Installation guide

TD 92408EN
9 December 2011 / Ver. G
System Planning
Ascom VoWiFi System
30
10.4 Beacon Period
A beacon is a periodic broadcast transmission from the AP to all STAs in the BSS. The beacon
has multiple purposes:
• To synchronize all clients within a BSS
• Beacon contains a traffic indication to notify STAs in power-save mode that the AP has
b
uffered packets waiting for delivery
• To advertise capabilities or changes in capabil
ities
The most important issue for configuration of the beacon pe
riod is the traffic indication for
power-saving STAs. STAs in power-save mode wake up at every beacon transmission and
check the traffic indication message for any frames being buffered in the AP (i.e. delivery of
frames to a STA in power-save mode is only done after a beacon transmission).
This means that a long beacon period will increase the battery l
i
fe, but also increase the
response time to power-save clients.
A short beacon period will decrease battery
life and response time. See also 10.5 DTIM
Interval on page 30.
The beacon peri
od is specified in number of 802.11 TUs (Tim
e Units). One TU is 1.024 ms,
however to make it easier most APs asks for the value in number of ms. The recommended
default value is 100 ms.
10.5 DTIM Interval
DTIM (Delivery Traffic Indication Message) interval is the periodic interval when broadcasts
and multicasts are delivered in a BSS.
The VoWiFi Handset in idle mode utilizes power-save mode and wakes up only at every DTIM
interval to receive broadcasts/multicasts and to check the
traffic indication message for any
buffered frames in the AP. (See section about beacon period).
This means that the DTIM interval in conjunction with the be
acon period affects the battery
life and the data response time. For good battery conservation and reasonable response
times we recommend a DTIM interval of 5 if a beacon period of 100ms is used.
10.6 Transmission Power
By default the VoWiFi Handset adapts its output power to the APs, but the output power
can be configured in five steps between 0-20 dBm as well. Make sure that the APs and
clients are configured to use the same output power to avoid asymmetric communication
link budgets. The use of anything else in the APs creates an asymmetric communication link
budget and is not recommended.
Note: The VoWiFi Handset
can be configured up
to 20 dBm on the a and b/g band (note
that between 14-20 dBm no fixed steps can be set because of a power amplifier).