[Blink] Digest user

[Emil Ivov]

На 30.04.10 16:12, Luci Stanescu написа:
> Hi,
> 
> On 30/04/10 08:32, Emil Ivov wrote:
>> It's probably worth noting that 3261 does authorize empty INVITEs. In
>> such cases you simply need to send an offer in the OK, and get the
>> answer in the ACK.
> 
> As simple as this might sound, 

Oh, I never said it was simple :). In SIP Communicator we also realized
we needed to support this only after we had implemented support for the
"regular" use case and we were just as unhappy :). It is a scenario that
does appear every now and then though so we ended up supporting it.

> it has some implications. If you're
> sending me an INVITE without an SDP, it means that you'd like to
> communicate with me, but you have no idea whatsover about how exactly
> you'd like to communicate. Do you want to talk to me or see me? Would
> you like to get a file from me or send me a file? Would you like to see
> my desktop or show me yours? Or maybe you'd prefer some plain old chat.
> As far as I'm concerned, I cannot possibly know what exactly it is that
> you want from me. And how exactly would you expect a client receiving
> such an INVITE behave? Should Blink pop-up a panel and say:
> 
> "Hey, X wants to get in touch with you, but he doesn't know how. You get
> to choose the communication medium" along with some buttons:
> Audio, Chat, File Transfer, Share local desktop, Request remote desktop

That's up to you I guess. In our case we simply send an offer for what
we consider to be the most likely and basic use case: an audio-only
call. So far, this seems to work.

> Even worse, after I send you a 200 OK with whatever stream(s) I choose,
> you can refuse my request, but the session will already be established.
> You'll have to send an ACK with the media streams I requested with 0
> ports. And then one of us should close the session, right? Or shouldn't
> we? After all, it's perfectly valid to have a session with all streams
> closed. I think supporting this raises more questions than would be
> immediately obvious.

Possibly, but it's still a MUST, and it appears it's not all that rare
to find deployments that are using it.

> And what applications are there for this type of session establishment?

3PCC?

Cheers,
Emil


-- 
Emil Ivov, Ph.D.                               67000 Strasbourg,
Project Lead                                   France
SIP Communicator
emcho at sip-communicator.org                     PHONE: +33.1.77.62.43.30
http://sip-communicator.org                    FAX:   +33.1.77.62.47.31