IAX Phone Cutouts (SIP Works Fine)

I’m having some strange problems with making calls with IAX, either using an IAXy or a VP168 based phone. Basically, when I make a call the sound drops out for about half a second to a second every once in a while. It happens enough that it makes having a conversation pretty much impossible. We had this same problem with Asterisk 1.2.0-1.2.3 on a Fedora 4 system, so we moved over to a Gentoo box with 1.2.4 and it seemed to go away, but now it’s back.

As I mentioned in the topic, SIP calls still work fine. Also, strangely enough, IAX calls which leave voicemail on the Asterisk server work fine, but IAX <-> ZAPTEL, IAX <-> IAX or IAX <-> SIP all have voice cutouts on the IAX transmitting side.

Does anyone have any ideas? This is with Asterisk 1.2.4 and Zaptel 1.2.3 I haven’t upgraded to 1.2.5 yet, as I don’t see anything likely to fix the issue in the changelog and I don’t want to risk breaking anything else. I’d post some log entries, but nothing seems to correspond to the problem. It’s just basic peer lookup stuff.