Mike Albano

Author Archives: Mike Albano

Interpreting and Graphing Aruba ARM Counters

Guest post by Mike Albano

The topic of "do you trust RRM" is often discussed. The most typical answer is: "Yes, if I understand it." I know I've personally spent numerous hours blaming RRM for a questionable Dynamic Channel Assignment (DCA), and I'm usually wrong.

For the purpose of this post, RRM = Radio Resource Management; be it ARM (Aruba), RRM (Cisco), ACSP (Aerohive), SmartRF (Extreme) etc. etc.

This post isn't about the topic of "trust", or if to use RRM. Here's a good post by @wirednot on that topic. (Read the comments!)

This is more about:

  • Finding a way to interpret and use the data available to identify if/when an AP will change channels (DCA).
  • Analyzing the state of the channel, from the AP's perspective, before & after a channel change.
  • Showing an example of tools I use regularly in troubleshooting (Python and AirRecorder).

The system in question is an Aruba Instant AP (Instant OS version 6.3.1.8-4.0.0.9).

Data Gathering

Typically, I use Pexpect for screen-scraping CLI output but Aruba has written a handy utility to do this for you. It's called Air Recorder, and is multi-platform (Java.) Will run on Continue reading

Optimized Roaming, RSSI Low Check, RX-SOP, Oh My!

In the Cisco landscape today, there are three features that usually come up in the same conversation. They all solve what I'd call "related" problems, but are not the same. They are incredibly useful features and do share one thing in common...you must know your RF environment before implementing them. I'll provide use-cases and examples below, but it should be noted that in the case of "Optimized Roaming", this is based on public information currently available and could change prior to the WLC AirOS version 8.0 release.

Optimized Roaming

The problem:
The well known "sticky client" issue. For the uninitiated, when a client refuses to roam to an assumedly "better" AP (closer, stronger RSSI, better SNR etc.) that client is being "sticky". Why is this bad? Consider the following example of a lecture hall: As the client enters the room, it associates to AP-1. As it moves farther away from AP-1 it's RSSI gets weaker, SNR gets worse, retransmissions occur, dynamic rate-shifting happens, and you end up with a client communicating at a much lower data-rate. Lower data-rate consumes more air-time to transfer the same information, resulting in higher channel utilization. Ideally, the client would roam to Continue reading