Ericsson

Hirsalantie 11 02420 Jorvas Finland christer.holmberg@ericsson.com

SIP SDP DTLS SCTP DATA CHANNEL DCEP DATA_CHANNEL_OPEN DATA_CHANNEL_ACK PPID TELEPRESENCE RTCWEB WEBRTC This document defines how to use the WebRTC data channel mechanism to realize a data channel, referred to as a Controlling Multiple Streams for Telepresence (CLUE) data channel, for transporting CLUE protocol messages between two CLUE entities.

Status of This Memo This document is not an Internet Standards Track specification; it is published for examination, experimental implementation, and evaluation. This document defines an Experimental Protocol for the Internet community. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are candidates for any level of Internet Standard; see Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .

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Table of Contents

• .  Introduction
• .  Conventions
• .  CLUE Data Channel
  • .  General
  • .  SCTP Considerations
    • .  General
    • .  SCTP Payload Protocol Identifier (PPID)
    • .  Reliability
    • .  Order
    • .  Stream Reset
    • .  SCTP Multihoming
    • .  Closing the CLUE Data Channel
  • .  SDP Considerations
    • .  General
    • .  SDP dcmap Attribute
    • .  SDP dcsa Attribute
    • .  Example
• .  Security Considerations
• .  IANA Considerations
  • .  Subprotocol Identifier "clue"
• .  References
  • .  Normative References
  • .  Informative References
• Acknowledgements
• Author's Address

Introduction This document defines how to use the WebRTC data channel mechanism to realize a data channel, referred to as a Controlling Multiple Streams for Telepresence (CLUE) data channel, for transporting CLUE protocol messages between two CLUE entities. This document also defines how to describe the SCTPoDTLS association (also referred to as "SCTP over DTLS" in this document) used to realize the CLUE data channel using the Session Description Protocol (SDP) and defines usage of the SDP-based "SCTP over DTLS" data channel negotiation mechanism . ("SCTP" stands for "Stream Control Transmission Protocol".) 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 procedures for negotiating usage of a CLUE data channel, are outside the scope of this document.

Conventions 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 when, and only when, they appear in all capitals, as shown here.

SCTPoDTLS association

Refers to an SCTP association carried over a DTLS connection .

WebRTC data channel

Refers to a pair of SCTP streams over an SCTPoDTLS association that is used to transport non-media data between two entities, as defined in .

CLUE data channel

Refers to a WebRTC data channel realization , with a specific set of SCTP characteristics, with the purpose of transporting CLUE protocol messages between two CLUE entities.

CLUE entity

Refers to a SIP User Agent (UA) that supports the CLUE data channel and the CLUE protocol.

CLUE session

Refers to a SIP session between two SIP UAs, where a CLUE data channel, associated with the SIP session, has been established between the SIP UAs.

SCTP stream

Defined in 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 stream identifier

Defined in as an unsigned integer. Identifies an SCTP stream.

CLUE Data Channel

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 , 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.

SCTP Considerations

General As described in , 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. describes how SCTP options are signaled using SDP.

SCTP Payload Protocol Identifier (PPID) A CLUE entity MUST use the PPID value 51 when sending a CLUE message on a CLUE data channel.

Reliability The usage of SCTP for the CLUE data channel ensures reliable transport of CLUE protocol messages . requires the support of the partial reliability extension defined in and the limited retransmission policy defined in . 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.

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

Stream Reset A CLUE entity MUST support the stream reset extension defined in . Per , the dynamic address reconfiguration extension parameter ('Supported Extensions Parameter') defined in must be used to signal the support of the stream reset extension defined in . Other features defined in MUST NOT be used for CLUE data channels.

SCTP Multihoming SCTP multihoming is not supported for SCTPoDTLS associations and therefore cannot be used for a CLUE data channel.

Closing the CLUE Data Channel As described in , to close a data channel, an entity sends an SCTP reset message 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.

SDP Considerations

General This section defines how to (1) construct the SDP media description ("m=" line) for describing the SCTPoDTLS association used to realize a CLUE data channel and (2) use the SDP-based "SCTP over DTLS" data channel negotiation mechanism for establishing a CLUE data channel on the SCTPoDTLS association. describes the SDP Offer/Answer procedures for negotiating a CLUE session, including the CLUE-controlled media streams and the CLUE data channel.

SDP Media Description Fields defines how to set the values of an "m=" line describing an SCTPoDTLS association. As defined in , for a CLUE data channel the values are set as follows: SDP "proto" Field Values

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 is used and the ICE procedures determine that TCP transport is required).

SDP sctp-port Attribute As defined in , 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 .

SDP dcmap Attribute The values of the SDP dcmap attribute , associated with the "m=" line describing the SCTPoDTLS association used to realize the WebRTC data channel, are set as follows: SDP dcmap Attribute Values

stream-id	subprotocol	label	ordered	max-retr	max-time
Value of the SCTP stream used to realize the CLUE data channel	"CLUE"	Application specific	"true"	N/A	N/A

SDP dcsa Attribute The SDP dcsa attribute is not used when establishing a CLUE data channel.

Example The example in shows an SDP media description for a CLUE data channel. Complete SDP examples can be found in .

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

Security Considerations This specification relies on the security properties of the WebRTC data channel described in , 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 for session establishment prior to establishing the data channel.

IANA Considerations

Subprotocol Identifier "clue" This document adds the subprotocol identifier "clue" to the "WebSocket Subprotocol Name Registry" as follows: Registration of 'clue' Value

Subprotocol Identifier	clue
Subprotocol Common Name	CLUE
Subprotocol Definition	RFC 8850
Reference	RFC 8850

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document describes Session Initiation Protocol (SIP), an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants. These sessions include Internet telephone calls, multimedia distribution, and multimedia conferences. [STANDARDS-TRACK] This document defines a mechanism by which two entities can make use of the Session Description Protocol (SDP) to arrive at a common view of a multimedia session between them. In the model, one participant offers the other a description of the desired session from their perspective, and the other participant answers with the desired session from their perspective. This offer/answer model is most useful in unicast sessions where information from both participants is needed for the complete view of the session. The offer/answer model is used by protocols like the Session Initiation Protocol (SIP). [STANDARDS-TRACK] This memo defines the Session Description Protocol (SDP). SDP is intended for describing multimedia sessions for the purposes of session announcement, session invitation, and other forms of multimedia session initiation. [STANDARDS-TRACK] This document obsoletes RFC 2960 and RFC 3309. It describes the Stream Control Transmission Protocol (SCTP). SCTP is designed to transport Public Switched Telephone Network (PSTN) signaling messages over IP networks, but is capable of broader applications. SCTP is a reliable transport protocol operating on top of a connectionless packet network such as IP. It offers the following services to its users: -- acknowledged error-free non-duplicated transfer of user data, -- data fragmentation to conform to discovered path MTU size, -- sequenced delivery of user messages within multiple streams, with an option for order-of-arrival delivery of individual user messages, -- optional bundling of multiple user messages into a single SCTP packet, and -- network-level fault tolerance through supporting of multi-homing at either or both ends of an association. The design of SCTP includes appropriate congestion avoidance behavior and resistance to flooding and masquerade attacks. [STANDARDS-TRACK] A local host may have multiple points of attachment to the Internet, giving it a degree of fault tolerance from hardware failures. Stream Control Transmission Protocol (SCTP) (RFC 4960) was developed to take full advantage of such a multi-homed host to provide a fast failover and association survivability in the face of such hardware failures. This document describes an extension to SCTP that will allow an SCTP stack to dynamically add an IP address to an SCTP association, dynamically delete an IP address from an SCTP association, and to request to set the primary address the peer will use when sending to an endpoint. [STANDARDS-TRACK] Many applications that use the Stream Control Transmission Protocol (SCTP) want the ability to "reset" a stream. The intention of resetting a stream is to set the numbering sequence of the stream back to 'zero' with a corresponding notification to the application layer that the reset has been performed. Applications requiring this feature want it so that they can "reuse" streams for different purposes but still utilize the stream sequence number so that the application can track the message flows. Thus, without this feature, a new use of an old stream would result in message numbers greater than expected, unless there is a protocol mechanism to "reset the streams back to zero". This document also includes methods for resetting the transmission sequence numbers, adding additional streams, and resetting all stream sequence numbers. [STANDARDS-TRACK] This document defines two additional policies for the Partially Reliable Stream Control Transmission Protocol (PR-SCTP) extension. These policies allow limitation of the number of retransmissions and prioritization of user messages for more efficient usage of the send buffer. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. The Stream Control Transmission Protocol (SCTP) is a transport protocol originally defined to run on top of the network protocols IPv4 or IPv6. This document specifies how SCTP can be used on top of the Datagram Transport Layer Security (DTLS) protocol. Using the encapsulation method described in this document, SCTP is unaware of the protocols being used below DTLS; hence, explicit IP addresses cannot be used in the SCTP control chunks. As a consequence, the SCTP associations carried over DTLS can only be single-homed. Unaffiliated Nokia Unaffiliated Unaffiliated Huawei Informative References This memo describes an extension to the Stream Control Transmission Protocol (SCTP) that allows an SCTP endpoint to signal to its peer that it should move the cumulative ack point forward. When both sides of an SCTP association support this extension, it can be used by an SCTP implementation to provide partially reliable data transmission service to an upper layer protocol. This memo describes the protocol extensions, which consist of a new parameter for INIT and INIT ACK, and a new FORWARD TSN chunk type, and provides one example of a partially reliable service that can be provided to the upper layer via this mechanism. [STANDARDS-TRACK] This document describes a protocol for Network Address Translator (NAT) traversal for UDP-based communication. This protocol is called Interactive Connectivity Establishment (ICE). ICE makes use of the Session Traversal Utilities for NAT (STUN) protocol and its extension, Traversal Using Relay NAT (TURN). This document obsoletes RFC 5245. Cisco Huawei Huawei

Acknowledgements Thanks to , , and for comments on this document.

Author's Address Ericsson

Hirsalantie 11 02420 Jorvas Finland christer.holmberg@ericsson.com