28-07-2014, 10:20 AM
TRANSMISSION MEDIA
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TRANSMISSION MEDIA
50,000 Km distance. The satellite amplifies week signals and transmits it back to the earth at the frequency less than 6 GHz.
In case of satellite communication, two different frequencies are used as carrier frequencies to avoid interference between incoming and outgoing signals. These are:
1. Uplink Frequency:
It is the frequency used to transmit signal from earth station to satellite.
2. Downlink Frequency:
It is the frequency used to transmit the signal from satellite to earth station. In other words, the downlink transmission is focused on a particular footprint, or area of coverage.
CHARACTERISTICS SATELLITE MICROWAVES:
High cost.
Extremely difficult and hare installation.
Variable attenuation.
Low immunity to EMI.
High security needed because a signal send to satellite is broadcasts through all receivers with in satellite.
These transmissions fall into two categories.
• Point to point
• Broadcast
(1) Point to Point:
- Point to point infrared transmission signal directly between two systems. Many lap top system use point-to-point transmission. These systems require direct alignment between many devices.
(2) Broad Cast:
- These infrared transmissions use sprayed signal, one broad cast in all directions instead of direct beam. This help to reduce the problems of proper alignment and abstraction. It also allows multiple receiver of signal.
INFRARED COMMUNICATION:-
Unguided infrared light waves are widely used for short range communication. The remote control used in TV, VCR and stereos all use infrared communication. They are relatively directional, cheap, and easy to build, but have major drawback; they do not pass through solid objects. On the other hand infrared waves do not pass through solid walls.
It means that infrared system in one room of a building. Security of infrared system is better than of radio system precisely for this reason, infrared light is suitable for indoor wireless LAN.
Conclusion:
• BEST security against unauthorized access?
Fiber-optic cables have proven to be more secure than the other media. Satellite transmission and copper wire can be violated (broke) with inexpensive equipment. Coaxial cable also can be violated more easily than other transmission media.