The customers LYNC 2010 server was connected to PSTN via and Audiocodes Mediant 1000 6.2x and the E1 ISDN trunk was working fine for most international and all local numbers.
When turning the LYNC traces the 603 DECLINE response was found.
In the AC syslog tool I found that the carrier send a “CALL RELEASED”
This is what I found in the syslog
Now the fun began, because after corresponding with the carrier (TDC) they told me, that the Call_released is send corresponding to the CANCEL that we send them.
So the gateway was sending PSTN commands without showing them in syslog – interesting. Anyway the tech informed me of the error code attached to the CANCEL message was T301 timer error code 102 Recovery on timer expired.
Okay, but the T301 setting In Audiocodes is controlled by the “PSTN alert timeout” setting found under Configuration tab > VoIP menu > PSTN Settings sub-menu > Trunk Settings – and this was set to default at -1 (which according to documentation is 180 seconds – FYI the CANCEL apparently was send after 4 seconds.
I then tried to adjust the PSTN alert timer to 300 and reboot the gateway – and HEY PRESTO – now the customer could dial the customer in Austria with no problems.