From Release 8.1,
controller supports 802.11v amendment for wireless networks, which describes
numerous enhancements to wireless network management.
One such enhancement
is Network assisted Power Savings which helps clients to improve battery life
by enabling them to sleep longer. As an example, mobile devices typically use a
certain amount of idle period to ensure that they remain connected to access
points and therefore consume more power when performing the following tasks
while in a wireless network.
is Network assisted Roaming which enables the WLAN to send requests to
associated clients, advising the clients as to better APs to associate to. This
is useful for both load balancing and in directing poorly connected clients.
Enabling 802.11v Network Assisted Power Savings
Wireless devices consume battery to maintain their connection to the
clients, in several ways:
By waking up at regular intervals to listen to the access point
beacons containing a DTIM, which indicates buffered broadcast or multicast
traffic that the access point will deliver to the clients.
By sending null frames to the access points, in the form of
keepalive messages– to maintain connection with access points.
Devices also periodically listen to beacons (even in the absence
of DTIM fields) to synchronize their clock to that of the corresponding access
All these processes consume battery and this consumption particularly
impacts devices (such as Apple), because these devices use a conservative
session timeout estimation, and therefore, wake up often to send keepalive
messages. The 802.11 standard, without 802.11v, does not include any mechanism
for the controller or the access points to communicate to wireless clients
about the session timeout for the local client.
To save the power of clients due to the mentioned tasks in wireless
network, the following features in the 802.11v standard are used:
Multicast Service (DMS), the client requests the access point to transmit the
required multicast packet as unicast frames. This allows the client to receive
the multicast packets it has ignored while in sleep mode and also ensures Layer
2 reliability. Furthermore, the unicast frame will be transmitted to the client
at a potentially higher wireless link rate which enables the client to receive
the packet quickly by enabling the radio for a shorter duration, thus also
saving battery power. Since the wireless client also does not have to wake up
at each DTIM interval in order to receive multicast traffic, longer sleeping
intervals are allowed.
BSS Max Idle
The BSS Max Idle
period is the timeframe during which an access point (AP) does not disassociate
a client due to nonreceipt of frames from the connected client. This helps
ensure that the client device does not send keepalive messages frequently. The
idle period timer value is transmitted using the association and reassociation
response frame from the access point to the client. The idle time value
indicates the maximum time a client can remain idle without transmitting any
frame to an access point. As a result, the clients remain in sleep mode for a
longer duration without transmitting the keepalive messages often. This in turn
contributes to saving battery power.