24.2 INTERNET ARCHITECTURE

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24.2 INTERNET ARCHITECTURE

The Internet is a complex network, and has no fixed topology. Figure 24.1 shows the simplified architecture. Internet service providers (ISPs) are connected to the backbone network. In fact, there are multiple backbone networks. Individual/ corporate users access the Internet through dialup or leased lines. Content providers set up servers and connect to ISPs.

Figure 24.1: Internet architecture.

The Internet is a connection of various internets, connected through routers (also called gateways). Also, the Internet is a very dynamic network—networks are added and removed almost on a daily basis. Web sites crop up and go down also on a daily basis. When a user invokes his browser and enters a URL, how does he get the information? The first requirement is that the server where the resource corresponding to the URL is located has to be known, and the request has to be forwarded to that server. Secondly, when the packets are transmitted from one node to another, the packets have to be routed properly.

To get connected to the Internet, we need to obtain an account from a local Internet service provider (ISP). As shown in Figure 24.2, the ISP has various servers such as mail server, domain name server, Web server, and authentication server. We can get access to the ISP server either through a dial-up line or a leased line. We log in to the server at the ISP, and the ISP provides access to the rest of the Internet through a router/gateway.

Figure 24.2: Accessing the Internet through ISP.

The Internet has multiple backbone networks. Internet service providers (ISPs) connect their networks to one of these backbone networks. The Internet is a network of networks, but it has no fixed topology.

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