Wireless/Redundant Edge Services xl Module Management and Configuration Guide WS.02.xx 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
requirements before they actually roam.
The Wireless Edge Services xl 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 xl Module
ProCurve Networking’s coordinated AP solution facilitates fast and seamless
roaming between wireless cells. A central device, the Wireless Edge Services
xl Module, controls all security settings and associations with wireless sta-
tions. The module generates and encrypts 802.11 frames and monitors a
station’s authentication state.