-----Original Message-----
From: Paul Kyzivat [mailto:[EMAIL PROTECTED]
Sent: Thursday, December 06, 2007 9:13 PM
To: Hadriel Kaplan
Cc: [email protected]
Subject: Re: [Sip] INFO use-cases
Hadriel,
I buy some of your use cases, but not others. Comments below.
A competitor for INFO in several of these is MESSAGE. I think a good
case can be made for that if the information is to be rendered to the
recipient.
Paul
Hadriel Kaplan wrote:
[snip]
/****************
* Use-cases that I think are potentially/possibly valid for INFO:
****************/
1) Sending a vcard asynchronously. Alice calls Bob, Alice says "can you
send me John's vcard?", Bob clicks something and voila it's sent.
-Alternatives: send a re-Invite or Update with a Call-Info, with
either a URL reference, data URI, or MIME and CID URL.
-Counter-argument: IMO this type of data really belongs in MIME
for a number of reasons, including length is less restricted for mime
attachments; one AD has said the Data URL may be deprecated. And sending
a re-Invite for this purpose seems odd.
-Also, the Call-Info header is really about the caller or
callee, and thus Bob shouldn't be sending me John's vcard info in it
technically. That may sound like a nit, but UA's may well store the call-
info vcards into their address-books automatically and so tie it to the
wrong user/call.
-Pros of using INFO: it's explicit what you're doing when you
send the vcard, and you can send it knowing the other end can accept it,
and you can send it based on user input.
2) Sending a user-icon jpeg/bitmap/gif. Alice calls Bob, Bob has an
icon that represents himself, sends it when he picks up the phone.
-Alternatives: send a 200ok, re-Invite, or Update with call-
info, which explicitly has a type for icon.
-Counter-argument: same as for vcard, plus with call-info there
is no way to know which picture format the far-end supports a priori.
With a supported-package negotiation one could know.
For this case MESSAGE seems entirely appropriate.
(Not so much so for vcard, which probably isn't intended to be directly
rendered to the recipient.)
3) Sending a vcalendar-type invitation. Alice calls Bob, Bob says "hey
let's have a con call at time X", clicks and voila his phone sends a
vcalendar.
-Whether the vcalendar is related to the session or not and thus
whether it should be sent in an in-dialog request or not is certainly
debatable. Message method can already be used for this anyway.
4) Sending an HTTP URL. Alice calls Bob, a sales guy; Alice asks for
more info or a datasheet and Bob sends a URL for Alice to open with her
web-browser.
-One could also argue this is just making SIP the new SMTP, or
this should be sent using MESSAGE (which really is the new SMTP).
Yes to MESSAGE.
5) Sending a session traceroute. Alice calls Bob, Bob answers, Alice
does a sip-traceroute to figure out the path to Bob, by sending Info with
an incrementing max-forwards type header starting at 0 (but not really
max-forwards), with a sip-frag type response body or some such.
-It's debatable if certain types of B2BUA's (ie, SBCs) would
ever allow this type of thing to happen, due to security concerns, but I
think they may do it at domain boundary hops. I think this is a
reasonable use for INFO though, maybe.
6) Sending geo-location information after call establishment. Alice
calls Bob, a hotel receptionist. Alice asks for directions to hotel,
clicks button and sends him location info of her phone (or Bob clicks
button and sends her his location).
-The location conveyance draft specifically calls out INFO as
acceptable for geo-loc info. Whether this is a real use-case is
debatable, and obviously it could be done with a sub/not.
UPDATE with geo-loc is reasonable here, or even reINVITE.
7) Sending softkey-labels (not digit-match maps, but rather softkey
button labels). Alice calls her vmail server. Vmail server sends
softkey-labels for the menu items available in the response, Alice presses
softkeys and sends them in INFO.
-This could (and maybe should) be done with sub/not, a la KPML,
where the vmail server sends the softkey labels in the Subscribe, UA sends
buttons pressed in Notifies. But this is similar to the DTMF use case so
may well have the same benefit of lower overhead since buttons are rarely
pressed.
8) Sending a screen-pop-up message, e.g., "Do you want to continue with
this session?"
-There is a patent for doing screen pop-ups using INFO. I guess
Alert-Info could be used for this, but it's not clear it should?
This is very definitely a use case for MESSAGE.
Also, all of the above could probably be justifiably sent via MSRP -
either directly or via the file transfer extensions.
/*****************
* Use-cases which have been proposed by others or even implemented,
* which are dubious for INFO (IMHO):
*****************/
1) Sending RTP/RTCP statistics during call.
-There is an implementation of this, and the rationale is the
signaling plane box that wants this info is not actually the media plane
box that gets RTCP. Again this could (and IMO should) be done with
sub/not, so it can get stats after the call is over, and since it will
probably want periodic reports the overhead of the Subscribe should be
dwarfed by the number of Notifies.
2) Sending access-location information after call establishment.
-There is a P-Access-Network-Info header, and some have proposed
to send an update for it as a phone roams access points or cells. But I
think this is an odd thing to do inside an Invite session, vs. in a
sub/not or Register (and besides half the time the network inserts this
header, not the UA).
3) Sending media-control indications (ie, remote-control
"play/pause/etc.")
-This is done today by at least one vendor, but is debatable if
it's the right model. The argument is it's like SDP re-Invite for hold,
except at a media content layer above RTP, so not done in RTCP nor SDP.
4) Sending video fast update command
-This is an informational draft, which documents what has been
implemented, but states it should really be done in the media plane.
5) Sending peripheral control commands (ie, USB commands)
-There is actually a patent on this, amazingly. Someone thinks
it makes sense to create a SIP session to your laptop, or vice-versa, and
then send USB commands inside MIME in INFO messages. Methinks this should
be media-plane, if anything.
6) Sending charging information for a call (i.e., minutes remaining or
cost so far).
-There was a proposal to use this for Advice of Charge
information in TISPAN. IMO it should be a sub/not though, as they want
this to survive the Invite session.
-hadriel
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