FreeSWITCH (Version 1.2.7 git 93e2a38) throws this error in the CLI when a REGISTER without CONTACT-header hits it. FS responds with 500 Internal Server Error
The requesting side is sending a second REGISTER with Contact then and it registeres.
Some "AVM FritzBox" hardware-boxes send such a REGISTER.
Here a (cleaned) SIP-Trace
------------------------------------------------------------------------
recv 620 bytes from udp/[1.2.3.4]:5060 at 11:01:06.214597:
------------------------------------------------------------------------
REGISTER
sip:sipproxy.somebusiness.com SIP/2.0
Via: SIP/2.0/UDP 1.2.3.4:5060;rport;branch=z9hG4bK4F974DA26FBE794A
From: <
sip:user.user2@sipproxy.somebusiness.com>;tag=3665871555
To: <
sip:user.user2@sipproxy.somebusiness.com>
Call-ID: 9BB803703627C9DF@1.2.3.4
CSeq: 2078 REGISTER
Max-Forwards: 70
User-Agent: AVM FRITZ!Box Fon WLAN 7390 84.05.50 (Dec 11 2012)
Supported: 100rel,replaces
Allow-Events: telephone-event,refer,reg
Allow: INVITE,ACK,OPTIONS,CANCEL,BYE,UPDATE,PRACK,INFO,SUBSCRIBE,NOTIFY,REFER,MESSAGE,PUBLISH
Accept: application/sdp, multipart/mixed
Accept-Encoding: identity
Content-Length: 0
------------------------------------------------------------------------
2013-03-21 12:01:06.214194 [ERR] sofia_reg.c:1914 NO CONTACT! ip: 1.2.3.4, port: 5060send 322 bytes to udp/[1.2.3.4]:5060 at 11:01:06.214998:
------------------------------------------------------------------------
SIP/2.0 500 Internal Server Error
Via: SIP/2.0/UDP 1.2.3.4:5060;rport=5060;branch=z9hG4bK4F974DA26FBE794A
From: <
sip:user.user2@sipproxy.somebusiness.com>;tag=3665871555
To: <
sip:user.user2@sipproxy.somebusiness.com>;tag=cFDNr9NQa5g9m
Call-ID: 9BB803703627C9DF@1.2.3.4
CSeq: 2078 REGISTER
Content-Length: 0
------------------------------------------------------------------------
recv 715 bytes from udp/[1.2.3.4]:5060 at 11:01:06.252877:
------------------------------------------------------------------------
REGISTER
sip:sipproxy.somebusiness.com SIP/2.0
Via: SIP/2.0/UDP 1.2.3.4:5060;rport;branch=z9hG4bK394B9487FAFBC468
From: <
sip:user.user2@sipproxy.somebusiness.com>;tag=3665871555
To: <
sip:user.user2@sipproxy.somebusiness.com>
Call-ID: 9BB803703627C9DF@1.2.3.4
CSeq: 2079 REGISTER
Contact: <
sip:user.user2@1.2.3.4;uniq=77F5786DCDB3B0B3999878F7FB4C0>
Max-Forwards: 70
Expires: 1800
User-Agent: AVM FRITZ!Box Fon WLAN 7390 84.05.50 (Dec 11 2012)
Supported: 100rel,replaces
Allow-Events: telephone-event,refer,reg
Allow: INVITE,ACK,OPTIONS,CANCEL,BYE,UPDATE,PRACK,INFO,SUBSCRIBE,NOTIFY,REFER,MESSAGE,PUBLISH
Accept: application/sdp, multipart/mixed
Accept-Encoding: identity
Content-Length: 0
------------------------------------------------------------------------
send 595 bytes to udp/[1.2.3.4]:5060 at 11:01:06.265145:
------------------------------------------------------------------------
SIP/2.0 200 OK
Via: SIP/2.0/UDP 1.2.3.4:5060;rport=5060;branch=z9hG4bK394B9487FAFBC468
From: <
sip:user.user2@sipproxy.somebusiness.com>;tag=3665871555
To: <
sip:user.user2@sipproxy.somebusiness.com>;tag=Dr6Dt46t7D7Ug
Call-ID: 9BB803703627C9DF@1.2.3.4
CSeq: 2079 REGISTER
Contact: <
sip:user.user2@1.2.3.4;uniq=77F5786DCDB3B0B3999878F7FB4C0>;expires=1800
Date: Thu, 21 Mar 2013 11:01:06 GMT
User-Agent: SIP-SERVER
Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY
Supported: timer, precondition, path, replaces
Content-Length: 0