Why DSDV is a Proactive routing protocol?

Destination Sequenced Distance Vector (DSDV) routing protocol

• Destination Sequenced Distance Vector (DSDV) routing protocol is one of the popular proactive routing protocols of ad hoc network.

• Destination Sequenced Distance Vector (DSDV) is a hop-by-hop vector routing protocol requiring each node to periodically broadcast routing updates.

. This is a table driven algorithm based on modifications made to the Bellman-Ford routing mechanism.

• In DSDV, each node keeps record of route information in the form of routing table.

• Each table contains the following information:

• ID of destination node

• Details of next hop

• Metric

• Sequence number

• Time-to-live parameter.

• Each route broadcast message includes the

• list of ID of destination node,

• number of hops required to reach the destination node,

• next hop,

• recent sequence number and

• metric parameter.

• In full dump update method, a node sends the whole routing table to the neighbors and thereby increases network overhead.

• In incremental update method, only the recent updated entries are sent.

•The incremental update method is more suitable when the network is large and stable so that heavy traffic can be avoided.

Table Maintenance in DSDV

• The steps followed for maintaining a routing table at each node is given below,

• Each node receives the route information with most recent sequence number from other nodes and updates its table.

• The node looks at its routing table in order to determine the shortest path to reach all the destinations.

• According to the shortest path information, each node constructs another routing table where the node has recently updated route information to reach destination with minimum distance.

• This new routing table will be broadcast to its neighbors.

• On receipt of these messages, the neighbor nodes update its routing table.

Network Topology, Routing Table in DSDV

• The connectivity between nodes are shown using wireless links.

• The routing table maintained at node- A

• If node-B is the destination for node A,

• then node-A can directly transmit . the packet with metric 1 and next hop is node-B.

• But, if node-A wants to transmit a packet to node-E, then it can find the route from the routing table.

• In this case, the node-E is not in the visibility of node-A.

• Therefore, the packet can be transmitted through the next hop C with metric 2.

Maintaining Metric Field

• In ad hoc wireless network, all the nodes are moving and relocate its position from time to time.

• When topology changes dynamically each node will broadcast a routing table update packet to its neighbors.

• The procedure for updating metric field in the routing table update packet is as follows,

• The routing table update packet starts with a metric of one.

• When the neighbor nodes receive this packet, it will increment this metric by one and then re-broadcast the updated packet to its neighbors.

• This process will be repeated until all the nodes in the network receive the copy of update message.

Significance of Sequence Number

• When a node broadcasts a routing table update packet, it has to increase the sequence number by one.

• This is used to find out the updated route packet. When a node receives an update packet from its neighbor node and if the sequence number is equal to or greater than the sequence number of already received packet, then the routing packet will be updated in the table.