Proactive Routing Protocols

Destination-Sequenced Distance-Vector (DSDV)
•When X receives information from Y about a route to Z
–Let destination sequence number for Z at X be S(X), S(Y) is sent from Y
–If S(X) > S(Y), then X ignores the routing information received from Y
–If S(X) = S(Y), and cost of going through Y is smaller than the route known to X, then X sets Y as the next hop to Z
–If S(X) < S(Y), then X sets Y as the next hop to Z, and S(X) is updated to equal S(Y)
DSDV Protocol
•Packets are transmitted between the nodes using route tables stored at each node.
•Each route tablelists all available destinations and the number of hops to each destination.
•For each destination, a node knows which of its neighbours leads to the shortest path to the destination.
•Consider a source node Sand a destination node D.
•Each route table entry in S is tagged with a sequence number that is originated by the destination node.
•For example, the entry for D is tagged with a sequence number that Sreceived from D (may be through other nodes).
•We need to maintain the consistency of the route tables in a dynamically varying topology.