Content for TR 23.757 Word version: 17.0.0

1 Scope p. 12

This Technical Report studies and evaluates architectural enhancements to the 5G System to address the following objective.

Objective A: Enabling general MBS services over 5GS

Support general multicast and broadcast communication services, e.g. transparent IPv4/IPv6 multicast delivery, IPTV, software delivery over wireless, group communications and IoT applications, V2X applications, public safety.

2 References p. 12

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]

TS 23.501: "System architecture for the 5G System (5GS)".

[3]

TS 22.101: "Service aspects; Service principles".

[4]

TS 23.246: "Multimedia Broadcast/Multicast Service (MBMS); Architecture and functional description".

[5]

TS 23.468: "Group Communication System Enablers for LTE (GCSE_LTE)".

[6]

TS 26.348: "Northbound Application Programming Interface (API) for Multimedia Broadcast/Multicast Service (MBMS) at the xMB reference point".

[7]

TS 23.316: "Wireless and wireline convergence access support for the 5G System (5GS)".

[8]

TS 23.502: "Procedures for the 5G System (5GS)".

[9]

TS 23.288: "Architecture enhancements for 5G System (5GS) to support network data analytics services".

[10]

TS 38.300: "NR; Overall description; Stage-2".

[11]

TR 23.748: "Study on enhancement of support for Edge Computing in 5G Core network (5GC)".

[12]

RP-193248: "New Work Item on NR support of Multicast and Broadcast Services", RAN#86.

[13]

TS 23.503: "Policy and charging control framework for the 5G System (5GS); Stage 2".

[14]

TS 23.280: "Common functional architecture to support mission critical services; Stage 2".

[15]

TS 24.379: "Mission Critical Push To Talk (MCPTT) call control; Protocol specification".

[16]

TS 23.003: "Numbering, addressing and identification".

[17]

TS 29.244: "Interface between the Control Plane and the User Plane Nodes; Stage 3".

[18]

TS 26.346: "Multimedia Broadcast/Multicast Service (MBMS); Protocols and codecs".

[19]

RFC 4867: "RTP Payload Format and File Storage Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio Codecs".

[20]

RFC 5795: "The RObust Header Compression (ROHC) Framework".

[21]

RFC 3095: "RObust Header Compression (ROHC): Framework and four profiles: RTP, UDP, ESP, and uncompressed".

[22]

RFC 6363: "Forward Error Correction (FEC) Framework".

[23]

TS 29.116: "Representational state transfer over xMB reference point between content provider and BM-SC".

[24]

RFC 8777: "DNS Reverse IP Automatic Multicast Tunneling (AMT) Discovery".

[25]

RFC 7450: "Automatic Multicast Tunneling".

[26]

RFC 3552: "Guidelines for Writing RFC Text on Security Considerations.".

3 Definitions of terms, symbols and abbreviations p. 13

3.1 Terms p. 13

For the purposes of the present document, the terms 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.

Broadcast communication service:

A communication service in which the same service and the same specific content data are provided simultaneously to all UEs in a geographical area (i.e. all UEs in the broadcast coverage area are authorized to receive the data).

Broadcast service area:

The area within which data of one or multiple Broadcast session(s) are sent.

Broadcast session:

A session to deliver the broadcast communication service. A broadcast session is characterised by the content to send and the geographical area where to distribute it.

Service Announcement:

Mechanism to inform users about one or several available MB services.

Multicast service area:

The area within which data of one or multiple Multicast session(s) are sent.

MBS session:

A multicast session or a broadcast session.

MBS QoS Flow:

The finest granularity for QoS forwarding treatment for MBS data. Providing different QoS forwarding treatment requires separate MBS QoS Flow in 5MBS system.

transport only mode:

MBS system transports data/content from the content provider to the content receiver in a transparent manner.

Multicast communication service:

A communication service in which the same service and the same specific content data are provided simultaneously to a dedicated set of UEs (i.e. not all UEs in the multicast coverage are authorized to receive the data).

Multicast session:

A session to deliver the multicast communication service. A multicast session is characterised by the content to send, by the list of UEs that may receive the service and optionally by a multicast area where to distribute it.

Receive Only Mode:

A UE configuration option that allows a UE to receive only broadcast service without the need to access and register with the PLMN offering the MBS service. Use of Receive Only Mode does not require USIM for the UE.

Shared MBS Network:

A network shared by multiple PLMNs that provides multicast or broadcast services. At least the northbound data entrance point in the 5GS is shared.

5GC Individual MBS traffic delivery:

5G CN receives a single copy of MBS data packets and delivers separate copies of those MBS data packets to individual UEs via per-UE PDU sessions, hence for each such UE one PDU session is required to be associated with a multicast session.

5GC shared MBS traffic delivery:

5G CN receives a single copy of MBS data packets and delivers a single copy of those MBS data packets to a RAN node.

3.2 Abbreviations p. 14

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.

MBS

Multicast/Broadcast Service.

4 Architectural Assumptions and Principles p. 14

4.1 Common architectural requirements and principles p. 14

The following common architectural requirements and principles apply:

Solutions shall build on the 5G System architectural principles as in TS 23.501, including flexibility and modularity for newly introduced functionalities.
The system shall provide an efficient transport for a variety of multicast and broadcast services.
Solutions shall minimize impact to existing external services.
Only NR of NG-RAN connected to 5GC is considered as RAT.
Architecture reference models defined in TS 23.501, clause 4.2 are used as the baseline architecture for supporting multicast and broadcast services in this study. In particular, Figure 4.1-1 shows the MBS architecture with 5G UE, NG-RAN and 5GC.

Copy of original 3GPP image for 3GPP TS 23.757, Fig. 4.1-1: High level MBS architecture

Figure 4.1-1: High level MBS architecture
(⇒ copy of original 3GPP image)

4.2 Specific architectural requirements and principles p. 15

The following IPTV requirements and principles apply:

Solutions to IPTV shall minimize the impact to IPTV network and STB.
Solutions to IPTV STB shall reuse IGMP/MLD message via user plane to join/leave an IPTV channel group.
Solutions to IPTV shall provide an efficient mechanism for the UE to join/leave an IP channel group, including reducing latency and signalling.

4.3 Baseline functionality p. 15

The sequence to establish and deliver an MBS session is assumed as follows:

Optional delivery of 5G MBS service info from application/service layer to 5GC.

NOTE 1:
A framework to deliver 5G MBS service info to 5G CN is available. However, this step may be replaced by pre-agreements without explicit signalling.
UEs participate in receiving MBS flow i.e. UE requests to join an MBS session (for Multicast session).
Establishment of MBS flow transport.

NOTE 2:
Step 3 may happen before step 2 for individual UEs joining an MBS session which is already started.
MBS data delivery to UEs.
UEs stop receiving MBS flow (for Multicast session).
Release of MBS flow transport (what used to be session stop).

4.4 MBS Traffic delivery methods p. 15

MBS traffic needs to be delivered from a single data source (Application Service Provider) to multiple UEs. Depending on many factors, multiple delivery methods may be used to deliver MBS traffic in the 5GS. For clarity, delivery methods are not referred to as unicast/multicast/broadcast but as described below.

From the view point of 5G CN, two delivery methods are possible for MBS multicast service:

5GC Individual MBS traffic delivery method: 5G CN receives a single copy of MBS data packets and delivers separate copies of those MBS data packets to individual UEs via per-UE PDU sessions, hence for each such UE one PDU session is required to be associated with a multicast session.
5GC Shared MBS traffic delivery method: 5G CN receives a single copy of MBS data packets and delivers a single copy of those MBS packets packet to a RAN node, which then delivers them to one or multiple UEs

If 5GC Individual MBS traffic delivery method is supported, a same received single copy of MBS data packets by the CN may be delivered via both 5GC Individual MBS traffic delivery method for some UE(s) and 5GC Shared MBS traffic delivery method for other UEs.

From the viewpoint of RAN, (in the case of the shared delivery) two delivery methods are available for the transmission of MBS packet flows over radio:

Point-to-Point (PTP) delivery method: a RAN node delivers separate copies of MBS data packet over radio to individual UE.
Point-to-Multipoint (PTM) delivery method: a RAN node delivers a single copy of MBS data packets over radio to a set of UEs.

A RAN node may use a combination of PTP/PTM to deliver an MBS packet to UEs.

As depicted in the following figure, PTP or PTM delivery (with 5GC shared delivery method) and 5GC Individual delivery method may be used at the same time for a multicast MBS session.

Copy of original 3GPP image for 3GPP TS 23.757, Fig. 4.4-1: Schematic showing delivery methods

Figure 4.4-1: Schematic showing delivery methods
(⇒ copy of original 3GPP image)

For MBS broadcast service, only 5GC Shared MBS traffic delivery method with PTM delivery is applicable.