Chapter 7. Routing and Internetworking

This chapter focuses on the networking structure of larger networks. One of the most important functions in computer networking, especially in wide area networks, is routing packets. In packet-switched networks, this function includes procedures through which a packet uses certain algorithms to find all the necessary paths from its source to its destination. In this chapter, we look at routing algorithms and protocols both within one WAN ( intradomain networking , or intranetworking ) and beyond it ( interdomain networking , or internetworking ). This chapter covers the following main topics:

• Network-layer routing

• Classification of routing algorithms:

  - least-cost- path algorithms

  - non-least-cost-path routing

  - intradomain routing protocols

  - interdomain routing protocols

• Network-layer congestion control

We begin with some basic material about routing, such as the definition of path cost and the classification of routing algorithms. A networking infrastructure deploys a variety of algorithms for routing packets, classified as those using optimal routes and those using nonoptimal routes. We also classify routing protocols by whether they are applied within a domain or beyond a domain.

We also look at congestion-control mechanisms that can be implemented either unidirectionally or bidirectionally among nodes at the network layer. At the end of the discussion on congestion control, an approximation method for calculating link blocking is introduced. This method provides a quick approximation method for the performance evaluation of links.