Subject: RE: SIP URLs and multicast sessions - a question

From: Kaya Bekiroglu <[email-masked]>
Date: Fri, 12 Sep 1997 15:08:44 -0700

I was confused - it *is* possible to include a message body within a URL
(must be too much coffee).  Still, the ability to obtain the multicast
media dynamically would be a nice feature, especially since common
codecs, and available bandwidth, could easily change.

	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
	|