[SIPForum-discussion] URI in the TO header

[FRANCISCO GIOIA]

Dear all, I have a doubt. Can you help me?



Question:

RFC 3261 (item 8.1.1.1) recommends that the REQUEST-URI of the initial message (Request-line) should be equal to the URI of the "TO" header field. The explicit exception in this item of the RFC is when it comes to the REGISTER method (where such information may be different).



We wonder if there are situations in which the URI in the TO header field may be different from the URI of the Request-Line?

An entity (UAS) that receives a SIP INVITE message must focus on which recipient to make the correct routing of the call (Request-Line URI or TO header Field URI)?



RFC 4497 (item 11.4) mentions the possibility of difference between REQUEST-Line URI and URI in the TO header field in case of interworking between SIP and QSIG. In this case should be considered that there was a call forwarding? This applies, by analogy, to other cases of interworking (SIP x SIP, SIP x ISUP, SIP x MGCP, ...)?



In the case of numerical regeneration done by the UAS, how does the Request-Line URI and the TO header field URI of the INVITE message must  be filled? Remembering that it is not Call Forwarding but regeneration(numerical manipulation).



Example:

UAS receives
Source = 22223333 (tel number of calling subscriber)
Destination = 1234 (dialed number) - UAS manipulates to 44445555

Thank you in advance for your attention and understanding.

Francisco Gioia.

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