User Manual

SPEEDLAN 9000 Series Installation and Operation User Guide Version 3.03
Using the Configurator to Set Up Special Parameters for Point-to-Point Routers 6-11
Signaling Rate Fallback
During the retransmission of a unicast frame, the signaling rate can "fall back" in order
to increase the chance of reception. Signaling Rate Fallback can occur multiple times
for a single frame. Signaling Rate Fallback occurs from the current rate and will only
include those signaling rates selected on the Channel and Rates page. After ten
consecutive successful unicast frames, the current rate is restored to the highest
selected rate.
The Signaling Rate Fallback parameter allows you to control when the signaling rate
will drop, depending on the check box(es) you selected. That is, the check box(es)
labeled, "Allow signaling rate fallback on retry" (circled in blue on previous figure).
The following parameters (check boxes) govern at which point in the re-transmission
process the rate may be dropped:
• 1st retry: Will drop signaling rate on first retry.
• 2nd retry: Will drop signaling rate on second retry.
• 3rd retry: Will drop signaling rate on third retry.
• 4th retry: Will drop signaling rate on forth retry.
• 5th retry: Will drop signaling rate on fifth retry.
• 6th retry: Will drop signaling rate on sixth retry.
• 7th retry: Will drop signaling rate on seventh retry.
Example:
The network administrator has configured the allowable transmit signaling rates to be
11, 5.5, 2, and 1 Mb/s. (These values can be selected on the Channel and Rates page
under the Wireless menu.) In addition, the network administrator has selected 7 from
the Max Tx Retries drop-down list and set the signaling rate to "fall back" on the
second, fourth, and sixth retry attempts (as shown in blue on previous figure). When the
intended recipient does not acknowledge a transmitted unicast frame, it will be
retransmitted again (after a short timeout) at the current rate (e.g., 11 Mb/s). If this
attempt is also unsuccessful (e.g., the receiver did not acknowledge it), the signaling
rate will drop to 5.5 Mb/s and another attempt will be made. If after the third retry, the
transmission is still not successful, the signaling rate will drop to 2 Mb/s for the fourth
and fifth retry, and then to 1 Mb/s for the sixth and seventh retry (if needed).