- Information
- AI Chat
Chapter-1 - BCN
BE IT (2019) (414442)
Savitribai Phule Pune University
Preview text
Chapter No: 1
Introduction to Data Communication
Data is defined as information which is stored in the digital form.
Data communication is the process of transferring digital information between two points.
Data can be alphabets, numeric or symbols and it consists of any one or the combination of the following:
Microprocessor op-codes, control codes, user addresses, program data or data base information.
At the source or destination the data are in digital form but during the transmission it may be analog or digital.
A data communication network can be simply consisting of two computers connected to each other a public telecommunication network.
Data Communications
When we communicate, we are sharing information. This sharing can be local or remote. Between individuals, local communication usually occurs face to face, while remote communication takes place over distance. The term telecommunication, which includes telephony, telegraphy, and television, means communication at a distance (tele is Greek for "far").
The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data.
Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. For data communications to occur, the communicating devices must be part of a communication system made up of a combination of hardware (physical equipment) and software (programs).
Characteristics of Data Communication System:
The effectiveness of a data communications system depends on four fundamental characteristics: Delivery, Accuracy, Timeliness, and Jitter.
- Delivery: The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user.
2 Accuracy: The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable.
Timeliness: The system must deliver data in a timely manner. Data delivered late are useless. In the case of video and audio, timely delivery means delivering data as they are produced, in the same order that they are produced, and without significant delay. This kind of delivery is called real-time transmission.
Jitter: Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets. For example, let us assume that video packets are sent every
ZEAL EDUCATION SOCIETY’S
ZEAL COLLEGE OF ENGINEERING AND
RESEARCH
NARHE │PUNE - 41 │ INDIA
Record No.: ZCOER-ACAD/R/01 Revision: 00 Date:01/04/
Q. Define data communications.
Q. Describe the characteristics of data communication system.
3D Ms. If some of the packets arrive with 3D-ms delay and others with 4D-ms delay, an uneven quality in the video is the result.
Components of Data Communications System
A data communications system has five components:
Message: The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video.
Sender: The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on.
Receiver: The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on.
Transmission medium: The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.
Protocol: A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese.
Communication Modes
Based on whether the system communicates only in one direction or otherwise, the communication systems are classified as
- Simplex systems
- Half duplex systems
- Full duplex systems
1. Simplex Systems
In Simplex mode, the communication is unidirectional, as on a one-way street.
Only one of the two devices on a link can transmit; the other can only receive.
Q. Draw the components of data communication systems and state the function of each block.
Q. Explain Simplex, Half Duplex and Full Duplex communication with examples.
receiving; or the capacity of the channel is divided between signals traveling in both directions.
One common example of full-duplex communication is the telephone network.
When two people are communicating by a telephone line, both can talk and listen at the same time. The full-duplex mode is used when communication in both directions is required all the time. The capacity of the channel, however, must be divided between the two directions.
Full Duplex mode of Communication
Protocol:
A protocol is a set of rules that govern data communications. A protocol defines what is communicated, how it is communicated, and when it is communicated.
In computer networks, communication occurs between entities in different systems.
An entity is anything capable of sending or receiving information. However, two entities cannot simply send bit streams to each other and expect to be understood. For communication to occur, the entities must agree on a protocol.
The key elements of a protocol are: syntax, semantics, and timing.
- Syntax: (what is to be communicated?)
The term syntax refers to the structure or format of the data, meaning the order in which they are presented.
For example, a simple protocol might expect the first 8 bits of data to be the address of the sender, the second 8 bits to be the address of the receiver, and the rest of the stream to be the message itself.
- Semantics: (how it is to be communicated)
The word semantics refers to the meaning of each section of bits.
How is a particular pattern to be interpreted, and what action is to be taken based on that interpretation? For example, does an address identify the route to be taken or the final destination of the message?
Q. Define Protocols. Explain key elements of protocols.
- Timing: (when it should be communicated)
- The term timing refers to two characteristics: when data should be sent and how fast they can be sent. For example, if a sender produces data at 100 Mbps but the receiver can process data at only 1 Mbps, the transmission will overload the receiver and some data will be lost.
Standards:
Standards provide guidelines to manufacturers, vendors, government agencies, and other service providers to ensure the kind of interconnectivity necessary in today's marketplace and in international communications.
Standards are essential in creating and maintaining an open and competitive market for equipment manufacturers and in guaranteeing national and international interoperability of data and telecommunications technology and processes.
Data communication standards fall into two categories: de facto (meaning "by fact" or "by convention") and de jure (meaning "by law" or "by regulation").
- De facto:
- Standards that have not been approved by an organized body but have been adopted as standards through widespread use are de facto standards.
- De facto standards are often established originally by manufacturers who seek to define the functionality of a new product or technology.
- De jure:
- Those standards that have been legislated by an officially recognized body are de jure standards.
Standards Organizations:
- Standards are developed through the cooperation of standards creation committees, forums, and government regulatory agencies.
Standards Creation Committees:
- While many organizations are dedicated to the establishment of standards, data telecommunications in North America rely primarily on those published by the following:
- International Organization for Standardization
- (ISO): The ISO is a multinational body whose membership is drawn mainly from the standards creation committees of various governments throughout the world.
- The ISO is active in developing cooperation in the realms of scientific, technological, and economic activity.
- International Telecommunication Union-Telecommunication Standards Sector (ITU-T):
- By the early 1970s, a number of countries were defining national standards for telecommunications, but there was still little international compatibility.
- The United Nations responded by forming, as part of its International Telecommunication Union (ITU), a committee, the Consultative Committee for International Telegraphy and Telephony (CCITT).
- This committee was devoted to the research and establishment of standards for telecommunications in general and for phone and data systems in particular. On March 1, 1993, the name of this committee was changed to the International Telecommunication Union - Telecommunication Standards Sector (ITU-T).
- American National Standards Institute (ANSI):
Q. Define Standard. Name any four Standard Organizations. Give their functions
Baud rate is expressed in the number of times a signal can change on transmission line per second. Usually, the transmission line uses only two signal states, and make the baud rate equal to the number of bits per second that can be transferred.
An example can illustrate it. For example, 1500 baud rate illustrates that the channel state can alter up to 1500 times per second. The meaning of changing state means that channel can change its state from 0 to 1 or from 1 to 0 up to 1500 times per second (in the given case).
◼ bit: a unit of information ◼ baud: a unit of signaling speed. ◼ Bit rate:b ❑ Number of bits transmitted per second. ◼ Baud Rate:s ❑ Number of symbols transmitted per second. ◼ General formula: ❑ b=s*n ❑ Where n is number of bits per symbol.
Key Differences Between Bit Rate and Baud Rate
1. Bit rate is the number bits (0’s and 1’s) transmitted per second.
On the other hand Baud rate is the number of times a signal is traveling comprised of
bits.
2. Baud rate can determine the bandwidth of the channel or its required amount to send
the signal while through Bit rate it is not possible Rate can be expressed by the
given equation:
Bit rate = baud rate x the number of bits per signal unit
In contrary Baud rate is expressed in the given equation:
Baud rate = bit rate / the number of bits per signal unit
Question: Calculate the baud rate for the given bit rate and type of modulation:
(i) 5000 bps, ASK (ii) 4000 bps, FSK
Answer:
For baud rate (S), we know that the formula is:
S=N/r.
N = S * r
Here, N is Bit rate, S is the Baud rate
r = number of bits in signal elements
So, at first we need to calculate r for each case.
We know, r = log 2 L.
i) For ASK, r = log 2 2 = 1
S=5000 bps/1=5000 baud
ii) For FSK, r = log 2 2 = 1
S=4000bps/1=4000 baud
Question: A signal carries five bits in each signal element. If 1600 signal elements are
sent per second, find the baud rate and bit rate in kbps.
Answer:
Baud rate is number of signal elements per second.
Bit rate is the number of bits per second.
We also know that S=N/r where S is the baud rate, N is the bit rate
and r is the bits in each signal element.
In this case 1600 signal elements are sent per second.
So baud rate is 1600.
Now S=1600,r=5 and N is unknown.
So N=Sr=16005=8000 bps or 8 kbps.
Therefore the bit rate is 8kbps
BASIS FOR
COMPARISON
BIT RATE BAUD RATE
Basic Bit rate is the count of bits per second.
Baud rate is the count of signal units per second.
Meaning It determines the number of bits traveled per second.
It determines how many times the state of a signal is changing.
Term usually used While the emphasis is on computer efficiency.
While data transmission over the channel is more concerned.
Bandwidth determination
Can not determine the bandwidth.
It can determine how much bandwidth is required to send the signal.
Equation Bit rate = baud rate x the count of bits per signal unit
Baud rate = bit rate / the number of bits per signal unit
Analog Signal and Digital Signal
Analog Signal
An analog signal is a continuous wave denoted by a sine wave (pictured below) and may vary
in signal strength (amplitude) or frequency (waves per unit time). The sine wave's amplitude
value can be seen as the higher and lower points of the wave, while the frequency value is
measured in the sine wave's physical length from left to right.
There are many examples of analog signals around us. The sound from a human voice is analog,
because sound waves are continuous, as is our own vision, because we see various shapes and
colors in a continuous manner due to light waves. Even a typical kitchen clock having its hands
moving continuously can be represented as an analog signal.
Digital Signal
A digital signal - a must for computer processing - is described as using binary (0s and 1s),
and therefore, cannot take on any fractional values. As illustrated in the graphic below, digital
Non-periodic signals
◼ A signal that does not repeats its pattern over a period is called aperiodic signal or non periodic.
◼ Both the Analog and Digital can be periodic or aperiodic: but in data communication periodic analog signals and aperiodic digital signals are used.
Analog and Digital data
◼ Analog data take on continuous values in time interval.
◼ For example, voice and video are continuously varying patterns of intensity. Most data collected by sensors, such as temperature and pressure, are continuous valued.
◼ The most familiar example of analog data is audio, which, in the form of acoustic sound waves, can be perceived directly by human beings.
◼ Digital data take on discrete values; examples are text and integers.
◼ They cannot be easily stored or transmitted by data processing and communications systems in character form.
◼ Morse code, International Reference Alphabet (IRA) are used to translate text into binary.
Analog transmission
◼ Analog transmission is a means of transmitting analog signals without regard to their content; the signals may represent analog data (e., voice) or digital data. ◼ In either case, the analog signal will become weaker (attenuate) after a certain distance. ◼ To achieve longer distances, the analog transmission system includes amplifiers that boost the energy in the signal. ◼ Unfortunately, the amplifier also boosts the noise components.
Digital transmission
◼ Digital transmission, in contrast, assumes a binary content to the signal. ◼ A digital signal can be transmitted only a limited distance before attenuation. ◼ To achieve greater distances, repeaters are used. A repeater receives the digital signal, recovers the pattern of 1s and 0s, and retransmits a new signal. Thus the attenuation is overcome.
Both analog and digital information can be encoded as either analog or digital signals. The particular encoding that is chosen depends on the specific requirements to be met and the media and communications facilities available.
- Digital data, digital signals(Digital data Transmission):
◼ The simplest form of digital encoding of digital data is to assign one voltage level to binary one and another to binary zero.
◼ More complex encoding schemes are used to improve performance, by altering the spectrum of the signal.
- Digital data, analog signal:
◼ A modem converts digital data to an analog signal so that it can be transmitted over an analog line.
Here baseband signals comes from a audio/video or computer. Baseband signals are also called modulating signal as it modulates carrir signal. Carrier signals are high frequecy radio waves it
generally comes from a radio frequency oscillators. These two signls are combined in modulator. Modulator takes the instantenious amplitute of baseband signal and varies amplitute/frequency/phase
of carrier signal. Resultant signal is a modulated signal. It goes to an RF-amplifier for signal power boosting and then feed to antenna or a co-axial cable.
There are two types of modulation analog and digital. Analog modulation delas with the voice, video and regular waves of base band signals. Where as digital modulations are with bit streams or symbols from computing vevices as base band signals.
- DeModulation:
Demodulation is the opposite process of modulation. Modulator is a part of signal transmitter where as demodulator is the receiving side. In broadcast system radio transmitting station does to
modulation part. A radio receiver acts as a demodulator. A modem receives signals and also transmits signals thus it does modulation and demodulation at the same time. Thus the name modem has been
given. A radio antenna receives low power signal. A co-axial cable end point can also take as an signal input. An RF amplifier boosts the signal amplitude. Then the signal goes to a demodulator.
demodulator does the reverse of modulation and extracts the backband signal from carrier. Then the base band signal is amplified to feed a audio speaker or video monitor or TTL/CMOS signal levels to
match computer inputs.
- What is De-modulation?
Demodulation is the opposite process of modulation where the varying amplitude, frequency or phase of carrier signal is extracted to construct the original the message signal.
Digital to Analog conversion
◼ The case of transmitting digital data using analog signals. ◼ The most familiar use is for transmitting digital data through the public telephone network. ◼ The telephone network was designed to receive, switch, and transmit analog signals in the voice-frequency range of about 300 to 3400 Hz. ◼ It is not at present suitable for handling digital signals from the subscriber locations. ◼ Thus digital devices are attached to the network via a modem (modulator-demodulator), which converts digital data to analog signals, and vice versa. ◼ Modulation involves operation on one or more of the three characteristics of a carrier signal: amplitude, frequency, and phase. ◼ Accordingly, there are three basic encoding or modulation techniques for transforming digital data into analog signals:
◼ Amplitude Shift Keying (ASK), ◼ Frequency Shift Keying (FSK), and ◼ Phase Shift Keying (PSK).
1. Amplitude Shift Keying (ASK)
◼ ASK is the digital carrier Modulation in which amplitude of carrier will take one of the two values in response to 0 or 1 value of digital data.
◼ Amplitude Shift Keying (ASK) is a type of Amplitude Modulation which represents
the binary data in the form of variations in the amplitude of a signal.
◼ Any modulated signal has a high frequency carrier. The binary signal when ASK
modulated, gives a zero value for Low input while it gives the carrier output
for High input.
◼ The following figure represents ASK modulated waveform along with its input.
ASK Modulator
The ASK modulator block diagram comprises of the carrier signal generator, the binary
sequence from the message signal and the band-limited filter. Following is the block diagram
of the ASK Modulator.
Application:
1. Used in our infrared remote controls
2. Used in fibre optical tranmitter and receiver.
produces a sinewave of frequency f 0 whereas corresponding to binary 1 input VCO produces
a sinewave of frequency f 1.
Question: Draw a BFSK waveform to represent the following bit stream 0 11 0 1 0.
Application:
1. Many modems used FSK in telemetry systems
3. Phase Shift Keying (PSK)
Phase Shift Keying (PSK) is the digital modulation technique in which the phase of the
carrier signal is changed by varying the sine and cosine inputs at a particular time. PSK
technique is widely used for wireless LANs, bio-metric, contactless operations, along with
RFID and Bluetooth communications.
PSK is of two types, depending upon the phases the signal gets shifted. They are −
Binary Phase Shift Keying (BPSK)
This is also called as 2-phase PSK or Phase Reversal Keying. In this technique, the sine
wave carrier takes two phase reversals such as 0∞ and 180∞.
BPSK is basically a Double Side Band Suppressed Carrier (DSBSC) modulation scheme, for
message being the digital information.
Quadrature Phase Shift Keying (QPSK)
This is the phase shift keying technique, in which the sine wave carrier takes four phase
reversals such as 0∞, 90∞, 180∞, and 270∞.
If this kind of techniques are further extended, PSK can be done by eight or sixteen values
also, depending upon the requirement.
BPSK Modulator
The block diagram of Binary Phase Shift Keying consists of the balance modulator which has
the carrier sine wave as one input and the binary sequence as the other input. Following is the
diagrammatic representation.
The modulation of BPSK is done using a balance modulator, which multiplies the two signals
applied at the input. For a zero binary input, the phase will be 0∞ and for a high input, the
phase reversal is of 180∞.
Following is the diagrammatic representation of BPSK Modulated output wave along with its
given input.
The output sine wave of the modulator will be the direct input carrier or the inverted (180∞
phase shifted) input carrier, which is a function of the data signal.
Question: Explain process of phase shift keying.(4 Marks)
Answer: Phase-shift keying (PSK) is a digital to analog modulation scheme based on
changing, or modulating, the initial phase of a carrier signal. PSK is used to represent digital
information, such as binary digits zero (0) and one (1).The modulation of PSK is done using a
balance modulator, which multiplies the two signals applied at the input. For a zero binary
input, the phase will be 180∞ and for a high input, the phase reversal is of 0∞. Following is the
diagrammatic representation of PSK Modulated output wave along with its given input.
- Analog to Analog Conversion
◼ Analog-to-analog conversion, or modulation, is the representation of analog information by an analog signal. ◼ It is a process by which a characteristic of carrier wave is varied according to the instantaneous amplitude of the modulating signal. ◼ Analog to Analog conversion can be done in three ways: ❑ Amplitude Modulation ❑ Frequency Modulation ❑ Phase Modulation
1. AMPLITUDE MODULATION:
◼ The modulation in which the amplitude of the carrier wave is varied according to the instantaneous amplitude of the modulating signal keeping phase and frequency as constant. ◼ AM is normally implemented by using a simple multiplier because the amplitude of the carrier signal needs to be changed according to the amplitude of the modulating signal. ◼ AM bandwidth: The modulation creates a bandwidth that is twice the bandwidth of the modulating signal and covers a range centered on the carrier frequency. Bandwidth= 2fm
AM Advantage
AM is the simplest type of modulation. Hardware design of both transmitter and receiver is very simple and less cost effective.
AM Disadvange:
- AM is very susceptible to noise.
Application:
AM radio broad cast is an example
2. Frequency modulation
FM or Frequency modulation is the process of varying the in instantaneous frequency of Carrier signal accordingly with instantaneous amplitude of message signal.
- FM Advantage
- Modulation and demodulation does not catch any channel noise.
- FM Disadvange:
- Circuit needed for FM modulation and demodulation is bit complicated than AM
- Application:
- FM radio broad cast is an example
Question: Compare amplitude modulation and frequency modulation (4 points).
Answer:
Chapter-1 - BCN
Course: BE IT (2019) (414442)
University: Savitribai Phule Pune University
This is a preview
Access to all documents
Get Unlimited Downloads
Improve your grades
