dahdi timing

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We heavily use meetme/SLA functionality in Asterisk, and continuously run into issues with dahdi timing. The two errors we get are:

ERROR[6518] res_timing_dahdi.c: Failed to configure DAHDI timing fd for 0 sample timer ticks

WARNING[22024] app_meetme.c: Unable to write frame to channel

Right now, dahdi in our setup uses the software timer (with res_timing_dahdi.so which gives much better results compared to res_timing_timerfd.so). On an idle system (Centos 6, Asterisk 1.8.7, dahdi 2.5), dahdi_test results are pretty good at about %99.99. However, when loaded, the numbers fluctuate between %99.90 and %99.99 which seem to cause the above errors.

We tried Sangoma UT50 as a timing device (it’s USB based), but the test results were worse (between 99.98 – 99.97 when idle, and had big dips when loaded and there is no IRQ sharing).

We are planning to order Digium AEX410 cards hoping they will be an improvement over dahdi_dummy and Sangoma. Does anyone have experience with these cards? Can we get a stable performance from them even under load?

Also (for Digium developers who might be reading this list), any plans for decoupling SLA from dahdi timing in future releases of Asterisk?