Wireless LAN’s

Brent Leopold

Geoff Guist

History of WLAN’s

Have been around for almost 40 years First WLAN came together in 1971 Project called ALOHNET Originally WLAN hardware was so expensive

that it was only used where cabling was difficult or impossible

Today it is very common

How WLAN’s Work

Supplement wired LAN’s Send radio waves to transmit a signal to an

access point Access point is connected to an ethernet

switch by a UTP cord Requires a wireless network interface card

(NIC) to connect to access point

How WLAN’s Work

Internal NIC External NIC

How WLAN’s Work

The radio transmission requires an antenna in order to send and receive information Omni directional Dish Antenna

Dish Antenna

How WLAN’s Work

Radio transmissions are sent out as a frequency

Service Bands High Bandwidth = Broadband Low Bandwidth = Narrowband Spread Spectrum

Frequency Hopping Spread Spectrum FHSS enables the user to choose from a large

number of frequency channels (75 or more in the US.). With this flexibility modems can be programmed to hop around virtually any electrical interference or interfering object. For example, if transmission is blocked at one frequency, the modem will automatically hop to the next frequency in the pattern, so reliable communications is maintained. FHSS modems remain synchronized at all times, so their latency can be very low.

Direct Sequence Spread Spectrum In DSSS, the stream of information to be transmitted

is divided into small pieces, each of which is allocated across to a frequency channel across the spectrum. A data signal at the point of transmission is combined with a higher data-rate bit sequence (also known as a chipping code) that divides the data according to a spreading ratio. The redundant chipping code helps the signal resist interference and also enables the original data to be recovered if data bits are damaged during transmission.

How WLAN’s Work

Advantages

Freedom No Cables Increased Productivity User Friendly Environment

Disadvantages

Lack of Security Electromagnetic interference Propagation and attenuation

Penalty's for Hackers

Illinois Case Man stole neighbor’s access Charged $250

Florida Case Charged with unauthorized access to a computer

network Man was found guilty and charged with a third-

degree felony

802.11 WLAN Standards

802.11 specifies an over-the-air interface between a wireless client and a base station or between two wireless clients

802.11a 802.11b 802.11g

Emerging Wireless Technology 802.11n

This new technology is said to transmit signals at 100 Mbps or more in the 5 Gigahertz band

Radio frequency Ids (RFIDs) A way to read UPC bar codes by radio over short

distances Ultra Wideband (UWB) transmission systems

Transmit signals across a much wider frequency than conventional systems and are usually very difficult to detect

Emerging Wireless Technology Fourth-generation (4G) station

Instead of using multiple pieces of hardware (many different NICs), 4G stations are focusing on software-defined radio, which will be reconfigured by software instead of hardware