9.1 IP Dial-up Service Components Introduction

A significant amount of the Internet's success can be contributed to the industrialisation, the creation of a carrier-scale solution, of dial access and its associated modems. It is the mass production of modems, the significant reduction of their cost, and the development of network systems which can handle hundreds of thousands of customers, that has brought the cost of Internet access within the reach of the majority of the population. This chapter introduces the major elements of a carrier-scale dial access platform and describes how they should be organised to deliver service.

The basic components for an IP dial-up service comprise:

• modems;

• terminal server;

• authentication system.

The modems act as the interface into the telephony network and provide asynchronous data streams into a terminal server function. The terminal server encapsulates the asynchronous data into IP packets for delivery over the IP network. Since this is a remote access system, some form of user authentication is normally a requirement of the overall service. In simple networks, authentication may be carried out by the host itself as shown in Fig 9.1.

Figure 9.1: Basic dial-up network.

The advent of public dial-up services to the Internet, by Internet service providers (ISPs), has stimulated developments in protocols and hardware integration. The banks of modems and terminal servers have been replaced by integrated network access servers (NASs). These are fitted with digital modems which exploit the fact that the telephony network operator has deployed a digital...