Introduction to Client/Server Architecture

Numerous applications run in a client/server environment, this means that client computers (computers forming part of the network) contact a server, generally a very powerful computer in terms of input/output, which provides services to the client computers. These services are programmes which provide data such as the time, files, a connection, etc.

The services are used by programs client programs which run on client computers. This is why the term "client" is applied (FTP client, email client, etc.), where a program is designed to run on a client computer, capable of processing data received from a server (in the case of the FTP client we are dealing with files whereas for the email client we deal with email email).

Advantages of Client/Server Architecture

The client/server model is particularly recommended for networks requiring a high degree of reliability, the main advantages being:

• centralised resources: given that the server is the centre of the network, it can manage resources that are common to all users, for example: a central database would be used to avoid problems caused by redundant and inconsistent data
• improved security: as the number of entry points giving access to data is not so important
• server level administration: as clients do not play a major role in this model, they require less administration
• scalable network: thanks to this architecture it is possible to remove or add clients without affecting the operation of the network and without the need for major modification

Disadvantages of the client/server model

Client/Server architecture also has the following drawbacks:

• increased cost: due to the technical complexity of the server
• a weak link: the server is the only weak ling in the client/server network, given that the entire network is built around it! Fortunately, the server is highly fault tolerant (primarily thanks to the RAID system)

Client/Server system operation

A client/server system operates as outlined in the following diagram:

• The client sends a request to the server using its IP address and the port, which is reserved for a particular service running on the server.
• The server receives the request and responds using the client IP address and port