Re: [AVT] Sockets in multicast DTLS-SRTP

> -----Original Message-----
> From: avt-bounces@ietf.org [mailto:avt-bounces@ietf.org] On 
> Behalf Of Romain Biehlmann
> Sent: Tuesday, March 23, 2010 5:27 AM
> To: avt@ietf.org
> Subject: [AVT] Sockets in multicast DTLS-SRTP
> 
> Hi all,
> 
> I hope my question is not too dumb, and not too
> implementation-oriented; if so, please accept my apologies and ignore
> it.
> 
> In http://tools.ietf.org/html/draft-ietf-avt-dtls-srtp-07 chapter
> 5.1.1, we can read the following:
> "When a user of DTLS wishes to send an RTP packet in SRTP mode it
> delivers it to the DTLS implementation as an ordinary application data
> write (e.g., SSL_write())."
> 
> From that, I understand that in the case of a unicast session, only
> one socket is needed for the transmission of STUN, SRTP and DTLS
> datagrams.

Right, and demultiplexed as shown in
http://tools.ietf.org/html/draft-ietf-avt-dtls-srtp-07#section-5.1.2

> I am not sure, though, to get how it should work in the case of a (one
> to many) multicast session.

Use DTLS-SRTP with EKT.  EKT allows telling each of the receivers
the same key.  The sender then sends the same multicast packet
(or if using unicast, the sender sends the same packet, unicast, 
to each NNN receivers).

EKT is http://tools.ietf.org/html/draft-ietf-avt-srtp-ekt-00

-d

> Isn't the server supposed to send SRTP datagrams to a broadcast
> address, whereas DTLS data must be sent directly to (unicast)
> designated clients? Is the sentence in the draft only applicable to
> unicast?
> 
> I thank you in advance for your valuable insight.
> 
> Romain
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