20: Wireless LAN

20.1 Wireless LAN basics

• The wireless LAN allows users to connect to the network, while they are moving. They do not have to sit in a fixed place.

• The wireless LAN decreases the need for cables.

• The disadvantage of the wireless LAN is that it is not as stable as the wired network.

• The antenna types and direction of the wireless LAN devices may affect the wireless LAN performance.

• The microwave ovens and the cordless phones can interfere with the wireless LAN, because they work in the same frequency range.

20.1.1 Wireless LAN protocols

• There are three main protocols that are used in the wireless LAN, they are ‘IEEE 802.1a’, ‘IEEE 802.1b’ and ‘IEEE 802.1g’.

• ‘IEEE802.1a’ works in the 5GHz frequency range, and it can support the speeds up to 54 Mbps.

• ‘IEEE802.1b’ works in the 2.4GHz frequency range, and it can support speeds up to 11 Mbps.

• ‘IEEE802.1g’ works in the 2.4GHz frequency range, and it can support speeds up to 54 Mbps.

20.1.2 Access point (AP)

• The wireless LAN main device is the ‘access point (AP)’.

• The access point (AP) is the central device in the wireless LAN; it sends and receives the signals with the wireless LAN clients.

• There are two wireless LAN hierarchies, the ‘BSS’, and the ‘ESS’.

5896.jpgFigure 20.1: an access point

BSS (Basic Service Set)

In ‘BSS’, the wireless clients use only one AP to connect to each other, as seen in figure (20.1). It is usually used in a small office or in a home.

ESS (Extended Service Set)

In ‘ESS’, two or more BSSs are connected by a distribution system. It is usually used when we need to cover a large geographical area.

Image2711.JPGFigure 20.2: ESS

20.2 AP configuration

There are three basic parameters that should be configured on the AP; they are the ‘SSID’, the ‘RF channel’ and the ‘authentication method’.

20.2.1 SSID (Service Set Identifier)

• Every wireless LAN must have its own SSID, which is a unique string of characters.

• The SSID is configured on the AP, and the AP broadcasts it to the wireless clients.

• If the AP is configured not to broadcast its SSID, the SSID of this AP should be manually configured on the wireless clients that need to connect to this AP.

20.2.2 RF channel

• Many RF channels can be used on every AP.

• Every AP can be configured to use a certain RF channel.

• If you have more than one AP in the same place, you can configure every AP of your APs to operate on a different non-overlapping RF channel, in order not to interfere with other APs.

20.2.3 Wireless security

• Wireless security prevents any unauthorized access to the wireless network.

• There are two types of encryption, the ‘WEP’ and the ‘WPA’.

• WPA is preferred over WEP because WPA changes the encryption key dynamically, which gives more security to the wireless LAN.

• All wireless clients should have the correct encryption key in order to be able to communicate with the AP.

• The network administrator can use the ‘open access’ option. This means that, no authentication is required to connect to this wireless LAN.

• ‘Open access’ is usually used in the public places to allow all people to use this wireless network.

• The network administrator can determine which devices can communicate with the AP. This is done by manually recording the MAC addresses of the allowed devices on the AP. This is called the ‘MAC address authentication’.