28 Advanced Power Management
MX2 Reference Guide E-EQ-MX2RG-L-ARC
Power Management at the Radio Card
To conserve battery life, the radio card has an inactivity sleep mode. The sleep mode is
automatically engaged when a certain period of time has elapsed since the computer has sent or
received data over the network. Once the card is asleep, it can be awoken by an access point
attempting to send data to it. The time before sleeping is calculated by adding the
Inactivity_min and Inactivity_sec parameter settings.
Note: Do not set an inactivity timeout on an RF MX2 being used as a master station. If the unit
goes to sleep, you will lose all communication with your network.
The access point buffers packets that are to be sent to the MX2s. A dozing radio card will receive
a sync message and wake-up list from the Access Point every 400 ms. The AP adds a media
access control (MAC) address to the wake-up list each time a send attempt fails. (The access point
buffers the packet and adds the MAC address of the MX2 to its wake-up list.)
If an MX2 detects that it is on the wake-up list, the radio card exits doze mode and enters receive
mode. Once the radio card wakes up to receive the packet, it stays awake for all future sends until
the inactivity timeout expires. This is why it is important to have the inactivity timeout as low as
possible. The advantages of a higher timeout value is that the radio card will remain in Receive
mode for longer periods of time; network throughput may be better because the unit will not have
the delay of coming in and out of doze mode or of waiting for the wake-up list to see if there are
any packets.
Generally, in the types of environments that the radio card will be used in, the user should strive
for maximum power management. Most MX2 RF applications will not be expecting asynchronous
network traffic, and it is doubtful that throughput differences due to power management will be
noticeable with these types of applications. Always set the Inactivity_min parameter to 0,
and set the Inactivity_sec parameter as low as possible (preferably to 1). Never set
Inactivity_sec to 0, as that turns off the power management completely, and the card will
always stay in receive mode.
