503 Server error response for REGISTER request (Asterisk v1.6.0.5)

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Hello,

Our setup involves a Sip softphone registering with a fresh install of
Asterisk v1.6.0.5 through an outbound proxy (Kamailio v3.1.1).

We observe that about 80% of the time, immediately after startup of the
softphone, when the softphone sends a REGISTER message, Asterisk replies
with a “503 Server error”. However, subsequent REGISTER messages are
replied to appropriately (with a 401 Unauthorized).

There are very few devices (under 5) registered with Asterisk, so this
is not an overload issue.

Please find attached a SIP trace for device registration.

– What might cause this behavior in Asterisk ?
– Are there any config file parameters that require to be changed ?
– Would it help to see any other specific logs, if so which ones ?

Thanks and Regards,
Vikram.

<--- SIP read from UDP://Proxy_IP:9090 —>
REGISTER sip:Asterisk_IP:5060 SIP/2.0
Via: SIP/2.0/UDP Proxy_IP:9090;branch=z9hG4bK54ba.4a00e294.0
Via: SIP/2.0/UDP 192.168.3.6:7160;received=Nat_IP;rport=62842;branch=z9hG4bKPju8xsdcZ1vD7-ykHX33rq78nBeEJ3k-eP
Route:
Max-Forwards: 69
From: “12345” ;tag=fCMU.J88N4jATP5d3d6zjXPbFyWAbz6Q
To: “12345”
Call-ID: 1o-UnqLhb-j4dSzDzHThXhF0uE-nQu4Z
CSeq: 34464 REGISTER
Contact: “12345”
Expires: 300
Allow: PRACK, INVITE, ACK, BYE, CANCEL, UPDATE, SUBSCRIBE, NOTIFY, REFER, MESSAGE, OPTIONS
Content-Length: 0
P-hint: outbound

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