Chapter - 1 Computer Network And Telecommunication

Data communication

The process of transferring data or information between computers called data communication.

Telecommunication

It refer all types of data transmission like characters, numerical, photos, audios and videos etc. using electronic or light emitting media. E.g. email, voice mail, video conference etc.

Cables (Guided Media)

Cables are the most common transmission media. Two or more devices are connected directly using cables. Three types of cables are used in computer networking they are:

Twisted pair cable

Twisted copper cables are used only for lower bandwidth. It consists of two isolated strands of copper wire twisted around each other. There are two types of twisted pair cables they are as follows:

UTP (Unshielded Twisted Pair)

UTP cables does not have metal shield expect plastic coating. It contains number of twisted pairs of wires with a simple plastic casing. It commonly used to for LAN and Telephony. It is cheaper and easier to work with, but do not offer high bandwidth and good protection from interferences. It can support data transmission rates from 10 to 100 mbps.

STP (Shielded Twisted Pair)

STP is similar to UTP but it is shielded with metal sheath along with plastic coating. It offers high bandwidth and good protection from interferences. It is cheaper than fiber optic cable. It can support data transmission rates from 10 to 500 mbps.

Co- axial cable

A co-axial carries higher bandwidth than twisted pair, it is easy to connect. It does not bend readily. This cable consists of one or more small cables in a protective covering. It offer very high data transfer rate and can be placed underground and laid on the floors of lakes and oceans.

Fiber Optic cable

Fiber optic cable is a thin filament of glass fiver wrapped in a protective jacket. It consists of strands of glass like thread, each about the diameter of a human hair. It offer high-speed data transmission rate because data travel as high-speed pulses of light.

Wireless (Unguided Media)

It is used to transfer data with in a large geographical areas or globally without the use of interconnecting wires or cables. It uses other components such as radio signals, microwaves, or infrared to connect network.

Types of wireless communication

Microwave System

Microwave signals are similar to radio and television signals and are used to transmit data through the space without the use of cable. It provides high-speed data transmission. These signals cannot bend or pass obstacles like hills and tall buildings, so very high towers are used to mount the signals. The transmission is limited about 30 miles. Chain of towers is required to transmit the microwave signals in a long distance

Satellite communication

Both microwaves signals and telephone signals can be relayed to a earth station for transmission to a communication satellite. The earth station consists of a satellite dish that functions as an antenna a communication equipment to transmit and receive data from satellite passing overhead. It is not disturbed by hills and tall buildings and visible from any point. So sender and receiver easily communicate with each other using antenna by aiming the satellite. It is very expensive for placing satellite along the earth orbit.

Modulation

The process of changing some characteristics (amplitude, frequency or phase) of carrier wave in accordance with the intensity of the signal is known as modulation.

Types of modulation

Amplitude Modulation (AM)

Frequency Modulation (FM)

Phase Modulation (PM)

Mode of communication

Simplex mode

Simplex is one-way data transmission that takes place only from sender to receiver. An example of this would be a television that allows the signal to pass in only one direction. Computer network connections do not use simplex.

Duplex mode

Duplex is two-way data transmission that takes place both directions over a communication channel. Computer use duplex channel. For example if computer A and computer B are connected together than both computer can share data or information. From computer A to computer B or computer B to computer A.

Types of Duplex Mode

Half duplex

Half duplex is two way data transmission that takes place in only one direction at a time. Eg walkie Talkie

Full duplex

Full duplex is two-way data transmission that takes place in both directions at a time. Eg mobile communication, voice call, video-conferencing etc.

Computer Network

A computer network is a logical or physical interconnection between two or more computers such that they could communicate with each other. It is used to provide users with the access to share resources. These shared resources include data files, application software and hardware.

Components of computer network.

Computer

Transmission media

Network software.

Protocols.

Networking cables (Transmission media)

Advantages of computer network:

·       Resources, data, software and hardware can be shared.

·       Faster & cheaper communication and data transmission.

·       It provides as the tools for e-mail teleconferencing videoconferencing which facilities communication.

·       Flexible working condition.

·       Office automation can be making very effective well managed.

Disadvantages of computer network.

·       High installation and administrative cost.

·       Attack on the privacy of the people.

·       Computer virus spread most easily through network.

·       Technologically very complicated.

·       If the server is out of order, then all workstations are hang up.

·       Well trained technical support is required.

Network architectures or (Types of Network Architecture) or LAN Architecture:

Client server Network Architecture

This is old model of computer network. In this kind of network model one main computer equipped with very powerful processor, large memory and network operating system works as a main computer or service provider. Other computers connected with server, which are also called workstation or node or terminals can use the hardware and software resources of server computer. There are different types of server such as file server, print server, network server or email server.

Advantages of client server network:

·       It works with any size or physical layout of LAN.

·       It does not tend to slow down with heavy use.

·       The network can be expanded to any size as we wish.

·       It provide very high level security

·       It reduces software installation time and cost to all computers.

Disadvantages of client server network:

·       It is very difficult to setup and well trained technicians are required to handle and setup.

·       It is expensive compare to peer to peer network.

·       All software and operating systems are installed in server computer so that other client computer has to depend on it.

·       Peer to peer Network Model

·       It is also called workgroups also. Because all computers in the network have equal responsibilities. All computers in the network have access to at least on e or more computers. It mostly used in LAN and every organizations, research centers such as banks, travel agencies, airlines educational institutions etc.

Advantages of peer to peer network:

·       It is easy to setup.

·       Users in each computer can determine the resources to be shared among other computers.

·       Any required software can be installed on individual computers , they don’t have to depend on the server.

·       It is suitable at home, office, banks and small organization.

·       It is cheaper compare to client server network.

Disadvantages of peer to peer network:

·       It is slow because of heavy load.

·       It is suitable for limited area such as school offices and small organization.

·       The network expansion is limited and can not be expanded as the wish.

·       It has limited security level.

Types of computer network on the basis of geographical area

Local Area Network(LAN)

The way of connecting two or more computers in a very limited area (about 100 to 300 meters) or within a same building or a group of adjacent building is called LAN. It enables very high speed communication through wire connection or wireless connection some times. Small organizations prefer it because of less expensive and faster communication.

Metropolitan Area Network(MAN)

The way of connecting computers inside a metropolitan area is called MAN. The area may be a part of city, whole part of city, district, zone or country. Radio wave is used to transmit the data for communication between the workstation and server in the system. Many different systems of networking and computing are brought together to form a MAN.

Wide Area Network(Wide Area Network)

The connection of computers of networks covering more distance or the world by the help of wave, frequency and satellite is called WAN or Internet. Different types of LAN and MAN are connected to form a WAN. It covers more area but it is slower than LAN and MAN.

Network Topology

The physical structure of network is called topology. It may contain software, hardware or geographical situation of the networking. Or in another words it is the pattern in which the computers are interconnected.

Types of Network Topology

BUS Topology

Uses a single length of cable to interconnect network devices. Uses terminators to dampen signal reflection at the ends of the cables

Advantages of Bus topology

·       Since each small segments of cables are joined to form a trunk or network bus it is easy to setup computers on the bus.

·       Since nodes are arranged in the linear form, it requires the less amount of cables.

·       The coaxial cables used for networking are inexpensive and joining connectors on the cables is also easy.

·       The position of server computer can be any where on the bus topology.

·       Failure of any node does not affect other nodes on the network. f. Well suited for temporary networks (quick setup)

Disadvantages of Bus topology

·       If the backbone cable i.e. network bus has problem then the entire network fails.

·       Finding fault on this topology is not easy.

·       It provides limited flexibility for change, so adding or removing nodes in between is not easy.

·       The performance degrades when the number of computers is more on the network. So, it is not suitable for big size network.

·       Ring Topology:

·       Devices are connected in a ring formation. It support very high data transmission rate

Advantages of Ring Topology

·       Since each node on the ring acts as a repeater, no any external repeater is required to boost up the signals.

·       It supports high data transmission rate.

·       It is easy to setup.

Disadvantages of Ring Topology

·       If any node or connecting cable fails the entire network does not work.

·       The diagnosis of the fault is difficult.

·       Since data or message reaches on the node in sequence, so addition of new nodes increases the communication delays.

·       It provides limited flexibility for change, so adding or removing nodes in between is not easy.

Star Topology:

Most commonly implemented network topology used today that uses centrally located device i.e hub or switch is known as Star Topology.

Advantages of star network

·       Computers can be added or removed easily without affecting the network.

·       If any of the workstation or the connecting cable fails, it does not affect the remaining portion of the network.

·       Fault detection in the star topology is easy.

·       It is easy to extend so it is suitable for a large network.

·       It is one of the most reliable network topology.

Disadvantage of Star Topology

·       Since each node is required to connect with the centralized hub or switch more cables are needed which increases the cost of installation.

·       The entire network fails if there is any problem on the hub or switch.

·       In comparison to Linear and Ring topologies, t is little expensive as it requires more length of cables and other controlling devices.

Different devices and terms used in Network:

MODEM

Modem is a device that directly converts digital signal from a computer or other digital devices into analog form for transmission over analog link i.e telephone line and vice versa. MODEM stands for Modulation and Demodulation. There are two types of modem used in computer they are as follows:

Internal modem and External modem.

NIC

It is a Network Interface Card, which connects each computer to the wiring to the network. A NIC is a circuit board that fits in one of the computer’s expansion slots. It provides a port on the back of the computer to connect in the network.

Hub

Hubs are connectivity devices, which contain multiple ports for connecting to network components. Hubs connect the computers in a star topology. It lies between server and clients computers.

Connector

Bridge and Gateway are the two different connectors, which play role to link between two network systems.

Bridge

Bridge connects networks using same communications protocols or similar networks so that information can be passed from one to the other.

Gateway

Gateway connects networks using different communications protocols or dissimilar networks so that information can be passed from one to the other.

Switch

A device that capable of forwarding packets directly to the ports associated with particular network addresses. Hubs and switches are almost same but switch is new technology and intelligent compare to hub.

Repeater

A device used on communications circuits that decrees distortion by amplifying or regenerating a signals so that it can be transmitted onward in its original strength and form as they pass through a network cable.

Protocols

Protocols are the set of rules and formats for sending and receiving data. It works as guidelines to govern the exchange between equipments. There are different types of protocols that we can use. Some of popular protocols are TCP/IP, HTTP, FTP, IPX/SPX.

Router

A router is a device that is used to connect different LAN in the network. It receives transmitted messages and forwards them their correct destinations over most efficient available route.

NOS (Network Operating System)

The operating, which can support network environment, is called Network Operating System. For example Windows XP, 2000, server, unix, linux, Novel Netware etc.

Network Protocol (Communication Protocol)

A set of rules by which computers on the network communicate with each other is known as network protocol. The common protocols used on the network are:

TCP/IP (Transmission Control Protocol / Internet Protocol)

SMTP (Simple Mail Transfer Protocol)

FTP (File Transfer Protocol)

HTTP (HyperText Transfer Protocol)

POP (Post Office Protocol)

IPX/SPX (Internet Packet Exchange/Sequential Packet Exchange)

NetBEUI (NetBIOS Extended user interface)

AppleTalk

VOIP(Voice Over Internet Protocol)

HTTPs (HyperText Transfer Protocol Secured)

UDP(User Datagram Protocol)