Media for Transmitting Data. Optical Communications Description of optical communications: –They...

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Media for Transmitting Data

Transcript of Media for Transmitting Data. Optical Communications Description of optical communications: –They...

Page 1: Media for Transmitting Data. Optical Communications Description of optical communications: –They use light as a carrier of information (as opposed to.

Media for Transmitting Data

Page 2: Media for Transmitting Data. Optical Communications Description of optical communications: –They use light as a carrier of information (as opposed to.

Optical Communications• Description of optical communications:

– They use light as a carrier of information (as opposed to electrical signals)

– Light waves can be used for the direct transmission of signals.– Use of Fibre Optics

• Advantages:– High bit rate – handles both speech and data– Better quality service as it is less susceptible to interference– Unaffected by electro magnetic disturbance (voltages, clicks,

atmosphere)– Difficult to tap into them - secure

• Disadvantages:– Only economical when the bandwidth is fully utilised– High cost of installation

Page 3: Media for Transmitting Data. Optical Communications Description of optical communications: –They use light as a carrier of information (as opposed to.

Examples of Optical Communications

• Computer networks – also utilise infra red

• Computer controlled telecommunications

• Transmitting signals in aircraft

• Measuring Instruments – devices that use laser to measure small distances

• High voltage installations

Page 4: Media for Transmitting Data. Optical Communications Description of optical communications: –They use light as a carrier of information (as opposed to.

Fibre optic cable

Summary• Sends pulses of light

rather than electricity. • Expensive. • Runs over long distances. • Is very quick. • Can be used for:

– video conferencing – interactive services.

Page 5: Media for Transmitting Data. Optical Communications Description of optical communications: –They use light as a carrier of information (as opposed to.

Wireless LANs

Communications that take place without the use of wires or cables– Mobile phones– Networked computers– Television broadcasts etc

– satellite– radio signals – infrared light beams– lasers

Each workstation and file server has some sort of transceiver/ antenna to send and receive the data.

Page 6: Media for Transmitting Data. Optical Communications Description of optical communications: –They use light as a carrier of information (as opposed to.

Wireless LANsAdvantages

• mobility and elimination of unsightly cables. • It's fast (11 - 125Mbps)• It has a long range (5,000 feet in open areas, 250 to

400 ft / 76 to 122 m in closed areas)• It's easily integrated into existing wired-Ethernet

networks. • Are great for allowing laptop computers or remote

computers to connect to the LAN. • Also beneficial where it may be difficult to install cables.

Page 7: Media for Transmitting Data. Optical Communications Description of optical communications: –They use light as a carrier of information (as opposed to.

Wireless communication methodsDisadvantages

potential for radio interference due to • weather, • other wireless devices, • obstructions like walls.

Page 8: Media for Transmitting Data. Optical Communications Description of optical communications: –They use light as a carrier of information (as opposed to.

Communications media

• Unshielded Twisted Pair (UTP) cable. used in telephone network and LANs– cheap to purchase – flexible and easy to install– used to provide telephone lines to offices– eases installation and management of the

cabling– easy to upgrade (future networks will

support this media)

Page 9: Media for Transmitting Data. Optical Communications Description of optical communications: –They use light as a carrier of information (as opposed to.

Other Communications media

• Coaxial cable– high quality, well insulated cable

• Communications satellite– in geosynchronous orbit

Page 10: Media for Transmitting Data. Optical Communications Description of optical communications: –They use light as a carrier of information (as opposed to.

CONNECTION OPTIONS FOR WANS

Dial up, using analogue modems• Cheap option

• Have to connect every time used

• Low bandwidth (54 kilobits)

Page 11: Media for Transmitting Data. Optical Communications Description of optical communications: –They use light as a carrier of information (as opposed to.

CONNECTION OPTIONS FOR WANS

Leased line• High bandwidth (can be gigabit with fibre

optic cable)

• Always on

• High cost (several £1000s per annum)

Page 12: Media for Transmitting Data. Optical Communications Description of optical communications: –They use light as a carrier of information (as opposed to.

CONNECTION OPTIONS FOR WANSADSL Asymmetric Digital Subscriber Line modem or cable modem• High bandwidth for price (e.g. 2 mb upload for £350 pa)• Always on• Not available in all areas

ISDNIntegrated Services Digital Network• The line is more expensive to rent than a standard line• There is no need for a modem as the signal is sent in

digital form.• Uses existing telephone cables.

Page 13: Media for Transmitting Data. Optical Communications Description of optical communications: –They use light as a carrier of information (as opposed to.

Factors affecting rate of data transmission

• The speed of the modem– Different modems vary in data transmission rates, typically from

9K to 56K bps (bits per second).• The nature of the transmission line

– A digital line such as an ISDN line has a much higher transmission speed than an analogue line.

• The type of cable used– Twisted pair has a transfer rate of 10Mbps; fibre optic cable is

about 10 times as fast.• The type of transmission

– synchronous or asynchronous.

Page 14: Media for Transmitting Data. Optical Communications Description of optical communications: –They use light as a carrier of information (as opposed to.

Definitions

• asynchronous transmission– In modem communication, a form of data

transmission in which data is sent intermittently, one character at a time, rather than in a steady stream with characters separated by fixed time intervals. Asynchronous transmission relies on the use of a start bit and stop bit(s), in addition to the bits representing the character (and an optional parity bit), to distinguish separate characters.

• synchronous transmission– Data transfer in which information is transmitted in

blocks (frames) of bits separated by equal time intervals.