Re: [MMUSIC] draft-ietf-mmusic-msrp-usage-data-channel - "a=setup" versus "a=dcsa:x setup"

[Christian Groves <[e-mail]>]

At this stage I don't care which method is chosen. The main is to 
progress the draft.

Regards, Christian

On 21/10/2015 8:10 PM, Christer Holmberg wrote:
> Hi,
>
>> The "rule of thumb" I had is covered by Juergen's text. It was basically that an endpoint only includes a=dsca:setup if it wanted a role
>> different than what is indicated in a=setup. However I think Christer has a separate view.
> Correct. I want a=setup to only impact the data channel itself - not what is "inside" the data channel.
>
>> I think the original source of the problem is that RFC6135 links the MSRP establishment role to the a=setup. I.e. the active side
>> is the one that sends the first MSRP message. So these are linked. To unlink it for MSRP over DC its proposed to use a=setup (which
>> was defined for transport connection setup) in the DC (via dsca) to control the MSRP protocol setup.
> You can always give a=dsca:setup the same value as a=setup.
>
>> I think at the end of the day the decision is whether we want every WebRTC endpoint to send "a=setup" and "a=dsca:setup" every time
>> it wants to set up a MSRP datachannel or whether it only has to send a=dsca:setup if wants a different role from the a=setup.
> I see no problem in sending both, as they are used for different things.
>
> Regards,
>
> Christer
>
>
> Regards, Christian
>
> On 16/10/2015 9:20 AM, Christer Holmberg wrote:
>> Albrecht, I can't parse what you said.
>>
>> If a piece of information is required in order for something to work,
>> then it must be mandatory to include that piece of information. Of
>> course, you may define an implicit default value, but the information
>> must be there.
>>
>> Regards,
>>
>> Christer
>>
>> Sent from my Windows Phone
>> ----------------------------------------------------------------------
>> --
>> From: Schwarz, Albrecht (Albrecht)
>> <mailto:[e-mail]>
>> Sent: ‎14/‎10/‎2015 20:09
>> To: Christer Holmberg <mailto:[e-mail]>;
>> Stoetzer-Bradler, Juergen (Juergen)
>> <mailto:[e-mail]>; [e-mail]
>> <mailto:[e-mail]>; Christian Groves
>> ([e-mail]) <mailto:[e-mail]>
>> Subject: RE: [MMUSIC] draft-ietf-mmusic-msrp-usage-data-channel -
>> "a=setup" versus "a=dcsa:x setup"
>>
>> Hello Christer,
>>
>> such a prescriptive sentence
>>
>> />//If a setup value is required for the MSRP session establishment,
>> then the dcsa setup attribute must be mandatory./
>>
>> relates to a “*conditionally ‘mandatory’*”, i.e., an *optional*
>> tagging in general, right?
>>
>> @Christian, you had a good rule of thumb proposed, covering the
>> conditionality.
>>
>> What’s your view?
>>
>> Regards,
>>
>> Albrecht
>>
>> *From:*mmusic [mailto:[e-mail]] *On Behalf Of *Christer
>> Holmberg
>> *Sent:* Dienstag, 13. Oktober 2015 15:01
>> *To:* Stoetzer-Bradler, Juergen (Juergen); [e-mail]
>> *Subject:* Re: [MMUSIC] draft-ietf-mmusic-msrp-usage-data-channel -
>> "a=setup" versus "a=dcsa:x setup"
>>
>> Hi,
>>
>> If a setup value is required for the MSRP session establishment, then
>> the dcsa setup attribute must be mandatory.
>>
>> Regards,
>>
>> Christer
>>
>> *From:*Juergen Stoetzer-Bradler
>> [mailto:[e-mail]]
>> *Sent:* 13. lokakuuta 2015 15:55
>> *To:* Christer Holmberg; [e-mail] <mailto:[e-mail]>
>> *Subject:* Re: [MMUSIC] draft-ietf-mmusic-msrp-usage-data-channel -
>> "a=setup" versus "a=dcsa:x setup"
>>
>> Hello Christer,
>>
>> Thank you for your comments.
>>
>> A dcsa embedded setup attribute does not have any MSRP transport
>> protocol related establishment role semantics.
>> But an MSRP over data channel endpoint still needs to know its MSRP
>> session establishment role.
>> In some data channel to TCP (or TLS) transport interworking cases,
>> which are described in section 6, this MSRP session establishment role
>> cannot always be derived from the DTLS/SCTP establishment role.
>> In such cases a dcsa embedded setup attribute for MSRP seems to be
>> required.
>> However, in some other interworking cases, and especially in
>> end-to-end data channel cases the MSRP session establishment role
>> could be tightly coupled with the DTLS/SCTP establishment roles and
>> hence with the "a=setup" attribute.
>> If we don't allow the "a=setup" attribute to also describe the MSRP
>> session establishment role (if no "a=dcsa:x setup"
>> attribute is present), then we should probably specify that a dcsa
>> embedded setup attribute is mandatory for MSRP over data channel
>> sessions.
>>
>> For MSRP as sub-protocol, would a mandatory "a=dcsa:x setup:<role>"
>> attribute be agreeable?
>>
>> Thanks,
>> Juergen
>>
>> On 10.10.2015 06:26, Christer Holmberg wrote:
>>
>>      Hi.
>>
>>      First, I think you suggest far too much text, but that is editorial.
>>
>>      Second, as you say, the media level 'setup' attribute is used to
>>      negotiate the SCTPoDTLS association establishment. But, I don't
>>      think it should be used to negotiate the MSRP roles etc in case
>>      the 'dcsa:x setup' is not present. The 'setup' attribute has
>>      nothing to do with the protocol carried within the data channel -
>>      the reason we defined the 'dsca' attribute was to be able to carry
>>      such information.
>>
>>      Regards,
>>
>>      Christer
>>
>>      Sent from my Windows Phone
>>
>>      
>> ----------------------------------------------------------------------
>> --
>>
>>      *From: *Juergen Stoetzer-Bradler
>>      <mailto:[e-mail]>
>>      *Sent: *‎09/‎10/‎2015 17:03
>>      *To: *[e-mail] <mailto:[e-mail]>
>>      *Subject: *[MMUSIC] draft-ietf-mmusic-msrp-usage-data-channel -
>>      "a=setup" versus "a=dcsa:x setup"
>>
>>      Hello,
>>
>>      An MSRP over data channel related SDP media description will have
>>      a media level "a=setup:<role>" attribute and may additionally
>>      contain an "a=dcsa" encapsulated setup attribute "a=dcsa:x
>>      setup:<role>". Current version
>>      draft-ietf-mmusic-msrp-usage-data-channel-02
>>      does not yet have any text related to the setup attribute except
>>      for listing it as potential dcsa encapsulated MSRP specific attribute.
>>      As the media level "a=setup" attribute is used to negotiation the
>>      DTLS and SCTP establishment roles, and as the setup attribute is
>>      also used
>>      in MSRP over TCP cases to negotiate the "active" role of MSRP
>>      session endpoints (RFCs 6135, 6714) we propose to explicitly describe
>>      the semantics of dcsa encapsulated setup attributes for MSRP over
>>      data channel in draft-ietf-mmusic-msrp-usage-data-channel.
>>
>>      We propose to add a new section 5.1.1.3 "Media Description Level
>>      setup Attribute Versus Data Channel Specific setup Attribute"
>>      after section 5.1.1.2 ("Use of dcsa Attribute") and to extend
>>      existing section 6 ("Gateway Configuration") with setup attribute
>>      related procedures.
>>
>>      Would the following new section 5.1.1.3 and modified section 6 be
>>      agreeable?
>>
>>      Thanks,
>>      Juergen
>>
>>      Proposed new Section 5.1.1.3:
>>
>>      5.1.1.3.  Media Description Level setup Attribute Versus Data
>>      Channel Specific setup Attribute
>>
>>         The SDP setup attribute, as introduced in [RFC4145], can be used in
>>         WebRTC data channel related SDP media descriptions as a media level
>>         attribute, which is directly associated with the corresponding
>>      DTLS/
>>         SCTP "m" line.  In this case the setup attribute is of the form
>>         "a=setup:<role>", where <role> assumes values as defined in
>>         [RFC4145].  Such a setup attribute is then used as specified in
>>         [I-D.ietf-mmusic-sctp-sdp] in order to negotiate the establishment
>>         roles of the DTLS connection and the SCTP association.
>>
>>         Additionally, the setup attribute can be embedded in a dcsa
>>      attribute
>>         and hence can explicitly be associated with an MSRP session over a
>>         specific data channel.  In such a case it is of the form "a=dcsa:x
>>         setup:<role>", with x being the data channel's SCTP stream
>>         identifier.  Such a dcsa attribute embedded setup attribute has no
>>         relationship with the DTLS connection and SCTP association
>>         establishment roles.
>>
>>         dcsa attribute embedded setup attributes are OPTIONAL for MSRP
>>         sessions over data channels.
>>
>>         If an MSRP over data channel description contains a dcsa embedded
>>         setup attribute, then this embedded setup attribute is used to
>>         negotiate, which MSRP session endpoint assumes the active role
>>      as per
>>         Section 4.2.2 of [RFC6135] and Section 5.4 of [RFC4975].
>>
>>         If an MSRP over data channel description does not contain a dcsa
>>         embedded setup attribute, then the media description level
>>      "a=setup"
>>         attribute, which is associated with the data channel's DTLS
>>         connection and SCTP association, is used to negotiate, which MSRP
>>         session endpoint assumes the active role.
>>
>>         If an MSRP over data channel endpoint wants to negotiate an
>>      active or
>>         non-active MSRP session establishment role, which is different from
>>         its DTLS connection and SCTP association establishment role,
>>      then it
>>         MUST include a dcsa embedded setup attribute for this MSRP session.
>>         In this case this dcsa embedded setup attribute's value is
>>      different
>>         from the value of the DTLS/SCTP "m" line's "a=setup" attribute.
>>
>>
>>      Proposed modified section 6:
>>
>>      6.  Gateway Configuration
>>
>>         This section describes the network configuration where one MSRP
>>         endpoint uses data channels as MSRP transport, the other MSRP
>>         endpoint uses TLS/TCP connections as MSRP transport, and the
>>      two MSRP
>>         endpoints interwork via an MSRP gateway.
>>
>>         Specifically, a gateway can be configured to interwork an MSRP
>>         session over a data channel with a peer that does not support data
>>         channel transport in one of two ways.  In one model, the gateway
>>         performs as a MSRP B2BUA to interwork all the procedures as
>>      necessary
>>         between the endpoints.  No further specification is needed for this
>>         model.
>>
>>         Alternately, the gateway can use CEMA procedures to provide
>>      transport
>>         level interworking between MSRP endpoints using different transport
>>         protocols as follows.
>>
>>         When the gateway performs transport level interworking between MSRP
>>         endpoints, all of the procedures in Section 5 apply to each peer,
>>         with the following additions:
>>
>>         o  The endpoint establishing an MSRP session using data channel
>>            transport SHALL NOT request inclusion of any relays, although it
>>            MAY interoperate with a peer that signals the use of relays.
>>
>>         o  The gateway receiving an SDP offer that includes a request to
>>            negotiate an MSRP session on a data channel can provide
>>      transport
>>            level interworking in the same manner as a CEMA SBC by
>>      forwarding
>>            TCP or TLS transport parameters in a new "m" line with the
>>            appropriate attributes within the forwarded SDP offer.
>>
>>            *  If the received data channel side SDP offer contains a dcsa
>>               embedded setup attribute for the to be negotiated MSRP
>>      session,
>>               then the gateway interworks this dcsa embedded setup
>>      attribute
>>               with the media description level "a=setup" attribute of this
>>               MSRP session's "m" line in its forwarded SDP offer.
>>
>>            *  If the received data channel side SDP offer does not
>>      contain a
>>               dcsa embedded setup attribute for the to be negotiated MSRP
>>               session, then the gateway interworks the media description
>>               level "a=setup" attribute, which is directly associated with
>>               the data channel's DTLS/SCTP "m" line, with the media
>>               description level "a=setup" attribute of this MSRP session's
>>               "m" line in its forwarded SDP offer.
>>
>>         o  Similarly, a gateway receiving an SDP offer to negotiate an MSRP
>>            session using TCP or TLS transport with an endpoint that only
>>            supports data channel transport for MSRP can provide transport
>>            level interworking in the same manner as a CEMA SBC by
>>            establishing a new data channel for the MSRP session with the
>>            target endpoint.
>>
>>            *  In this case the gateway interworks the TCP or TLS associated
>>               media description level "a=setup" attribute of the to be
>>               negotiated MSRP session's received "m" line either with the
>>               media description level "a=setup" attribute of the data
>>               channel's DTLS/SCTP "m" line, or with the dcsa embedded setup
>>               attribute of this MSRP session's new data channel.
>>
>>            *  If the gateway's DTLS connection and SCTP association
>>               establishment role on its data channel side is equal to the
>>               "a=setup" attribute's value of the received MSRP over TCP or
>>               TLS "m" line, then the gateway MAY add a dcsa embedded setup
>>               attribute to the description of the MSRP session's new data
>>               channel in its generated data channel side offer.
>>               Alternatively, in this case the gateway MAY omit adding
>>      such a
>>               dcsa embedded setup attribute to the description of the MSRP
>>               session's new data channel in its generated data channel side
>>               offer.  Otherwise, if the gateway's DTLS connection and SCTP
>>               association establishment role is different from the MSRP
>>      over
>>               TCP or TLS associated received "a=setup" attribute's value,
>>               then the gateway MUST add a dcsa embedded setup attribute to
>>               the description of the MSRP session's new data channel in its
>>               generated data channel side offer.
>>
>>            *  If the gateway adds a dcsa embedded setup attribute
>>      associated
>>               with this MSRP session to its data channel side SDP
>>      offer, then
>>               the value of this embedded setup attribute MUST be equal
>>      to the
>>               value of the "a=setup" attribute, which is associated
>>      with this
>>               MSRP session's "m" line in the received TCP or TLS side SDP
>>               offer.
>>
>