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What is meant by wired and wireless communication system? List their advantages and disadvantages.

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The medium is the matter or substance that carries the voice or data transmission. It can be copper, glass, or wave. A circuit is nothing more than the path over which data moves. Communication media is of two types:

(A) Wired Media: In this type of media, wires are used. It is further classified into three categories:

1. Twisted Pair Cable: Twisted pair of wires is the main media used in local telephone communication and short distance (less than 1 km) digital data transmission. Pairs of wire are twisted together to reduce interference by adjacent wires. Wires are usually made of copper. This medium is inexpensive. The main advantages of twisted pair cable are its simplicity and ease of installation. It is physically flexible, has a low weight and can be easily connected.

The twisted pair is used for audio telephone communication with speech signal bandwidth of 4 kHz. However, it has much higher bandwidth of about 50 kHz. The speed of digital signal transmission using telephone lines is 1200 bps (bits per second) (Also commonly quoted as 1200 bands).

Twisted pairs are used to connect terminals to the main computer. In this case, the speed of transmission is up to 9.6 kbps, if the length is less than 100 metres. Noise pick up by twisted wire which results in high error rates when the line length is more than 100 metres. This limits the use of twisted pair.

2. Coaxial Cable: Coaxial cables are groups of specially wrapped and insulated wire lines that are able to transmit data at high rates. They consist of a central copper wire surrounded by a PVC insulation over which a sleeve of copper mesh is placed. The metal sleeve is again shielded by an outer shield of thick PVC material. The signal is transmitted by the inner copper wire and is electrically shielded by the outer metal sleeve. Coaxial cables offer much higher bandwidth and are capable of transmitting digital signals at a very high rate of 10 Mbps. They are extensively used in long-distance telephone lines and cable TVs. They can handle 15,000 telephone calls simultaneously. Coaxial cables have much higher noise immunity and can offer data transmission without distortion or loss of signal.

3. Fibre Optic Cable: Physically, an optical fibre consists of a glass core, a plastic or glass cladding and a protective coating. The ore diameter is between 8 and 200 micrometres. Optical fibres have several advantages. They are:

  • Very high bandwidth.
  • Protection against electromagnetic interference.
  • More secure as they cannot be tapped easily.
  • Lightweight and no corrosion.

The major disadvantages of fibre optic cables are:

  • It is difficult to align and join two fibres in the field without using special equipment.
  • They are fragile and cannot have sharp bends.

In fibre optic communications, electrical signals are transformed into light pulses by a modulator, transmitted over the fibre as light waves, detected and converted back to electrical signals by photoelectric diodes.

(B) Wireless Media: In this type of media, wires are not used, hence, there is no physical connection. It is further classified into two categories:

1. Microwave: Parabolic antennas are mounted on towers to send beams. It is cheaper than digging trenches for laying cables, and maintaining repeaters of cables if cables get broken by a variety of causes. Transmitter and receiver must be in the line of sight—30 miles apart because of earth curvature, possible interference from the environment, lack of security, high initial equipment cost. Relatively high-speed data rates up to 250 Mbps. Usage: Voice Communication (Cellular Services).

2. Satellite: There is a need of 12 to 24 transponders per satellite. These transponders receive, amplify, change frequency and transmit. Geosynchronous orbit (22,300 miles) Low security-anyone with satellite dish and right frequency can tune in. Ease of adding stations. Data rates up to 50 Mbps. Microwave signal at 6 GHz is beamed to it from a transmitter on the earth. It is amplified and retransmitted to the earth at 4 GHz by a system called transponder mounted on the satellite to avoid interference.

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