Before diving into software coding, you should have a broad architectural plan for your application. Keep in mind that the architecture of an application is distinctly different from the network architecture. From the point of view of the application developer, the network architecture is fixed and provides a specific set of services to application programs. The application architecture, however, has been designed by the application developer and dictates how the application is structured on different end systems. In the choice of 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 architecture (P2P).
In a client-server architecture, there is an ever-on a host named server, which services the requests from many other hosts, called clients. The client hosts can be both time-on and always-on. A classic example is the Web application for which an always-on Web server Services required 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 the client-server architecture, clients do not communicate directly with each other; for example, in the Web application, two browsers do not communicate directly. Another feature of the client-server architecture is that the server has a fixed, well-known address, called an IP address (which we will discuss shortly). Because the server has a well-known fixed address, and why the server is always on, a client can always contact the server by sending a packet to the server address. Some of the best known applications with a client-server architecture include the Web, F1'R Telnet, and e-mail.
Often in a client-server application, a single host server is able to keep up with all the demands of its customers. For example, a popular social networking site can quickly become overwhelmed if it has only one management of all its requests to the server. For this reason, a group of host-sometimes referred to as a server farm-is often used to create a powerful virtual server in client-server architectures. application services that are based on client-server architecture are often infrastructure intensive, since they require the service providers to buy, install and manage server farms. In addition, service providers have to pay the running costs of interconnection and bandwidth for sending an4 receiving data to and from the Internet. Popular services such as search engines (eg Google), Internet commerce (eg, Amazon and e-Bay), Web-based v-mail (for example, Yahoo Mail), social networking (eg MySpace and Facebook), and video sharing (eg, YouTube) are infrastructure intensive and costly to provide.
In a P2P architecture, there is minimal (or not) always rely on server infrastructure. Instead the application exploits direct communication between pairs of hosts connected intermittently, called peers. The comrades are not the property of the service provider, but are instead desktops and laptops controlled by users, with most of the residents peers in homes, universities and offices. Because the peers communicate without passing through a dedicated server, the architecture is called peer-to-peer. Many of the most popular applications and intensiye traffic today is based on P2P architectures. These applications include file distribution (eg, BitTorrent), file searching / sharing (eg, eMule and LimeWire), Intemet telephony (eg, Skype), and IPTV (eg, PPLive).
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