Phone not ringing

I have Asterisk I connect phone Grandstream GXP2000 to it. After registration all is OK, after 10 minutes (sometimes after 1 hour) phone dont ring. On console is:

-- Dial("SIP/511-0000072c", "SIP/892,40,Tt") in new stack == Using SIP RTP CoS mark 5 -- Called SIP/892 [Jun 12 13:03:48] WARNING[29707]: chan_sip.c:3629 retrans_pkt: Retransmission timeout reached on transmission 505e5c7a396a161d51400cd742643d58@ for seqno 102 (Critical Request) -- See Packet timed out after 32000ms with no response == Everyone is busy/congested at this time (1:0/0/1)
There is missing SIP/892-xxxxxx is ringing

In sip.conf is:

[892] type = friend context=home username = 892 host = dynamic canreinvite=no nat=yes qualify=yes mailbox = 892 dtmfmode=rfc2833 secret=xxxxxxxx disallow=all allow=alaw callerid="892" <892>
Asterisk is connected direct to Internet with own public IP.

Can you help me?


P.S. Sorry for my english.

The SIP/892-xxxxxx is ringing is missing because Asterisk hasn’t received any responses from the device. That either means the INVITE never reaches the device, in which case it will not actually be ringing, or the response didn’t get back to Asterisk, in which case it might actually be ringing.

Generally a firewall or NAT problem.

You should try lowering the value of "Register Expiration " on your phone down to 60 secs.

Thank you, I decreased “Register Expiration” to 60 sec and set “Keep Alive” on device and it looks OK now.