Skip to content

Latest commit

 

History

History
55 lines (33 loc) · 2.78 KB

chapter-7.md

File metadata and controls

55 lines (33 loc) · 2.78 KB
Raw

Chapter 7: Transmission Media

Introduction

Transmission media are actually located below the physical layer 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 is free space.

Guided Media

Guided media, which are those that provide a conduit from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable. A signal traveling along any of these media is directed and contained by the physical limits of the medium.

  • Twisted-pair and coaxial cable: use metallic (copper) conductors that accept and transport signals in the form of electric current.
  • Optical fiber: is a cable that accepts and transports signals in the form of light.

Twisted-Pair Cable

Coaxial Cable

Fiber-Optic Cable

Unguided Media: Wireless

Unguided medium transport electromagnetic waves without using a physical conductor.

Summary

  • Transmission media are actually located below the physical layer and are directly controlled by the physical layer. We could say that transmission media belong to layer zero.
  • A guided medium provides a physical conduit from one device to another.
  • Twisted-pair cable consists of two insulated copper wires twisted together. Twisted-pair cable is used for voice and data communications.
  • Coaxial cable consists of a central conductor and a shield. Coaxial cable is used in cable TV networks and traditional Ethernet LANs.
  • Fiber-optic cables are composed of a glass or plastic inner core surrounded by cladding, all encased in an outside jacket. Fiber-optic transmission is becoming increasingly popular due to its noise resistance, low attenuation, and high-bandwidth capabilities. Fiber-optic cable is used in backbone networks, cable TV networks, and Fast Ethernet networks.
  • Unguided media (free space) transport electromagnetic waves without the use of a physical conductor.
  • Wireless data are transmitted through ground propagation, sky propagation, and line-of-sight propagation. Wireless waves can be classified as radio waves, microwaves, or infrared waves. Radio waves are omnidirectional; microwaves are unidirectional. Microwaves are used for cellular phone, satellite, and wireless LAN communications. Infrared waves are used for short-range communications such as those between a PC and a peripheral device. They can also be used for indoor LANs.