[SR-Users] To tags in 407 challenges

[Henning Westerholt]

Am Dienstag, 27. März 2018, 15:30:01 CEST schrieb Emmanuel BUU:
> [..]
> > Honestly, in ten years of doing SIP, this is the first time I am
> > confronting this question. I was accustomed to the notion that To tags
> > are only added to a reply when it is desirable to form an early dialog
> > (in the case of a non-100 1xx reply). But the passage you quote seems to
> > settle it.
> 
> An additional question!
> Does  second authenticated INVITE sent by UAC should also mention this
> to tag and the called UA should also accept it as part of the dialog id ?
> 
> Or does the second authenticated INVITE open a new dialog ?

Hello Emmanuel,

the first dialog is created at the second successful INVITE. The second INVITE 
is just a re-send of the first INVITE with the authentication credentials. To 
quote from RFC 3261, section 12.1:


Creation of a Dialog
Dialogs are created through the generation of non-failure responses
to requests with specific methods.  Within this specification, only
2xx and 101-199 responses with a To tag, where the request was
INVITE, will establish a dialog.  A dialog established by a non-final
response to a request is in the "early" state and it is called an
early dialog.


You will find a good example for a sessions establishment including 
authentication and two proxies in RFC 3665, section 3.2.

Best regards,

Henning