Lecture handouts-Data Communication.pdf

EC351 : Data Communication
• Study Plan
• Syllabus
• Study methodology:
(i) Class-room Teaching
(ii) Assignments
(iii) Seminars
(iv) Tutorials
(v) Queries
• Mini-Projects
• Discussion forum
• Assessment
• Lao Tsu: A journey of a thousand miles must begin with a single step.

EC-351 : Data Communication
◼ Study Plan:
Lectures: 3 ( 2 lectures + 1 Tutorial)
◼ Syllabus:
Module I
Data Communication Techniques: Data Communication model, Transmission line Impairments,
Channel Capacity, Guided Transmission media, Digital data to Digital Signal, Different
encoding schemes like NRZ, Multilevel Binary, Bi phase, Differential Manchester, Scrambling
techniques, Self clocking codes, CODEC and MODEM. Synchronous and Asynchronous
transmission, Backward and Forward Error Control, Error detection techniques like CRC, Shift
register implementation, Error correction, Block Code principles, Hamming distance,
Interfacing standards like V.24/EIA-232.F, CCITT-X.21 Interface
Module II
Implementation of various flip flops and their applications: RS, JK and D Flip Flops,
Registers, SISO, PIPO registers with Load and Enable control lines, Counters,
controlled binary counter, Ring Counter, UP/DOWN Counters, Modulo 10 Counter.
Examples of Counting of Events, display of count in Seven Segment display system,
Alarm generation with terminal counts.

Module II
Data Link Control: Line Configurations, Flow Control using Stop and Wait ARQ, Sliding
window protocol, Error control using Stop and Wait ARQ, Go-back-to N ARQ, Selective
Reject ARQ, Data Link Control Protocol HDLC, Basic characteristics, Frame structure and
operation of HDLC, Data transparency control using bit stuffing, Utilization efficiency of a
link, Point-to-Point Protocol (PPP), Introduction to LCP, PAP, CHAP, NCP and IPCP
Module III
Multiplexing and switched Network Frequency Division Multiplexing, Carrier standards,
Synchronous Time Division Multiplexing, TDM link control, Digital Carrier systems,
SONET/SDH, Statistical Time Division Multiplexing, Performance, Cable Modem, ADSL
Design, Discrete multitone, xDSL.
Comparison of Circuit switching, Message switching and Packet switching techniques,
Digital switching concepts like Space division switching, 3-Stage Space division switch,
Control Signalling, Common-channel Signalling, TDM Bus switch, TSI switch, Time
Multiplexed Switches like STS and TST, Routing in circuit switched networks.

Module IV
Packet Switching: Datagram packet switching and Virtual circuit Packet switching, Use of Least
cost algorithms like Dijkstra’s and Bellman-Ford algorithms, Routing characteristics, Routing
strategies, Example system of ARPANET (all 3 generations) Congestion, Congestion control
techniques, Traffic management, Congestion control in Packet switched networks, CCITT X.25
Interface.
Module V
Protocols : The need for a Protocol Architecture, OSI layered structure, TCP/IP Protocol Suite,
Fundamental differences between OSI and TCP/IP, Primitives and PDUs. Network topology,
LAN protocol architecture, Function of LLC and MAC.
Connecting devices like Repeaters, Hubs, Bridges, Two-layer switches, Routers and Three layer
switches. IP header and IP addressing. QoS in internetworking, Transport protocols TCP and
UDP.

• Communication is the process of exchanging information. It is the process of
establishing connection path between two end users to send or receive data
* Communication involves the transmission of information from one place to another
• Electronic communications can be viewed as the transmission, reception and
processing of information between two or more locations using electronic circuit/
devices
Fig. Different stages of a communication system
EC 351: Data Communication
Module I-Data Communication Techniques

Milestones in the History of Electronic Communication
•1837, Samuel Morse invented the telegraph (patented in 1844)
•1843, Alexander Bain invented facsimile
•1876, Alexander Bell invented the telephone
•1879, George Eastman invented photography
•1887, Heinrich Hertz discovered radio waves
•1887, Guglielmo Marconi demonstrated “wireless communications” by radio
waves •1901, Marconi performed the first trans-Atlantic radio contact (from
Cornwall, England to Newfoundland, Canada
• 1906, Reginald Fessenden invented AM
•1906, Lee de Forest invented triode vacuum tube
•1920, KDKA Pittsburgh made the first radio broadcast (AM signals)
•1923, Vladimir Zworykin invented and demonstrated the television
•1933-1939, Edwin Armstrong invented the superheterodyne receiver and FM
• 1939, first use of two-way radio (walkie-talkies) happened in United States
•1958-1959, Jack Kilby and Robert Noyce invented the integrated circuits
•1958-1962, the first communication satellite was tested in the United States
•1961, citizens band radio was first used in the United States
•1977, the first use of fiber-optic cable transpired in the United States
Electronic Communication: History

Fig. Examples of communication system
Source Destination

Input signal=message to be transferred
1. Information or input signal
Module V-Electronic Communication
Sound
Image
Data
Video
Multimedia

2. Input transducer
Transducer- A device which converts one form of energy to another form.
Input transducer-A device which converts input signal to electrical energy
293

3. Transmitter
Transmitter increases the power of the signal and transmit it via the communication media
available.
294

4. Communication channel
Medium used for transmission of signal from one place to another.
Guided media, the
waves are guided
along a physical
path
Unguided media, also called
wireless, provide a
means for transmitting
electromagnetic waves but
do not guide them; examples
are
propagation through air,
vacuum, and seawater

5. Noise

6. Receiver

7. Output transducer
8. Output

Communication system: Analog and Digital

Digital Communication system

Modes of communication
1. Simplex: information can be sent in only one direction.
e.g.- AM/FM broadcast radio, TV broadcast transmissions, cable TV, Pagers and radio
astronomy
2. Half-duplex: information can be sent in both directions but in one direction only at a
time.
e.g.- Walkie-talkie radio sets used by police and para-military services
3. Full-duplex: information can be sent in both directions simultaneously sharing the
common communications channel.
e.g.- Landline telephone calls, two-way radio, cellular communication links, radar,
satellite, data communications and LANs.
*- In full/full-duplex mode, data transmission is possible in both directions at the same
time but not between the same two stations. It is possible on multipoint communication
links. It implies that one station is transmitting data to a second station and receiving
different data from a third station at the same time.
Modes of Communication

Modulation is process in communication systems in which a very high-frequency carrier
wave is used to transmit the low-frequency message signal so that the transmitted signal
continues to have all the information contained in the original message signal.
Need for modulation:
1. Practical Length of Antenna.
2. Narrow Banding of Signal
3. Frequency Multiplexing -Modulation allows frequency division multiplexing (FDM)
for simultaneous transmission of many baseband signals over a common channel
having much wider bandwidth.
4. Effective Power Radiated By Antenna
5. Modulation makes the designing and processing of signal in transmitter and receiver
devices much more convenient and simpler.
6. Modulated signals can minimize the effects of noise and distortion introduced in the
communications channel.
Modulation and its need

Types of modulation

Lecture handouts-Data Communication.pdf

Channel Capacity
Data rate
Bandwidth: Nyquist bandwidth, Shannon capacity formula
Noise: SNR
Error rate: BER
Baud rate
Throughput

Antenna parameters
Antenna radiation pattern: It is defined as a mathematical function or graphical
representation of the radiation properties of the antenna as a function of the space
coordinates.
An antenna will radiate power in all directions but, typically, does not perform equally
well in all directions. The radiation pattern characterizes this performance of antenna.
Field pattern: A graph of the spatial variation of the electric or magnetic field along a
constant distance path is called a field pattern.
Effective Isotropic Radiated Power (EIRP): The power radiated within a given
geographic area is usually specified either with reference to isotropic antenna or an
omnidirectional dipole antenna.
Directivity: The directivity of a transmitting antenna is defined as the ratio of the radiation
intensity flowing in a given direction to the radiation intensity averaged over all direction.
Absolute gain: The absolute gain of a transmitting antenna in a given direction is defined
as the ratio of the radiation intensity flowing in that direction to the radiation intensity that
would be obtained if the power accepted by the antenna were radiated isotropically.
Relative gain: The relative gain of a transmitting antenna in a given direction is defined
as the ratio of the absolute gain of the antenna in the given direction to the absolute gain
of a reference antenna (a perfect omnidirectional isotropic antenna) in the same
direction. The power input to the two antennas must be the same.

Antenna gain: Antenna gain is directional gain, not power gain, due to focusing of the
radiated energy in specified direction.
Efficiency: The efficiency of a transmitting antenna is the ratio of the total radiated power
radiated by the antenna to the input power to the antenna.
Antenna factor: The antenna factor is the ratio of the magnitude of the electric field
incident upon a receiving antenna to the voltage developed at the antenna’s output
connector (assuming a 50-ohm coaxial connector).
Radiation resistance: The radiation resistance of a half-wave dipole antenna situated in
free space
and fed at the center is approximately 70.
The impedance is completely resistance at resonance.
Polarization:
Front-to-back ratio: It is generally expressed in dB.
It is a measure of antenna’s ability to focus radiated power in intended direction
successfully, without interfering with other antennas behind it.
Effective area or aperture of a receiving antenna

Communication tasks
1. Transmission system utilization
2. Interfacing
3. Signal Generation
4. Synchronization
5. Exchange Management
6. Error Detection and Correction
7. Addressing and Routing
8. Recovery
9. Message formatting
10.Security
11.Network Management

Impairment
causes
Attenuation Distortion Noise
Transmission line Impairments

Transmission line Impairments: Attenuation
1. Attenuation: Loss of energy

Transmission line Impairments: Distortion
2. Distortion: Change in form or shape
a. Delay distortion
b. Amplitude distortion, Harmonic distortion, Phase distortion
Delay distortion occurs because the velocity of propagation of a signal through a guided medium
varies with frequency. Because of delay distortion, some of the signal components of one bit
position will spill over into other bit positions, causing intersymbol interference

Transmission line Impairments: Noise
3. Noise: Random or unwanted signal mix-up with original signal
Different types of noises are:
a. Thermal noise : The thermal noise is random motion of electrons in a conductor that
creates an extra signal not originally sent by the transmitter.
It is also known as white noise because it is distributed across the entire spectrum (as
the frequency encompass over a broad range of frequencies).
b. Intermodulation noise: More than one signal share a single transmission channel,
ntermodulation noise is generated.
For instance, two signals S1 and S2 will generate signals of frequencies (S1 + S2) and
(s1 - S2), which may interfere with the signals of the same frequencies sent by the
sender. due to If nonlinearity present in any part of the communication system,
intermodulation noise is introduced.

c. Crosstalk: Cross talk is an effect a wire on the another. One wire acts as a sending
antenna and the transmission medium acts as the receiving antenna.
Just like in telephone system, it is a common experience to hear conversation of other
people in the background. This is known as cross talk.
d. Impulse noise: Impulse noise is irregular pulses or spikes( a signal with high energy
in a very short period) generated by phenomena like that comes from power lines,
lightning, spark due to loose contact in electric circuits and so on.
It is a primary source of bit-errors in digital data communication that kind of noise
introduces burst errors
Transmission line Impairments: Noise
3. Noise: Random or unwanted signal mix-up with original signal

Guided Transmission media
Guided media, the
waves are guided
along a physical
path
Unguided media, also called
wireless, provide a
means for transmitting
electromagnetic waves but
do not guide them; examples
are
propagation through air,
vacuum, and seawater

A number of design factors relating to the transmission medium and the signal determine the data
rate and distance:
• Bandwidth
• Transmission impairments: Impairments, such as attenuation, limit the distance.
For guided media, twisted pair generally suffers more impairment than coaxial cable, which in
turn suffers more than optical fiber.
• Interference: Interference from competing signals in overlapping frequency bands can distort
or wipe out a signal. Interference is of particular concern for unguided media, but is also a
problem with guided media. For guided media, interference can be caused by emanations from
nearby cables. For example, twisted pairs are often bundled together and conduits often carry
multiple cables. Interference can also be experienced from unguided transmissions. Proper
shielding of a guided medium can minimize this problem.
• Number of receivers: A guided medium can be used to construct a point to-point link or a
shared link with multiple attachments. In the latter case, each attachment introduces some
attenuation and distortion on the line, limiting distance and/or data rate.

Encoding
Schemes
Analog data to
Analog signal
Analog data to
Digital signal
Digital data to
Analog signal
Digital data to
Digital signal

Encoding Schemes
Analog data to
Analog signal
Analog data to
Digital signal
Digital data to
Analog signal
Digital data to
Digital signal
Amplitude
Modulation,
Frequency
Modulation,
Phase Modulation
Pulse Code
Modulation
(PCM), Delta
Modulation
Amplitude Shift
Keying (ASK),
Phase SK(PSK),
Frequency
SK(FSK)
Unipolar
encoding, Polar
encoding, Bipolar
encoding

S = c x N x 1/r
where N is data rate
c is the case factor (worst, best & avg.)
r is the ratio between data element & signal element

Summary of line coding schemes

Block coding is normally referred to as mB/nB coding;
it replaces each m-bit group with an n-bit group.

Self Clocking codes
self-clocking signal is one that can be decoded without the need for a separate
clock signal or other source of synchronization.

Self clocking codes
Isochronous
(clock signals are sent
at the same time)
Anisochronous
(clock signals are sent
at different time)
Self Clocking codes

Self Clocking codes
Clock extraction circuit

Self Clocking codes

Example uses of self-clocking signal protocols include:
• Isochronous
o Manchester code, where the clock signals occur at the
transition points.
o Plesiochronous Digital Hierarchy signals
o Eight-to-Fourteen Modulation
o 4B5B
o 8b/10b encoding
o HDLC
o Modified Frequency Modulation
• Anisochronous
o Morse code
o Asynchronous start-stop

Codec
The device used for converting analog data into digital form for transmission, and
subsequently recovering the original analog data from the digital, is known as a codec
(coder-decoder).

Codec

Errors
Errors
Single bit Multiple bit Burst

Errors: Single bit error: majorly in parallel transmission; single bit error

Errors: Multiple bit error: both in serial and parallel transmissions; 2 or
more bits error

Errors: Burst error: majorly in serial transmission; 2 or more consecutive
bit error

Error Control
Error control can be done in two ways:
• Error detection − Error detection involves checking whether any error has
occurred or not. The number of error bits and the type of error does not matter.
Error detection uses concept of redundancy
• Error correction − Error correction involves ascertaining the exact number of
bits that has been corrupted and the location of the corrupted bits.
Errors: Error control

Error detection
Parity check
Cyclic redundancy
check
Checksum
Error Detection Techniques
There are three main techniques for detecting errors in frames: Parity Check,
Checksum and Cyclic Redundancy Check (CRC).
Errors: Error control-detection

Errors: Error control-detection-Parity: 1-D

Errors: Error control-detection-Parity: 2-D

Checksum
In this error detection scheme, the following procedure is applied
•Data is divided into fixed sized frames or segments.
•The sender adds the segments using 1’s complement arithmetic to get the sum. It then
complements the sum to get the checksum and sends it along with the data frames.
•The receiver adds the incoming segments along with the checksum using 1’s
complement arithmetic to get the sum and then complements it.
•If the result is zero, the received frames are accepted; otherwise, they are
discarded.
Cyclic Redundancy Check (CRC)
Cyclic Redundancy Check (CRC) involves binary division of the data bits being sent by a
predetermined divisor agreed upon by the communicating system. The divisor is
generated using polynomials.
•Here, the sender performs binary division of the data segment by the divisor. It then
appends the remainder called CRC bits to the end of the data segment. This makes the
resulting data unit exactly divisible by the divisor.
•The receiver divides the incoming data unit by the divisor. If there is no
remainder, the data unit is assumed to be correct and is accepted. Otherwise, it is
understood that the data is corrupted and is therefore rejected.
Errors: Error control-detection

Errors: Error control-
detection: Checksum

Errors: Error control-detection: Cyclic redundancy check (CRC)

Error Correction Techniques
Error correction techniques find out the exact number of bits that have been corrupted
and as well as their locations. There are two ways
•Backward Error Correction (Retransmission) − If the receiver detects an error in the
incoming frame, it requests the sender to retransmit the frame. It is a relatively simple
technique. But it can be efficiently used only where retransmitting is not expensive as in
fiber optics and the time for retransmission is low relative to the requirements of the
application.
•Forward Error Correction − If the receiver detects some error in the incoming frame,
it executes error-correcting code that generates the actual frame. This saves bandwidth
required for retransmission. It is inevitable in real-time systems. However, if there are too
many errors, the frames need to be retransmitted.
The four main error correction codes are
•Hamming Codes
•Binary Convolution Code
•Reed – Solomon Code
•Low-Density Parity-Check Code
Errors: Error correction techniques

Lecture handouts-Data Communication.pdf

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