| Internet-Draft | CLUE data channel | July 2019 |
| Holmberg | Expires 3 January 2020 | [Page] |
This document defines how to use the WebRTC data channel mechanism to realize a data channel, referred to as a CLUE data channel, for transporting CLUE protocol messages between two CLUE entities.¶
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This document defines how to use the WebRTC data channel mechanism [I-D.ietf-rtcweb-data-channel] to realize a data channel, referred to as a CLUE data channel, for transporting CLUE protocol [I-D.ietf-clue-protocol] messages between two CLUE entities. See RFCs 5725 and 7509.)¶
The document defines how to describe the SCTPoDTLS association [RFC8261] used to realize the CLUE data channel using the Session Description Protocol (SDP) [RFC4566], and defines usage of the SDP-based "SCTP over DTLS" data channel negotiation mechanism [I-D.ietf-mmusic-data-channel-sdpneg]. This includes SCTP considerations specific to a CLUE data channel, the SDP Media Description ("m=" line) values, and usage of SDP attributes specific to a CLUE data channel.¶
Details and procedures associated with the CLUE protocol, and the SDP Offer/Answer [RFC3264] procedures for negotiating usage of a CLUE data channel, are outside the scope of this document.¶
NOTE: The usage of the Data Channel Establishment Protocol (DCEP) [I-D.ietf-rtcweb-data-protocol] for establishing a CLUE data channel is outside the scope of this document.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
SCTPoDTLS association refers to an SCTP association carried over an DTLS connection [RFC8261].¶
WebRTC data channel refers to a pair of SCTP streams over a SCTPoDTLS association that is used to transport non-media data between two entities, as defined in [I-D.ietf-rtcweb-data-channel].¶
CLUE data channel refers to a WebRTC data channel [I-D.ietf-rtcweb-data-channel] realization, with a specific set of SCTP characteristics, with the purpose of transporting CLUE protocol [I-D.ietf-clue-protocol] messages between two CLUE entities.¶
CLUE entity refers to a SIP User Agent (UA) [RFC3261] that supports the CLUE data channel and the CLUE protocol.¶
CLUE session refers to a SIP session [RFC3261] between two SIP UAs, where a CLUE data channel, associated with the SIP session, has been established between the SIP UAs.¶
SCTP stream is defined in [RFC4960] as a unidirectional logical channel established from one to another associated SCTP endpoint, within which all user messages are delivered in sequence except for those submitted to the unordered delivery service.¶
SCTP identifier is defined in [RFC4960] as an unsigned integer, which identifies an SCTP stream.¶
This section describes the realization of a CLUE data channel, using the WebRTC data channel mechanism. This includes a set of SCTP characteristics specific to a CLUE data channel, the values of the "m=" line describing the SCTPoDTLS association associated with the WebRTC data channel, and the usage of the SDP-based "SCTP over DTLS" data channel negotiation mechanism for creating the CLUE data channel.¶
As described in [I-D.ietf-rtcweb-data-channel], the SCTP streams realizing a WebRTC data channel must be associated with the same SCTP association. In addition, both SCTP streams realizing the WebRTC data channel must use the same SCTP stream identifier value. These rules also apply to a CLUE data channel.¶
Within a given CLUE session, a CLUE entity MUST use a single CLUE data channel for transport of all CLUE messages towards its peer.¶
As described in [I-D.ietf-rtcweb-data-channel], different SCTP options (e.g., regarding ordered delivery ), can be used for a data channel. This section describes the SCTP options used for a CLUE data channel. Section 3.3 describes how SCTP options are signaled using SDP.¶
NOTE: While SCTP allows SCTP options to be applied per SCTP message, [I-D.ietf-rtcweb-data-channel] mandates that, for a given data channel, the same SCTP options are applied to each SCTP message associated with that data channel.¶
A CLUE entity MUST use the PPID value 51 when sending a CLUE message on a CLUE data channel.¶
NOTE: As described in [I-D.ietf-rtcweb-data-channel], the PPID value 51 indicates that the SCTP message contains data encoded in a UTF-8 format. The PPID value 51 does not indicate which application protocol the SCTP message is associated with, only the format in which the data is encoded.¶
The usage of SCTP for the CLUE data channel ensures reliable transport of CLUE protocol [I-D.ietf-clue-protocol] messages.¶
[I-D.ietf-rtcweb-data-channel] requires the support of the partial reliability extension defined in [RFC3758] and the limited retransmission policy defined in [RFC7496]. A CLUE entity MUST NOT use these extensions, as messages are required to always be sent reliably. A CLUE entity MUST terminate the session if it detects that the peer entity uses any of the extensions.¶
A CLUE entity MUST use the ordered delivery SCTP service, as described in [RFC4960], for the CLUE data channel.¶
A CLUE entity MUST support the stream reset extension defined in [RFC6525].¶
As defined in [I-D.ietf-rtcweb-data-channel], the dynamic address reconfiguration extension ('Supported Extensions Parameter' parameter) defined in [RFC5061] must be used to signal the support of the stream reset extension defined in [RFC6525]. Other features of [RFC5061] MUST NOT be used for CLUE data channels.¶
SCTP multi-homing is not supported for SCTPoDTLS associations, and can therefore not be used for a CLUE data channel.¶
As described in [I-D.ietf-rtcweb-data-channel], to close a data channel, an entity sends an SCTP reset message [RFC6525] on its outgoing SCTP stream associated with the data channel. When the remote peer receives the reset message, it also sends (unless already sent) a reset message on its outgoing SCTP stream associated with the data channel. The SCTPoDTLS association, and other data channels established on the same association, are not affected by the SCTP reset messages.¶
This section defines how to construct the SDP Media Description ("m=" line) for describing the SCTPoDTLS association used to realize a CLUE data channel. The section also defines how to use the SDP-based "SCTP over DTLS" data channel negotiation mechanism [I-D.ietf-mmusic-data-channel-sdpneg] for establishing a CLUE data channel on the SCTPoDTLS association.¶
NOTE: Other protocols than SDP for negotiating usage of an SCTPoDTLS association for realizing a CLUE data channel are outside the scope of this specification.¶
[I-D.ietf-clue-signaling] describes the SDP Offer/Answer procedures for negotiating a CLUE session, including the CLUE controlled media streams and the CLUE data channel.¶
| fruit | color | amount | price |
|---|---|---|---|
| apple | red | 5 | 1 |
| apricot | orange | 6 | 2 |
| peach | peach | 7 | 3 |
| lime | green | 8 | 4 |
[I-D.ietf-mmusic-sctp-sdp] defines how to set the values of an "m=" line describing an SCTPoDTLS association. As defined in [I-D.ietf-mmusic-sctp-sdp], for a CLUE data channel the values are set as following:¶
| media | port | proto | fmt |
|---|---|---|---|
| "application" | UDP port value | "UDP/DTLS/SCTP" | "webrtc-datachannel" |
| "application" | TCP port value | "TCP/DTLS/SCTP" | "webrtc-datachannel" |
CLUE entities SHOULD NOT transport the SCTPoDTLS association used to realize the CLUE data channel over TCP (using the "TCP/DTLS/SCTP" proto value), unless it is known that UDP/DTLS/SCTP will not work (for instance, when the Interactive Connectivity Establishment (ICE) mechanism [RFC8445] is used and the ICE procedures determine that TCP transport is required).¶
As defined in [I-D.ietf-mmusic-sctp-sdp], the SDP sctp-port attribute value is set to the SCTP port of the SCTPoDTLS association. A CLUE entity can choose any valid SCTP port value [I-D.ietf-mmusic-sctp-sdp].¶
The values of the SDP dcmap attribute [I-D.ietf-mmusic-data-channel-sdpneg], associated with the "m=" line describing the SCTPoDTLS association used to realize the WebRTC data channel, are set as following:¶
| stream-id | sub-protocol | label | ordered | max-retr | max-time |
|---|---|---|---|---|---|
| Value of the SCTP stream used to realize the CLUE data channel | "CLUE" | Appli-cation specific | "true" | N/A | N/A |
NOTE: As CLUE entities are required to use ordered SCTP message delivery, with full reliability, according to the procedures in [I-D.ietf-mmusic-data-channel-sdpneg] the max-retr and max-time attribute parameters are not used when negotiating CLUE data channels.¶
The SDP dcsa attribute [I-D.ietf-mmusic-data-channel-sdpneg] is not used when establishing a CLUE data channel.¶
The example in Figure 1 shows an SDP media description for a CLUE data channel. Examples of complete SDP examples can be found in [I-D.ietf-clue-signaling].¶
m=application 54111 UDP/DTLS/SCTP webrtc-datachannel
a=sctp-port: 5000
a=dcmap:2 subprotocol="CLUE";ordered=true
This specification relies on the security properties of the WebRTC data channel described in [I-D.ietf-rtcweb-data-channel], including reliance on DTLS. Since CLUE sessions are established using SIP/SDP, protecting the data channel against message modification and recovery requires the use of SIP authentication and authorization mechanisms described in [RFC3261] for session establishment prior to establishing the data channel.¶
[RFC EDITOR NOTE: Please replace RFC-XXXX with the RFC number of this document.]¶
This document adds the 'CLUE' value to the "WebSocket Subprotocol Name Registry" as follows:¶
Subprotocl Identifier: CLUE
Subprotocol Common Name: CLUE
Subprotocol Definition: RFC-XXXX
Reference: RFC-XXXX
¶
Thanks to Paul Kyzivat, Christian Groves and Mark Duckworth for comments on the document.¶
[RFC EDITOR NOTE: Please remove this section when publishing]¶
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