Wireless/Redundant Edge Services xl Module Management and Configuration Guide WS.02.xx and greater

3-21
Radio Port Configuration
Configuring Radio Settings
4. Click the OK button.
To force another Wireless Edge Services xl Module to adopt a particular radio,
change the radio’s preference ID to the ID on that second module, as explained
in “Configuring Advanced Properties for a Particular Radio” on page 3-32.
Enabling Support for a Short Preamble. As part of the 802.11 standards,
stations and radios are required to prepend a preamble to transmitted frames.
A preamble is a known string of bits that signals the destination device to
prepare to receive data, and alerts all devices sharing a common channel that
a data transmission is beginning.
There are two types of preambles: a long preamble and a short preamble. It
takes a maximum of 192 ms to process the long preamble and 96 ms to
process the short preamble. Because the short preamble yields about
50 percent savings in frame overhead, it can improve the throughput of a
network, particularly one transmitting traffic such as VoWLAN and streaming
video frames.
However, 802.11b devices do not support the short preamble, and by default,
RP 802.11bg radios allow stations to use either the short or the long preamble.
You can configure these radios to require the short preamble—raising overall
throughput in wireless cells. But you should never require the short preamble
in an environment with any 802.11b stations; this configuration prevents your
wireless devices from avoiding interference with those stations.
The short preamble is part of the 802.11a standard. So you cannot configure
this option for radios of that type: the short preamble is always required.
To configure 802.11bg radios to support a short preamble, complete
these steps:
1. Select Network Setup > Radio Adoption Defaults and click the
Configuration tab.
2. Select the radio type and click the Edit button.
3. Check the Short Preambles only box.
4. Click the OK button.
Setting the RTS Threshold. Your wireless network may have “hidden” sta-
tions: two stations that can each hear RP beacons but cannot hear each other’s
transmissions because of a wall or other barrier between them. Because these
stations cannot detect contention from each other, their frames may collide;
valuable transmission time is spent in resending data.