Transmission Media | Physical layer | networking
Transmission media are mainly of two types, one is Guided Transmission Media and Unguided Transmission Media or Wireless Media.
Guided Transmission Media
Guided transmission media generally two types of materials are used.
- Copper Cable
- Coaxial Cable
- Twisted Pair
- Shielded twisted pair
- Unshielded twisted pair
- Optical Fiber
Coaxial Cable: Coaxial means common axis. Coaxial cable are the cables whose conductors are coaxial to each other. It is consist of two conductors, say inner and outer conductor. Generally inner conductor is made up of copper and covered by an insulating layer. Outer conductor is hollow cylindrical in structure and placed outside insulating plastic of inner conductor. Outer conductor is once again covered by plastic jacket. Diameter of coaxial cable ranges from 1 cm to 3 cm approximately. It has low attenuation and high bandwidth.
Twisted Pair: Twisted pair consist of two copper wires twisted in a helical form. Each of which is generally of 1 mm thickness. One or more pairs are together covered inside a plastic jacket to form a cable. Wires are twisted to decrease cross talk interference between different pairs. Twisted pair are generally cheaper than coaxial cables but attenuation is high and susceptible to electromagnetic interference and other noises. Twisted pair can run multiple kilometers without amplification but repeater ( signal amplifier) are needed for long distance signal transmission. The band width depends on thickness of wire and distance. They are generally limited in distance traveled, data transmission rate and band width. Twisted pair is generally used in the telephone system and LAN connections.
Twisted pair can be classified into two categories-
- Unshielded twisted pair: No shield / insulation is provided, so they are susceptible to interference.
- Shielded twisted pair: A thick insulation are used to protect from interference. They are generally costlier so are not commonly used
Optical Fiber: Optical fiber are the medium that transfers data using light. Inner core is made of either glass or plastic which is surrounded by cladding of same material as core but different refractive index. The cladding is covered by plastic jacket to prevent electromagnetic interference and harsh environmental condition. Optical fiber uses principle of total internal reflection to transfer data. Optical fiber provides much higher bandwidth than copper wires as negligible attenuation and electromagnetic interference. Hence quality signal is transferred even for long distance. End points devices are expensive, is one main disadvantage of optical fiber.
Optical fiber can be classified into different kinds
- Based on material: Glass and Plastic
- Based on radius: Thick and Thin optical fiber
- Based on light source: LED(low band width) and Injection based diode(for high bandwidth)
UNGUIDED TRANSMISSION MEDIA
Unguided transmission media are the transmission media where no physical connection are made. Commonly known as wireless transmission media. e.g. Radio, Terrestrial microwave, Satellite communication.
Radio: communication are done using radio frequency comes under radio communication. Radio frequency are the lower frequency band. Generally used in Wireless LAN, Wireless Ethernet, cordless keyboard and mouse etc. They are limited in range to few hundred feet only. They offer different bandwidth depending upon frequency they use for communication.
Terrestrial microwave: Terrestrial microwave communication are made using higher frequencies. Antennas are required at both receiving and sending end. A focused beam emerges from antenna to another antenna. No obstacle should be in between them and they must be facing to each other. Due to curvature of the earth long distance communication can be done with high bandwidth. They are beneficial as there in no need of lay down wires across the city. Telecommunication companies are using it as towers.
Satellite communication: Artificial satellite are used in satellite communication. Satellite acts as a switch in the sky. On the surface of the earth Very Small Aperture Terminal (VSAT) are used to transmit and receive data from satellite. Generally one such station transmits data which received by many others. Satellite is used in some remote area or area where it is very difficult to obtain line of sight. e.g. highly irregular terrestrial regions. In case of broadcasting satellite communication is highly preferential. Point to point communication using satellite is expensive compared to guided media.