REUNITE: A Recursive Unicast Approach to Multicast
Despite ten years of research and development, global
deployment of IP multicast is still far from being the reality. One
of the primary challenges is that existing IP multicast routing
protocols scale poorly with large number of groups as each router
needs to maintain a multicast forwarding table entry for every group
whose distribution tree passes through the router. We propose a novel
multicast scheme called REUNITE (REcursive UNicast
TreE). Unlike all existing IP multicast protocols, REUNITE does not
use class D IP addresses. The entire protocol is based on unicast
forwarding. Multicast data forwarding is implemented with a novel
technique called recursive unicast. Compared with existing IP
multicast solutions, REUNITE has several important advantages:
Enhanced scalability by reduction of forwarding state
With REUNITE, only routers that are acting as multicast tree branching
points for a group need to keep multicast forwarding state of the
group. Non-branching-point routers simply forward packets by unicast
No need for class D IP address
With REUNITE, a multicast group
is identified by a two tuple (unicast_IP_address, port_number)
and there is no need for a separate block of class D IP addresses. In
this case, the allocation of unique group identification becomes
trivial. In addition, the maximum number of simultaneously active
multicast groups increases dramatically.
Native support for incremental deployment
addresses are used as destination addresses in REUNITE, a router
that does not implement REUNITE will simply forward the packets onto
the next hop based on the unicast destination address, without any
adverse effect on the protocol other than the potential loss of
efficiency. This allows REUNITE to be incrementally deployed with a
subset of network nodes, without the need of tunnelling.
Load balancing and graceful degradation
With REUNITE, when a router does not have resources
(forwarding table entry, buffer space, processing power) to support
additional multicast groups, it can simply ignore further protocol
messages and the branching point will be automatically migrated to
Support for access control
Access control can be
implemented by authenticating senders at the root node.
Click here for a presentation on REUNITE.
Ion Stoica, T. S. Eugene Ng, Hui Zhang,
"REUNITE: A Recursive Unicast Approach to Multicast",
Tel-Aviv, Israel, March 2000.
The CMU Technical Report version is also available.
Tze Sing Eugene Ng,
eugeneng+reunite at cs.cmu.edu
Last modified: Wed Jan 3 15:21:25 EST 2001