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

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

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

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

11. Replier election and subcast IP multicast DyRAM DyRAM R1R1 R2R2 R3R3 R4R4 R5R5 R7R7 0 1 2 10 NAK 2,@ NAK 2 from link2 NAK 2 from link1 NAK 2 Repair 2 D0D0 D1D1 NAK 2

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

13. The active loss detection implementation The Track List (TL) structure which 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. core network Gbits/s wireless LAN 1Mbits/s, 10MBits/s PSTN 10Mbits/s GSM, UMTS visio-conferencing ISDN xDSL 100Mbits/s Server

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

19. Simulation model

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

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.