1. Communications Channel & transmission media
Communications Channel & transmission media

2. 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

3. 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.

4. 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

5. 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

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

7. 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

8. 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

9. 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
2G, transmitted digital data at speeds of kbps
3G, speed from 144 Kbps to 2.4 Mbps; display multimedia and graphics

10. Transmission Media – Wireless – cellular radio
Transmission Media – Wireless – cellular radio
Cellular radio

11. 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

12. Transmission Media - Wireless
Transmission Media - Wireless
Microwave

13. 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

14. 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