1. The Physical Layer Dr. ir. S.S. Msanjila RIS 251

2. Theoretical Basis for Data Communication Fourier Analysis Bandwidth-Limited Signals Maximum Data Rate of a Channel Information can be transmitted through wires by varying some physical property Voltage or current Representing the value of voltage or current as a single-valued function of time can support modeling the behavior of the signal and its mathematical analysis

3. Guided Transmission Media  Main purpose of physical layer is to transport a raw bit stream from one machine to another.  Various physical media can be used for transmission but they differ in terms of:  Bandwidth, cost, delay and ease of installation and maintenance Groups of transmission media: Guided media: uses physical materials (copper wire or fiber optics) Unguided media: uses non physical materials namely through air (radio or lasers)

4. Types Transmission Media Magnetic Media: writing the data onto magnetic tape or removable media and physically transport them to another machine. Reliable in terms of bandwidth High delay and too much cost Twisted Pair: Coaxial Cable Fiber Optics

5. Twisted Pair (a) Category 3 UTP. (b) Category 5 UTP.  Consists of two insulated copper wires twisted together in a helical form  Mostly used in telephone systems  Can transmit either digital or analog signal  Bandwidth depends on the thickness of the wire and distance traveled UTP: Unshielded twisted pair

6. Coaxial Cable A coaxial cable.  Consists of a stiff copper wire as the core, surrounded with insulating materials  Can be used for longer distance data transmission

7. Fiber Optics (a) Three examples of a light ray from inside a silica fiber impinging on the air/silica boundary at different angles. (b) Light trapped by total internal reflection. Optical transmission has three key components: Light source Transmission media Detector

8. Fiber Cables (a) Side view of a single fiber. (b) End view of a sheath with three fibers.

9. Fiber Cables (2) A comparison of semiconductor diodes and LEDs as light sources.

10. Fiber Optic Networks A fiber optic ring with active repeaters.  Can be used for both LAN and longer distance transmission using either  Passive star  Active repeater

11. Wireless Transmission The Electromagnetic Spectrum Radio Transmission Microwave Transmission Infrared and Millimeter Waves Lightwave Transmission

12. The Electromagnetic Spectrum The electromagnetic spectrum and its uses for communication.

13. Radio Transmission (a) In the VLF, LF, and MF bands, radio waves follow the curvature of the earth. (b) In the HF band, they bounce off the ionosphere.

14. Lightwave Transmission Convection currents can interfere with laser communication systems. A bidirectional system with two lasers is pictured here.

15. Communication Satellites Geostationary Satellites Medium-Earth Orbit Satellites Low-Earth Orbit Satellites Satellites versus Fiber

16. Communication Satellites Communication satellites and some of their properties, including altitude above the earth, round-trip delay time and number of satellites needed for global coverage.

17. Communication Satellites (2) VSATs using a hub.

18. Low-Earth Orbit Satellites (a) The Iridium satellites from six necklaces around the earth. (b) 1628 moving cells cover the earth.

19. Globalstar (a) Relaying in space. (b) Relaying on the ground.

20. Public Switched Telephone Network Structure of the Telephone System The Politics of Telephones The Local Loop: Modems, ADSL and Wireless Trunks and Multiplexing Switching

21. Structure of the Telephone System (a) Fully-interconnected network. (b) Centralized switch. (c) Two-level hierarchy.

22. Structure of the Telephone System A typical circuit route for a medium-distance call.

23. Major Components of the Telephone System Local loops  Analog twisted pairs going to houses and businesses Trunks  Digital fiber optics connecting the switching offices Switching offices  Where calls are moved from one trunk to another

24. The Local Loop: Modems, ADSL, and Wireless The use of both analog and digital transmissions for a computer to computer call. Conversion is done by the modems and codecs.

25. Modems (a) A binary signal (b) Amplitude modulation (c) Frequency modulation (d) Phase modulation

26. Wireless Local Loops Architecture of an LMDS system (Local Multipoint Distribution Service).

27. Trunks and Multiplexing Transmission channels can be shared by multiplexing a single physical trunk Frequency division multiplexing Wavelength division multiplexing Time division multiplexing

28. Frequency Division Multiplexing (a) The original bandwidths. (b) The bandwidths raised in frequency. (b) The multiplexed channel.

29. Wavelength Division Multiplexing Wavelength division multiplexing.

30. Time Division Multiplexing The T1 carrier (1.544 Mbps).

31. Time Division Multiplexing (2) Delta modulation.

32. Switching (a) Circuit switching (b) Message switching (c) Packet switching

33. Packet Switching A comparison of circuit switched and packet-switched networks.

34. The Mobile Telephone System First-Generation Mobile Phones: Analog Voice Second-Generation Mobile Phones: Digital Voice Third-Generation Mobile Phones: Digital Voice and Data

35. Channel Categories The 832 channels are divided into four categories: Control (base to mobile) to manage the system Paging (base to mobile) to alert users to calls for them Access (bidirectional) for call setup and channel assignment Data (bidirectional) for voice, fax, or data

36. Third-Generation Mobile Phones: Digital Voice and Data Basic services an IMT-2000 network should provide High-quality voice transmission Messaging (replace e-mail, fax, SMS, chat, etc.) Multimedia (music, videos, films, TV, etc.) Internet access (web surfing, w/multimedia.)

37. Cable Television Community Antenna Television Internet over Cable Spectrum Allocation Cable Modems ADSL versus Cable

38. Community Antenna Television An early cable television system.

39. Internet over Cable Cable television

40. Internet over Cable (2) The fixed telephone system.

41. Cable Modems Typical details of the upstream and downstream channels in North America.