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

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

TCP/IP protocol layers from 1,000 feet up Application Transport Internet Data link Physical Programs that do useful work like retrieve Web pages, copy files, send and receive , etc. Make client-server connections and optionally control transmission speed, check for errors, etc. Route data between networks Route data within the local area network Specify what medium connects two nodes, how binary ones and zeros are differentiated, etc.

Physical characteristics of wired media

Physical characteristics of wireless media Frequencies and channels Power

Coverage g WiFi access point, < 1 watt 200 feet 125 feet Mbps 5-10 Mbps Mbps Mbps

Estimated coverage for 600 watt KPCC Radio locator Irregularity due to varying terrain

Wolfman Jack Coverage, southwest US, 250,000 watt XERF

Frequency Central carrier frequency, for example 89.3 mHz for KPCC FCC frequency allocation, zip code KPCC

Signal AM FM AM and FM modulation Animation

or Modulation schemes

Paul Revere’s one-bit message By land (0) By sea (1)

More old ways to transmit ones and zeros Electric

Morse code Dot = 0 Dash = 1

Radio

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 The transmitter can generate these differences and the receiver can detect them.

A more sensitive receiver – 4 levels, not 2

Spring wave Waves are the result of a disturbance or variation that transfers energy progressively from one point to another. String wave Click slowly or rapidly (change the frequency) to see the effect on wavelength (the distance between successive peaks). Particle wave This is how sound is transmitted. Note that the disturbance propagates, but the particles stay in the same place. Tsunami wave Note that the wave attenuates as it loses energy. (Its amplitude (height) diminishes). Doing the wave Again, the people stay in the same seats as the disturbance propagates. Other types of wave with geek terms

Claude Chappe’s semaphore, 1792

The operator used two cranks to move the arms.

Early 1800s

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

A few questions If an AM transmitter and receiver can differentiate between four different amplitudes, how many bits are transmitted in each carrier clock period? If an FM transmitter and receiver can differentiate between 8 different frequencies, how many bits are transmitted in each carrier clock period?