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  1. A Forward end-to-end delaysAnalysis for packetswitched networks Georges Kemayo, Frédéric Ridouard, Henri Bauer, Pascal Richard LIAS, Université de Poitiers, ISAE/ENSMA, France RTNS’2014 October 08-10, 2014, Versailles, France

  2. LIAS - ISAE/ENSMA - Université de Poitiers 1 Context Outline • The AFDX network 2 State of the art • End-to-End delayvariability • Network Calculus and TrajectoryApproach 3 Contribution • Forward end-to-end delayAnalysis (FA) 4 Conclusion and future work

  3.  Context • State of the art • Contribution • Conclusion The AFDX network: Generalities (1/2) v1,v2 v1 Analysis of AFDX networks used in avionicssystems AFDX = Avionics Full Duplex Switched Ethernet • FullystaticSwitched Ethernet network • « End/Systems » interconnected by « switches » and « physical links » • A physicallinkbetween 2 components is full duplex  no loss of frames due to collisions ES1 v1,v3 S1 ES5 S3 v2 ES2 v2 S2 ES6 v3 ES7 v3,v4 v3,v4,v5 v3,v4 ES3 v6 S5 ES8 v5,v6 S4 v5,v6 ES4 8 End/Systems ESi 5 SwitchesSi 6 Virtual links vi

  4.  Context • State of the art • Contribution • Conclusion The AFDX network: Generalities (2/2) AFDX = Avionics Full Duplex Switched Ethernet • End/System: • Switch: Message 1 Message n Control and Routing … …

  5.  Context • State of the art • Contribution • Conclusion The AFDX network: Virtual link v1,v2 v1 Virtual link = static, unidirectionnal and monotransmitterlogicalchannel • generated by only one source End/System towards one or many End/Systems (multicast) • avionics data flows correspond to virtual links • Anyvirtuallink respects a trafficcontract: • Fmin ≤ data frame lenght ≤ Fmax • BAG = minimum inter-generation time of frames on its source End/System: • guaranteedbandwidth for any data flow:Fmax / BAG ES1 v1,v3 S1 ES5 S3 v2 ES2 v2 S2 ES6 v3 ES7 v3,v4 v3,v4,v5 v3,v4 ES3 v6 S5 ≥BAG <BAG ES8 v5,v6 S4 v5,v6 ES4 ES1 (v1) 8 End/Systems ESi 5 SwitchesSi 6 Virtual links vi

  6.  Context • State of the art • Contribution • Conclusion The AFDX network: Notion of ETE delay ES2 The ETE delay of a data frame in the AFDX: Necessity to use a method to compute the worst ETE delay S1 S2 Variable waitingdurations in buffers (difficult to evaluate) ETE delay ES1 Objective:Guarantee the worst ETE delay of any frame of any flow vicrossing the AFDX (Mandatory for certification)

  7. LIAS - ISAE/ENSMA - Université de Poitiers 1 Context Outline • The AFDX network 2 State of the art • End-to-End delayvariability • Network Calculus and TrajectoryApproach 3 Contribution • Forward end-to-end delayAnalysis (FA) 4 Conclusion and future work

  8. Context •  State of the art • Contribution • Conclusion End-to-End delayVariability The variability of the waitingduration in eachcrossed buffer implies: • The ETE delayisbetween a lowerbound and an exact worst case Can miss some rare scenarios leading to the exact worst ETE delay Combinatorial explosion whencomputing the exact worst ETE delay Model Checking Network Calculus, TrajectoryApproach Network Calculus, TrajectoryApproach Simulation miss of rare Scenarios ETE delay distribution obtained by simulation Lowerbound of the ETE delay Worst ETE delay (observed) Exact worst case ETE delay Upperbound of the ETE delay time

  9. Context •  State of the art • Contribution • Conclusion Network Calculus and TrajectoryApproach • FA (Forward end-to-end delayAnalysis)  correct the disadvantages of the existingmethods Whatis the necessity to design a new method? Serialization: (comingsoon ) (to bestudied) • Global charge:sum of charges of all the flowsencountered on anycrossednode S S 1 2 1 2 Frames 1 and 2 not are serializedtheycandelayeachother Frames 1 and 2 are serialized, frame 1 cannotdelay frame 2

  10. LIAS - ISAE/ENSMA - Université de Poitiers 1 Context Outline • The AFDX network 2 State of the art • End-to-End delayvariability • Network Calculus and TrajectoryApproach 3 Contribution • Forward end-to-end delayAnalysis (FA) 4 Conclusion and future work

  11. Context • State of the art •  Contribution • Conclusion Analysis of the worst ETE delay of flowswith FA (1/10) Modelization of AFDX by the FA method (1/2) 1 output port (Switch or End/System) a network node 1 virtuallinkvi flow, characterized by: ≥ Ti i vi i Ci Maximum transmission time: Ci= Fmax/ R (R = rate of the physicallink) Minimum inter-generation time betweentwoconsecutive frames: Ti = BAG

  12. Context • State of the art •  Contribution • Conclusion Analysis of the worst ETE delay of flowswith FA (2/10) Modelization of AFDX by the FA method (2/2) v1,v2 v1 1 ES1 v1,v3 S1 ES5 S32 S3 2 v2 v1 1 ES2 v2 S2 ES6 v3 AFDX : 1 ES1 ES7 v3,v4 v1 2 v3,v4,v5 v3,v4 ES3 2 v6 S5 v2 v1,v3 S21 S31 ES2 ES8 v5,v6 v2 S4 v5,v6 ES4 ES3 S22 S51 v3,v4,v5 v2 v2 ES1 S1 ES4 S4 S52 v1 Modelization by FA : v3 v3 S51 v3,v4 v3,v4 v3,v4 S52 v5 v6 v5,v6 v5,v6 v6

  13. Context • State of the art •  Contribution • Conclusion Analysis of the worst ETE delay of flowswith FA (3/10) The FA principle Worst ETE delayRi of a flow vi: -Maximum backlogencountered by fi on lasti( FIFO policy) -Maximum delayincurred by fi to arrive on lasti: Generation time of fi … Worst arrived time of fi fi

  14. Context • State of the art •  Contribution • Conclusion Analysis of the worst ETE delay of flowswith FA (4/10) Computation of the maximal delay How to compute ? - Iterative computation,knowingthat Generation time of fi fi … L = propagation delay of a frame on the linkbetweenh and h+1

  15. Context • State of the art •  Contribution • Conclusion Analysis of the worst ETE delay of flowswith FA (5/10) Maximum interference of frames of a same flow on a nodeh (1/3) Theorem:considering a temporal interval [a,b] on h,the scenario leading, for any flow vj, to itsgreatestamount of workisobtainedwhen: Question: how to compute on a nodeh ? … with

  16. Context • State of the art •  Contribution • Conclusion Analysis of the worst ETE delay of flowswith FA (6/10) Maximum interference of frames of a same flow on a nodeh (2/3) [a, b] = [20, 110] • When no other frame of vjcan catch up the frame fjon h • When one frame of vj catches up the frame fjon h • Whenalways one frame of vjstill catches up the frame fjon h • Whentwo frames of vj catch up the frame fjon h Example: determination of the worst case backlog of a single flow vj on h: …

  17. Context • State of the art •  Contribution • Conclusion Analysis of the worst ETE delay of flowswith FA (7/10) Maximum interference of frames of a same flow on a nodeh (3/3) [a, b] = [20, 110] frames … Example: determination of the worst case backlog of a single flow vj on h: General case: … …

  18. Context • State of art •  Contribution • Conclusion Analysis of the worst ETE delay of flowswith FA (8/10) Maximum interference of frames of all the flowscrossing a nodeh: t = b - a iscomputedbased on Usage of the requestboundfunctiontheory for computing the maximal transmission duration of vj frames arrived in [a,b]: … Total transmission duration of frames of all the flowscrossingh and arriving in [a,b]: …

  19. Context • State of the art •  Contribution • Conclusion Analysis of the worst ETE delay of flowswith FA (9/10) Comparative study of the FA method on an AFDX example (1/2) S32 v1 ES1 v1 v2 v1,v3 S21 S31 ES2 v2 ES3 S22 S51 v3,v4,v5 v2 v2 S1 ES4 S4 S52 v1 L= 16 v3 v3 v3,v4 v3,v4 v3,v4 v5 v6 v5,v6 v5,v6 v6

  20. Context • State of the art •  Contribution • Conclusion Analysis of the worst ETE delay of flowswith FA (10/10) Comparative study of the FA method on an AFDX example (2/2) FA = Our approachwhitoutserialization NC = Network Calculustakingintoaccount the serialization Worst case ETE delays NCNS = Network Calculus Not takingintoaccount the Serialization TA = TrajectoryApproachtakingintoaccount the serialization 1) TA is not optimistic in thisexample 2) TA cannotcompute the delay of flow v5, its global charge isgreaterthan 1 but cancompetewith NC only for flowsv1, v2, v3 3) FA isbetterthan NCNS, Remarks: 4) FA is more pessimisticthan TA, but obtainssameresults for flowsv1, v2, v3 5) No methodisbetterthan the others

  21. LIAS - ISAE/ENSMA - Université de Poitiers 1 Context Outline • The AFDX network 2 State of the art • End-to-End delayvariability • Network Calculus and TrajectoryApproach 3 Contribution • Forward end-to-end delayAnalysis (FA) 4 Conclusion and future work

  22. Context • State of the art • Contribution •  Conclusion Conclusion and Perspectives • Conclusion: • Analysis of the ETE delay of flows on AFDX networks • Comparative study of the ETE delay computation methods for the AFDX • Proposition of a new method, Forward end-to-end delayAnalysis, for the AFDX • FIFO policy Future work on FA: • Takeintoaccount the serialization • Large cases comparisonwithothersexistingmethods • Extension to otherpolicies: Fixedpriorities, …

  23. LIAS - ISAE/ENSMA - Université de Poitiers Thankyou for your attention! ?