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