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.

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

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 email, 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 802.11g WiFi access point, < 1 watt
200 feet
20-22 Mbps 15-20 Mbps 10-15 Mbps 5-10 Mbps

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

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

KPCC
Frequency
FCC frequency allocation, zip code 90747
Central carrier frequency, for example 89.3 mHz for KPCC

AM and FM modulation
Signal
AM
FM
Animation

Modulation schemes or

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

Other types of wave with geek terms
Spring wave
String wave
Particle wave
Waves are the result of a disturbance or variation that transfers energy progressively from one point to another.
Click slowly or rapidly (change the frequency) to see the effect on wavelength (the distance between successive peaks).
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.

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?