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 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 feet125 feet

20-22 Mbps 5-10 Mbps10-15 Mbps15-20 Mbps

Estimated coverage for 600 watt KPCC

Radio locatorIrregularity 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 90747

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 amplitude1: high amplitude

                          

Frequency modulation 0: low frequency1: high frequency

                          

Phase shift modulation 0: no phase shift during a clock period1: 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?