Re: [Perc] Last Call: <draft-ietf-perc-private-media-framework-08.txt> (A Solution Framework for Private Media in Privacy Enhanced RTP Conferencing) to Proposed Standard

+1 on ssrc rewriting, and on the consensus not reached on this and other topics.

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> On 2 Feb 2019, at 17:18, Lorenzo Miniero <lorenzo@meetecho.com> wrote:
> 
> +1, SSRC rewriting is pretty much fundamental to all SFUs out there.
> 
> Lorenzo
> 
> Il 2 febbraio 2019 10:19:06 CET, Emil Ivov <emcho@jitsi.org> ha scritto:
>> 
>> I want to second that as it is a particularly major problem: not allowing SSRC rewriting makes the entire framework unusable with SFU implementation I represent as well as every other SFU I am familiar with.
>> 
>> I am also not sure that I agree with “SSRC rewriting could not be allowed” is a conclusion that ever had any consensus in PERC, regardless of what WG leadership is trying to make everyone believe.
>> 
>>> On Sat 2 Feb 2019 at 06:21, Bernard Aboba <bernard.aboba@gmail.com> wrote:
>>> Richard said:
>>> 
>>> "Again, the answer is clear here, but the document should be clearer.  The working group discussed SSRC rewriting several times, and concluded that SSRC rewriting could not be allowed in this system.  This decision is reflected, e.g., in the fact that the Double transform does not allow modification of SSRCs."
>>> 
>>> [BA]  Not being able to rewrite SSRCs has some major implications with respect to requirements on PERC endpoints.  Typically today's MDD will switch between the simulcast streams provided by an endpoint, forwarding only a single stream to other participants, based on the bandwidth, resolution and framerates.  If rewriting of SSRCs is not possible, do PERC endpoints need to be able to receive simulcast? If PERC endpoints do need to be able to receive simulcast, what are the requirements for endpoints?  For example, should endpoints expect the MDD to use RID header extensions to identify the incoming simulcast streams? 
>>> 
>>> Receiving of simulcast is tricky because the endpoint is receiving multiple streams with different sequence number spaces which may contain holes because of reordering or loss. This not only complicates the application of RTX, RED and FEC, but also the operation of the endpoint.  As a result, as noted in the WEBRTC specification Section 5.4.1, support for reception of simulcast is optional. I am aware of two ORTC implementations that have attempted to support simulcast reception, neither of which is robust in scenarios with considerable loss and/or reordering.  And neither implementation supports the RID header extension on received simulcast streams.
>>> 
>>> 
>>> 
>>> 
>>>> On Fri, Feb 1, 2019 at 12:23 PM Sergio Garcia Murillo <sergio.garcia.murillo@gmail.com> wrote:
>>>>> On 01/02/2019 17:18, Richard Barnes wrote:
>>>>> So I would propose we add something like the following to this definition: 
>>>>> 
>>>>> "In the context of WebRTC, where control of a session is divided between a JavaScript application and a browser, the browser acts as the Trusted Endpoint for purposes of this framework (just as it acts as the endpoint for DTLS-SRTP in one-to-one calls).
>>>> 
>>>> If we decide to adopt perc (big if) in webrtc, shouldn't this be defined within the https://tools.ietf.org/html/draft-ietf-rtcweb-security-arch-17 doc ?
>>>> 
>>>> 
>>>> 
>>>>    Optimally, we would not rely on trust in any entities other than the
>>>>    browser.  However, this is unfortunately not possible if we wish to
>>>>    have a functional system.  Other network elements fall into two
>>>>    categories: those which can be authenticated by the browser and thus
>>>>    can be granted permissions to access sensitive resources, and those
>>>>    which cannot be authenticated and thus are untrusted.
>>>> 
>>>> 
>>>> WebRTC already IdP as trusted for identity purposes, so it should be up to the RTCWEB group to decide what is a trusted endpoint and what is not in webrtc. As Bernard is stating, we could decide that there are other key management solutions trusted (even in JS or WASM), as for for example is being done in EME:
>>>> 
>>>> https://github.com/WICG/media-capabilities/blob/master/explainer.md#encryption
>>>> 
>>>> Best regards
>>>> 
>>>> Sergio
>>>> 
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