Routing protocol in NS2

Routing protocol

• A formula used by routers to determine the appropriate path ontowhich data should be forwarded
• It also specifies how routers report changes and share information with the other routers in the network that they can reach
•  This decides whether the network should dynamically adjust tochanging conditions, otherwise all routing decisions have to be predetermined and remain static
•  NS2 can simulate both static and dynamic techniques

Approaches to routing

 Static routing

• Routing table is created when a router boots for first time.Once decided, the route cannot be altered

•  Network problems such as link down, congested router cannot be solved

Dynamic routing

•  The routing table is created with initial routing decisions and updates itself when there is a change in network condition

•  This is clearly better but complex than static routing

 

Routing Algorithm

To calculate shortest path between two routers:

•  Knowledge about the whole network

•  Sharing information with neighbors

i) Periodic sharing
ii) Share when network has any changes

Types:

1) Distance vector routing
2) Link state routing

Distance Vector routing

• Uses Bellman-ford algorithm to calculate path

•  Suitable for small and medium sized network

•  Calculates path based on link cost

•  Routing based on calculating the direction and distance to any link in a network

•  Direction refers to a port that leads to the next router along the path to the destination, and distance is a metric that indicates the number of hops to the destination

 Link state routing

•  Information is exchanged about its neighborhood with all other routers in the network

• Sharing the information is called flooding.

•  Sharing period interval is much longer (say for DVR is 30 secs, in LSR is 30 min)

•  Packet cost based on security levels, traffic, state of the link

Routing schemes

•  Classification is based on Message Delivery Semantics

•  Unicast – to single specified node by the host

•  Multicast – to a group of nodes that have expressed interest in receiving messages

•  Broadcast – to all nodes in the network