Re: [MMUSIC] WGLC on draft-ietf-mmusic-msrp-usage-data-channel-16

Christer Holmberg <christer.holmberg@ericsson.com> Wed, 13 May 2020 17:18 UTC

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From: Christer Holmberg <christer.holmberg@ericsson.com>
To: Paul Kyzivat <pkyzivat@alum.mit.edu>, "mmusic@ietf.org" <mmusic@ietf.org>
Thread-Topic: [MMUSIC] WGLC on draft-ietf-mmusic-msrp-usage-data-channel-16
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Date: Wed, 13 May 2020 17:17:58 +0000
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Subject: Re: [MMUSIC] WGLC on draft-ietf-mmusic-msrp-usage-data-channel-16
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Hi,

    >>>>>- Added text to make more clear the scope of path and MSRP URI:
    >>>>
    >>>>>Data channels are negotiated independently of the value of the "path"
    >>>> attribute. This means that when MSRP messages are transported on a data
    >>>> channel, the "path" attribute
    >>>>
    >>>>>is not used for transport negotiation or routing of the messages. MSRP
    >>>> endpoints using data channels can set the value of the "path" attribute,
    >>>> including the MSRP URI, and use it as described in RFC4975
    >>>>
    >>>> I think we need to be a little more explicit, so I suggest something like:
    >>>>
    >>>> "When MSRP messages are transported on a data channel, the "path"
    >>>> attribute is not used for routing of the messages. The MSRP data channel
    >>>> is established using the SDP offer/answer procedures defined in
    >>>> [I-D.ietf-rtcweb-data-channel], and the MSRP messages are then
    >>>> transported on that data channel. Because of that an MSRP endpoint can
    >>>> set the MSRP-URI authority value of the "path" attribute at its own
    >>>> discretion, following the syntax and rules in [RFC4975]."
    >>>
    >>> I'm concerned that this might imply that an msrp(s) URI is not
    >>> sufficient information to establish communication. (That some additional
    >>> information, received out-of-band, might be a prerequisite.)
    >>>
    >>> Do you intend that to be a possible situation?
    >>>
    >>> I would hope that it is not - that an msrp(s) URI is sufficient. In that
    >>> case, both the transport setup and the path attribute would be derived
    >>> from the same source.
    >> 
    >>      I am not sure I understand....
    >> 
    >>      The MSRP URI is *not* enough to establish the SCTP association and the data channel. The procedures
    >>      for establishing a data channel are defined in [I-D.ietf-rtcweb-data-channel], and then each usage have some specific attribute values etc.
    >> 
    >>     We are not modifying the procedures how to establish a data channel - we are defining how to send MSRP messages over a data channel.
    >
    > [I-D.ietf-rtcweb-data-channel] defines *procedures* for establishing a 
    > data channel, just as SIP provides procedures for establishing a sip 
    > session. In both cases, those procedures must be parameterized. In the 
    > case of SIP a sip URI is generally sufficient. (In some environments you 
    > might need some extra environmental information, such as how to get 
    > yourself registered first and the need to use an access proxy.)
    >
    > In this case, the msrp(s) uri should provide all the parameterizing 
    > information I need to send msrp messages to this destination, over and 
    > above info about my environment and basic standards. The "dc" parameter 
    > in the URI tells me that I need use a data channel.
    >
    > I shouldn't need to supply any extra information *about the destination*.

    You know that you are going to send the MSRP message on the data channel - that's all you need to know.

    Regards,

    Christer