User Manual

Psion Teklogix 9160 Wireless Gateway User Manual 181
Chapter 19: Quality of Service (QoS)
Configuring AP EDCA Parameters
cwMin
(Minimum
Contention Window)
This parameter is input to the algorithm that determines the initial random backoff wait time
(“window”) for retry of a transmission.
The value specified here in the Minimum Contention Window is the upper limit (in milliseconds)
of a range from which the initial random backoff wait time is determined.
The first random number generated will be a number between 0 and the number specified here.
If the first random backoff wait time expires before the data frame is sent, a retry counter is incre-
mented and the random backoff value (window) is doubled. Doubling will continue until the size of
the random backoff value reaches the number defined in the Maximum Contention Window.
Valid values for the “
cwmin ” are 1, 3, 7, 15, 31, 63, 127, 255, 511 , or 1024 . The value for
“
cwmin ” must be lower than the value for “ cwmax ”.
For more information, see “Random Backoff And Minimum/Maximum Contention Windows” on
page 177.
cwMax
(Maximum
Contention Window)
The value specified here in the Maximum Contention Window is the upper limit (in milliseconds)
for the doubling of the random backoff value. This doubling continues until either the data frame
is sent or the Maximum Contention Window size is reached.
Once the Maximum Contention Window size is reached, retries will continue until a maximum
number of retries allowed is reached.
Valid values for the “cwmax” are 1, 3, 7, 15, 31, 63, 127, 255, 511 , or 1024 . The value for
“cwmax” must be higher than the value for “cwmin”.
For more information, see “Random Backoff And Minimum/Maximum Contention Windows” on
page 177.
Max. Burst Length AP EDCA Parameter Only (The Max. Burst Length applies only to traffic flowing from the
access point to the client station.)
This value specifies (in milliseconds) the Maximum Burst Length allowed for packet bursts on the
wireless network. A packet burst is a collection of multiple frames transmitted without header
information. The decreased overhead results in higher throughput and better performance.
Valid values for maximum burst length are
0.0 through 999.9 .
For more information, see “Packet Bursting For Better Performance” on page 178.
Field Description
Table 19.1 AP EDCA Parameters