Second Chapter Lesson-4: Data Communication Medium(Wired).

At the end of this lesson-

  • 1. You will be able to explain the concept of data communication medium.
  • 2. You will be able to describe the types of wired medium.
  • 3. You will be able to describe the twisted pair cable.
  • 4. You will be able to describe the Co-axial cable.
  • 5. You will be able to describe the fiber optic cable.


Medium: Physical path through which data is transferred by establishing a  link between sender and receiver is called medium.

There are two types of medium:

Wire or Guided Medium

  • Twisted Pair Cable
  • Co-axial Cable
  • Fiber Optic Cable

Wireless or Unguided Medium

  • Radio wave
  • Microwave
  • Infrared

Channel: Specific wave frequency or wire connection which is used to establish a link between sender and receiver for data transmission is called channel.

Wire or Guided Medium: It is defined as the physical medium through which the signals are transmitted. It is also known as Bounded media.

Twisted Pair Cable: A type of cable that consists of two independently insulated copper wires which are twisted together and run in parallel. The copper wires are typically 1mm in diameter. One of the wires is used to transmit data and the other is the ground reference.

Reason for Twisting:

All transmissions are prone to noise, interferences, and crosstalks. When the wires are twisted, some part of the noise signals is in the direction of data signals while the other parts are in the opposite directions. Thus the external waves cancel out due to the different twists. The receiver calculates the difference in the voltages of the two wires for retrieving data. Thus a much better immunity against noise is obtained.

Image result for twisted pair cableTypes of Twisted Pair Cable-

There are two types of twisted pair cables:

Unshielded twisted pair (UTP):

  • ‘Unshielded’ meaning it does not rely on physical shielding to block interference
  • Most commonly used cable of the two, often utilized for both residential and business use

Shielded twisted pair (STP):

  • ‘Shielded’ with a foil jacket to cancel any external interference
  • Commonly used for large-scale enterprises for high-end applications as well as exterior cabling that may be exposed to environmental elements.

Unshielded Twisted Pair:

Transmission Distance: 155 m

Transmission Speed: 10Mbps

Shielded Twisted Pair:

Transmission Distance: 100m

Transmission Speed: 16Mbps

Advantages of Twisted Pair Cable:

  • Less costly and easy to install.
  • Can be used for both analog and digital signal.
  • Can be used for communication at 100 meter distance only.
  • Can transmit data at gigabit range.

Disadvantages of Twisted Pair Cable:

  • For every unit of length transmission delay increases and data transfer rate decreases.
  • Transmission loss is very high.

Uses of Twisted Pair Cable:

  • Used in telephone system.
  • Used in Local Area Computer Network.


Co-axial Cable: In these cable there are two conductive layers which share the same axis. Thus this cable is called co-axial cable. Coaxial cables are high-frequency transmission cables made up of two conductive and two non-conductive parts. Data is transferred electrically over the inner conductor and has 80X more transmission capacity than twisted pair cables.

There are four parts in this cables. Such as:

  • The inner conductor of the coaxial cable is made up of copper, and the outer conductor is made up of copper mesh. The middle core is made up of non-conductive cover that separates the inner conductor from the outer conductor.
  • The middle core is responsible for the data transferring whereas the copper mesh prevents from the EMI(Electromagnetic interference).

Co-axial cables are of two types. Such as:

Thin net:

Diameter: 0.25 inches

Transmission Distance: 185 m

Transmission Speed: 10Mbps

Thick net:

Diameter: 0.5 inches

Transmission Distance: 500 m

Transmission Speed: 10Mbps

Advantages of Co-axial Cable:

  • Comparatively less data transmission loss.
  • Its higher bandwidth makes it more suitable for video applications
  • Can be used for both digital and analog data.
  • Allows data transmission over longer (1km) distances.

Disadvantages of Co-axial Cable:

  • Data transmission rate depends on the length of the cables.
  • More expensive compared to twisted pair cables.

Usage of Co-axial Cable:

  • Used for Cable TV network
  • Used in CCTV Network
  • Used in Local Area Network.


Fiber Optic Cable: Fiber is the newest form of  transmission cable technology. Instead of transferring data over copper wires, these cables contain optical fibers that transmit data via light, rather than pulses of electricity. Each optical fiber made with di-electric substant or crystal clear silica and multi-component glass material which is chemically neutral. and individually coated with plastic layers and contained in a protective tube, making it extremely resistant to external interference. The result is a very reliable and super fast connection that has 26,000X more transmission capacity than twisted-pair cables, but that also comes with a much higher cost.

Basic elements of Fibre optic cable:

  • Core: The optical fibre consists of a narrow strand of glass or plastic known as a core. A core is a light transmission area of the fibre. The more the area of the core, the more light will be transmitted into the fibre.
  • Cladding: The concentric layer of glass is known as cladding. The main functionality of the cladding is to provide the lower refractive index at the core interface as to cause the reflection within the core so that the light waves are transmitted through the fibre.
  • Jacket: The protective coating consisting of plastic is known as a jacket. The main purpose of a jacket is to preserve the fibre strength, absorb shock and extra fibre protection.

There are two types of fiber optic cable based on core diameter. Such as:

  • Single mode fiber optic cable (Diameter: 8-10 micron)
  • Multi mode fiber optic cable (Diameter: 50-100 micron)

Single mode:

  • Has a small core and only allows one mode of light to propagate at a time
  • Because of this, the number of light reflections decrease as they pass through the core
  • The result is low attenuation and data that is able to travel further and faster
  • Commonly used in telecom, CATV networks, and Universities.


  • Has a larger core diameter that lets multiple modes of light propagate
  • The amount of light reflections increase as they travel through the core, which allows more data to pass through
  • Because of its high dispersion, multimode cables have lower bandwidth, higher attenuation and reduced signal quality further it travels
  • Most commonly used for communication over short distances such as LAN, security systems, and general fiber networks.
  • Step-index fiber: Step index multimode fiber optic has uniform core refracting index.
  • Graded-index fiber: Core refracting index of Graded index multimode fiber optic is gradually decreased from center to outward.

Characteristics of Fiber Optic Cable:

  • The cable is light weight and very thin.
  • Uses light signal for transmitting data.
  • Data can be transferred to very long distance (100 km) with high speed (gigabit range +).
  • Free from EMI.
  • Not influenced by temperature or pressure of the environment.


Lesson Evaluation-

Knowledge Based Questions:

  • a. What is twisted pair cable?
  • a. What is co-axial cable?
  • a. What is fiber optic cable?

Comprehension Based Questions:

  • b. Which cable is more effective in data communication-explain.
  • b. Explain the reason for using twist in twisted pair cable.
  • b. Why is fiber optic cable more effective in data transmission?
  • b. “Fiber optic cable is said to the backbone of network”-explain.
  • b. “It is possible to transfer data in the speed of light”-explain.
  • b. Why optical fiber is free from EMI?

Creative Questions:

Multiple Choice Questions:


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