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

On the other hand, this protocol works under an assumption that receivers are working in
groups, an idea that is not correct in real Internet environment. Xcast+ will work as Xcast
because each DR will carry small number of receivers and the Xcast message will carry huge
number of DR(s) which will decrease the scalability issue in this protocol. This issue is the
main disadvantage that may be considered in this protocol.

3.2.3 A REcursive UNicast TreE (REUNITE) Protocol

REUNITE [65] is a multicast routing protocol which uses recursive unicast tree idea to
implement the multicast service. REUNITE uses two types of messages, Join message and
Tree message, in addition of implementing two tables in the routers: - Multicast Forwarding
Table (MFT) and Multicast Control Table (MCT). This protocol was developed to improve
the scalability over networks by reducing the amount of information stored in the multicast
group members.

REUNITE protocol implements multicast service by using a recursive unicast scheme. Each
REUNITE group builds a tree rooted by a designated node called a root. Every branching
node (node with two or more different next hops) maintains a list of receivers in its MFT,
where each receiver is maintained by one branching node only. When the root needs to send
(multicast) packet it sends a copy to each receiver in its MFT list. When this packet arrives at
branching node the branching node does the same by sending a copy of this packet to each
receiver in its MFT list. This process is repeated until each receiver gets the packet.

As mentioned above, each router at REUNITE maintains a Multicast Forwarding Table
(MFT) which contains entries for receivers where data delivery packet should branch at this
router. Another table maintained by this protocol is Multicast Control Table (MCT) which
contains an entry for receivers that the tree does not branch in this router. This protocol uses
two types of control messages: JOIN message, which is sent (unicastlly) from the receiver
periodically towards the root, and TREE message, which is sent (multicast) by the root along
the multicast delivery tree. The TREE message is used to create and refresh the entries at
MCT and the group entries at MFT, while the JOIN message is used to create and refresh the

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