Appendix B
About Wireless LANs

This Appendix provides some background information about using Wireless LANs (WLANs).

Modes

Wireless LANs can work in either of two (2) modes:

Ad-hoc
Infrastructure

Ad-hoc Mode

Ad-hoc mode does not require an Access Point or a wired (Ethernet) LAN. Wireless Stations (e.g. notebook PCs with wireless cards) communicate directly with each other.

Infrastructure Mode

In Infrastructure Mode, one or more Access Points are used to connect Wireless Stations (e.g. Notebook PCs with wireless cards) to a wired (Ethernet) LAN. The Wireless Stations can then access all LAN resources.

Access Points can only function in "Infrastructure" mode, and can communicate only with Wireless Stations which are set to "Infrastructure" mode.

BSS/ESS

BSS

A group of Wireless Stations and a single Access Point, all using the same ID (SSID), form a Basic Service Set (BSS).

Using the same SSID is essential. Devices with different SSIDs are unable to communicate with each other.

ESS

A group of Wireless Stations, and multiple Access Points, all using the same ID (ESSID), form an Extended Service Set (ESS).

Different Access Points within an ESS can use different Channels. In fact, to reduce interference, it is recommended that adjacent Access Points SHOULD use different channels.

As Wireless Stations are physically moved through the area covered by an ESS, they will automatically change to the Access Point which has the least interference or best performance. This capability is called Roaming. (Access Points do not have or require Roaming capabilities.)

Channels

The Wireless Channel sets the radio frequency used for communication.

Access Points use a fixed Channel. You can select the Channel used. This allows you to choose a Channel which provides the least interference and best performance. In the USA and Canada, 11 channel are available.
Client (PC) Wireless Stations normally scan all Channels, looking for an Access Point. If more than one Access Point can be used, the one with the strongest signal is used. (This can only happen within an ESS.)
If your PC's wireless card does NOT automatically scan all wireless channels, then you must manually set it to the Channel used on the Access Point.

WEP

WEP (Wired Equivalent Privacy) is a standard for encrypting data before it is transmitted.

This is desirable because it is impossible to prevent snoopers from receiving any data which is transmitted by your Wireless Stations. But if the data is encrypted, then it is meaningless unless the receiver can decrypt it.

If WEP is used, the Wireless Stations and the Access Point must have the same settings for each of the following:

WEP

Off, 64 Bit, 128 Bit

Key

For 64 Bit encryption, the Key Table must match.
For 128 Bit encryption, the Key value must match.

WEP Authentication

Open System or Shared Key.

Access Control

The Access Control feature allows you to determine which Wireless Stations can use the Access Point. You need to identify each Wireless Station by its Hardware or physical Address.

On Windows, you can determine the Hardware (physical) Address using WinIPCfg, as follows:

Use Start - Run to open the "Run" dialog.
Type WINIPCFG and press Enter (or click OK).

Figure 53: WinIpCfg
WinIPCfg will then run, as shown above.
Select your Wireless adapter from the drop-down list, and check the Adapter Address field.

Wireless LAN Configuration

To allow Wireless Stations to use the Access Point, the Wireless Stations and the Access Point must use the same settings, as follows:

Mode

On client Wireless Stations, the mode must be set to "Infrastructure".
(The Access Point is always in "Infrastructure" mode.)

SSID (ESSID)

Wireless Stations must use the same SSID (ESSID) as the Access Point they wish to connect to.

WEP

The Wireless Stations and the Access Point must use the same settings for WEP (Off, 64 Bit, or 128 Bit).

WEP Key: If WEP is enabled, the Key Table (for 64 Bit encryption) or Key (for 128 Bit Encryption) must be the same on the Wireless Stations and the Access Point.

WEP Authentication: If WEP is enabled, all Wireless Stations must use the same setting as the Access Point (either "Open System" or "Shared Key").

WEP	Off, 64 Bit, 128 Bit
Key	For 64 Bit encryption, the Key Table must match. For 128 Bit encryption, the Key value must match.
WEP Authentication	Open System or Shared Key.

Mode	On client Wireless Stations, the mode must be set to "Infrastructure". (The Access Point is always in "Infrastructure" mode.)
SSID (ESSID)	Wireless Stations must use the same SSID (ESSID) as the Access Point they wish to connect to.
WEP	The Wireless Stations and the Access Point must use the same settings for WEP (Off, 64 Bit, or 128 Bit). WEP Key: If WEP is enabled, the Key Table (for 64 Bit encryption) or Key (for 128 Bit Encryption) must be the same on the Wireless Stations and the Access Point. WEP Authentication: If WEP is enabled, all Wireless Stations must use the same setting as the Access Point (either "Open System" or "Shared Key").