The majority of multicast routing protocol constructs a reverse shortest path tree from the
source to the group members [22]. The data packets from the source to the receiver
follow the unicast path used to go from the receiver to the source. If these paths have
different characteristics, e.g Different delays, the use of symmetric paths may discard the
QoS deployment. So the ability to use asymmetric routes will give an improvement to the
multicast routing protocols.
Routing protocols for wireless ad hoc networks are classified into: unicast, multicast or
broadcast routing protocols [71]. In unicast the source node sends a separate copy of each
packet for each receiver, while multicast routing protocols process is to send one copy from
the source to a group of receivers. Those receivers share the same group number and run the
same application. Broadcasting is the process of sending the packets without considering the
number or the nature of receivers. Upon receiving packets, the intermediate nodes just
rebroadcast the packet until hopefully all the receivers will receive this packet.
In typical ad hoc networks, hosts work in groups to carry out a given task. Hence, multicast
plays an important role in ad hoc networks. In the past few years, a number of multicast ad
hoc routing protocols have been proposed. Depending on the method of data propagation,
these routing protocols are classified into two types:
J Tree-Based multicast routing protocols, a spanning tree is built to connect the group
nodes with other intermediate nodes to help in forwarding packets between group
members. This type of routing protocols guarantees the loop free feature. Examples
regarding this type are Multicast Ad hoc On-demand Distance Vector protocol
(MAODV) [57], Ad-hoc Multicast routing protocol using incrementing Id-numbers
(AMIRS) [68] and Ad-hoc Multicast Routing protocol (AMRoute) .
J Mesh-based multicast routing protocols, a mesh is built to connect the group
members. These protocols will give redundant routes between group members. These
redundant routes will reduce the packet delivery loss because of link failure.