Rene - I was wondering if you could clear up this item for me — regarding VoWLAN.
The WLAN/WLC course material I have been using discusses aggressive load balancing.
The following statement is presented as a footnote on the course slide — Information About Aggressive Client Load Balancing:
The Aggressive Client Load Balancing feature allows lightweight access points to load balance wireless clients across access points. When a wireless client attempts to associate to a lightweight access point, the associated response packets are sent to a client with an 802.11 response packet including status code 17. This code 17 indicates that the corresponding AP is busy. The AP does not respond with the response ‘success’ if the AP threshold is not met (WHAT THRESHOLD ARE THEY TALKING ABOUT ?), and with code 17 (AP busy) if the AP utilization threshold is exceeded, and another less busy AP hears the client request. For example, if the number of clients on AP1 is more than the number of clients on AP2 and the load-balancing window, then AP1 is considered to be busier than AP2. When a client attempts to associate to AP1, the client receives an 802.11 response packet with status code 17, indicating that the access point is busy, and the client attempts to associate to a different access point. You can configure the embedded wireless controller to deny client associations up to 10 times (if a client attempts to associate 11 times, it will be allowed to associate on the 11th try).
You can also enable or disable load balancing on a particular WLAN, which is useful if you want to disable load balancing for a select group of clients, such as time-sensitive voice clients. A voice client does not authenticate when delay is configured to more than 300 ms. To avoid this, configure a central-authentication, local-switching WLAN with Cisco Centralized Key Management (CCKM), configure a pagent router(A WHAT??) between an AP and WLC with a delay of 600 ms (300 ms UP and 300 ms DOWN), and try associating the voice client.
This is the first time that I encountered the term “pageant router” but after some research I discovered that this is a term specific to Cisco. In any event it is not clear to me exactly where to place this router in the WLAN topology ( assuming a 3-tier architecture) and how this device resolves the issue of delay > 300 ms if there is an actual (physical) delay in the network.
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.
Hello Lazarus,
Thank you for taking the time to formulate this explanation which was very helpful and comprehensive.
While some items are still unclear the overall concept of a “pagent” router makes a bit more sense now — particularly after reading the NetworkLessons note. This document also revealed that “pagent” is actually a Cisco acronym — in hindsight, I should have suspected this…
I think you are correct that this solution is really for lab environments that are destined for testing.
One more thing that I forgot to mention is that the Cisco Performance Agent software has been around for many years. It’s last iteration, version 1.7 has an end of life of January 31st, 2024, and it seems that newer versions are not being developed. Instead, users are recommended to migrate to the Evolved Programmable Network Manager. So as a product, Cisco pagent routers are no longer actively supported devices. I’ve updated the related NetworkLessons note with this information and with additional links too.
