From Release 8.1, controller supports 802.11v amendment for wireless networks, which describes numerous enhancements to wireless
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.
Another enhancement 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 point.
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
Directed Multicast Service
Using Directed 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 Period
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.
If you have enabled optimized roaming, the controller sends a BSS Transition Management (BTM) query to forcibly roam a client.
This will enable the dissociation imminent field, irrespective of the WLAN configuration. Load balancing and XOR roaming adhere
to the disassociation imminent configuration of the WLAN.
This section contains the following subsections: