Computer Networks

NETWORK DEFINITIONS:-

A Computer network is any computer system that links two or more computers.

OR

Network is a computer system that uses communications equipment to connect two or more computers and their resources.

OR

Computer network is an integration of computer system, terminal and communication links.

OR

Computer network is a system composed of two or more computers or terminals.

TYPES OF NETWORK

1.        LOCAL AREA NETWORK (LAN):-

A local Area network (Lan) is a network in which the computer are close to each other ,usually in the same building within  1 Kilometer. A typical local Area network  includes a collection of computers and peripherals. Each computer and shared peripheral is an individual node on the network. Transmission speed in LANs is very high. 

        i.            CLIENT /SERVER NETWORK:-

A client/Server Network involves a server a computer that controls the network. The server has hard disk holding shared files and often has the highest quality printer. The processing is usually done by the server and only the results are sent to the node:

     ii.            PEER TO PEER NETWORKS:-

 

All computers in peer to peer arrangement have equal status, no one computer is in control. User share one another’s data and device as needed However peer to peer networks slow/down under heavy use.

LOCAL AREA NETWORK COMPONENTS

LANS are made up of a standard set of components.

        i.            Coaxial cable/Fiber optics /wireless:-

All network need some system for interconnection. In LANs the node are connected with twised wire pairs, coaxial cable or optic or fibric optics cable. Some LANs are wireless using infrared or radio wave transmission instead of cables.

     ii.            Network Interface Card ( NIC):-

NIC may be inserted into a slot inside the computer to handle sending receiving and error cheek of transmitted data.

   iii.            Bridge:-

If two LANs are similar they may send messages among their nodes by using a bridge.

    iv.            Gate way:-

A gate way is a collection of hardware and software resources to connect two dissimilar networks.

ADVANTAGES OF LANS:-

        i.            Low Cost Application Software

The cost of a LAN based word processing program in less than the cost of a word processing program for each PC in the LAN.

     ii.            Links To Main Frames

It is easier to link the mainframe to a single LAN than to many individual PCs.

   iii.            Communication Capabilities:-

A dedicated outside telephone line or a fax modem can be shared by many users.

   iv.            Input Out Put Devices:-

Input output devices like a single page printer, plotter, or scanner can services the printing needs up to 10 LAN users.

      v.            Storage Devices:-

Data base on a LAN can be shared.

   vi.            Add-On-Boards:-

Add on boards such as a fax modem board can be shared by many PCs.

1.       WIDE AREA NETWORK:-

A wide Area Network connects node in widely dispersed geographic areas such as cities states and even countries. Each network site a node on the network. Wide area network are possible because of the web of telephone lines microwaves relay towers and satellites that span the globe.

WANs allow people to share data and software programs increasing efficiency and productivity. WAN  users often share other hardware resources. Many WANs included powerful mainframes ad super computers that can be accessed by authorized users at remote sites.

DIFFERENTIATE BETWEEN LOCAL AREA NETWORK

(LAN) and Wide Area Network (WAN)

1.  A local Area network  is a network in which the computer are close  to each other usually in the same building.	1.Wide area network is a network of geographically distant and Computer Terminals.
2.Component used in LANs coaxial cable, Networking Interface card (NIC) and bridge.	2.Components used in WANs are telephone lines, microwaves and satellite links.
3.Various topologies ring, bus, star, hierarchical and hybrid are used in LANs	3. Topologies are not used in WANs.

MODES OF DATA TRANSMISSION

1)     SIMPLEX:-       

Simple transmission sends data in one direction only. For example television broad casting and arrival or departure screens at airport.

2)     HALF DUPLEX:-

Half duplex transmission allows transmission in either direction but only one way at a time. In a bank a teller can send the data about a deposit and after it is received the computer can send a confirmation reply.

3)     FULL DUPLEX TRANSMSSION:-

Full duplex transmission allows transmission in both directions at once. Example is telephone conservation.

DIFFERENT TYPE OF COMMUNICATION LINKS IN NETWORKING

• Wire pairs
• Coaxial cables
• Fiber optics
• Microwave Transmission
• Satellite Transmission
• Standard Telephone Lines

1)     WIRE PAIRS:-

Wire twisted together in an insulated cable are wire pair. They are also called twist pair. Wire pairs frequently used to transmit data over short distance. However they are prove to electrical interference or noise.

Wire Pairs Diagram

1)     COAXIAL CABLES:-

A Coaxial cable is a single conductor shielded wire. Bundles of cables can be laid underground or undersea. These cables are used to transmit data much faster than wire pairs and are less prone to noise.

Cox Cable Diagram

1)     FIBER OPTICS:-

Fiber optics is made up of glass fibers. Each glass fiber is thinner than a human hair that can guide light beams for miles. Fiber optics use light instead of electricity to transmit data. It is well suited for handing all types of data voice, picture, music and video at the same time.

fiber optic cable diagram

1)     MICRO WAVE TRANSMISSION:-

Microwave transmission is a line of sight transmission of data signals through the atmosphere for reply station to relay station. These signals can not bend to follow the curvature of the earth so antennas in high places such as the top of mountains and buildings are positioned at points approximately 30 miles a part to continue the transmission.

2)     SATELLITE  TRANMISSION:-

Satellite Transmission is transmission of data from one earth station to another earth station via communication satellites receives the transmission from one earth station  amplifier the signal changes the frequency and retransmits the data to a receiving earth station. Entire process takes only a few seconds communication satellite are launched into space where they are suspended about 22,300 miles above the earth.

3)     STANDARD TELEPHONE LINE:-

Standard telephone lines are used as communication links all over the world. Complex network of telephone lines that has already been established permits data to be transmitted to almost any location in the world.

ASYNCHRONOUS AND SYNCHRONOUS TRANSMISSION

v ASYNCHRONOUS TRANSMISSION

Asynchronous transmission is also called start/stop transmission. In asynchronous transmission data is transmitted on as needed basis. A modem is usually involved in asynchronous transmission. When asynchronous transmission is used a special start signal is transmitted at the beginning of each group (character) of message bits, like wise a stop signal is sent at the end of the group of message bits, when the receiving device gets the start signal it sets up as timing mechanism to accept the group of message bits.

Start

Character

Stop

Start

Character

Stop

Start

Character

v SYNCHRONOUS TRANSMISSION.

In synchronous transmission characters are transmitted together in a continuous stream. In synchronous transmission sending and receiving device are synchronized by having their internal clocks put in time with each other, Further more error bits transmitted at the end of each message to make sure all characters were received properly. Synchronous transmission can send many characters even many messages between one start /stop set. Data transmission between computers routers multiplex and front end processor is normally synchronous.

Start

Message

Error check bit

Stop

Start

Error check bit

Stop