Subject: [siprec] Content (RFC 4796) attribute in SDP or XML

From: "Parthasarathi R (partr)" <[email-masked]>
Date: Mon, 27 Jun 2011 12:37:59 +0530

Hi all,

As per the last interim SIPREC meeting, there is a consensus to describe
the content of an MS using RFC 4796 & its extension. As per RFC 4796,
the multiple instance of content attribute is possible to exist in SDP
which shall be used in RS SDP. SRS shall group the same media content
types by "content" attribute in RS SDP. We are interested in knowing any
specfic reason for this attribute to be duplicated in Metadata XML.

Thanks

Partha

last Interim SIPREC meeting Note:

Slide 7: On the question of how to describe the content of an MS, there
was no objection to basing this on the types in the RFC 4796 registry
(new values could be specified via the appropriate means if needed).
Paul had a slight concern that you might be mixing multiple CS MSs into
a single RS media stream and whether this might result in cases not
describable in this way, but in the end accepted the consensus. It needs
to be discussed on the list whether this is conveyed in XML or in the RS
SDP a=content attribute.

---

From: "Elwell, John" <[email-masked]>
Date: Mon, 27 Jun 2011 09:47:43 +0200

> -----Original Message-----
> From: Parthasarathi R (partr) [mailto:[email-masked]] 
> Sent: 27 June 2011 08:08
> To: [email-masked]; Elwell, John
> Cc: Ram Mohan R (rmohanr); Paul Kyzivat (pkyzivat)
> Subject: Content (RFC 4796) attribute in SDP or XML
> 
> Hi all,
> 
> As per the last interim SIPREC meeting, there is a consensus 
> to describe the content of an MS using RFC 4796 & its 
> extension. As per RFC 4796, the multiple instance of content 
> attribute is possible to exist in SDP which shall be used in 
> RS SDP. SRS shall group the same media content types by 
> "content" attribute in RS SDP. We are interested in knowing 
> any specfic reason for this attribute to be duplicated in 
> Metadata XML.
[JRE] I don't have a reason for **duplication**. However, I think there is a valid question to be asked whether the content type of an MS should be represented:
A) in XML; or
B) in RS SDP as a=content.

The content type we are talking about is an MS content type, i.e., relating to the CS. One could argue that the corresponding RS stream is NOT the same content type. For example:
- CS MS content type is "slides".
- RS media stream content type is "recording of slides".
On this basis, I think the correct option for conveying the MS content type "slides" is A) (in the XML).

Note that this would not involve duplication. The SDP a=content attribute is optional, so we need not use it for the RS.

Perhaps my distinction is too theoretical, but I do feel a little more comfortable using the XML rather than the RS SDP.

John (as individual)

> Slide 7: On the question of how to describe the content of an 
> MS, there was no objection to basing this on the types in the 
> RFC 4796 registry (new values could be specified via the 
> appropriate means if needed). Paul had a slight concern that 
> you might be mixing multiple CS MSs into a single RS media 
> stream and whether this might result in cases not describable 
> in this way, but in the end accepted the consensus. It needs 
> to be discussed on the list whether this is conveyed in XML 
> or in the RS SDP a=content attribute.
> 
>

---

From: "Parthasarathi R (partr)" <[email-masked]>
Date: Tue, 28 Jun 2011 15:15:27 +0530

John,

In case if it is the argument of whether CS MS content type or RS MS
content type in the metadata, it is better for us to re-open ticket #71
(http://www.ietf.org/mail-archive/web/siprec/current/msg02106.html).
Please let me know your opinion here.

The basic idea in metadata format is to re-use as much as SDP attribute
(like direction, content) in media level for RS dialog (using SDP label
attribute as a pointer) until otherwise there is a restriction in using
in such manner. As per RFC 4796, there is no such restriction and so, I
prefer to reuse as content SDP attribute rather than introducing the new
<content-type> element for this purpose.

Thanks
Partha 

-----Original Message-----
From: Elwell, John [mailto:[email-masked]] 
Sent: Monday, June 27, 2011 1:18 PM
To: Parthasarathi R (partr); [email-masked]
Cc: Ram Mohan R (rmohanr); Paul Kyzivat (pkyzivat)
Subject: RE: Content (RFC 4796) attribute in SDP or XML

> As per the last interim SIPREC meeting, there is a consensus to 
> describe the content of an MS using RFC 4796 & its extension. As per 
> RFC 4796, the multiple instance of content attribute is possible to 
> exist in SDP which shall be used in RS SDP. SRS shall group the same 
> media content types by "content" attribute in RS SDP. We are 
> interested in knowing any specfic reason for this attribute to be 
> duplicated in Metadata XML.
[JRE] I don't have a reason for **duplication**. However, I think there
is a valid question to be asked whether the content type of an MS should
be represented:
A) in XML; or
B) in RS SDP as a=content.

The content type we are talking about is an MS content type, i.e.,
relating to the CS. One could argue that the corresponding RS stream is
NOT the same content type. For example:
- CS MS content type is "slides".
- RS media stream content type is "recording of slides".

On this basis, I think the correct option for conveying the MS content
type "slides" is A) (in the XML).

Note that this would not involve duplication. The SDP a=content
attribute is optional, so we need not use it for the RS.

Perhaps my distinction is too theoretical, but I do feel a little more
comfortable using the XML rather than the RS SDP.

John (as individual)

> Slide 7: On the question of how to describe the content of an MS, 
> there was no objection to basing this on the types in the RFC 4796 
> registry (new values could be specified via the appropriate means if 
> needed). Paul had a slight concern that you might be mixing multiple 
> CS MSs into a single RS media stream and whether this might result in 
> cases not describable in this way, but in the end accepted the 
> consensus. It needs to be discussed on the list whether this is 
> conveyed in XML or in the RS SDP a=content attribute.
> 
>

---

From: "Elwell, John" <[email-masked]>
Date: Tue, 28 Jun 2011 12:11:18 +0200

I would like other opinions on whether the SDP a=content attribute in the RS SDP has the correct semantics for representing the content type of the recorded CS media stream.

John 

> Sent: 28 June 2011 10:45
> To: Elwell, John; [email-masked]

---

From: "Charles Eckel (eckelcu)" <[email-masked]>
Date: Wed, 29 Jun 2011 09:17:13 -0700

I think it is sufficient, especially since we can assign new values if
necessary.
Are there any examples of what people think they might want to capture
in the SDP and/or metadata field?

Cheers,
Charles

> From: [email-masked] [mailto:[email-masked]] On
Behalf Of Elwell, John
> Sent: Tuesday, June 28, 2011 3:11 AM
> Subject: Re: [siprec] Content (RFC 4796) attribute in SDP or XML
> 
> I would like other opinions on whether the SDP a=content attribute in
the RS SDP has the correct
> semantics for representing the content type of the recorded CS media
stream.
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