Network Routing – The Meaning and Definition
Routing in inter-networks adds additional complexity to the algorithm design compared to the case of intra-network routing.
Since, route may span through several networks across several countries, the individual policies of the countries about data and information exchange needs to be considered.
Many a time, the interior routing table model and algorithms of component networks adds a lot of burden to the routing algorithm design for inter-networks.
Variation in Quality of Service in individual network complicates the achievement of global acceptable Quality of service.
It is already mentioned that, several component networks are connected through multiprotocol routers, which can understand frames of different protocols. So, a graph having these multi protocol routers, which can understand frames of different protocols. So, a graph having these multi-protocol routers as nodes or vertices, connected by edges is constructed. An edge between two routers A and B shows the reachability of A from B and vice versa i.e. A can directly send packets to B.
Once the graph has been constructed, routing algorithms like link-state or distance-vector are applied on it. So, there exists two-level routing algorithm.
- Interior Gateway Protocol: To route within a network
- Exterior Gateway Protocol: To route across networks
Each network in an inter-network is called Autonomous System (AS). Packets destined to other networks reach multi-protocol routers, which forward packet either directly or using tunneling depending on the routing protocol used in the other network.