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Network Architecture (R02) IP Multicast Deployment Woes

Network Architecture (R02) IP Multicast Deployment Woes. Jon Crowcroft, http://www.cl.cam.ac.uk/~jac22 http://www.cl.cam.ac.uk/teaching/1213/R02/. IP Multicast. Could be useful traffic reduction tool Load reduction for transmitter of N Load reduction in ISP of ln(N)

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Network Architecture (R02) IP Multicast Deployment Woes

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  1. Network Architecture (R02)IP Multicast Deployment Woes Jon Crowcroft, http://www.cl.cam.ac.uk/~jac22 http://www.cl.cam.ac.uk/teaching/1213/R02/

  2. IP Multicast • Could be useful traffic reduction tool • Load reduction for transmitter of N • Load reduction in ISP of ln(N) • Scale out Live IP TV/Radio • Possibly useful for s/w distribution • Natural API/Model for Groupware • N-way video/whiteboard/CSCW • Very easy to understand “just join”

  3. Multicast - Classic • Make the Internet one big Ethernet • Steve Deering (w/ Dave Cheriton) 1988 • New address (“Class D”) = Host Group, G • Forwarding Scheme = away from S • Prune/Graft per interface “towards” G • Need (S,G) state, Per Router… • State Management…

  4. Group State Management • Implicit • Traffic Driven • Explicit • IGMP Driven • More Overheads! • So not only state overhead is S*G • But also control overhead O(G) messages • Aggregation probably doesn’t do much • Any Source v. Source Specific v. Single

  5. Single Source • Can use reverse path fwd only • Can auth/check source • (exactly same as Best Practice RPF check) • Not much use for many-to-many apps? • N.b. looking at main early use of multicast (“mbone”) - • was many-to-many video conf • main use now? IPTV, Radio, S/W

  6. Reliable Multicast • Seems to be no “one size fits all” • Nack, Ack Aggr & Code based schemes • Need various ordering semantics (if n-m) • Interesting e.g. of new style WG in standards • Did “building blocks” • Then composed RM protocols from these • One v. interesting idea - GRA • minimal router processing engine needed for e2e protocol support • Precursor of other middle box ideas…

  7. RM - Congestion Control & Failures • Two things hard to define • How should multicast flow “compete” with TCP? • What are the “late join”, “early leave” and “fail” semantics for some members? • Again, no “one size fits all” answer…

  8. The IEEE Network Problem Paper @ARTICLE{Diot00deploymentissues, author = {Christophe Diot and Brian Neil and Levine Bryan and Kassem Doug Balensiefen},title = {Deployment issues for the IP multicast service and architecture},journal = {IEEE Network},year = {2000},volume = {14},pages = {78--88} abstract = {IP multicast offers scalable point-to-multipoint delivery necessary for using group communication applications on the Internet. However, the IP multicast service has seen slow commercial deployment by ISPs and carriers. The original service model was designed without a clear understanding of commercial requirements or a robust implementation strategy. The very limited number of applications and the complexity of the architectural design — which we believe is a consequence of the open service model — have deterred widespread deployment as well. We examine the issues that have limited the commercial deployment of IP-multicast from the viewpoint of carriers. We analyze where the model fails, what it does not offer, and we discuss requirements for successful deployment of multicast services. } } Cited > 195 times! (to calibrate, >10 cites is <1% of papers) N,b. Sprint Advanced Tech Lab author co-lo with operations in Burlingame

  9. The Sprint Viewpoint • Sprint is a Tier-1 ISP • Fastest US backbone at time • Zero packet loss on their net • In 2000, > 8 years of WWW expo growth • Since 1988, very little multicast growth • So what’s the problem with ipmc?

  10. Sprint list of pbs • Domain independence • PIM DM v. SM • RP for traffic • RP for group management • Address Allocation – • SD mechanism doesn’t scale • Group Management – • IGMP • Multicast Security – • none (or ipsec or app)

  11. Sprint • Non-technical aspects • Network Management • Billing for multicast • Cost/Benefit at all? • Eg. Router migration pain • Training ops in new mess • Debugging overheads • Smart people tried and only very partly succeeded in solving these problems – see On Scalable Internet Multimedia Conferencing Systems http://www0.cs.ucl.ac.uk/staff/m.handley/papers/ Protocol independent multicast pricing http://www.cs.st-andrews.ac.uk/~tristan/pubs/nossdav00.pdf • Alternatives possible • Single Sender (won for IPTV) • Multipeer application layer service • Re-unite, I^3 etc

  12. The “Truth” about Multicast • In fact, in a conference in 2006 • Berkeley Sys Admins reported that • Turning on IP multicast broke Unicast! • Basically terrible code • Also reported multicast self-inflicted RP worm… • Classic deployment dilemma • Specially Bad Case • Multicast has to be in “fast path” • Multicast routing depends closely on Unicast (viz PIM) • It also depended on monitoring data to drive routing update • So new control plane interface to fast path :-(

  13. So what now for multicast? • Not in Sprint/IEEE Network paper but • AT&T and Telefonica world #1&#3 ISP use single soruce multicast for IPTV • For data centers and link-local, heavily used • Given up on interdomain • but flattening of Internet Topology means don’t need it really. • & see how digital broadcast TV works too application layer relays between BBC, Sky, etc

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