[asterisk-users] Horrible problem - calls losing sound

[John Hughes]

We're having a horrid problem with our asterisk setup.

Sometimes calls just go dead - we can't hear what the other end is
saying.  (I think they can't hear us either).  The call doesn't hang up
until one of the callers gets bored.

Internaly we use Thomson ST2030 SIP phones.

Externaly we have 3 ISDN BRI lines (6 channels total), connected to an
Eicon Diver server card (4BRI).

We're using Asterisk 1.4.11 (1.4.11-BRIstuffed-0.4.0-test4) on a Debian
system, with chan-capi 1.0.1.

Any idea what could be going wrong, where to look &c?