[OpenSER-Devel] question on t_relay on CANCEL

[Juha Heinanen]

Dan Pascu writes:

 > Not necessarily. You may have parallel forking and get multiple 180. Until 
 > you get a 200 OK, no dialog is really established. 

from section 12.1 of rfc3261:

  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 ÈearlyÉ state
  and it is called an early dialog.

thus, a single 180, for example, does establish a dialog, which is in
early state.  looks like this creates confusion to UA implementers, who
consider cancel after 180 as an in-dialog message and accordingly, add
route header to it based on received r-r.  

i don't have experience on what would happen when such an UA receives
180 from more than one destination, i.e., would it send more cancels.

 > I've even seen devices 
 > that send a CANCEL after a 200 OK, but before the ACK, as they consider 
 > that the dialog is not established until confirmed by the ACK. Which 
 > makes sense because is cleaner to cancel a call setup with a CANCEL 
 > before it is confirmed, than to send an ACK and then a BYE (for example 
 > if I do not want to accept the session because the 200 OK contains 
 > something I do not agree on or is badly formatted, then I don't want to 
 > confirm the session with an ACK and then close it with a BYE).

many things would make sense, but they are not conforming to rfc3261.

-- juha