hi eparedesburga,
There is no tool available in the controller, but you can check with some of the following:
a> ping <ip of ap> (or from some desktop device, set to route via the controller, can do longer term ping)
b> show ap details advanced ap-name <the ap>
For b> above, here is some interpretation of some of the info (mostly in the first page of output)
(sg-3200) #show ap details advanced ap-name ap125
AP "ap125" Basic Information
----------------------------
Item Value
---- -----
AP IP Address 192.168.1.9
<snip>
<snip>
ap RTT total, hiwmk: 10, 1
Currently in reglist No
Reglist Entries, Exits: 86 86
<snip>
<snip>
the line of interest here is "ap RTT tota, hiwmk". In this case it has a value of 10,1 which means there has been 10 times where the RTT (in terms of response to a msg from controller to AP) has been between 1 and 1.99 seconds.
if the value showed 10,5 then it would imply that there was a moment where the latency was 5 seconds max, and there has been some total amount of latency of 10 seconds.
Also just below the above outpout, there are per message RTT counts, granulatiry is 1 second, so for 0-1.0 it will show as 0, for 1.01 to 2.00 it will show 1.
Rebootstraps and Control Messages Log
-------------------------------------
Recent Messages Time now: Fri May 9 11:51:49 2014
--------------- ----------------------------------
Time Offset Message details
----------- ---------------
-286 RCVD: KEEPALIVE len=20 peer=192.168.1.9 seq_num=602 rtt=0 result=OK
-885 RCVD: KEEPALIVE len=20 peer=192.168.1.9 seq_num=601 rtt=0 result=OK
-1486 RCVD: KEEPALIVE len=20 peer=192.168.1.9 seq_num=600 rtt=0 result=OK
hope that helps.
-jeff