RFC 8850 EXPERIMENTAL TELEPRESENCE · DATA CHANNELS · SCTP

CLUE data channel: Controlling Multiple Streams for Telepresence (CLUE) Protocol Data Channel

The path that carries CLUE messages between two telepresence devices.

RFC EDITOR

Holmberg, C., "Controlling Multiple Streams for Telepresence (CLUE) Protocol Data Channel", RFC 8850, DOI 10.17487/RFC8850, January 2021, <https://www.rfc-editor.org/info/rfc8850>.

BIBTEX

@misc{rfc8850,
  series = {Request for Comments},
  number = 8850,
  howpublished = {RFC 8850},
  publisher = {RFC Editor},
  doi = {10.17487/RFC8850},
  url = {https://www.rfc-editor.org/info/rfc8850},
  author = {C. Holmberg},
  title = {{Controlling Multiple Streams for Telepresence (CLUE) Protocol Data Channel}},
  pagetotal = 9,
  year = 2021,
  month = jan,
}

PUBLISHED: January 2021
AUTHORS: C. Holmberg
STREAM: IETF
SCTP PAYLOAD PROTOCOL IDENTIFIER: 51
SUBPROTOCOL IDENTIFIER: clue
SDP FORMAT TOKEN: webrtc-datachannel
EXAMPLE MEDIA PORT: 54111
EXAMPLE SCTP PORT: 5000
EXAMPLE STREAM IDENTIFIER: 2
DOI: 10.17487/RFC8850

RFC text

Contents

Original text · RFC Editor View on rfc-editor.org ↗

Internet Engineering Task Force (IETF)                       C. Holmberg
Request for Comments: 8850                                      Ericsson
Category: Experimental                                      January 2021
ISSN: 2070-1721


     Controlling Multiple Streams for Telepresence (CLUE) Protocol
                              Data Channel

Abstract

   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
   https://www.rfc-editor.org/info/rfc8850.

Copyright Notice

   Copyright (c) 2021 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
   (https://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.  Closing the 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.  Subprotocol Identifier "clue"
   6.  References
     6.1.  Normative References
     6.2.  Informative References
   Acknowledgements
   Author's Address

1.  Introduction

   This document defines how to use the WebRTC data channel mechanism
   [RFC8831] to realize a data channel, referred to as a Controlling
   Multiple Streams for Telepresence (CLUE) data channel, for
   transporting CLUE protocol messages [RFC8847] between two CLUE
   entities.

   This document also defines how to describe the SCTPoDTLS association
   [RFC8261] (also referred to as "SCTP over DTLS" in this document)
   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 [RFC8864].  ("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 [RFC3264] 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) [RFC8832] 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", "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 a DTLS connection
      [RFC8261].

   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 [RFC8831].

   CLUE data channel
      Refers to a WebRTC data channel realization [RFC8831], with a
      specific set of SCTP characteristics, with the purpose of
      transporting CLUE protocol messages [RFC8847] 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
      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 stream identifier
      Defined in [RFC4960] as an unsigned integer.  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 [RFC8831], 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 [RFC8831], 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.

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 [RFC8831], the PPID value 51 indicates
      |  that the SCTP message contains data encoded in 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.

3.2.3.  Reliability

   The usage of SCTP for the CLUE data channel ensures reliable
   transport of CLUE protocol messages [RFC8847].

   [RFC8831] 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.

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].

   Per [RFC8831], the dynamic address reconfiguration extension
   parameter ('Supported Extensions Parameter') defined in [RFC5061]
   must be used to signal the support of the stream reset extension
   defined in [RFC6525].  Other features defined in [RFC5061] MUST NOT
   be used for CLUE data channels.

3.2.6.  SCTP Multihoming

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

3.2.7.  Closing the CLUE Data Channel

   As described in [RFC8831], 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 (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 [RFC8864] for establishing a CLUE data
   channel on the SCTPoDTLS association.

      |  NOTE: Protocols other than SDP for negotiating usage of an
      |  SCTPoDTLS association for realizing a CLUE data channel are
      |  outside the scope of this specification.

   [RFC8848] 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

   [RFC8841] defines how to set the values of an "m=" line describing an
   SCTPoDTLS association.  As defined in [RFC8841], for a CLUE data
   channel the values are set as follows:

     +===============+==========+============+======================+
     |     media     |   port   |   proto    |         fmt          |
     +===============+==========+============+======================+
     | "application" | UDP port | "UDP/DTLS/ | "webrtc-datachannel" |
     |               |  value   |   SCTP"    |                      |
     +---------------+----------+------------+----------------------+
     | "application" | TCP port | "TCP/DTLS/ | "webrtc-datachannel" |
     |               |  value   |   SCTP"    |                      |
     +---------------+----------+------------+----------------------+

                    Table 1: SDP "proto" Field Values

   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).

3.3.1.2.  SDP sctp-port Attribute

   As defined in [RFC8841], 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 [RFC8841].

3.3.2.  SDP dcmap Attribute

   The values of the SDP dcmap attribute [RFC8864], associated with the
   "m=" line describing the SCTPoDTLS association used to realize the
   WebRTC data channel, are set as follows:

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

                    Table 2: SDP dcmap Attribute Values

      |  NOTE: As CLUE entities are required to use ordered SCTP message
      |  delivery, with full reliability, according to the procedures in
      |  [RFC8864] the max-retr and max-time attribute parameters are
      |  not used when negotiating CLUE data channels.

3.3.3.  SDP dcsa Attribute

   The SDP dcsa attribute [RFC8864] is not used when establishing a CLUE
   data channel.

3.3.4.  Example

   The example in Figure 1 shows an SDP media description for a CLUE
   data channel.  Complete SDP examples can be found in [RFC8848].

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

          Figure 1: SDP Media Description for a CLUE Data Channel

4.  Security Considerations

   This specification relies on the security properties of the WebRTC
   data channel described in [RFC8831], 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.

5.  IANA Considerations

5.1.  Subprotocol Identifier "clue"

   This document adds the subprotocol identifier "clue" to the
   "WebSocket Subprotocol Name Registry" as follows:

                  +-------------------------+----------+
                  | Subprotocol Identifier  | clue     |
                  +-------------------------+----------+
                  | Subprotocol Common Name | CLUE     |
                  +-------------------------+----------+
                  | Subprotocol Definition  | RFC 8850 |
                  +-------------------------+----------+
                  | Reference               | RFC 8850 |
                  +-------------------------+----------+

                  Table 3: Registration of 'clue' Value

6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <https://www.rfc-editor.org/info/rfc3261>.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              DOI 10.17487/RFC3264, June 2002,
              <https://www.rfc-editor.org/info/rfc3264>.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
              July 2006, <https://www.rfc-editor.org/info/rfc4566>.

   [RFC4960]  Stewart, R., Ed., "Stream Control Transmission Protocol",
              RFC 4960, DOI 10.17487/RFC4960, September 2007,
              <https://www.rfc-editor.org/info/rfc4960>.

   [RFC5061]  Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
              Kozuka, "Stream Control Transmission Protocol (SCTP)
              Dynamic Address Reconfiguration", RFC 5061,
              DOI 10.17487/RFC5061, September 2007,
              <https://www.rfc-editor.org/info/rfc5061>.

   [RFC6525]  Stewart, R., Tuexen, M., and P. Lei, "Stream Control
              Transmission Protocol (SCTP) Stream Reconfiguration",
              RFC 6525, DOI 10.17487/RFC6525, February 2012,
              <https://www.rfc-editor.org/info/rfc6525>.

   [RFC7496]  Tuexen, M., Seggelmann, R., Stewart, R., and S. Loreto,
              "Additional Policies for the Partially Reliable Stream
              Control Transmission Protocol Extension", RFC 7496,
              DOI 10.17487/RFC7496, April 2015,
              <https://www.rfc-editor.org/info/rfc7496>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8261]  Tuexen, M., Stewart, R., Jesup, R., and S. Loreto,
              "Datagram Transport Layer Security (DTLS) Encapsulation of
              SCTP Packets", RFC 8261, DOI 10.17487/RFC8261, November
              2017, <https://www.rfc-editor.org/info/rfc8261>.

   [RFC8831]  Jesup, R., Loreto, S., and M. Tüxen, "WebRTC Data
              Channels", RFC 8831, DOI 10.17487/RFC8831, January 2021,
              <https://www.rfc-editor.org/info/rfc8831>.

   [RFC8841]  Holmberg, C., Shpount, R., Loreto, S., and G. Camarillo,
              "Session Description Protocol (SDP) Offer/Answer
              Procedures for Stream Control Transmission Protocol (SCTP)
              over Datagram Transport Layer Security (DTLS) Transport",
              RFC 8841, DOI 10.17487/RFC8841, January 2021,
              <https://www.rfc-editor.org/info/rfc8841>.

   [RFC8864]  Drage, K., Makaraju, M., Ejzak, R., Marcon, J., and R.
              Even, Ed., "Negotiation Data Channels Using the Session
              Description Protocol (SDP)", RFC 8864,
              DOI 10.17487/RFC8864, January 2021,
              <https://www.rfc-editor.org/info/rfc8864>.

6.2.  Informative References

   [RFC3758]  Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
              Conrad, "Stream Control Transmission Protocol (SCTP)
              Partial Reliability Extension", RFC 3758,
              DOI 10.17487/RFC3758, May 2004,
              <https://www.rfc-editor.org/info/rfc3758>.

   [RFC8445]  Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
              Connectivity Establishment (ICE): A Protocol for Network
              Address Translator (NAT) Traversal", RFC 8445,
              DOI 10.17487/RFC8445, July 2018,
              <https://www.rfc-editor.org/info/rfc8445>.

   [RFC8832]  Jesup, R., Loreto, S., and M. Tüxen, "WebRTC Data Channel
              Establishment Protocol", RFC 8832, DOI 10.17487/RFC8832,
              January 2021, <https://www.rfc-editor.org/info/rfc8832>.

   [RFC8847]  Presta, R. and S P. Romano, "Protocol for Controlling
              Multiple Streams for Telepresence (CLUE)", RFC 8847,
              DOI 10.17487/RFC8847, January 2021,
              <https://www.rfc-editor.org/info/rfc8847>.

   [RFC8848]  Hanton, R., Kyzivat, P., Xiao, L., and C. Groves, "Session
              Signaling for Controlling Multiple Streams for
              Telepresence (CLUE)", RFC 8848, DOI 10.17487/RFC8848,
              January 2021, <https://www.rfc-editor.org/info/rfc8848>.

Acknowledgements

   Thanks to Paul Kyzivat, Christian Groves, and Mark Duckworth for
   comments on this document.

Author's Address

   Christer Holmberg
   Ericsson
   Hirsalantie 11
   FI-02420 Jorvas
   Finland

   Email: christer.holmberg@ericsson.com

ISO Plain Language

On this page

PROBLEMThe CLUE protocol needs a reliable, ordered path between the two ends of a telepresence call, and that path has to be described in the session description so that both ends agree on it.

MECHANISMThe CLUE data channel is built on the WebRTC data channel mechanism, which is a pair of SCTP streams over an SCTP association carried inside a DTLS connection. The RFC fixes the SCTP options used, including reliable ordered delivery and the payload protocol identifier 51, and defines the SDP lines that describe the channel.

WHY IT MATTERSThe channel gives the CLUE protocol a transport that delivers every message in order and can be closed on its own without affecting other data channels on the same association. The document is Experimental.

§1What the CLUE Data Channel Is

The CLUE data channel carries the CLUE protocol messages between two CLUE entities. It is built on the WebRTC data channel mechanism, so it is a pair of SCTP streams over a single SCTPoDTLS association, which is an SCTP association carried over a DTLS connection. A CLUE entity is a SIP user agent that supports the CLUE data channel and the CLUE protocol, and a CLUE session is a SIP session between two user agents in which such a channel has been established.

The RFC also defines how the association is described in the Session Description Protocol (SDP), and how the SDP-based data channel negotiation mechanism is used to create the channel. The details of the CLUE protocol itself, and the offer and answer procedures for negotiating a CLUE session, are outside the scope of this document. So is the use of the Data Channel Establishment Protocol.

Two rules from the WebRTC data channel mechanism apply here. Both SCTP streams that make up the channel must belong to the same association, and both must use the same stream identifier. Within a given CLUE session, a CLUE entity must use a single CLUE data channel for all the CLUE messages it sends to its peer.

The CLUE data channel is the path that carries the CLUE messages between two devices in a call. It is built on the WebRTC data channel, which runs inside an encrypted DTLS connection.

Where the CLUE data channel sits

CLUE protocol messagesThe control messages the channel carries
CLUE data channelTwo SCTP streams on one association
SCTPoDTLS associationSCTP carried over a DTLS connection
DTLSEncrypted transport for the association
UDP or TCPThe network transport underneath

§3.2SCTP Settings for the Channel

Several SCTP options are fixed for a CLUE data channel.

A CLUE entity must use the payload protocol identifier 51 when sending a CLUE message. That value says the message holds data encoded in UTF-8. It does not say which application protocol the message belongs to.

The channel is reliable and ordered. The WebRTC data channel mechanism requires support for the partial reliability extension and for the limited retransmission policy, but a CLUE entity must not use them, because CLUE messages are required to always be sent reliably. If an entity detects that the peer uses either extension, it must terminate the session. The entity must also use the ordered delivery service of SCTP, so that messages are delivered in the order they were sent.

The entity must support the stream reset extension, and the dynamic address reconfiguration parameter of SCTP must be used to signal that support. The other features of that parameter must not be used for CLUE data channels. SCTP multihoming is not supported for an SCTPoDTLS association, so it cannot be used for a CLUE data channel either.

Closing the channel means sending an SCTP reset message on the outgoing stream of the channel. When the peer receives it, it also sends a reset message on its own outgoing stream, unless it has already done so. The association, and any other data channels established on the same association, are not affected by those reset messages.

CLUE messages must arrive, and they must arrive in the order they were sent, so the channel is set to reliable and ordered delivery. The data is marked as UTF-8 text, and the channel can be closed on its own without disturbing anything else sharing the connection.

§3.3Describing the Channel in SDP

The media line for the association carries the media type application, a port, a protocol name and the format webrtc-datachannel. The protocol name is either UDP/DTLS/SCTP or TCP/DTLS/SCTP. Entities should not use the TCP form unless it is known that UDP will not work, for instance when the Interactive Connectivity Establishment mechanism determines that TCP transport is required. The sctp-port attribute carries the SCTP port of the association, and the entity may choose any valid value.

The dcmap attribute describes the channels carried on the association. For a CLUE data channel, the stream identifier is the value of the SCTP stream used to realise the channel, the subprotocol is CLUE, the label is application specific, and the ordered flag is true. The max-retr and max-time parameters are not used, because the channel is always reliable and ordered. The dcsa attribute is not used at all when establishing a CLUE data channel.

The RFC's own example is short: an application line on port 54111 using UDP/DTLS/SCTP, an sctp-port of 5000, and a dcmap line naming stream 2 with the CLUE subprotocol and ordered delivery set.

The session description lists the data channel like any other media line. It names the protocol, the port and the SCTP port, and a dcmap line records the stream number, the CLUE subprotocol name and that delivery is ordered.

SDP media description for a CLUE data channel, as given in the RFC

CLUE data channel in SDP

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

The dcmap attribute values for a CLUE data channel

stream-idSCTP stream value — The value of the SCTP stream used to realise the CLUE data channel.
subprotocolCLUE — The subprotocol name registered for CLUE.
labelApplication specific — A label chosen by the application using the channel.
orderedtrue — Messages are delivered in the order they were sent.
max-retrnot used — The channel is always reliable, so no retransmission limit is needed.
max-timenot used — The channel is always reliable, so no retransmission timer is needed.

§4Security Considerations

The specification relies on the security properties of the WebRTC data channel described in RFC 8831, including the reliance on DTLS. Because CLUE sessions are established using SIP and SDP, protecting the data channel against message modification and recovery also requires the SIP authentication and authorization mechanisms described in RFC 3261, used for session establishment before the data channel is established.

The channel relies on DTLS for its security. Because the session is set up with SIP, the SIP authentication and authorization mechanisms must also be used before the channel is established.

§5References

[RFC8831]RFC 8831Jesup, R., Loreto, S., and M. Tüxen, "WebRTC Data Channels", RFC 8831, January 2021.January 2021 [RFC8864]RFC 8864Drage, K., Makaraju, M., Ejzak, R., Marcon, J., and R. Even, Ed., "Negotiation Data Channels Using the Session Description Protocol (SDP)", RFC 8864, January 2021.January 2021 [RFC8841]RFC 8841Holmberg, C., Shpount, R., Loreto, S., and G. Camarillo, "Session Description Protocol (SDP) Offer/Answer Procedures for Stream Control Transmission Protocol (SCTP) over Datagram Transport Layer Security (DTLS) Transport", RFC 8841, January 2021.January 2021 [RFC8261]RFC 8261Tuexen, M., Stewart, R., Jesup, R., and S. Loreto, "Datagram Transport Layer Security (DTLS) Encapsulation of SCTP Packets", RFC 8261, November 2017.November 2017 [RFC4960]RFC 4960Stewart, R., Ed., "Stream Control Transmission Protocol", RFC 4960, September 2007.September 2007 [RFC6525]RFC 6525Stewart, R., Tuexen, M., and P. Lei, "Stream Control Transmission Protocol (SCTP) Stream Reconfiguration", RFC 6525, February 2012.March 2012 [RFC8848]RFC 8848Hanton, R., Kyzivat, P., Xiao, L., and C. Groves, Ed., "Session Signaling for Controlling Multiple Streams for Telepresence (CLUE)", RFC 8848, January 2021.January 2021 [RFC8847]RFC 8847Presta, R. and S. P. Romano, "Protocol for Controlling Multiple Streams for Telepresence (CLUE)", RFC 8847, January 2021.January 2021