Re: [MMUSIC] [Technical Errata Reported] RFC8864 (7805)

[Harald Alvestrand <[e-mail]>]

On 4/4/24 15:58, Christer Holmberg wrote:
> Hi,
> 
>>> I am not sure what you mean be "pre-agreed data channels", but I was
>>> referring to applications that use both DCEP and SDP.
>>
>> I was specifically referring to datachannels created with the "negotiated"
>> flag
>> set to "true".
> 
> Gotcha.
> 
> So, you are saying there ARE applications that use both DCEP and SDP
> ("negotiated" flag set to "true") to negotiate data channels?

Yes. We've seen it used.

> 
>> WebRTC, as currently specified, will ignore all attempts to negotiate
>> datachannels using SDP, so those channels can only be created by the
>> application parsing the SDP, extracting the information, and calling
>> "createDataChannel" with "negotiated" set to true.
> 
> Correct.
> 
>>> Also, your claim that the DCEP odd/even restriction would not apply for
>>> certain cases is (AFAIK) not defined anywhere. Also, I don't understand why
>>> the odd/even restriction would not apply in the case where you have pre-
>>> agreed data channels.
>>
>> The WebRTC spec, at
>> https://eur02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fw3c.gi
>> thub.io%2Fwebrtc-pc%2F%23dom-rtcdatachannelinit-
>> id&data=05%7C02%7Cchrister.holmberg%40ericsson.com%7C3bd0b5c63c86
>> 470f330f08dc54a2bc12%7C92e84cebfbfd47abbe52080c6b87953f%7C0%7C0
>> %7C638478305114832628%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLj
>> AwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C0%7C%7C
>> %7C&sdata=HbedMunDcF%2Fvy7YawmqPo%2FFBhqi7kjeflQWO185SXvQ%3
>> D&reserved=0, does not
>> mention the odd/even rule. For good reason; both ends have to call
>> createDataChannel with the same value for "id", so it *has* to "violate"
>> the odd/even rule.
> 
> Both endpoints obviously have to use the same "id", but one endpoint has to
> decide which "id" to use, and when using SDP the idea was to re-use the DCEP
> odd/even rule.

And that re-use is exactly the thing that we can't do.

> 
> I DO agree that the odd/even rule does not work in SDP actpass cases (where
> the id has to be set before the DTLS roles have been determined), and should
> be corrected, but I am not sure whether the correction suggested in the errata
> is the right way.

I'm happy to see alternate text suggested. My suggestion was only in 
order to have something specific to suggest in order to get rid of the 
inappropriate MUST.