WESM zl Management and Configuration Guide WT.01.28 and greater

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Introduction
Layer 2 and Layer 3 Roaming Between RPs and Modules
Layer 2 and Layer 3 Roaming Between RPs
and Modules
One of the principle attractions of wireless networking is the mobility that it offers
users, and users often want to roam further than the range of a single radio. The 802.11
standard gives guidelines for roaming between the coverage areas, or cells, provided
by two APs (or RPs), but leaves the implementation largely to the makers of wireless
network interface cards (NICs).
Typically, a station monitors the signal strength of beacons from its AP. When the
signal fades below a certain level, the station looks for another AP that supports the
same SSID (WLAN) but has a stronger signal. The station then disassociates from
the first AP and associates to the second.
For roaming, you must consider the speed of the roam and also whether, during and
after the roam, the station can preserve its IP address and active sessions.
The actual process of reassociating is very fast, but other requirements for connecting
to a WLAN can slow roaming. For example, an AP might require users to authenticate
to the network with 802.1X. Without special provisions, the AP does not realize that
the user has already completed this authentication with another AP. To speed up
roaming, developers design ways to get the information necessary for connecting a
station to an AP before the station needs to roam to that AP:
■ APs can communicate necessary information to each other.
■ Wireless stations can complete some association and authentication require-
ments before they actually roam.
The Wireless Edge Services zl Module supports many of these mechanisms. In
addition, by its very nature as a controller of coordinated RPs, the module enables
fast roaming between its own RPs.
Roaming Between RPs on a Single Wireless Edge Services
zl Module
ProCurve Networking’s coordinated AP solution facilitates fast and seamless roam-
ing between wireless cells. A central device, the Wireless Edge Services zl Module,
controls all security settings and associations with wireless stations. The module
generates and encrypts 802.11 frames and monitors a station’s authentication state.