Media for Transmitting Data. Optical Communications Description of optical communications: –They...
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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.](https://reader036.fdocuments.in/reader036/viewer/2022071718/56649e9d5503460f94b9e488/html5/thumbnails/1.jpg)
Media for Transmitting Data
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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
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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
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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.
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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.
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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.
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Wireless communication methodsDisadvantages
potential for radio interference due to • weather, • other wireless devices, • obstructions like walls.
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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)
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Other Communications media
• Coaxial cable– high quality, well insulated cable
• Communications satellite– in geosynchronous orbit
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CONNECTION OPTIONS FOR WANS
Dial up, using analogue modems• Cheap option
• Have to connect every time used
• Low bandwidth (54 kilobits)
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CONNECTION OPTIONS FOR WANS
Leased line• High bandwidth (can be gigabit with fibre
optic cable)
• Always on
• High cost (several £1000s per annum)
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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.
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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.
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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.