Basics of Data Communication,

7/28/2019 Basics of Data Communication,

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Telelabs Wireless Technologies Private Limited, Mumbai Hub, C-18, Gr. Floor, Kailash Esplanade, LBS Road,

Opp. Shreyas Cinema, Ghatkopar West, Mumbai 400086, Ph022 6448 0114 website: www.teleleabs.in

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1. DATA COMMUNICATION NETWORKS1.1. INTRODUCTIONElectronic communications consist of telecommunication and data communication.

Telecommunication consists of telephone, teletype-writing, telegraph and radio or televisionfacilities to transmit information either directly or via-computer. Data communication is the

transfer of data or information between computer devices.

1.2. DATA COMMUNICATION: It refers to the exchange of data (represented as a bit pattern ora sequence of bits) between two devices via some transmission medium such as a wire

cable. The data communication system consists of five main components:

1.2.1. Message: It is the data or information to be communicated.1.2.2. Sender: It refers to the device which transmits or sends the data message.1.2.3. Receiver: It is the device that receives the message.1.2.4. Transmission medium: It is the medium or path through which the message

travels from sender to receiver.

1.2.5. Protocol: These are the set of rules that has to be followed while transmission ofdata and these rules governs data communication.

1.2.6. Network: It is a set of devices (or nodes) connected by communication links. Anode can be a computer, printer or any other device capable of sending or

receiving data generated by other nodes on the network.

The effectiveness of the data communication system depends on four factors:

1.2.7. Delivery: The system should deliver the data to the correct destination and datamust be received by the receiving device.

1.2.8. Accuracy: The data delivered at the destination must be accurate. Data should notbe altered in transmission and left uncorrected.

1.2.9. Timeliness: The system must be capable of delivering the data message in time.Data delivered late in case of real time application like video streaming, are

useless.

1.2.10. Jitter: It is the variation in the packet arrival time. It is the uneven delay in thedelivery of audio or video packets.

1.3. BASIC TERMINOLOGIES USED IN DATA COMMUNICATION:1.3.1. BAUD RATE: The rate at which the data transfers over the communication is called

communication rate or data rate. Baud is the number of signal level changes per

second in the signal line.

1.3.2. Bits Per Second (BPS): It is the rate of transfer of information bits. The ratio of BPSto baud rate entirely depends on the information coding scheme used.

1.3.3. Hartley-Shannon Theorem: It states that the maximum rate at which the data canbe transmitted error-free over a communication channel is the Channel Capacity,

which is given by,

C= B log2 (1+ (S/N))

Where B is bandwidth (in hertz), S/N is signal to noise ratio (in decibels) and C is the channel

capacity measured in bits/second.


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1.3.4. Parallel Interface: Interfaces are used to transfer data from one place to another.In parallel interface, 8 wires are used to transmit a byte (8 bits) of data. It is very

expensive and very fast as compared to serial interfaces. It is basically a

simultaneous transmission of data. It is used to transfer data on same sites i.e.

between one printer and one computer.

1.3.5. Serial Interface: It is a sequential transmission of data of eight bits of a data. Atransmitter breaks each byte into eight bits and sends it one by one sequentially;

the receiver reassembles all the eight bits into a single byte. It is slower than the

parallel since, each bit is transmitted one by one. It is used when data is

transferred between two computers.

1.4. Data Transmission techniques: For the communication between computers and line, thedigital data need to be converted into analog signal. The data at transmitter is converted

into analog, by modulation technique and similarly at receiver the data is again converted

into digital using demodulation technique. This is done by using MODEM at both the ends.1.5. Data Transmission methods: Data transmissions methods are divided into three

categories.

1.5.1. Synchronous Transmission: Synchronous is the method in which the data istransmitted in clock cycles. Each block of characters is marked with a

synchronisation character. The receiver will receive the data until the synchronous

character is detected. Timing errors are reduced and it can perform error detection

so that cyclic redundancy checks are performed on the data on both the sides.

(image)

1.5.2. Asynchronous Transmission: It is the method of transmission in which onecharacter is transmitted at a time. Each character is encapsulated with start and

stop bits which indicates the beginning and end of a data stream. A telephone

conversation is asynchronous because each party can talk whenever they like. If, it

would have been synchronous then one party has to wait for a period of time

before speaking again. (image)

1.5.3. Isochronous Transmission: Isochronous means basically time dependent. In this,the data is transferred within certain time frame. For example: ATM networks are

said to be isochronous because they guarantee a specified throughput. Even the

oscillations are produced by pendulum.

1.6. DATA TRANSMISSION MODES:

1.6.1. Simplex mode: In this mode of transmission, data is transferred in only onedirection. In this mode, a device can either send or receive data. For example: TVs

and radios.

1.6.2. Half Duplex mode: In this mode of transmission, data can be transmitted back toand fro between the two devices but at any instant of time, data can go only in one

direction. Only one end transmits at a time and the other end receives. For

example: Internet surfing.

1.6.3. Full Duplex mode: In this mode of transmission, the data can be transmitted inboth the direction simultaneously. This mode is fast as it avoids the delay caused

by the half duplex circuit each time. For example: Mobile communication.


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1.7. NETWORK TOPOLOGY: The topology of a network is the geometric representation ofthe relationship of all the links and linking devices to one another. There are mainly four

types of network topologies:-1.7.1. MESH TOPOLOGY: In this topology, every device (or nodes) has a dedicated point-

to-point link to every other device.

1. ADVANTAGES:-a) The use of dedicated links eliminates the traffic problems by

guarantying that each connection can carry its own load.

b) This topology is robust i.e. if one link becomes unusable, itdoes not incapacitate the entire system.

c) High security and privacy is maintained due to dedicatedpaths.

2. DISADVANTAGES:-a) Its major disadvantage is that the number of connections

grows quadratic ally with the number of nodes, per the

formula And so it is extremely impractical

for large networks.

b) Installation and reconnection are difficult because everydevice is connected to every other device.

c) Practical application e.g.:- connection of telephone regionaloffices.

1.7.2. STAR TOPOLOGY: - In this topology, every device (or nodes) has a dedicated point-to-point link only to a central controller, usually called a hub. The controller acts as

an exchange: if one device wants to send data to another, it sends the data to

controller which then relays the data to other connected device.

1. ADVANTAGE:-a) Less expensive compared to mesh topology.b) Easy to install and reconfigure.c) This topology also had robustness feature.

2. DISADVANTAGE:-a) Its major disadvantage is the dependency of the whole

topology on a single point, the hub.

b) If hub goes down then whole system is dead.c) Practical application:- used in Local Area Networks (LANs).

1.7.3. BUS TOPOLOGY: - This topology is a multi-point links. One long cable acts as thebackbone to link all the other devices in a network. Nodes are connected to the

bus cable by drop lines and taps. A tap is a connector that either splices or

punctures the sheathing to create a contact with metallic core.

1. ADVANTAGE:-a) Very easy to install and backbone cable is laid along the most

efficient path.

b) Uses less cabling and redundancies are eliminated.2. DISADVANTAGE:-

a) Difficult reconnection and fault isolation.


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b) Signal reflection at the taps can cause degradation in quality.1.7.4. RING TOPOLOGY: - In this topology, every device has a dedicated point-to-point

link with only the two devices on either side of it. A signal is passed along the ring

in one direction, from device to device, until it reaches its destination. Each devicein the ring incorporates a repeater.

1. ADVANTAGE:-a) To add or delete a device requires changes in only two

connections.

b) Fault isolation is simplified, if one device does not receive asignal within a specified time, it can issue an alarm which alerts

the operator.

2. DISADVANTAGES:-a) Traffic is unidirectional.b) A break in the ring can disable the entire network.

1.7.5.

HYBRID TOPOLOGY: - Hybrid networks use a combination of any two or moretopologies in such a way that the resulting network does not exhibit one of the

standard topologies (e.g., bus, star and ring).A hybrid topology is always produced

when two different basic network topologies are connected. Two common

examples for Hybrid network are: star ring networkand star bus network. A Star

ring network consists of two or more star topologies connected using a

multistation access unit (MAU) as a centralized hub. A Star Bus network consists of

two or more star topologies connected using a bus trunk (the bus trunk serves as

the network's backbone).

1.8. CATEGORIES OF NETWORKThe category of a network is determined by its size. Mainly the networks are divided into 3

types of categories:-

1.8.1. Local Area Network: - A LAN is a computer network that interconnects computersin a limited area such as a home, school, computer laboratory, or office building

using network media. Normally LAN covers an area up to 3km.LANs are designed

to allow resources to be shared between personal computers or workstations. The

resources to be shared can be hardware, software or data. The most common LAN

topologies are bus, ring and star. Speeds of data rate in LAN are 100 to

1000Mbps.It is normally privately owned.1.8.2. Wide Area Network: - A WAN provides long-distance transmission of data, image,

audio and video information over large geographical areas that may be a country,

continent or whole world using private or public network transports. Business and

government entities utilize WANs to relay data among employees, clients, buyers,

and suppliers from various geographical locations. In essence, this mode of

telecommunication allows a business to effectively carry out its daily function

regardless of location. The Internet can be considered a WAN as well, and is used

by businesses, governments, organizations, and individuals for almost any purpose

imaginable.1.8.3. Metropolitan Area Network: - A MAN is a network with a size between a LAN and

a WAN. It normally covers the area inside the town or a city. It is designed for the

customers who need a high-speed connectivity to the internet, and have endpointsspread over a city or part of a city. One of the examples is cable TV network that


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originally was designed for cable TV, but today can also be used for high-speed

data connection to the internet.

1.9. ANALOG, DIGITAL AND COMPOSITE SIGNALS1.9.1. ANALOG SIGNALS: An analog signal has infinitely many levels of intensity over a

period of time. The term analog data refers to information that is continuous.

Analog data are continuous and takes continuous values. For example, an analog

clock that has hour, minute, and second hands gives information in a continuous

form; the movement of the hands are continuous. These signals can be classified

as periodic and non-periodic signals:

1. Periodic Signals: A periodic signal completes a pattern within ameasurable time frame, called period and repeats the pattern over a

subsequent identical period. A periodic analog signal can be classified

as simple or complex. A simple periodic analog signal, sine wave

cannot be decomposed into simpler signals. A composite periodic

analog signal is composed of multiple sine waves.2. Non-periodic signals: A non-periodic signal changes without exhibiting

a pattern or cycle that repeats over time.

1.9.2. DIGITAL SIGNALS: Digital data have discrete states and take discrete values. Adigital signal canhave only a limited number of defined values. These times instant

need not be equidistant, but generally they are taken at equally spaced intervals

for convenience.

1.9.3. ADVANTAGES OF DIGITAL COMMUNICATION:1. Digital communication systems are cheaper and simpler than analog

communication.

2. Using data encryption, only permitted receivers are1.10. TRANSMISSION MEDIA

A TRANSMISSION MEDIUM is defined as anything that can carry information from a source

to a destination or a path over which a signal propagates. It is usually a free space, metallic

cable, or fibre-optic cable. In telecommunications, transmission media can be divided into

two broad categories:

a. Guided media- includes twisted pair cable, coaxial cable, and fibre-optic cableb. Unguided media- means free space

1.10.1. GUIDED MEDIA: Guided media are those which provides a conduit from onedevice to another, includes twisted-pair cable, coaxial cable and fibre -optic cable.

It can also be define as, in this media waves are guided along a solid medium such

as transmission line. A signal travelling along any of these media is directed and

contained by the physical limits of the medium.

1. Twisted-pair cable:-It consists of two conductors, each with its ownplastic insulation and twisted together. One wire is used to carry

signals and other acts as a ground reference. The difference between

two is used by the receiver. The number of twists per unit length has

some effect on the quality of the cable. Twisted pair are used in


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telephones to provide voice and data channels. These are of two

types:

2. Unshielded twisted-pair cable: This is commonly used for computernetworks within a building that is for Local area networks. Data rate of

LANs using twisted pair is 10Mbps to 100Mbps. The data rate depends

on the thickness of the cable and distance between the transmitter

and receiver. Two types of UTP are common in LANs: category 3 and

category 5. This is also used in telephones. The most common UTP

connector is RJ45 (RJ stands for registered jack); it is a keyed

connector, meaning the connector can be inserted in only one way.

3. Shielded twisted-pair cable: STP cable has a metal foil or braided-mesh covering that encases each pair of insulated conductors. Metal

casing improves the quality of cable by preventing the penetration of

noise or crosstalk; it is also bulkier and more expensive.4. Coaxial cable: - It carries signal of higher frequency ranges than those

in twisted-pair cable. It has a central core conductor of solid wire

enclosed in an insulating sheath, which is, in turn, encased in an outer

conductor of metal foil, braid, or a combination of the two. Coaxial

cables are categorized by their radio government ratings. Each cable

defined by an RG rating is adapted for a specialized function such as

a. RG-59 -75 ohm impedance - cable TVb. RG-58 -50 ohm impedance -Thin Ethernetc. RG-11 -50 ohm impedance -Thin Ethernet

The attenuation is much higher in coaxial cables than in twisted-

pair cable. It requires the frequent use of repeaters due to rapid

signal weakening. These are widely used in analog telephone networks

and also used in traditional Ethernet LANs. Cable TV networks also use

coaxial cables

5. Fibre-optic cable: - It is made of glass or plastic and transmits signals inthe form of light. Optical fibre uses reflection to guide light through a

channel. A glass or plastic core is surrounded by a cladding of less

dense glass or plastic. The difference in density of two materials mustbe such that a beam of light moving through the core is reflected off

the cladding instead of being refracted into it. It is often found in

backbone networks because its wide bandwidth is cost-effective.

Advantages and disadvantages of optical fibre:

a. Higher bandwidth and less signal attenuation.b. Immunity to electromagnetic interference and to tapping.c. Resistance to corrosive materials.d. Light weighte. Difficult to install and maintain.f. Unidirectional light propagation.


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1.10.2. UNGUIDED MEDIA: - (or WIRELESS) this media transport electromagnetic wavewithout using a physical conductor. Signals are broadcast through free space.

These signals can travel in several ways:1. GROUND PROPAGATION: - In this, radio waves travel through the

lowest portion of the atmosphere, or near the earths surface.

Distance of transmitting depends on the power of the signal.

2. SKY PROPAGATION: - In this, higher frequency radio waves radiateinto the ionosphere and get reflected back to the earth at destination.

It allows greater distance with lower output power.

3. LINE-OF-SIGHT PROPAGATION: - In this type of propagation, veryhigh-frequency signals are transmitted in straight lines directly from

antenna to antenna.

1.11. WIRELESS TRANSMISISSION WAVES:-1.11.1. RADIO WAVES: electromagnetic waves ranging between 3 KHz to 1GHz are called

radio waves. These are Omni-directional i.e. the sending and receiving antennas do

not have to be aligned but radio wave from one antenna may interfere another

antenna sending signal at same frequency.

The Omni directional characteristic of radio waves makes them useful for

Multicast communications (or multicasting). AM and FM radio, TV, cordless

phones, and paging are examples of multicasting.

1.11.2. MICROWAVES: Electromagnetic waves having frequencies between 300 MHz to300 GHz are called microwaves. These are unidirectional i.e. the sending andreceiving antennas need to be aligned. Microwave propagation is line-of-sight.

Very high-frequency microwaves cannot penetrate walls.

1.11.3. INFRARED WAVES: These waves with frequency 300GHz to 400THz can be used forshort range communication. Infrared waves, having high frequencies, cannot

penetrate walls. Infrared signals can be used for short-range communication in a

closed area using line of sight propagation.

1.12. SWITCHINGSWITCHED NETWORK: It is a network which consists of a series of interlinked nodes , called

switches. A switch is a telecommunication device which receives message from any device

connected to it and transmits it to the device for which it was meant. There are generally 2

types of switching networks:

1.12.1. Circuit switched networks:1. A circuit-switched network is a data transmission service requiring the

establishment of a circuit-switched connection before data can be

transferred.

2. It is made of a set of switches connected by physical links, in whicheach link is divided into n-channels.

3. Circuit switching takes place at physical layer.


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4. The resource must remain dedicated during the entire duration of datatransfer until the teardown phase.

5. Data transferred between the two stations are not packetized, itscontinuous flow.

6. No addressing is involved during the data transfer. The switches routethe data based on their occupied band (FDM) and time slot (TDM).

1.12.2. Packet switched networks:1. A packet-switched network is a digital communications network that

groups all transmitted data, irrespective of content, type, or structure

into suitably sized blocks, calledpackets.2. The network over which packets are transmitted is a shared network

which routes each packet independently from all others and allocates

transmission resources as needed.

3.

Data is divided into packets and then transmitted over the network.4. No resource allocation for a packet i.e. no reserved bandwidth on thelinks.

5. Main goal is to optimize utilization of available link capacity, minimizeresponse times and increase the robustness of communication.

1.12.3. Circuit Switching Technique in Telephone: The Circuit Switching Technique isused in telephones. A circuit switching telephone circuit is only 30-40% efficient as

most of the time is spent in listening mode. A synchronous Transfer Mode (STM)

uses circuit switching. In telephones also works like circuit switching:

1. First, before communicating, a dedicated path is established. Here, theconnection set up means creating dedicated channels between the

switches. The connection is established only when the

acknowledgement sent by a system is received by the other system.

2. After the connection set up, the data is transferred between the twocommunicating parties.

3. When a party needs to disconnect, a signal is sent to each switch torelease the resource and the call is disconnected.

Connection is established

before data transfer

Wired link

Wired link


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Figure: 1.1

1.12.4. DATAGRAM NETWORKS: In this technique, the data is divided into severaldatagram and then sent them independently into the network. This is also called

connectionless network. Main features of this network are:

1. Each packet is treated independently of all other packets.2. Datagram switching is done at the network layer.3. The switch does not keep information about the connection state.4. No teardown and setup phase is present.5. High efficiency for short exchanges.6. Its simple and robust property.7. Packet size is large because the address of source and destination is

present within the datagram.

1.12.5. VIRTUAL-CIRCUIT NETWORKS: These networks are a cross between circuit-switched network and datagram network. Its features are:

1. There are setup and teardown phase along with data transfer phase.2. The data is divided into several packets and resource can be allocated

during the setup phase.

3. All the packets follow the same path established during theconnection.

4. It is implemented normally in data link layer.5. Smaller packets and sequence number are allotted to each packet.6. Efficient for long transfers.

1.13. TELEPHONE AND CABLE NETWORK FOR DATA TRANSFERTELEPHONE NETWORKS: Telephone networks use circuit switching. The telephone

network is made of three major components:

Local loops: The local loop is a twisted pair cable that connects the subscriber telephone to

the nearest end office or local central office. The local loop, when used for voice, has a

bandwidth of 4000Hz.

Trunks: Trunks are the transmission media that can handle the communication between

offices. A trunk handles hundreds or thousands of connections through multiplexing.

Switching offices: Two avoid having a permanent physical link between any two

subscribers; the telephone company has switches located in switching offices.1.13.1. INTRODUCTION OF LATAs: In 1970 the U.S government sued the AT&T Bell System

believing that they are monopolizing the telephone service industry as it was

providing almost all local and long-distance services, resulting in the AT&T

divestiture of 1984, which divided the country into more than 200 LATAs; some

companies allowed to provide services inside the LATA (LECs) and other to provide

services between the LATAs (IXCs).

LATAs: It stands for Local-access transport areas. A LATA can be small or largemetropolitan area. These are divided into two categories:


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Intra-LATA services: The services offered by the common carriers inside a LATA are

called intra-LATA services. The carrier that handles these services is called a local

exchange carrier. Since 1996, there are two types of LECs: Incumbent local

exchange carriers, provides the main services and Competitive local exchange

carriers, which provides other services such as mobile telephone service, toll calls

inside a LATA.

Inter-LATA services: The services between LATAs are handled by Interexchange

carriers (IXCs).These carriers provide communication services between two

customers in different LATAs. Carriers providing inter-LATA services include AT&T,

MCI, WorldCom, Sprint and Verizon.

1.14. DIAL-UP MODEMS: The term modem refers to the two functional entities that make upthe device: a signal modulator and a signal demodulator. A modulator creates a band pass

analog signal from binary data and a demodulator recovers the binary data from the

modulated signal. These are used on both the ends of the communication system. Thedigital data sent from the sender is converted into analog signal by the modem at senders

end and this analog signal is then sent on the telephone lines and the modem at receiver

end converts the analog signal into digital data and delivers it to the receiver. Most popular

modems available are:

1.14.1. V.32 modem: This uses a combined modulation and encoding technique calledtrellis- coded modulation. The V.32 calls for 32-QAM with a baud rate of 2400.

Because only 4 bits of each pentabit represent data, the resulting data rate is

4*2400=9600. V.32bis has an automatic fall-back and fall-forward feature that

enables the modem to adjust its speed upward or downward depending on the

quality of the line or signal.

1.14.2. V.34bis: This modem provides a bit rate of 28,800 with a 960-point constellationand a bit rate of 33,600bps with a 1664-point constellation.

1.14.3. V.90: these modems with a bit rate of 56,000bps available; these are called 56Kmodems. These modems may be used only if one party is using digital signalling.

These are asymmetric.

1.14.4. V.92: The standard above V.90 is called V.92. These modems can adjust theirspeed, and if the noise allows, they can upload data at the rate of 48Kbps. The

downloading speed is still 56Kbps. This modem can interrupt the internet

connection when there is an incoming call.

1.15. DIGITAL SUBSCRIBER LINE: This technology supports high-speed digital communicationover the existing local loops. It is a set of technologies, each differing in the first letter,

these are:

1.15.1. ADSL: This technology is introduced first in DSL technology. It stands forasymmetric DSL. These lines provide higher speed (or bit rate) in the downward

direction than in the upward direction. Thats why they are called asymmetric.

ADSL uses the existing local loops (these loops can handle bandwidths up to

1.1MHz). This is an adaptive technology. The system uses a data rate based on the

condition of the local loop.

1.15.2. ADSL Lite: This is a new version of ADSL technology. This technology allows anADSL Lite modem to be plugged directly into a telephone jack and connected to


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the computer. The splitting id done at the telephone company. It uses 256DMT

carriers with 8-bit modulation. It provides a maximum downstream data rate of

1.5Mbps and an upstream data rate of 512Kbps.

1.15.3. HDSL: The high-bit-rate digital subscriber line was designed as an alternative to T-1 line. The T-1 line uses alternate mark inversion (AMI) encoding, which is very

susceptible to attenuate at high frequencies, whereas HDSL uses 2B1Q encoding

which is less susceptible to attenuation. It uses two twisted pairs to achieve full-

duplex transmission.

1.15.4. SDSL: The symmetric digital subscriber line is a one twisted-pair version of HDSL. Itprovides full-duplex symmetric communication supporting 768kbps data rate in

both the directions. It is not much suitable for businesses that send and receive

data in large volumes in both the directions.

1.15.5. VDSL: The very high -bit-rate digital subscriber line, an alternative for ADSL, usescoaxial, fibre-optic, or twisted pair cable for short distances. It uses DMTmodulating technique. It provides a range of bit rates 25 to 55Mbps for upstream

and 3.2mbps for downstream.

1.16. CABLE TV NETWORKS: The cable TV network started as a video service provider, but it hasmoved to the business of internet access.

1.16.1. TRADITIONAL VABLE NETWORKS: Cable TV started to broadcast video signals inlate 1940s. It was called community antenna TV because an antenna at the top of

a tall hill or building received the signals from the TV stations and distributed them,

via coaxial cables, to the community. The cable TV office receives video signals

from broadcasting stations and feeds to the coaxial cables. The signals became

weaker and weaker with distance, so amplifiers are installed through the network

to renew it. Communication in the traditional cable TV network is unidirectional.

1.16.2. HYBRID FIBER-COAXIAL NETWORK: This network uses a combination of fibre-opticand coaxial cable. The regional cable head serves up to 400,000 subscribers. The

distribution hub is responsible for modulation and demodulation of signals. The

signals are then fed to fibre nodes through fibre-optic cable. The use of fibre-optic

cable reduces the need for amplifiers. Communication in an HFC cable TV network

can be bidirectional.

1.17. CABLE TV FOR DATA TRANSFER:1.17.1. BANDWIDTH: The coaxial cable has a bandwidth that ranges from 5 to 750MHz.

To provide internet access , this bandwidth is divided into two bands:

1. Downstream Video Band: It occupies frequencies from 54 to 550MHz.Since each channel is of 6MHz, it can accommodate more than 80

channels.

2. Downstream Data Band: It occupies the upper band, from 550 to750MHz.Downstream data band uses the 64-QAM modulation

technique. There are 6 Bits/baud in 64-QAM. One bit is used for

forward error correction and other 5 bits for data. Downstream data

can be received at 30MHz.

3. Upstream Data Band: It occupies the lower band, from 5 to 42MHz.This band is also divided into 6MHz channels. Since it uses lower


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frequencies that are more susceptible to noise and interference, QPSK

modulation technique is preferred. There are 2 bits/baud in QPSK,

therefore upstream data can be sent at 12MHz.

1.17.2. CM and CMTS:1. CM: The cable modem is installed on the subscriber premises. It is

similar to an ADSL modem.

2. CMTS: The cable modem transmission system is installed inside thedistribution hub by the cable company. It receives data from the

internet and passes them to the combiner, which sends them to the

subscriber. The CMTS also receives data from the subscriber and

passes them to the internet.

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Documents

Basics of Data Communication,