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

[Christian Groves <[e-mail]>]

Hello Juergen,

Your proposed update sounds good to me.

Regards, Christian

On 17/03/2015 3:49 AM, Juergen Stoetzer-Bradler wrote:
> Hello Christian,
>
> Regarding your comment and question to section 5.1.5:
>
>> 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? 
>
> [Juergen] Actually, current text in section 5.2.4 of 
> draft-ietf-mmusic-data-channel-sdpneg-01 recommends (using SHOULD)
> closing the data channel "after a successful SDP answer is 
> sent/received".
> In the MSRP case we would propose not to change this default behavior, 
> which would result in the SDP answerer triggering
> the reset procedure of its associated outgoing SCTP stream right after 
> having accepted the received SDP offer with the data channel's
> a=dcmap and a=dcsa attribute lines being removed, and close to the 
> point in time it sends its SDP answer back to the SDP offerer.
> I would assume that typically the SDP offerer would then see an 
> outgoing SCTP stream reset request on its associated
> incoming SCTP stream  before it receives the SDP answer.
> Thus we could add this information and say:
>
> “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],
> where the actual data channel closure procedure is typically initiated 
> by the SDP answerer right after having
> accepted the SDP offer.”
>
> Thanks again,
> Juergen
>
>
> On 12.03.2015 03:19, Christian Groves wrote:
>> 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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