Self Learning Material. Computer Networks (BSBC-603) Course: Bachelor of Computer Applications Semester-VI. Distance Education Programme

(1)

Self Learning Material

Computer Networks

(BSBC-603)

Course: Bachelor of Computer Applications

Semester-VI

Distance Education Programme

I.K. Gujral Punjab Technical University

Jalandhar

(2)

Syllabus

I.K. Gujral Punjab Technical University

BSBC 603 Computer Networks

SECTION- A

Data communications concepts: Digital and analog transmissions-Modem, parallel and serial, synchronous and asynchronous, Modes of communication: Simplex, half duplex, full duplex, Concept of multiplexing, De-multiplexing.

Types of Networks: LAN, MAN, WAN

Network Topologies: Bus, Star, Ring, Mesh, Tree, Hybrid

Communication Channels: Wired transmissions: Telephone lines, leased lines, switch line, coaxial cables-base band, broadband, optical fiber transmission.

SECTION- B

Wireless Transmission: (Standards and Specification) Microwave transmission, Infrared transmission, Laser transmission, Radio transmission and Satellite transmission and Blue Tooth, Frequency Spectrum.

Communication Switching Techniques: Circuit Switching, Message Switching, Packet Switching.

Network Reference Models: OSI Reference Model, TCP/IP Reference Model, Comparison of OSI and TCP/IP Reference Models.

SECTION- C

Data Link Layer Design Issues: Services provided to the Network Layer, Framing, Error Control (error detection and correction code), Flow Control, Data Link Layer in the Internet (SLIP, PPP).

Types of Multiplexing: FDM, TDM, CDMA SECTION- D

MAC sub layer: CSMA/CD/CA, IEEE standards (IEEE802.3 Ethernet, Gigabit Ethernet, IEEE 802.4 Token Bus, IEEE 802.5 Token Ring)

The Network Layer: Design Issues, Routing Algorithms: Optimality Principle, Shortest Path Routing, Congestion Control Policies, Concept of Internetworking.

(3)

Suggested Books:

1. Computer Networks, Tanenbaum, Andrew, Fifth Edition, PHI

2. Data Communication and Networking, Behrouz A. Forouzan, Fourth Edition 3. Data Communication System, Black, Ulysse, Third Edition, PHI

4. Data and Computer Communications, Stalling, Ninth Edition, PHI

(4)

© IK Gujral Punjab Technical University Jalandhar

All rights reserved with IK Gujral Punjab Technical University Jalandhar

(5)

Lesson 1: Introduction to Data Communication Contents

1.0Introduction to Data Communication 1.1Components of Data Communication Analog and Digital Data

1.2.1Analog Data Representation

1.2.2 Digital Data Representation 1.3 Transmission Impairments

1.3.1 Attenuation 1.3.2 Delay distortion 1.3.3 Attenuation Distortion 1.3.4 Noise

1.4 Modulation

1.4.1 Amplitude Modulation 1.4.2 Frequency Modulation 1.4.3 Phase Modulation

1.5 Multiplexing

1.5.1 Frequency Division Multiplexing 1.5.2 Wave Division Multiplexing 1.5.3 Time Division Multiplexing 1.6 Switching

1.6.1 Circuit Switching 1.6.2 Message Switching 1.6.3 Packet Switching 1.7 Summary

1.8 Glossary

Objectives:

After studying this chapter students will understand :

 Explain the term data communication.

 Explain the components of data communication.

 Become familiar with the types of transmission medium

 Explain the modulation and its types

 Compare the modulation types

 Explain the multiplexing and its types

 Compare the multiplexing types

 Explain the switching and its types

 Compare the switching techniques

(6)

1.1 Introduction to Data communication

The process of communicating or exchanging the data between any two locations using some transmission medium is called Data Communication. In this process, data transmission is governed by certain rules and regulations. Data communication can be local or remote.If the communicating devices are in same building then the communication is local else it is remote.

The three factors that determines the efficient data transfer are:

1.Delivery:The data should be delivered to the accurate destination by the sender in a network . 2.Accurately:Accurate data should be sent to the destination.

3.Timeliness:Data should be should be delivered in time to the right destination.

1.1.1 Components of Data Communication

The basics components or elements of data communication system are as follows:

1. Message 2. Sender 3. Receiver

4. Medium or Communication Channel

Fig. 1.1: Components of data communication

(http://www.datacom2u.com/ENDataCommunication.php) A Communication system has following components:

1. Message: It is the information or data to be sent. Message can consist of text, numbers, pictures, sound or video or any combination of these.

2. Sender: It is the deviceor the systen that generates and sends that message.

3. Receiver: It is the device or computer that receives the message. The location of receiver computer is generally different from the sender computer. The distance between sender and receiver depends upon the types of network used in between.

(7)

4. Medium: It is the channel or physical path through which the message is carried from sender to the receiver. The medium can be wired like twisted pair wire, coaxial cable, fiber-optic cable or wireless like laser, radio waves, and microwaves.

5. Protocol: It is a set of rules that govern the communication between the devices. Both sender and receiver follow same protocols to communicate with each other.

1.2 Analog and Digital Data

To understand this we should know about the signal first. What is a Signal?

A signal is physical quantity which may vary with respect to time, distance, pressure,

temperature etc. Signal is used to represent some useful information. It is mainly classified into two categories:

1. Analog 2. Digital

1.2.1 Analog Data Representation

A signal which may vary continuously with respect to time is said to be Analog Signal. It can take infinite number of values in a given range. The example of analog signal is Human Voice, The analog signal may be represented in sinusoidal wave as it varies its strength

(Amplitude) continuously with respect to time(or frequency). The sound of human voice is also analog in nature because it varies continuously with respect to time. The sound of human voice can be captured in air as it is continuous in nature and can be converted into analog signals by using microphones.

(Amplitude)

(Time)

Fig. 1.2 : Analog Data Representation

An analog signal is represented in the above figure where horizontal axis will be Time(in Sec.) or Time Axis and Vertical axis will represent the strength(Amplitude).

1.2.2 Digital Data Representation

A digital signal can take finite number of values in a given range, and is derived from analog signal by using sampling. An Analog signal is divided into the number of samples to create the digital signal. The samples are decided on the basis of

(8)

t = N T (or T = t / N)

Where t is the time period of o Analog Signal

N is the number of samples required to create the Digital or Discrete Signal T is the Time interval among the samples(Sample Time)

Fig. 1.3 :Representation of Digital Signal from Analog Signal (https://www.ibiblio.org/kuphaldt/electricCircuits/Digital/DIGI_13.html) The accuracy of digital or discrete signal depends upon the number of samples. If number of samples are more than signal will be more accurate. The major advantages of the digital signal is that it can be readily stored in the computer memory which enhances the processing speed. The digital signal can be represent in binary form(‘0’s or ‘1’s)

1.3 Transmission Impairments

Whenever a signal is transmitted over a communication medium, it is prone to different types of impairments. That is signal received is never identical to signal sent because of imperfect characteristics of the channel. As a consequence, the received and the transmitted signals are not the same. The quality of analog signal detiorates due to distortion whereas errors are introduced in digital signal. The

impairments can be broadly categorized into the following three types:

1. Attenuation and attenuation distortion 2. Delay distortion

3. Noise 1.3.1 Attenuation

Either the transmission medium is guided(wired) or unguided(Wireless), the strength of the signal becomes low with increase in distance. This is known as attenuation. It means loss of energy. As signal travels the distance it dissipates the energy in form of heat. It is expressed in the form of Signal to Noise ratio i.e. It is measured in decibels units

(9)

Attenuation(in db)=10log10 (Pout / Pin) Where , Pout is power at sending end

And Pin is power at receiving end.

1.3.2 Delay distortion

This impairment usually occurs in guided media. In guided media the velocity of the signal propagated varies with frequency component of the signal which leads to delay distortion. The velocity is maximum at center where as it is reduced as the signal moves away from the center.

The various components of the frequency arrives at different points of time. And thus results in phase shift of the different frequencies.

This leads to distortion of the signal called delay distortion. Due to intersymbol interference, there is restriction on the maximum bit rate of transmission. The delay distortion can also be neutralized

using suitable equalizers.

1.3.3 Attenuation Distortion

At the receiving end, when the signal is received , it may not properly recovered or detected if the strength of the transmitted signal is very low. So, while transmitting the signal, the strength of the signal should be so high that it may be truly detected by a receiver even in the presence of noise which may get added in the channel during communication. Amplifying devices can be used to manage the attenuation occurred in the transmission line during transmission. So sometimes, attenuation may decides how far we can send a signal without using amplifier in a specified medium. Attenuation of all the frequency components present in the signal may not same. Due to this, few frequencies can pass through the medium without attenuation and some may get blocked. So, the communication media dependence on the frequency component of the signal may lead to different kind of attenuation distortion e’g; if we transmits triangular wave through any media at the output side we may not get the triangular wave because of more attenuation of the high frequency components in the connecting channel. An Equalizer circuit can be used to reduce the attenuation distortion which may help to receive the signal with good strength at the receiver end.

1.3.4 Noise

Whenever a signal is transmitted over a channel, it is liable to add noise. Noise is nothing but the unwanted signal which gets added to the original signal along with dealy distortion. Broadly we classify the noise into two categories :

I. Internal II. External

I. Internal Noise : This type of noise is generated with in the circuit. Further, Internal Noise can be of the following four types:

1. Thermal Noise

2. Intermodulation Noise 3. Cross talk

4. Impulse Noise

(10)

1. Thermal Noise :

The thermal noise is due to thermal agitation of electrons in a conductor. It is present in all the transmission medium and electronic equipments .It is uniformly distributed over the whole frequency spectrum. Therefore it is also called white noise. It can be reduced by reducing the temperature or bandwidth.

2. Intermodulation Noise

When multiple signals of different frequencies are sent on a common transmission medium, It results in intermodulation noise .It produces sum and difference components of the frequencies. For example, two signals f1and f2 will generate signals of frequencies (f1+ f2 ) and (f1- f2 ), which may interfere with the signals of the same frequencies sent by the transmitter.

3. Cross talk

It is a result of interference of signals in several conductors together in a single cable. Wires carry signal which generate electromagnetic radiation, which give rise to cross talk due to the closeness of conducting wires. Cross talk can be reduced by introducing the guard band so that the signals should not overlap with each other.

4. Impulse noise

This type of noise is completely different from other types of noises as it is non continuous in nature. It comprises of irregular pulses or noise spikes which are of of short duration generated due to lightning, sparks due to external electromagnetic disturbances. Impulse noise never effects the analog communication but effects digital data communication badly.

This type of noise introduces burst errorsin. This Noise is popularly known as Gaussian Noise.

II. External Noise :

This type of noise is produced outside the circuit. Its sources are external It is of following type :

1. Atmospheric Noise

2. Industrial Noise(Man-Made Noise) 3. Extraterrestrial Noise

1. Atmospheric noise

This type of noise is caused by lighting discharges in thunderstorms. The field strength of this type of noise is inversely proportional to frequency.

2. Industrial Noise

It is also called man-made noise which is caused by aircraft engine ignition, switchgear and electric motors, Leakage from high voltage lines etc.

3. Extraterrestrial Noise

There are various types of extraterrestrial or spice noises are present in the universe depending upon various source. Further, it is classified as :

(11)

a) Solar Noise b) Cosmic Noise Self Assessment

Q1.What is data communication?

Q2.What are various components of data Communication?

Q3.What is a signal?

Q4.How will you represent the data in analog and digital form?

Q5.Compare analog and digital signal.

Q6.Discuss various transmission impairments.

Q7.What is attenuation and attenuation distortion?

Q8.What is noise ?Discuss the various types of noise?

Q9.What is a thermal noise?

1.4 Modulation

In today’s communication era, various signals like audio, video etc. are required to transmit to remote places at every instant of time, which is not possible without the use of modulation.

Modulation is the process to superimpose and vary the characteristics like amplitude, frequency, phase etc. of carrier wave(High Frequency Sinusoidal waveform) with information-bearing signal. The information-bearing signal is also said to be Modulating signal whereas output of the modulation process is called Modulated Signal. However, modulation is also one of the fundamental aspect of any radio communication. The process of modulation is carried out in a device called Modulator.

Fig. 1.4 : Amplitude Modulation (https://en.wikipedia.org/wiki/Amplitude_modulation) The modulation is broadly classified into following :

1. Analog (Modulated Parameter has infinite value) 2. Digital(Modulated Parameter has finite value) Further, Analog Modulation is categorized as :

(12)

1. Amplitude Modulation 2. Frequency Modulation 3. Phase Modulation

1.4.1 Amplitude Modulation

Amplitude Modulation is abbreviated as AM. In it, amplitude or intensity of the carrier signal is varied in accordance with modulating or information-bearing signal whereas the phase and frequency of carrier signal remains same. AM technique is being used since 18^th Century but first recorded instance in the year 1901 by Canadian Engineer Reginald Fessenden. Its widely used in the following applications:

1. Ground to Air Communication named as Air Band Radio

2. Quadrature Amplitude Modulation(QAM) like short range wireless link(Wi – Fi) 3. Broadcast transmission

4. Single Sideband is used for High Frequency Radio links.

Advantages and Disadvantages:

Advantages:

1. Easy to implement

2. AM receivers are economical

3. Easy to design AM Demodulator circuit Disadvantages :

1. AM Demodulators are sensitive to noise.

2. Not effective in terms of use of Power and bandwidth.

1.4.2 Frequency Modulation

Frequency Modulation is abbreviated as FM. In it, frequency of the carrier signal is varied in accordance with modulating or information-bearing signal whereas the phase and amplitude of carrier signal remains same. As shown in figure below that it is only possible to change the frequency of carrier signal to get FM. The variation of frequency is known as deviation e.g; if signal deviation is + 5KHz, it means carrier frequency is moved up and down by 5KHz.FM is used for various Radio Communications applications like taxis, Mobile communication, vehicles etc. However Wideband FM is widely used in high quality transmission.

(13)

Fig. 1.5 : Frequency Modulation

(http://www.radio-electronics.com/info/rf-technology-design/fm-frequency- modulation/what-is-fm-tutorial.php)

Advantages and Disadvantages:

Advantages:

1. Less immune to noise occurred during transmission.

2. No need of linear amplifier at the transmitter end.

3. More transmitter efficiency because of use of Non- Linear amplifiers.

Disadvantages:

1. Complex demodulator circuit is used.

2. Less Spectral efficiency in comparison to Phase and Quadrature Amplitude modulation(QAM).

1.4.3 Phase Modulation

Phase Modulation is abbreviated as PM. In it, phase of the carrier signal is varied in accordance with modulating or information-bearing signal whereas the frequency and amplitude of carrier signal remains same. Phase modulation is also the basis of various another Digital modulation like phase shift Keying(PSK). However PM has some similarities

(14)

with FM, one is the derivative of other. As shown in figure below red line indicates phase at any instant whereas blue bidirectional indicates deviation.

Fig. 1.6: Phase Modulation (http://www.radio-electronics.com/info/rf-technology- design/modulation-techniques/modulation-basics-tutorial.php

3.1 Multiplexing

It is a technique to combine the various signals, may be analog or digital, together into a single composite signal over a single medium for transmission over a shared link. The number of communication channels can be increased by dividing the high capacity channels into low capacity channels by using multiplexing, so that more information can be exchanged at the same instant by different streams. Both guided and unguided media are capable of multiplexing. Towards transmitting side where various signals are combined together to form a single composite signal we use multiplexer, which transmits the signal over the shared communication link whereas at the receiving end, the signals are sorted to its originality and sent to various receivers by using the de-multiplexer.

Sometimes, the composite signal may be used to modulate the carrier signal before transmission, and can be said as modulated signal. At the receiving end, the de- multiplexer is used to demodulate or de-multiplex the modulated or multiplexed signal and sent it to the receivers. The multiplexer can be said as many-to-one means many inputs and single output whereas de-multiplexer can be said as one-to many means one input and many outputs. The concept of multiplexing can be easily understood by the following figure 1.1 where four different channels(four inputs) are used at the transmitting side and combined together into single composite signal(output of multiplexer) by using the multiplexer. The output of the multiplexer in the form of composite signal is connected to single communication channel which is further, connected to the de-multiplexer at receiving side. The de-multiplexer sorts the signals to their originality and send it to various receivers as shown in figure. The four different receivers are used in the given example.

(15)

Fig. 3.4 MULTIPLEXING (http://ecomputernotes.com/images/Multiplexing.gif) Multiplexing techniques may be analog or digital and mainly categorised as :

1) FDM - Frequency Division Multiplexing 2) WDM - Wave Division Multiplexing 3) TDM - Time Division Multiplexing 4) CDM - Code Division Multiplexing

3.1.1 Frequency Division Multiplexing

It is multiplexing technique used for analog data. In this type of multiplexing technique the entire bandwidth of the communication channel is divided into multiple logical frequency channels with smaller capacity. Each channel is allocated to individual user and every individual can exclusively access that channel for transmission as well as reception of data. All the channels are separated by guard band so that they cannot overlap each other. Guard band is the frequency which is not in use. In the multiplexer there are different carrier frequencies. The signal generated by input lines are modulated and then processed together to form a single composite signal. This signal is transferred over the link having substantial bandwidth and filters are deployed as one for each output line. The filter break downs the multiplexed signal into different consistent signals. Then these individually separated signals are processed into the demodulator which isolates these individual signals from the carrier signal and transfer them towards the output. So, we can say that FDM is an analog multiplexing technique which combines various analog signals together to result into one signal.

CDMA

(16)

Applications of FDM:

1. It is used by the telephone Companies. There, many switched or leased lines are combined into fewer but bigger channels. The hierarchal system used by AT&T. To understand this in good manner, let us consider an example where 12 voice channels are multiplexed together with each channel frequency 5KHz to create a group of higher bandwidth i.e; 12 x 5 =60KHz. Further, such type of 5-groups are multiplexed together to form a composite signal, and such group is said to be super group with bandwidth of 60 x 5 = 300KHz and 60 Voice channels.

In the next level of hierarchy, such 10 super groups are again multiplexed together to form a master group with bandwidth 300 x 10 = 3000KHz or 3 MHz with 60 x 10 = 600 voice channels.

This 3MHz bandwidth is not sufficient because of the need of the guard band, which is also required between super groups. Let us assume a guard band with bandwidth of 10KHz between the channels, we assume initially 12 Voice channels then guard band bandwidth = 12 x 100 = 1200KHz or 1.2MHz. Than bandwidth required for super group is 3 + 1.2 = 4.2MHz.

Then, further, these master groups can be multiplexed to form a Jumbo group, let us assume six master groups then bandwidth requirement for the jumbo group is 4.2 x 6 = 25.2MHz with voice channels 600 x 6 = 3600

FDM is widely used for Amplitude Modulation(AM) and Frequency Modulation(FM) radio, TV broadcasting and cellular phones

2. Radio stations make use of air to transmit their signals. All the AM radio stations use the frequency band from 530 – 1700 KHz, which is specially allocated to AM Radio . Every Individual radio station is assigned a different carrier frequency and all the signals are multiplexed into one combined signal. This signal goes to the air, a receiver receives this combined signal and keep the desired signal after filtering . Without using multiplexing, there will be single AM station able to broadcast the signal to the common communication link.

Fig. 3.6: FDM(http://www.dcs.bbk.ac.uk/~ptw/teaching/IWT/link-layer/notes.html) 3.1.2 Wave Division Multiplexing

(17)

Wave Division Multiplexing(WDM) has the capacity to use high data rate of optical fibre. As we know that the transmission cable data rate is always less than optical fibre. But use of optical link for dedicated(Point-to-Point) communication will be merely wastage of the resources, so its advisable to use multiplexing for optimized cost. However, WDM is some what identical to Frequency Division Multiplexing(FDM), but the Multiplexing and demultiplexing used in WDM includes optical signal with high range of frequencies. Even WDB seems complex, but the basic process applied in it is quite simple, number of light sources are combined together to form a composite light signal at the multiplexer and reverse is done at the de-multiplexer means one composite light signal is separated into individual light sources. It is also used for analog data but for fiber optics cable which carries optical signals.

Light has different wavelength emitting different colors. In this multiplexing optical signals of different wavelengths with varying energy levels are combined with the help of optical transmitter having multiplexer built in it and optical receiver is used to receive the signal , diverges the beams based angle of indigence and frequency thus bifurcating the signal and send it to the appropriate receiver. Bandwidth of single fibre band is about 25000GHz, therefore many channels can be multiplexed together on long routes. The major application of WDM is used in Synchronous Optical Network(SONET), a standard for joining fibre optics, and various optical fiber links are multiplexed and de-multiplexed as per the requirement of the network.

3.1.3 Time Division Multiplexing

Time Division Multiplexing(TDM) is mainly used for digital signals but sometimes analog signals can also be used in it. In this multiplexing technique, the whole bandwidth of the channel is allocated to the user on the time basis. Each user can use the channel exclusively to transmit the data for specified period of time. User can send the frames which carries Digital signals. The size of the frame can be said as equivalent to time slot, means in a given time slot a frame of an optimal size can be sent on the communication channel. The Multiplexer and De-multiplexer used in TDM should be properly synchronized with each other, and should switch to the next user simultaneously, which is the basic need of the TDM. This is more clear by the following figure, suppose there is communication between transmitter and receiver, channel A sends the frame, at the other side de-multiplexer connects the media to channel A for proper frame delivery. This process will remain continue till then time slot of channel A is not being expired, as soon as it happens, the side switches to channel B. Frames from various channels propagate to the communication link or media in interleaved manner.

Self Assessment Questions : Exercise 1 Q1) What is multiplexing?

Q2) What are the applications of FDM?

Q3) What is the use of WDM?

Q4) What is the need of the modulation?

(18)

Fig. 3.7: TDM(http://campusnikalo.blogspot.in/hhhhhhhhhhhhhhhhhhhhhhhhhhhhb hn 2013/02/multiplexing-types-with-advantages.html)

TDM is classified into following ways:

 Synchronous Time Division Multiplexing

 Statistical Time Division Multiplexing 3.1.3.1 Synchronous TDM

In this multiplexing technique, individual units are considered which are created by dividing the data flow of each input connection. A unit may be single bit, single character or single block of data . A sequence of data units in single round sent by each input connection is gather together into a frame, One time slot is provided to each input channel for one data unit to be sent . After one data unit from one channel, the time slot is provided to next channel for the transmission of one data unit by that channel. When data units from all input channels are received they constitute one frame. In this way, the time slot continues to route at input lines. Each input connection has a finite time slot or allotment at the output side even that input connection is in idle state. The output link always have faster data rate in comparison to input link or connection. Normally, we assume ‘n’ times faster than input connection for proper flow of the data.

Whereas n is the number of input channels.

Interleaving: When the switch has to open in front of device at that time device has an chance to send the specified amount of data on to the channel or path. The switch always open in front of device in specified order with constant data rate, this process is known as interleaving. In Time Division Multiplexing(TDM) two switches are considered, one at the multiplexing side and other at the demultiplexing side, both are synchronized with each other and rotate at the same constant speed.

(19)

Fig:3.8: Synchronous TDM(www.daenotes.com/electronics/communication-system/multiplexing) Empty Slot:

As shown in fig., the frame 4 has three slots, this frame is sent over the path from multiplexing side whereas towards the demultiplexing side which is already synchronized with multiplexer the same frame 4 is received containing two slots empty units i.e; without data, this is called empty slot. So, we can say that Synchronous TDM is not much efficient as the slots of frame 4 in the output side will remain empty.

Data rate Management:

As we discussed that we consider that all the input lines transfer the same data rate, but sometimes its not feasible that all the input lines should send the data at the same rate., so, there is a need to manage the data rate by using following strategies:

 Multilevel Multiplexing

 Multiple-slot Allocation

 Pulse stuffing

Multilevel Multiplexing:- This strategy is used when an input line has data rate of multiple of other lines as shown in fig. below, data rate of input lines is multiple of 30kps, as we have two inputs lines of data rate 30 kbps and another two inputs lines has data rate of 60 kbps. We can multiplexed the first two input lines together to give data 60Kpbs which is also equal to other two input lines. Again multiplexing is done at the next level and data rate produced as 60 x 3 = 180 Kbps.

(20)

30Kpbs 60Kpbs

30Kpbs 180Kpbs 60Kpbs

60Kpbs

Fig. 3.9: Multilevel Multiplexing

Multiple-slot Allocation:- As a name suggests that Multiple-slot Allocation means a slot can be provided to a frame at the input side by using serial to parallel converter. It is more clear by the following fig. when we have an input line that has a data rate that is multiple of data rate of rest of input line, them it is more efficient to called more than one slot in a frame to a single input line. As shown in fig., where each input line has data rate 60Kbps, whereas first input line data rate is divided into two 30Kbps by using serial to parallel converter and finally at the output side data rate is 180Kbps.

60Kbps 30Kbps 30Kbps

60Kbps 180Kbps

60Kbps

Fig. 3.10 : Multiple-slot Allocation

Pulse Stuffing: Till now we assume that data rates are integer multiple of each other, but sometimes its also not possible that all the data rates are integer multiple of each other, this problem can be overcome by adding extra bits to that stream and process is known as Pulse Stuffing or Bit Stuffing or Bit Padding. Which is shown in the fig. given below:

(21)

54Kbps 60Kbps

60Kbps 180Kbps

60Kbps

Fig.3.11 : Pulse Stuffing

Frame synchronizing: The main problem which occur in the TDM is the synchronization in between the multiplexer and the demultiplexer. Sometimes, it may happen that multiplexer and the demultiplexer are not properly synchronized, so data can be received at the wrong channel. To overcome this problem, one or more extra bits are also being added at the beginning of the frame known as framing bits. Tits may vary from frame to frame, and allows the demultiplexer to get synchronized with the incoming bit stream and easy for demultiplexer to separate the time slots.

Digital Signal Service:

Telecommunication companies mainly deal in telephones implement TDM through some hierarchy of digital signals, may be called as digital hierarchy or digital signal service .

 DS-0 : A channel of 64 kbps.

 DS-1 : It is a 1.5 Mbps and 1.5M / 64K = 24 times of overhead.

 DS-2 : It is a 6.3 Mbps service, can be used to multiplex 96 DS-O channels and four DS-1 channels, or combination of both.

 DS-3 : It is a 44.4 Mbps service, can be used to multiplex 672 DS-O channels, 28 DS-1 channels, 7 DS-2 channels, or a combination of all.

 DS-4 : It is a 274.2 Mbps service, can be used to multiplex 4032 DS-0 channels, 42 DS-2 channels, 6 DS-3 channels, or a combination of all.

 T Lines:

T -lines(T1-T4) are used by Telephone companies for implementation of digital signals.

T- lines have with capacity to match DS1-DS4 service’s data rates . DS-0 is not connected, so it does not offer any service, T1 is used for implementation of DS-1, T2 is used for the implementation of DS-2, T3 is used for the implementation of DS- 3 and so on DS-0.

DS-1 line needs 8 Kbps of overhead. To understand this more clearly how the overhead is being calculated, we take an example of a 24 voice channel frame. So total bits required 24 x 8 = 192 + 1

=194, one extra bit is used for synchronization of multiplexer and demultiplexer.

Bit Stuffing

(22)

E Lines: T Lines in European system is said to be E lines, even both the systems are conceptually identical but differ in their capacity.

3.1.2 Statistical Time Division Multiplexing:

As we have already discussed that, in TDM, time slots are allocated even there is no information to send, which is a simply a wastage of the bandwidth. This problem is being overcome by the Statistical Time Division Multiplexing(STDM). This is a technique which allows various users to be multiplexed on the same channel even more than the capacity of the channel which it can afford. In this technique, time slots are not permanently allotted to the users, its dynamically allocated on demand. That’s why this technique is also known as Intelligent TDM. Each TDM channel is also called as an I/O line. Multiplexer

repeatedly checks the input buffer of the channels, as soon as the frame is filled, it is immediately

transferred. It is clearly understood by the following fig., the four Input lines are there and each frame has 3 slots. Frame 2, 3 and 4 has one slot empty, but during the transmission, no frame is transferred with empty slots. It waits as soon as all the three slots in the frame are occupied, multiplexer checks each input line in a Round Robin fashion and sends for transmission towards the output

Addressing: The reassigned relationship along with synchronization between input and output will act as address. So, we can say that Station Multiplexing does not require addressing. The input and output does not have any fixed relationship with each other because there are no reserved slots are available. We need n bit to define N different outputs i.e; N = 2ⁿ e.g; for 16 different output lines we need address of 4-bit as : 16 = 2ⁿ or 2⁴ = 2ⁿ, this shows that N = 4.

Slot Size: In Statistical Time Division Multiplexing, a slot may contain data and address, So the address also plays the significant role in data transmission. The ratio of data size to address must be in some proportion for effective transmission.

No synchronization Bit: The major difference between Statistical and Synchronous TDM that Statistical TDM does not require additional synchronous bit, so frames are not required to be synchronized in TDM.

Bandwidth: In statistical TDM, if the capacity of every channel is being added, then it will definitely exceeded by the capacity of the link. So, the designers of Statistical TDM explains the statistics of the load based on the capacity of the link.

(23)

Fig. 3.12 : Synchronous and Statistical TDM

(https://plus.google.com/104155985791429645987/posts/UesYxS3JemP

3.2 Comparison of FDM Vs TDM

S.No. FDM TDM

1. It is primarily used for analog data

It is primarily used for digital data signals

2. No Synchronization is required Synchronization is must 3. FDM is not flexible TDM is very flexible 4. It requires complex circuitry

both at transmitting and receiving ends

Less complex circuitry will work

5. No Transmission Delays Random transmission delays will be

(24)

there

6. Very Expensive Moderately expensive 7. Resources and lines are not

efficiently used

Resources and lines are efficiently used

8. There is severe problem of crosstalk and noise

Less severe problem of crosstalk

9. All the channels will be equally effected by fading

Only few channels will be effected by fading

10. More flexible Less flexible

3.3 Code Division Multiplexing/Code Division Multiple Access

Code-Division Multiple Access is abbreviated as CDMA. It is a channel access method used by Radio communication technologies widely use this channel access method. It comes under the category of multiple access where numerous transmitters can transmit the data parallely over the single communication medium with use of optimal bandwidth. CDMA is a type of multiplexing which is used in wireless communications like Second and third-generation, abbreviated as 2G and 3G. CDMA technology is also used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands.

A spread spectrum technique is used in CDMA, which is quite useful in converting Analog-to- Digital (ADC) signal . As shown in firg., an audio signal is converted into its equivalent binary form. The frequency of the this converted( from audio to binary) signal which is communicated over the transmission media is varied according to the defined pattern in form of defined codes.

So, it can easily be intercepted by a receiver over the communication link, whose frequency response is already programmed with the same code. In USA, data transmission speed is 14.4 Kbps in single channel whereas 115 Kbps in an eight-channel form. Whereas, Wideband CDMA and CDMA2000 may transfer data many times faster than other available CDMA standards.

Self Assessment Questions : Exercise 2

Q1) What do you understand by the term pulse stuffing in TDM?

Q2) What do you mean by slot size in STDM?

Q3) What is Multilevel Multiplexing?

(25)

Fig. 3.13 CDM(http://www.ustudy.in/node/7098)

Characteristics of CDMA:

 The transmission bandwidth is much greater than the minimum required bandwidth in Spread Spectrum technique

 Spread Spectrum technique is used because of its high security.

 Narrow band interference is easily rejected in CDMA. As small portion of the spread spectrum signal is affected which can also be removed by using notch filter with minimum loss of original signal.

 Rake receivers are used by CDMA devices. Rake receiver can exploit multipath delay components which will be quite useful to improve the performance of the system.

 Each cell uses the same frequency because of the channelization which is done by using the pseudo-random codes.

 Minimum frequency planning is required in CDMA system because of reuse of the same frequency in every cell

 More reliable and high quality signals because of the use of soft hand off.

Advantages of CDMA techniques:

 It makes effective use of fixed frequency spectrum as resource allocation very easy.

 It is also compatible with all other GSM operators so its beneficial for its applications in roaming.

 Hackers also find tough to decrypt the code.

 When the signal is handed off from one site to the another the user can never sense the change of the cell cite as signal quality is very high.

 Users can be easily added, modified and deleted from the cell site .

Disadvantages to using CDMA:

(26)

 The overall quality of service decreases with increase of users

 Self-jamming

 Uses of CDMA:

 GPS (Global Positioning System) and Reliance Telecommunication in India

3.5 Glossary

 Multiplexing - Scheme that allows multiple logical signals to be transmitted simultaneously across a single physical channel

 Modulation - Process to superimpose original signal onto carrier signal

 AM - Process to change amplitude of carrier signal with respect to intensity of the signal

 FM - Process to change frequency of carrier signal with respect to intensity of the signal

 PM - Process to change phase of carrier signal with respect to intensity of the signal 3.6 Answers to Self Assessment Excercises

Answers to Self Assessment Questions (Exercise – 1)

Ans 1 : It is a technique to combine the various signals, may be analog or digital, together into a single composite signal over a single medium for transmission over a shared link. The number of communication channels can be increased by dividing the high capacity channels into low capacity channels by using multiplexing, so that more information can be exchanged at the same instant by different streams. Both guided and unguided media are capable of multiplexing.

Ans 2 : It is used by the telephone Companies and Radio Stations.

Ans 3 : WDM is used in Synchronous Optical Network(SONET), a standard for joining fibre optics, and various optical fiber links are multiplexed and demultiplexed as per the requirement of the network.

Ans 4 : Without modulation we can not send the signal to applicable places. The need can be explained as :

1) Antenna Length :

Velocity of light(c) = wavelength * frequency Wavelength = c / frequency

Wavelength = 3 x 10⁸ / frequency

By substituting the value of frequency e.g; 20 KHz we will calculate the wavelength = 15000 m, so it is very tough to construct a huge antenna.

2) Operating Range : Energy of signal is directly proportional to frequency. Larger the frequency than greater the energy possessed by signal. The frequency of audio signals is quite low, so its not possible to transmit audio signal directly into the air, it will get lost in the way. So, practical solution of this problem is to mix the audio signal with high frequency carrier signal than it should be transmitted into the space to the desired long distances.

(27)

Answers to Self Assessment Questions (Exercise – 2)

Ans 1: The data rates are integer multiple of each other, but sometimes it is also not possible that all the data rates are integer multiple of each other, this problem can be overcome by adding extra bits to that stream and process is known as Pulse Stuffing or Bit Stuffing or Bit Padding.

Ans 2 : a slot may contain data and address, So the address also plays the significant role in data transmission. The ratio of data size to address must be in some proportion for effective transmission.

Ans 3 : when an input line has data rate of multiple of other lines as shown in fig. below, data rate of input lines is multiple of 30kps, as we have two inputs lines of data rate 30 kbps and another two inputs lines has data rate of 60 kbps. We can multiplexed the first two input lines together to give data 60Kpbs which is also equal to other two input lines. Again multiplexing is done at the next level and data rate produced as 60 x 3 = 180 Kbps.

Self Assessment

Q1.What is modulation? What are various types of modulation?

Q2.What is multiplexing and demultiplexing? Compare FDM and TDM.

Q3.What is switching? What are its types? Compare datagram and virtual circuit Switching.

1.6 Switching

When the data is send on WAN ,public network or internetwork it can follow different paths from source to destination .So it is the process in the connections and path to be followed for the data transfer is decided. In this multiple switches and nodes are joined together to form a path for data to be transferred. Every switch have some incoming port and outgoing port. The data is received at incoming port whereas it leaves for the destination from outgoing port. This technique in which data keeps on moving from one switch to another till it reach the destination node it is called switching. Switching can be classified into three type

1. Circuit Switching 2. Message Switching 3. Packet Switching

1.6.1 Circuit Switching: Circuit switching follows connection oriented approach in which circuit is set up before the data transmission takes place. There is point to point dedicated communication path between two end points i.e; source and destination. A path to be followed by the data is known in advance. The circuit is established and maintained through the entire session till the data transfer is complete. All the packets of the same traffic will follow the same route to the destination whichever is followed by first packet of the traffic. After the transmission is over the circuit is released .The transfer mode involves following three phases

 Establish a circuit

 Transfer the data

 Disconnect the circuit

(28)

Circuit switching ensures guaranteed delivery of data with no delay because of dedicated path. It also leads to wastage of resources as path will remain dedicated even if there is no data to send.

It may take long time to establish the connection. The best example for circuit switching is telephone networks.

Fig. 1.10 :Circuit Switching (http://www.slideshare.net/tameemyousaf/switching- techniques)

1.6.2 Message Switching

In Message switching there is no dedicated path between sender and receiver. Each message is treated as independent unit of data transfer. The message is transmitted over the internetwork. Any intermediate machine which receives this message ,stores it and then if it finds the next machine idle only then it will forward the message to next node.The messages can travel through any node and will assemble at the destnation. If the next machine is busy or does not have enough resource to process large size message, the message is stored in the switch and waits.The best example for message switching is telegram.Message switching provides efficient traffic management by reducing congestion in the network and it can also share the channel bandwidth. This technique is not suitable for voice and video traffic due to delay at intermediate nodes.It may also require large buffer space to process large messages.

(29)

Fig.1.11: Message Switching (http://itmcp.com/message-switching/) 1.6.3 Packet Switching

In this type of switching the whole message is broken down into smaller fixed size units called packets. Header is added to the packet which contains the information about the source and the destination address It also contain the address of the next hop. All the individual packets take the individual path to reach their destination. There are two major advantages of packet switching first the bandwidth is reduced by splitting data onto different routes. Second if one link goes down then the then the other routes can be used to send the packets. In this the packet size is fixed so it can be stored in switching element itself.The priorities are assigned to the packets and they are stored and forwarded according to their priority.The packet switching can be of two types:

1. Datagram packet switching.

2. Virtual circuit packet switching 1. Datagram Switching:

In this method a message is divided into small packets .Each packet having a given separate address which move independently through the network. The sequence numbers and and destination addresses are appended to the packets in advance.This information is gathered by exchanging the control signals between sender, network and the receiving terminal.

(30)

Fig.1.12: Datagram Switching

(http://computernetworkingsimplified.com/physical-layer/overview-circuit- switching-packet-switching)

2. Virtual Circuit Packet Switching

This type of switching establishes a logical path between the sender and the receiver which is known as virtual circuit. The sender enters into an agreement of quality of service such as message size, the path to be taken etc. Once the Virtual circuit established the all the packets belonging to same traffic will follow the same route. So delay is reduced and packet is routed whenever required. With this technique bandwidth is increased as many devices can communicate through the network channel.Packet switching do suffers from drawbacks.Switching elements do require more RAM and processing power.Packets can be easily lost on the way .

(31)

Fig. 1.13: Virtual Circuit Packet Switching (http://computernetworkingsimplified.com/wp-

content/uploads/2013/11/packetswitching.jpg) Self Assessment

Q1.What is modulation? What are various types of modulation?

Q2.What is multiplexing and demultiplexing? Compare FDM and TDM.

Q3.What is switching? What are its types? Compare datagram and virtual circuit Switching.

1.7 Summary

 The process of communicating or exchanging the data between any two locations using some transmission medium is called Data Communication. The basic components or elements of data communication system are Message, Sender, Receiver and Medium or Communication Channel

 A signal is physical quantity which may vary with respect to time, distance, pressure, temperature etc. Signal is used to represent some useful information. It is either Analog or Digital

 The quality of analog signal deteriorates due to distortion whereas errors are introduced in digital signal. The impairments can be Attenuation and attenuation distortion,Delay distortion and Noise

 Modulation is the process to superimpose and vary the characteristics like amplitude, frequency, phase etc. of carrier wave(High Frequency Sinusoidal waveform) with information-bearing signal. The information-bearing signal is also said to be Modulating signal whereas output of the modulation process is called Modulated Signal.

 Multiplexing is a technique by which multiple streams of analog and digital data can be simultaneously transmitted on a shared link. Using multiplexing we can increase the number of communication channels by dividing the high capacity of transmission media into low capacity channels so that they can be shared by different streams at same instant of time.

 Switching is a technique in which data keeps on moving from one switch to another till it reach the destination node it is called switching. Switching can be classified into three type

1. Circuit Switching 2. Message Switching 3. Packet Switching

1.8 Glossary

(32)

a) Analog Transmission:Signal transmission over wires or through the air in which information is conveyed through variation of some combination of signal amplitude, frequency, and phase.

b) Attenuation:A loss in the amplitude or strength of a signal due to an interaction with the signal's media. Generally expressed in decibels.

c) Protocol:In networking, a specification of the data structures and algorithms necessary to accomplish a particular network function.

d) Communication: Transmission of information.

e) Network: The infrastructure that supports electronic data exchange

f) Multiplexing: Scheme that allows multiple logical signals to be transmitted simultaneously across a single physical channel.

References

1. Computer Networks, 4th Edition, Pearson Education by Andrew S. Tanenbaum 2. Data Communication & Networking, 4th Edition, Tata McGraw Hill. By Behrouz A.

Forouzan.

Model Questions :

Q1 : What is multiplexing? Explain its various types.

Q2 : Compare FDM and TDM.

Q3. Explain the different types of TDM.

Q4: What do you understand by the Interleaving in TDM.

Q5: Describe CDMA along with its characteristics.

(33)

LESSON 2

Lesson-2 Types of network

Structure of the lesson 2.0 Objective

2.1 Introduction 2.2 LAN

2.3 MAN 2.4 WAN

2.5 Wireless Network 2.6 Internetworks Layer 2.7 Protocols

2.8 Interfaces and Services 2.9 Summary

2.10 Answers to check your progress/self assessment questions 2.11 References/Suggested readings

2.12 Model Questions 2.13 Glossary

2.0 Objective

After studying this chapter student will able to:

 Explain different types of network

 Identify the wireless network and their uses

 Identify the functionality of internetworks layer

 Understanding about protocols, interfaces and services 2.1 Introduction

When we discuss the topic of networks, there are three main types of network: local area network (LAN), metropolitan area network (MAN), and wide area network (WAN). The type of network is defined on its size, distance, its ownership and its physical architecture.

(34)

Fig. 1 Types of Network 2.2 Local Area Network (LAN)

LAN stands for local area network. A local area network (LAN) is a computer network that established in limited area such as college building, school, or residence. The maximum range of the local area network is near about 1km. The speed in the local area network is 10.0Mbps that is quit higher than WAN and MAN. The wired LAN requires the wire to connect the different computers with each other, but in the case of wireless LAN a mobile user can easily connect with a local area network (LAN) through a wireless (radio) connection. (As in Fig.2)

The information and resource sharing is easy in case of LAN. LAN technology connects people and machines within a site. In LAN all the computers are connected with a same cable. In LAN the topologies such as Bus, Ring, Star, and Tree etc. are used. According to the requirements of an organization and the type of technology used, a LAN can be as simple as two machines and a printer in any office or home or it can expand throughout a office along with voice, sound and video peripherals.

Network

Local Area Network Metropolitan Area Network

Wide Area Network

(35)

Fig. 2 Local Area Network 2.2.1 Components of LAN

Each pc of the local area network, which might be a PC, a barcode reader or an application, will work as autonomous instrumentation; however they're connected to a central dominant unit, through that they will communicate (exchange knowledge, share software package or hardware) with alternative computers of the network. The every digital computer will act severally, they're ineffective of dominant the activities of alternative stations of the network.

(a) Communication medium: the medium which connects all the computers and other peripheral devices.

(b) File server: a computer which is responsible for providing shared access to a main storage device.

(c) Print server: a computer which is responsible for providing shared printing services.

(d) Gateway: a computer providing access to other networks.

(e) Workstation: a computer used in network.

Local Area

Network

(36)

4.3.2 TOPOLOGY :It is arrangement of the network either physically or logically. Computers can be physically arranged by using wires or logically arranged with help of satellite communication. There are following types of topologies

1.Bus 2.Star 3.Ring 4.Mesh

Bus: A linear bus topology consists of a single cable with a terminator at each end. All nodes like server, workstations and peripherals are connected to the linear cable using a drop cable. In this topology one node act as a master that is allowed to transmit and others receive. If more than one machine want to transmit then there may be conflict then arbitration mechanism is used to resolve the conflict.

Fig.4.2: Bus Topology (http://homepages.uel.ac.uk/u0330814/bus.html) Advantages of a Linear Bus Topology

 Peripherals can be connected easily to a linear bus.

 It is easy to install and require less cabling Disadvantages of a Linear Bus Topology

 Limited no. of devices can be attached to main cable

 The whole network shuts down if the main cable breaks at certain point.

 It is difficult to diagnose the problem if the whole network shuts down.

Star

In this topology each node is connected directly to a central network hub, switch, or concentrator . The data passes through the hub, switch, or concentrator before going to its destination. The hub, switch, or concentrator manages and controls all functions of the network. It also works like a multiport repeater .

(37)

The star can be commonly configured with twisted pair cable. It can also be configured with coaxial cable or fiber optic cable.

Fig. 4.3: Star topology (http://fcit.usf.edu/network/chap5/chap5.htm) Advantages of a Star Topology

 It is easy to configure a star topology.

 Nodes can be easily connected or removed without disrupting the network.

 It is easy to diagnose the faults and rectify it.

Disadvantages of a Star Topology

 It requires more cable length .

 If the central hub, switch, or concentrator fails, all the connected nodes get disabled.

 It is more expensive because of the cost of connecting devices etc.

RING TOPOLOGY

In ring topology the computers are connected together to form a ring. Each system passes the data to its successor after receiving from its predecessor . The data flows unidirectionally in a circular manner in ring ,either clockwise or counter clockwise. It works on the mechanism of token passing. Any system in a ring which want to transmit data requires to acquire token, modifies it ,adds data and address to it .Afterwards it is retransmitted. Every system in a ring will get this token one by one until the designated address matches. Once the address is matched ,the data is copied onto that machine. Thereafter the token is released.

Fig. 4.4: Ring Topology (http://www.louiewong.com/archives/166)

(38)

ADVANTAGES of RING TOPOLOGY:

a. It ensures speedy transmission of the data.

b. It is easy to install and maintain.

c. All the participating systems get equal chance to transmit the data DISADVANTAGES of RING TOPOLOGY

a.The failure of one system can lead to failure of the whole network . b. It is difficult to diagnose a fault.

c. Adding or removing a device is not possible without disturbing the entire network.

MESH TOPOLOGY

STRUCTURE of MESH TOPOLOGY

In mesh topology redundant and separate cabling is done to connect every system to every other system on the network, providing a dedicated communication path between two connected system. Here when one link fails it is taken over by other to take over the load. The data from the sender is directly sent to receiver because each system has individual and separate pair of wires.

Fig. 4.5 : Mesh Topology(http://webpage.pace.edu/ms16182p/networking/topologies.html) ADVANTAGES of MESH TOPOLOGY :

a. If one link fails it does make any effect to other nodes.

b. Easy to detect the fault because there is point to point link between two nodes.

c. There will not be any congestion because of fully connected network

(39)

DISADVANTAGES of MESH TOPOLOGY:

a. Complex to install and maintain.

b. Very Expensive.

c. Requires lot of cable so high cost is involved

4.3.3 CATEGORIES OF COMPUTER NETWORK

Computer networks can be categorized based on the size as well as their purpose.

The size of a network can be expressed in terms of the geographic area they occupy and the number of computing system that forms the network. Networks can cover anything right from a few devices within a single room to millions of devices that are across the entire globe.

Some of the different networks based on size are:

 Local area network, or LAN

 Metropolitan area network, or MAN

 Wide area network, or WAN

Some networks are made specific to serve a particular purpose. Some purpose based networks are:

 Storage area network, or SAN

 Enterprise private network, or EPN

 Virtual private network, or VPN 2.5 Wireless Network

Wireless network means “Network without wires”. A wireless network allows people to communicate and access information and applications without wires. Wireless networking is the new face of networking. The wireless network allows people to extend their communication from one place to the other place.

The working of the wireless network is similar to the wired network like the normal networks but the difference is that in the wireless network there is no use of wires as compared to wired network. They can use the unguided transmission medium for the transmission.

2.5.1 Types of Wireless Network

WLANS: Wireless Local Area Networks

WLANS is similar to the LAN, the difference is that in WLANS there is no use of wires form communication. In WLAN the user makes the temporary connection for communication with the help of access point etc. The area covered by the WLAN is similar to the LAN.

(40)

WPANS: Wireless Personal Area Networks

In WPANS the user makes the personal network with a short range of 20-30 feet. For making that network the users use the options like Bluetooth or infra red. In the case of infra red it requires direct line of site and the range of infra red is very short.

WMANS: Wireless Metropolitan Area Networks

In WMAN the user connect different WLAN into the network. The communication area is wider as compared to the WLAN.

WWANS: Wireless Wide Area Networks

WWAN is similar to the WAN. It can cover large geographical area like city, country etc. This can be achieved with the help of satellites systems and antenna. These satellites systems and antenna can be managed by the ISP.

Comparison of Wireless Network Types:

Type Coverage Performance Standards Applications

Wireless

PAN Less area restrained Using Bluetooth, infra red No wire required

Wireless LAN

In same building or office

More Access point, Hiper LAN Wire free network

Wireless MAN

Covers

complete city More WIMAX, broadband wireless

communications standards Required less wires Wireless

WAN universal Less 2G, 3G, and 4G Wire free access of

internet

Table-1 Comparison of wireless network types

(41)

2.5.2 Advantages of wireless network (i) Increased wireless access and association

 Move from one place to other with same network

 Worked with other users in affected manners

Users while using the wireless LAN can move from one place to the other place with the same network access. Assuming all users who use the wireless LAN either in that block or in the other block they all use the same applications and files that are used by the other users.

(ii) Better receptiveness

 Provide the required information at the same time

 Provide improved users services

By using the same network by all the users they can easily provide the solution for the customer’s quires and problems. This can be improved by using the wireless network by the users. For example: A person check online status of the company by moving in any block or department of the company with the help of wireless network.

(iii) Improved and easy access of information

 Covered every location

 Enhance productivity

Wireless network covered every location that defined within the boundaries. The access of the network is available at every location under the specified boundaries. The customer’s quires response is available in quick time.

(iv) Easy to expand the network

 Easy to add new users

 Expansion of network is economical

The addition of the new user is easy in the network and by the same time of adding that user in the network, it will start using the facilities provide by that network. The users can easily move and add in the network without any cost, because there is no need of extra wires to add new user.

(v) Improve guest entries in the network

(42)

 Provide safe network access for the guest users

Everyone interested in the safe network access. A wireless network allows you to provide a safe network access to the guest users like customers, business partners etc. A safe communication means the customers easily share and exchange the data on the network.

2.6 Internetworks Layers

Every network is organized with set of different layers. These layers are build one upon the other. Each layer has different from the other layer and have a different specific set of operations.

The layer functions are carried by layer entity that may be a hardware or software.

The internet layer is a combination of methods, protocols and specifications that are used to send the packets from sending host through the network boundaries to the destination host. The main function of the internet layer is to forming an internet or facilitates internetworking, means connecting multiple networks with each other through gateways.

(43)

End system

Functional layers

Fig. 5 Layered architecture of an end system 2.7 Protocols

Protocol refers to the set of rules and regulations are used by someone. Basically the protocols used in networking means how the networking is proceed in between the different computers. A number of protocols used by a network and one protocol per layer is called protocol stack. The communication occurred between devices through network is run by some specific set of rules that called communication protocol standards. The rules can be expressed by data structures and algorithms in digital computer systems. The protocols are made in groups instead of making a single protocol that is called suits or families. In those suits all the protocols do their defined work. By working in collaborative environment these protocols solve the complete problem.

Layer N

Layer N-1

Layer 1

Interconnection Medium

Self Learning Material. Computer Networks (BSBC-603) Course: Bachelor of Computer Applications Semester-VI. Distance Education Programme