What is meant by transmission media?

A communication channel that transmits data from a source to a recipient is referred to as "transmission media." Electromagnetic impulses are used to transmit data. Transmission media's primary purpose is to transmit data in the form of bits via a local area network (LAN). In data transport, it is the physical link that connects the transmitter and receiver. Transmission medium is part of layer 1 or physical layer of the ISO/OSI (Open System Interconnection) model.

Choice of transmission media

When selecting transmission media to be used in the network, a few things must be kept in mind.

  • Data transmission rate refers to number of bits of data that can be transferred per second. Transmission medium that supports data transmission rate which meets the requirements of the network must be chosen.
  • Transmission deterioration occurs when the received signal differs from the transmitted signal due to transmission link failure. Transmission link that is highly durable must be chosen.
  • The process of adding undesired signals to a signal as it passes across a communication medium, causing it to be interrupted, is called interference. Transmission medium which is less susceptible to interference must be chosen.

Transmission Media Classification

  • Transmission media for guided transmission
  • Transmission media for unguided transmission

Transmission media for guided transmission

The physical channel through which signals are transferred is known as transmission medium/bounded media.

Guided media types;

  • Twisted-pair
  • Cable with coaxial connectors
  • Fiber optic


Twisted-pair is a type of physical media made up of two twisted cables. Twisted-pair cable is less expensive compared to other media. The twisted-pair wire is lightweight and it is simple to set up. The twisted-pair cable has a frequency range between 0 - 3.5KHz. The number of turns each step makes determines how much noise interference can be reduced. To avoid noise interference, increase the number of turns per foot.

Types of twisted-pair

(a) Unshielded twisted-pair

In telecommunication, an unshielded twisted-pair(UTP) is commonly employed.

Unshielded twisted-pair benefits:

  • UTP is cost-effective.
  • An unshielded twisted-pair is simple to set up.
  • UTP is capable of connecting to a high-speed LAN.
  • Because of the attenuation, this cable can only be utilized for smaller distances.

(b) Shielded twisted-pair

A mesh surrounds the wire in a shielded twisted-pair cable, allowing for a greater transmission rate.

Shielded twisted-pair characteristics:

  • The shielded twisted-pair cable is neither prohibitively expensive nor prohibitively cheap.
  • It has a higher capacity as compared to an unshielded twisted-pair cable.


  • When compared to coaxial cable, it is more expensive.
  • It has a higher rate of attenuation.

Coaxial cable

  • Coaxial cable is a common communication medium which is used in television broadcasting.
  • When compared to a twisted-pair cable, it has a greater frequency.
  • The coaxial cable's internal conductor is copper, while the outside conductor is copper mesh. The inner conductor is separated from the exterior conductor by a non-conductive cover which forms the intermediate core.
  • The center core is in charge of data transmission, while the copper mesh protects against EMI (Electromagnetic interference).
  • Baseband transmission is a high-speed transmission of a single signal.
  • Broadband transmission involves transmission of many signals at the same time.
  • It has better insulation than a twisted-pair cable.
  • It has a much larger bandwidth.
  • It costs more compared to twisted-pair cable.

Fiber Optic

Light impulses are used in fiber optic cable.

The plastic coating protects against heat, cold, and electromagnetic interference from other types of wiring

Following are the basic components of fiber optic cable:

The core of an optical fiber consists of a thin strand of glass or plastic. The core of a fiber carries the light pulses. If the core area of the fiber is larger, then more light can be transferred into it.

Unguided transmission media

  • Electromagnetic waves are conveyed without the use of any physical material in an unguided transmission medium. Therefore, it is referred to as "wireless transmission".
  • Air is the easiest medium through which electromagnetic radiation can flow in unguided transmission channels.

Types of unguided transmission media

  • Radio waves
  • Microwaves
  • Infrared waves

Radio waves

Electromagnetic waves that move in all directions via open space are referred to as radio waves.


Microwaves transmission types are listed below:

  • Microwaves on the ground (terrestrial microwave).
  • Microwave communication through satellite (satellite microwave communication).

Terrestrial microwave communication

The focal beam of a radio signal is transmitted from one ground-based microwave transmission antenna to another in a terrestrial microwave transmission.

Satellite microwave communication

A satellite is a physical entity that travels at a specific height around the earth. Because satellite communication is more adaptive than cable and fiber optic networks, it is considered to be more reliable.


  • Infrared communication is a wireless communication technology that works across short distances.
  • Infrared rays operates at a frequency ranging between 300 GHz-400 THz.

Infrared Characteristics

  • Because of a large amount of bandwidth available, the data rate will be high.
  • The barriers prevent infrared rays from penetrating. As a result, communication in one area is unaffected by a conversation in adjacent rooms.
  • Infrared communication offers greater security while reducing interference.

Context and Applications

This topic is important for postgraduate and undergraduate courses, particularly for, 

  • Bachelors in Computer Science Engineering.
  • Associate of Science in Computer Science.

Practice Problems

Question 1: Which of the following is not a guided transmission medium?

  1. Twisted pair cable
  2. Microwave
  3. Coaxial cable
  4. Fiber optic cable

Answer: Option B is correct.

Explanation: Microwave transmission is not bounded since it travels through open space.

Question 2: Which of the following is the range of radio frequencies for communication through open space?

  1. Few hundreds of Hz to a few kHz
  2. Few hundreds of kHz to a few GHz
  3. Few hundreds of MHz to a few GHz
  4. None of these

Answer: Option A is correct.

Explanation: Radio waves are used to communicate over free space over a very large frequency range, ranging from a few hundreds of Hz to a few kHz. This frequency band is further segmented and assigned to different services.

Question 3: Identify the range of optical communication from the following.

  1. Microwaves to ultraviolet
  2. Visible to ultraviolet
  3. Microwaves to x rays
  4. None of these

Answer: Option A is correct.

Explanation: Optical communication, also known as optical telecommunication, is a method of long-distance communication that uses light to transmit data.

Question 4: Optical fiber is _______ susceptible to interference.

  1. less
  2. more
  3. moderately
  4. None of these

Answer: Option A is correct.

Explanation: Fiber optic cable carries data in the form of light pulses and therefore, it is not affected by electromagnetic interference.

Question 5: Expand ITU.

  1. Internal telecommunication union
  2. International telephone union
  3. International telecommunication union
  4. None of these

Answer: Option C is correct.

Explanation: The International telecommunication union (ITU) is expanding. It is a United Nations specialized agency in charge of all topics relating to information and communication technologies. The ITU is in charge of frequency allocation.

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