Specifications

Troubleshooting AOS-W Environments 589
Chapter 27
General
The Wi-Fi Alliance has made great strides in testing interoperability between
802.11 devices from many different manufacturers. Despite these efforts,
however, client incompatibility remains the primary complaint from network
managers deploying wireless LANs. A wide range of wireless hardware and
software is in use, with a corresponding wide range of quality – a given client
adapter card may work fine with one revision of driver software, but
experience numerous problems with another. A given operating system may
perform poorly on a wireless network until specific vendor patches are
applied. For this reason, Alcatel recommends that enterprise network
managers develop standard supported configurations for their deployment.
This configuration should consist of:
z Device type and model (laptops, PDAs, handheld devices, voice handsets,
etc.)
z Operating system (Windows 2000, Windows XP, MacOS X, Linux, etc.)
z Wireless NIC hardware manufacturer and model
z Wireless NIC software driver
z Wireless NIC firmware revision, if required
z Wireless NIC client utility or radio manager, if needed
z Authentication and encryption software (VPN client, 802.1x supplicant,
etc.)
Spending the time up front to develop and test such configurations will
greatly reduce troubleshooting time and effort after the network is deployed
and operational. A table of configurations tested by Alcatel appears in the
Design Guide, but this testing cannot take into account all possibilities.
Network managers can use these recommendations but should always
perform testing in their own environments with their own applications.
Client cannot find AP
Before a wireless client can associate to a network, it must locate at least one
Access Point. Most wireless clients locate available network by broadcasting
a series of 802.11 probe-request frames on multiple channels. APs hearing
these probe-request frames should answer with probe-response frames
containing the AP’s ESSID and various other capability parameters. Two
types of probe-request frames are possible:
Broadcast Probe Request – In a broadcast probe request, a client looks for
any available ESSID. It does so by leaving the ESSID field empty in the
probe-request frame. Normally, all AP’s receiving the probe-request,
regardless of ESSID, will answer. This is how Windows XP, for example,
populates the list of available wireless networks.