Re: [payload] [MMUSIC] Comments on draft-ietf-mmusic-media-loopback-16

[Magnus Westerlund <[e-mail]>]

On 2011-10-25 20:01, Hadriel Kaplan wrote:
> 
> On Oct 21, 2011, at 5:25 AM, Magnus Westerlund wrote:
> 
>> 11. Section 5.3 "    Note: A loopback offer in a given media
>> description MUST NOT contain the standard mode attributes sendonly,
>> recvonly, sendrecv, or inactive. The loopback-mode attributes
>> (loopback-source and loopback-mirror) replace the standard
>> attributes."
>> 
>> This appears to be a strange MUST NOT which I think might
>> encounter issues. Considering that SIP proxies that looks into this
>> SDP requires the direction attribute to be present and adds it,
>> what happens now. And why isn't sendrecv and inactive possible
>> values? sendrecv appears to be requried for loopback to work, and
>> inactive would put media transport in an established session on
>> hold. Isn't that reasonable?
> 
> How about this: Since media loopback requires bidirectional RTP, its
> normal direction mode is "sendrecv"; the "sendrecv" direction
> attribute MAY be encoded in SDP or not, as per section 5.1 of
> [RFC3264], since it is implied by default.  If either the loopback
> source or mirror wish to disable loopback use during a session, the
> direction attribute "inactive" MUST be used as per [RFC3264].  The
> direction mode attributes "recvonly" and "sendonly" are incompatible
> with the loopback mechanism and MUST NOT be indicated when generating
> an SDP Offer or Answer.  When receiving an SDP Offer or Answer, if
> "recvonly" or "sendonly" is indicated for loopback, the SDP-receiving
> agent MAY treat it as a failure of the loopback negotiation or ignore
> the direction attribute.
> 

That is much better. I think the only "controversial" from my
perspective is the "ignore" part. It is clearly an error.

Cheers

Magnus Westerlund

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