Re: [rtcweb] New use-case proposed

Justin Uberti <> Fri, 11 May 2012 14:24 UTC

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From: Justin Uberti <>
Date: Fri, 11 May 2012 10:24:12 -0400
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To: Stefan Hakansson LK <>
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Subject: Re: [rtcweb] New use-case proposed
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SRTP encryption is cheap, practically free on today's CPUs. I agree with
the general use case but I don't agree with the conclusion that we need to
require that the middlebox does not rewrite packets or perform crypto,
mainly since it will increase system complexity (and the system is already
quite complex).

On Fri, May 11, 2012 at 9:01 AM, Stefan Hakansson LK <> wrote:

> I've been sketching on a new use-case. The use-case is intended to
> derive requirements that enable low complex central nodes for multi
> party sessions, which in turn leads to requirements regarding
> (essentially) keying solution for SRTP and the possibility for the app
> to control/set things in the media configuration (in other words, for
> JSEP):
> Multi-party with low complexity central node
> ==============================**================
> A geographically spread (charity, non-profit, school) organization
> offers its members multi-party video communication via a shared virtual
> room that participants can enter and leave at any time. At times there
> are many persons in the virtual room (20+), at other times very few
> (3-5, or even 0-1).
> The application will control if few participants (a subset) are shown at
> a higher fidelity or if many (all) are shown at a lower fidelity or a
> mix of some few at high fidelity and the rest at much lower fidelity
> given the existing bandwidth limitations between participants.
> Since there are at times many persons in the virtual room, it is not
> feasible to set up a mesh. The bandwidth needed by a participant exceeds
> what many members have access to, especially in their uplinks, so
> instead a central media node is deployed. In addition, the organization
> does not have access to much funds, but has to rely on cheap hardware
> (often donated) operated by volunteers.
>  From this use-case a high level requirement saying something like
> "It must be possible to set up media streams and encryption in such
> a way that processing in a central node is minimized (no transcoding
> required, no RTP packet rewriting, no decryption/re-encryption for every
> outgoing flow - just simple forwarding)."
> can be derived. This can in turn be broken down into more detailed
> requirements such as:
> - The keying solution must allow each participants to encrypt to
> multiple receivers without any decryption+encryption in the middle node
> - RTP sessions that have SSRCs from multiple PeerConnections being
> interconneted must be supported. From a given end-point all SSRCs will
> come over one PC, but the full path will be different towards different
> sets of SSRCs.
> - Signalling must be capable of establishing a common set of receiver
> configurations over all participants.
> - The API must allow for the above, i.e.:
> -- The app must be able to chose a keying solution that enables
> encryption to multiple receivers (if the app can have any control over
> keying method used)
> -- The app must be able to control SSRCs to use for outgoing streams
> -- The app must be able to control the receiver configuration the
> browser uses
> Is this something we should consider adding to the use-case document?
> Br,
> Stefan
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