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A loss detection Service for Active Reliable Multicast Protocols

A loss detection Service for Active Reliable Multicast Protocols. Moufida MAIMOUR & C. D. PHAM INRIA-RESO RESAM UCB-Lyon – ENS Lyon. Tuesday, July 16th, 2002. INC’02, Plymouth. Outline. Introduction The DyRAM protocol The active loss detection service

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A loss detection Service for Active Reliable Multicast Protocols

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  1. A loss detection Service for Active Reliable Multicast Protocols Moufida MAIMOUR & C. D. PHAM INRIA-RESO RESAM UCB-Lyon – ENS Lyon Tuesday, July 16th, 2002 INC’02, Plymouth

  2. Outline • Introduction • The DyRAM protocol • The active loss detection service • An active-based reliable multicast architecture • Some results (analysis, simulation, implementation) • Conclusion

  3. From unicast… Sender • Problem Sending same data to many receivers via unicast is inefficient. data data data data data data Receiver Receiver Receiver

  4. …to multicast on the Internet. Sender • Problem Sending same data to many receivers via unicast is inefficient. data data data • Solution Using multicast is more efficient data Receiver Receiver Receiver

  5. Reliable multicast • At the routing level : IP Multicast provides efficient delivery without any reliability guarantees. • Many multicast applications require reliability. • Reliability has to be addressed at a higher level.

  6. Reliable multicast protocols • End-to-end solutions : Only the end hosts (the source and/or the receivers) are involved. • In-network solutions : Routers are involved in the recovery process. Active routers-based solutions

  7. What are active routers ? Active routers are able to perform customized computations on the messages flowing through them.

  8. DyRAM main characteristics • DyRAM is based on active services (router-assisted). • the recovery is performed from the receivers (no data cache at the routers) • A recovery tree is constructed on a per-packet basis via a replier election mechanism. • Use of NACKs combined with periodic ACKs.

  9. Main Active Services in DyRAM • NACK suppression • Subcast of repair packets • Dynamic replier election

  10. NACK4 NACK4 data4 NACK4 NACK4 only one NACK is forwarded to the source NACK4 NACKs suppression

  11. NAK 2 from link2 NAK 2 from link1 IP multicast IP multicast IP multicast IP multicast IP multicast NAK 2 Repair 2 NAK 2,@ Repair 2 NAK 2 NAK 2,@ NAK 2,@ NAK 2 Repair 2 Replier election and subcast D0 DyRAM 0 2 1 D1 DyRAM Repair 2 R1 1 0 R2 R3 R4 R5 R7

  12. NACK4 NACK4 data4 NACK4 NACK4 A NACK is sent by the router NACK4 The active loss detection service

  13. The active loss detection implementation The Track List (TL) structurewhich maintains for each multicast session, • lastOrdered :the sequence number of the last received packet in order • lastReceived :the sequence number of the last received data packet • lostList :list of not received data packets in between.

  14. The active loss detection implementation (cont.) • On reception of a data packet with a sequence number seq > TL.lastOrdered+1 • for each lost data packet (TL.lastOrdered < lostseq < seq & lostseq Є TL.lostList), • send a NACK for lostseq toward the source. • ignore similar NACKs from downstream links for a given period.

  15. Where to place the active routers ?

  16. ISDN xDSL PSTN GSM, UMTS 10Mbits/s core network Gbits/s Server 100Mbits/s wireless LAN 1Mbits/s, 10MBits/s visio-conferencing

  17. Location of the loss detection-capable routers • The loss detection service should be located not too far from the source so the corresponding overhead is justified !

  18. Specialized active routers architecture source The active router associated to the source can perform early processing on packets. core network Gbits rate A hierarchy of active routers can be used for processing specific functions at different layers of the hierarchy : NACK suppression, subcast, replier election.

  19. Simulation model

  20. Simulation results 4 receivers/group #grp: 6…24 p=0.25 #grp: 6…24

  21. DyRAM implementation • Tamanoir execution environment • Java 1.3.1 and a linux kernel 2.4 • A set of receivers and 2 PC-based routers (Pentium II 400 MHz 512 KB cache 128MB RAM) • Active processing cost of a • data packet : 20 micro sec • NACK packet : 135 micro sec • repair packet : 123 micro sec

  22. Conclusion & future work • Reliability on large-scale multicast session is difficult. Active services at the edges can provide efficient solutions for reducing implosion, recovery delays and exposure problems and so achieving scalability. • Optimizing the replier election based on an estimation of the receivers power (by means of BW, delay …) • A congestion control is currently under evaluation and will be integrated into DyRAM in the near future.

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