181
ACK Timeout :
ACK timeout is in the range of
1~255
and set in unit of
microsecond
. The default value is
32
microsecond.
All data transmission in 802.11b/g request an “Acknowledgement” (ACK) send by receiving radio. The transmitter will
resend the original packet if correspondent ACK failed to arrive within specific time interval, also refer to as “ACK
Timeout”.
ACK Timeout is adjustable due to the fact that distance between two radio links may vary in different deployment.
ACK Timeout makes significant influence in performance of long distance radio link. If ACK Timeout is set too short,
transmitter will start to “Resend” packet before ACK is received, and throughputs become low due to excessively high
re-transmission.
ACK Timeout is best determined by distance between the radios, data rate of average environment. The Timeout
value is calculated based on round-trip time of packet with a little tolerance, So, if
experiencing re-transmissions or
poor performance the ACK Timeout could be made longer to accommodate.
Slot Time and ACK Timeout settings are for long distance links. It is important to tweak settings to achieve the
optimal result based on requirement.
Beacon Interval :
Beacon Interval is in the range of
20
~
1024
and set in unit of
millisecond
. The default value is
100
msec.
Access Point (AP) in IEEE 802.11 will send out a special approximated 50-byte frame, called “Beacon”. Beacon is
broadcast to all the stations, provides the basic information of AP such as SSID, channel, encryption keys, signal
strength, time stamp, support data rate.
All the radio stations received beacon recognizes the existence of such AP, and may proceed next actions if the
information from AP matches the requirement. Beacon is sent on a periodic basis, the time interval can be adjusted.
By increasing the beacon interval, you can reduce the number of beacons and associated overhead, but that will
likely delay the association and roaming process because stations scanning for available access points may miss the
beacons. You can decrease the beacon interval, which increases the rate of beacons. This will make the association
and roaming process very responsive; however, the network will incur additional overhead and throughput will go
down.
DTIM Interval :
The DTIM interval is in the range of
1
~
255
. The default is
1
.
DTIM is defined as
Delivery Traffic Indication Message
. It is used to notify the wireless stations, which support power
saving mode, when to wake up to receive multicast frame. DTIM is necessary and critical in wireless environment as
a mechanism to fulfill power-saving synchronization.
A DTIM interval is a count of the number of beacon frames that must occur before the access point sends the
buffered multicast frames. For instance, if DTIM Interval is set to 3, then the Wi-Fi clients will expect to receive a
multicast frame after receiving three Beacon frame. The higher DTIM interval will help power saving and possibly
decrease wireless throughput in multicast applications.
