An Active Reliable Multicast Framework for the Grids

1. An Active Reliable Multicast Framework for the Grids M. Maimour & C. Pham ICCS 2002, Amsterdam Network Support and Services for Computational Grids Sunday, April 21st, 2002 Action INRIA-RESO http://www.ens-lyon.fr/LIP/RESAM

2. Outline • Motivations behind (reliable) multicast • Use of active networks : the DyRAM protocol • DyRAM main services • Simulation results • 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. • Solution Using multicast is more efficient data data data data Receiver Receiver Receiver

5. Reliable multicast • At the routing level, IP Multicast efficiently delivers packets to all the receivers subscribed to a multicast session but without any reliability guarantees. • Reliability (including flow and congestion control) is to be addressed at the transport level.

6. Reliable multicast: a big win for grids Data replications Database updates Code & data transfers Data communications for distributed applications (collective & gather operations, sync. barrier) SDSC IBM SP 1024 procs 5x12x17 =1020 224.2.0.1 NCSA Origin Array 256+128+128 5x12x(4+2+2) =480 CPlant cluster 256 nodes Multicast address group 224.2.0.1

7. Reliable multicast strategies • End-to-end solutions : Only the end hosts (the source and/or the receivers) are involved. Problem : the lack of topology information at the end hosts. • In-network solutions : Some intermediate nodes (router/server) are involved in the recovery process.

8. Active networking solutions • Active routers are able to perform customized computations on incoming packets: • cache of data, • feedback aggregation, • filtering, subcasting, • …

9. The DyRAM framework for grids(Dynamic Replier Active Reliable Multicast) In order to enable distributed grid applications, main design goals are : • low recovery latency using local recovery • low memory usage in routers : local recovery is performed from the receivers (no cache in routers) • low processing overheads in routers : light active services

10. DyRAM loss recovery strategy : main active services DyRAM is NACK-based … • Global NACK suppression • Early packet loss detection • Subcast of repair packets • Dynamic replier election

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

12. data3 data4 NACK4 data5 NACK4 NACK4 NACK4 A NACK is sent by the router NACK4 Early loss packet detection The repair latency can be reduced if the lost packet could be requested as soon as possible These NACKs are ignored!

13. Replier election • A receiver is elected to be a replier for each lost packet (one recovery tree per packet) • Load balancing can be taken into account for the replier election

14. NAK 2 from link 1 NAK 2 from link 2 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 repair subcast D0 DyRAM 0 2 1 D1 DyRAM Repair 2 R1 1 0 R2 R3 R4 R6 R5 R7

15. The DyRAM framework for grids The backbone is very fast so nothing else than fast forwarding functions. source • Nacks suppresion • Subcast • Loss detection 1000 Base FX active router active router Any receiver can be elected as a replier for a loss packet. core network Gbits rate active router A hierarchy of active routers can be used for processing specific functions at different layers of the hierarchy. 100 Base FX active router active router • Nacks suppression • Subcast • Replier election

16. Some simulation results • Network model and metrics used • Local recovery from the receivers • DyRAM vs. ARM (cache in routers) • DyRAM : early lost packet detection

17. Network model 10 MBytes file transfer Source router

18. Metrics • Load at the source : the number of the retransmissions from the source. • Load at the network : the consumed bandwidth. • Completion time per packet (latency).

19. Local recovery from the receivers (1) • Local recoveries reduces the end-to-end delay (especially for high loss rates and a large number of receivers). 4 receivers/group #grp: 6…24 p=0.25

20. Local recovery from the receivers (2) • As the group size increases, doing the recoveries from the receivers greatly reduces the bandwidth consumption 48 receivers distributed in g groups  #grp: 2…24

21. DyRAM vs ARM • ARM performs better than DyRAM only for very low loss rates and with considerable caching requirements

22. DyRAM: early lost packet detection 4 receivers/group #grp: 6…24 • The end-to-end latency is decreased when the early lost packet detection is enabled #grp: 6…24

23. Conclusions • Reliability on large-scale multicast is difficult. • Active services can provide more efficient solutions for reliable multicast related problems. • Main DyRAM design goal is reducing the end-to-end latencies using active services • which are keeped as light as possible making DyRAM more suitable to grid applications.