Re: [MMUSIC] Bundling data channel and RTP?

Christian Groves <> Thu, 21 May 2015 00:21 UTC

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Date: Thu, 21 May 2015 10:21:46 +1000
From: Christian Groves <>
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Subject: Re: [MMUSIC] Bundling data channel and RTP?
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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?

Regards, Christian

On 29/04/2015 10:08 PM, Christian Groves wrote:
> Hello
> According to draft-ietf-rtcweb-data-channel-13 and 
> draft-ietf-rtcweb-transports-08, multiplexing of DTLS and RTP over the 
> same port pair must be supported and application layer protocol 
> payloads over this DTLS connection are SCTP packets, i.e. RTP and 
> datachannel share the same address:port.
> I assume this needs to be specified in SDP by two m-lines bundled 
> together. E.g. one with "UDP/TLS/RTP/SAVPF" & one with "UDP/DTLS/SCTP" 
> . However I can't find in any of the related drafts where this is 
> stated. I would think the BUNDLE and JSEP drafts should mention 
> something about this. Is there a draft that I've missed where this is 
> stated?
> Regards, Christian
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