A new networking technology has been making waves since its release a few years ago. The LAN network is a medium for transmitting data and the place of a cable is taken by radio waves or infrared. WLAN (Wireless Local Area Network) is a flexible data communication system, used as an extension or alternative to wired LAN in a building or group of buildings nearby. Using electromagnetic waves, WLAN devices transmit and receive data through the air, eliminating the need for cables and making a LAN network to work. Thus, if a company has a LAN, you do not have to move to another office using cabling and also there is no need for drilling into walls and ceilings. You simply use the computers’ ability of using Wireless and the network can operate immediately. True, Wireless networks are generally used together with conventional LANs, especially for network printing part where they need a connection to the server.
WLAN is using electromagnetic radio waves and infrared. The first type is the most widespread, since radio waves pass through walls and other solid objects, while infrared radiation is less used, as light cannot pierce the opaque objects and has a much smaller range. However, this latter type is considered by some a solution for connecting equipments that do not move while the data transfer is made.
In most cases there must be a connection between WLAN and LAN. This is done through the so-called access points (AP). An access point is a transmitter or a Wireless receiver connected to a wired LAN. It receives, stores and transmits data from / to the devices in the WLAN and the LAN and has an operating range that goes from 30 to 300 meters. For example Air Connect equipment from 3Com has a range of action of 60 meters in a standard office buildings. The equipment is used outdoors, although they are mainly designed for use in rooms and if used outside it reaches up to 300-400 meters.
The users access the WLAN network through special adapters, which are in the form of PCI or ISA cards for desktop PCs, or some external devices, for notebooks. It works like traditional network card and it is installed into the computer and the operating systems treat it as a network card. Basically, there is a Wireless connection instead of cable and is transparent when going into the computer.
The phase configurations are similar to the ones of LANs, but the WLAN has more topologies. The simplest is the independent WLAN. Each time when two computers are in reach of their Wireless adapters, you can establish a connection. This configuration requires no special configuration or administration. An access point added to this configuration almost doubles the range of action, functioning as a receiver.
Extending the analogy with LAN network, an access point acts as a hub, doubling the maximum distance between PCs. The second topology is called infrastructure, where multiple access points link the WLAN to the wired LAN, allowing users to efficiently use the network resources. APs are not only about the LAN, but they also manage traffic through WLAN in their radius of action. Several APs can cover a very large building.
Wireless communication distance is limited. WLAN use cells, which are called micro-cells to extend the range of the WLAN. A micro-cell gives the coverage of an access point. The principle is similar to cellular telephony. At any time a user that has a mobile PC equipped with WLAN adapter is associated with a single micro-cell. Because partially the micro-cells switching data from one network to another do not interrupt the communication, they can be used in this way. There is one case where this communication is not continuous: if using TCP / IP. When transferring data via TCP / IP, the transition from one to another changes the AP, but the IP address is not changed.
This can lead to packet loss. But even in this case, there are solutions to restore the connection without losing data. Let’s take 3Com phones as an example: for the transition from AP to another WLAN adapter, they first address the second AP so that all packets are routed first to the second access point and notifies the user that this has not changed the AP.
