by using the Multi Point Rely (MPR) to reduce the routing overhead. At the same time,
DSDV uses an event-driven style to reduce the number of periodical messages.
AODV and DSR are reactive routing protocols; which is suitable for networks with light
traffic load. An advantage of this kind of routing protocols is the small amount of routing
overhead compared to proactive routing protocols. This is due to that reactive routing
protocols are on-demand routing protocols; the route established when needed. On the other
hand, the protocols have large response time as they usually are not ready when needed. DSR
overcomes AODV by using fast storage mechanism to store the most recent routes used
leading to more than one route that may be available to the destination. However, AODV
supports local connectivity among neighbouring nodes by using periodical small sized hello
messages, this issue is important for MANETs environments.
Taking the advantages of the previous kinds, a third type of unicast routing protocol is
proposed called hybrid routing protocols. ZRP is an example of this kind of routing
protocols; it proposed to work as a proactive for the nodes in a zone with radius P where P
the number of nodes far from the source, and works as reactive for outside the zone. It
provides higher scalability than pure proactive and pure reactive routing protocols. The
scalability is achieved by this kind of routing protocols by grouping the related nodes into
zones and each zone communicates with other zones using border nodes. Another advantage
of ZRP as a hybrid routing protocol is that there is no one point of failure between zones, as
any of the border nodes can establish a connection with other zones on-demand. However,
hybrid protocols require complex management in the case of high node mobility, which will
cause frequent changes for the zone members causing a high overhead. This overhead
because this type of protocols needs to keep information about the nodes in zone every time
the zone members changed.
The basic idea behind designing multicast routing protocols for ad-hoc networks is to
establish and maintain a connection between group members efficiently and with less effort.
Table 2.2 summarizes features of protocols belonging to this type of ad-hoc routing
31