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Topic : Communication Channels

Presented by:

Saniya Adeen

MIT01093010

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Communication is an exchange of feelings,

ideas, and information, whether by speaking,

writing, signals ,or behaviors

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� A channel is a communication medium, the

path that data takes from source to

destination.

� A channel can be comprised of so manydifferent things: wires, free space, and

entire networks

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 A medium through which a message is

transmitted to its intended audience , such

as print media or broadcast (electronic)

media

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� Digital (discrete) or analog (continuous) channel

� Baseband and passband channel

� Computer network virtual channel

� Simplex communication, duplex communication

or half duplex communication channel

� Return channel

� Uplink or downlink (upstream or downstreamchannel)

� Broadcast channel, unicast channel or multicast

channels

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R adioTelevision

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Receiving an AM signal

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�AM radio - 535 kilohertz to 1.7 megahertz

� Short wave radio - bands from 5.9

megahertz to 26.1 megahertz

�Citizens band (CB) radio - 26.96 megahertzto 27.41 megahertz

�Television stations - 54 to 88 megahertz for

channels 2 through 6

� FM radio - 88 megahertz to 108 megahertz

�Television stations - 174 to 220 megahertz

for channels 7 through 13

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Radio waves have the longest wavelengths inthe electromagnetic spectrum.

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Different wavelengths of EM radiation cause

the radiation to react differently with

different materials

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Is the distribution of video signals which

transmit programs to an audience

Network transmits their signals frombroadcasting studios via satellite signals to

local stations or cable distributors. Then

broadcast signals travel over cable television

lines, satellite distribution systems or theairwaves from a station·s transmission tower

to the antennas of the television

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�Digital channel is the sending and receiving

of moving images and sound by discrete

(digital) signals

� Transmitting a broadcast signal by encodingit as zeroes and ones ² the digital code used

in computers. DTV can be compressed to

provide four, five or more channels in the

same bandwidth required for one channel ofthe current standard television. .

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�Analog (or analogue) television encodes

television picture and sound information and

transmits it as an analog signal: one in which

the message conveyed by the broadcastsignal is a function of deliberate variations in

the amplitude and/or frequency of the

signal. ...

� The video signal of analog television istransmitted in AM, while the audio is

transmitted in FM.

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� A baseband channel (or system, or network)

is a communication channel through which

digital signals are sent without frequencyshifting

� Ethernet is an example of a basebandnetwork

� A passband is the range of frequencies orwavelengths that can pass through a filter

without being attenuated

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� A logical channel number (LCN), also known

as virtual channel, is a channel designation

which differs from that of the actual radiochannel (or range of frequencies) on which

the signal travels.

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� Simplex communication refers to

communication that occurs in one direction

only

� Examples

�Commercial radio broadcast (not walkie-

talkies, etc.)

� Television broadcast

� Keyboard to CPU communication

� Internet multicast

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A half-duplex channel can send and receive,

but not at the same time. It's like a one-lane

bridge where two way traffic must give way

in order to cross. Only one end transmits at atime, the other end receives

Example:

walkie-talkies

IN full duplex data can travel in bothdirections simultaneously

Full duplex allows both way communication

simultaneously

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� In a duplex transmission channel, it is

sometimes the case that the main channel

operates only in one direction (i.e. simplex),

but that a channel of much lower capacity

(and much lower cost) operates in the

opposite direction, this is the return channel.

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� The communication going from a satellite to

ground is called downlink, and when it is

going from ground to a satelliteit is called uplink.

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�Unicast is a type of transmission in which

information is sent from only one sender to

only one receiver. In another words, Unicast

transmission is between one-to-one nodes(involving two nodes only).

� Examples of Unicast transmission are http,

smtp, telnet, ssh, pop3 where the request

 for information is directed from one sender to only one receiver.

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� Broad cast is a type of transmission in whichinformation is sent from just one computer but is received by all the computersconnected to the network. This would meanthat every time a computer or a node would transmit a packet of type ¶broadcast·, allthe other computers will receive thatinformation packet.

� Examples of broadcast are many but one thatwould be best to understand here is acomputer booting up and requesting for a IPaddress

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� A type of transmission or communication in

which there may be more than one senders

and the information sent is meant for a set

of receivers� Example of Multicast based network is video

transmission network in which one computer

needs to transmit video channel to a specific

group of computers.

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The broadcast tower refers to a tall structureproviding mounting space for FM radio,AMradio antennas, and TV tower is constructed

to support Television antennasThe structure of broadcast tower 

and TV tower not only meet

the requirement of broadcast

and television antenna but also isaesthetical in appearance and 

coordinate with the surrounding

environment.

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