> -----Original Message-----
> From: Paul Kyzivat [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, May 30, 2001 7:10 PM
> To: [EMAIL PROTECTED]
> Subject: [Sip-implementors] bis-03 SDP usage rules
>
>
> I have some questions regarding usage of SDP with SIP as specified in
> bis-03:
>
> 1) Is there any reason why I can't choose to request a bidirectional
> hold by sending a reinvite that rejects the media by setting
> the port to
> zero? I realize this isn't the recommended way of handling
> hold, but it
> seems like it would have the desired effect. It also means I
> don't have
> to consume a port for rtcp.
Hold and disabling the stream are two different things. They may have a
similar effect on a gateway, but might not on a PC, particularly one which
spawns a media tool for each stream. Therefore, I think its best to stick
with the standardized way of hold.
You don't need to allocate a port for RTCP when you place it on hold,
though, so I'm not sure I see the issue.
>
> 2) If (1) is ok, then is it ok to resume use of the medium by
> sending a
> reinvite that updates the same m= line with a non-zero port?
>
> 3) Suppose I want to reinvite to add a new media. Further
> assume that in
> the current call there was a m= line that was rejected. The rules as
> written appear to require me to add an additional m= line.
> But it seems
> like there would be no ambiguity in reusing the slot from the rejected
> media for this purpose. (This could prevent a buildup of unusued m=
> lines in a call that switches media a lot.) In a way this just probes
> the difference between changing media type and dropping one media and
> adding another.
I don't see a semantic issue, in the same way there is a difference between
on-hold and rejected streams. However, its yet-another-case for a client to
deal with. Now, when a re-INVITE comes, it has to inspect each line to see
if any rejected media streams have now been replaced with new ones.
I don't see adding and removing media streams in their entirety as such a
common case to be worried about this buildup issue.
-Jonathan R.
---
Jonathan D. Rosenberg, Ph.D. 72 Eagle Rock Ave.
Chief Scientist First Floor
dynamicsoft East Hanover, NJ 07936
[EMAIL PROTECTED] FAX: (973) 952-5050
http://www.jdrosen.net PHONE: (973) 952-5000
http://www.dynamicsoft.com
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