Cabletron Systems 3Com The following terms describe elements of the extended roaming feature

Theory of Operation 23

Enabling the extended roaming feature is like giving an individual a local post office forwarding address when leaving home for an extended period. When mail arrives for the individual home address, it is forwarded by the local post office to the current care-of-address. Using this method, only the local post office requires notification of the individual current address. While this example represents the general concept of extended roaming operation and functionality, it does not represent the implementation of extended roaming used.

If you wish to use extended roaming, set your wireless clients for extended roaming as specified in the AirConnect Wireless PC Card User Guide.

The following terms describe elements of the extended roaming feature:

■A tunnel is the path taken by the original packet encapsulated within the payload portion of a second packet to some destination on the network.

■A Home Agent is an AP acting as a router on the wireless client home network. The home agent intercepts packets sent to the wireless client home address and tunnels the message to the wireless client at its current location. This happens as long as the wireless client keeps its home agent informed of its current location on some foreign link.

■A Foreign Agent is an AP acting as a router at the wireless client location on a foreign link. The foreign agent serves as the default router for packets sent out by the wireless client connected on the same foreign link.

■A care-of-addressis the IP address used by the wireless client visiting a foreign link. This address changes each time the wireless client moves to another foreign link. It can also be viewed as an exit point of a tunnel between the wireless client home agent and the wireless client itself.

Security Security involves two distinct areas: authentication and privacy. Authentication ensures that only authorized users access the wireless network. Privacy ensures that communication between authenticated users and the network cannot be intercepted or overheard. The Access Control List provides authentication using the wireless LAN service area and a system administrator-supplied list of all the wireless client MAC addresses authorized to access the Home Service Area. Privacy is ensured by enabling the 40-bit WEP encryption option.

Supporting CAM and Continuously Aware Mode (CAM) stations leave their radios on continuously to PSP Stations hear every beacon and message transmitted. These systems operate without any

adjustments by the AP.

A beacon is a uniframe system packet broadcast by the AP to keep the network synchronized. A beacon includes the wireless LAN service area, the AP address, the Broadcast destination addresses, a time stamp, Delivery Traffic Indicator Maps, and the Traffic Indicator Message (TIM).

Power Save Polling (PSP) stations power off their radios for long periods. When a wireless client in PSP mode associates with an AP, it notifies the AP of its activity status. The AP responds by buffering packets received for the wireless client. The PSP-mode wireless client wakes up to listen to the AP beacon every nth Beacon Interval where n is a PSP-mode value from the 1 to 5-range; the Beacon Interval is set on the wireless client. When the wireless client wakes up and sees its bit set in the TIM, it issues a poll request to the AP for packets stored for it. The AP sends