Someone please help. Second incoming call disconnects first

I had posted this a while ago but haven’t received any reply. I would appreciate it if anyone has any insight into our problem.

Our setup uses Digium card, Asterix 1.2, and Cisco 7940 phones. We have three incoming lines.

While in the middle of one call, if we receive a second call, the first call just gets dropped.

  1. This does not happen every time. I would say it happens once in four times. I have not been able to find any pattern
  2. The problem happens only if the second call goes to the same extension. At first, I suspected that our Cisco phone had the problem. However, all phones cannot possibly have the same problem.

Does anyone have any idea on what could be happening?

Thank you in advance for your help.


describe configuration(nat,firewall?) and write config part, please,
i have no problem with it. i have this phone.

Thank you for your help.

There is no NAT or firewall in place. The external lines are standard telephone lines.

The configuration files are pretty much the standard files. There have been a few modifications for our case but nothing special.

Appreciate your help.