Can someone help me to debug my problem?
 
I have ser between asterisk and my clients.
When I try to call a sip client, it is going to ring. But asap the callee pickup the phone the call goes down.
 
Doing a logging on port 5060 i see that after the ack i get 400 bad request from the sip client.
 
This is the trace: 
 
Session Initiation Protocol
    Request-Line: ACK sip:0681140017@83.211.248.158:62746 SIP/2.0
        Method: ACK
        Resent Packet: False
    Message Header
        Record-Route: <sip:19x.6x.19x.4x;ftag=as6d07dd0a;lr=on>
        Via: SIP/2.0/UDP 19x.6x.19x.4x;branch=0
        Via: SIP/2.0/UDP 19x.24x.16x.9x:5060;branch=z9hG4bK368ed369;rport=5060
        From: "anonymous" <sip:asterisk@voip.convergenze.it>;tag=as6d07dd0a
            SIP Display info: "anonymous"
            SIP from address: sip:asterisk@voip.convergenze.it
            SIP tag: as6d07dd0a
        To: <sip:08281895109@voip.convergenze.it>;tag=b1385811e50f0aai1
            SIP to address: sip:08281895109@voip.convergenze.it
            SIP tag: b1385811e50f0aai1
        Contact: <sip:asterisk@19x.24x.16x.9x>
            Contact Binding: <sip:asterisk@19x.24x.16x.9x>
                URI: <sip:asterisk@19x.24x.16x.9x>
                    SIP contact address: sip:asterisk@19x.24x.16x.9x
        Call-ID: 3ff0ae307575f1df61408b205af01196@voip.convergenze.it
        CSeq: 102 ACK
        User-Agent: Convergenze VoGW1
        Max-Forwards: 16
        Content-Length: 0
 
and then
 
Session Initiation Protocol
    Status-Line: SIP/2.0 400 Bad Request
        Status-Code: 400
        Resent Packet: False
    Message Header
        To: <sip:08281895109@voip.convergenze.it>;tag=b1385811e50f0aai1
            SIP to address: sip:08281895109@voip.convergenze.it
            SIP tag: b1385811e50f0aai1
        From: "anonymous" <sip:asterisk@voip.convergenze.it>;tag=as6d07dd0a
            SIP Display info: "anonymous"
            SIP from address: sip:asterisk@voip.convergenze.it
            SIP tag: as6d07dd0a
        Call-ID: 3ff0ae307575f1df61408b205af01196@voip.convergenze.it
        CSeq: 103 INVITE
        Via: SIP/2.0/UDP 19x.6x.19x.4x;branch=z9hG4bK9f79.7854d9e5.0
        Via: SIP/2.0/UDP 19x.24x.16x.9x:5060;branch=z9hG4bK493c6be2;rport=5060
        Record-Route: <sip:19x.6x.19x.4x;ftag=as6d07dd0a;lr=on>
        Server: Sipura/SPA2100-3.2.5(d)
        Content-Length: 0
 
Any help is appreciated.
Regards
Rosairio