TelecommunicationsTelecommunications

Communications ModelCommunications Model Trasmission ModesTrasmission Modes Transmission DirectionTransmission Direction Transmission MediaTransmission Media Communication NetworksCommunication Networks

Communications ModelCommunications Model

Sender Receiver

Message

Medium

Transmission of Digital Data over Analog LinksTransmission of Digital Data over Analog Links

Transmission ModesTransmission Modes

byte byte byte

startbit

startbit

endbit

endbit

startbit

endbit

byte byte byte

Asynchronous transmission: Low-speed transmission of one character at a time, using control bits (i.e., start & stop bits)

Synchronous transmission: High-speed simultaneous transmission of large blocks of data

byte

Transmission DirectionTransmission Direction

Simplex transmissionSimplex transmission– Transmission occurs in one direction onlyTransmission occurs in one direction only– e.g., radio or TV wavese.g., radio or TV waves

Half-duplex transmissionHalf-duplex transmission– Transmission occurs in both directions, but only one at a timeTransmission occurs in both directions, but only one at a time– e.g., Walkie-Talkie, CB radio, pagerse.g., Walkie-Talkie, CB radio, pagers

Full-duplex transmissionFull-duplex transmission– Transmission occurs in both directions simultaneouslyTransmission occurs in both directions simultaneously– e.g., telephonese.g., telephones

Transmission Medium: Transmission Medium: wire-basedwire-based

Twisted wire pairTwisted wire pair– A pair of copper wires are twisted to avoid signal interferenceA pair of copper wires are twisted to avoid signal interference– The cost is low, and widely used in local loops of telephone net.The cost is low, and widely used in local loops of telephone net.– Subject to communication noisesSubject to communication noises

Coaxial cableCoaxial cable– Layers of copper conductors covered with shieldings Layers of copper conductors covered with shieldings – can transmit data, video, voice signals over one linecan transmit data, video, voice signals over one line

Fiber optics cableFiber optics cable– Fastest wire-based transmission mediumFastest wire-based transmission medium– The cost is too high, and ideal as a corporate back-bone cable to interconnect The cost is too high, and ideal as a corporate back-bone cable to interconnect

many LAN’smany LAN’s

Transmission Medium: Transmission Medium: wirelesswireless

Terrestrial microwaveTerrestrial microwave– microwave dishes needed at certain intervals (appr. 50km)microwave dishes needed at certain intervals (appr. 50km)– allows for very high-speed transmissions, and used by phone companies or common allows for very high-speed transmissions, and used by phone companies or common

carrierscarriers

Satellite microwaveSatellite microwave– involves uplinks & downlinks travelling to and from the satelliteinvolves uplinks & downlinks travelling to and from the satellite– widely used for GPS applicationswidely used for GPS applications

Cellular communicationCellular communication– An area is divided up into many small cells, and an antenna installed in each cell An area is divided up into many small cells, and an antenna installed in each cell

handles signal transmissionshandles signal transmissions

Microwave and Satellite Microwave and Satellite Transmissions - Cont’dTransmissions - Cont’d

Microwave Microwave antennaantenna

The satellite and The satellite and the antennathe antenna

Cellular phone

Mobile Mobile telecommunicationstelecommunications

IMT-2000video phone

Communications NetworksCommunications Networks

LAN(Local Area Network)LAN(Local Area Network)– ideal for small area networking needs (e.g., room, floor, building)ideal for small area networking needs (e.g., room, floor, building)– widely used to support computing needs in the office environmentwidely used to support computing needs in the office environment

MAN(Metropolitan Area Network)MAN(Metropolitan Area Network)– a backbone cable linking small LAN’s throughout an organizationa backbone cable linking small LAN’s throughout an organization– e.g., A network interconnecting agencies of an insurance firme.g., A network interconnecting agencies of an insurance firm

WAN(Wide Area Network)WAN(Wide Area Network)– networking support covers a large geographical areanetworking support covers a large geographical area– used by airlines, banks, etc.used by airlines, banks, etc.