2. Skills: none Concepts: wired hardware characteristics, wireless hardware characteristics (frequency and power), modulation schemes This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License. The physical layer

3. Where does this topic fit? Internet concepts – Applications – Technology (communication) – Implications Internet skills – Application development – Content creation – User skills

4. The physical layer LayerFunction ApplicationDo useful work like Web browsing, email, and file transfer TransportTransport data between application programs running on two hosts InternetRoute packets between networks (inter network) Data linkSend data within the local area network PhysicalSpecify hardware characteristics and ways to differentiate between ones and zeros

5. Copper and fiber

6. Frequency

7. ApplicationFrequency rangeLicense AM radio535-1,700 KHzYes FM radio88 to 108 MHzYes TV54 to 216 MHzYes WiFi 802.11 b, g, n2.401 to 2.473 GHzNo WiFi 802.11 a 5.15 to 5.825 GHzNo Visible light400 to 700 THzNo Frequency range examples

8. Electromagnetic radiation applications

9. What is power?

10. Radio power

11. Estimated coverage for 600 watt KPCC

12. Wolfman Jack, 250,000 watt XERF Click to hear the Wolfman

13. Coverage 802.11g WiFi access point, < 1 watt 200 feet 125 feet 20-22 Mbps 5-10 Mbps 10-15 Mbps 15-20 Mbps

14. Inside my house

15. In the back yard

16. Antenna focus

17. or Modulation mehtod

18. Modulation – transmit ones and zeros Amplitude modulation 0: low amplitude 1: high amplitude Frequency modulation 0: low frequency 1: high frequency Phase shift modulation 0: no phase shift during a clock period 1: 180 degree phase shift

19. Signal AM FM AM and FM modulation 10 1 http://som.csudh.edu/fac/lpress/presentations/Amfm.gif

20. Summary We saw that the two major functions of the physical layer are defining the hardware and the modulation method. We discussed both wired and wireless hardware specifications, noting that wireless links are characterized by their frequency and transmission power level.

21. Self study questions 1.We mentioned two wired technologies, what were they? 2.WiFi is commonly used for wireless network links. Can you think of other wireless technologies that are used for network links? 3.In our modulation example, the AM transmitter and receiver could differentiate two different frequencies – one high the other low. In other words, we could transmit one bit during each clock cycle. If a more sensitive radios could differentiate between four different frequencies, how many bits could we transmit during a clock cycle? 4.Why isn’t the signal strength at a given distance the same in all directions? 5.What is the unit of measure for radio power? 6.What is the unit of measure for radio signal frequency? 7.The FCC allows WiFi radios with narrowly focused antennae to transmit at higher power levels than WiFi radios which transmit In all directions. Why is that?

22. Resources Locate radio stations and unused FM frequency bands: http://www.radio-locator.com/