Digital Modulation

BCA -DDU CHINTAN SIRDigital Modulation

In digital modulations digital signals are modulated. Binary signal is has

two different value.

1 → H → T → on

0 → L → F → OFF

There are three type of digital modulation

1. ASK → Amplitude shift key

2. FSK → Frequency shift key

3. PSK → Phase shift key

What happens if value is 1 & 0

Ask

0 → no signal

1 → Carrier signal

Fsk

1 → carrier signal

0 → carrier signal with 180° phase shift.

NARAYAN XEROX (NXC) 1

BCA -DDU CHINTAN SIRASK

In ASK whenever source signal is 1. the output is same as carrier signal

and when it is zero there is no signal

FSK

In FSK whenever source signal is 1 the carrier signal with same frequency

will pass for zero signal with different frequency is generated.

PSK

In PSK whenever source signal changes the value from 1-0 or 0-1 th signal

is shifted by 180°.

Shift key

Source signal works as a key for carrier to shift amplitude, frequency and

phase so, it is called shift key.

Advantages of Digital modulation

1. Noise is reduced

2. Distortion is less

3. Power efficiency more

4. Easy to understand

5. Circuit designing is simple.

6. Error detection is easy

Disadvantages of Digital modulation

1. Signal must be converted into digital the cost of this conversion is high

2. It requires more band width.

Combined Modulation (AM – FM)

About figure

indicates how AM and FM types of modulations are combined. For part A and B


BCA -DDU CHINTAN SIRfrequency remains same but the amplitude is changing do it is AM. For part B

and C Frequency is changing but the amplitude remains same. So it is FM. For

part C and D again frequency is same but the amplitude is changing so it is AM.

Combined modulation is used to reduce the were and distortion and to increase

change .

Digital Code

Digital codes are used to represent the binary or digital signal. There are

mainly three types of digital codes.

1. ON/OFF codes RZ (Return to zero)

NRZ (Non – Return to Zero)

2. Polar code RZ

NRZ

3. Bipolar code

Represent a binary signal using various digital code for following binary

sequence :

ON / OFF


BCA -DDU CHINTAN SIRIn ON/OFF code each ‘1’ is represented by a pulse for each ‘O’ there is no

pulse.

∅ →

1 → Pulse

2 → No pulse

In RZ [Return to zero] after representing each pulse come back to zero while in

NRZ. If consequite ‘1’ ‘S’ are there then don’t return back to zero

Polar

In polar code each ‘1’ is represented by positive pulse while each zero is

represented by –ve pulse

1 = (+ve pulse)

0 = ( - pulse)

In RZ after representing each ‘1’s & ‘0’ come back to zero line. In NRZ If

there are consequiteve ‘1’s or ‘0’s don’t come back to 0 line. Return back to

zero if the value is changing from 0 → 1 or 1 → 0.

Bipolar code

In Bipolar code ‘1’ is represented by either +ve or –ve pulse and for zero

no pulse

For first 1 = use positive pulse while for the next one use pulse

and so on.

Represent following Binary sequence using various digital codes.

“1110011100”

“1011010111”


BCA -DDU CHINTAN SIR

Factors for selecting or designing the codes

1. Error detection should be there NARAYAN XEROX (NXC) 5

BCA -DDU CHINTAN SIR2. User must able to correct the errors

3. Power requirement must be as small as possible

4. Band width must be as small as possible.

Demodulation

The process of separating source signal from modulated signal is do-

modulation.

How to demodulate FM signal.

PLL (Phase Locked Loop) is used for demodulating of FM signals

The demodulation is always at receiver side.

Multiplier

F1-F2 (source signal)

FM O/p

Carrier signal

LPF → Low Pass Filter

VCO → Voltage Control Oscillator

In PLL as a input signal, frequency modulated signal is applied.

PLL is made up with three main components

1. Multiplier

2. LPF (Low Pass Filter)

3. VCO (Voltage Control Oscillation)

Multiplier multiplies two different frequencies and as a result it gives, sum

frequency and different frequency.

Low pas fitter is used to pass law frequency only means sum frequency is

blocked and different frequency

VCO is used to solve any type of errors generated in output signal it

generates output frequency according to input voltage.


X LPF

VCO


Difference between syncronus and Asynoronus modulation

Syncronus Asyncronus Sender & receiver will use same

clock signal

There is no chance of data loss due

to same clock signal

‘Sync’ characters are not required.

Sender has to send clock signal with

the message

It is difficult to design

The cost is high

In synoronus it is reliable

Sender and receiver will use

difference clock signal

There may be chance of data loss

due to different clock signal

‘Sync’ characters well used to avoid

data loss

Sender will not require to send clock

It is simple to design

The cost is low

It is not reliable

Multiplexing copy


U1

U2

U3

U4

U1

U2

U3

U4

U5

U6


Chanel

Dif. : The process of sharing a single or common channels by multiple user is

known as multiplexing

Factors for designing multiplexing

1. Type of channel used

2. No of users

3. Amount of data to be transmitted

4. Bandwidth of a channel

5. Power requirement

6. Whether it is economical or not

7. Type of circuit

There are three type of multiplexing

1. SDM → Space Division multiplexing

2. FDM → Frequency Division multiplexing

3. TDM → Time Division multiplexing

In SDM each user is given a separate channel to send the data.

In FDM each user is given a separate band of frequency

In TDM each user is given a specific time to share the channel

1. SDM

S1 S2 S3


BCA -DDU CHINTAN SIRS4 S4 S6

S7 S8 S9

SDM is the simplest and the oldest method of multiplexing where each

user has been given a separate channel

It supports two way communication between users means each user has

separate transmitter and receiver

Telephone system is the best example of SDM, where each user is

connected to local telephone office using a separate cable.

Each user is connected to local office using a pair of wires which is not

shared by any other users.

SDM uses the concept of base band signal

Advantages

1. It is easy to design

2. Any technical faults or problem can be detected easily

3. Any technical problem of one user does not effect other user’s

4. It is technically easy to add more no. of users because it requires a single

transmitter, receiver and channel only.

5. The initial cost is high bet after that there is a low cost to add and

maintain users.

6. The performance of the system is guaranteed and predictable.

7. No user has to wait for other user’s to be free.

Disadvantages

1. The initial cost is high.

2. When three are large number of users system becomes complex

2. FDM



µ = user T – transmitter

S = single R – Receiver

M = module DM – Demodular

In FDM Cach user has given separate modulator so that they can use

separate carrica signal and use separate frequency in terms of modulated

signal. There is a common channel

Due to separate carrier frequency for each user there is no interference of

signal in above figure FL1, FC2, FC3 are different carrier frequencies which

are not equd

Drift : “Change in frequency due to temperature variation in the system is

known as Drift.”

Advantages :

There is no separate cable for each user so the cost is law

Any extra users can be added in the system easily

Disadvantages :

Initial cost is high

The problem of one user some times affect other user

The problem of channel affects the whole system NARAYAN XEROX (NXC) 10

BCA -DDU CHINTAN SIR For each user carrier frequency must remain fixed but sometimes it is

changing due to drift.

3. TDM

In TDM each user has given a specific time to use a common channel. It is

a serial system. TDM is a serial system because each user is sending the data in

sequential manner. (One by one)

FDM is parallel system all users can be able to send the data parallel

fashion.

Generally TDM use base-band signal

Q. For user 1 constant amplitude +100

For user 2 constant amplitude +200

For user 3 constant amplitude – 200

Draw TDM signal if time interval = 5


BCA -DDU CHINTAN SIRQ. In TDM there are 4 users. For user 1. constant amp is -1, user 2 is

+3 for user 3 is – 2, for user 4 is +1 Draw TDM signal if time interval is

5.

Block Diagram of term circuit



In TDM circuit design extra switches are required to shift between various users

modulator carries frequencies may be same or different generally, TDM is

preferred for long distance communication

Advantages of TDM circuit

Only single cable is required

For this cost is low, addition of users is easy

Different carrier frequencies are not required

Problem of one user cannot affect the other user.

Disadvantage of TDM

1. Initial cost is high

2. If there is problem in channel it affects

3. Time delay is there in data transmission.

At transmitter side TDN requires, multiplexing process. Four user share a

common channel to transit the data following specific components are require.

1. Two bit counter

x y

0 → 0 0 → Vo

1 → 0 1 → V1

2 → 1 0 → V2

3 → 1 1 → V3

Two bit counter is required because in the system there are four users (0,1,2,3).

Each user has given a specific time period to use the channel one by one. To

support this method two bit counter is required.

2. 2 x 4 decoder

The decoder selects users one by one for data transmission. There are two

bits which allows to soled the user means n = 2. The size of decoder is n x

24 = (2 x 4).


BCA -DDU CHINTAN SIR3. Clock circular generator

The clock circuit is required to provide various clock signal to various parts

of TDM circuit

4. Switches

At transmitter side 4 switches are required when the user is selected the

switch will change the position to “ON” and the user can send the data through

channel. The default position of the switches is at “OFF”

At receiver’s side Demultiplexing operators is performed. Above components

are also required at receiver’s side


BCA -DDU CHINTAN SIRQ. Design TDM circuit for Eight users

Combined multiplexing

.

Communication system requirement

Hierarchy of levels

Message


BCA -DDU CHINTAN SIRCode

Format

Protocol

Physical connected → R

To send info. User must require the message this message must be written or

represented using specific codes. Specify the proper syntax and format of the

message. Define the rules for info. Exchange between sender & receiver.

Protocol :-

A set of rules define for info. exchange between transmitter and receiver

is known as protocol. Use channel or physical connecter through which message

can be send to receiver.

The format or code used to represent the message must be same.

The voltage or current level use to define 1’s and 0’s must remain same in

the communication system.

Eg. of protocol is Handshaking

HANDSHAKING

RTS

CTS

DTR

ASK

NSK

RTS → Request to send

CTS → Clear to send

ACK → Acknowledgement

NAK → No ACK

The protocol plan in which transmitter and receiver send signals to each

other is known as handshaking.


T R

BCA -DDU CHINTAN SIRSteps of Handshaking

1. Transmitter sends RTS signal to indicate the request to receiver

2. If receiver is free it gives permission to send the data using CTS signal

3. Transmitter now sends the message or data to receiver

4. If receiver has received the data correctly. It acknowledge the transmitter

using ACK signal

5. If message is not received receiver sends NAK signal to indicate negative

acknowledgement.

Format

Message No

Receiver No

Message Character count

Add. Info End

1

Preamble Part

2 3

Post amble part Each message must have 3 main part

1. Preamble part

2. Message

3. Post amble part

1. Preamble part

It includes 2 fields (1) msg no (2) Rec. no msg no: is used to indentify

each message in unique way. Rec. No indicates the address of receiver when

there are multiple receiver it shows whom to send the data

Message

It contains actual information or data

Post amble part


BCA -DDU CHINTAN SIRIt has 3 fields (1) Character count (2) Additional Information (3) End character

count indicates the total number of characters or size of the message. It is used

to find the errors in receiving addition at information field includes special type

of information such as security. End indicates ending of message.

Ch – 5 RS232 Interface

RS. : Recommended Standard

It is a special type of interface cable which is developed by

EIA : Electronics Industry Association.

IEEE : is one more institute which develops similar type of interface cable

IEEE : Institute of Electrical & Electronics Engineers

Main Application of RS 232 :

1. Connection between 2 computer

2. Connection between computer and peripheral device

3. Connection between & components in distributed system.

RS 232 is used for shorter distance the maximum length is upto 50 feat.

RS232 Channel RS 232

SS


Comp 1

Comm1 box1

Comm Box2

Comp 2

BCA -DDU CHINTAN SIR In RS. 232 1 is represented as mark while 0 is represented as space. There are

two different methods to represent marks & space.

High

1. 1 0 law positive logic

In positive logic binary 1 is represent ex by high voltage and binary 0 is

represented by law voltage.

High

2. 1 0 law negative logic

In negative logic binary 1 is represented by law voltage & binary 0 is

repented by high voltages

The range of high voltage is +3 to +25 while the range of law voltage is

--3 to -25

RS 232 use the concept of negative logic

+25

+3

0 0

- 3

+25

Mark (1)

Single ended system

A system where voltage send to receiver from transmitter is measured

with reference to o voltage point is known as single ended system.

0 voltage is sometimes known as common grand voltage

Common ground voltage

OV


T R

BCA -DDU CHINTAN SIR Slew rate

Slew rate = ( )( )

2 1

2 1

V VV

t t t

−∆ =∆ −

V2

V1

0 t1 t2t→

The rate at which mark or space value changes is known as “slew rate”

Slow rate ↓↑ - Time ↓↑

Time ↑↓ - Frequency ↓↑

Frequency ↑↓ - Bandwidth ↑↓

Above relation shows that if there is a change in slew rate, band width is

changing due to that system becomes unstable so slew rate must be fixed in

specific range.

Q. How to represent data using RS 232 Specification?

Low voltage – 1 – mark

High voltage – 0 – space

Rules :

1. When no data is transmitting signal is at mark position.

2. when data, comes, one start bit is required which is always 0

3. transmits the data for LBS to MSB

4. Once data is over include parity bit, which is used to determine errors in

data transmission

Parity bit is 1 for odd parity &

Parity bit is 0 for even parity

5. After parity bit one or two stop bits are required which is always 1.

Represent ASCII D with parity and without parity using RS 232 specifications

64 32 16 8 4 2 1

= ( 1 0 0 0 1 0 0 )2


BCA -DDU CHINTAN SIRMSB LSB

Represent 114 in RS 232

= ( 1 1 1 0 0 1 0)

RS 232 Errors

There are three main types of errors related to RS 232

1. Framing error

2. Over run error

3. Parity error

1. Framing error :-

When is a problem in receiving start bit or stop bit then the error occurred

in the system is known as framing error

2. Over run error :


BCA -DDU CHINTAN SIRWhen there is a problem in receiving data. Due to slow receiving rate

compared to fast transmission rate then the error occurred in the system is

known as over run error.

3. Parity error

If parity bit received by the receiver is incorrect then the type of error is

parity error

RS 232 Signals

DTE → DCE

Data Terminal Data Communication

Equipment Equipment

(Comp) (Comm. box)

DTE

A computer or terminal which transmits the data to communication box is

known as DTE

DCE

A communication box which receives data from computer or terminal is

known as DCE

RS 232 has 25 lines which are divided into 4 groups

1. Ground lines

2. Data lines

3. Timing lines

4. Control lines

1. Ground Lines :-

There are two main types of ground line

i. Signal ground

ii. Protective ground

Signal ground is used to define zero reference voltage

Protective ground is used to prevent the useRS from electrical

2. Data Lines :


BCA -DDU CHINTAN SIRT x D

R x D

Sec T x D

Se R x D

There are four types of data lines :

1. TXD (Transmitted Data) :

It is used to transmit the actual data from DTE to DCE

2. R x D [Received Data]

It is used to receive actual data from DCE to DTC

3. Sec T X D

It is used to transmit the secondary data to DTC to DCE of security

information. Additional information about security error etc.

4. Sec R x D

It is used to receive the secondary data from DCE to DTE

3. Training line :

TSE timing(T)

TSE timing(R)

RSE timing(T)

There are three different timing signal which were used to provide

synornization between transmitter and receiver. These lines are preferred with

synchronus application.

TSE Timing (T) [Transmitted Signal Element Timing of Transmitter]

TSE Timing (R) [Transmitted Signal Element Timing of Receiver]

RSE Timing [Receiver Signal Element Timing ]

4. Control lines

It is largest group of signal line which includes 12 lines out of twelve a

lines primary and 3 lines are secondary.

1. Primary control lines


DTE DEC

DTE DEC

BCA -DDU CHINTAN SIRRTS

CTS

DTR

DSR

1. RTS – [Rest To Send]

It indicates the request from DTC to DCE

2. CTS – [Clear to send]

It indicates permission to send the data from DTE to DCE

3. DTR – [Data Terminal Ready]

When transmitter is ready to transmit the data DTR is set.

4. DSR – [Data Set Ready]

When receiver is ready to get the data DSR is activated

5. Ring Indicator

This signal is used to active the ring.

6. Received line signal detector :

When data is received by receiver this signal is activated.

7. Signal Quality detector :

This signal indicates quality according to signal, strength and weakness

8. Data signal rate selector (T)

This indicates transmitting rate

9. Data signal rate selector [R]

This indicates receiving rate

2. Secondary controller / lines

1. Secondary RTS

2. Secondary CTS

Secondary RTS and Secondary CTS are used to provide handshaking for

secondary data.

RTS indicates request while CTS permits the permission

3. Secondary signal rate selector

It indicates rates for secondary data. Out of 25 remaining four lines are

not used


DTE DEC

BCA -DDU CHINTAN SIR RS – 232 Application

1. Temperature meter :

RS – 232

Data

Ground Voltage

RS–232

Temperature meter is a device which is used to monitor the temp at

remote location. It measures the temp either in analog or digital form and send

it is to main compacter RS 232 is required between temp meter and computer.

The connection is simple because it require data and ground line only. Data is

flowing in one direction only. Handshaking line are not require. If there is a

change in temp beyond specific limit, then temp controller is required.

The main disadvantage is that if computer is not ready to receive the data

then data will be lost.

2. Computer & Printer

DATA

CTS

Common Ground Signal

Above figure indicates interfacing between computer and printer.

It uses CTS line handshaking

The RTS line is not required

There is no flow of data in reverse direction

3. Computer to keyboard and monitor

Data

CTS RTS Ground

Ground data


Comp Comp

Comp KB

Monitor

TC

TM COMP

BCA -DDU CHINTAN SIR Keyboards sends data to computer without handshaking lines

Computer receives data from keyboard and echo back the data to monitor

so sometime it is known as echo back scheme.

4. Computer to computer

RTS

CTS

DTR

DSR

T X D

R X D

Ground

Between two computer all hard sharing line can be used. Some of the

examples are RTS, CTS, DTR, DSR etc.

For synchronous application timing lines can be used.

All control lines and secondary lines are not always required

BAUD

It is a measurement unit which defines the number of bits transmitted per

sec. [bits/sec]

Introduction to networking

Network :

1. The system with large number of separated but interconnected computers

is known as network

2. Interconnected collection of autonomies computer.


Comp1 Comp 2

C1

C2

C4

C3


Technical issue to design the n/w

1. Topology :

It is the way interconnection between several computers is made.

2. Protocols :

The set of rules defined for information exchange between two

computers.

3. Layers :

It is a group of protocols for specific applications or functions.

4. Medium :-

Select the type of medium for data transmission

5. Modulation :

Select the type of modulation method

6. Interference :

Find out whether the signal is interfaced by other signal or not.

Used of Network ?

1. Resource of data sharing

2. Multi-user and multitasking facility

3. Centralized control

4. The data transfer time will be reduced

5. Due to resource sharing there is no need to purchase extra resources

which reduces the amount of cost

6. It provides the transmission with reliability and security.

Net work stricture (How n/w is foneds)

The network is made up with two main components

1. Host

2. Subnet

1. Host : A computer connected in network is known as host


C1

C2

C3

C4

BCA -DDU CHINTAN SIR2. Subnet : The group of physical components used to connect the host is

known as subnet

Types of network (in terms of facility or function)

There are two types of network

i. Open loop network

A network which is available for all user is known as open loop n/w. E.g.-

Internet.

ii. Closed loop network

A network which is available for specific user is known as closed loop n/w.

E.g. Internet

Line configuration

It is the way two or more computers are connected to each other using

channel. There are two types of line configuration.

1. Point to point (Peer to peer)

2. Multiple

1. Point to point

It is this configuration each user has been given a separate channel for

communication which is not shared by any other user.

1

6

4 2

5

3

2. Multiple


C1

C2

C4

C3

C1

C2

C4

C3


In multipoint configuration a signal or common channel is shared by users.

Types of Topology

1. Mesh Topology

In mesh topology one computer is connected to another using a specific

link. It uses the principle of point to point configuration

a) 2-comps

1

Link = 1

b) 3 – comp

1 2

Links = 3

3

c) 4 – compt.

Links = 6

Link = n(n – 1) 2

Draw mesh topology network for 5 and 6 use RS also find for out no of

links.

No of links = ( 1)

2

n n −

= 6 (6 1)

2

−

= 6 (5)

2


C1

C2

C2

C3

C1

C1

C2

C4

C3


= 30

2

= 15 links

5 users

Q. Draw mesh topology network for 7 and 8 use RS

Q. Find out no. of links and part for 50.

links = 100 (100 1)

2

−

= 100 (99)

2

= 9900

2

= 4950 links


C1

C2

C3

C4

C6

C5

C1

C2

C5

C4

C3


50 users

links = 50 (50 1)

2

−

= 50 (49)

2

= 2450

2

= 1225 links

Advantages of mesh topology

Due to a special or separate cable there is no chance of interference

If problem occurs in one link then it will not affect other users.

Fault detecting / finding is easy

Privacy and security is there in data transmission

Disadvantages of Mesh topology

When no of users are increased it requires more no of links. Which

increase the cost of the system

It is proffered for shorter distance only.

Setup and installation of network is difficult.

2. Star Topology

In star topology each user or computer is connected to an extra device

which is known as “Hub.” Hub controls the flow of data and send the data to

specific user. All the users will not require internal connection. It uses point to

point configuration.


C1

C2

C3

C4

HUB


Advantages of Star Topology

Fault finding is easy

Problem of one user will not affect other users

Less number of cable are required compared to mesh topology

Less expensive

Installation and setup is easy

Disadvantages

When degree of data transfer is high three

Additional hardware devices are required.

3. Tree Topology

It is a variation of star topology where more no of HUBS are used to

connect more no. of users in network. There are two different types of Hubs

used in tree topology

1. Active Hub. (Primary / central)

2. Passive Hub (Secondary)

1. Active Hub :

It is used to control the flow of data as well as it regenerates the signal so

that it can travel for longer distance

2. Passive Hub:

Passive hub contains internal circuit which controls the flow of data all

passive hub are connected to central / active hub.


BCA -DDU CHINTAN SIRAdvantages of Tree topology

More number of users are supports in network

Due signal can travel for longer distance also

Fault finding is easy

Problem of one user does not affect other user.

Additional of new users is easy

Disadvantages of tree topology

Due to extra hubs the cost of n/w is increased.

It requires more cabling

Collision problem is there

4. Ring Topology

In ring topology each device is connected to other using ring structure

A single cable is used which is shared by all users so it is multi-point

configuration

Each user is connected to ring using drop line

A signal from one device to another can travel in one direction only.


BCA -DDU CHINTAN SIRAdvantages

It requires of less number of cables.

It is easy to install and setup

Addition or deletion of users is easy

Cost is reduced.

Disadvantages


Signal can be traveled in one direction only

Fault finding is difficult

Problem or break in the ring can disable to entire network.

5. BUS Topology

It is multipoint configuration where one thick and long cable known as

backbone is used to connect various users in the n/w

Each user is connected to back bone using a tap and a ‘drop line’.

Drop line is a connection between a user and main cable.

A tap is a connector which is inserted in main cable

A terminator is used on both side of cable to terminate the cable

Sometimes two more devices are required between computer and

backbone in bus topology

i. Repeater

ii. Transceiver

i. Repeater

It is a device which is used to regenerate the signal.


BCA -DDU CHINTAN SIRii. Transceiver

it is a device which is used to control transmission and receiving process.

Advantages

More number of users are supported in Bus topology

New user can be added easily

Installation and setup is easy

Disadvantages


Fault finding is difficult

It requires extra devices like repeaters and transceivers which in creates

the cost of n/w

6. Hybrid Topology

It is combination of various topology to get efficient network system and

to get specific advantages from the various type of topology above network

uses the principal of star, tree, ring, bus and mesh topology

Types of n/w based on no. of users and distance

LAN (Local Area N/w)

MAN

WAN

INTERNET



Chapter – 7

Introduction to OSI modeling

OSI

It is used to define interconnection between two or more open system. It

is developed by ISO (International Standard Organization).

OSI model is made up with different types of layers.

Layers

It is a group of protocol used for specific function

There are 7 different types of layers used in OSI model.

1. Physical layer

2. Data link layer N/w support (near to n/w)

3. Network layer

4. Transport layer

5. Session layer

6. Presentation layer user support (near to user)

7. Duplication layer

Layer are divided in two main categories

i. network support layer

ii. User support layer

i. Network Support Layer

A layer which deals with physical concepts of moving data. Physical

connection between transmitter and receiver hard ware devices and electrical

specification is known as network support layer.

Physical data link and network layers are included in this group.

ii. User support layer

The layer which is used to given flexibility to the users by specific app. Or

software is known as user support layer.

Session, presentation and application layers are the example of user

support layer.


BCA -DDU CHINTAN SIRTransport layer

Transport layer is a intersection between user and network support layer.

BLOCK DIAGRAM OF OSI MODEL

The figure how data is transferred from transmitter A to receiver B viz.

two computer “node 1” and “node 2”. Each side includes the concept of

all 7 layers while intermediate nodes use the concept of lower 3 layers

only.

At transmitter side each layer uses the services provided by upper layer

and provide services to lower layers

For eg. : Transport layer uses the services provided by session layer and

provide services to network layer.

At receiver side each layer use the services provided lower layer and

provide services to upper.

Each layer is connected with other using specific interface.


BCA -DDU CHINTAN SIR Each layer adds a special type of information known as “Hader” and is

denote by (H).

Application layer is directly connected with user.

Physical layer is directly connected with channel or hardware.

Above figure indicates how various information are added at different

layers

Header bits are added at layers 6, 5, 4, 3, 2

Application and physical layer do not add any header info.

The data link layer (2) adds “trailer bits” to indicate ending of the

message.

1. Physical layer



Physical layer

accepts data unit from data link layer convert it into suitable format and send it

to transmission medium. At receiver’s side it receives the data from channel

and give it to data link layer. It is directly connected with hardware. It takes care

about all electrical specification and mechanical specification.

Factors

Transmission medium. [type of channels]

Types of signal (Analog, digital etc)

End coding (What types of code has been used )

Types of topology (Bus ring etc.)

2. Data Link Layer

Header



DLL accepts data from network layer and adds header information and

trailer information

At receiver’s side it accepts data from physical layer, removes header

information and trailer info. and send it to network

A data unit of data link layer is known as frame.

In above frame info. about source (1) and destinations (5) is added

Functions of DLL

It is responsible for node – to node transmission of data

It provides address

It indicates ending or terminating of the massage

It performs error handling

It controls flow of data

3. Network layers



It accepts data from transport layer and send it to data link layer.

Above figure indicates how data is send from one network to another

network using the concept of network and data link layer.

Network layer provides two main services 1. Routing 2. switching

Routing :

Selecting the best path for data transmission is routing

Switching :

The process of changing temporary connection is known as switching

The data unit of n/w layer is known as packet

Function

1. It provide routing to elect the path


BCA -DDU CHINTAN SIR2. Provides switching to make temporary connection

3. it supports multiplexing

4. it provides logical address which does not change. While transferring the

data from and n/w to another, it is permanent address.

Def. of physical layer

The address provided by DLL is changing from node to node which is

known as physical address.

It is responsible for source to destination delivery of data

4. Transport layer

Transport layer accepts message from session layer divides the message

into number of segments and includes header bits which indicates segment

number for each segment.

The unit of transport layer is TPDU [Transport Protocols Data Unit]

Function :

1. Segmentation at transmitter side

2. Reassembling of segment at receivers side

3. It is responsible for end-to-end delivery of entire message

4. Error control

5. Flow control



5. Session Layer :

Session layer accepts data from presentation layer divides it into number

of layer and adds reader bits to indicates ending of message transport layer

accepts this data and for each session it creates a segment

Function of Session

1. Session management

2. It indicates ending of message

3. It provides virtual connection transmitter and receiver

4. It provides synchronization

5. It work as dialog controller because it knows who sends the data, when

the data is sent, and to whom to send the data.

6. Presentation layer

A.L.

P.L.


Data

Data H

Data

BCA -DDU CHINTAN SIRSL.

It accepts the data from application layer and encodes the data. If the

message size is too large. It performs compression, to provide security it uses

encryption at receiver’s side it performs all reverse operation like decoding, un-

compression and decryption. The header bits includes information about various

transmission parameter.

7. Application Layer

A.L.

P.L.

It provide interface between user and layer

Application layers enables users to access the network. It provides interface

between user and other layers no header bits are include at app. layer.

Function

1. Mailing service : It supports or message services like email, chat etc.

2. FTAM (File Transfer and Management): It provides app. for file transfer

3. Directory services : It allow user to set the data base source

4. Virtual Terminal : It allows user to log an remote computer.

Physical Layer

Physical layer is the lowest layer of OSI model which is directly connected

with hardware or channel

There are main 5 types of transmission medicine or channel.

1. Lo-axial cable

2. Fiber optics

3. Magnetic medium

4. twisted pair


User

Data

Data

BCA -DDU CHINTAN SIR5. wireless medium

Co-axial cable

There are two types of co-axial cable

1. Base band – 50 Ω (digital)

2. Broad Band – 75 Ω (analog)

The base-band co-axial cable is used for shorter distance while broad

band cable is proffered for longer distance.

There are two different techniques for co-axial cable designing

1. Single cable technique

2. Data cable technique

Single cable technique

In single cable technique only one cable is used to send and received the

data.

Due cable technique

Fig.

In dual cable technique there all separate wires to transmit and to receive

the data.

Fiber Optics

Same as first session

Magnetic medium

In magnetic medium data is copied from one computer and taken to

another computer. The data is stored in magnetic form. For e.g. : Floppy Disk

This type of medium is time consuming

Twisted pair


U1

U2

U1

U2


In twisted pair two different wires are twisted together in helical form the

purpose of twisting is to reduce the electrical interference from other signals.

Two wires are not used in parallel because it works as an antenna. In telephone

system twisted pair can be used.

Advantages

Electrical interference is less

The cost is low

It supports both analog and digital signals

Data transmission speed is high.

Disadvantages

Energy radiation is there

Wireless medium

Geostationary satellite

Switching

It is the process of making temporary connection between multiple useRS

or multiple lines.

There are three different type of switching

1. Circuit switching

2. Packing switching

3. Message switching

Circuit switching

Circuit switching is a hard ware switching method while packet and

message switching are software switching method circuit switching is relating

with physical layer and packet switching is related with network layer.



Above figure indicates the example of circuit switching S1, S2, S3 are

different switches used to connect various networks for eg. To send data from A

to E join 1 – 2 of S1 and 1, 3, of S2

ISDN (Integrated Service Digital Network)

The integration of whole communication service using digital technology

is known as ISDN

ISDN

IDN (Integrated Digital n/w) :

The integration of specific part of fun. using digital technology in network

know as IDN.



IDN

There are two of ISDN B – ISDN

N – ISDN → Narrow band ISDN

B – ISDN → Broad Band ISDN

N – ISDN

N – ISDN SERVICE :

1. Bearer services

2. Tele services

3. Supplementary services

1. Bearer services

The services related with first three layer [Lower three layers] of OSI

model is known as bearer services

Eg. Circuit switching

Packed switching

Addressing

Frame sending etc.

2. Tele – services

The services related with upper four layers of OSI model is known as Tele-

services are used by the user of network

Eg. Compress the file


BCA -DDU CHINTAN SIRProviding the security

File Transfer

E-mail etc.

3. Supplementary

The services which provides some additional functions to bear and tele

services are supplementary services

N – ISDN Channel

There are tree channel supported by N-ISDN

1. B – channel (Bearer channel)

2. D – Channel (Data channel)

3. H – Channel (Hybrid Channel)

1. B - Channel (Bear channel) :

It is defined at the rate of 64 kbps. It carries the actual digital information.

2. D – channel [Data Channel]

It carrier various types of control signals to support the data. It is defined

at the rate of 16 or 64 kbps

3. H – Channel [Hybrid Channel]

It is defined at the rate of 384, 1536 or 1920 kbps

It is used to support high data rate application

N – ISDN Interface

There are main two types of interface

1. BRI –Basic Rate Interface (Access)

2. PRI –Primary Rate Interface (Access)

BRI



BIR is made up with two B-channel of 64 kbps and one D channel or 16

kbps

It require extra 48 kbps to start the process

BRI Data Transfer Rate :

= 2B + D

= 2 (64) + 16 + 8 = 144 + 8 kbps.

PRI

It contains 23 B channels with 64 kbps and one D channel of 64 kbps. It

requires additional 8 kbps for operating

PRI Data transfer Rate :

= 23B + D

= 23(64) + 64 + 8

= 1544 kbps

N – ISDN SYSTME ARCHITECTURE (N-ISDB FUNCTION 4)

USER



There are five main components N-ISDN system

1. TE 1 (Terminal Equipment No 1)

2. TE 2 (Terminal Equipment No 2)

3. TA (Terminal Adapter)

4. NT1 (Network Terminator 1)

5. NT2 (Network Terminator 2)

1. TE1 :

It is a devices which directly works with ISDN interface

2. TE2 :

It is a device which uses non-ISDN interface. It require extra device which

converts it into ISDN interface.

3. TA :

It is a device or protocol converter which convents non-ISDN interface to

ISDN interface.

4. NT1 :

It is a device which is used to terminate the final network or entire

network.

5. NT2

It will terminate intermediate network lines.

6. Reference points

There are 4 reference points R, S, T, U which indicates connection

between various components of ISDN system

R define connection for non-ISDN interface [TE2 & TA]

S define connection of ISDN interface [TA/TE1 & NT/NT2]

T define connection between two network terminator [NT2 TO NT1]

U define connection between NTI and ISDN offices

B-ISDN Technology

ATM – [Asynchronous Transfer mode]

ATM technology is used by B-ISDN because B-ISDN is used to support high

data rate application

There are three different layers in ATM technology


BCA -DDU CHINTAN SIR1. A & L [Application Adaptation Layer]

a. CS [Convergence sub layer]

b. SAR [Segmentation and Reassembly]

2. ATM Layer

3. Physical layer

The unit of ATM is known as cell which is made up with 53 bytes.

Cell network

A network which uses cell as data unit for transferring the info. as cell

network.

Cell Relay

A communication technology which uses cell as the data unit is known as

cell relay.

Designing Issues

Data Link Layer :



DLL accept services from network layer and provides services to physical layer.

If also provides interface between network layer and physical layer.

Design Issue :

There are 4 major design issues

1. Service provided to network layer and physical layer

2. Framing

3. Error Control

4. Flow control

1. Service provided to N.L. & P.L.



The physical connection a hardware or channel

Virtual connection or path is established using handshaking methods.

There are three main types of service provided by DLL.

a. Unacknowledged connectionless services

b. Acknowledged connectionless services

c. Acknowledged connection orient services

Connectionless :

Virtual connection using handshaking is not there.

a. Unacknowledged Connectionless services :

T R

Data

(frame)

In this services transmitter sends the frame without handshaking signals.

It will not check whether the receiver is ready or not receiver may receive the

data but will not send any acknowledgement.

If a frame is lost in between it cannot be resent

It is a unreliable service

It is preferred when receiver is always ready and errors rate is low

b. Acknowledge connectionless services



Frame

ACK

In this method no connection is established between transmitter and

receiver

Each frame will be sent without checking whether the receiver is ready or

not.

After receiving each frame receiver sends ACK signal

If ACK signal is not received in time then the frame will be resent.

c. Acknowledge connection-oriented services

BTS

CTS

Frame

ACK

Fig.

It is the most reliable service where a virtual connection is established

between transmitter and receiver.

After receiving frame receiver sends acknowledgement, error control flow

control is there.

2. Framing

Framing is the method to create frames DLL accepts packet from network

layer and creates a frame using any of the following methods.

a. Character count

b. Character stuffing

c. Bit stuffing

a. Character count :


T R

T R


In this method a header is included to specify no. of character in the

frame. This header is known as character count which includes the total number

of characters present in the frame. If any character count received is incorrect

then all remaining frames are not identified prospers

b. Character staffing

In character stuffing each frame is started with DLE STX frame is started

with DLE STX and ends with DLE ETX

When any DLE is there in the data then add an extra DLE which is known

as stuffed DLE – it is used to reduce the chance of an error at receiver’s ride this

staffed DLE is removed. NARAYAN XEROX (NXC) 56


c. Bit Stuffing

In this method instead of characters group of bits are used.

Each frame starts and ends with a special bit pattern 0 1 1 1 1 1 1 0. This

pattern is known as flag byte.

When DLL finds 5 consecutive 1’s in the data. It automatically adds or

staffs a 0 bit which is known a stuffed bit.

At receiver’s side when 5 consecutive 1’s are followed by 0 then it

removes that 0

3. Error control

For error control following steps are required.

Receiver sends ACK signal to transmitter to indicate whether the frame is

receive or not. There are two types of ACK

1. +ve ACK (Frame is received)

2. –ve ACK Frame is not received


BCA -DDU CHINTAN SIR If due some channel problem frame or ACK signal are not received properly

then sender has to retransmit the frame for that purpose times is required

as transmitter side. Before timer goes off if ACK is not received it will

resend the frame.

When frames are transmitted for multiple times then at receiver’s side

there may be duplication of frame to solve this problem specify sequence

same frame cannot be received again.

4. Flow control

Flow control is required when transmitter sends the data at higher speed

compared to slow receiving rate. To solve this problem use handshaking

principle.


Digital Modulation

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