Copyright © 2004-2005, Vivato, Inc.
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to the medium at the same time and tried to transmit data simultaneously. The more active users you have
on a network, the more significant the performance gains of the backoff timer will be in reducing the
number of collisions and retransmissions.
The random backoff used by the AP/Bridge is a configurable parameter. To describe the random delay, a
"Minimum Contention Window" (MinCW) and a "Maximum Contention Window" (MaxCW) is defined.
•
The value specified for the Minimum Contention Window is the upper limit of a range for the initial ran-
dom backoff wait time. The number used in the random backoff is initially a random number between 0
and the number defined for the Minimum Contention Window.
•
If the first random backoff time ends before successful transmission of the data frame, the AP/Bridge
increments a retry counter, and doubles the value of the random backoff window. The value specified
in the Maximum Contention Window is the upper limit for this doubling of the random backoff. This
doubling continues until either the data frame is sent or the Maximum Contention Window size is
reached.
Packet Bursting for Better Performance
The Vivato Wi-Fi AP/Bridge includes 802.11e based
packet bursting
technology that increases data
throughput and speed of transmission over the wireless network. Packet bursting enables the transmission
of multiple packets without the extra overhead of header information. The effect of this is to increase
network speed and data throughput. The size of packet bursts allowed (maximum burst length) is a
configurable parameter.
Navigating to QoS Settings
To set up queues for QoS, navigate to the
TRAFFIC MANAGEMENT > Quality of Service
tab, and configure
settings as described below.
1
5
10
15
20
Backoff time
in milliseconds
Backoff
2
= MinCW doubled
Initial Backoff = random number in
Backoff
4
= re-doubled
range of MinCW
25
Doubling continues on each try until MaxCW is reached
at which point this wait time is used on retries
until data is sent or until retries limit is reached
