UnitI Introduction to Computer Networking Introduction What is

Unit-I Introduction to Computer Networking ü Introduction: What is Computer communication? Communication system, Signal and Data, Channel Characteristics, Transmission Modes, Synchronous and asynchronous transmission ü Transmission Media: Guided Media – Twisted Pair, Coaxial and Fiber-optic cables, Unguided Media: Radio, VHF Micro Waves and Satellite Multi-channel Data Communication: Circuits, channels and multi-channeling, Multiplexing: FDM, TDM, CDM and WDM Prof. Deshmukh Santosh S. (MCA SIT)

What is Computer Communication? • The interaction and transmission of data from one computer to another via a telecommunications media. • The basic concept of data communication is data sent from one place to another place. • Sharing of Information that can be local or remote. • Data communication is the exchange of data between two devices via some form of transmission medium such as a wire cable. • The effectiveness of data communication system depends on Three fundamental characteristics: • Delivery : The system must deliver data to the correct destination. • Accuracy : The system must deliver the data accurately. • Timeliness : The system must deliver the data in timely manner. Data deliver late are useless. Prof. Deshmukh Santosh S. (MCA SIT)

• What is Computer Network ? § § Computer Network means a collection of autonomous computer s interconnected by a single technology. Two computers are said to be interconnected if they are able to exchange information. The connection need not be via a copper wire , fiber optics, microwaves, but also using communication satellites. Data Communication System Components Prof. Deshmukh Santosh S. (MCA SIT)

• The Data communication system has five components : ØMessage: The Massage is the information or data to be communicated. It can consist of text, number, picture, sound or video etc. Ø Sender: The sender is the device that sends the data message. It can be computer, workstation, telephone handset, video camera and so on. Ø Receiver: The receiver is the device that receives the message. It can be computer, workstation, telephone, television and so on. Ø Medium: The transmission medium is the physical path by which a message travels from sender to receiver. It could be twisted-pair wire, coaxial cable, fiber optic cable or radio waves (satellite). Ø Protocol: A protocol is set of rules that governs data communication. Without a protocol, two devices may be connected but not communicating. Prof. Deshmukh Santosh S. (MCA SIT)

A Communications Model/System • Source – generates data to be transmitted • Transmitter – Converts data into transmittable signals • Transmission System – Carries data • Receiver – Converts received signal into data • Destination – Takes incoming data Prof. Deshmukh Santosh S. (MCA SIT)

Signals and Data Entities that convey meaning Data can be analog or digital A collection of facts in raw forms that become information after processing. Data must be transformed to electromagnetic signals. The term Analog data refers to information that is continuous. digital data refers to information that has discrete states. Analog data take on continuous values. Digital data take on discrete values. Signals Electric or electromagnetic representations of data Signals can be analog or digital Electric or electromagnetic encoding of data. Transmission Communication of data by propagation and processing of signals. Communication of data achieved by the processing of signals. • Analog and digital • Aperiodic/non periodic. Prof. Deshmukh and Periodic signals Santosh S. (MCA SIT)

Data • Analog – Continuous values within some interval – e. g. sound, video, analog clock • Digital – Discrete values – e. g. text, integers, digital clock Prof. Deshmukh Santosh S. (MCA SIT)

Example : Analog and Digital data by Clocks Prof. Deshmukh Santosh S. (MCA SIT)

Signals • Means by which data are propagated • Analog – Continuously variable – Can have an infinite number of values in a range – Various media • wire, fiber optic, space – Speech bandwidth 100 Hz to 7 k. Hz – Telephone bandwidth 300 Hz to 3400 Hz – Video bandwidth 4 MHz • Digital – Can have only a limited number of values Prof. Deshmukh Santosh S. (MCAcomponents SIT) – Use two Data Communication

Comparison of Analog and Digital Signals ü The vertical axis represents the value or strength of a ü ü ü signal. The horizontal axis represents the time. The curve representing the analog signal passes through an infinite number of points. The vertical lines representing the digital signal. Prof. Deshmukh Santosh S. (MCA SIT)

Data and Signals • Usually use digital signals for digital data and analog signals for analog data. • Can use analog signal to carry digital data – Modem • Can use digital signal to carry analog data – Compact Disc audio Prof. Deshmukh Santosh S. (MCA SIT)

Transformation of Information to Signals Prof. Deshmukh Santosh S. (MCA SIT)

Digital Signal Prof. Deshmukh Santosh S. (MCA SIT)

Analog Signals Carrying Analog and Digital Data Prof. Deshmukh Santosh S. (MCA SIT)

Digital Signals Carrying Analog and Digital Data Prof. Deshmukh Santosh S. (MCA SIT)

Analog Transmission • Analog signal transmitted without regard to content • May be analog or digital data • Attenuated over distance • Use amplifiers to boost signal • Also amplifies noise Prof. Deshmukh Santosh S. (MCA SIT)

Digital Transmission • • Concerned with content Integrity endangered by noise, attenuation etc. Repeaters used Repeater receives signal Extracts bit pattern Retransmits Attenuation is overcome Noise is not amplified Prof. Deshmukh Santosh S. (MCA SIT)

Advantages of Digital Transmission • Digital technology – Low cost LSI/VLSI technology • Data integrity – Longer distances over lower quality lines • Capacity utilization – High bandwidth links economical – High degree of multiplexing easier with digital techniques • Security & Privacy – Encryption • Integration Prof. Deshmukh Santosh S. (MCA SIT) – Can treat analog and digital data similarly

Transmission Impairments • Signal received may differ from signal transmitted • Analog - degradation of signal quality • Digital - bit errors • Caused by – Attenuation means loss of energy and attenuation distortion – Delay distortion means that the signal changes its form or shape – Noise Prof. Deshmukh Santosh S. (MCA SIT)

TRANSMISSION IMPAIRMENT ü Signals travel through transmission media, which are not perfect. ü The imperfection causes signal impairment (harm). ü 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. üThree causes of impairment are Attenuation, Distortion, and Noise. Topics discussed in this section: 1) Attenuation 2) Distordions 3) Noise Prof. Deshmukh Santosh S. (MCA SIT)

Causes of impairment Prof. Deshmukh Santosh S. (MCA SIT)

Figure 3. 26 Attenuation Prof. Deshmukh Santosh S. (MCA SIT)

Distortion Prof. Deshmukh Santosh S. (MCA SIT)

Noise Prof. Deshmukh Santosh S. (MCA SIT)

Periodic and Nonperiodic Signals • A periodic signal completes a pattern within a measurable time frame called a period and repeats that pattern over subsequent identical periods. • The completion of one full pattern is called a cycle. • A nonperiodic/aperiodic signal changes without exhibiting a pattern or cycle that repeats over time. • Both analog and digital signals can be periodic or nonperiodic. • In data communications, we commonly use periodic analog signals (because need less bandwidth) and nonperiodic digital signals (because variation in data). Prof. Deshmukh Santosh S. (MCA SIT)

Periodic Signals Prof. Deshmukh Santosh S. (MCA SIT)

Aperiodic/ Nonperiodic Signals Prof. Deshmukh Santosh S. (MCA SIT)

• Frequency is the rate of change with respect to time. • Period refers to the amount of time in seconds, a signal needs to complete 1 cycle. • Frequency refers to the number of periods in 1 sec. • Frequency and period are the inverse of each other. • The range of frequencies contained in a composite signal is its bandwidth. • The bandwidth of a composite signal is the difference between the highest and the lowest frequencies contained in that signal. • Phase describes the position of the waveform relative to time 0. Prof. Deshmukh Santosh S. (MCA SIT)

PERIODIC ANALOG SIGNALS Periodic analog signals can be classified as simple or composite. A simple periodic analog signal, a sine wave, cannot be decomposed into simpler signals. A composite periodic analog signal is composed of multiple sine waves. Topics discussed in this section: üSine Wave ü Wavelength ü Time and Frequency Domain ü Composite Signals üBandwidth Prof. Deshmukh Santosh S. (MCA SIT)

A sine wave Prof. Deshmukh Santosh S. (MCA SIT)

Two signals with the same phase and frequency, but different amplitudes Prof. Deshmukh Santosh S. (MCA SIT)

Note Frequency and period are the inverse of each other. Prof. Deshmukh Santosh S. (MCA SIT)

Two signals with the same amplitude and phase, but different frequencies Prof. Deshmukh Santosh S. (MCA SIT)

Note Ø Frequency is the rate of change with respect to time. Ø Change in a short span of time means high frequency. Ø Change over a long span of time means low frequency. Ø If a signal does not change at all, its frequency is zero. Ø If a signal changes instantaneously, its frequency is infinite. Ø Phase describes the position of the waveform relative to time 0. Prof. Deshmukh Santosh S. (MCA SIT)

Three sine waves with the same amplitude and frequency, but different phases Prof. Deshmukh Santosh S. (MCA SIT)

Wavelength and period Note A single-frequency sine wave is not useful in data communications; we need to send a composite signal, a signal made of many simple sine waves. Prof. Deshmukh Santosh S. (MCA SIT)

Note If the composite signal is periodic, the decomposition gives a series of signals with discrete frequencies; if the composite signal is nonperiodic, the decomposition gives a combination of sine waves with continuous frequencies. A composite periodic signal Prof. Deshmukh Santosh S. (MCA SIT)

Note The bandwidth of a composite signal is the difference between the highest and the lowest frequencies contained in that signal. The bandwidth of periodic and nonperiodic composite signals Prof. Deshmukh Santosh S. (MCA SIT)

Prof. Deshmukh Santosh S. (MCA SIT)

Simplex • If transmission is simplex, communication can take place in only one direction. • Devices connected to such a circuit are either a send-only, or a receive -only device. • In simplex mode the communication can take place in one direction. The receiver receives the signal from the transmitting device. In this mode the flow of information is Uni. -directional. Hence it is rarely used for data communication. e. g. Television, printer Prof. Deshmukh Santosh S. (MCA SIT)

Half-Duplex • Can transmit data in both direction, but only one way at a time. Hence alternately send and receive data. • It requires two wires. In half-duplex mode the communication channel is used in both directions, but only in one direction at a time. Thus a half-duplex line can alternately send and receive data. e. g. police radio, connect terminal with a computer Prof. Deshmukh Santosh S. (MCA SIT)

Full-Duplex • In full duplex the communication channel is used in both directions at the same time. • Use of full-duplex line improves the efficiency as the line turn-around time required in half-duplex arrangement is eliminated. • Both directions data flow at the same time • It requires four wires • e. g. telephone Prof. Deshmukh Santosh S. (MCA SIT)

TRANSMISSION MODES The transmission of binary data across a link can be accomplished in either parallel or serial mode. In parallel mode, multiple bits are sent with each clock tick. In serial mode, 1 bit is sent with each clock tick. While there is only one way to send parallel data, there are three subclasses of serial transmission: asynchronous, and isochronous. Topics discussed in this section: 1) Parallel Transmission 2) Serial Transmission. Prof. Deshmukh Santosh S. (MCA SIT)

Data transmission and modes Prof. Deshmukh Santosh S. (MCA SIT)

Parallel transmission * In parallel transmission, a group of bits is sent simultaneously, with each bit on a separate line. Prof. Deshmukh Santosh S. (MCA SIT)

Serial transmission * In serial transmission, there is only one line and the bits are sent sequentially. * Serial transmission can be either synchronous or asynchronous. Prof. Deshmukh Santosh S. (MCA SIT)

Asynchronous transmission • Data is transmitted character by character at irregular intervals. That is, the sender can send a character at any convenient time and the receiver will accept it. • Advantage is that it does not require any local storage at the terminal or the computer, because transmission takes place character by character. Hence it is cheaper to implement. • E. g. Keyboard Note In asynchronous transmission, we send 1 start bit (0) at the beginning and 1 or more stop bits (1 s) at the end of each byte. There may be a gap between each byte. Asynchronous here means “asynchronous at the byte level, ” but the bits are still synchronized; their durations are the same. Prof. Deshmukh Santosh S. (MCA SIT)

Asynchronous transmission Character i. e. Irregular time intervals between two characters/ byte In asynchronous serial transmission, each byte (group of 8 bits) is framed with a start bit and a stop bit. There may be a variable-length gap between each byte. * Prof. Deshmukh Santosh S. (MCA SIT)

Synchronous Transmission • Synchronous mode of data transmission involves blocking a group of characters like records are blocked on magnetic tape. • The number of characters in a block may be variable, and may consist of hundreds of characters. • Each block is framed by header and trailer information. • Header containing synchronizing and other information to identify the sender and receiver. • The trailer contains an end of message character, followed by a check character to aid detection of any transmission error. Hence, with synchronous transmission, entire blocks of characters are framed and transmitted together. Note In synchronous transmission, we send bits one after another without start or stop bits or gaps. It is the responsibility of the receiver to group the bits. Prof. Deshmukh Santosh S. (MCA SIT)

Synchronous Transmission • In synchronous serial transmission, bits are sent in a continuous stream without start and stop bits and without gaps between bytes. • Regrouping the bits into meaningful bytes is the responsibility of the receiver. Prof. Deshmukh Santosh S. (MCA SIT)

Synchronous transmission • Synchronous transmission is to remote communication between a computer and such devices a buffered terminals and printers. • The primary advantage is its efficiency. • Another advantage is use of much higher data rates because it eliminates the need for individual start-stop bits on each character. • Disadvantage : The need for local buffer storage at the two ends of the line to assemble blocks. • Synchronous equipment usually costs more. Prof. Deshmukh Santosh S. (MCA SIT)

Isosyncronous Transmission • The communications system in which the source and target are each synchronized but each transmission contains a start bit and a stop bit. • It was initially started to commercialize a technology called isosynchronous Ethernet, which carries voice calls using a special signaling method much the same way ISDN-based phone systems operated bit. • Isochronous can be contrasted with Asynchronous, which refers to processes in which data streams can be broken by random intervals, and synchronous processes, in which data streams can be delivered only at specific intervals. • Isochronous service is not as rigid as synchronous service, but not as lenient as asynchronous service. Prof. Deshmukh Santosh S. (MCA SIT)

Simplified Communications Model - Diagram Prof. Deshmukh Santosh S. (MCA SIT)

Simplified Data Communications Model Prof. Deshmukh Santosh S. (MCA SIT)

Networking • Point to point communication not usually practical – Devices are too far apart – Large set of devices would need impractical number of connections • Solution is a communications network Prof. Deshmukh Santosh S. (MCA SIT)

Computer Network • An interconnected collection of autonomous computers. • Two computers are said to be interconnected if they are able to exchange information. • A system with one control unit and many slaves is not a network. • Networking is the practice of linking computing devices together with hardware and software that supports data communications across these devices. Prof. Deshmukh Santosh S. (MCA SIT)

Simplified Network Model Prof. Deshmukh Santosh S. (MCA SIT)

Data Transmission Terminology (1) • Transmitter • Receiver • Medium – Guided medium • e. g. twisted pair, optical fiber – Unguided medium • e. g. air, water, vacuum Prof. Deshmukh Santosh S. (MCA SIT)

Terminology (2) • Direct link – No intermediate devices • Point-to-point – Direct link – Only 2 devices share link • Multi-point – More than two devices share the link Prof. Deshmukh Santosh S. (MCA SIT)

Terminology (3) • Simplex – One direction • e. g. Television • Half duplex – Either direction, but only one way at a time • e. g. police radio • Full duplex – Both directions at the same time • e. g. telephone Prof. Deshmukh Santosh S. (MCA SIT)

Transmission Media ü Guided Media ü Unguided Media

Transmission medium and physical layer Prof. Deshmukh Santosh S. (MCA SIT)

Classes of transmission media Radio, VHF, Micro waves, Satellite Prof. Deshmukh Santosh S. (MCA SIT)

Overview • Guided - wire • Unguided - wireless • Characteristics and quality determined by medium and signal • For guided, the medium is more important • For unguided, the bandwidth produced by the antenna is more important Prof. Deshmukh Santosh S. (MCA SIT)

GUIDED MEDIA Guided media, which are those that provide a conduit (channel or pipe or tube or trough protecting insulated electric wire) from one device to another, include twistedpair cable, coaxial cable, and fiber-optic cable. Topics discussed in this section: Ø Twisted-Pair Cable Ø Coaxial Cable Ø Fiber-Optic Cable Prof. Deshmukh Santosh S. (MCA SIT)

Twisted-pair cable Twisted Pair Prof. Deshmukh Santosh S. (MCA SIT)

ü Twisted-pair cable consists of two insulated copper wires twisted together , about 1 mm thick. . ü Twisted-pair cable can be used for transmitting either analog or digital signals. üThe bandwidth depends on the thickness of the wire & the distance traveled. üTwisted-pair cable is used in telephone lines for voice and short distance (up to about 1 km) digital data communications. ü They are normally used to connect terminals to the main computer. E. g. keyboard, printer etc. ü Data transmission speed of up to 9600 bits per second (or 9600 baud), if the distance is not more than 100 meters. ü For longer distance data transmission, local telephone lines are used. ü Typical speed of digital signal transmission is 1200 baud. ü Prof. Deshmukh Santosh S. (MCA SIT)

Twisted Pair - Applications • Most common medium • Telephone network – Between house and local exchange (subscriber loop) • Within buildings – To private branch exchange (PBX) • For local area networks (LAN) – 10 Mbps or 100 Mbps Prof. Deshmukh Santosh S. (MCA SIT)

Twisted Pair • • Cheap Easy to work with Low data rate Short range Prof. Deshmukh Santosh S. (MCA SIT)

Twisted Pair - Transmission Characteristics • Analog – Amplifiers every 5 km to 6 km • Digital – Use either analog or digital signals – Repeater every 2 km or 3 km • Limited distance • Limited bandwidth (1 MHz) • Limited data rate (100 MHz) Prof. Deshmukh Santosh S. (MCA SIT)

Unshielded Twisted-Pair Cable Ø It is also called unshielded twisted-pair (UTP) cable because other than the plastic coating around the two individual of copper wires, nothing shields it from outside interference. Ø UTP cables are inexpensive medium of data transmission. Ø They are easy to install and use. Prof. Deshmukh Santosh S. (MCA SIT)

UTP and STP cables Prof. Deshmukh Santosh S. (MCA SIT)

Unshielded and Shielded TP • Unshielded Twisted Pair (UTP) – Ordinary telephone wire – Cheapest – Easiest to install – Suffers from external EM interference • Shielded Twisted Pair (STP) – Metal braid or sheathing (close fitting cover) that reduces interference – More expensive – Harder to handle (thick, heavy) Prof. Deshmukh Santosh S. (MCA SIT)

Shielded Twisted-Pair Cable Prof. Deshmukh Santosh S. (MCA SIT)

UTP Categories • Cat 3 – up to 16 MHz – Voice grade found in most offices – Twist length of 7. 5 cm to 10 cm • Cat 4 – up to 20 MHz • Cat 5 – up to 100 MHz – Commonly pre-installed in new office buildings – Twist length 0. 6 Prof. Deshmukh cm to 0. 85 cm Santosh S. (MCA SIT)

UTP connector Prof. Deshmukh Santosh S. (MCA SIT)

Coaxial cable Prof. Deshmukh Santosh S. (MCA SIT)

v A Coaxial cable consists of a stiff copper wire as the core, surrounded by an insulating material. v The insulator is encased by a cylindrical conductor, often as a closelywoven braided mesh. v The outer conductor is covered in a protective plastic sheath. v The construction & shielding of the Coaxial cable give it a good combination of high bandwidth & excellent noise immunity. v There are two kinds of Coaxial cables, 50 -ohm Coaxial cable is used for digital transmissions & 75 -ohm Coaxial cable is used for analog transmission, cable television. v Coaxial cable can carry signals of higher frequency ranges than twisted-pair cable and are capable of transmitting digital signals at rates of 10 mega baud. v Coaxial cable is used in cable TV networks and traditional Ethernet LANs as well as long distance telephone lines and also used by telephone companies to transmit data. v Data transmission without distortion or loss of signal. Prof. Deshmukh Santosh S. (MCA SIT)

Coaxial Cable Applications • Most versatile medium • Television distribution – Ariel to TV – Cable TV • Long distance telephone transmission – Can carry 10, 000 voice calls simultaneously – Being replaced by fiber optic • Short distance computer systems links • Local area networks Prof. Deshmukh Santosh S. (MCA SIT)

Coaxial Cable - Transmission Characteristics • Analog – Amplifiers every few km – Closer if higher frequency – Up to 500 MHz • Digital – Repeater every 1 km – Closer for higher data rates NOTE : - If signals are sent in digital mode. In this case modem are not needed. When digital transmission is used over long distances, a repeater is used to receive and then transmit the signal. Like an amplifier, The purpose of a repeater is to strengthen a weak digital signal over long distances. Prof. Deshmukh Santosh S. (MCA SIT)

Optical fiber Cladding : covering or coating on a structure or material Fiber Construction Prof. Deshmukh Santosh S. (MCA SIT)

Ø Fiber-optic cables are composed of a glass or plastic inner core surrounded by cladding, all encased in an outside jacket. Ø Fiber-optic cables carry data signals in the form of light. That is optical fiber transmit light signals instead of electrical signals. Because light travels much faster than electricity, optical fibers can transmit data at much higher speed than copper wires or coaxial cables. Ø Fiber-optic transmission is becoming increasingly popular due to its noise resistance, low attenuation, and high-bandwidth capabilities. Ø Fiber-optic cable is used in backbone networks, cable TV networks, and Fast Ethernet networks. Prof. Deshmukh Santosh S. (MCA SIT)

Optical Fiber Prof. Deshmukh Santosh S. (MCA SIT)

Optical Fiber - Benefits üGreater capacity, large bandwidth --Data rates of hundreds of Gbps üSmaller size & lightweight üLow loss üSecurity üSafety and electrical insulation üAnalog and digital signals transmission üLower attenuation üElectromagnetic isolation üGreater repeater spacing -10 s of km at least Prof. Deshmukh Santosh S. (MCA SIT)

Optical Fiber - Applications • • • Long-haul trunks (main stream) Metropolitan trunks Rural exchange trunks Subscriber loops LANs Prof. Deshmukh Santosh S. (MCA SIT)

Optical Fiber - Transmission Characteristics üAct as wave guide for 1014 to 1015 Hz – Portions of infrared and visible spectrum üLight Emitting Diode (LED) – Cheaper – Wider operating temp range – Last longer ü Injection Laser Diode (ILD) – More efficient – Greater data rate ü Wavelength Division Multiplexing Prof. Deshmukh Santosh S. (MCA SIT)

Fiber construction Prof. Deshmukh Santosh S. (MCA SIT)

Fiber-optic cable connectors Prof. Deshmukh Santosh S. (MCA SIT)

UNGUIDED MEDIA: WIRELESS • Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. • Unguided media (usually air) transport electromagnetic waves without the use of a physical conductor. • Wireless data is transmitted through ground propagation, sky propagation, and line-of-sight propagation. Topics discussed in this section: 1)Radio Waves 2) VHF (Very high Frequency) 3) Microwaves 4) Satellite Prof. Deshmukh Santosh S. (MCA SIT) 5) Infrared

Wireless Transmission • Unguided media • Transmission and reception via antenna • Directional – Focused beam – Careful alignment required • Omnidirectional – Signal – spreads in all directions – Can be received by many antennae Omnidirectional antenna Prof. Deshmukh Santosh S. (MCA SIT)

• Radio Waves • There are two principal ways in which electromagnetic energy (radio waves) travels from a transmitting antenna to a receiving antenna. One way is by ground waves and the other is by sky waves. • Ground waves are radio waves that travel near the surface of the Earth (surface and space waves). • Sky waves are radio waves that are reflected back to Earth from the ionosphere. • Radio frequencies are in the range of 300 k. Hz to 10 GHz. • Radio is the transmission of signals by modulation of electromagnetic waves with frequencies below those of visible light. • Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space Prof. Deshmukh Santosh S. (MCA SIT)

• Information is carried by systematically changing (modulating) some property of the radiated waves, such as amplitude, frequency, phase, or pulse width. • When radio waves pass an electrical conductor, the oscillating fields induce an alternating current in the conductor. • This can be detected and transformed into sound or other signals that carry information. • The properties of radio waves are frequency dependent. Prof. Deshmukh Santosh S. (MCA SIT)

• VHF (Very High Frequency) • The VHF spectrum is defined as the part of the electromagnetic spectrum which includes any radiation with a wavelength between 1 to 10 meters and a frequency between 30 to 300 megahertz. • VHF signals are widely employed for television and radio transmissions. VHF electromagnetic waves, unlike longer electromagnetic waves, are not strongly reflected from the atmosphere; therefore, they do not bend readily around the Earth's curvature and cannot be transmitted beyond the horizon. • VHF systems are limited to use in short-range, line-of-sight communications, including radio and television broadcasting, and in marine communication and navigation systems. • VHF signals of the same frequency can be used by transmitters several hundred miles apart without interfering with one another. Prof. Deshmukh Santosh S. (MCA SIT)

Note Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs. Prof. Deshmukh Santosh S. (MCA SIT)

Broadcast Radio • Omnidirectional • FM radio • UHF (ultra high frequency) and VHF (very high frequency) television • Line of sight • Suffers from multipath interference – Reflections Prof. Deshmukh Santosh S. (MCA SIT)

Note Radio waves are used for multicast communications, such as radio and television, and paging systems. Prof. Deshmukh Santosh S. (MCA SIT)

• Microwaves : ØMicrowave transmission is line of sight transmission. ØThe transmit station must be in visible contact with the receive station. ØThis sets a limit on the distance between stations depending on the local geography. Typically the line of sight due to the Earth's curvature is only 50 km to the horizon! Repeater stations must be placed so the data signal can hop, skip and jump across the country. ØMicrowaves operate at high operating frequencies of 3 to 10 GHz. This allows them to carry large quantities of data due to their large bandwidth. Prof. Deshmukh Santosh S. (MCA SIT)

• Advantages of Microwave Transmission : ü They require no right of way acquisition between towers. ü They can carry high quantities of information due to their high operating frequencies. ü Low cost land purchase: each tower occupies only a small area. ü High frequency/short wavelength signals require small antennae. • Disadvantages of Microwave Transmission : ü ü Attenuation by solid objects: birds, rain, snow and fog. Reflected from flat surfaces like water and metal. Diffracted (split) around solid objects. Refracted by atmosphere, thus causing beam to be projected away from receiver. Prof. Deshmukh Santosh S. (MCA SIT)

Satellite Communication Prof. Deshmukh Santosh S. (MCA SIT)

Satellite Microwave/Communication Satellites q. Satellites are transponders (units that receive on one frequency and retransmit on another) that are set in geostationary orbits directly over the equator. q. These geostationary orbits are 36, 000 km from the Earth's surface. At this point, the gravitational pull of the Earth and the centrifugal force of Earth's rotation are balanced and cancel each other out. q Centrifugal force is the rotational force placed on the satellite that wants to fling it out into space. q. Satellite is relay station q. Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency q. Requires geo-stationary orbit o Height of 35, 784 km q. Television q. Long distance telephone Prof. Deshmukh Santosh S. (MCA SIT) q. Private business networks

Geosynchronous Orbit Prof. Deshmukh Santosh S. (MCA SIT)

Cellular System Prof. Deshmukh Santosh S. (MCA SIT)

Cellular Bands Prof. Deshmukh Santosh S. (MCA SIT)

Frequencies • 2 GHz to 40 GHz – Microwave – Highly directional – Point to point – Satellite • 30 MHz to 1 GHz – Omnidirectional – Broadcast radio • 3 x 1011 to 2 x 1014 – Infrared – Local Prof. Deshmukh Santosh S. (MCA SIT)

Infrared • • Modulate noncoherent infrared light Line of sight (or reflection) Blocked by walls e. g. TV remote control, IRD port Prof. Deshmukh Santosh S. (MCA SIT)

Note Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation. Prof. Deshmukh Santosh S. (MCA SIT)

Electromagnetic spectrum for wireless communication Prof. Deshmukh Santosh S. (MCA SIT)

Propagation methods Prof. Deshmukh Santosh S. (MCA SIT)

Bands Prof. Deshmukh Santosh S. (MCA SIT)

Unidirectional antennas Prof. Deshmukh Santosh S. (MCA SIT)

Multiplexing § Multiplexing is the transmission of multiple data communication sessions over a common wire or medium. § Multiplexing reduces the number of wires or cable required to connect multiple sessions. § A session is considered to be data communication between two devices: computer to computer, terminal to computer, etc. • Many to one/one to many • Types of multiplexing • Telephone system

Multiplexing vs. No Multiplexing Prof. Deshmukh Santosh S. (MCA SIT)

Prof. Deshmukh Santosh S. (MCA SIT)

FDM(Frequency Division Multiplexing ) § Frequency-division multiplexing (FDM) is a scheme in which numerous signals are combined for transmission on a single communications line or channel. § Each signal is assigned a different frequency (subchannel) within the main channel. § A typical analog Internet connection via a twisted pair telephone line requires approximately three kilohertz (3 k. Hz) of bandwidth for accurate and reliable data transfer. § Twisted-pair lines are common in households and small businesses. § FDM does not require all channels to terminate at a single location. Channels can be extracted using a multi-drop technique; terminals can be stationed at different locations within a building or a city. Prof. Deshmukh Santosh S. (MCA SIT)

FDM, Time Domain When FDM is used in a communications network, each input signal is sent and received at maximum speed at all times. Prof. Deshmukh Santosh S. (MCA SIT)

Multiplexing, Frequency Domain Demultiplexing, Time Domain Prof. Deshmukh Santosh S. (MCA SIT)

TDM(Time Division Multiplexing ) Ø Time Division Multiplexing is a technique where a short time sample of each channel is inserted into the multiplexed data stream. Ø Each channel is sampled in turn, and then the sequence is repeated. Ø TDM is the process of dividing up one communication time slot into smaller time slots. ØTime-division multiplexing (TDM) is a digital technology. Ø TDM involves sequencing groups of a few bits or bytes from each individual input stream, one after the other, and in such a way that they can be associated with the appropriate receiver Prof. Deshmukh Santosh S. (MCA SIT)

CDM(Code division multiplexing ) Ø CDM is a technique in which each channel transmits bits as a coded channel-specific sequence of pulses. Ø This coded transmission typically transmitting a unique timedependent series of short pulses, which are placed within chip times within the larger bit time. ØAll channels, each with a different code, can be transmitted on the same fiber and asynchronously demultiplexed. Ø Other widely used multiple access techniques are Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA). ØCDM techniques are used as an access technology, namely Code Division Multiple Access (CDMA), in Universal Mobile Telecommunications System (UMTS) standard for the third generation (3 G) mobile communication identified by the ITU. Ø Another important application of the CDMA is the Global Positioning System (GPS). Prof. Deshmukh Santosh S. (MCA SIT)

WDM(wavelength Division Multiplexing ) § WDM is a technique that multiple signals are carried together as separate wavelengths (color) of light in a multiplexed signal. § WDM is used in optical fiber networks. § Wavelength Division Multiplexer is a device that combines optical signals from multiple different single-wavelength end devices onto a single fiber. Wavelength Division Multiplexer carries two to four wavelengths per fiber. § WDM and FDM are both based on the same principles but WDM applies to wavelengths of light in optical fiber while FDM is used in electrical analog transmission. § A WDM optical system using a diffraction grating is completely passive, unlike electrical FDM, and thus is highly reliable. § Further, a carrier wave of each WDM optical channel is higher than that of an FDM channel by a million times in frequency (THz versus MHz). Prof. Deshmukh Santosh S. (MCA SIT)

WDM Multiplexer is a device that combines optical signals from multiple different single-wavelength end devices onto a single fiber. The same device can also perform the reverse process with the same WDM techniques: de-compose the data stream with multiple wavelength into multiple single wavelength data streams, a process call de-multiplexing. Prof. Deshmukh Santosh S. (MCA SIT)

Self learning Session 1. 2. 3. 4. 5. 6. 7. 8. 9. What is Computer Communication? What are the basic characteristics of communication system? What are the importance of communication system? Explain the basic components/elements of communication system with diagram? What is data and signals? What is Analog and digital data with give the example? What are the characteristics of Analog and digital signals? What are the advantages of digital transmission? Name three types of transmission impairment. Or causes of impairment. Prof. Deshmukh Santosh S. (MCA SIT)

Self learning Session 1. 2. 3. 4. 5. 6. 7. 8. 9. Differentiate among simplex, half duplex and full duplex modes of data transmission. What is periodic and nonperiodic signals? Explain it with diagram. Write a short note on a) Frequency b) Bandwidth c) Period d) Phase e) Amplitude f) Wavelength g) Composite signal Describe the asynchronous and synchronous modes of data transmission. List out the relative advantages and disadvantages of asynchronous and synchronous modes of data transmission. Write a short note on Guided and Unguided media. What is wire pair? In what situations are they suitable for use in data transmission? What is the major advantage of shielded twisted pair over unshielded twisted pair cable? What is a coaxial cable? Give some of its practical uses. Prof. Deshmukh Santosh S. (MCA SIT)

Self learning Session 1. 2. 3. 4. 5. 6. 7. 8. 9. Explain how microwave systems can be used for communication between two stations. How are communications satellites used? What are the possible advantages and limitations of using a communications satellite? What is an optical fiber? How is it used for data communications? What are its advantages? What is repeater? How is it different from an amplifier? What do you understand by modulation and demodulation? What is a multiplexer? Explain its function with the help of a diagram. Describe the two basic methods of multiplexing. Give uses of both the methods. What is the purpose of Guard band? List out the difference between FDM and TDM. Which method is Prof. Deshmukh Santosh S. (MCA SIT) suitable for communication between computers and why?

Self learning Session 1. 2. 3. How does TDM combine multiple signals into one? How is one TDM signal separated into its original components? How is WDM is similar to FDM? How are they different? Prof. Deshmukh Santosh S. (MCA SIT)