[Ekiga-list] After a couple of minutes in the call, the called side can't hear us anymore

[wonder75 <wonder75 gmail com>]

Hi.
We are running an Asterisk setup in a call center.
The Agents use SIP-softphones to connect to the Asterisk-server via
local office LAN (no NAT). Asterisk is connected to an E1 line with a
Digium Te122. The Agents are using Ekiga for Windows as softphone at
the moment.

Our problem: sometimes, after being a couple of minutes into a call,
the called party can't hear our agent anymore, the agent can hear the
called party fine. this happens randomly in every 20th call or so, it
doesn't happen at all for some agents.

i am puzzled where to start to search for the error? is this probably
an Asterisk/zaptel problem or would the error rather be on the
softphone/windows side? The microphones are still working when that
happens, the talk-volume indicator bar is working in ekiga, but the
called party can't hear.

tnx for any ideas
greetings wonder