What is computer Networks?

A computer network is a system for communication among two or more computers. These networks may be fixed (cabled, permanent) or temporary (as via modems).

Computer networking is the scientific and engineering discipline concerned with communication between computer systems. Such networks involves at least two computers, which can be separated by a few centimeters (e.g. via Bluetooth) or thousands of kilometers (e.g. via the Internet)

Types of network

Types of computer Networks: Computer networks may be classified into two types:

1.     On the basis of architecture:

a.     Peer to peer

b.    Client/server

c.      Hybrid

2.     On the basis of geographical location:

a.     LAN (Local Area Networks)

b.    WAN (Wide area networks)

c.      MAN (Metropolitan area networks)

1.     On the basis of architecture:

Peer to Peer(P2P): A peer-to-peer (or P2P) computer network is a network that relies primarily on the computing power and bandwidth of the participants in the network rather than concentrating it in a relatively low number of servers.

Such networks are useful for many purposes. Sharing content files (see file sharing) containing audio, video, data or anything in digital format is very common, and realtime data, such as telephony traffic, is also passed using

P2P technology.

A pure peer-to-peer network does not have the properties of clients or servers, but only equal peer nodes that simultaneously function as both "clients" and "servers" to the other nodes on the network

• Peers act as equals, merging the roles of clients and server
• There is no central server managing the network
• There is no central router

Advantages:

·        Easy to install and configure

·        Individual users control their own shares resources

·        Inexpensive to operate

·        No additional hardware and software beyond a suitable operating system is needed

·        No dedicated administrated are required.

Disadvantages:

·        Network security applies only to a single resource at a time

·        Each machine must be backed up individually to protect all shared data.

·        There is no centralized organizational scheme to locate or control access to data

Client-Server

Client-server is a network architecture which separates the client (often a graphical user interface) from the server. Each instance of the client software can send requests to a server or application server. There are many different types of servers; some examples include: a file server, terminal server, or mail server.

The term server is most commonly applied to a complete computer system today, but it is also used occasionally to refer only to the hardware or software portions of such a system.

Server software generally, but not always, runs on powerful computers dedicated for exclusive use to running the business application. Client software on the other hand generally runs on common PCs or workstations.

Properties of a server:

• Passive (Slave)
• Waiting for requests
• On requests serves them and send a reply

Properties of a client:

• Active (Master)
• Sending requests
• Waits until reply arrives

Advantages:

·        Simplified user accounts, security, and access controls to simplify network administration

·        Single password for network login delivers access to all

·        More powerful equipment means more efficient access to network resources.

Disadvantages:

·        At worst, server failures leads to whole network failure

·        Dedicated hardware and special software (Network Operating Ssystem: NOS) add to the cost. Increases expenses, it may need system administrator to handle.