Hello Sandro
The Aggressive Client Load Balancing feature is a mechanism that attempts to actively distribute wireless clients among APs more evenly by denying the association of clients to a particular AP when there is a neighboring AP that is comparatively underutilized, thus causing the clients to attempt to associate with that neighboring AP. The “threshold” mentioned here is a poor choice of words, in my opinion, adding confusion to the explanation. I believe it refers to the predefined limit set within the AP to determine how much client load the AP can handle before it is considered too busy to accept new clients. This limit is configured using the Aggressive Load Balancing Window (clients) and Aggressive Load Balancing Denial Count values configured in the WLC.
Now the whole explanation of the related problems with voice client association in the document seems strange to me. And the introduction of a pagent router is also strange. It seems like they’re mentioning in passing an issue with voice clients in an environment where aggressive load balancing is applied, with a very superficial and almost makeshift solution that you can “try” if you need it, but with no additional explanation or resources.
As you have probably found out, a pagent router is a router equipped with Cisco’s Performance Agent software. More info about that can be found in this NetworkLessons note. The peculiar thing is that a Pagent router is not typically deployed in a production network, but most often in a lab environment primarily for testing purposes. It seems that they are asking you to use a pagent router to adjust the expected network conditions in such a way that the voice client will be able to associate with an AP. Sounds like a very sketchy solution.
It’s not quite clear why they’re using the 300 ms delay here, as delays in VoIP applications are typically detrimental. And it’s also not clear where to place the router either. The pagent router is said to be placed “between an AP and WLC”. This placement is not necessarily in the direct physical path between the AP and the WLC because APs usually connect to WLCs over a network, not through a direct, singular path. It would probably be integrated within the network infrastructure in such a way that it can intercept and affect the traffic going between the APs and the WLC. But where that would be physically depends upon the network design and architecture.
In any case, that’s an interesting document you shared, and I hope what I have shared will shed some light on your understanding of the concepts involved.
I hope this has been helpful!
Laz