Problem with asterisk and aastra phones


Our setup consists of an asterisk server (version 1.4.8 ) with a TDM400 card (4 FXO ports) and about 10 aastra 5Xi phones (2 phones are 57i and the rest 55i). The asterisk server is also configured with two SIP trunks.

The problem that we’re having is that if at any time there is an internet connection interruption to the asterisk server all the aastra phones freeze. If we disable the two SIP trunks in the asterisk configuration the phones are fine.

We wrote to aastra support about the problem and they said that the phones freeze because their receive sip packages from the asterisk server in some strange order and that they are working on fixing the problem (this was 3 months ago and no fix yet).

My question is if anybody here has any idea of what might be happening or of any asterisk settings that might help prevent this problem?

Thank you.