB Works? Credit-Based Saper (CBS) States of credit value A credit value for eac AVB traffic class Increasing parts making AVB queuing (idle slope idsl_m); Decreasing parts due to AVB transmission (send slope sdsl_m); Frozen parts due to AVB gate closed. 10 /36

11 Wat Are We Going to Researc? Timing analysis for TT or BE Te scedulability of te sceduled TT traffic can be guaranteed during design pase; Timing analysis for AVB BE doesn t require any timing guarantees. An AVB flow is scedulable only if its worst-case end-to-end delay (WCD) is smaller tan its deadline. 11 /36

12 WCD Example TT windows AVB frames target AVB frame 12 /36

13 Related Works and Callenges Timing analysis of AVB traffic in AVB networks [15] [18] Do not consider te effect tat TT traffic as on te AVB traffic in TSN. Timing analysis of Rate-Constrained (RC) traffic wit consideration of TT in TTEternet [19] [21] RC traffic differs from AVB; TSN scedules TT traffic differs from TTEternet. Te AVB Latency Mat equation for AVB network as been extended to consider te TT traffic in TSN [22] Analysis is overly pessimistic; Can only be used to AVB Class A traffic. 13 /36

14 Outline Introduction System Model Arcitecture Model Application Model Timing Analysis for AVB Traffic in TSN Network Performance Evaluation Conclusions & Future Work 14 /36

15 Wat is Network Calculus? A teory to get guaranteed upper bounds for delays; Based on te min-plus (min,+) algebra Two basic matematics operators Convolution: f g t = inf τ 0, t Deconvolution: f g t = sup τ 0 f t τ + g τ ; f t + τ g τ. 15 /36

16 Network Calculus Make intensive use of four notions, basis of te network calculus Flows; Arrival Curve; Servers; Service Curve. 16 /36

17 Network Calculus Flow R(t) A flow is represented by its cumulative function R(t) ; te total number of bits sent by tis flow up to time t. Arrival curve α(t) Te flow is in general unknown; An envelope of te arrival flow s, t R 0, R s + t R s α t, i. e., R R α 17 /36

18 Network Calculus Server A server S is a relation between te input and output flow R(t) S R (t) R(t) R (t) Service curve β(t) S Te minimum service obtained by te arrival flow R R β 18 /36

19 Network Calculus Upper bounds on latency α t β t α, β α, β = sup inf τ 0 α s β s + τ s 0 = inf τ 0: α β τ 0 19 /36

20 Goal Arrival curve for AVB flows before an output port ; Service curve for AVB flows in an output port ; Maximum latency of AVB flows in te output port ; Disseminate te computation of latency bounds along te routing Worst-case end-to-end delays. 20 /36

21 Arrival Curve for AVB Maximum burst σ and long-term rate ρ of an AVB flow Maximum frame size; Minimum time interval between two consecutive frames. α AVB t = σ AVBi \ + ρ AVBi \ τ AVBi τ AVBi Disseminate te burst and rate along te routing t 21 /36

22 Service Curve for AVB TT Traffic Arrival curve for TT traffic Locations of TT traffic windows are determined by GCLs Periodicity of TT traffic window and yperpriod; Lengt of TT traffic window L j ; Relative offset of TT windows o j,i. t o \ in 1, max \ ji TT t L\ j C 0iN 1 ji pgcl yperperiod p G C L L L L o 1,0 o 2, t 1 a fram e of 2 TT 1 a fram e of TT 2 3 a fram e of TT 3 22 /36

23 Service Curve for AVB Non-preemption Two integration modes Wen an AVB frame is already in transmission at te beginning of te TT time window. Non-preemption Guard band, stopped transmission in advance; AVB gate closed. Wasted bandwidt, no latency for TT; contention f A V B _ T C f TT a non-preemption f TT f A V B _ T C guard band t 23 /36

24 Service Curve for AVB Non-preemption Guard bands constraint for non-preemption mode In te worst-case, guard bands before eac TT traffic window Te maximum AVB frames competing te output port; Idle time interval between two consecutive TT traffic windows. to L \ L in 1,,, max j i GB j GB i GB\ TT t, Lj LGB \ j C 0iN 1 ji pgcl yperperiod p G C L L L L GB,0 GB,1 GB,2 1 o 1,0 o 2,0 a fram e of 2 TT 1 a fram e of TT a fram e of TT 3 t 24 /36

25 Service Curve for AVB Preemption Two integration modes Preemption Interrupted, resumed from te stopping point; Overead, reassemble; Reduce te latency for AVB, improve utilization of bandwidt, jitter for TT f TT contention f A V B _ T C (a) non-preemption f TT f A V B _ T C guard band t b preemption f f TT A V B _ T C additional fragment overead t 25 /36

26 Service Curve for AVB Preemption Overeads constraint for preemption mode Overeads can be taken as te separate part causing te latency of AVB traffic; In te worst-case, eac TT traffic window preempts an AVB frame. t o \ L j in 1, max j i OH \ t LOH \ C 0iN 1 ji pgcl yp e rp e rio d p G C L o 1, 0 L OH o L OH 2, 0 L OH t 1 a fra m e o f 2 TT 1 a fra m e o f TT 2 3 a fra m e o f TT 3 26 /36

27 Service Curve for AVB CBS Variation of credit value t = t + + t + t 0 Dividing any time interval into tese tree parts; AVB obtain te service only during t. credit f BE guard band f TT f 1 A V B _ A f 1 A V B _ B f 2 A V B _ A t 0 1 t t 1 t 1 2 t 2 0 t 1GB 0 t 1TT t 27 /36

28 Service Curve for AVB Left-over service curve for AVB traffic wit non-preemption npr β AVB_M t = C idsl M idsl M sdsl M sup 0 s t s α GB+TT C s credit M max idsl M + Left-over service curve for AVB traffic wit preemption pr β AVB_M t = C idsl M idsl M sdsl M sup 0 s t s α TT C s α OH C s idsl M sdsl M idsl M 28 /36

29 Outline Introduction System Model Arcitecture Model Application Model Timing Analysis for AVB Traffic in TSN Network Performance Evaluation Conclusions & Future Work 29 /36

30 Performance Evaluation - Implementations C++ Java API of te RTC toolbox Min-plus and max-plus algebra operators for Network Calculus Orion-Crew Exploration Veicle (CEV) Uses TTEternet; No realistic test cases for TSN yet available; Adapted CEV by using te same topology; Used te Integer Linear Programming (ILP) [24] to generate te GCL; Considered Rate-Constrained (RC) flows as AVB flows. 30 /36

31 Performance Evaluation - Input Topology 1 Gbps 31 ESes 15 SWs 39 routes AVB flows table idsl of Class A 60%; idsl of Class B 15%; sdsl = idsl - link rate 31 /36

32 Performance Evaluation - Comparison (1) Evaluate te scalability 15 TT flows 100 TT flows Preemption mode; As expected, WCDs of AVB flows are increased by te increasing number of TT flows 32 /36

33 Performance Evaluation - Comparison (2) Evaluate te metod on te two integration modes Preemption Non-preemption As expected, WCDs wit te preemption mode are lower tan te bounds wit non-preemption mode. 33 /36

34 Outline Introduction System Model Arcitecture Model Application Model Timing Analysis for AVB Traffic in TSN Network Performance Evaluation Conclusions & Future Work 34 /36

35 Conclusions & Future Work Conclusions Timing analysis for AVB traffic in TSN network Non-overflow condition for AVB credit Performance evaluation on syntesis and realistic test cases Future work Speed up te analysis Latency bounds of AVB traffic can be applied for optimizing te configuration design of TSN. Te worst-case latency for multiple classes of AVB traffic 35 /36

36 Tank you! 36 /36