Unit 1 syllabus
Data and Signal fundamentals Analog Signals and Digital Signals
Transmission Media: Guided and Unguided Media
Transmission Impairments
Categories of Networks
Reference
The contents of this presentation has been presented using the following book:
”Data Communication and Networking” by Behrouz A. Forouzan, 4th
Data and Signal fundamentals
The term telecommunication meanscommunication at a distance.
The word datarefers toinformation presented in whatever form is agreed
upon by the parties creating and using the data.
Data and signal fundamentals
Analog Signals and Digital Signals
Analog data refers to information that iscontinuous;digital data refers
to information that has discretestates.
Analog Signals and Digital Signals
Digitization
Digital Data representations
Data is represented as bits (either 0 or 1 in binary format). Now various kinds of data needs to be transmitted. Some of them are:
Text
Numbers
Images Audio
Videos
History of data representation
Earliest form of data representation is using a Morse Code.
Assignment 1:
1 Write in detail about more code and how telegraph is used to
transmit data using Morse code.
Note:
Reference:
https://youtu.be/Mvqlsd3prW8 https://youtu.be/HcMHam54EOI
Data representation of text data
Text Data in digital age
Text is represented as a pattern of bits called a code
Each character is a distinct code
Most prevalent code isUnicode
Ref: http://unicode.org/standard/WhatIsUnicode.html
Unicode uses 32 bitsfor coding.
For digital text data, ASCII codes are used to represent text data where 127 symbols are defined.
ASCII = American Standard Code of Information Exchange
http://www.asciitable.com/
Self Testing question:
What is the ASCII code in binary format for the following text:
Data representation for numbers
Data representation for images
Images are represented as a two dimensional matrix of numbers.
Each element gives the value of intensity at a pixel.
Depending on hardware, which generated the image, number of pixels will vary and hence the size of matrix will change.
Spatial resolution depends on how small is the pixel i.e which spatial area each pixel is capturing.
For each pixel, most basic representation is using just two values i.e. 0 for black and 1 for white.
If we use 2-bit pattern i.e 00,01,10,11 then one can define 4-level grayscale.
Data representation of color images
RGB method
RGB stands for Red, Blue, Green
Intensity of each color is measured and a bit pattern is assigned to each pixel
Ref: https://en.wikipedia.org/wiki/RGB_color_model
CMYK method:
A color is made of three primary colors: Cyan, Magenta, Yellow, Key (Black)
Depending on intensity of each color, a bit pattern is assigned to a pixel Ref: https://en.wikipedia.org/wiki/CMYK_color_model
Data representation of video images
A video can be a series of images presented in a series to provide an
illusion of motion.
Each image is called a frame
Rate at which frames are displayed is called the frame rate
Number of pixels in width and height gives the frame size.
Ref: https://en.wikipedia.org/wiki/Digital_video
Self Test Question://
Check out how much storage space in MB’s will a 1 minute movie take
Data representation of audio
A digital microphone has a diaphragm attached to a magnet
When diaphragm moves due to sound waves, magnet moves within a coil assembly
This movement produces induced emf in coils which can be amplified, digitized and stored
Data flow
There can be three modes of data flow:
Data flow
Simplex
Unidirectional flow at all times Keyboard and monitor
Half-duplex
Unidirectional flow at a particular instant of time Walkie-Talkie
Full-duplex
Networking
Using the above three modes of data flow, devices can now be
connected to form a network.
A network is a set of devices (often referred to asnodes) connected
by communicationlinks.
A link is acommunications pathway that transfers data from one
device to another.
For visualization purposes, it is simplest to imagine any link as a line
Networking
Types of links
point-to-point
Dedicated link between two points Example: IR remote for TV
multi-point
More than two devices share the same link
Spatial sharing: Several devices use the link simultaneously
Network Topology
Physical topology refers to thescheme of networking physically i.e. scheme of connections of nodes using the links
Its best understood in term so geometric representations.
Four basic topologies:
Mesh
Mesh
In this every device has a dedicated p-2-p link to every device. We need n(n2−1) duplex mode links.
Each device on network must have n−1 I/O ports.
It eliminates the traffic problem.
Mesh topology is robust. Even if one link is unusable , it does not effect the entire network.
The system has advantage of privacy & security.
Easy fault identification & correction
Star
Star
Each device has a dedicated P-2-P link only to central controller called as hub.
It does not allow direct traffic between devices. The controller acts as an exchanger.
If one sends data to another, it sends data to the controller, which then relay the data to another connected device.
In this each device needs only 1 I/O port.
Bus
Bus
It is a multi point communication system.
One long cable acts as backbone to link all the devices in the network.
Nodes are connected to bus cable by drop lines and taps.
Advantage:
Nodes can be connected and disconnected with ease Each node requires just one I/O port.
Disadvantage:
As the signal travels along the bus some of its energy is transformed into heat due to ohmic losses. So the signal becomes weaker & weaker as it travels farther & farther.
It is difficult to fault isolation and reconnection.
Ring
Ring
Each device has a dedicated P-2-P connection with only two devices on either sides.
A signal passes along the ring in one direction only, from device to device, until it reaches its final destination.
In this each device is incorporated with repeater, when a device receives a signal intended for another device, its repeater regenerates the bits and passes them along.
Ring
Various networks
Using the topologies, LAN, WAN, MAN and Internet is constructed.
Transmission Media: Guided and Unguided Media
Transmission media
A transmission media can be defined as anything that can carry information from source to destination.
The transmission medium is usually free space, metallic cable or fiber-optic cable.
In telecommunications, transmission media can be divided into two
Transmission Media: Guided and Unguided Media
Guided Transmission media
Twisted pair cable
Coaxial cable
Fiber-optic cable
A signal traveling along any of these media is directed and contained by the physical limits of the medium. Types of signals in medias:
Twisted-pair and coaxial cable use metallic (copper) conductors that accept and transport signals in the form of electric current.
Transmission Media: Guided and Unguided Media
Figure:Transmission media types
A twisted pair consist of two conductors (normally copper), each with its own plastic insulation and twisted together.
One of the wires is used to carry signals to the receiver, and the other is used only as a ground reference.
Cancellation of noise in TPC
If the two wires are parallel, the effect of these unwanted signals is not the same in both wires because they are at different locations relative to the noise or crosstalk sources (e,g., one is closer and the other is farther).
This results in a difference at the receiver. By twisting the pairs, a balance is maintained.
Twisting makes it probable that both wires are equally affected by external influences (noise or crosstalk).
Hence the number of twists per unit of length (e.g., inch) has some effect on the quality of the cable.
TPC can also be shielded by a metal cover or a metal braid to decrease noise penetration.
Shielded and unshielded
Figure: Shielded and unshielded
Co-axial cable
Figure: Co-axial cable
Coaxial cable has a central core conductor of solid wire (usually copper) enclosed in an insulating sheath, which is, in turn, encased in an outer conductor of metal foil, braid, or a combination of two. The outer metallic wrapping serves both as a shield against noise and as the second conductor.
Optical fiber
Optical fiber based communication is based on the phenomenon of
Optical fiber based communication
Wireless transmission
Ground propagation
Signal travel along the lowest portion of atmosphere.
Low frequencies up to 2 MHz.
Sky propagation
Signals of higher frequencies are emitted by antenna towards
ionosphere which reflects them back towards other antennas ANtennas must be directional in nature.
Line-of-sight propagation
Very high frequencies are propagated from antenna to antenna which ae placed along the line-of-sight.
Categories of wireless transmission
Categories of wireless transmission
Radio waves (3KHz to 1GHz) are used for multicast transmission like radio, television etc.
RW are omnidirectional hence antenna alignment is not necessary. Low frequency RW can penetrate walls.
Microwave (1−300 GHz) is used for unicast transmission like cellular
telephone, satellite networks and wireless LANs.
Microwave based communciation is unidirectional.
Assignment
1 Find out which ranges of frequencies are used for:
FM radio transmission
Mobile phone companies for 4 different companies Walkie Talkie
Military communications Wireless LAN at GDGU Wireless LAN at your home
2 Find out how does an antenna for mobile phone, wireless LAN and
FM radio differ in their features.
3 How to we generate frequencies for question no.1.
4 Describe how HAM radio works and which architecture of wireless
propagation does it use.
Ideas for Project!
Make an FM transmitter and receiver and show transmission of high-quality voice signal. Measure the efficiency of transmission.
Make an AM transmitter and receiver and show transmission of high-quality voice signal. Measure the efficiency of transmission. Study the transmission system of a mobile phone company.
Study the transmission system of FM radio station.
Study the transmission system of walkie-talkie based communication system.
Transmission Impairmentss
Since transmission media are not ideal, various kinds of imperfection
occur during signal transmission.
This means that the signal at the beginning of the medium is not the same as the signal at the end of the medium. What is sent is not what is received.
Attenuation
Attenuation means reduction, which indicates loss of signal power Attenuation can be seen in any property of a wave i.e amplitude, frequency and phase.
Attenuation is caused by resistance to flow of signal offered by transmission medium and hence depends on both medium and signal properties.
Distrotion
Distortion means change of signal waveform shape.
Phase-difference between input waves determines the shape of output wave
Hence phase mismatching produces distortions when individual signals signals experience different phase differences in a medium.
Noise
Mixing of unwanted signal in original signal results in noise. Quality of signal is measured in signal to noise ratio.
Find out various sources of noise
Noise
References:
https://en.wikipedia.org/wiki/Noise_(electronics)
https://en.wikibooks.org/wiki/Electronics/Noise_in_ electronic_circuits
