Subject: [Perc] OHB usage in the client

From: Nils Ohlmeier <[email-masked]>
Date: Tue, 7 Mar 2017 22:10:32 -0800

Hello,

While starting to implement support for double encryption in Firefox I encountered the following issue:

Can the originating client use the OHB RTP header extension as a marker between RTP header extension which can be removed by the MDD?

One example which comes to mind might be the RID header extension for simulcast, where it makes little sense to include that extension all the way end-to-end to the receiving clients.
So in such a case I think it might make sense for the originating client to
- build the RTP packet with all header extensions intended e2e
- add the OHB header extension
- do the e2e encryption
- add header extension which can be removed by the MDD, like RID
- do the HBH encryption
- send the packet to the MDD

I did not find any wording in the current drafts which either encourages this usage or forbids it. I assume this is a use case which has not been considered so far. Is this something we should add to the drafts?

Best regards
  Nils Ohlmeier

---

From: "Paul E. Jones" <[email-masked]>
Date: Thu, 09 Mar 2017 03:39:49 +0000

Nils,

In section 5.1, we have:

      If the endpoint wishes to insert header extensions that can be
      modified by an Media Distributor, it MUST insert an OHB header
      extension at the end of any header extensions protected end-to-end
      (if any), then add any Media Distributor-modifiable header
      extensions. ...

There's a bit more there in that same paragraph, but that's the answer 
to your question.

However, it might actually be good to define those extensions that 
should be placed after the OHB.  Otherwise, one client might insert a 
set of extensions before the OHB and another might do it after.  We 
could try to document those here or perhaps have another draft that 
provides recommendations for various extensions.

Paul

------ Original Message ------
From: "Nils Ohlmeier" <[email-masked]>
To: "[email-masked]" <[email-masked]>
Sent: 3/8/2017 1:10:32 AM
Subject: [Perc] OHB usage in the client

>Can the originating client use the OHB RTP header extension as a marker 
>between RTP header extension which can be removed by the MDD?
>
>One example which comes to mind might be the RID header extension for 
>simulcast, where it makes little sense to include that extension all 
>the way end-to-end to the receiving clients.
>I did not find any wording in the current drafts which either 
>encourages this usage or forbids it. I assume this is a use case which 
>has not been considered so far. Is this something we should add to the 
>drafts?
>
>Best regards
>   Nils Ohlmeier
>

---

From: Cullen Jennings <[email-masked]>
Date: Fri, 10 Mar 2017 14:57:48 -0700

> On Mar 7, 2017, at 11:10 PM, Nils Ohlmeier <[email-masked]> wrote:
> 
> 

Yes, and I think that is generally a good thing for implementations to do.