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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