AODV combines the use of destination sequence numbers as in DSDV with the on-demand route discovery technique in DSR to formulate a loop-free, on-demand, single path, distance vector protocol.
In contrast to DSR, AODV uses hop-by-hop routing instead of source routing. Below we review some of the key features of AODV to provide sufficient background for AOMDV described here after.
Route Discovery of AODV and AOMDV
A route discovery process will be started When a source needs a route to required destination. Route discovery typically involves broadcast of a route request (RREQ) for the destination and waiting for a route reply (RREP) as response. Source ID and broadcast id are used to detect the redundant RREQ. These unnecessary duplicated RREQs will be discarded coming from the various Path. An intermediate node receiving a non-duplicate RREQ first sets up a reverse path to the source using the previous hop of the RREQ as the next hop on the reverse path. If a valid route is available, then the intermediate node generates a RREP, else the RREQ is rebroadcast.
But in MULTI PATH environment the duplicate RREQ cannot be simply neglected as duplicated RREQs may come from different path. For making multiple reverse path these redundant RREQs play major role. So they need to be examined every then and now whether they are coming from same or different path as these each duplicate may define alternate route.
These initially route discovery is an extra overhead for AOMDV then AODV But also it reduces the calculation of new path when one route fails out of available other paths new path is selected.
Sequence Numbers Strategy of AODV and AOMDV
The beauty of DSDV was destination sequence number to avoid the loop during route forming. This property is taken in AODV. Every node maintains the increasing destination sequence number for itself and also maintains the highest known sequence number for the each destination in the routing table. For preventing routing loops, only highest and latest sequence numbers in the routing updates will be considered. AOMDV also provide loop freedom as in the AODV but the techniques is different. The basic structure of a routing table entry in the AOMDV in comparison with AODV is altered. There are two main differences: (i) the hop-count is replaced by advertised hop-count in the AOMDV and (ii) the nexthop is replaced by the route list. The route list is simply the list of nexthops and hop-counts corresponding to different paths to the destination. The advertised hop-count represents the maximum of the hop counts of each of those multiple paths so long as a strict route update rule is followed.
The packet delivery ratio is expressed as the percentage of CBR data traffic that has been received by all destinations (sinks) over the total number of packets sent by all the sources within the period of simulation.
The packet delivery ratio can be interpreted as the loss ratio that will be experienced at the routing layer which in turn has an impact on the overall throughput of what the network can support. It is a fundamental characterization of the performance of routing protocols.