[Serusers] MSRTC DLL Bug with SER

[Andrew Mee]

After much more discovery we have figured out what the issue is with the 
MS RTC 1.2 and SER.

This isn't so much as a bug with SER but with MS RTC 1.2, it is caused 
by MS RTC sending incorrect Request-URI in the headers. This only occurs 
in request routed mode from the callee end.

Take the example:
RTC Client A            SIP Server           RTC Client B
-----INVITE-------------->  
<----100 Trying-----------
                             -----INVITE---------------->
                             <----100 Trying-------------
<----180 Ringing----------   <----180 Ringing------------
<----200 OK w/ INVITE-----   <----200 OK w/ INVITE-------
-----ACK----------------->   -----ACK------------------->

All is fine at this point, however now lets send a message from A to B:
RTC Client A            SIP Server           RTC Client B
----MESSAGE b at server---->    ----MESSAGE b at server---->
<----200 OK -------------   <----200 OK --------------

All is still fine, However if we send a message back from B to A:
RTC Client A            SIP Server           RTC Client B
                             <----MESSAGE b at server----
                             -----MESSAGE b at server---->
                             <----481 Call Leg/T DNE---
This is obvious because the SER server sees this message as needing to 
go back to B when it should be forwarded to A as per "8.1.1.1 
Request-URI" of the rfc (as far as my understanding on this). This issue 
occurs with BYE commands and possibly other types of commands.

I might add the To: and From: header fields are correct.

Solution to this problem could (or is there an existing way) a 
module/control could be created that checks if the To: field doesn't 
equal the request-uri that the request-uri be changed to the information 
in the To: field?

Yes I agree that while this is a MS RTC problem, I figure this is going 
to be a better/quicker short term solution. I have not tested if this 
problem exists with other SIP servers.

I can send some ngrep logs if anyone likes?

-- 
Andrew Mee
 


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