1. DATA COMMUNICATION Lecture-25

2. Recap of Lecture 24  Cable Modems  Electromagnetic Spectrum  Transmission Media and its Types  Guided Media

3. Overview of Lecture 25  Guided Media – Twisted Pair – Coaxial Cable – Optical Fiber

4. Classes of Transmission Media

5. Categories of Guided Media

6. Twisted-Pair Cable  Two forms – Unshielded twisted-pair (UTP) – Shielded twisted-pair (STP)

7. UTP Cable

8. Shielded Twisted Pair (STP) Cable  UTP cable + metal casing (foil or braided-mesh)  The metal casing prevents EM noise

9. Shielded Twisted Pair (STP) Cable

10. Coaxial Cable  Inner conductor + outer conductor (foil or braid)  Outer conductor is both a shield and a conductor

11. Coaxial Cable

12. Frequency Range of Coaxial Cable

13. Coaxial Cable Standards  RG-8  RG-9  RG-11 – Used in Thick Ethernet  RG-58 – Used in Thin Ethernet  RG-59 – Used for TV

14. 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

15. Coaxial Cable Connectors  Other connectors – T-connectors – Terminators

16. Optical Fiber  Optical fiber is made of glass or plastic  It transmits signals in the form of light

17. 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

18. 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

19. Refraction

20. Critical Angle  The incident angle at which the refracted angle is 90 degrees

21. 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

22. Reflection

23. Propagation Modes

24. Multimode Step-Index Fiber  Light is guided through the core (high-density)  Core is surrounded by the cladding (low density)

25. Multimode Step-Index Fiber

26. Multimode Graded-Index Fiber  Density is highest at the center and decreases gradually to the edge  Greater precision than the step-index multimode

27. Multimode Graded-Index Fiber

28. Summary  Transmission Media and its Types  Guided Media – Twisted Pair – Coaxial Cable – Optical Fiber

29. Suggested Reading  Section 7.1, “Data Communications and Networking” 2 nd Edition by Behrouz A. Forouzan