In data communication, a transmission medium can be broadly defined as anything that can carry information from a source to a destination i.e. it is the channel through which data is sent from one place to another. For example, the transmission medium for two people having a dinner conversation is the air.
Transmission media can be classified into :
fig: Classes of transmission media
Guided media :
Guided media, also called Wired or Bounded transmission media, provides a conduit from one device to another by using physical links. It includes twisted-pair cable, coaxial cable, and fiber-optic cable.
- Twisted-pair cable :
It comprises two separate insulated conductor wires wound around each other. Several such pairs are usually bundled together in a protective sheath. There are two types of twisted-pair cables :
- Unshielded Twisted Pair (UTP): Most commonly used for Ethernet networks. It consists of pairs of twisted copper wires, and each pair is further insulated and twisted to reduce crosstalk and interference.
- Least expensive
- Easy to install
- High-speed capacity
- Susceptible to external interference
- Lower capacity and performance in comparison to STP
- Short-distance transmission due to attenuation
- Shielded Twisted Pair (STP): Similar to UTP but with additional shielding to better protect against external electromagnetic interference.
- Better performance at a higher data rate in comparison to UTP
- Eliminates crosstalk
- Comparatively faster
- Comparatively difficult to install and manufacture
- highly expensive
2. Coaxial Cable:
Consists of a central copper conductor surrounded by an insulating layer, a metallic shielding, and an outer protective sheath. Used in older Ethernet networks (10BASE2 and 10BASE5), as well as for cable television (CATV) and broadband internet connections.
- easy installation
- high bandwidth
- Better immunity to noise
- Connections are in series, therefore single cable can disrupt the entire network
3. Optical Fiber Cable:
The optical fiber cable works on the concept of refraction of light through a core made up of glass or plastic. Its core is surrounded by a less denser glass which is also called the cladding. The cable can be unidirectional or bidirectional. It is used for the transmission of large volumes of data.
- Increased capacity and bandwidth
- Less signal attenuation
- Immunity to electromagnetic interference
- Resistance to corrosive materials
- Difficulty in installation
- high maintenance
Unguided media :
Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. In this media, different types of waves are transferred such as Radio Waves, Microwaves, and infrared waves.
- Radio Wave :
Radio waves are used for multicast communications, such as radio and television, and paging systems. They can penetrate through walls. Highly regulated. Use Omni directional antennas. Range: 3KHz – 1GHz
2. Microwave :
Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs. Higher frequency ranges cannot penetrate walls. Use directional antennas – point-to-point line-of-sight communications. Frequency Range:1GHz – 300GHz
3. Infrared waves :
Infrared signals can be used for short-range communication in a closed area using line-of-sight propagation. Frequency Range:300GHz – 400THz .
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