University:
College
Course:
College Engineering
Academic year:

2023
Views:

129

Pages:

2
Author:

Dipin K.

Routing Protocol On-demand Routing Protocols Ad hoc On-Demand Distance Vector (AODV) Routing The AODV algorithm is the on demand counter part of the table based Destination Sequenced Distance-Vector (DSDV) algorithm. Their primary difference lies in the fact that AODV creates routes on-demand while DSDV maintains the list of all rotes. AODV a route on-demand while DSDV maintains the list of all the routes. In AODV a route is created only when requested by a network connection and information regarding this route is stored only in the routing tables of those nodes that are present in the path of the route. The procedure of route establishment is shown in Figure1.. Figure 1: Propagation of RREQ packet. In this example, we assume that node A wants to set up a connection with node B. In Fig.1 node A initiates a path discovery process in an effort to establish a route to node B, by broadcasting a Route Request (RREQ) packet to its immediate neighbor. Each RREQ packet is identified through a combination of transmitting node's IP address and broadcast ID. The latter is used to identify different RREQ broadcasts by the same node and is incremented for each RREQ broadcast. Furthermore, each RREQ packet carries a sequence number (similar to that OF DSDV) which allows intermediate nodes to reply to route requests only with up to date route information. Upon reception of an RREQ packet by a node this is forwarded to the immediate neighbors of the node and procedure continues until the RREQ is received either by node B or by a node that has recently established a route to node B. If subsequent copies of the same RREQ are received by a node these are discarded. When a node forwards a RREQ packet to its neighbors it records in its routing tables the address neighbor node where the first copy of the RREQ was relieved. This fact helps nodes to establish a reverse path, which will be used to carry the response to the RREQ. When RREQ has reached its destination a rote reply packet is sent back to A. Notice that the RREP follows the route B-D-F-A due to the fact that the first reception of the RREQ packet from B was due to node D and the First reception of the RREQ packet from D due to node F. As the RREP packet travels along the reverse path, the nodes that the RREP packet travels along the reverse path travelled by the RREQ: AODV supports only the use of symmetric links. Support for asymmetric links is not provided. Upon establishment of route each route entry at each node is associated with a lifetime value a timer stars running when the route is not used. If the timer exceeds the value of the lifetime, then the route entry is deleted. Routes may change due to the movement of a node (e.g., node X) with in the path of the route. In such a case the upstream neighbor of this node generates a link failure notification message which notifies about the deletion of the part of the route and forwards this to its upstream neighbor. The procedure continues until the source node is notified about the deletion of the route part caused by the movement of node X. Upon reception of the failure notification message. The source node can reinitiate discovery of a route to the destination node.