A computer network is a group of computers that use a set of common communication protocols over digital interconnections for the purpose of sharing resources located on or provided by the network nodes.

Computer network, is defined as two or more computers that are connected with one another for the purpose of communicating data electronically.

What is computer network and types?

Two basic network types are local-area networks (LANs) and wide-area networks (WANs). LANs connect computers and peripheral devices in a limited physical area, such as a business office, laboratory, or college campus, by means of links (wires, Ethernet cables, fibre optics, Wi-Fi) that transmit data rapidly.

Client-server architecture,

Client server architecture of a computer network is a situation  in which many clients (remote processors) request and receive service from a centralized server (host computer). Client computers provide an interface to allow a computer user to request services of the server and to display the results the server returns. Servers wait for requests to arrive from clients and then respond to them. Ideally, a server provides a standardized transparent interface to clients so that clients need not be aware of the specifics of the system (i.e., the hardware and software that is providing the service. Clients are often situated at workstationsor on personal computers, while servers are located elsewhere on the network, usually on more powerful machines. This computing model is especially effective when clients and the server each have distinct tasks that they routinely perform. In hospital data processing, for example, a client computer can be running an application program for entering patient information while the server computer is running another program that manages the database in which the information is permanently stored. Many clients can access the server’s information simultaneously, and, at the same time, a client computer can perform other tasks, such as sending e-mail. Because both client and server computers are considered independent devices, the client-server model is completely different from the old mainframe model, in which a centralized mainframe computer performed all the tasks for its associated “dumb” terminals, which merely communicated with the central mainframe.

Types of Client Server Architecture :

• 1 tier architecture
• 2 tier architecture
• 3 tier architecture

1 tier architecture :

In this type of client server environment the user interface, business logic & data logic are present in same system. This kind of client server service is cheapest but it is difficult to handle because of data inconsistency that allows repetition of work.

2 tier architecture :

In this type of client server environment user interface is stored at client machine and database are stored on server. Database logic & business logic are stored at either client or server but it must be unchanged. If Business Logic & Data Logic are stored at client side, it is called fat client thin server architecture. If Business Logic & Data Logic are stored on server, it is called thin client fat server architecture. This kind of architecture are affordable and comparatively better

2-tier architecture is useful where a client talks directly to a server. There is no intervening server. It is typically used in small environments. Here, the user interface is placed at user’s desktop environment and the DBMS services are usually placed in a server.Information processing is split between the user system interface environment and the database management server environment.

3 tier architecture :

In this kind of client server environment an additional middle-ware is used that means client request goes to server through that middle layer and the response of server is firstly accepted by middle-ware then to client. This architecture overcomes all the drawbacks of 2-tier architecture and gives best performance. It is costly and easy to handle. The middle-ware stores all the business logic and data access logic. If there are multiple Business Logic & Data Logic, it is called n-tier architecture. The purpose of middle-ware is to database staging, queuing, application execution, scheduling etc. middle-ware can be file server, message server, application server, transaction processing monitor etc. It improves flexibility and gives best performance.

The middle-ware are implemented in different ways such as transaction processing monitors, message servers or application servers. The middle-ware perform several functions like queuing, application execution, database staging. It also adds scheduling and prioritisation for work in progress.

Characteristics of Client Server Computing

The salient points for client server computing are as follows:

• The client server computing works with a system of request and response. The client sends a request to the server and the server responds with the desired information.
• The client and server should follow a common communication protocol so they can easily interact with each other. All the communication protocols are available at the application layer.
• A server can only accommodate a limited number of client requests at a time. So it uses a system based to priority to respond to the requests.
• Denial of Service attacks hindera servers ability to respond to authentic client requests by inundating it with false requests.
• An example of a client server computing system is a web server. It returns the web pages to the clients that requested them.

Advantages of Client Server Computing

The different advantages of client server computing are −

• All the required data is concentrated in a single place i.e. the server. So it is easy to protect the data and provide authorisation and authentication.
• The server need not be located physically close to the clients. Yet the data can be accessed efficiently.
• It is easy to replace, upgrade or relocate the nodes in the client server model because all the nodes are independent and request data only from the server.
• All the nodes i.e clients and server may not be build on similar platforms yet they can easily facilitate the transfer of data.

Disadvantages of Client Server Computing

The different disadvantages of client server computing are −

• If all the clients simultaneously request data from the server, it may get overloaded. This may lead to congestion in the network.
• If the server fails for any reason, then none of the requests of the clients can be fulfilled. This leads of failure of the client server network.
• The cost of setting and maintaining a client server model are quite high.

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