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Re: [MMUSIC] SDP Capabilities Negotiation : Delete attributes





Ingemar Johansson S wrote:
SDP Capabilities Negotiation : Delete attributes

Hi

I have some questions regarding the delete attributes mentioned section 3.5.1 (page 24) as I still after reading through the same text a few times may have misunderstood:

The example
  a=pcfg:1 a=-m:1,2,[3,4]|1,7,[5]
My interpretation is : delete all the attributes on media level and specify the new attributes. Is this correct ?

That's correct.

When is this needed ?, is the projected use case that one send a reinvite with a new SDP. I miss some text that actually motivates the use of the delete attributes option.

The motivation is provided in Section 3.6.2. Section 3.76 and 3.13.1 provide additional specific use cases. Briefly, the use case is when you have SDP attributes in the actual configuration SDP that may conflict or interfere with SDP attributes from a potential configuration SDP. For example, my actual configuration may include an rtpmap attribute that maps payload type 96 to codec A, but another potential configuration maps it to payload type B. Another example is that I propose use of MIKEY as the keying method (using a=kmgmt) for an SRTP stream as the actual configuration, however my potential configuration uses sdescriptions, or perhaps vanilla RTP instead; to be on the case side, we remove the kmgmt attribute using delete-attributes.

-- Flemming


/Ingemar
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Ingemar Johansson
Senior Research Engineer, IETF "nethead"
EAB/TVP - Multimedia Technologies
  Ericsson Research Ericsson AB
  Box 920 S-971 28 Luleå, Sweden
Tel: +46 (0)8 4043042
ECN: 850-43042
ECC: 850-43074
Mobile: +46 (0)730 783289
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