Computer Science – 14.2 Circuit switching, packet switching | e-Consult

Routers are essential devices in a packet-switched network. Their primary role is to forward packets between different networks. They examine the destination address in the packet header and determine the next hop towards the destination.

Routers make forwarding decisions based on the destination address and a routing table. The routing table contains information about the best paths to reach different networks. The decision-making process involves:

• Destination Address Lookup: The router examines the destination address in the packet header.
• Routing Table Search: The router searches its routing table for the best match to the destination address.
• Forwarding Decision: Based on the routing table entry, the router forwards the packet to the next hop (another router or the destination network).

Factors that influence routing decisions include:

• Distance Metric: A numerical value representing the cost of traversing a particular link (e.g., hop count, bandwidth, delay). Lower values are generally preferred.
• Bandwidth: The capacity of a link. Higher bandwidth links are generally preferred.
• Delay: The time it takes for a packet to traverse a link. Lower delays are generally preferred.
• Congestion: The amount of traffic on a link. Less congested links are generally preferred.

Example of a Routing Protocol: Distance-vector routing protocols, such as RIP (Routing Information Protocol), are a common example. RIP works by exchanging routing tables with neighboring routers. Each router maintains a table of distances to all known networks. The protocol uses a distance metric (hop count) to determine the best path. However, RIP has limitations, such as slow convergence and a maximum hop count of 15.