[SR-Users] 503 Server error response for REGISTER request (Asterisk v1.6.0.5)

[Vikram Ragukumar]

Daniel,

>> I had posted this question earlier on asterisk-users, but didn't
>> receive any reply, so I'm posting on sr-users in the hope that someone
>> can provide guidance on how to debug this problem.
>>
>> 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 "500 Server error". However, subsequent REGISTER
>> messages are replied to appropriately (with a 401 Unauthorized).
>>
> you should set sip debug on for asterisk in order to get more verbose
> output related to the 503 case. I couldn't spot something wrong for
> register that got 503. Next ones have two contact headers, but that is
> fine in SIP.
>
> Cheers,
> Daniel

I have recently had the chance to do some more debug and here is more 
information. It appears that the 500 Server Error is generated by 
Asterisk as a response to an offending REGISTER request from the 
softphone that has an invalid CSeq number. I have attached an excerpt of 
a sip trace that shows these messages. The offending REGISTER message 
has a CSeq that is lower than that of the earlier REGISTER message with 
the same Call-ID.

My questions are

1) Is the response from Asterisk (500 Server Error) valid ? Wouldn't a 
4xx Client Failure response be more appropriate ?

2)The source of this error would probably be a bug in the SIP stack of 
the soft phone (PJSIP), correct ?

Thanks and Regards,
Vikram.
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