1 Computer Communications - CSCI 551 Copyright © William C. ChengCS551Single Source Multicast[Holbrook99a]Bill Chenghttp://merlot.usc.edu/cs551-f12makes multicast tree easier to configureUse channels: a single sender, many subscribes2Key Ideas Computer Communications - CSCI 551 Copyright © William C. Chengeasier to tell who can sendAdd mechanism to let you countEasier to think about billingGoal: define a simpler modelneed to know number of subscribersNeed billing mechanism3Multicast Problems Computer Communications - CSCI 551 Copyright © William C. Chengneed to limit who can send and subscribeNeed access controlIPv4 multicast addresses too limitedCurrent protocols too complexISPs concerned about multicastAny source multicastWhat we’ve discussed so farHow do you charge users?Problems:Multicast state aggregationOther problemsIs there a simpler alternative we can deploy now?How do you manage the bandwidth allocation?How can you ensure secure communication?All of these are still research topics4Changing the Service Model Computer Communications - CSCI 551 Copyright © William C. ChengIf the multicast service model restricted the sendersISP acceptance will be higherIf there was a way to figure out how many receivers therewereThey can then have a viable billing and accounting modelSimplest such schemeSingle-source per multicast groupReceivers can still join and leave at will5Single Source Multicast Computer Communications - CSCI 551 Copyright © William C. Cheng224 channels (232.*.*.* reserved by IANA) per source6Single Source Multicast (Cont...) Computer Communications - CSCI 551 Copyright © William C. ChengAll addresses are source specificonly source can sendAccess controlsub-cast support (encapsulate packet to any router on thetree, if you know who they are)Best-effort couting servicechannels optionally protected by "key" (really just a secret)a group in SSM is denoted by (S,G)S is the source’s addressG is the group identifieraddress allocation -- no problem (unlike for any-sourcemulticast, G doesn’t have to be globally unique)232 sourcesBut this is already being designed in IGMP v3!Receiver specifies that it wants to join source S on group GBut PIM-SM already does this!Routers send source-specific joins towards SRouters silently drop other traffic if there is no stateOnly source S allowed to send traffic to group GNote that we don’t need a special inter-domain multicastrouting protocol!7SSM Details Computer Communications - CSCI 551 Copyright © William C. Chenglike IGMP, but also adds count supportnot clear how general this isECMP: Express Count Management Protocol8Express Components Computer Communications - CSCI 551 Copyright © William C. Chengcounts used to determine receivers or for other things likevotingservice at source that can relay data on to tree (similar toPIM tunneling)Session relaysSimpler indeed9Observations Computer Communications - CSCI 551 Copyright © William C. ChengEnough to justify multicast to ISPs? (not clear)SSM Statuscurrently being standardized and is partially deployeddo we need anything more for Internet multicast?so, if 90% of multicast applications can use SSM, and therest need
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