Manual

Chapter 15: Configuring Quality of Service (QoS)
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would occur if multiple access points got access 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 access point 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 random 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 access point 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 AT-WA7400 Management Software 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.
Transmission Opportunity (TXOP) Interval for Client Stations
The Transmission Opportunity (TXOP) is an interval of time when a Wi-Fi
Multimedia (WMM) client station has the right to initiate transmissions onto
the wireless medium (WM).
15 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