Agenda

• Last class: Network Protocols

• Today: Wireless Technology– How do computers talk to each other…

with no wire connecting them?

Wireless Technology

• Examples you already know:

Wireless Technology

• Uses radio waves, infrared, microwavesto send signals (0 and 1’s)

Wireless Technology Issues

• Range – short vs long

• Line of sight – walls?– Why does the car radio not work in a tunnel?– Why do people go outside to talk on cell

phone?

• One-way or two-way– Talk & listen?– Download & Upload?

Radio

• A radio station is a bigantenna that sends outradio waves

• Wavelength ~10 mFrequency ~ 100 MHz

• Radio channels!– AM 1320 or 101.3 FM

Radio

• Short range – only in one city

• One way: only receives signals from one radio station (only 1 frequency)

• Mobile – can move anywhere

Cell Phones

• The city is divided into CELLS

• Each cell has a station within line of sight

• The stations talk to each otherand also to your cell phone(by using radio waves)

• If you move to another cell, the stations know this.

Cell Phones• So when you call your friend

– You send a signal to the nearest station– The station talks to other stations to find your

friend. If your friend’s cell phone is on, it will find it.

– When you talk, your voice is DIGITIZED and sent as radio waves from station to station to your friend’s phone.

– At your friend’s phone, the radio waves are Reconstructed into voice.

• All this happens in seconds!

0110000101011100101…

DIGITIZATION

RECONSTRUCTION

How Cell Phones Work:

WIFI

• WIFI = Wireless Fidelity

• Wireless Networks– Laptop computer to printer– IPhone to internet in the city– Need a Wireless Access Point (WAP) nearby

(usually a router)

Questions?

Almost Finished

• What you WANT to learn– How to make your computer faster?

– How to fix your computer?

How to make computer faster?

• Run the Disk Cleaner– Delete files that you don’t use or don’t need– Free up space

• Run the Disk Defragmenter– Put blocks of memory together– Computer only needs to search one place for

files

How to fix your computer?

• Find the problem– Hardware? Test it with other hardware– Software? Re-install, download updates– Virus? uh oh, re-install operating system or

load a back-up

• Double check and try again

• BING the problem, search for a solution

• Call for help