| Infrastructure Wireless communication involves the use of two major componentsthe client device and an access point, or AP. The AP acts as a bridge between the client or station and the wired network. As with other forms of network communication, before transmissions between devices can occur, the wireless access point and the client must first begin to talk to each other. In the wireless world, this is a two-step process involving association and authentication. The association process occurs when a wireless adapter is first turned on. The client adapter will immediately begin to scan across the wireless frequencies for wireless APs or if using ad hoc mode, other wireless devices. When the wireless client is configured to operate in infrastructure mode, the user can choose a wireless AP with which to connect. The wireless adapter switches to the assigned channel of the selected wireless AP and negotiates the use of a port. The authentication process requires that a keyed security measure be negotiated between the AP and the client. The keyed authentication setting can be set to either shared key authentication or open authentication. On many wireless devices, the default setting is set to open authentication. Open authentication requires identity verification between the wireless client and the AP. When set to shared key mode, the client must meet security requirements before communication with the AP can occur.  | The 802.11 standard allows a wireless client to roam between multiple APs. An AP will transmit a beacon signal every so many milliseconds and includes a time stamp for client synchronization and an indication of supported data rates. A client system will use the beacon message to identify the strength of the existing connection to an AP. If the connection is too weak, the roaming client will attempt to associate itself with a new AP. This allows the client system to roam between distances and APs. |
Several components combine to enable wireless communications between devices. Each of these must be configured on both the client and the AP. The Service Set Identifier (SSID) Whether your wireless network is using infrastructure mode or ad-hoc mode, an SSID is required. The SSID is a configurable client identification that allows clients to communicate to a particular base station. Only clients systems that are configured with the same SSID as the AP can communicate with it. SSIDs provide a simple password arrangement between base stations and clients. Wireless Channel RF channels are important parts of wireless communications. A channel refers to the band of frequency used for the wireless communication. Each standard specifies the channels that can be used. The 802.11a standard specifies radio frequencies ranges between 5.15 and 5.875GHz. In contrast, 802.11b and 802.11g standards operate between the 2.4 to 2.497GHz ranges. Fourteen channels are defined in the IEEE 802.11b/g channel set; 11 of which are available in North America. Security Features IEEE 802.11 provides for security using two methods, authentication and encryption. Authentication refers to the verification of client system. In the infrastructure mode, authentication is established between an AP and each station. Wireless encryption services must be the same on the client and the AP for communication to occur.
| Wireless devices ship with default SSIDs, security settings, channels, passwords, and usernames. To protect yourself, it is strongly recommended to change these default settings. Today, many Internet sites list the default settings used by manufacturers with their wireless devices. This information is used by people who want to gain unauthorized access to your wireless devices. |
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