Re: [MMUSIC] Bundling data channel and RTP?

[Paul Kyzivat <[e-mail]>]

On 5/24/15 9:59 PM, Christer Holmberg wrote:
> 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.

	Thanks,
	Paul

> Regards,
>
> Christer
>
> -----Original Message-----
> From: mmusic [mailto:[e-mail]] On Behalf Of Christian Groves
> Sent: 22 May 2015 10:20
> To: [e-mail]
> 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<[e-mail]>  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
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>>
>
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