[SIPForum-discussion] UAS Processing of the INVITE request

sreekant nair sreekant_nair at yahoo.com
Mon Aug 13 12:42:22 UTC 2007

Hi Vijay, 

One of the means of distinguishing a new INVITE from a re-INVITE is the TO Tag. The presence of the TO-Tag indicates that this is a mid-call INVITE that belongs to a dialog. 
A typical scenario when a re-INVITE is sent (in a VOIP perspective) is HOLD/3way call/Conference etc. You need to out the original call on hold and call the next person and then conference all three. That would have a re-INVITE.

So in between if the system crashes while on hold, the re-INVITE would come and not find that dialog.So assuming that the system crash was a fatal error, there may not have been time or the environmental conditions would not have been favorable to print/throw/display any kind of log. Even if it did , the log may not be a SIP-UAS log. 


----- Original Message ----
From: Donald Lee <baolovebao at gmail.com>
To: Vijay T <vijaycec at yahoo.co.in>
Cc: discussion at sipforum.org
Sent: Sunday, August 12, 2007 9:56:04 PM
Subject: Re: [SIPForum-discussion] UAS Processing of the INVITE request

Hi Vijay:


      Here are some of my considerations, please check them inline.




2007/8/12, Vijay T <vijaycec at yahoo.co.in>:
Dear All
          This is vijay...i have a doubt reg INVITE req processing...
During the handling of INVITE request(UAS core) RFC3261 states that in the section

13.3 UAS Processing

13.3.1 Processing of the INVITE
  3."If the request has a tag in the To header field but the dialog
     identifier does not match any of the existing dialogs, the UAS

     may have crashed and restarted"

My Qns: 
1.Here the request itself fill the tag of the To header field.How???

Donald: It doesn't mean that the request fill the tag. On example of this case: During an exist dialog one of the UE has some fatal error to reboot, so it doesn't send any request to the other UE. after the former one up again, if the other one want to send a re-INVITE to change the "current dialog", that would lead to this case.

2.In crashed & restarted  case why not UAS generated corresponding error response for that???

Donald: I think in this case there is no time for UAS to generate corresponding error response, it's dying:-P.


and another separate query is 
please tell me about "mid-dialog" request and when it'' happen???


Donald: After a dialog is estabilished(an ACK in a dialog send successfully). Any request within this dialog(have the same

Call-ID, From-Tag, To-Tag) will be called "mid-dialog" request.

i'm little bit confused abt this request....

Thanks in Advance

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