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List: sip-implementors
Subject: Re: [Sip-implementors] Session-level value overriden by media-levelvalue in SDP (RFC 4566)
From: <nataraju.basavaraju () wipro ! com>
Date: 2007-12-12 8:03:03
Message-ID: 01949ABCDD38EF4A95B8C347C399D1CE05DEE000 () BLR-EC-MBX02 ! wipro ! com
[Download RAW message or body]
Comments inline...
Regards,
Nataraju A B
________________________________
From: Jagan Mohan [mailto:jaganmk@gmail.com]
Sent: Wednesday, December 12, 2007 12:49 PM
To: Nataraju Alilughatta basavaraju (WT01 - TES-Mobility &
Carrier Infrastructure)
Cc: sip-implementors@lists.cs.columbia.edu
Subject: Re: [Sip-implementors] Session-level value overriden by
media-levelvalue in SDP (RFC 4566)
Hi Nataraju,
I agree with you that we should not use "a=sendonly" as well
as "c=IN IP4 0.0.0.0" in the same SDP.
.
This test scenario was provided as part of a third party
vendor certification. Hence, the doubt.
Let me try to bring out the contradiction in the RFC.
(1) Section 5, Page 8 mentions the following:
In general, session-level values are the default for all
media unless overridden by an equivalent media-level value.
(2) Section 5, Page 10 mentions the following:
The connection ("c=") and attribute ("a=") information in
the session-level section applies to all the media of that session
unless overridden by connection information or an attribute of
the same name in the media description.
Considering the call-on-hold scenario, a=inactive and c=IN
IP4 0.0.0.0 are equivalent. Say, a=inactive is present in media level
info. and c=IN IP4 0.0.0.0 is present in session level info. of the same
SDP.
(1) mentioned above states the parameters might be equivalent
for overriding the session-level values.
(2) mentioned above states that the connection information or
an attribute in media-level description should be of the same name for
overriding the session-level description.
As per (1), a=inactive will override the 'c' line, but can not
as per (2).
[ABN] I don't think a= line in media description would override
c= line in session description. i think we need to read (2) as c= and a=
in session attributes would be overridden by c= and a= lines in media
attributes respectively.
AFAIU, (1) and (2) describe about overriding with same
attributes. c= in media attribute would override c= line in session
attribute (same for a= line also), not any other attributes.
[ABN] in (2) you can see word "same name" which convey same
attributes would override. not any other attributes.
I have used this scenario only to bring out the contradiction.
Please let me know if my understanding is not correct.
Thanks,
Jagan
On 12/12/07, nataraju.basavaraju@wipro.com
<nataraju.basavaraju@wipro.com > wrote:
Comments inline...
Regards,
Nataraju A B
> -----Original Message-----
> From: sip-implementors-bounces@lists.cs.columbia.edu
> [mailto:sip-implementors-bounces@lists.cs.columbia.edu
] On
> Behalf Of Jagan Mohan
> Sent: Wednesday, December 12, 2007 11:54 AM
> To: SIP list; SIP Implementors
> Subject: [Sip-implementors] Session-level value
overriden by
> media-levelvalue in SDP (RFC 4566)
>
> Hi,
>
> For example, a SIP message has the following
SDP:
>
> v=0
> c=IN IP4 0.0.0.0
> t=2873397496 2873404696
> m=audio 49170 RTP/AVP 0
> a=sendonly
>
> I would like to know whether a=sendonly or c=IN IP4
> 0.0.0.0 should take into effect in this particular
case.
>
> From RFC 4566:
> ============
>
> Section 5, Page 8 mentions the following:
>
> An SDP session description consists of a
session-level section
> followed by zero or more media-level sections. The
session-level
> part starts with a "v=" line and continues to the
first media-level
> section. Each media-level section starts with an
"m=" line and
> continues to the next media-level section or end of
the
> whole session
> description. In general, session-level values are
the default for
> all media unless overridden by an equivalent
media-level value.
>
>
> Section 5, Page 10 mentions the following:
>
> [The connection ("c=") and attribute ("a=")
information in the
> session-level section applies to all the media of
that
> session unless
> overridden by connection information or an
attribute of
> the same name
> in the media description.]
>
> I find the above statements to be slightly
contradictory.
>
[ABN] I don't see any confusion here... Session level
information is
always overridden by media level attributes if they both
carry similar
information.
Also its not a good idea to use "a=sendonly" as well as
"c=IN IP4
0.0.0.0" in the same SDP.
Probably if you consider the following SDP, you can
understand session
and media attributes better
v=0
o=jdoe 2890844526 2890842807 IN IP4 10.47.16.5
s=SDP Seminar
i=A Seminar on the session description protocol
u=http://www.example.com/seminars/sdp.pdf
e=j.doe@example.com (Jane Doe)
c=IN IP4 224.2.17.12/127
t=2873397496 2873404696
a=sendrecv
m=audio 49170 RTP/AVP 0
a=sendonly
m=video 51372 RTP/AVP 99
c=IN IP4 224.2.17.100/127
a=rtpmap:99 h263-1998/90000
Here for audio m= line a=sendonly and c=IN IP4
224.2.17.12/127 is
applicable.
And for video m= line a=sendrecv and c=IN IP4
224.2.17.100/127 is
applicable.
Rest all session level attributes applies to both m=
lines...
> Please clarify.
>
> Thanks,
> Jagan
> _______________________________________________
> Sip-implementors mailing list
> Sip-implementors@lists.cs.columbia.edu
>
https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
>
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