Re: [straw] Review of draft-ietf-straw-b2bua-rtcp-10

[Christer Holmberg <[e-mail]>]

(As co-chair)

ACK!

Regards,

Christer

Sent from my Windows Phone
________________________________
From: Ben Campbell<mailto:[e-mail]>
Sent: ‎10/‎06/‎2016 00:04
To: Lorenzo Miniero<mailto:[e-mail]>
Cc: [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; Christer Holmberg<mailto:[e-mail]>
Subject: Re: [straw] Review of draft-ietf-straw-b2bua-rtcp-10


I did a quick scan of the new revision, and I think it's addressed most of my editorial concerns. I encourage the chairs to re-request publication as soon as the authors address the one or two outstanding items mentioned below.

Thanks!

Ben.

On 9 Jun 2016, at 15:51, Ben Campbell wrote:

Hi,

Comments to your email inline. I removed sections that don't seem to need further discussion. I will send any comments about the new draft revision separately.

Thanks!

Ben.

On 31 May 2016, at 6:12, Lorenzo Miniero wrote:

On Fri, 27 May 2016 17:17:35 -0500
"Ben Campbell" [e-mail]<mailto:[e-mail]> wrote:

[...]

Hello again, Ben,

I just posted a new version of the document (an announcement should get
to the ML soon) that tries to address most, if not all, of your points.
You can find some additional comments inline on the parts I haven't
addressed yet (or I only partly addressed), for one reason or another.
To make this more readable, I snipped the parts that I already
integrated.

  *   The intended status is proposed standard. Do people really expect b2bua vendors to implement the rules in this draft? Do they expect existing b2bua implementations to be updated?

I already answered to this in my previous mail, but just to reinstate,
I'll leave the decision to WG and chairs/ADs as to what the intended
status should be. I personally would keep it a proposed standard, but
again wouldn't object to a BCP, if needed.

Let's leave this as PS for now, but realize that may change at some point as we go forward. As far as getting the WG's opinion goes, it might be worth it to send a separate email to the list about this one question. Otherwise people may miss it buried in the rest of the review comments.

  *   Section 3, last paragraph - This paragraph seems to argue that the fact that existing b2buas do not follow specs is a reason to create more specs. That seems questionable.

Fair point. I haven't changed that part in the doc yet, as I wanted to
be sure I'd get it right, first. Do you think it would be ok to say
something along the lines of "due to the mixed nature of B2BUAs, they
sometimes can't or won't implement all specifications, so they should
at least do this"?

I think that logic is reasonable.

[...]

  *   Section 4
     *   Last paragraph, 2nd to last sentence - If you think people will really pay attention, then this might be a good place for a MUST or SHOULD

Do you mean where we say "behaviour is unspecified and discouraged"? Or
more in general about the fact that a B2BUA can only follow the
guidelines when it has access to editing fields without breaking
hashes? Not sure which MUST or SHOULD we might add there, considering
that, if the media the B2BUA is encrypted, it can't possibly edit RTP
related information without disrupting the communication, which in
turn means no RTCP editing will be needed/possible either.

Do you think a "B2BUAs MUST NOT modify RTP/RTCP data if media is
encrypted" to be enough, in case?

In retrospect, I wrote that comment without thinking about it in context of b2bua-dtls-srtp. Since you already reference that draft, I withdraw that comment. No change is really needed.

 * Third paragraph:
     * "It SHOULD NOT, though, blindly forward all SDP


attributes,"
- Isn’t
the idea that it should forward any attributes that it
doesn’t
have a specific reason not to forward? (i.e. default to
forwarding?)

The issue here is the reason not to forward itself. In order to figure
out whether an attribute can be forwarded or not, the B2BUA must have
some knowledge of it and of its impact. What I wanted to highlight in
that sentence is that there are attributes that, if left where they are
by a B2BUA unaware of their purpose, can actually cause issues. Just
think, for instance, of 'rtcp' attribute that is explained in the text,
or other attributes supporting features a B2BUA may not support itself.

Aren't those attributes that the b2bua must, by definition, know about and have a "specific reason" not to forward.

Of course, as you point out there could be reasons to actually keep
attributes you don't know about in there, e.g., because they advertize
support for an end-to-end feature the B2BUA doesn't need to worry
about. Besides, the attributes that can cause issues are probably not
that many anyway.

Right. One of the big issues with b2buas is that they tend to make SIP networks brittle to new features. I think we need to discourage that as much as possible. I realize we can't write guidance on how to handle a "foo" attribute that works in all cases of "foo", but we can at least err on the side of letting things through.

I'll think about a way to make this clearer in the next for next
version.

Okay.