IP Multicast Channels: EXPRESS Support for Large-scale Single-source Applications

1. IP Multicast Channels: EXPRESS Support for Large-scale Single-source Applications Authors: Hugh W. Holbrook and David R. Cheriton Presenter: Mridul Sharma

2. Contents • Introduction • IP Multicast Channels • ECMP • Multi-source Multicast Applications • Cost and Scalability • Costing Overhead and Proactive Counting • Conclusion

3. Focus Provide explicit support for large-scale multicast applications by extending the IP Multicast service model to support multicast channels

4. IP Multicast: Group Model • Hosts aggregated into groups with single address • Good for multicast discovery & small scale meetings over the internet

5. Problems • Strained for very large scale multicast applications such as Internet TV • Violates common ISP billing models • Provides no indication of group size • No restriction on allowed senders • World-wide unique multicast address • Scaling IP multicast routing for conventional group semantics remains an issue

6. IP Multicast Channels • A multicast channel is a datagram delivery service identified by a tuple (S, E) where S is the sender’s source address and E is a channel destination address. • Only the source host S may send to E.

7. S S Channel vs. Group Addressing (S,E) G

8. 224 class D addresses allocated by IANA Routers identify a channel multicast datagram by its destination address Same service interface as IP Multicast for packet transmission to, and reception on, a channel Single-source IP Multicast Addresses 222.0.0.0 239.255.255.255 IP Multicast addresses Single-source multicast Addresses (232.*.*.*)

9. EXPRESS Service Interface Extensions • Source service interface • Count = CountQuery(channel, countId, timeout) • channelKey(channel, K(S, E) ) • Subscriber service interface • Result = newSubscription(channel [, K(S, E) ]), • Count(channel, countId, count)

10. Advantages • Source • 224 channels per source • Address management is simplified • Authenticated subscription option • CountQuery mechanism (number of subscribers or subscriber vote)

11. Advantages (Contd.) • Subscriber • Receives traffic only from the source it designates • Ability to provide feedback

12. Advantages (Contd.) • ISP • Provides basis for charging • Counting facility increases revenue • EXPRESS is relatively simple to implement and manage

13. EXPRESS Count Management Protocol • A single common management protocol • Maintains both the distribution tree and supports source-directed counting and voting • RPF is used to route subscriptions and unsubscriptions towards the source

14. ECMP • Generic Counting Operation • CountQuery • Count • CountResponse • A router can initiate a query without source co-operation

15. ECMP (Contd.) • Distribution Tree Maintenance • New subscription • Unsubsciption • Router can use either TCP or UDP mode for ECMP

16. ECMP: Subscription

17. ECMP (Contd.) • Neighbor Discovery • Periodic CountQuery message • countId: neighbors; all channels • EXPRESS Packet Forwarding • Forwarding Information Base entries at each router • Forwarding procedure is nearly identical to IP Multicast

18. ECMP (Contd.) • Authenticated ECMP vs. End-to-end Encryption • Authentication provides restricted access while encryption provides confidentiality

19. ECMP Advantages • Simple integrated protocol • Supports subscription, multicast channel maintenance and counting • No change in host OS if it supports IP Multicast • Multicast traffic travel only along paths from source to subscribers

20. Multi-source Multicast Applications • Multiple channels, one per source • Applicable when new source is going to transmit for extended period of time • Several sources sharing a channel using higher level relaying through the channel’s source host • Supported by middleware layer for session management

21. The Session Relay Approach

22. Advantages of SR Approach • Appropriate placement of SRs to minimize communication is under application control • Applications can have additional backup SRs for fault tolerance, placement, switching over etc • “Hot” and “cold” standby • SR can provide application-specific functionality

23. Session Relaying • As an ISP Service • For other applications • Cost/ Performance

24. Cost and Scalability • Cost of router FIB memory for channels • Cost of management-level router state • Cost of maintaining this state

25. Counting Overhead & Proactive Counting • Counting Overhead • Small for large-scale channels if approximated over long time periods • Excessive use of counting is expensive • Proactive Counting • Receivers and routers proactively send count messages upstream

26. Related Work • Service Models and Routing • Accounting • Counting

27. Conclusions • Straightforward extension to the conventional IP multicast • Simple implementation • Additional capabilities like access control, accounting and local-to-host multicast address allocation • Almost single source and truly multi source multicast applications can be implemented