27 Mar
2018
27 Mar
'18
9:28 p.m.
Am Dienstag, 27. März 2018, 15:30:01 CEST schrieb Emmanuel BUU:
[..]
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
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 ?