Re: [MMUSIC] New draft version: draft-ietf-mmusic-msrp-usage-data-channel-01

[Christian Groves <[e-mail]>]

Hello Juergen,

No problem, please see my responses below.

Regards, Christian

On 12/03/2015 2:41 AM, Juergen Stoetzer-Bradler wrote:
> Hello Christian,
>
> Thanks much for your comments.
> Please see my remarks inserted below.
>
> Thanks,
> Juergen
>
> On 10.03.2015 04:25, Christian Groves wrote:
>> Hello Juergen,
>>
>> Thanks for the update. Some comments:
>> 5.1.1.1 - The section indicates that the max-retr, max-time and
>>    ordered parameters shall not be used. I take it then that the SCTP 
>> Stream used for MSRP must be DATA_CHANNEL_RELIABLE? If so it might be 
>> better to say what is used rather than what is not.
>
> [Juergen] Agree. Would propose to replaced current sentence "The 
> max-retr, max-time and ordered parameters shall not be used" with
> "Ordered and reliable data channels MUST always be used, such that the 
> 'max-retr' and 'max-time' parameters SHALL NOT be used.
> If the 'ordered' parameter is used, then its value MUST be equal to 
> 'true'."
[CNG] OK
>
> ..snip..
>
>>
>> 5.1.1.2: MSRP "max-size" would it be worth to note that this must be 
>> less than the SCTP SDP max-message-size value?
>
> [Juergen] That's a good point. As far as I understand the 
> a=max-message-size value
> is related to the “maximum message size that an SCTP endpoint is 
> willing to receive”
> as per draft-ietf-mmusic-sctp-sdp-14, sec 6.1, whereas the MSRP 
> specific a=max-size attribute
> refers to the maximum MSRP message size an endpoint is willing to 
> accept (as per 4975, sec 8.6),
> thus is not related to the maximum MSRP message chunk size.
> Would you be OK if we added a sentence to 5.1.1.2 saying that an MSRP 
> session endpoint
> MUST NOT send MSRP message chunks larger than  the peer’s 
> a=max-message-size value?
[CNG] Yes.
>
>>
>> 5.1.1.2: "Setup" is this relevant for MSRP using data channel? The 
>> SCTP-SDP draft etc. give rules as to which endpoint establishes 
>> different parts of the transport connection?
>
> [Juergen] Good point, too. The msrp-usage draft requires MSRP UAs 
> using data channel transport
> to support the MSRP CEMA extension as described in RFC 6714. This 
> again refers to RFC 6135,
> which uses the a=setup attribute value to determine the "active" MSRP 
> UA, which is responsible for sending
> the initial MSRP SEND message (which might be empty).
> Also msrp-usage draft's section 5.1.2 currently requests the "active" 
> MSRP endpoint to send an
> MSRP SEND message as as soon as the associated data channel instance 
> is opened.
> Per draft-ietf-mmusic-sctp-sdp-14 the "a=setup" attribute contained in 
> the DTLS/SCTP based media description
> is used to determine the TCP (if used) and DTLS client/server roles. 
> But this usage of the "a=setup" attribute
> is different than the usage of "a=setup" as described in RFC 6135's 
> section 4.2.
> I assume we may have to describe more explicitly in msrp-usage how it 
> is determined if an MSRP endpoint
> becomes "active" (and sends the initial MSRP SEND message).
[CNG] Yes I think its important to cover the this aspect.
>
>>
>> 5.1.1.3: a=sctp-port 5000 should have a colon e.g. a=sctp-port:5000
>
> [Juergen] Thanks. We'll correct this.
>
>>
>> 5.1.5: This section indicates that closing is done as per 
>> I-D.ietf-mmusic-data-channel-sdpneg. However clause 
>> 5.2.4/I-D.ietf-mmusic-data-channel-sdpneg indicates that closure is 
>> sub-protocol specific. Its not clear to me whether this the 
>> sub-protocol should indicate the use of the SCTP reset or the use of 
>> SDP O/A?
>
> [Juergen] The intention in 5.1.5 is to refer to the generic data 
> channel closure procedure based on
> the SCTP stream reset mechanism, and that additionally per new SDP 
> offer / answer exchange
> the a=dcmap and a=dcsa attribute lines associated with the MSRP 
> session need to be removed
> from the DTLS/SCTP based media description.
> Would you agree if we explicitly said:
> “The closure of an MSRP session MUST be signaled via an SDP offer / 
> answer exchange which
> removes the "a=dcmap:" and "a=dcsa:" attribute lines associated with 
> the MSRP session from
> the associated DTLS/SCTP based media description.
> This results in the associated data channel being closed as well as 
> per [I-D.ietf-mmusic-data-channel-sdpneg].”
[CNG] This wording is better. Is the SCTP reset at the same time as the 
SDP Offer?
>
>>
>> Regards, Christian
>>
>>
>
> [snip]
>
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