Symbol Technologies WS 2000 - Manual (Page 48)

WLAN—Advanced Access Port Settings
The advanced Access Port settings are found at the bottom of the screen. For most
installations, the default settings for the advanced settings are appropriate.
1. Select either Indoors or Outdoors from the Placement pop-up menu. The setting will
affect the selection available for several of the other advanced settings.
2. Select a channel number from the Channel drop-down list on which the Access Port
should communicate with associated MUs. (The available channels vary depending on
the location setting of the switch.)
3. Select a power level from the Power Level drop-down list that will be used for radio
communications between the Access Port and the MUs.
4. Select both the Slowest Supported Rate and the Fastest Supported Rate from
the respective drop-down lists to specify the allowable transmission rates for
communication between the Access Port and the associated MUs.
5. Check the Antenna Diversity checkbox to enable Antenna Diversity if the Access
Port has an external antenna.
6. Check the Support Short Preamble checkbox to allow the Access Port to
communicate with the MUs using a short 56-bit preamble.
A preamble is the beginning part of a frame. The preamble comprises such elements as
robust carrier sensing, collision detection, equalizer training, timing recovery, and gain
adjustment. The administration can choose between a long or short preamble for data-
frame transmission from the WLAN’s adopted access ports.
Use the long preamble setting (the default) for legacy wireless equipment that is not
capable of dealing with short preambles. Use the short preamble setting where legacy
equipment is not an issue and maximum throughput is desired, for example when
streaming video or Voice-over-IP applications are used.
7. Set the Request to Send Threshold (RTS Threshold) by specifying a number.
RTS is a transmitting station’s signal that requests a Clear To Send (CTS) response
from a receiving station. This RTS/CTS procedure clears the air when many mobile
units (MUs) are contending for transmission time. Modifying this value allows the
administrator to control the number of data collisions and thereby enhance
communication with nodes that are hard to find because of other active nodes in the
transmission path.
In this field, the administrator can specify a Request To Send (RTS) threshold (in bytes)
for use by the WLAN’s adopted access ports.
This setting initiates an RTS/CTS exchange for data frames that are larger than the
threshold, and sends (without RTS/CTS) any data frames that are smaller than the
threshold.
Consider the tradeoffs when setting an appropriate RTS threshold for the WLAN’s
access ports. A lower RTS threshold causes more frequent RTS/CTS exchanges. This
consumes more bandwidth because of the additional latency (RTS/CTS exchanges)
before transmissions can commence. A disadvantage is the reduction in data-frame
throughput. An advantage is quicker system recovery from electromagnetic interference
and data collisions. Environments with more wireless traffic and contention for
transmission make the best use of a lower RTS threshold.
A higher RTS threshold minimizes RTS/CTS exchanges, consuming less bandwidth for
data transmissions. A disadvantage is less help to nodes that encounter interference and
collisions. An advantage is faster data-frame throughput. Environments with less
wireless traffic and contention for transmission make the best use of a higher RTS
threshold.
Copyright © 2004 Symbol Technologies, Inc. All Rights Reserved 48
WS 2000 Wireless Switch: 1.0 Date of last Revision: March 2004