ASHOK GARG MOBILE : 9312249405 · 2015. 6. 8. · An interconnected collection of autonomous...

ASHOK GARG MOBILE : 9312249405

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An interconnected collection of

autonomous computers is called

Computer Network. It means two

computers are said to be interconnected

if they are capable of exchanging the

information.



Need for NetworkingSharing of Hardware and Software

Resources

Reliability

To enable different computers to

communicate

To reduce cost of transfer of

data



Evolution of Networking1. ARPANET : This was the first network

which was planted in 1969. It meansAdvanced Research Projects And NETwork.Its aim was to connect different computersof different universities and U.S. defense toof different universities and U.S. defense toexchange messages and data.

2. NSFnet : This was the network which wasstarted in 1980 by National ScienceFoundation. It was a high capacity networkthan ARPANET. It was used to do researchwork on the network.



3. INTERNET : It is a network of networks. Itis a worldwide network of Computersnetwork.It was developed in 1990 bydifferent companies to allow the users toconnect one network to the other tocommunicate.It is a super network.

4. INTERSPACE : It is a client/server4. INTERSPACE : It is a client/serversoftware program that allows multipleusers to communicate online with real timeaudio , video and text in dynamic 3Denvironment.



Basic TerminologyNodes or Workstations

The differentterminals orcomputers which

Server

A Computer whichfacilitates thesharing of data ,software andcomputers which

are attached to anetwork and areable to share theresources are callednodes orworkstations.

software andhardwareresources likePrinter , Modemetc. on thenetwork is called aServer.



Servers are of two types

Dedicated ServerIt is a computer which canonly be used as a server notas a node . It means its onlyjob is to provide facilities of

Non - Dedicated ServersIn a network a workstationwhich can double up as aserver is called a non-

job is to provide facilities ofdata , software , hardwareresources etc. to the nodes.

server is called a non-dedicated Server . It meansit can be used as a serverand as a node.



Communication Channels :

Network Interface Unit

It is a device which is attached to server and all the workstations to maintain the connection between them.

Communication Channels :

They refer to the connecting cables that connect two or

more workstations . The following are the important

types of cables :



Types of Communication Channels

1. Guided media : The medium of communication

which includes the cables.



( a ) Twisted Pair Cable : This is the most common form of

wiring in data communication applications . It is consisted of

two identical wires wrapped together. Its main advantage is its

simplicity and ease of installation . It is flexible and can be

connected easily. In this the data transmission characteristics

are not so good. It is incapable in carrying a signal over long

distances.

Its Advantages :

(1) It is physically flexible and easy to install.(1) It is physically flexible and easy to install.

(2) It is inexpensive and can be connected easily.

Its Disadvantages :

(1) It is incapable to carry a signal over long distances without the

use of repeaters.

(2) Its bandwidth is very low and so can not be used for broadband

applications.ASHOK GARG MOBILE : 9312249405


( b ) Coaxial Cable : This type of cable is consisted of a solid

wire core surrounds by one or more wire shields each separated

by some insulating material . The inner core carries the signal

and shield provides the ground. It is very cheap and has better

transmission characteristics than twisted pair cable.

Its Advantages :

(1) Its bandwidth is higher than the twisted pair cable.

(2) It can be used for broadband transmission. It means several(2) It can be used for broadband transmission. It means several

channels can be transmitted simultaneously.

Its Disadvantages :

(1) It is more expensive than twisted pair cable .

(2) It is not compatible with twisted pair cable .



( c ) Optical Fibers : It is consisted of glass like material

which carry light form source to the destination. Its bandwidth

is very high. It is difficult to install them and they need special

care. It is one of the attractive transmission indeed.

Its Advantages :

(1) Its bandwidth is very high and so can be used for broadband

transmissions where several channels are handled in parallel.

(2) It can be used for broadband transmission. It means several(2) It can be used for broadband transmission. It means several

channels can be transmitted simultaneously.

Its Disadvantages :

(1) It is more expensive than other type of cables .

(2) It sometimes can not be installed easily.

(3) Connection loss is a common problem in optical fiber.



2. Unguided media : The medium of communication

which includes the waves through air ( vacuum ) .



( a ) Micro Wave : These are the signals which are used to

transmit data and are similar to the TV signals. These are used

for long distances. It is a line-of-sight transmission. These

signals pass through the atmosphere and they travel from one

antenna to the other. It is very cheap and can be used for very

long distances. Sometimes these signals are insecure.

Its Advantages :

(1) It has the ability to communicate over the oceans .

(2) It is cheaper than laying the cables.(2) It is cheaper than laying the cables.

Its Disadvantages :

(1) It is an insecure communication.

(2) Bandwidth allocation is very limited in microwave.

(3) Is design and maintenance cost is very high.



( b ) Radio Wave : These are the signals which are used to

transmit data at radio frequencies. It has two parts : transmitter

and receiver. The transmitter takes messages and encodes it and

transmit it into radio waves which is received by receiver. It is

very cheap and needs less repairing . In this communication is

very easy. Sometimes these signals are insecure.

Its Advantages :

(1) It provides a more easy and convenient way of communication.(1) It provides a more easy and convenient way of communication.

(2) It is cheaper than laying the cables.

Its Disadvantages :

(1) It is an insecure communication to some extent.

(2) It is susceptible to weather conditions like rain etc.



( c ) Satellites : In this transmission the earth station

communicate to send and receive the data using transponders.

In the area coverage is more and it is very attractive. It is costly

and due to atmospheric losses it has a definite limit of

frequency.

Its Advantages :

(1) The area coverage for the transmission is very large.(1) The area coverage for the transmission is very large.

(2) It is cheaper than laying the cables.

Its Disadvantages :

(1) It is available with high investment cost and with significant

probability of failure.

(2) It has a high atmospheric loss above a fixed frequency.



TYPES OF NETWORK� LOCAL AREA NETWORK (LAN )

� METROPOLITAN AREA NETWORK (MAN)

� WIDE AREA NETWORK (WAN )



LOCAL AREA NETWORK ( LAN )

It is a small computer network that are confined to a localized area like an office , a building etc. Only a definite number of computers can be connected in this network to share the resources . Its range can be up to a few Kilometers.Its main features are

� Total diameter not more than 5 km� Total diameter not more than 5 km

� Data communication at the rate of 100 Mbps

� Owned by single organization

� Low Error Rates

� Provides user access to several resources like

printers, Modem etc.



Metropolitan Area Network ( MAN )

This network is larger in size than LAN and it spreadsover a city. It means a very large number of computerscan be connected in this in a city or from one city to theother.



WIDE AREA NETWORK ( WAN )

� This network spreads across the countries and it is agroup of computers that are separated by very largedistances. The computers of even one continent canbe connected to the other continent.

Its main features are :Its main features are :

� Spans large geographical area, often a country or continent

� Helps in E-Mailing

� Data can be received from or sent to remote areas with the help of satellite with less cost



LAN WAN .� Diameter of not more than

a few kms.

� Total data rate of at least several Mbps

� Span entire countries

� Data rate less than 1 Mbps

� Owned by multiple several Mbps

� Complete ownership be a single organization

� Very low error rates

� Owned by multiple organizations

� Comparatively higher error rates.



MODEM

( MOdulation/DEModulation )The device which is used to connect and communicate with computers with the help of telephonic lines . It converts digital data into analog form and vice versa.

Working :A modem is a computer peripheral thatallows to connect and communicate with the othercomputers through telephone lines. In MoDem , Moallows to connect and communicate with the othercomputers through telephone lines. In MoDem , Mostands Modulation and Dem stands forDemodulation . Modulation means to convertdigital signals to analog signals and Demodulationis reverse of that. The data is transferred form sourceto the destination through telephone wires and theycan only understand analog signals so there is needto convert digital signals to analog . And computercan only understand digital signals . This conversionis done by MoDem.



Analog signals Analog signals

WORKING OF MODEM

MODEM MODEM

Digital SignalsDigital Signals

Source ComputerDestination (Remote Computer)ASHOK GARG MOBILE : 9312249405


Network Switching Techniques( 1 ) Circuit Switching : In this technique first of all the

complete physical connection between two computers is established

and then data is transmitted from the source computer to the

destination computer. Its important property is to set up an end-to-

end connection between computer before any data can be sent.

( 2 ) Message Switching : In this technique the source

computer sends data or the message to the switching office firstcomputer sends data or the message to the switching office first

which stores the data. It then looks for a free link to another

switching office and then sends the data to this office. Hence it is

also known as store and forward.

( 3 ) Packet Switching : In message switching there is no limit

on block size but in Packet switching a fixed size of packet which

can be transmitted across the network is specified. In this all the

packets of fixed size are stored in the main memory. It improves the

performance as the access time is reduced.ASHOK GARG MOBILE : 9312249405


Network TopologiesThe way of interconnection of the nodes in a network is called the

Topology.

The different factors on which selection of a topology depends are :

( a ) Cost : A Network of computers can reduce the cost to a large

extent.

( b ) Reliability : It is more reliable to work in a Computer Network .( b ) Reliability : It is more reliable to work in a Computer Network .

Hence if a node fails to work the data can be achieved from some

other nodes.

( c ) Flexibility : The topology should allow for easy reconfiguration

of the network.

The different topologies are :



Star Topology It is consisted of a central node to which all other nodes are

connected by a single path. Its different advantages anddisadvantages are :

Advantages :( 1 ) One Device per connection : In this topology failure of a

single connection typically involves disconnecting one nodefrom an otherwise fully functional network.from an otherwise fully functional network.

( 2 ) Simple Access protocols : In this access protocols are verysimple.

Disadvantages :( 1 ) Long Cable Length : This topology uses a very long cable as

each node id directly connected to the centre.

( 2 ) Central Dependency : If the central node fails , the entirenetwork stops working.



WS1 WS3

Server

WS4WS2



Bus or Linear Topology It is consisted of a single length of the transmission medium

onto which the various nodes are attached . Its differentadvantages and disadvantages are :

Advantages :

( 1 ) Short Cable Length : There is a single common data pathconnecting all nodes , so this topology uses a very short cable .

( 2 ) Easy to Expand : In this topology additional nodes can beconnected at any point along its length.

Disadvantages :

( 1 ) Fault detection : In this topology it is very difficult to detecta faulty node .

( 2 ) Nodes must be intelligent : All the nodes working in thistopology must be intelligent.



Server WS2WS1

WS4WS3 Printer



Ring or Circular Topology In this each node is connected to two and only twoneighbouring nodes. Data is transmitted from one to anothernode and is transmitted onwards to another. In this topologythe data travels only in one direction.

Its different advantages and disadvantages are :

Advantages :

( 1 ) Short Cable Length : There is very short cable which is usedto develop a Computer Networkto develop a Computer Network

( 2 ) Suitable for optical fibers : In this topology for very fastspeed transmission optical fibers can be used.

Disadvantages :

( 1 ) Node Failure causes network failure : In this topology if onenode fails to pass the data through itself , the entire networkfails.

( 2 ) Network reconfiguration is difficult : It is not possible toshut down a small section of the ring .



C1 C3C2

C4C6 C5



Tree Topology

A variation of bus topology is the tree topology. The shape of

the network is just like an inverted tree with the central root

branching and sub-branching to the extremities of the

network.

Advantages :

( 1 ) Easy to Expand : It is very easy expand this topology . It

means nodes can be connected easily.means nodes can be connected easily.

( 2 ) Fault isolation is easy : It is easy to find the faulty node in

this topology.

Disadvantages :

( 1 ) Dependency on root computer : The total dependence is on the root

computer . If it fails to work , the entire network will stop working.

( 2 ) Complex Access Protocols : The protocols designed for this topology are

generally very complex.



WS1 WS3

Server

WS6WS2 WS5WS4



Backbone Network� A backbone is a central interconnecting

structure which is used to connect two or more networks e.g. LANs together to form a WAN

e.g. FDDI – Fiber Distributed Data InterfaceASHOK GARG MOBILE : 9312249405


REPEATERA repeater is a device that amplifies a signal beingtransmitted on a network for long distances.

It is used in long network lines, which exceed theIt is used in long network lines, which exceed themaximum rated distance for a single run.



Bridge

A bridge is used to connect twoLANs which are physicallyseparated but logically same i.e.separated but logically same i.e.follow the same topology.



Router

It is a device that links twonetworks which can handledifferent protocols. The routers usedifferent protocols. The routers usephysical addresses. It improves theperformance of the network.



GatewayA gateway is a device that connects dissimilar

networks. It gives an intelligent connection between a

local network and an external network with different

structures .structures .

It is a special device which allows different networks to

talk to internet that uses TCP/IP.



Some Important Terms ( 1 ) Data Channel : A channel is a medium that is used to carry

information or data from one point to the other.

( 2 ) Baud : It is a unit to measure the rate of transfer of data.

( 3 ) bps : It stands for Bits per seconds. It is also a unit to

measure the rate of transfer of data. The higher units to measure themeasure the rate of transfer of data. The higher units to measure the

rate of transfer of data are :

( a ) kbps : Kilo bits per seconds

( b ) mbps : mega bits per seconds

( c ) Mbps : million bits per seconds

( d ) Gbps : Giga bits per seconds

( e ) Tbps : Tera bits per seconds



( 4 ) Bandwidth :

It is the difference between the highest and lowest

frequencies of a transmission channel. It refers the

amount of the information travelling through a single

channel at one point of time. High bandwidth channels

are called broad bandwidth channels and low bandwidthare called broad bandwidth channels and low bandwidth

channels are called narrow bandwidth channels. Some of

the commonly used units for this are :

Hz , kHz , MHz , GHz , THz



( 5 ) Data Transfer Rate : It means the amount of data

transferred per second by a communication channel or a storage

device.

( 6 ) RJ-45 Connector : It stands for Registered Jack - 45. It is

a 8 wire connector which can be used to connect computers in a

LAN .

( 7 ) Ethernet Card : It is LAN architecture which can be used

in bus and star topologies. It can be used to transfer the data up to a

rate of some Mbps. The computers which are a part of Ethernet userate of some Mbps. The computers which are a part of Ethernet use

a special card called Ethernet Card. It has connections for coaxial

and twisted pair cable.

( 8 ) Hub : It is a device that can be used to connect a number of

computers. It provides a central connection point for workstations ,

server and other devices. It ca be of two types :

( a ) Active Hub : A hub that electrically amplifies the signals. It

means it is used as a repeater.

( b ) Passive Hub : A hub that allow the signals to pass from one

computer to the other without any change.ASHOK GARG MOBILE : 9312249405


( 9 ) Switch : It is a device which can be used to segment

networks into different sub networks called subnets. It

prevents traffic overloading in the network.It transforms

the data in the form of forwarding packets and it supports

packet protocols.

( 10 ) Wireless communication : It is a way to transfer

data without any use of landlines. This may involve

cellular phone , satellite communication etc.cellular phone , satellite communication etc.

( 11 ) EDGE : It stands for Enhanced Data Rates for

Global Evolution . It is a radio based high speed mobile

data standard. It allows data transmission speeds up to 384

kbps.



( 12 ) GSM : It means Global System for Mobile

communication. To connect to the specific service

provider in different countries GSM users use SIM (

Subscriber Identification Module ) Card . GSM digitises

and compresses the voice data.It uses narrowband TDMA

(Time Division Multiple Access).

( 13 ) SIM Card : It stands for Subscriber Identification

Module. It is a small removable disk which are used to

slip in and out in cell phones. They store all the

connection data and identification number which can be

used to access. It is basically a small computer having

memory , processor and ability to interact.



( 14 ) CDMA : It stands for Code-Division Multiple Access. It is

a digital cellular technology which does not use any specific

frequency. CDMA is a form of spread spectrum that means the data

is sent in small pieces over a number of discrete frequencies

available to use any time in a specified range. At the receiver end

the same unique code is used to recover the signal.

( 15 ) WLL : It stands for Wireless Local Loop . It is analogous

with local telephone service but with more capabilities. It serves as with local telephone service but with more capabilities. It serves as

a multiple transmit/receiver base stations. It is consisted of a radio

transceiver and the WLL interface assembled in one metal box. A

fax or a modem can also be connected with it for communication.

Advantages :

( 1 ) WLL facilities are not suffered by weather problems.

( 2 ) It offers a better bandwidth for communication.



( 16 ) 3G : It stands third generation . It is a broadband mobile

communication technology in which the packet based transmission

of text , digitised voice , video etc. is done. It offers a consistent set

of services to the mobile computer and phone users no matter where

they are located in the world.

( 17 ) Mobile Computing : It means a way to communicate

where the computing device is not continuously connected to the

central network e.g. laptop computer .

( 18 ) SMS : It stands for Short Message Service. It is the

transmission of short text messages to and from a mobile phone ,

fax machine etc. In this the messages must not be longer than a

fixed number of numeric characters and contain no images and

graphics. The sent SMS is received by SMSC (Short Message

Service Centre ) and forwarded to Home Location Register ( HLR ).

( 19 ) DNS : It stands Domain Name System. It is a character

based naming system by which the servers are identified . ASHOK GARG MOBILE : 9312249405


Important Definitions ( 1 ) Protocols : The protocols refer some rules and regulations

that are applicable for a network. They define standardized formats

for the data packets , techniques for detecting and correcting errors.

Most common examples of the used protocols are :

( a ) HTTP : It stands for Hypertext Transfer Protocols and it is an

application-level protocol for speed necessary and hypermedia

information systems. It has various built-in request methods which

allow users to read a web page.allow users to read a web page.

( b ) TCP / IP : It stands for Transmission Control Protocol /

Internet Protocol. It is layered set of some protocols. These

protocols are responsible for making sure that the commands get

through to the other end. It keeps track what is sent. If a message is

very large TCP will split it up into several datagrams.

( c ) FTP : FTP stands for File Transfer Protocols .This protocols

are helpful for uploading and downloading the files.ASHOK GARG MOBILE : 9312249405


( d ) SLIP : It stands for Serial Line Internet Protocols. These are

used to relay over dial up lines.

( e ) PPP : It stands for Point to Point Protocols. It is layered

protocols which is consisted of 3 types of Protocols .

(1) IPCP : IP Control Protocols – used for IP packets over PPP link.

(2) NCP : Network Control Protocols – used for traffic transport

over PPP link.

(3) LCP : Link Control Protocols – used for link establishment



( 2 ) Datagram : It is a collection of the data that is sent as a

single message.

( 3 ) Internet :A very large network of networks is called internet.

It is the world’s largest network which provides facilities like :

( a ) E-mail : E-mail stands for Electronic mail. It is facility of

internet which can be used to send and receive messages. This facility is

becoming very popular all over the world now a days. Its different

advantages are :advantages are :

( I ) Low Cost : It is very cheap to send or receive a message through

E-mail.

( II ) Speed : The messages can be sent from one location to the other

very fast.

( III ) Reliable : It is more reliable and safe to send a message by

E-mail in comparison to conventional mailing system.

( IV ) Easy to use : It is also very easy to send or receive messages by

this.ASHOK GARG MOBILE : 9312249405


( b ) WWW : It stands for World Wide Web . It is a set of some

protocols that allows to access any document on the Internet through a

naming system based on URL(Uniform Resource Locators).It also

specifies a way to send and receive a document over the internet .It

means it is a way of visiting a Web Site.

( c ) Video Conferencing : It is a service of internet by which the

user can talk to another person via the microphone and speakers

connected to the computer system. It can be used to send images andconnected to the computer system. It can be used to send images and

voice from one place to the other. Instead of typing messages the user

can see the face of the other person and can transmit the voice and

the video.

( d ) Chat : Online textual talk in real time is called Chatting. It is a

service of internet by which the user can communicate with the other

user by typing the messages on the screen and gets the response

immediately.



( 4 ) URL: It stands for Uniform Resource Locators .

These are the unique addresses of the web sites in

the Internet which serve as the page’s worldwide

address . It has three parts :

1. The Protocol

2. The DNS name of the machine on which the page is2. The DNS name of the machine on which the page is

located

3. A local name uniquely indicating the specific page.

It can be of three types Absolute URL , Relative

URL and Fragment URL.



( 5 ) Web Browser : It a software that navigates

through the WWW and displays the Web Page. The

different examples of Web Browser are Internet

Explorer and Netscape Navigator.

( 6 ) Web Server : It is a World Wide Web Server that

responds to the requests made by the web browsers.

( 7 ) Web Site : It is collection of web pages which are ( 7 ) Web Site : It is collection of web pages which are

hyper linked with each other belonging to a particular

person or organization . It may contain information in

the form of text , images etc. It can be called a location

on the net .



( 8 ) Web Page : A web page is a single unit of information that is

available through a World Wide Web. A web page is an HTML page

that is stored on a web server and has a URL so that is can be

accessed via the web.

( 9 ) NFS : It stands for Network File System. It means( 9 ) NFS : It stands for Network File System. It means

how the files are organised and retrieved on it. It depends

on the operating system used by the network.



( 10 ) Telnet :It is an Internet facility which allows us to log in to other computers

over the internet. This facility is generally used to check the E-mail

messages by the users irrespective of the physical location from

where the connection has been taken. Most ISP provides this service

to the account holders. This facility needs a Telnet program. After

entering the user name and password this can be used.

(11) ISP:It stands for Internet Service Provider .It is a

company or an organization that provides the internet

( 12 ) Intranet :An intranet is a network that exists in a single

organization and can be handled by it . It is based on the internet

technology.

company or an organization that provides the internet

access.It provides domain name service etc. It also

provides the technical support to the users.



( 13 ) E-Commerce : It is a collection of some tools and

practices that are involved in Internet technologies which

allow the users to create , maintain and optimise business

relations with consumers and other businesses.

( 14 ) HTML : It stands for Hyper Text Markup Language .

It is used to design the layout of a document and to specify the

hyper links. This language tells the web browser how to display hyper links. This language tells the web browser how to display

the contents of a hypertext document.

This language provides many layout commands which are called

tags.



( 15 ) DHTML : It stands for Dynamic Hyper Text Markup Language. It

refers to the web contents that change each time when it is viewed e.g.

Time of Day , Profile of the Reader etc. This allows a web page to

change after it is loaded into the web browser.

( 16 ) XML : It stands for eXtensible Markup Language. This language

is used for the documents containing structured information which is used for the documents containing structured information which

contains words and picture both. This neither specifies semantics nor a

tag set. In this language there is no predefined tag set.



Some Common Domains are –

com Commercial

edu Education

gov Government

mil military

co company

org Organizationorg Organization

( 17 ) Web Hosting : It is a way of hosting the web

server application on a computer where the contents

are available to any web browser clients. Its different

types are :

( a ) Free Hosting : A type of web hosting which offers

visiting many websites free of cost.ASHOK GARG MOBILE : 9312249405


( b ) Virtual or Shared Hosting : A type of web hosting

which is provided under one’s own domain . Using this

one can present himself as a fully independent identity

to his web audience.

( c ) Dedicated Hosting : A type of web hosting in

which a company or an organization hires a web which a company or an organization hires a web

server from the hosting company.

( d ) Co-location Hosting : A type of web hosting in

which a company or an organization owns its own

server on which the site is hosted. In this the company

owning the website is responsible for all server

administration. ASHOK GARG MOBILE : 9312249405


( 18 ) Cookies : These are the messages which a web server

transmits to the web browser so that the server can keep a track on

the user’s activities on a web site.

( 19 ) Hackers : The people who are interested in learning

programming languages and computer system and can be

considered computer experts. This is term is used for those who

gain unauthorized access to use computer systems for stealing and

corrupting data.corrupting data.

( 20 ) Crackers :The programmers who break into the network

security system.

( 21 ) Cyber law : It refers to all the legal and regulatory aspects

of Internet and the WWW. It is a way to check your legal

transactions in the Internet Environment.



Network Security

The different Prevention methods are used while

working in Network environment for security.

( 1 ) Authorization : It determines whether the ISP has

granted the access to the web service or not. It is done granted the access to the web service or not. It is done

by asking the user legal login-Id.

( 2 ) Authentication : It is a way to check the password

protection of an authorised user.

( 3 ) Firewall : It is a system designed to prevent the

unauthorised users to access to or from a private

network. In this we can also encrypt the data.



Sno Short Form Full Form

1 3G & EDGE Third Generation, Enhanced data rates for Global Evaluation

2 ARPANET Advanced Research Projects Agency Network

3 CDMA Code Division Multiple Acess

4 DGM Data Grade Medium

5 DHTML Dynamic Hypertext Markup Language

6 DNS Domain Name System

7 FTP File Transfer Protocol

8 GSM Global System For Mobile

9 HTML Hypertext Markup Language

10 HTTP Hypertext Transfer Protocol

11 IMAP Internet Mail Access Protocol

12 IP Internet Protocol

13 ISP Internet Service Provider

14 Kbps Kilobyte per second

15 MAC Media Acess Control

16 Mbps Mega Bits Per Seconds

17 Mhz MegaHertzASHOK GARG MOBILE : 9312249405


18 MIME Multipurpose Internet Mail extension

19 MMS Multimedia Message Service

20 NIU Network Interface Unit

21 NSFnet National Science Foundation Network

22 NTP Network time Protocol

23 PDA Personal data Assistant

24 POP Post Office Protocol

25 SIM Subscriber Identity Module Extension

26 SLIP/PPP Serial Line Internet Protocol/Point to Point protocol

27 SMS Short Message Service27 SMS Short Message Service

28 SMTP Simple Mail transfer Protocol

29 TCP/IP Transmission Control Protocol/Internet Protocol

30 TDMA Time Division Multiple Access

31 URL Uniform Resource Locator

32 VGM Voice Grade Medium

33 WLL Wireless Local Loop

34 www World Wide Web

35 XML eXtensible Markup Language



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