Re: [rtcweb] Review comments on draft-ietf-rtcweb-data-protocol-03

[Magnus Westerlund <[e-mail]>]

On 2014-05-13 17:51, Michael Tuexen wrote:
> On 13 May 2014, at 17:26, Magnus Westerlund <[e-mail]> wrote:

>>>>
>>>>>>
>>>>>>>>
>>>>>>>> 2. Section 4:
>>>>>>>>
>>>>>>>> The method
>>>>>>>> used to determine which side uses odd or even is based on the
>>>>>>>> underlying DTLS connection role when used in WebRTC, with the side
>>>>>>>> acting as the DTLS client using even stream identifiers.
>>>>>>>>
>>>>>>>> Isn't this unnecessary using the vague word of WebRTC instead of simply
>>>>>>>> pointing to the DTLS roles of the established data channel?
>>>>>>
>>>>>>> The point is that in the WebRTC you use DCEP/SCTP/DTLS/UDP and therefore
>>>>>>> you can refer to the DTLS role. However, you could use DCEP/SCTP/IP
>>>>>>> or DCEP/SCTP/UDP/IP or DCEP/SCTP over something not involving DTLS.
>>>>>>> In that case DTLS is not used and you can not refer to the DTLS role.
>>>>>>> That is why the restriction is used.
>>>>>>
>>>>>> Ok, if that concern then you still should be able to write a normative
>>>>>> specification under the condition that it is SCTP over DTLS. If not how
>>>>>> do you determine that? Are suggesting just to hand way or point to a
>>>>>> higher signaling layer.
>>>>> So what about using:
>>>>>
>>>>> when using <xref target='I-D.ietf-tsvwg-sctp-dtls-encaps'/>, the method used to
>>>>> determine which side uses odd or even is based on the underlying DTLS
>>>>> connection role: the side acting as the DTLS client MUST use Streams with even
>>>>> SCTP stream identifiers, the side acting as the DTLS server MUST use Streams
>>>>> with odd SCTP stream identifiers.</t>
>>>>
>>>> I think that is fine for when using over DTLS. And to my understanding
>>>> this do require DTLS? If not we need alternative text.
>>
>>> Our current use-case is for SCTP/DTLS. But we don't need DTLS except for
>>> its security properties. However, if someone doesn't use DTLS, he has to
>>> figure out how to determine the even/odd. This is covered by:
>>>
>>> <t>To avoid glare in opening Channels, each side MUST use Streams with 
>>> either even or odd SCTP stream identifiers when sending a DATA_CHANNEL_OPEN
>>> message.
>>> When using <xref target='I-D.ietf-tsvwg-sctp-dtls-encaps'/>, the method used to
>>> determine which side uses odd or even is based on the underlying DTLS
>>> connection role: the side acting as the DTLS client MUST use Streams with even
>>> SCTP stream identifiers, the side acting as the DTLS server MUST use Streams
>>> with odd SCTP stream identifiers.</t>
>>>
>>> However, we can't provide a method in the general case...
>>
>> Yes, as long as you use DTLS it is well specified. The issue I am trying
>> to get my head around is if this specification and the data channel is
>> possible to use without DTLS. This is one of the few (only?) things that
>> requires it beyond the security features. Thus, should this be
>> explicitly noted as saying, if you don't use DTLS you will be required
>> to find an alternative solution to the roles.

> Isn't this be said by the first sentence of the paragraph? It states
> the requirement of having a rule and provides on the second sentence
> such a rule for the case where DTLS is used.
> 

Yes, it does. And I see no risk of this being misunderstood in the
context of WebRTC usage. So I will accept this, but note that this may
be one of these cases where some poor guy will swear over this
specification not being clearer on how to apply it in other contexts.

Cheers

Magnus Westerlund

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