1. 7.1 Chapter 7 Transmission Media Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 7.2 Figure 7.1 Transmission medium and physical layer

3. Where transmission media is located? Transmission media is actually located below the physical layer and directly controlled by the physical layer. One may say that the transmission media belong to layer zero. 7.3

4. Transmission media Definition General/ broad definition any thing that carries information from source to destination. E.g. the medium between two people is air. The signal can be: conversation, smoke, semaphore ( A visual signaling apparatus with flags, lights, or mechanically moving arms, as one used on a railroad.) Specific to Data Communication Transmission medium is either: air, Space, water, metallic cable, fiber optic cable. Signal can be any portion of electromagnetic spectrum or ultra sounds. 7.4

5. Electromagnetic Spectrum 7.5

6. 7.6 Figure 7.2 Classes of transmission media

7. 7.7 7-1 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. Twisted-Pair Cable Coaxial Cable Fiber-Optic Cable Topics discussed in this section:

8. Twisted Pair Cable Consists of two conductors (normally copper), each with its own plastic insulation, twisted together. Twists Purposes: canceling out electromagnetic interference (EMI) from external sources; and crosstalk between neighboring pairs. More twists produce high quality signal. 7.8

9. 7.9 Figure 7.3 Twisted-pair cable

10. 7.10 Figure 7.4 UTP and STP cables

11. Categories The Electronic Industries Association (EIA) has developed standards to classify unshielded twisted-pair cable into seven categories. Categories determine cable quality, with 1 as the lowest and 7 as the highest. Each category is suitable for specific use. 7.11

12. 7.12 Table 7.1 Categories of unshielded twisted-pair cables

13. Connector RJ 45 (Registered jack) It is a keyed connector, this means that the connector can be connected in only one way. 7.13

14. 7.14 Figure 7.5 UTP connector

15. Applications Telephone lines Local loop the line that connects subscriber to the central telephone office commonly use UTP. DSL lines Used by the telephone companies to provide high data rate connections, Also use high bandwidth capability of UTP cable. LANs (10 base T, 100 base T) 7.15

16. 7.16 Figure 7.7 Coaxial cable

17. Coaxial Cable Coaxial cable (or Coax) carries signals of higher frequency ranges than TP cables. It has a central core conductor (usually copper). Core conductor is enclosed in insulating material. Then there is an outer conductor of metal foil, braid, or a combination of two. This outer conductor serves as: Shield against noise As a 2 nd conductor to complete circuit Then there is again a layer of insulator and finally a plastic coating. 7.17

18. 7.18 Table 7.2 Categories of coaxial cables

19. Connectors Bayone-Neill-Concelman (BNC) connector Three Types: BNC Connector Connects the end of the cable to a device, such as a TV set. BNC T Connector Used in networks to branch out to a connection to a computer or another device. BNC Terminator Used at the end of the cable in a network to prevent the reflection of signal. 7.19

20. 7.20 Figure 7.8 BNC connectors

21. Applications Analog telephone networks A single coaxial network could carry 10,000 voice signals. Digital telephone networks A single coax cable could carry digital data up to 600 Mbps. NOTE: Coax cable in telephone networks has largely been replaced today with fiber- optic cable. 7.21

22. Applications (Continued) Cable TV Transmission In the past whole network was of Coax. Now also replaced at network side with fiber optic cables. Still use coax at consumer premises. In Ethernet Transmission 7.22

23. 7.23 Figure 7.10 Bending of light ray

24. 7.24 Figure 7.11 Optical fiber

25. 7.25 Figure 7.12 Propagation modes

26. 7.26 Figure 7.13 Modes

27. 7.27 Table 7.3 Fiber types

28. 7.28 Figure 7.14 Fiber construction

29. 7.29 Figure 7.15 Fiber-optic cable connectors

30. 7.30 Figure 7.16 Optical fiber performance

31. 7.31 7-2 UNGUIDED MEDIA: WIRELESS Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication. Radio Waves Microwaves Infrared Topics discussed in this section:

32. 7.32 Figure 7.17 Electromagnetic spectrum for wireless communication

33. 7.33 Figure 7.18 Propagation methods

34. 7.34 Table 7.4 Bands

35. 7.35 Figure 7.19 Wireless transmission waves

36. 7.36 Figure 7.20 Omnidirectional antenna

37. 7.37 Radio waves are used for multicast communications, such as radio and television, and paging systems. Note

38. 7.38 Figure 7.21 Unidirectional antennas

39. 7.39 Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs. Note

40. 7.40 Infrared signals can be used for short- range communication in a closed area using line-of-sight propagation. Note