Chapter 7 Transmission Media

Chapter 7 of Data Communications and Networking by Behrouz A. Forouzan is titled "Transmission Media". It discusses the different types of transmission media used in data communication systems. Here are detailed notes on this chapter:

1. Introduction to Transmission Media

• Transmission Media: Defined as anything that can carry information from a source to a destination. Transmission media are positioned below the physical layer in the OSI model, controlled directly by it.

• Types of Media: In data communications, the transmission medium can be free space, metallic cables, or fiber-optic cables. These media carry electromagnetic signals used to transmit data.

2. Types of Transmission Media

Transmission media can be broadly categorized into two types:

1. Guided Media (Wired): The signal travels along a physical path.

2. Unguided Media (Wireless): The signal travels freely through the air or vacuum.

3. Guided Media

• Twisted-Pair Cable:

  • Consists of two insulated copper wires twisted together.

  • It can be shielded (STP) or unshielded (UTP).

  • Commonly used in telephone networks and LANs.

  • Categories range from CAT1 (used in voice telecommunication) to CAT7 (used for high-speed Ethernet).

• Coaxial Cable:

  • Has a central conductor, an insulating layer, a metallic shield, and an outer jacket.

  • It can carry higher frequencies than twisted-pair cables and is used in cable TV networks and Ethernet LANs.

• Fiber-Optic Cable:

  • Consists of a core (usually glass or plastic) that carries light, surrounded by cladding that reflects the light back into the core.

  • It offers higher bandwidth and lower attenuation compared to copper cables.

  • Commonly used in backbone networks, cable TV networks, and high-speed LANs.

• Advantages of Fiber-Optic Cable:

  • Higher bandwidth, less signal attenuation, immunity to electromagnetic interference, resistance to corrosive materials, lightweight, and more secure against tapping.

• Disadvantages of Fiber-Optic Cable:

  • More expensive, requires special expertise for installation, and has unidirectional light propagation (requiring two fibers for bidirectional communication).

4. Unguided Media (Wireless)

• Radio Waves:

  • Used for broadcasting and multicasting.

  • Omnidirectional, meaning they can travel in all directions.

  • Used in AM/FM radios, cordless phones, and satellite communications.

• Microwaves:

  • Used for unicast communication, such as cellular telephones, satellite networks, and wireless LANs.

  • Microwaves are unidirectional and travel in straight lines, requiring line-of-sight communication.

• Infrared Waves:

  • Used for short-range communication like remote controls and wireless LANs within a building.

  • Cannot penetrate walls, making them suitable for short-range indoor communication with minimal interference.

5. Summary of Media

• Guided Media includes twisted-pair cables, coaxial cables, and fiber-optic cables, which physically guide the signal.

• Unguided Media refers to free space (air, vacuum), where signals travel without a physical medium, primarily through radio waves, microwaves, and infrared waves.

6. Performance and Application of Media

• Each type of transmission medium has its own performance characteristics in terms of bandwidth, attenuation, and resistance to noise and interference.

• Fiber-optic cables offer the highest performance in terms of bandwidth and attenuation, making them ideal for long-distance and high-data-rate applications.

These notes capture the essential concepts and details from Chapter 7, explaining the different types of transmission media used in networking systems【7:1†source】【7:2†source】【7:3†source】.