Re: [MMUSIC] 10 BUNDLE questions

Eric Rescorla <ekr@rtfm.com> Wed, 24 April 2013 02:17 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Tue, 23 Apr 2013 19:16:25 -0700
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To: Justin Uberti <juberti@google.com>
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Subject: Re: [MMUSIC] 10 BUNDLE questions
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After reading the thread, here are my proposed answers...

> Can you create a BUNDLE with a single m= line? (assuming yes)

Yes.


> Can you create multiple BUNDLEs? (assuming yes)

Yes.


> When creating an initial offer, how should we deal with the case
> where a "null" port is to be used with trickle ICE (since 6.1:1
> indicates the ports MUST be different)

I think it's ok for the null port to not be equal.


> From 6.1, list 1 - are conditions 2, 5, 7 really necessary? (MUST
>  use same c=, add rtcp-mux, same a=fingerprint)

I don't know if rtcp-mux is necessary, but it seems stupid not to
have it.

I think we do need to have matching fingerprints because we can
only have one DTLS-SRTP association and it's hard to understand
what the security properties are if the two associations
in principle might have different credentials.


> From 6.1, list 2 - is condition 6 right? Why would we use different
> SDES keys for a single RTP session?

So, I note that this list requires that the other side *support*
bundle not that he accept it. So, there's still some chance
of getting things unbundled, no?


> If you start with a m= line with one SDES config (e.g. 32-bit MAC),
> and then BUNDLE with another SDES line with a different (non
> overlapping) SDES config (e.g. 80-bit MAC), what happens? (assume
> fail)

So, this seems like an argument for using distinct SDES lines
since then you can just keep the SDES line associated with its
associated m-line.


> If the BUNDLE mids in the answer doesn't match the BUNDLE mids in the
> offer, what happens? (assume fail)

That sounds right to me.


> If you add a m= line to an existing BUNDLE, can the recipient reject
> that BUNDLEing (assume no)

I think life would be simpler if this just caused a negotiation
fail if the other side was sad about it.


> If m= lines are rejected, should their mids show up in the BUNDLE
> answer? (assume yes?)

That sounds easiest.


> Is there any way, in a single PeerConnection, to unBUNDLE m= lines
> that were previously BUNDLEd (assume no)

I would say no.

After all, you can always discard those lines and offer new lines.

-Ekr