DATA COMMUNICATION Lecture-25
Recap of Lecture 24 Cable Modems Electromagnetic Spectrum Transmission Media and its Types Guided Media
Overview of Lecture 25 Guided Media – Twisted Pair – Coaxial Cable – Optical Fiber
Classes of Transmission Media
Categories of Guided Media
Twisted-Pair Cable Two forms – Unshielded twisted-pair (UTP) – Shielded twisted-pair (STP)
UTP Cable
Shielded Twisted Pair (STP) Cable UTP cable + metal casing (foil or braided-mesh) The metal casing prevents EM noise
Shielded Twisted Pair (STP) Cable
Coaxial Cable Inner conductor + outer conductor (foil or braid) Outer conductor is both a shield and a conductor
Coaxial Cable
Frequency Range of Coaxial Cable
Coaxial Cable Standards RG-8 RG-9 RG-11 – Used in Thick Ethernet RG-58 – Used in Thin Ethernet RG-59 – Used for TV
Coaxial Cable Connectors Barrel connectors – BNC(bayonet network connector): Pushes on and locks into place with a half turn – Screw type: more effort to install – Push-on type: Without locking, less secure
Coaxial Cable Connectors Other connectors – T-connectors – Terminators
Optical Fiber Optical fiber is made of glass or plastic It transmits signals in the form of light
The Nature of Light The speed of light – 300,000 Km/sec in a vacuum – Depends on the density of the medium through which it is traveling
Refraction Change of direction of a light ray – When a ray of light enters another substance, its speed changes abruptly, causing the ray to change direction
Refraction
Critical Angle The incident angle at which the refracted angle is 90 degrees
Reflection A phenomenon which occurs when the incident angle is greater than the critical angle Light no longer passes into the less dense medium Incident angle = reflected angle
Reflection
Propagation Modes
Multimode Step-Index Fiber Light is guided through the core (high-density) Core is surrounded by the cladding (low density)
Multimode Step-Index Fiber
Multimode Graded-Index Fiber Density is highest at the center and decreases gradually to the edge Greater precision than the step-index multimode
Multimode Graded-Index Fiber
Summary Transmission Media and its Types Guided Media – Twisted Pair – Coaxial Cable – Optical Fiber
Suggested Reading Section 7.1, “Data Communications and Networking” 2 nd Edition by Behrouz A. Forouzan