Cabletron Systems 3Com manual For extended roaming to work, you must use a static IP address

22CHAPTER 1: OVERVIEW OF DIGITAL WIRELESS NETWORKING

and the addition of the AP to the AP table with a proximity classification. An unsuccessful AP packet transmission generates another wireless client probe on the same channel. If the wireless client fails to receive a probe response within the time limits, it repeats the probe process on the next channel in the sequence. This process continues through all channels in the range.

A wireless client can roam within the coverage area by switching APs. Roaming is transparent and virtually instantaneous in high-level applications. Roaming occurs when:

■An unassociated wireless client attempts to associate or reassociate with an available AP.

■The supported rate changes or the wireless client finds a better transmit rate with another AP.

■The signal quality of a potential AP exceeds that of the current AP.

■The ratio of good-transmitted packets to attempted-transmitted packets falls below a threshold.

■The wireless client detects an imbalance in the number of wireless clients associated with available APs and roams to a less loaded AP.

A wireless client selects the best available AP and adjusts itself to the AP direct-sequence channel to begin association. Once associated, the AP begins forwarding any frames it receives addressed to the wireless client. Each frame contains fields for the current direct-sequence channel. The wireless client uses these fields to resynchronize to the AP.

Roaming The AirConnect Roaming feature enables a wireless client on the Internet to move from one AP to another within a single subnet. The scanning and associating process continues for active wireless clients. This allows the wireless clients to find new APs and discard out-of-range or deactivated APs. By testing the airwaves, the wireless clients can choose the best network connection available.

Extended Roaming The AirConnect extended roaming (roaming across routers) feature enables a wireless client on the Internet to move from one subnet to another while keeping its IP address unchanged. extended roaming enables a wireless client to communicate with other hosts using only its home IP address after changing its point-of-attachment to the Internet/Intranet.

For extended roaming to work, you must use a static IP address.

The Internet Protocol identifies the wireless client point of attachment to a network through its IP address. The AP routes packets according to the location information contained in the IP header. If the wireless client roams across routers to another subnet with extended roaming disabled, the following situations occur:

■The wireless client changes its point of attachment without changing its IP address, causing forthcoming packets to become undeliverable.

■The wireless client changes its IP address when it moves to a new network, causing it to lose connection.