JLSNet :: Projects : NetSwap - 2. Network Technology Research

NetSwap - 2. Network Technology Research

Around 1992, research began into the first Wireless LAN (WLAN) protocols operating in the unlicensed 2.4GHz frequency band. It was based on technology used by the military for mission-critical communication systems. Initially it was taken up by two business sectors ? Healthcare and Education. Healthcare made the use of mobile computers which could be used in hospitals to gain access to patient information, while schools started installing wireless networks to avoid the high costs of wiring buildings.

In 1997, the IEEE (Institute of Electrical and Electronic Engineers) released the 802.11 standard for wireless networking.

Today several 802.11 standards exist. 802.11b is an expansion of the standard that allows transmission speeds of up to 11Mbps using FHSS (Frequency Hopping Spread Spectrum) and DSSS (Direct Sequence Spread Spectrum) in the 2.4Ghz radio frequency band. This radio band is free to use worldwide and has no licensing restrictions, thus it is widely used for other wireless devices like cordless phones, microwave ovens, garage doors and, more recently, Bluetooth - all of which can interfere with 802.11b. [ADDA03]

The next generation 802.11a is a bit more complex than 802.11b, but has greater benefits. Also known as WiFi5 for its use of the 5GHz band, 802.11a is based on OFDM (Orthogonal Frequency Division Multiplexing) technology, rather than DSSS. It operates in the 5.2GHz radio frequency band that has much less interference from other devices, resulting in its super fast data speeds of up to 54 Mbps or even higher. [CISCO03c]

802.11g is the newest addition to the WiFi family and was officially registered as a final IEEE standard in June 2003. 802.11g supports speeds of up to 54Mbps but still works in the 2.4Ghz radio range.

Recently, the idea of ?Hotspots? has been created to satisfy the need for wider, faster wireless internet access. The service industry sectors such as Hotels, Service Stations, Airports and Train Stations were amongst the first to provide wireless access on a pay per hour, subscription, scratch card or free ?service-add? basis.

2.2.2 WiFi Technology/Infrastructure

A wireless network consists of two main components ? an access point and a wireless adapter. WiFi wireless networking works easily with any Ethernet network and can be installed by attaching an access point to existing switches. WiFi wireless adapters can work in two modes:

Infrastructure mode works by having one or more base stations called access points. An access point acts as a wireless base to which many mobile devices can connect. They are then ordinarily connected to a standard Ethernet network. Wireless mobile devices can not talk directly to each other and can only communicate through an access point.

Ad-Hoc mode allows Wireless Mobile Nodes to talk directly to each other without the need for an access point. Ad-Hoc mode is only ideal for two or three computers.

Frequency hopping works very much like its name implies. It takes the data signal and modulates it with a carrier signal that hops from frequency to frequency as a function of time over a wide band of frequencies. With frequency hopping spread spectrum, the carrier frequency changes periodically. This technique reduces interference because an interfering signal from a narrowband system will only affect the spread spectrum signal if both are transmitting at the same frequency simultaneously. Thus, the aggregate interference will be very low, resulting in little or no bit errors. A frequency hopping radio, for example, will hop the carrier frequency over the 2.4 GHz frequency band between 2.4 GHz and 2.483 GHz.

2.2.3 WiFi Frames

The 802.11 family uses a MAC layer known as CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance). note: Classic Ethernet uses CSMA/CD (Collision Detection). CSMA/CA is, like all Ethernet protocols, peer-to-peer and there is no requirement for a master base station such as an access point.