Adhoc on demand distance vector [ AODV ]
It is a source initiated routing protocol in mobile adhoc networks.
The algorithm consist of 2 phases
1.Route discovery phase
2.Route maintenance phase
In route discovery phase the path from source to destination is identified by broadcasting route request packet [RREQ]. When the intermediate node receive RREQ they will create a backward pointer and continue the broadcast when the route request packet reaches the destination a route reply would be generated [RREP]. The route reply will have information about the path that can be chosen for the packet transmission.
The route request packet can have following information.
1.Source id
2.Destination id
3.Sequence number
4.Backward pointer information
5.CRC and
6.Time to live[TTL]
In the above network the RREQ will be broadcasted by the source node 1 to its neighbor and neighbors will check whether RREQ is already processed. If it is already processed the packet will be discarded.
If it is not processed a backward pointer is created and the broad cast continues. When the packet is reached at destination a route reply is created [RREP] in the above network the first RREP is sent to the source can have the path information as 1-2-4-6-8.
When the source receives this information it will be stored in the routing table. Mean while the destination can create one more RREP which can have the information as 1-3-7-8 the destination will send this RREP to the source and will also ask the source to discard old path as the new path is having minimum number of hops.
Route maintainence phase
The nodes in the network periodically exchange hello messages to inform that they are still a part of network and the path is valid. Whenever there is a link failure detected. A route error packet [RERR] will be sent to the source indicating the path is no more valid.
Temporary ordered routing algorithm [TORA]
It is also a source initiated routing algorithm, creates multiple routes for any source/ destination pair. The advantage of multiple routes is that route discovery is not required for every alteration in the network topology.
TORA consists of three phases,
1.Route Creation/discovery
2.Route maintenance
3.Route erasure
TORA uses three types of packets: Query Packets for route creation, Update Packets for both creation and maintenance
The route will be discovered from the source to destination only when a request is made for the transmission. In this algorithm the source will generate a query packet which will be broadcasted in the network this continues as long as a node that is directly connected to the destination is identified.
When the destination is identified an update packet will be generated and sent back to the source. The update packet will have the path information if there are more than one update packet received by the source, it means there are multiple paths to the destination, the source has to choose best path available.
Security in adhoc networks: The following are the security threat in adhoc network.
1.Limited computational capabilities : the nodes in the mobile adhoc network are modular, independent and will have limited computational capability.It becomes a source of vulnerability when they handle public key cryptography.
2.Limited power supply :since nodes have limited power supply attacker can exhaust batteries by giving excessive computations to be carried out.
3.Challenging key management :the key management becomes extremely difficult as the mobile devices will be under movement.