Audio dropouts w. 1.4.21.2

Asterisk Asterisk Support
1

Help! I’m completely stumped, and I don’t have a fix – nor does the Voxilla forum!

I’m running Asterisk 1.4.21.2 on a small (Pentium 4 3GHz/2GB RAM) SOHO server with 4 SIP channels. OS is Fedora 8. The box is also the main NAT router for the LAN and Asterisk has a direct Internet connection. The ISP provides a sustained 10-12Mb down 1.5-2 Mb/up.

For some time, 99% of the SIP providers I’ve used have random audio dropouts 5-10 seconds in length. I usually can’t hear the other side. Two are exceptions:

  1. Adams Telecom (Had to drop them for other reasons)
  2. Voipjet

I can make calls just fine, and even with SIP to SIP calls, I have dropouts. (No provider trunk.)

  1. Nothing shows in the logs, nothing shows in the /var/adm/messages
  2. No disk or network errors are found

Just to further diagnose it, I took a SIP phone (SPA941) and set it to directly use a SIP termination provider. This same provider is also used by the Asterisk server.

  1. If the phone uses the SIP provider directly, no dropouts
  2. If the phone goes through the Astersk server, I get 5-10sec dropouts

It can’t be firewall software (or at least its’ unlikely) because the SIP phone uses the same gateway. I’d think that rules out the hardware.

  1. How do I further diagnose this issue?
  2. How do I solve it?