WESM zl Management and Configuration Guide WT.01.03 and greater

9-9
Fast Layer 2 Roaming and Layer 3 Mobility
Overview
The previous sections have introduced you to different types of roaming,
which are defined briefly as follows:
■ Fast roaming—A fast roam is under 50 milliseconds. Fast roaming, as a
standard, refers to pre-authentication as specified by 802.11i, which
applies only to WPA/WPA2 with 802.1X. However, other types of roaming
might be under 50 milliseconds. When a roam is described as fast, it also
is assumed to be seamless.
■ Seamless roaming—The defining feature of a seamless roam is not
speed, but preservation of the user’s authentication, IP address, and active
sessions. The user does not need to re-login, and a user browsing the
Internet probably would not notice a seamless roam; a user accessing a
real-time application may detect a slight lag.
■ Not seamless roaming—If a roam is not seamless, the user must log in
again so that his or her station can re-authenticate or change its IP address.
A Wireless Edge Services zl Module handles roaming between its own RPs
automatically—this roaming is always fast. To enable the best possible roam-
ing between RPs adopted by different modules, however, you may need to
take some additional steps.
If you configure and group your modules correctly, you can always enable at
least seamless, and sometimes fast, roaming. Table 9-1 explains how to enable
the best possible roaming depending on the WLAN’s security and on whether
the roam occurs at Layer 2 or Layer 3.