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Re: B2B proposal

  • From: Binod < >
  • To:
  • Subject: Re: B2B proposal
  • Date: Fri, 14 Jun 2013 17:25:43 +0530


" type="cite">
>
> --- SipInviteRequest.getUnacknowledgedProvisionalResponse ---
>
> Why do we need to pass in the SipSession? If we do, it seems like this
> method should be on the SipSession as opposed to the request. Since it
> is on the request, I would assume this method would only return
> responses for this particular transaction, correct? And if so, the
> SipSession is not needed since the request you are operating on
> explicitly is associated with a SipSession, or perhaps I'm missing
> something...
>
> Version 2 of my proposal did have this method on the SipSession. I realised
> a problem with that as explained in the email that accompanied version 3.
>
> The rseq value in a reliable provisional is only unique for that dialog. Due
> to forking there can be several dialogs which return provisional responses.
> In order to locate a specific response at a UAC which is downstream of a
> forking proxy we need to pass the session (or derived session) along with
> the rseq to the method on SipInviteRequest.
>
> If we put the method on the SipSession there is still a problem with the
> uniqueness of the rseq value. PRACK can arrive after the corresponding ACK
> by which time a new INVITE transaction can be in progress which also has
> provisional responses. To retrieve the correct response we would need to
> pass it the requestId of the INVITE transaction as well as the rseq.
>
> It seems best to avoid cluttering the SipSession interface with methods such
> as this one.
Ok, I think you lost me but I guess my original question was also that
the request itself is uniquely associated with a particular sip
session (it cannot have two) so if you ask the request, the sip
session is implied. Right?

A SIP request is uniquely associated with a SIP dialog, which is uniquely associated with a SipSession. This all seems simple enough, until you consider forking. When downstream forking occurs, you will have more than one SipSession, but still only have one SipServletRequest. This is not so bad when you are acting as a UAC, but when you are running a B2BUA and acting as a UAS, what happens when you want to "fork back" to the caller?

    Alice          B2BUA          Proxy          Bob1          Bob2
 1. INV(a1)---------->
 2.                   INV(b1)------->
 3.                                 INV(b1)------->
 4.                                 INV(b2)--------------------->
 5.                                 <-------180(b1)
 6.                   <-------180(b1)
 7. <----------180(a1)
 8.                                 <---------------------180(b2)
 9.                   <-------180(b2)
10. <----------180(a2)

Here we have an example of parallel downstream forking. Assume that the B2BUA is an app running on a SipServlet container. Everything else is a normal SIP actor outside of the container. At step (9), the response from Bob2 leads the container to realise that forking has occurred, and so it creates a derived SipSession from the session used to send the initial INVITE to Bob in step (2). When we need to send the first response to Alice in (7), then the existing SipSession is used, but to create the second response in (10) requires a new SipSession to be created. After all this forking: Alice has two SipSessions, but only one INVITE SipServletRequest - when that SipServletRequest is queried for Alice each has one INVITE. When you call getSession() on the INVITE SipServletRequest, it will return the original SipSession. All quite weird.
Containers are likely to clone the SipServletRequest when the derived session is created.
So, though I see your point, we can not assert that there can be more than one sipsession
for a sipservlet request.

thanks,
Binod.
" type="cite">


Anyway, I suck at the prack stuff so I'm going to go with whatever you
want as long as we make sure that the methods are clear, the
documentation is there and we don't run the risk of confusing
container implementors as well as users.
 
As for the PRACK stuff, we are discussing this and Keith is writing up a further proposal that is hopefully a little more clear when it comes to handling PRACK transactions from one INVITE transaction overlapping with a different INVITE transaction (and thus possibly overlapping with its PRACK transactions).

Tom

>>
>> --- SipSession.getActiveInvites ---
>>
>> What about getActiveXXX? i.e., what about all the other methods?
>
> Only INVITE transactions require an ACK, other transactions are complete
> once the final response is sent/received. Similarly only INVITES can have
> reliable provisional responses.

Sure, but until you get a final response the "other" type of requests
are still "active". And if you are after only whether or not you have
received an ACK or not, wouldn't a method following the other
getUnacknowledgedXXXX methods be more appropriate?

--
Tom Strickland, Software Developer, Thrupoint Software. Tel: +44 (0) 2920 005110
 
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Re: B2B proposal

Jonas Borjesson 06/12/2013

Re: B2B proposal

Binod 06/13/2013

Message not available

Message not available

Fwd: B2B proposal

Strickland, Tom 06/13/2013

Re: B2B proposal

Jonas Borjesson 06/13/2013

Re: B2B proposal

Strickland, Tom 06/14/2013

Re: B2B proposal

Binod 06/14/2013

Re: B2B proposal

Strickland, Tom 06/14/2013

Re: B2B proposal

Binod 06/17/2013

Re: B2B proposal

Nitzan Nissim 06/17/2013

Re: B2B proposal

Strickland, Tom 06/17/2013

Re: B2B proposal

Jonas Borjesson 06/14/2013

Re: B2B proposal

Lewis, Keith 06/15/2013
 
 
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