Data CommunicationData Communication

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Data CommunicationsData Communications

Data communication system components:Data communication system components: MessageMessage

Information (data) to be communicated.Information (data) to be communicated. SenderSender

Device that sends the data message.Device that sends the data message. A computer, video camera, or any other device that can be A computer, video camera, or any other device that can be

connected to network etc.connected to network etc. ReceiverReceiver

Device that receives the data message.Device that receives the data message. A computer, a Television, etc.A computer, a Television, etc.

Transmission mediumTransmission mediumThe physical path by which a message travels from sender to receiver.The physical path by which a message travels from sender to receiver.

Twisted pair, coaxial cable, optical fiber, radio waves.Twisted pair, coaxial cable, optical fiber, radio waves.

Data CommunicationData CommunicationModemsModems A computers voice is digital; that is, it consists of on/off A computers voice is digital; that is, it consists of on/off

pulses representing 1s and 0s. pulses representing 1s and 0s. A device called modem (short for modulator-A device called modem (short for modulator-

demodulator) is needed to translate these digital signals demodulator) is needed to translate these digital signals into analog signals that can travel over standard into analog signals that can travel over standard telephone lines.telephone lines.

In its modulation phase, the modem turns the computers In its modulation phase, the modem turns the computers digital signals into analog signals, which are then digital signals into analog signals, which are then transmitted across the telephone line.transmitted across the telephone line.

The reverse takes place during its demodulation phase, The reverse takes place during its demodulation phase, as the modem receives analog signals from the phone as the modem receives analog signals from the phone line and converts them into digital signals for the line and converts them into digital signals for the computer.computer.

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Uses for a modemUses for a modem

File transfer is the process of exchanging File transfer is the process of exchanging files between computers, either through files between computers, either through telephone lines or a network. telephone lines or a network.

UploadingUploading

DownloadingDownloading

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Broadband ConnectionsBroadband Connections

The term broadband is used to describe any data The term broadband is used to describe any data connection that can transmit data faster than is possible connection that can transmit data faster than is possible through a standard dial up connection using a modem.through a standard dial up connection using a modem.

Digital Subscriber Line (DSL) Digital Subscriber Line (DSL) transmission speeds ranging from several hundred transmission speeds ranging from several hundred Kbps to millions of bits per second (Mbps) Kbps to millions of bits per second (Mbps)

Cable Modem Cable Modem transmission speeds of 1.5 Mbps or more. transmission speeds of 1.5 Mbps or more. Fiber Fiber speeds far exceeding current DSL or cable modem speeds, speeds far exceeding current DSL or cable modem speeds,

typically by tens or even hundreds of Mbps. typically by tens or even hundreds of Mbps.

Wireless Wireless speeds are comparable to DSL and cable modem speeds. Satellite Satellite receive (download) at a speed of about 500 Kbps and send receive (download) at a speed of about 500 Kbps and send

(upload) at a speed of about 80 Kbps(upload) at a speed of about 80 Kbps

Broadband over Power lines (BPL)Broadband over Power lines (BPL) speeds are comparable to DSL and

cable modem speeds. 55

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Data CommunicationsData Communications

ProtocolProtocolA set of rules that govern the data communication.A set of rules that govern the data communication.

Without a protocol, devices may be connected but not Without a protocol, devices may be connected but not communicating.communicating.

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Rules of communications: ProtocolRules of communications: Protocol

Protocol - Protocol - a set of rules for the exchange of a set of rules for the exchange of data between a terminal and a computer or two data between a terminal and a computer or two computerscomputers Agreement on how data is to be sent and Agreement on how data is to be sent and

receipt acknowledgedreceipt acknowledged Needed to allow computers from different Needed to allow computers from different

vendors to communicatevendors to communicate Transmission Control Protocol/Internet Transmission Control Protocol/Internet

Protocol (TCP/IP) permits any computer to Protocol (TCP/IP) permits any computer to communicate with the Internetcommunicate with the Internet

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Data Communications ModeData Communications Mode

Data flow between two devices can occur in 3 waysData flow between two devices can occur in 3 ways SimplexSimplex

The communication is unidirectional (i.e. on one way). One sends and the other The communication is unidirectional (i.e. on one way). One sends and the other only receives.only receives.

Ex.: Ex.: Keyboards and traditional monitors, Keyboards and traditional monitors, television broadcastingtelevision broadcasting

Half-DuplexHalf-DuplexEach station can both transmit and receive but not at the same time.Each station can both transmit and receive but not at the same time.

Ex.: Walkie-talkies Ex.: Walkie-talkies

Full-Duplex Full-Duplex Both stations can transmit and receive simultaneously.Both stations can transmit and receive simultaneously.

Ex.: Telephone networkEx.: Telephone network

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Data CommunicationsData Communications

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Coordinating sender and receiver deviceCoordinating sender and receiver device

Sending data to remote location only works Sending data to remote location only works if receiving device is ready to accept itif receiving device is ready to accept it

Two approaches to keeping devices in Two approaches to keeping devices in step:step: Asynchronous transmissionAsynchronous transmission Synchronous transmissionSynchronous transmission

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Asynchronous TransmissionAsynchronous Transmission

Also called start/stop transmissionAlso called start/stop transmission Start bit transmitted at the beginning of each group of Start bit transmitted at the beginning of each group of

bitsbits Stop bit sent at end of each groupStop bit sent at end of each group Data is transmitted one byte at a timeData is transmitted one byte at a time Each group typically consists of one characterEach group typically consists of one character

Receiving device gets start signal and sets up Receiving device gets start signal and sets up mechanism to accept the groupmechanism to accept the group

Used for low-speed communicationsUsed for low-speed communications

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Synchronous TransmissionSynchronous Transmission

Large block of characters transmittedLarge block of characters transmitted

Data is transmitted block by block or word by Data is transmitted block by block or word by wordword

Error-check bits make sure all characters Error-check bits make sure all characters receivedreceived

Much faster, but equipment is more expensiveMuch faster, but equipment is more expensive

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Communications MediaCommunications Media

Physical means of data transmission from one Physical means of data transmission from one place to anotherplace to another

Bandwidth is measure of the capacity of the Bandwidth is measure of the capacity of the communications linkcommunications linkTypes of Communications MediaTypes of Communications Media

1.Guided Media 1.Guided Media

2.Unguided Media2.Unguided Media

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Communications MediaCommunications Media

Guided /Bounded Media:Guided /Bounded Media: Communication devices are directly linked with each other via Communication devices are directly linked with each other via

cables or physical media i.e.cables or physical media i.e. Wire pairsWire pairs Coaxial cablesCoaxial cables Fiber opticsFiber optics

Unguided /unbounded /Wireless MediaUnguided /unbounded /Wireless Media Data is communicated between communicating Data is communicated between communicating

devices in the form of wavedevices in the form of wave Microwave transmissionMicrowave transmission Satellite transmissionSatellite transmission

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Guided Media :Guided Media : Wire Pairs Wire Pairs

Also known as twisted pairAlso known as twisted pair Two wires twisted around each other to Two wires twisted around each other to

reduce electrical interferencereduce electrical interference

InexpensiveInexpensive

It is used for short distance data communication.It is used for short distance data communication.

Easily affected by electromagnetic waves and Easily affected by electromagnetic waves and noise noise Noise - anything that causes signal distortionNoise - anything that causes signal distortion

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Coaxial CableCoaxial Cable

Coaxial cable consists of a copper wire core Coaxial cable consists of a copper wire core covered by insulating material.covered by insulating material.The insulated copper wire is covered by copper The insulated copper wire is covered by copper mesh.mesh.It protects the cable from electromagnetic It protects the cable from electromagnetic waves.waves.It is used for long distance data communication.It is used for long distance data communication.It is more expensive than wire cable.It is more expensive than wire cable.Commonly used to connect to cable TVCommonly used to connect to cable TVHigher bandwidth and less effected to noise Higher bandwidth and less effected to noise than twisted pairthan twisted pair

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Fiber OpticsFiber OpticsIt is also known as light pulse media.It is also known as light pulse media.It is made up of thin glass fiber.It is made up of thin glass fiber.It is thinner than a human hair.It is thinner than a human hair.Data transfer rate of fiber optics is very fast.Data transfer rate of fiber optics is very fast.There is no chance of data loss.There is no chance of data loss.An important characteristics of fiber optics is refraction.An important characteristics of fiber optics is refraction.Refraction is a characteristics of a material to either pass or reflect light.Refraction is a characteristics of a material to either pass or reflect light.The advantage of fiber optic is that the data has to be converted into The advantage of fiber optic is that the data has to be converted into light only because it is already in binary form.light only because it is already in binary form.It is very expensive and difficult to install.It is very expensive and difficult to install.Use light instead of electricity to send dataUse light instead of electricity to send dataMuch higher bandwidth than coaxial cableMuch higher bandwidth than coaxial cableImmune to electrical interferenceImmune to electrical interferenceIt is very expensive and difficult to installIt is very expensive and difficult to install

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Microwave TransmissionMicrowave Transmission

Microwaves are radio waves that are used to Microwaves are radio waves that are used to provide high-speed transmissionprovide high-speed transmission

Uses line-of-sight transmission of data signalsUses line-of-sight transmission of data signals It means signals travel in straight line and cannot It means signals travel in straight line and cannot

bendbend

Requires microwave stations approximately Requires microwave stations approximately every 20-30 milesevery 20-30 miles

Offers high speed transmissionOffers high speed transmission

Susceptible to weather conditionsSusceptible to weather conditions

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Satellite TransmissionSatellite Transmission

A form of microwave transmissionA form of microwave transmission Satellite acts as relay stationSatellite acts as relay station

ComponentsComponents Earth station sends and receives signal to Earth station sends and receives signal to

satellitesatellite Transponder receives and amplifies signal, Transponder receives and amplifies signal,

changes frequency, and retransmits datachanges frequency, and retransmits data

Useful when signal must travel thousands of Useful when signal must travel thousands of milesmilesA large volume of data can be A large volume of data can be communicated at once.communicated at once.The disadvantage is that bad weather can The disadvantage is that bad weather can affect the quality of satellite transmission.affect the quality of satellite transmission.

Wireless NetworksWireless Networks

Wireless: 802.11Wireless: 802.11 The wireless standard that is becoming popular follows The wireless standard that is becoming popular follows

the family of specifications called 802.11 or Wi-Fi.the family of specifications called 802.11 or Wi-Fi. The 802.11b standard describes specification for The 802.11b standard describes specification for

wireless speeds upto 11 Mbps, which is a little faster wireless speeds upto 11 Mbps, which is a little faster than the slowest form of Ethernet(10Mbps) but much than the slowest form of Ethernet(10Mbps) but much faster than the typical 1.5Mbps high end DSL faster than the typical 1.5Mbps high end DSL connection.connection.

The 802.11g standard describes specification for The 802.11g standard describes specification for wireless LANs that provide 20+ Mbps connection speed.wireless LANs that provide 20+ Mbps connection speed.

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Wireless NetworksWireless Networks

Wireless Access PointWireless Access Point

Wireless Wireless access pointsaccess points (WAPs) are specially (WAPs) are specially configured nodes on wireless local area configured nodes on wireless local area networks (WLANs). Access points act as a networks (WLANs). Access points act as a central transmitter and receiver of WLAN radio central transmitter and receiver of WLAN radio signals. Access points used in home or small signals. Access points used in home or small business networks are generally small, business networks are generally small, dedicated hardware devices featuring a built-in dedicated hardware devices featuring a built-in network adapter, antenna, and radio transmitter. network adapter, antenna, and radio transmitter. Access points support Wi-Fi wireless Access points support Wi-Fi wireless communication standards. communication standards.

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