CLUE Protocol data channel
draft-ietf-clue-datachannel-10

Abstract

This document defines how to use the WebRTC data channel mechanism in order to realize a data channel, referred to as a CLUE data channel, for transporting CLUE protocol messages between two CLUE entities.

The document defines how to describe the SCTPoDTLS association used to realize the CLUE data channel using the Session Description Protocol (SDP), and defines usage of SDP-based "SCTP over DTLS" data channel negotiation mechanism for establishing a CLUE data channel.

Details and procedures associated with the CLUE protocol, and the SDP Offer/Answer procedures for negotiating usage of a CLUE data channel, are outside the scope of this document.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on March 10, 2016.

Copyright Notice

Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

• 1. Introduction
• 2. Conventions
• 3. CLUE data channel
• 3.1. General
• 3.2. SCTP Considerations
• 3.2.1. General
• 3.2.2. SCTP Payload Protocol Identifier (PPID)
• 3.2.3. Reliability
• 3.2.4. Order
• 3.2.5. Stream Reset
• 3.2.6. SCTP Multihoming
• 3.2.7. Close CLUE data channel
• 3.3. SDP Considerations
• 3.3.1. General
• 3.3.2. SDP dcmap Attribute
• 3.3.3. SDP dcsa Attribute
• 3.3.4. Example
• 4. Security Considerations
• 5. IANA Considerations
• 5.1. New WebRTC data channel Protocol Value
• 6. Acknowledgments
• 7. Change Log
• 8. References
• 8.1. Normative References
• 8.2. Informative References
• Author's Address

1. Introduction

This document defines how to use the WebRTC data channel mechanism [I-D.ietf-rtcweb-data-channel] in order to realize a data channel, referred to as a CLUE data channel, for transporting CLUE protocol messages between two CLUE entities.

The document defines how to describe the SCTPoDTLS association [I-D.ietf-tsvwg-sctp-dtls-encaps] 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.

2. Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [RFC2119].

SCTPoDTLS association refers to an SCTP association carried over an DTLS connection [I-D.ietf-tsvwg-sctp-dtls-encaps].

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.

3. CLUE data channel

3.1. General

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.

3.2. SCTP Considerations

3.2.1. General

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 signalled 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.

3.2.2. SCTP Payload Protocol Identifier (PPID)

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 what application protocol the SCTP message is associated with, only the format in which the data is encoded.

3.2.3. Reliability

The usage of SCTP for the CLUE data channel ensures reliable transport of CLUE protocol [I-D.ietf-clue-protocol] messages.

A CLUE entity MUST NOT use the partial reliability and limited retransmission SCTP extensions, described in [RFC3758], for the CLUE data channel.

NOTE: [I-D.ietf-rtcweb-data-channel] requires the support of the partial reliability extension defined in [RFC3758]. This is not needed for a CLUE data channel, as messages are required to always be sent reliably. [I-D.ietf-rtcweb-data-channel] also mandates support of the limited retransmission policy defined in [RFC7496].

3.2.4. Order

A CLUE entity MUST use the ordered delivery SCTP service, as described in [RFC4960], for the CLUE data channel.

3.2.5. Stream Reset

A CLUE entity MUST support the stream reset extension defined in [RFC6525].

The dynamic address reconfiguration extension 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.

3.2.6. SCTP Multihoming

SCTP multi-homing is not supported for SCTPoDTLS associations, and can therefore not be used for a CLUE data channel.

3.2.7. Close CLUE data channel

As described in [I-D.ietf-rtcweb-data-protocol], in order 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.

3.3. SDP Considerations

3.3.1. General

This section defines how to construct the SDP Media Description (m- line) for describing the SCTPoDTLS association used to realize a WebRTC 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 WebRTC 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.

3.3.1.1. SDP Media Description Fields

As defined in [I-D.ietf-mmusic-sctp-sdp], the field values of an m- line describing an SCTPoDTLS association are set as following:

							
		m=application 54111 UDP/DTLS/SCTP webrtc-datachannel
		a=sctp-port: 5000
		a=dcmap:2 subprotocol="CLUE";ordered=true

           				

	Subprotocl Identifier:		CLUE
	Subprotocol Common Name:	CLUE
	Subprotocol Definition:		RFC-XXXX