Re: [rtcweb] [avtext] Fwd: New Version Notification for draft-fineberg-avtext-temporal-layer-ext-00.txt

[Jonathan Lennox <[e-mail]>]

Hi, Adam –

(Speaking as an individual.)

I think there’s a problem with the use case as you’ve described here, which I think calls into question the usefulness of the whole mechanism.

As I understand you, you’re planning to send a single VP8 stream containing all the layers, and then have a media-aware middlebox selectively drop some of the stream’s packets to do temporal scaling without needing the middlebox to be in the crypto context.

Unfortunately, RTP doesn’t really let you do this.  The problem is that by just dropping packets without rewriting RTP sequence numbers or RTCP sender reports, this is going to look like enormous packet loss to RTP (which, in a sense, it is).  A middlebox like this – which is acting as a media-modifying RTP translator, in RTP terminology – needs to rewrite RTP headers and RTCP sender reports in order to keep the stream and its metadata consistent and valid.

Unfortunately, the translator needs to have the crypto keys in order to make these modifications, so I’m not sure this header extension adds much benefit over just validating the authentication, decrypting (say) the initial block of the packet (wherever the temporal layer information is known to be), modifying the headers, and then re-authenticating the packet.

Is there something I’m missing here?

From: Adam Fineberg [mailto:[e-mail]]
Sent: Wednesday, July 17, 2013 6:37 PM
To: [e-mail]
Subject: [avtext] Fwd: New Version Notification for draft-fineberg-avtext-temporal-layer-ext-00.txt

Hi,

I'm working on WebRTC services and have found that while developing services that forward VP8 video streams if we want to take advantage of the VP8 temporal scaling we must get the temporal layer information from the RTP header which requires us to decrypt the SRTP packets.�� This is undesirable both because the middlebox needs to have acesss to the keys as well as the because of the added overhead of the decrypt/encrypt cycle.�� This draft proposes an RTP header extension that will allow us to use the VP8 temporal layer information included in the header extension and therefore do forwarding without SRTP decryption.�� Comments welcome.

Regards,
Adam Fineberg
[e-mail]<mailto:[e-mail]>

-------- Original Message --------
Subject:

New Version Notification for draft-fineberg-avtext-temporal-layer-ext-00.txt

Date:

Tue, 09 Jul 2013 10:02:05 -0700

From:

[e-mail]<mailto:[e-mail]>

To:

Adam Fineberg <[e-mail]><mailto:[e-mail]>



A new version of I-D, draft-fineberg-avtext-temporal-layer-ext-00.txt

has been successfully submitted by Adam Fineberg and posted to the

IETF repository.



Filename:       draft-fineberg-avtext-temporal-layer-ext

Revision:       00

Title:          A Real-Time Transport Protocol (RTP) Header Extension for VP8 Temporal Layer Information

Creation date:  2013-07-08

Group:          Individual Submission

Number of pages: 6

URL:             http://www.ietf.org/internet-drafts/draft-fineberg-avtext-temporal-layer-ext-00.txt

Status:          http://datatracker.ietf.org/doc/draft-fineberg-avtext-temporal-layer-ext

Htmlized:        http://tools.ietf.org/html/draft-fineberg-avtext-temporal-layer-ext-00





Abstract:

   This document defines a mechanism by which packets of Real-Time

   Tranport Protocol (RTP) video streams encoded with the VP8 codec can

   indicate, in an RTP header extension, the temporal layer information

   about the frame encoded in the RTP packet.  This information can be

   used in a middlebox performing bandwidth management of streams

   without requiring it to decrypt the streams.









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