Subject: [payload] AD Evaluation of draft-ietf-payload-rtp-ancillary-05

From: "Ben Campbell" <[email-masked]>
Date: Thu, 25 Aug 2016 17:36:46 -0500

Hi,

This is my AD evaluation of draft-ietf-payload-rtp-ancillary-05. I'd 
like to at least resolve the substantive comments before going to IETF 
last call.

Thanks!

Ben.
----------------

*** Substantive Comments *** :

- General:
There's a lot of use of 2119 keywords in situations where you talk more 
about definitions/
statements of fact than procedure. I mention some specific instances 
below, but may not
have caught all of them.

- Section 1:

A quick mention of the meaning of horizontal and vertical ancillary 
spaces would be
helpful.

The 6th paragraph says ancillary data flag (ADF) word is not carried in 
this payload.  But
section 2.1, under "horizontal offset" says "A value of 0 means that the 
Ancillary Data
Flag (ADF) of the ANC data packet begins immediately following SAV." 
These seem to
conflict--are they talking about something different?

- section 2:
-- timestamp:
"For progressive scan video, the timestamp SHALL denote the
sampling instant of the frame to which the ancillary data in
the RTP packet belongs."

That's a definition. I suggest "... timestamp denotes..." (occurs twice)

-- Marker Bit:

"The marker bit set to "1" SHALL indicate the last ANC RTP packet ..."

Consider "The marker bit set to "1" indicates..."

- section 2.1:
Am I correct to assume the various length or count fields are unsigned 
integers? Network
byte order?

-- ANC count:
"A single ANC RTP packet payload SHALL NOT carry more than 255 ANC data 
packets."
  Isn't this a statement of fact, since the number is limited by the 8 
bit ANC_Count field?
If so, consider s/SHALL NOT/cannot

  On the other hand, the "may" in "additional RTP packets carrying ANC 
data may be sent
with the same RTP timestamp but with different sequence numbers." seems 
to be an
appropriate place for a 2119 "MAY"

  "ANC_Count of 0 SHALL indicate that there are no ANC data packets"
  Please consider s/SHALL indicate/indicates

  -- Horizontal Offset:
  All 3 instances of "SHALL" seem more like statements of fact.

- 3.1, Required Parameters:
"When an ANC RTP stream is to be associated with an RTP video stream, 
the RTP timestamp
rates SHOULD be the same to ensure that ANC data packets can be 
associated with the
appropriate frame or field."

Why not MUST? Do you anticipate that there might be situations where 
it's reasonable for
the rates not to match?

-- intended usage: Is "Common" the right choice? Do you expect this to 
be widely used, or
just in some very specific applications?

- 3.2, encoding of the subtype name:
It would be helpful to mention the "rate" parameter here as well.

-- mapping of "DID_SDID" parameters:
It would be helpful to mention the ability to carry multiple types 
earlier in the document
(perhaps where types are first mentioned, or where DID_SDID was first 
mentioned.)

- 5: The security considerations do not include the recommended text 
from
draft-ietf-payload-rtp-howto-14, section A.13. Should it?

- References: It seems like the references to [RFC3264] and [RFC5888] 
should be normative.

*** Editorial Comments ***:

- General: An early description of the meaning of ANC data packet types 
would be helpful.

- section 1: A quick mention of the meaning of horizontal and vertical 
ancillary spaces
would be helpful.

- section 1.1, last paragraph: By "data model", does this talk about the 
packet format, or
something else?

-3.1, optional parameters:
Is this link reasonably permanent? Also, consider moving this to the 
references section
(perhaps in a separate "URLs" section) and citing it normally.

It would be helpful to mention that DID_SDIS can occur multiple times 
(or be a list of
values, depending on your perspective.)

-- Change controller:
I suspect this should say “ The IETF PAYLOAD working group, or other 
party as designated
by the IESG.”"

- 3.2.1

What does "essence" mean in the context of "video essence stream"? Am I 
correct to assume
it refers to the actual video content?