Setting The Transmit Rates; Setting Medium Reservation; Setting The Channel - 3Com WL-311 User Manual

3 Configuring the Bridge
24

Setting the Transmit Rates

The transmit-rate-settings parameter controls the rates at which the wireless bridge makes
physical layer transmissions. The rates listed are those supported by the 802.11b radio.
These rates refer to the physical layer transmissions, and do not necessarily correspond to
the data throughput that you will achieve. Data throughput is affected by many factors,
including distance, signal quality, and network protocol.
Use the check boxes to specify the allowed transmit rates for the radio. If you select
multiple allowed transmit rates the unit will automatically use the highest available
rate based on signal quality. When the signal quality is poor the radio will drop back to
lower rates.
NOTE: 3Com recommends that you select all the Transmit rate settings (11, 5.5,
2, 1 Mbps) to achieve the best performance.
If you force the radio to a lower rate, then it will operate better with poor signal quality.
If you force the radio to a higher rate, then it will operate only when the signal quality is
high. In general, you should leave this setting at the default of all rates allowed.
The following table shows the allowable combinations of transmit rate settings. You
should use the same transmit rate settings for all wireless bridges sharing WLAN service
area (ESSID):
Combination
A
B
C

Setting Medium Reservation

The medium reservation parameter controls the 802.11 Request to Send/Clear to Send
(RTS/CTS) mechanism. It is used to force the radio to perform a Request to Send and
receive a Clear to Send before transmitting packets. One of the bridges in the system acts
as the coordinator for all transmissions. The coordinator issues the Clear to Send messages
for all other bridges that are making Requests to Send. There is not a way to specify which
bridge will be the coordinator.
When medium reservation is enabled you must specify the RTS threshold. The threshold is
the packet length, in bytes, above which the radio will make the RTS and wait for CTS
before sending the packet. For example, if you enable medium reservation with an RTS
threshold of 500, then all packets of length greater than or equal to 500 bytes will not be
transmitted until the radio first issues an RTS and then receives a CTS from the coordinator.
Packets less than 500 bytes will be sent as soon as the channel is free, without first
undergoing the RTS/CTS mechanism.

Setting the Channel

The 802.11 standard specifies a number of different frequency channels. The regulatory
bodies of your country control the frequency channels that you may use. Use the pull-
down menu to see the list of channels supported by your wireless bridge unit.
NOTE: To ensure operation on a specific channel, all bridges with the same WLAN
Service Area Name (see step 1 on page 17) must have the same channel setting.
Settings (On) Description
1, 2, 5.5, 11 Mbps 11 Mbps with auto-fallback
1, 2 Mbps 2 Mbps with auto-fallback
1 Mbps 1 Mbps