An analysis of a router-based loss detection service for active reliable multicast protocols

1. An analysis of a router-based loss detection service for active reliable multicast protocols M. Maimour, C. Pham RESAM UCB Lyon - INRIA RESO ENS Lyon ICON’02, Singapor Thursday, August 29th, 2002

2. Sender data data data data data data Receiver Receiver Receiver A (very) quick overview of multicast Sender data with multicast without multicast IP multicast RFC 1122 data data data Receiver Receiver Receiver

3. Everybody's talking about multicast! Really annoying ! Why would I need multicast for by the way? multicast! multicast! multicast! multicast! multicast! multicast! multicast! multicast! multicast! multicast! multicast! multicast! alone multicast! multicast! multicast!

4. Challenges for the Internet Think about… • high-speed www • video-conferencing • video-on-demand • interactive TV programs • remote archival systems • tele-medecine, white board • high-performance computing, grids • virtual reality, immersion systems • distributed interactive simulations/gaming…

5. The Wild Wild Web heterogeneity, link failures, congested routers packet loss, packet drop, bit errors… important data ?

6. Multicast difficulties • At the routing level • management of the group address (IGMP) • dynamic nature of the group membership • construction of the multicast tree (DVMRP, PIM, CBT…) • multicast packet forwarding • At the transport level • reliability, loss recovery strategies • flow control • congestion avoidance

7. Reliable multicast • What is the problem of loss recovery? • feedback (ACK or NACK) implosion • replies/repairs duplications • difficult adaptability to dynamic membership changes • Design goals • reduces recovery latencies • reduces the feedback traffic • improves recovery isolation

8. Logging server/replier TRAM RMTP End to End XTP RMF SRM LMS LBRM Layered/FEC Router supported, active networking MTP CIFL AFDP RLM ALMI ARM RLC DyRAM FLID AER YOID PGM RMANP HBM Application-based 10 human years (means much more in computer year) The reliable multicast universe

9. ARM DyRAM AER PGM RMANP Router supported, active networking • Routers have specific functionalities/services for supporting multicast flows. • Active networking goes a step further by opening routers to dynamic code provided by end-users. • Open new perspectives for efficient in-network services and rapid deployment.

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

11. The case of loss detection • Traditionally the loss detection is performed by : • the sender (use of ACKs) in sender-initiated protocols • the receivers (use of NACKs) in receiver- initiated protocols • We want to investigate a router-supported loss detection service

12. Motivations and design choices • Enable early packet loss detection (EPLD) to reduce the latency • Routers keep track of the packet sequence: 2 variables per multicast session • Implemented as an active service, executed by an active router • EPLD services are enabled at specific locations in the network

13. "Satellite picture" of the Internet from UREC, http://www.urec.fr

14. Users' accesses residentials offices PSTN ADSL Cable … Internet Data Center metro ring Network Provider Network Provider campus Internet

15. 1st step: Analysis and network model • Each node is modeled by a M/G/1 queue. • The delay analysis is based on the mean waiting time of the system.

16. The methodology • The different mean flow rates λ1, λ2,... λnof the node with their respective service requirement X1, X2, ..., Xn. • The load ρ at this node can be computed using : ρ = Σλi E[Xi]. • The mean waiting time (P-K formula) : E[W]= Σλi E[Xi2] / 2(1- ρ)

17. Performance comparaison • Protocol A : • Nacks suppression • Subcast • Protocol D : • Nacks suppression • Subcast • Early Packet Loss Detection service

18. Numerical results • The router position influence • Loss detection service as a function of the loss rate • Maximum loss rate supported by the system • Required processing power at the routers so they are never the bottleneck • Load at the different nodes • The gain as a function of B (# recv)

19. Router position

20. Router position (cont.)

21. Loss detection service gain

22. Max loss rate supported as a function of the processing power of the routers

23. Required processing power at the routers so they are never the bottleneck

24. Load at the different nodes low overhead!

25. The gain as a function of B

26. 2nd step: Adding EPLD in DyRAM • DyRAM is an active reliable multicast protocol with local recoveries from elected repliers more accurate model

27. Simulation results 4 receivers/group #grp: 6…24 simulation results very close to those of the analytical study EPLD is very beneficial to DyRAM p=0.25 #grp: 6…24

28. Conclusions • Early packet loss detection by routers is found to enhance the performances of reliable multicast • Reduction of the recovery latency is targeted to enable distributed applications on computational grids • Simulations and experimental test-beds are encouraging • Incorporated into egde-routers?