Q. Mention and explain the two types of transmission media.
Answer: The transmission medium is the physical path by which a message or
information travels from sender to receiver. Some examples of transmission media
include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.
Transmission media are actually located below the physical layer of OSI model and are directly
controlled by the physical layer.
In telecommunications, transmission media can be divided into two broad categories: guided and
unguided. Guided media include twisted-pair cable, coaxial cable, and fiber-optic cable. Unguided
medium includes terrestrial wireless, satellite, and lasers as shown in the following figure.
Bounded/Guided Transmission Media
It is the transmission media in which signals are confined to a specific path using wire or cable. For
guided transmission media, the transmission capacity, in terms of either data rate or
bandwidth, depends critically on the distance and on whether the medium is point-to-point
or multipoint.
Some examples are:
a. Co-axial cable: Coaxial is called by this name because it contains two conductors that are
parallel to each other. Copper is used in this as centre conductor which can be a solid wire or
a standard one. It is surrounded by PVC installation, a sheath which is encased in an outer
conductor of metal foil, barid or both.
b. Twisted Pair Cable: This cable is the most commonly used and is
cheaper than others. It is lightweight, cheap, can be installed easily, and
they support many different types of network. Twisted Pair is of two types :
■Unshielded Twisted Pair (UTP)
■Shielded Twisted Pair (STP)
c. Fiber Optic Cable: These are similar to coaxial cable. It uses electric signals to transmit
data. At the centre is the glass core through which light propagates.
UnBounded/UnGuided Transmission Media
Unguided or wireless media sends the data through air (or water), which is available to anyone who
has a device capable of receiving them. Types of unguided/ unbounded media are discussed below :
•Radio Transmission : Its frequency is between 10 kHz to 1GHz. It is simple to
install and has high attenuation. These waves are used for multicast communications.
•MicroWave Transmission : It travels at high frequency than the radio waves. It
requires the sender to be inside of the receiver. It operates in a system with a low gigahertz
range. It is mostly used for unicast communication. There are 2 types of Microwave
Transmission :
1. Terrestrial Microwave
2. Satellite Microwave
