Re: [MMUSIC] Bundling data channel and RTP?

Christer Holmberg <christer.holmberg@ericsson.com> Tue, 26 May 2015 00:50 UTC

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From: Christer Holmberg <christer.holmberg@ericsson.com>
To: Paul Kyzivat <pkyzivat@alum.mit.edu>, "mmusic@ietf.org" <mmusic@ietf.org>
Thread-Topic: [MMUSIC] Bundling data channel and RTP?
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Date: Tue, 26 May 2015 00:50:01 +0000
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Subject: Re: [MMUSIC] Bundling data channel and RTP?
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Hi,

>> I wonder whether we should have a "DTLS considerations" section in 
>> BUNDLE, and specify that all bundled media MUST use the same DTLS 
>> connection for key management, encryption etc.
>
> Yes, that makes sense.
>
>> Would it even be possible to establish multiple DTLS connections on a single 5-tuple?
>
> I don't think so.
>
> Note that RTP is "special" in this regard, in that it uses DTLS for the keying, but 
> it doesn't use DTLS payload packets.
>
> If there were more than one m-line that used DTLS payload packets then they 
> would also have to specify how to multiplex among them. AFAIK there is currently 
> no way to do that, so there can only be one m-line that uses DTLS payload packets.

This is covered in section 9.

Section 9.2 contains the following statement:

	"[RFC5764] does not describe how to identify different protocols
   	transported on DTLS, only how to identify the DTLS protocol itself.
   	If multiple protocols are transported on DTLS, there MUST exist a
   	specification describing a mechanism for identifying each individual
   	protocol. In addition, if a received DTLS packet can be associated
   	with more than one "m=" line, there MUST exist a specification which
   	describes a mechanism for associating the received DTLS packet with
   	the correct "m=" line."

Regards,

Christer



> -----Original Message-----
> From: mmusic [mailto:mmusic-bounces@ietf.org] On Behalf Of Christian 
> Groves
> Sent: 22 May 2015 10:20
> To: mmusic@ietf.org
> Subject: Re: [MMUSIC] Bundling data channel and RTP?
>
> Hello Magnus and Martin,
>
> Thanks for confirming that.
>
> It would be good to cover bundling the SRTP and DTLS/SCTP m-lines the BUNDLE and JSEP drafts.
>
> Regards, Christian
>
>
>
> On 20 May 2015 at 17:21, Christian Groves<Christian.Groves@nteczone.com>  wrote:
>
>> Can anyone confirm the intention that a single DTLS connection is 
>> used for SRTP key exchange and also SCTP packets?
>
> Yes, the record layer carries SCTP and exporters from the same session are used to key SRTP.
>
>
>
> On 21/05/2015 7:34 PM, Magnus Westerlund wrote:
>> Christian Groves skrev den 2015-05-21 02:21:
>>> Can anyone confirm the intention that a single DTLS connection is 
>>> used for SRTP key exchange and also SCTP packets?
>>>
>>> draft-ietf-rtcweb-transports-08 indicates:
>>>
>>> /WebRTC implementations MUST support multiplexing of DTLS and RTP over//
>>> //   the same port pair, as described in the DTLS_SRTP specification//
>>> //   [RFC5764], section 5.1.2.  All application layer protocol
>>> payloads//
>>> //   over this DTLS connection are SCTP packets./
>>>
>>> To me this implies a single DTLS connection. However in RFC5764 
>>> clause
>>> 4.1 it says:
>>> /Once the "use_srtp" extension is negotiated, the RTP or RTCP//
>>> //   application data is protected solely using SRTP. Application
>>> data is//
>>> //   never sent in DTLS record-layer "application_data" packets.
>>> Rather,//
>>> //   complete RTP or RTCP packets are passed to the DTLS stack, which//
>>> //   passes them to the SRTP stack, which protects them appropriately.//
>>> /
>>> In the second sentence "application data" is not qualified with "RTP 
>>> or RTCP" so it could be taken that its not possible to use the DTLS 
>>> connection for anything else. However I take it that as the rest of 
>>> the paragraph talks about RTP or RTCP that these were meant when 
>>> application data is mentioned?
>>>
>>> Can only one add some clarity?
>>>
>>
>> Yes, that is clearly the intention as I understand it in WebRTC.
>>
>> Cheers
>>
>> Magnus Westerlund
>>
>> ---------------------------------------------------------------------
>> - Services, Media and Network features, Ericsson Research EAB/TXM
>> ----------------------------------------------------------------------
>> Ericsson AB                 | Phone  +46 10 7148287
>> Färögatan 6                 | Mobile +46 73 0949079
>> SE-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com
>> ---------------------------------------------------------------------
>> -
>>
>>
>
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