The Rate Control Firmware Bug
HPE Aruba
Situation
During pre-release validation testing, I discovered a 40% throughput regression in a firmware build that was about to ship to thousands of enterprise customers. The regression was subtle — it only appeared under mobility conditions, not in static lab tests.
Task
Find the root cause and prevent the defective firmware from reaching production. The release was scheduled for that week and engineering was under pressure to ship.
Action
I dug into the Minstrel-HT rate adaptation algorithm and discovered the EWMA (Exponentially Weighted Moving Average) window was too long for mobile scenarios. The algorithm was designed for relatively static conditions but failed when clients moved between APs. I built a test harness that specifically exercised the rate control path under simulated mobility, proving the regression was real and reproducible.
Result
Blocked the release. The engineering team implemented an adaptive EWMA window that shortened during detected mobility events. The fix shipped in the next release cycle with my test harness integrated into the nightly regression suite. This likely prevented thousands of customer complaints.