Page 115 - Handout Computer Network.

Routing algorithms use different metrics to determine the best route. Each routing algorithm
interprets what is best in its own way. The routing algorithm generates a number, called the metric
value, for each path through the network.

Sophisticated routing algorithms can base route selection on multiple metrics, combining
them in a single composite metric. Typically, the smaller the metric, the better the path.

Metrics can be based on a single characteristic of a path or can be calculated based on several
characteristics.
The metrics that are most commonly used by routing protocols are as follows:

• Bandwidth

A link’s data capacity. (Normally, a 10-Mbps Ethernet link is preferable to a 64-kbps
leased line.)

• Delay

The length of time required to move a packet along each link from source to destination. Delay
depends on the bandwidth of intermediate links, port queues at each router, network congestion,
and physical distance.

• Load

The amount of activity on a network resource such as a router or link.

• Reliability

Usually refers to the error rate of each network link.

• Hop count

The number of routers that a packet must travel through before reaching its destination.
Whenever data goes through a router, this is one hop.

A path that has a hop count of 4 indicates that data traveling along that path passes
through four routers before reaching its final destination.

If there are multiple paths to a destination, the router chooses the path with the fewest hops.
• Cost

An arbitrary value, usually based on bandwidth, monetary expense, or another measurement,
that is assigned by a network administrator.

5.5 Interior and Exterior Routing Protocols