...
For each node in the network, the route is predefined in the routing tables. Changes to the route can only be achieved by changing the topology and the routing tables.
The topology must be known in order to build the routing tables.
Simple
Works well in reliable network with stable load in a reliable network
Lack of flexibility
Doesn’t react to failure or network congestion
Flooding Algorithms
Requires no network information like topology
Every incoming packet to a node is sent out on every outgoing
All possible routes between Source and Destination are tried. A packet will always get through if the path exists
As all routes are tried, there will be at least one route that is the shortest
All nodes directly or indirectly connected are visited
Flooding generates a vast number of duplicate packets
A suitable dampening mechanism must be used to ensure the network is not overwhelmed
A hop counter may be contained in the packet header which is decremented at each hop, the packet is discarded when the counter becomes zero
Are highly robust, emergency or immediate messages can be sent (eg military applications)
Flooding always chooses the shortest path
Broadcast messages to all the nodes
Adaptive Algorithms (dynamic routing)
These algorithms change their routing decisions whenever network topology or traffic load changes. These algorithms make use of dynamic information such as current topology, load, delay, etc. to select routes. Optimization parameters are distance, number of hops, and estimated transit time.
Routing tables algorithms may be
Isolated
Centralized
Distributed
Non-Adaptive Algorithms (status routing)
These algorithms do not change their routing decisions once they have been selected. The route to be taken is computed in advance and downloaded to routers when a router is booted.
Routing tables algorithms may be
Flooded
Random Walk