Subject: SIP URLs and multicast sessions - a question

From: Kaya Bekiroglu <[email-masked]>
Date: Fri, 12 Sep 1997 10:25:49 -0700

I don't quite understand a passage in the latest draft of the SIP
specification.  On page 22, this example SIP URL is given:

	For example, to specify to call [email-masked] using multicast to
239.255.255.1 with a ttl of 15, the following URL would be used:

	sip://[email-masked];maddr=239.255.255.1;ttl=15

My understanding from this specification is that a URL with a multicast
parameter (such as the one above) can only be used to INITIATE a
multicast conference.  Is there any mechanism in SIP to allow a URL,
perhaps embedded in a web page, to give enough information to allow a
user to join an already existing multicast conference?  I would assume
the answer is no, since SDP descriptors cannot be contained in a SIP
URL.  Is this true?  Can the OPTIONS command, sent to a multicast
address, be used to query the other participants for the common media
for the conference in question (assuming the user can authenticate
himself to a conference participants satisfaction)?  This would seem to
me to be a reasonable addition to the protocol.

Any information would be greatly appreciated.

---
Kaya Bekiroglu
Program Manager, TAPI 3.0
Windows NT Networking

---

From: Jeff Smith <[email-masked]>
Date: Fri, 12 Sep 1997 12:55:42 -0700

You can make an http accessible object with contents of SDP.  A helper
application can be used to parse the MIME type (x-sdp or something)
and launch your conferencing tools.

No need for SIP.  I think this is how Precept and others are already
doing their web-based program guides.

js

|
|I don't quite understand a passage in the latest draft of the SIP
|specification.  On page 22, this example SIP URL is given:
|
|	For example, to specify to call [email-masked] using multicast to
|239.255.255.1 with a ttl of 15, the following URL would be used:
|
|	sip://[email-masked];maddr=239.255.255.1;ttl=15
|
|My understanding from this specification is that a URL with a multicast
|parameter (such as the one above) can only be used to INITIATE a
|multicast conference.  Is there any mechanism in SIP to allow a URL,
|perhaps embedded in a web page, to give enough information to allow a
|user to join an already existing multicast conference?  I would assume
|the answer is no, since SDP descriptors cannot be contained in a SIP
|URL.  Is this true?  Can the OPTIONS command, sent to a multicast
|address, be used to query the other participants for the common media
|for the conference in question (assuming the user can authenticate
|himself to a conference participants satisfaction)?  This would seem to
|me to be a reasonable addition to the protocol.
|
|Any information would be greatly appreciated.
|
|---
|Kaya Bekiroglu
|Program Manager, TAPI 3.0
|Windows NT Networking
|

---

From: Henning Schulzrinne <[email-masked]>
Date: Sun, 14 Sep 1997 20:24:53 -0400

Kaya Bekiroglu wrote:
> URL.  Is this true? 

Not quite. This seems to come up periodically; I added it to the
fledgling SIP FAQ at http://www.cs.columbia.edu/~hgs/sip

 Can the OPTIONS command, sent to a multicast

-- 
Henning Schulzrinne        email: [email-masked]
Dept. of Computer Science  phone: +1 212 939-7042 (@Bell Labs: 908 949
8344)
Columbia University        fax:   +1 212 666-0140
New York, NY 10027         URL:   http://www.cs.columbia.edu/~hgs