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Re: [Perc] Consensus call: SSRCs are immutable

"Roni Even" <ron.even.tlv@gmail.com> Wed, 11 November 2015 22:34 UTC

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From: Roni Even <ron.even.tlv@gmail.com>
To: 'Jonathan Lennox' <jonathan@vidyo.com>, 'Richard Barnes' <rlb@ipv.sx>
References: <CAL02cgSn_wVYpiPGrnRM2=rJnwvjAuCnOC=+UitLN7zpo8h1hw@mail.gmail.com> <8E19B154-6072-4B10-84F7-2D2F674E491F@vidyo.com>
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Date: Thu, 12 Nov 2015 00:34:49 +0200
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Cc: perc@ietf.org
Subject: Re: [Perc] Consensus call: SSRCs are immutable
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Hi,
Agree with Jonathan and want to add that collision detection when the endpoint assign SSRC should also work for the cascaded case as described in Magnus' draft and if the MDD assigns SSRCs it should not complicate using RFC5576 SSRC attribute.
Roni




-----Original Message-----
From: Perc [mailto:perc-bounces@ietf.org] On Behalf Of Jonathan Lennox
Sent: Wednesday, November 11, 2015 9:14 PM
To: Richard Barnes
Cc: perc@ietf.org
Subject: Re: [Perc] Consensus call: SSRCs are immutable


> On Nov 11, 2015, at 1:49 PM, Richard Barnes <rlb@ipv.sx> wrote:
> 
> tl;dr: Do we have consensus that PERC should regard SSRCs as something 
> that an MDD MUST NOT change?  Please reply by Nov. 25.
> 
> At the PERC meeting at IETF 94, there was a discussion of which 
> portions of an SRTP packet an MDD should be allowed to modify.  At the 
> end of this discussion, there was pretty much unanimous agreement in 
> the room that MDDs should *not* be allowed to modify SSRC.  The only 
> people who were not explicitly in agreement were a couple of folks who 
> said they wanted to think about it.
> 
> This email is a formal call to confirm the consensus in the room.  If 
> you have any objections to the conclusion reached at the meeting -- 
> especially if you were not at the meeting -- please reply to this 
> message no later than Wednesday, November 25.

I’d like to have a convincing story about how SSRC uniqueness is guaranteed before we make this decision.

Having the KDF hand out SSRC values would be one possibility, but it has architectural implications — there are parts of the RTP architecture that implicitly assume endpoints can self-assign SSRC values as needed, e.g. RFC 7160.

Alternately, the MDD could probably make collisions visible (even for sources that aren’t currently being routed) by forwarding/generating RTCP as necessary, but we need to make sure this scales for large conferences, and that it doesn’t open up the possibility for a malicious MDD to do anything too nasty.

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