Subject: [AVTCORE] draft-ietf-avtcore-rfc5285-bis-05 -- fun special case

From: [email-masked] (Dale R. Worley)
Date: Wed, 01 Feb 2017 22:09:06 -0500

Suppose that in the offer and the answer all of the identifiers are less
than 15.  And suppose that mixing one-byte and two-byte formats is *not*
negotiated.

RTP packets are sent containing one-byte extension headers, and
everything is going along well, and suddenly, the current data part for
an extension is over 16 bytes.  That data can't be encoded in the
one-byte format.

I think there needs to be a rule that a UA can't commit to the one-byte
format unless all of the extensions that might be sent are defined to
have data lengths between 1 and 16 bytes.  So instead of the current
rule

    A client MUST NOT send an extension header with the one-byte format
    if any negotiated valid identifier exceeds 14 and extmap-allow-mixed
    is not negotiated.

we need

    A client MUST NOT send an extension header with the one-byte format
    if:
        (1) extmap-allow-mixed is not negotiated, and
	(2) (a) some negotiated valid identifier is more than 14, or
	    (b)some negotiated extension may have a data length of 0
	    bytes or more than 16 bytes.

Dale

---

From: Magnus Westerlund <[email-masked]>
Date: Thu, 16 Feb 2017 15:57:07 +0100

Hi,

If one follows RFC5285, then one can setup a number of formats with IDs 
in 1-14 range. Then one can decide on RTP stream level which format one 
or two byte. However, one you started sending one or two-byte in a 
particular RTP stream, you are not allowed to switch.

In addition the sender doesn't know if two-byte will work. It can assume 
that one-byte is available. So there is clearly issues here about 
capability determination from a sender perspective. Which is why RFC 
5285bis exists.

So the limiation on length is clearly present. I think the question is 
if this needs to be lifted in this part or not. I would note that 
actually the rule needs to be considered in the context of a particular 
RTP stream. Because one can actually consider that one RTP stream will 
only send a sub-set of header extension and thus be capable of using 
one-byte headers in this RTP stream, but another RTP stream requires the 
2-byte header and thus should use that from the start if the 
extmap-allow-mixed is not negotiated.

Looking at the -05 and -06 I can't find this rule in either version. 
Where was it included?

Based on that I can't find the context for this, I can't judge how 
important it is to make any changes.

Cheers

Magnus

Den 2017-02-02 kl. 04:09, skrev Dale R. Worley:
> _______________________________________________
> Audio/Video Transport Core Maintenance
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> https://www.ietf.org/mailman/listinfo/avt
>

-- 

Magnus Westerlund

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