PBX Timer Underrun Can Sound Like an Endpoint Bug

Server scheduling can inject media timing problems even when embedded firmware has not changed.

PBX Timer Underrun Can Sound Like an Endpoint Bug became a separate note because the failure crossed more than one subsystem. During LOUP testing the Asterisk timer under-ticked during a call, and restarting the PBX improved the observed behaviour.

That observation mattered because audio defects were easy to attribute to the ESP32-S3. Comparing endpoint logs with PBX timing and then repeating the call after a server restart helped isolate a server-side contribution.

The fix came from assigning one owner to the behaviour and refusing to hide a hardware or network fault with an unrelated firmware workaround. Evidence marker: asterisk-timer-undertick.

Distributed real-time systems can fail at either endpoint or in the middle. Keep server timing in the audio-debugging evidence. The value is not only the fix itself; it is having a repeatable way to prove the same class of failure has not returned.

Project evidence

LOUP engineering marker: asterisk-timer-undertick. This note records the design or debugging lesson without publishing device credentials, private keys, customer data or manufacturing secrets.