the header of the data packet will carry the whole address information from the source to the
destination. The intermediate nodes do not require maintaining any up-to-date routing
information about the neighbourhood nodes to forward the data packet, but they just use the
information kept in the header of the data packet to forward the data packet. The main
disadvantage of this type of reactive routing protocols is that these protocols did not perform
well on large networks [3]. This drawback will happen because at large networks the header
of data packet needs to maintain routing information for a large number of intermediate
nodes which will cause a huge overhead at the data packet delivery. Another reason for this
drawback over large networks is that the data packet will be forwarded to a large number of
intermediate nodes which means high probability of link failure at these nodes, in other
words high probability of active route failure. For that reason, in large networks the hop-by-
hop reactive routing protocol is more commonly used. The header of the data packet carries
the destination and the next hop address, as soon as the data packet reaches the intermediate
node this node update the header of the data packet by inserting the address of the new next
hop and forwards data packets. All the intermediate nodes perform similarly until the data
packet reaches its destination node.
This type of reactive routing protocols has the advantage of low volume of overhead
information at the data packet header and it will use better and fresh route to the destination.
On the other hand the disadvantage of this type of routing protocols is that each node in the
network should keep fresh information about active routes and fresh information about its
neighbours which means that each node will send periodical messages to keep fresh
information which will cause high overhead over the network.
Examples of these kind of protocols: Ad hoc on demand Distance Vector routing protocol
(AODV) [54] , Dynamic Source Routing Protocol (DSR) [43] and Temporally-Ordered
Routing Algorithm (TORA) [51]. This section describes a number of reactive routing
protocols.
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