Communications Channel & transmission media   Communications Channel & transmission media

Communications Channel & transmission media   Communications Channel & transmission media Bandwidth, measures the transmission rate of a communications chanel. Speed at which data is transmitted is expressed as bits per second, bps. Broadband media, transmits multiple signals over a single communication line, UTP (Unshielded Twisted Pair) e.g. CAT5 100 mbps. Physical transmission media Coaxial cable Shielded from interference Needs terminator at end of cable Used by cable television because it can be laid over longer distances than twisted-pair cable

Communications Channel & transmission media   Communications Channel & transmission media Physical transmission media, contd. Twisted-pair cables Cable containing twisted-pair wires bundled together, graded as eg. Cat 5, 100 mbps or Cat 5 e Wires twisted together to reduce noise.

Transmission Media Physical Transmission Made of glass   Transmission Media Physical Transmission Made of glass Optical, not electrical – little signal fade and no danger of sparks in hostile environments Multiple signals on a single fibre Resists EMI Fibre-optic cable

Transmission Media Physical Transmission, Fibre-optic cable   Transmission Media Physical Transmission, Fibre-optic cable Core is as thin as a human hair Not very flexible – needs thick coat VERY fast, carrying more signals than wire cables Less susceptible to noise or interference Very secure (can’t be tapped or snooped) Disadvantages: Costs more than twisted pair or coax Difficult to install and modify

Transmission Media, c/f transfer rates   Transmission Media, c/f transfer rates

Transmission Media - Wireless   Transmission Media - Wireless Broadcast radio A wireless transmission medium distributing radio signals through the air over long and short distances Bluetooth and Wi-Fi communications technologies use these radio signals Need a transmitter to send and a receiver to accept signals Bluetooth short range radio waves Maximum distance 10 mtrs Data transfer rate of 2mbps c/f wireless 54mbps Good for use with hand-held devices, eg. PDA’s

Transmission Media - Wireless   Transmission Media - Wireless Broadcast radio, contd. Wi-Fi networks Data is transmitted as radio signals between wireless NICs and base stations relatively short distances (e.g. 80m-200m), reduced by obstacles speeds are increasing – now about 11Mbps encrypted communications to prevent eavesdropping many PCs can connect to a base station PCs can “roam” and will automatically connect to the base station that has the strongest signal

Transmission Media - Wireless   Transmission Media - Wireless Cellular radio A form of broadcast radio used widely for mobile communications, wireless modems & mobile phones Users connect their notebook computer or other device to a mobile telephone to access the web 7 email 2G, transmitted digital data at speeds of 9.6-19.2 kbps 3G, speed from 144 Kbps to 2.4 Mbps; display multimedia and graphics

Transmission Media – Wireless – cellular radio   Transmission Media – Wireless – cellular radio Cellular radio

Transmission Media - Wireless   Transmission Media - Wireless 3 Microwave, radio waves providing high-speed signal transmission, 150 Mbps Use microwave stations to transmit data as high frequency radio signals from one microwave station to another Use line-of-sight transmission, stations must be located relatively close together, (<50kms) & on top of mountains or buildings Used in wide-open areas, eg. deserts, lakes, b/w buildings Handles high data rates over short distances

Transmission Media - Wireless   Transmission Media - Wireless Microwave

Transmission Media Communications Satellite   Transmission Media Communications Satellite A space station that receives microwave signals from an earth-based station, (microwave station) and amplifies the signals and broadcasts back over a wide area Devices such as hand help computers and GPS receivers also function as earth-based stations Air navigation, TV and Radio broadcasts, paging & GPS use communications satellites. Speed of downloading from internet faster than uploading More expensive than cable internet but may be only high speed option in remote areas

Transmission Media - Wireless   Transmission Media - Wireless 5 Infra-red Uses light waves and requires line-of-sight access Uses an IrDA port to connect Effective over short distances, up to 5 metres Slow data transfer c/f cable, 115 Kbps – 4 Mbps