Design and investigation of scalable multicast recursive protocols for wired and wireless ad hoc networks

This protocol provides the best routes in asymmetric networks and enhanced tree stability in
presence of group dynamics as mentioned at [22]. In addition, this protocol constructs the
shortest path tree between the source and the receivers. On the other hand this protocol may
share the same drawbacks that of REUNITE protocol.

3.2.5 Simple Explicit Multicast (SEM) Protocol

Simple Explicit Multicast (SEM) [11] protocol is one of the recent proposed protocols that
adapt the explicit messages method in order to support multicast routing over networks. SEM
[11] builds a multicast tree by using two types of messages: Branch and previous_branch.
Moreover, SEM uses a periodical alive message to maintain the multicast tree. Joining and
leaving of receivers is also done by Join and Leave messages sent by the receiver toward the
source. The routing state for the multicast channel (S,G), where S is the source unicast
address and G is the standard group multicast address, is only kept at branching routers table
(TRM). Entries in TRM(S,G) are S, source address; G, multicast group address; Pb previous
branching router address and the next branching router address.

3.2.5.1 Receivers and tree construction

A receiver wanting to join the multicast group (S,G) sends an IGMP join message addressed
to this group . When receiving the join message by designated router (DR), this DR creates a
join(S,G) message to the source. When the source receives this message this DR is added to a
list kept in a Multicast Control Table (MCT), which contains all the DRs that have
receiver(s) belonging to this multicast group (S,G). Each entry at MCT are S, Source node
address, G, Multicast group address and the list of DRs.

Intermediate nodes do not need to maintain any state information for the multicast session.
Thus, it is necessary for the DR routers to know the source address, the previous and the next
DR.

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