Host Multicast A Framework for Delivering Multicast to

Host Multicast: A Framework for Delivering Multicast to End Users Jonghak Kim Hyungik Oh Huo Da 1 June, 2002 INFOCOM

Motivation l l Fast increasing need for scalable and efficient group communication Slow deployment of IP Multicast – l Emerging End-host based Multicast – – 2 Deployment imposes dependency on routers Member hosts duplicate and forward packets Easy to deploy, but less efficient

Host Multicast l l l A hybrid approach Goal: Ubiquitous Multicast Design Requirements – Deployable on the current Internet l l – Compatible with IP Multicast to the furthest extent l l – Use IP Multicast where available Provide incentive to future deploy Scalability and Efficiency l 3 No support is required from OS, routers and servers Enable multicast applications Multicast group should not be a limiting factor

Architecture Rendezvous Point (HMRP) RP Designated Member (DM) DM Host IP Multicast Island 4 Host DM Host Unicast Tunnel DM Host Normal Member Host Group Management Protocol (HGMP) for intra-island To A network Each bootstrap member Multicast of new any runs Tree size members our Protocol that daemon supports (HMTP) program IPto. Multicast, atbuild user-space inter-island e. g. single tunnels host, management Ethernet, campus network etc.

Host Multicast Tree Protocol (HMTP) l l Build a bi-directional shared-tree connecting all islands The tree should be congruent to physical network topology to be efficient – l The tree should be robust – 5 use member-to-member round-trip time as distance metric in current design be able to handle node failure, dynamic join/leave etc.

Join Group root HMRP always knows the root of the tree. A B A newcomer does a depth-first search of the tree to find a close member as its parent. C D F E 6 Clustering nearby members makes the tree congruent to physical network topology to the first order. H G Where is my group? Root of your group is A RP

Tree Maintenance l l 7 Each member keeps its children list and root path up to date by exchanging REFRESH and PATH messages with neighbors. Root sends REFRESH message to HMRP. A B C D F E H G RP

Member Leave and Partition Recovery l l Parent deletes the leaving node from children list. Direct Children repair the tree by running join procedure in the reverse order. l 8 If root is leaving, the first node contacting HMRP is assigned as new root. A B C D F E H G RP

Tree Improvement l Periodically re-run the join procedure – – – 9 To accommodate changes in network conditions and group membership Start from a randomly picked node in the root path. Less frequent than REFRESH and PATH messages.

Loop Detection and Resolution l Loop is possible: – l 10 A C D One’s root path contains itself Resolution: – l B Detection: – l Multiple conflicting joins happen at the same time. Leave the current parent and re-join the tree from the root. Loop is rare. E F G

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