Internet Service Providers (ISPs)

Few users are directly connected to WANs. The cost of bringing high speed, high performance networks to individual user sites is usually far too expensive. For users requiring only modest transmission rates (e.g. kbps to Mbps), the users may connect to an Intermediate System (a Router) which aggregates all the packets before forwarding them on to a WAN. The Intermediate Systems are connected in a regional network (sometimes also called an Access Network, or Metropolitan Area Network (MAN)). The network size falls intermediate between LANs and WANs. It typically covers an area of between 5 and 50 km diameter. Many of these networks cover an area the size of a city, or even a whole country. In some cases they may be as small as a group of buildings or as large as the North of Scotland.

In the Internet case, the organisation which operates this network is known as an Internet Service Provider (ISP). ISPs manage communications circuits to individual users, they must also ensure that they can monitor user performance and usage, and operate a billing procedure to ensure they can collect the appropriate revenue. The ISP is responsible for meeting individual customer needs and charges a fee for doing this. In turn, the ISP pays the WAN (NSP) for the connectivity it requires. Many ISPs are connected at more than one point to one or more NSPs. The additional connections improve resilience to failures.


Gorry Fairhurst - Date: 01/10/2001 EG3557