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[Sip] Re: [Sip-implementors] Hold SDP



Udit_Goyal at 3com.com wrote:
I want to know is it the genral behaviour of all UAC?

There are a lot of UAs out there. Its hard to say what the "general" behavior is.

because as per RFC, c=0 has not been recommended for RTCP purposes,
anyway in these cases, we might need RTCP reports also,

The use of c=0 is an old (now deprecated) action in response to a request to initiate hold. The mechanism still exists, and is still important for some call flows unrelated to hold. There is of course nothing to prevent a UA from using it when initiating Hold, and the peer should do something reasonable in response.

Why cant we have one more attribute "a=hold" which indicates its meant for hold and not for one-way media audio stream,

I think mostly because hold is a feature, and IETF doesn't standardize features. The existing directionality attributes are mechanisms that may be used for hold or other things.

If you introduced a hold attribute, then there would be a lot of call to have different flavors of hold - one way, two way, with music, without music, etc. And of course you would need to get into the precise semantics of hold.

As things stand, Hold is a local feature on an endpoint. The corresponding signaling should not really be considered as signaling "hold" - it is only signaling the desired media behavior. I think there is no expectation, or need, for the other UA, or servers in the path to be able to determine that the call is "held".

	Paul

Thanks,
Udit





"Avasarala Ranjit-A20990" <ranjit at motorola.com> Sent by: sip-implementors-bounces at cs.columbia.edu
10/04/2005 02:23 AM

To
Udit Goyal/C/US/3Com at 3Com, "SIP Implementors" <sip-implementors at cs.columbia.edu>
cc
SIP IETF <sip at ietf.org>
Subject
RE: [Sip-implementors] Hold SDP






Udit

You can use c=IN IP4 0.0.0.0 to indicate hold in addition to a-sendonly.



Regards
Ranjit




-----Original Message-----
From: sip-implementors-bounces at cs.columbia.edu
[mailto:sip-implementors-bounces at cs.columbia.edu] On Behalf Of
Udit_Goyal at 3com.com
Sent: Monday, October 03, 2005 10:42 PM
To: SIP Implementors
Cc: SIP IETF
Subject: [Sip-implementors] Hold SDP

Hi,

As per RFC 3264, user agent indicate hold by sending "sendonly attribute
(assuming sendrecv mode stream).
So when UAS receives this SDP, it should respond with "recvonly"
attribute.

But same mechanism can be used by user agent if he wants to play
announcement or music to user, so it can send "sendonly" attribute for
media stream.
I mean if it simply wants one-way connection (this is not hold).

For 3PCC (as B2B), if it wants to provide MOH service, how can it
differentiate between two SDP because it will play MOH only in the first
scenario when user press hold.

Is there any other way where user agent can indicate that this is hold
scenario and not one-way audio.

Thanks,
Udit
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