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TCP over OBS

TCP over OBS. Julien Reynier. Joint Work with F. Baccelli, D. Hong, G. Petit, F. Poppe. Article available at http://www.eleves.ens.fr/home/jreynier/. Overview. Introduction Optical Burst Switching (OBS) : description FDL Optimization problem The formula Conclusion. Goal.

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TCP over OBS

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  1. TCP over OBS • Julien Reynier • Joint Work with F. Baccelli, D. Hong, G. Petit, F. Poppe Article available at http://www.eleves.ens.fr/home/jreynier/

  2. Overview • Introduction • Optical Burst Switching (OBS) : description • FDL • Optimization problem • The formula • Conclusion

  3. Goal • Understand the interaction between TCP and physical layers for data transmission over OBS • OBS : Optical Burst Switching TCP layer IP layer OBS layer electrical optical electrical

  4. Overview • Introduction • Optical Burst Switching (OBS) : description • FDL • Optimization problem • The formula • Conclusion

  5. Burstification of IP packets into Data Bursts (DBs) IP packets BHP BHP BHP Electronic processing of Burst Header Packets (BHPs) SituationOptical Burst Switching : Optimize burst size IP router Channel Group (CG) DWDM link OBS edge router control (CCG) data (DCG) OBS core router

  6. Bursts disassembly DB DB DB IP packets DBs are routed in the optical domain SituationOptical Burst Switching IP router OBS Ingress edge router OBS core router

  7. Specificity of OBS • At the ingress edge router, IP packets are assembled in lrager processing units, namely the Data Bursts (DBs). • The loss of a single DB is the loss of many TCP-IP packets at the same time. • In the core routers, bursts wait in a queue implemented with optical fibers : the Fiber Delay Lines (FDLs). • Bursts are not released as soon as the link becomes ready. • “Classical” queuing models do not work. • Certain methods as Void Filling mitigate this effect. • The drawback is a complex architecture and a possible reordering of bursts, therefore of IP packets. Classical queue FDL length D

  8. Overview • Introduction • Optical Burst Switching (OBS) : description • FDL • Optimization problem • The formula • Conclusion

  9. FDL and a classical queue : • Without FDL : • With FDL : • The Void size is :

  10. Voids Tn Tn+1 input : Tn+kD Tn+1+k’D output : sn Vn

  11. Load factor for an FDL with infinite capacity

  12. Example of an FDL workload D=0.1 hpkt m=7.8 1/hpkt l=1 hpkt/s 1 hpkt=100 IP-packets r’=95% Workload distribution of an FDL queue and for an M/M/1 queue with the same equivalent load

  13. Loss rate due to buffer overflow with FDL b=1/m B=8D l=1/b’ B:buffer D:delay line b:burst size b’:burst size + void size The loss rate at a “congestion epoch” is affine for a large range of values.

  14. Overview • Introduction • Optical Burst Switching (OBS) : description • FDL • Optimization problem • The formula • Conclusion

  15. Notation RTT R • N users share a bottleneck router with capacity C (Mb/s) with queue size B (byte), their RTT being R (ms). Link capacity C N sources TCP- controlled Queue size B Bottleneck router

  16. Small bursts or large bursts ? • For large bursts • Lower bandwidth waste due to guard bands • OBS needs time to reconfigure its switching array • Lower processing time inside nodes • For small bursts • Lower synchronization between sources due to TCP • Lower burst formation time

  17. Slow start Congestion avoidance: additive increase, multiplicative decrease Multiplicative Decrease Ti-3 TS T1 T2 T3 Ti-2 Ti TE Ti-1 Synchronization - AIMD • TCP is AIMD : Additive Increase, Multiplicative decrease • The proportion of sources that lose packets at that time is the synchronization X(t) = throughput seen by a user Ti = congestion epochs in the network Additive Increase X(t) t

  18. Overview • Introduction • Optical Burst Switching (OBS) : description • FDL • Optimization problem • The formula • Conclusion

  19. AIMD framework The AIMD framework models the impact of losses on the TCP-bandwidth. • AIMD : “The AIMD model” : Infocom ‘02 by F. Baccelli et D. Hong The goodput is : The synchronization p(b,D) is :

  20. Formula • The study of FDL allows one to deduct the ratio of lost busts from the bandwidth. • This leads to a simple formula : For X=B/2 and Y=1/2

  21. Overview • Introduction • Optical Burst Switching (OBS) : description • FDL • Optimization problem • The formula • Conclusion

  22. Our results • Model FDL • Determine impact of burst size on aggregate TCP throughput • the impact of FDL on synchronization of TCP sources • the AIMD model allows one to find the bandwidth. • Determine the optimal burst size • maximize the bandwidth. • minimize the bandwidth waste due to OBS (Burst Header Packets, voids, guard bands).

  23. Further research • A better representation of the increase of RTT due to burstification • Model Void Filling • Core routers with wavelength converters

  24. www.alcatel.com

  25. Backup slides

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