The Network

The Network

In a client-server architecture, there is an always-on host, called the server, which services requests from many other hosts, called clients. A classic example is the Web application for which an always-on Web server services requests from browsers running on client hosts. When a Web server receives a request for an object from a client host, it responds by sending the requested object to the client host.

Note that with the client- server architecture, clients do not directly communicate with each other; for example, in the Web application, two browsers do not directly communicate. Another characteristic of the client-server architecture is that the server has a fixed, well- known address, called an IP address (which we’ll discuss soon). Because the server has a fixed, well-known address, and because the server is always on, a client can always contact the server by sending a packet to the server’s address. Some of the better-known applications with a client-server architecture include the Web, F1′R Telnet, and e-mail.

Keep in mind that an application’s architecture is distinctly different from the network architecture. From the application developer’s perspective, the network architecture is fixed and provides a specific set of services to applications.

The application architecture, on the other hand, is designed by the application developer and dictates how the application is structured over the various end systems. In choosing the application architecture, an application developer will likely draw on one of the two predominant architectural paradigms used in modern network applications: the client-server architecture or the peer-to-peer (P2P) architecture.

Often in a client-server application, a single server host is incapable of keeping up with all the requests from its clients. For example, a popular social-networking site can quickly become overwhelmed if it has only one server handling all of its requests.

Application services that are based on the client-server architecture are often infrastructure intensive, since they require the service providers to purchase, install, and maintain server farms.

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