Dropped Calls (Seqno 102 - no reply to our critical packets)

I’ve a asterisk, is not behind a NAT, it’ve a real public IP. My problem is when some users make a call with PAP2 that are located behind NAT, in some occasion the call are dropped exactly to the 20 seconds and give this error in console

[Jul 3 23:17:13] WARNING[2698]: chan_sip.c:1944 retrans_pkt: Maximum retries exceeded on transmission 1ade2729-c1e8765c@ for seqno 102 (Critical Response)
[Jul 3 23:17:13] WARNING[21698]: chan_sip.c:1968 retrans_pkt: Hanging up call 1ade2729-c1e8765c@ - no reply to our critical packet.

This happen only some times, I’ve readed that is because the server don’t “find” the pap2 (like Ping Timeout)

Is there any solution for this in asterisk or in the voip adapters? (I don’t know if this problem is only in PAP2 or not, because we’ve only PAP2 here)


And the sip.conf entries for these users look like ???


The sip.conf of the asterisk server?