Re: [MMUSIC] comments on draft-ietf-mmusic-sdp-g723-g729-03

["Parthasarathi R" <[e-mail]>]

Hi Aurelien,

Sorry for the delay response. Thanks for the review comments. 

Please read inline.

Thanks
Partha

> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]]
> Sent: Thursday, June 27, 2013 1:52 PM
> To: [e-mail]; [e-mail]; [e-mail]
> Subject: comments on draft-ietf-mmusic-sdp-g723-g729-03
> 
> Hi
> 
> I reviewed draft-ietf-mmusic-sdp-g723-g729-03 and I have some comments.
> They are quite symmetrical between G723 and G729.
> 
> 
> ** Section 3
> 
> 1)
> -----
>    Based on the above, it is best not to use comfort noise frames if
> the
>    SDP offer or answer indicates that comfort noise is not supported.
> -----
> The words "it is best not to use" are not strong enough, because it can
> not work if one of the party do not support comfort noise frames (SID
> frames in the ITU-T Annexes specs). It is rather a "MUST NOT use".
> 
> The word "restrict the use" in the RFC3551 quote is to be interpreted
> as "forbid the use".
> 
<Partha> It is fine. We will add this as a normative statement in case no
objection </Partha>

> 
> 
> ** Section 3.1
> 
> 2)
> After the first paragraph, I suggest to insert the new paragraph below:
> 
> ---NEW
>  The Annex A of the codec concerns both sending and receiving, so both
>  sides of a bi-directional session MUST have the same setting.  If
>  one party indicates that it does not support Annex A, Annex A  must be
>  deactivated both ways.
> -----
> That defines the general rationale of the following paragraphs.
>
<Partha> I agree with that it is the objective of this O/A requirement but
how this statement qualifies for normative statement is not clear. From the
offerer perspective, there is no control on same setting in both sides. In
case you look at the combine requirements of this draft, this object is met.
</Partha>
 
> 
> 3)
> -----
>    When the offer has G723 with annexa=no then the answer MUST NOT have
>    annexa=yes for G723.  Thus the annexa parameter can be turned off by
>    the answerer, but cannot be turned on.
> -----
> I don't think this new requirement is needed.
> Anyway implementation that will not implement this RFC-to-be will not
> comply with it.
> 
<Partha> As per based G723 RFC, it is expected for all the implementation to
support annexa. This issue is discussed in
http://www.ietf.org/mail-archive/web/mmusic/current/msg11165.html </Partha> 

> Plus, with the following paragraph, it breaks the equivalence between
> annexa=yes and annexa omitted.
> 
> Note that RFC3264 allows the SDP answer to include media format that
> are not present in the SDP offer, so it could be the same for the Annex
> A support.
> 
<Partha> RFC 3264 recommends to define offer/answer behavior per media
format whereas it is not defined for G723 & G729 and it is addressed as part
of this draft </Partha>

> 
> 4)
> -----
>    When the offer has G723 with annexa=no, the reason for not mandating
>    that the answer MUST have annexa=no for G723 is that there are there
>    implementations that omit the annexa parameter in answer and expect
>    the least common denominator to be used.
> -----
> 
> Add the following sentence at the end of the paragraph, to be explicit
> about the "least common denominator":
>    In such cases the offerer and answerer MUST proceed as if G723 is
>    negotiated with annexa=no.
> 
<Partha> Agreed. We will update the text </Partha>
> 
> 
> ** Section 3.2
> 
> 5)
> After the first two paragraphs, I suggest to insert the new paragraph
> below:
> 
> ---NEW
>  The Annex B of the codec concerns both sending and receiving, so both
>  sides of a bi-directional session MUST have the same setting.  If
>  one party indicates that it does not support Annex B, Annex B must be
>  deactivated both ways.
> -----
> That defines the general rationale of the following paragraphs.
> 

<Partha> Same as comment 2 reply. I agree with that it is the objective of
this O/A requirement but how this statement qualifies for normative
statement is not clear. From the offerer perspective, there is no control on
same setting in both sides. In case you look at the combine requirements of
this draft, this object is met. </Partha>

> 
> 6)
> -----
>    When the offer or answer has G729 and the annexb parameter is
> absent,
>    it MUST be considered as if the offer or answer has G729 with
>    annexb=yes.
> -----
> This paragraph is redundant with what is said before.
> Remove it.
> 
> 

<Partha> As per based G729 RFC, it is expected for all the implementation to
support annexb. This issue is discussed in
http://www.ietf.org/mail-archive/web/mmusic/current/msg11165.html </Partha>

> 7)
> -----
>    When the offer has G729 with annexb=no then the answer MUST NOT have
>    annexb=yes for G729.  Thus the annexb parameter can be turned off by
>    the answerer, but cannot be turned on.
> -----
> I don't think this new requirement is needed.
> For the same reason as for G723
> 
<Partha> Same reply as comment 3. As per based G729 RFC, it is expected for
all the implementation to support annexb. This issue is discussed in
http://www.ietf.org/mail-archive/web/mmusic/current/msg11165.html </Partha>

> 
> 8)
> -----
>    When the offer has G729 with annexa=no, the reason for not mandating
>    that the answer MUST have annexa=no for G729 is that there are there
>    implementations that omit the annexa parameter in answer and expect
>    the least common denominator to be used.
> -----
> 
> Replace annexa by annexb  (copy/paste error I guess)
> 
<Partha> Agreed </Partha>
> And add the following sentence at the end of the paragraph, to be
> explicit about the "least common denominator":
>    In such cases the offerer and answerer MUST proceed as if G729 is
>    negotiated with annexb=no.
> 
<Parta> Agreed </Partha>
> 
> 
> Best regards,
> Aurelien
> 
> 
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