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Content for  TS 24.371  Word version:  17.1.0

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1  Scopep. 7

The present document provides the details for allowing Web Real-Time Communication (WebRTC) IMS Clients (WIC) to access the IP Multimedia (IM) Core Network (CN) subsystem.
The present document is applicable to WebRTC IMS client (WIC), eP-CSCF, eIMS-AGW, WebRTC Web Server Function (WWSF) and WebRTC Authorization Function (WAF).

2  Referencesp. 7

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
  • References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific.
  • For a specific reference, subsequent revisions do not apply.
  • For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
[1]
TR 21.905: "Vocabulary for 3GPP Specifications".
[2]
RFC 7118:  "The WebSocket Protocol as a Transport for the Session Initiation Protocol (SIP)".
[3]
TS 24.229: "IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3".
[4]
TS 23.228: " IP Multimedia Subsystem (IMS); Stage 2".
[5]
RFC 5763:  "Framework for Establishing a Secure Real-time Transport Protocol (SRTP) Security Context Using Datagram Transport Layer Security (DTLS)".
[6]
RFC 5764:  "Datagram Transport Layer Security (DTLS) Extension to Establish Keys for the Secure Real-time Transport Protocol (SRTP)".
[7]
TS 22.173: "IP Multimedia Core Network Subsystem (IMS) Multimedia Telephony Service and supplementary services; Stage 1".
[8]
TS 24.173: "IMS multimedia telephony communication service and supplementary services; Stage 3".
[9]
TS 33.203: "Access security for IP based services".
[10]
RFC 6750  (October 2012): "The OAuth 2.0 Authorization Framework: Bearer Token Usage".
[11]
TS 23.292: "IP Multimedia Subsystem (IMS) Centralized Services; Stage 2".
[12]
RFC 5009  (September 2007): "Private Header (P-Header) Extension to the Session Initiation Protocol (SIP) for Authorization of Early Media".
[13]
TS 23.334: "IMS Application Level Gateway (IMS-ALG) - IMS Access Gateway (IMS-AGW) interface".
[14]
RFC 4145  (September 2005): "TCP-Based Media Transport in the Session Description Protocol (SDP)".
[15]
RFC 8122  (March 2017): "Connection-Oriented Media Transport over the Transport Layer Security (TLS) Protocol in the Session Description Protocol (SDP)".
[16]
RFC 8831  (January 2021): "WebRTC Data Channels".
[17]
RFC 8832  (January 2021): "WebRTC Data Channel Establishment Protocol".
[18]
RFC 8841  (January 2021): "Stream Control Transmission Protocol (SCTP)-Based Media Transport in the Session Description Protocol (SDP)".
[19]
RFC 3261  (June 2002): "SIP: Session Initiation Protocol".
[20]
RFC 3264  (June 2002): "An Offer/Answer Model with the Session Description Protocol (SDP)".
[21]
RFC 7675  (October 2015): "STUN Usage for Consent Freshness".
[22]  Void.
[23]
RFC 8261  (November 2017): "Datagram Transport Layer Security (DTLS) Encapsulation of SCTP Packets".
[24]
RFC 6455  (December 2011): "The WebSocket Protocol".
[25]
RFC 8843  (January 2021): "Negotiating Media Multiplexing Using the Session Description Protocol (SDP)".
[26]
RFC 3581  (August 2003): "An Extension to the Session Initiation Protocol (SIP) for Symmetric Response Routing".
[27]
RFC 8898  (September 2020): "Third-Party Token-Based Authentication and Authorization for Session Initiation Protocol (SIP)".
[28]
RFC 6544  (March 2012): "TCP Candidates with Interactive Connectivity Establishment (ICE)".
[29]  Void.
[30]
RFC 8825  (January 2021): "Overview: Real-Time Protocols for Brower-Based Applications".
[31]  Void.
[32]
RFC 3310  (September 2002): "Hypertext Transfer Protocol (HTTP) Digest Authentication Using Authentication and Key Agreement (AKA)".
[33]
RFC 4169  (November 2005): "Hypertext Transfer Protocol (HTTP) Digest Authentication Using Authentication and Key Agreement (AKA) Version-2".
[34]
TS 26.114: "IP multimedia subsystem (IMS); Multimedia telephony, Media handling and interaction".
[35]
RFC 7519  (May 2015): "JSON Web Token (JWT)".
[36]
RFC 8864  (January 2021): " Negotiation Data Channels Using the Session Description Protocol (SDP)".
[37]
RFC 8873  (January 2021): " Message Session Relay Protocol (MSRP) over Data Channels".
[38]
RFC 5761  (April 2010): "Multiplexing RTP Data and Control Packets on a Single Port".
[39]
RFC 8858  (January 2021): "Indicating Exclusive Support of RTP and RTP Control Protocol (RTCP) Multiplexing Using the Session Description Protocol (SDP)".
[40]
RFC 8865  (January 2021): "T.140 Real-Time Text Conversation over WebRTC Data Channels".
[41]  Void.
[42]
RFC 8035  (November 2016): "Session Description Protocol (SDP) Offer/Answer Clarifications for RTP/RTCP Multiplexing".
[43]
RFC 8838  (January 2021): "Trickle ICE: Incremental Provisioning of Candidates for the Interactive Connectivity Establishment (ICE) Protocol".
[44]  Void.
[45]
RFC 8445  (July 2018): "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal".
[46]
RFC 8839  (January 2021): "Session Description Protocol (SDP) Offer/Answer Procedures for Interactive Connectivity Establishment (ICE)".
[47]
RFC 8656  (February 2020): "Traversal Using Relays around NAT (TURN): Relay Extensions to Session Traversal Utilities for NAT (STUN)".
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3  Definitions and abbreviationsp. 9

3.1  Definitionsp. 9

For the purposes of the present document, the terms and definitions given in TR 21.905 and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905.
For the purposes of the present document, the following terms and definitions given in TS 23.228 Annex U apply:
P-CSCF enhanced for WebRTC (eP-CSCF)
WebRTC Authorization Function (WAF)
WebRTC IMS Client (WIC)
WebRTC Web Server Function (WWSF)
For the purposes of the present document, the following terms and definitions given in RFC 8445 apply:
ICE Lite
Full ICE
Host ICE candidates
For the purposes of the present document, the following terms and definitions given in RFC 8825 [30] apply:
WebRTC endpoint
WebRTC non-browser
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3.2  Abbreviationsp. 9

For the purposes of the present document, the abbreviations given in TR 21.905 and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905.
CN
Core Network
CSCF
Call Session Control Function
DCEP
Data Channel Establishment Protocol
eP-CSCF
enhanced Proxy CSCF
IM
IP Multimedia
IP
Internet Protocol
WAF
WebRTC Authorization Function
WebRTC
Web Real-Time Communication
WWSF
WebRTC Web Server Function
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4  Overview of WebRTC access to IMSp. 10

4.1  Generalp. 10

The relationship between functional entities for the interface at the W1 reference point, between the WWSF and the UE, the interface at the W2 reference point, between the eP-CSCF and the UE, the interface at the W3 reference point, between the UE and the eIMS-AGW, and the interface at the W4 reference point, between the WWSF and the WAF, are defined in Annex U of TS 23.228.
The relationship between the functional entities for interface at the Mw reference point, between the eP-CSCF and the remainder of the IP multimedia core network subsystem, is defined in TS 23.228.
A number of appropriate mechanisms exist for signalling communication between the WIC and the eP-CSCF. Sucessful use of a mechanism other than those specified in this document will require some form of prior agreement between the operator of the WWSF and the operator of the eP-CSCF, as to the nature of the signalling mechanism that is to be adopted, and therefore the interworking required at the eP-CSCF. The mechanism of prior agreement and the nature of such agreement is not defined in this document.
A signalling transport mechanism for SIP is standardised in this release of this document, i.e. SIP over websockets (see RFC 7118), but this is not a mechanism that has to be supported by all eP-CSCFs.
When SIP over websockets is used, it can be appropriate for the SIP used to conform to the definitions for SIP on the Gm reference point as specified in TS 24.229. Such a requirement is not mandatory, but where other SIP mechanisms are used:
  1. the usage will require some form of prior agreement with the operator of the eP-CSCF, as to the nature of the signalling mechanism that is to be adopted; and
  2. the SIP mechanisms will have to enable the eP-CSCF to conform to the SIP requirements over the Mw reference point to the remainder of the IP multimedia core network subsystem as specified in TS 24.229.
SDP is used for the signalling session information between the WIC and the eP-CSCF. Such SDP conforms to requirements for SDP on the Gm reference point.
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5  Functional entitiesp. 10

5.1  Generalp. 10

5.2  WIC (WebRTC IMS Client)p. 10

A WebRTC IMS Client (WIC) establishing the service control signalling path over W2 interface, that is compliant with this specification shall implement the role of WIC capabilities defined in clause 6.2, clause 7.2 and clause 8.2.
Where SIP over websockets is used, as specified in RFC 7118, and no alternative SIP profiles have been agreed between the operator of the eP-CSCF and the operator of the WWSF, then the SIP used by the WIC over the W2 reference point shall conform to the requirements for UE over the Gm reference point as specified in TS 24.229.
When the WebSocket protocol is used, the WIC shall act as a WebSocket Client, as defined in RFC 6455.
The SDP used shall conform to the requirements for UE over the Gm reference point as specified in TS 24.229 and further specified in the present document.
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5.3  WWSF (WebRTC Web Server Function)p. 11

The WebRTC Web Server Function (WWSF) is the initial point of contact in the Web that controls access to the IMS communications services for the WIC as specified in TS 23.228.

5.4  WAF (WebRTC Authorisation Function)p. 11

The WebRTC Authorisation Function (WAF) issues authorization tokens that are provided to the WIC via the WWSF as specified in TS 23.228 and TS 33.203.

5.5  eP-CSCF (P-CSCF enhanced for WebRTC)p. 11

For the Mw reference point, the eP-CSCF shall conform to the requirements for the P-CSCF as specified in TS 24.229.
Where SIP over websockets is used, as specified in RFC 7118, and no alternative SIP profile have been agreed between the operator of the eP-CSCF and the operator of the WWSF, then the SIP used by the eP-CSCF over the W2 reference point shall conform to the requirements for P-CSCF over the Gm reference point as specified in TS 24.229.
The SDP used by the eP-CSCF over the W2 reference point shall conform to the requirements for UE over the Gm reference point as specified in TS 24.229 and further specified in the present document.
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5.6  eIMS-AGW (IMS Access Gateway enhanced for WebRTC)p. 11

The functionality of the eIMS-AGW is specified in TS 23.228 and in TS 23.334.

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