Chapter 4. Computer Networks

Chapter 4. Computer Networks

A computer network is a collection of autonomous, geographically distributed computers inter connected together to enable meaningful transmission and exchange of information among them.

Advantages of Networks

Ø Resource sharing: - It can exchange stored information all over the world.

Ø Reliability: - The information exchanged through the network will be reliable.

Ø Economy: - Can exchange information with low cost.

Ø Security, Scalability, Communication, Remote database accessing.

Terminologies used in a network

Node: - An individual computer connected in to a network is called workstation or node or client.

Server: - A server in a network is a computer that store and serve sufficient data and programs to the nodes. It may be file server, primary server, application server, print server etc.

Network Interface Unit (NIU): - It is used to connect a computer or other device to a network. It is also called network adapter. It consists of electronic circuit to retrieve and transfer data.

Protocols: - A communication network protocol describes the rules, conventions and regulations that govern the transmission of data over the network.

Types of Networks

Ø LAN (Local Area Network)

Ø WAN (Wide Area Network)

Ø MAN (Metropolitan Area Network)

LAN (Local Area Network)

They are privately owned networks with a geographical coverage of less than a kilometre. They are usually setup with in a building or a campus. Its speed is 10 Mbps to 1GBps. Here twisted pair cable, coaxial cables, optical fibre are used as the communication media. It has less error rate, less expensive. Ethernet uses LAN.

WAN (Wide Area Network)

It covers across large geographical area such as countries and continents. Otherwise it interconnects multiple LANs. Its speed is 1200Bps to 2MBps. It has more errors than LAN and expensive. Telephone lines, satellite channels are uses WAN. ARPANET and ERNET are examples for WAN.

MAN (Metropolitan Area Network)

It is usually cover a wider geographic area about 100 KM in diameter. Its speed is nearer to LAN. They also used to connect LANs. Coaxial cable is used as communication media in MAN.

Network Topologies

It refers the way of connecting node in to network to work together.

They are classified in to six. They are

Ø Bus Topology

Ø Star Topology

Ø Ring Topology

Ø Tree Topology

Ø Mesh Topology

Ø Graph Topology

Bus Topology

Here all nodes are connected to a single shared communication link (Bus).

Advantages

Ø It is simple, reliable and less expensive.

Ø Easy to install and extend.

Ø Less hardware is needed.

Disadvantages

Ø It slows when huge amount of data is transmitted.

Ø Collisions happened.

Ø More connections weaken the signal.

Ø A cable break affects the whole.

Ø Difficult to trouble shoot.

Star Topology

Here nodes are connected to a central server with different cables.

Advantages

Ø It is a centralized monitoring and network management.

Ø A cable break does not affect the whole.

Ø Easily to trouble shoot.

Disadvantages

Ø Hub failure affects the network.

Ø More hardware and cabling are needed.

Ø Powerful server is needed.

Ring Topology

Here each node is connected only two adjacent nodes only in a circular order. Here the method token passing is used to transmitting data. 

Advantages

Ø Less cabling is needed.

Ø A particular node transmitted data at a time.

Ø Performance is stable.

Disadvantages

Ø Data is passed through every node.

Ø Trouble shooting is difficult.

Ø Network configuration is difficult.

Tree Topology

Here all other nodes are branched from a central node. Here transmission is takes place in broadcast method. It is only a variation of bus topology.

Mesh Topology

Here each and every node is connected to other nodes. Any one of the connection is failed it will not affect the others. It is expensive because more cables and adapters are used. Reconfiguration is difficult.

Graph Topology

There is no definite order for the nodes. There are multiple paths between nodes.

Internet and Intranet

Internet is a very large network of computers that interconnect many different networks in different parts of the world. It is a global network or network of networks. So it is a public networks and it is accessible for everyone. Here the transmission is done by using TCP/IP (Transmission Control Protocol/Internet Protocol). It provides different services like www, E-mail, video conferencing, chatting etc.

Intranet is a private network owned by an organization. It used to connect various offices in that organization. It is used to transfer files, information, accessing centralized database etc.

Hardware & Software Requirements for Internet Connection

Ø A personal computer with facility to connect modem.

Ø A modem convert analog signals to digital and vice versa.

Ø A telephone connection.

Ø An account and registration from ISP (Internet Service Provider).

Ø Communication software like Internet explorer, Netscape navigator, Mozilla, yahoo messenger, Skype, MS outlook express etc.

Types of Connectivity

To access internet the following connectivity are used.

1.    ISDN

2.    Dial Up Connection

ISDN

Integrated service digital network (ISDN) is used to transfer voice, video and text between individual computers simultaneously. It is a very fast method and it uses fibre optic cable to transmit data.

Dial Up Connection

It uses telephone line to transmit data by using a modem. It is less expensive, low transmission speed.

Browsing

www is an internet service, used to exchange information over internet in the form of hyper text called webpage. It includes text, images, audio, video, animations, etc.

Browsing refers to visiting various websites on the internet by using browsers like Internet explorer, Mozilla, Netscape navigator, Opera etc.

The website address or URL (Uniform Resource Locater) is used to identify a website. (e.g. http://www.airindia.co.in)

Here http is scheme, www is the host, airindia is the domain name, .co is the type of firm and .in is the region code.

E-mail

It is electronic mail, enables to send electronic messages across the internet by using an email address (Example: airindia@gmail.com).

Advantages

Ø Easy to create and send messages to more than one people.

Ø Very fast

Ø Less expensive.

Ø An ideal way for busy people.

Ø Any type of data can send by using e-mail.

Disadvantages

Ø It is not legally accepted.

Ø It may contain viruses.

Ø It may contain pornographic contents.