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

Paul Kyzivat <pkyzivat@alum.mit.edu> Wed, 13 May 2020 18:16 UTC

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From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Date: Wed, 13 May 2020 14:16:44 -0400
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Subject: Re: [MMUSIC] WGLC on draft-ietf-mmusic-msrp-usage-data-channel-16
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On 5/13/20 1:21 PM, Christer Holmberg wrote:
> One more thing: if you by "destination" mean the IP address and port of the remote peer, you get that from the c/m- line.

And where does *the* m line get the fqdn/ip from???

Assume you gave me your msrp address once, and I have it in my address 
book. Today I decide I want to chat with you. I need to set up a session 
with you, and your msrp url is what I have to work with.

Because the URL has the "dc" parameter I can infer that I will need a 
data channel. I must set up the the DTLS session and then create a data 
channel to do that. How do I know what to put into the c/m- line? Are 
you saying that I need some *other* information about you before I can 
do that? Or can I derive the c/m- line data from it?

For that matter, to be doing O/A, I need a sip connection. How do I 
figure that out?

	Thanks,
	Paul


> Regards,
> 
> Christer
> 
> On 13/05/2020, 20.18, "mmusic on behalf of Christer Holmberg" <mmusic-bounces@ietf.org on behalf of christer.holmberg=40ericsson.com@dmarc.ietf.org> wrote:
> 
>      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
> 
> 
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