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Re: [AVT] Sockets in multicast DTLS-SRTP

Romain Biehlmann <romain.biehlmann@gmail.com> Wed, 24 March 2010 08:20 UTC

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Date: Wed, 24 Mar 2010 09:20:28 +0100
Message-ID: <9a06dcf1003240120g29db1b1bxb0f0a3e719336720@mail.gmail.com>
From: Romain Biehlmann <romain.biehlmann@gmail.com>
To: Dan Wing <dwing@cisco.com>
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Cc: avt@ietf.org
Subject: Re: [AVT] Sockets in multicast DTLS-SRTP
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Hi,

And thank you for your fast answer!

I actually already planned on using KTR, which uses EKT, but got stuck
by this socket problem.

I don't get how the data should be multiplexed in the case of a
multicast session since two sockets will be opened on the clients'
side (as shown on the drawing below)... Or am I completely wrong?

----------
| server |---- SRTP multicast session -------------------
----------                                              |
  | | |                                  ------------   |
  | | |--- DTLS KTR unicast session 1 ---| client 1 |---|
  | |                                    ------------   |
  | |                                    ------------   |
  | |----- DTLS KTR unicast session 2 ---| client 2 |---|
  |                                      ------------   |
  |                                      ------------   |
  |------- DTLS KTR unicast session 3 ---| client 3 |---|
                                         ------------

Thank you very much for the time you take to read me.

Romain



2010/3/23 Dan Wing <dwing@cisco.com>:
>> -----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
>> _______________________________________________
>> Audio/Video Transport Working Group
>> avt@ietf.org
>> https://www.ietf.org/mailman/listinfo/avt
>
>

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