Buffer size of AP for clients in power save mode

Aruba Employee

Question : How many frames can an AP buffer for a client when it is in Power-Save mode?

 

Answer : It is a feature of the clients that they can be in power save mode to conserve battery. A client will enter into power save mode by informing the Ap by setting the power-management bit to 1 as shown below:

 

rtaImage.png

 

At this point the client enters the power save mode. From here, the Ap will start to buffer the data it receives for the client and would store in its memory. based on the type of power save mode: Legacy or U-APSD, the client will wake up when it sees its Association ID in the beacon frame(TIM) sent by the AP and start requesting for the buffered data.

If the client takes longer time to wake up or the AP receives too many frames for the client, then the Ap will not be able to keep all the buffered data, thus resulting in data loss.

In Aruba AP's there is a limit for how many frames an AP can buffer for each client. This is a hardware limit.

Latest 802.11ac capable AP's like 225 can store approximate first 500 unicast frames for individual clients associated to it and the rest will be dropped.
Non 802.11ac like 105's can store approximately first 50 unicast frames for individual clients associated to it.


For broadcast and multicast traffic, the AP will store a value of "Avail TX Buffer" * 2000 bytes will be used.

NOTE: "Avail TX buffer" can be seen from the command:

# Show ap debug radio-stats ap-name <ap-name> radio 0 or 1 advanced | include Avail
   Avail TX Buffers                 512

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Last update:
‎06-30-2014 03:21 PM
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