- MBS: broadcast, multicast join and leave, activation, mobility, multicast in RRC_INACTIVE (Release 18), broadcast over NR non-terrestrial networks (Release 19), access to MBS of a VPLMN while roaming (Release 20), QoS, security and more.
- Each feature shows the clause that defines it and, folded, the services, APIs or procedures that realise it.
- Grouped by what they do: broadcast sessions, multicast sessions, mobility and coverage, service control and policy, and device and network.
TS 23.247 groups the MBS procedures in three: a "Common procedure for Multicast and Broadcast" (clause 7.1), "MBS procedures for multicast Session" (clause 7.2) and "MBS procedures for broadcast Session" (clause 7.3). Each feature below says which of MBS Broadcast and MBS Multicast it applies to, from the clauses that define it.
Broadcast sessions
Broadcast MBS session
Applies to: MBS Broadcast · Defined in TS 23.247 clauses 4.2.2 and 6 · procedure clause 7.3.1 · NG-RAN TS 38.300 clause 16.10.6
The AF starts a broadcast MBS session with TMGI allocation and MBS Session Create, which sets up resources in the MB-UPF and in NG-RAN for 5GC Shared delivery. The MB-SMF asks the AMFs serving the MBS service area to create a broadcast context, and they send the setup request to all NG-RAN nodes that support MBS in the area. A UE that is pre-configured with the needed configuration does not need to interact with the network. In NG-RAN, the UE receives the broadcast configuration on the MCCH in any RRC state. Broadcast has no HARQ-ACK feedback, uses dynamic scheduling only, and supports slot-level repetition of MTCH (TS 23.247 V20.0.0 clause 7.3.1; TS 23.247 V20.0.0 clause 4.2.2; TS 38.300 V19.4.0 clause 16.10.6.2; TS 38.300 V19.4.0 clause 16.10.6.6).
Services and procedures
| Interface | Service or procedure | Clause |
|---|---|---|
| AF or NEF to MB-SMF | Nmbsmf_TMGI_Allocate, Nmbsmf_MBSSession_Create | TS 23.247 cl. 7.1.1.2, 9.1 |
| MB-SMF to AMF | Namf_MBSBroadcast_ContextCreate, ContextUpdate, ContextRelease | TS 23.247 cl. 7.3.1 to 7.3.3, 9.3.2 |
| AMF to NG-RAN | NGAP Broadcast Session Setup, Modification, Release, Release Required, Transport | TS 38.413 cl. 8.17 |
| NG-RAN to UE | SIB20, MCCH (MBSBroadcastConfiguration), MTCH | TS 38.331 cl. 5.9 |
Frequency selection for broadcast
Applies to: MBS Broadcast · Defined in TS 23.247 clause 6.5.4 · NG-RAN TS 38.300 clause 16.10.6.5, SIB21 in TS 38.331
The MBS Frequency Selection Area (FSA) ID guides the UE's frequency selection for a broadcast session. It is sent in the service announcement, and the UE compares it with the FSA IDs in the SIBs. NR MBS supports frequency layer prioritisation for broadcast sessions (TS 23.247 V20.0.0 clause 6.5.4; TS 38.300 V19.4.0 clause 16.10.6.5.0).
Broadcast over NR NTN
Applies to: MBS Broadcast · Added in Release 19 · Defined in TS 23.247 clause 6.21 · NG-RAN TS 38.300 clause 16.14.12, SIB27 in TS 38.331
A broadcast MBS session can be transmitted over NR non-terrestrial networks (NTN). For NR NTN, the MBS service area in the 5G Core may be given as an NR NTN Intended Service Area together with a TAI list and/or a cell ID list, for instance to denote an area smaller than a cell; NG-RAN uses it to further restrict the MBS service area. The 5G Core carries it transparently: the MB-SMF selects the AMFs, and the AMF the NG-RAN nodes, from the TAIs. NG-RAN broadcasts the intended service areas (ISAs) in SIB27 and associates them with broadcast services in the MCCH. A UE inside an ISA may establish the broadcast MRB and prioritise the frequency that provides the service, and may release it and stop prioritising that frequency when it leaves the ISA. Location dependent MBS services are not supported for broadcast over NR NTN in this release (TS 23.247 V20.0.0 clause 6.21; TS 23.247 V20.0.0 clause 7.3.1 steps 2, 3 and 9; TS 23.247 V20.0.0 clause 4.1; TS 38.300 V19.4.0 clause 16.14.12; TS 38.300 V19.4.0 clause 7.3.1).
Multicast sessions
Multicast join and leave
Applies to: MBS Multicast · Defined in TS 23.247 clauses 4.2.1 and 6.1 · procedures clauses 7.2.1 and 7.2.2
A UE joins a Multicast MBS session with a PDU Session Modification Request on an associated PDU Session, carrying the MBS Session IDs and a join request. The SMF authorises the join from the UE's MBS subscription data and whether the session is open to any UE. An NG-RAN node sets up shared delivery when it serves at least one UE of the session, and may release it when the last UE leaves (TS 23.247 V20.0.0 clause 7.2.1.3 step 1 and 4; TS 23.247 V20.0.0 clause 7.2.1.4; TS 23.247 V20.0.0 clause 7.2.2.4).
Services and procedures
| Interface | Service or procedure | Clause |
|---|---|---|
| UE to SMF (NAS) | PDU Session Modification (or Establishment) Request with join or leave | TS 23.247 cl. 7.2.1.3, 7.2.2.2 |
| SMF to MB-SMF | Nmbsmf_MBSSession_ContextStatusSubscribe, ContextUpdate | TS 23.247 cl. 7.2.1.3, 9.1.3 |
| NG-RAN to AMF to MB-SMF | NGAP Distribution Setup, Distribution Release; Nmbsmf_MBSSession_ContextUpdate | TS 38.413 cl. 8.18.1, 8.18.2; TS 23.247 cl. 7.2.1.4, 7.2.2.4 |
Multicast session activation and deactivation
Applies to: MBS Multicast · Defined in TS 23.247 clause 4.3 · procedures clause 7.2.5 · NG-RAN TS 38.300 clause 16.10.5.2
Activation and deactivation apply to multicast only. The MB-SMF triggers them on a notification from the MB-UPF (downlink data, or none for some duration) or on a request from the AF, directly or through the NEF. To notify UEs in RRC_IDLE or RRC_INACTIVE that a session has been activated, the gNB uses group notification: a paging message containing the MBS session ID pages all UEs that joined the session (TS 23.247 V20.0.0 clause 7.2.5.1; TS 38.300 V19.4.0 clause 16.10.5.2).
Procedures
| Interface | Procedure | Clause |
|---|---|---|
| AMF to NG-RAN | NGAP Multicast Session Activation, Deactivation, Update | TS 38.413 cl. 8.18.3 to 8.18.5 |
| NG-RAN to UE | Group notification by paging (P-RNTI) | TS 38.300 cl. 16.10.5.2 |
Multicast reception in RRC_INACTIVE
Applies to: MBS Multicast · Added in Release 18 · defined in TS 23.247 clause 6.17 · NG-RAN TS 38.300 clauses 16.10.5.2 and 16.10.5.3.5, TS 38.331 clause 5.10
To provide a multicast service to more UEs in a cell, NG-RAN may move UEs that can receive in RRC_INACTIVE out of RRC_CONNECTED. The gNB decides in which state the UE receives. In RRC_INACTIVE, multicast uses PTM only, without HARQ feedback. The configuration comes in the RRCRelease message and on the multicast MCCH, whose scheduling is in SIB24. TS 38.331 V17.17.0 has no SIB24 and no clause 5.10; they appear in Release 18.
Mobility and coverage
Mobility and switching between shared and individual delivery
Applies to: MBS Multicast (TS 23.247 clause 6.3.1); MBS Broadcast mobility is clause 6.3.2 · Defined in TS 23.247 clause 6.3 · procedures clause 7.2.3 · NG-RAN TS 38.300 clause 16.10.5.3
Multicast mobility is supported between NG-RAN nodes that both support MBS, and between a node that supports MBS and one that does not. At handover to a node without MBS, delivery switches from 5GC Shared to 5GC Individual; on the way back, the SMF switches it to 5GC Shared. To minimise data loss, the MB-UPF adds a sequence number per MBS QoS flow. A broadcast service continues in the target node if the same session is established there with 5GC Shared delivery (TS 23.247 V20.0.0 clause 6.3.1; TS 23.247 V20.0.0 clause 6.3.2; TS 23.247 V20.0.0 clause 7.2.3.5; TS 23.247 V20.0.0 clause 7.2.3.4).
Procedures
| Case | Procedure | Clause |
|---|---|---|
| Xn handover from an MBS supporting node | Path Switch Request with the MBS support indication | TS 23.247 cl. 7.2.3.2; TS 38.300 cl. 16.10.5.3.2 |
| N2 handover from an MBS supporting node | Handover Required, Handover Request Acknowledge | TS 23.247 cl. 7.2.3.3 |
| Handover from a node without MBS | Switch to shared delivery after the handover | TS 23.247 cl. 7.2.3.4; TS 38.300 cl. 16.10.5.3.3 |
| Minimisation of data loss | Sequence numbers, data forwarding, shared NG-U termination | TS 23.247 cl. 7.2.3.5; TS 38.300 cl. 16.10.5.1 |
Local and location dependent MBS
Applies to: MBS Broadcast and MBS Multicast · Defined in TS 23.247 clause 6.2 · procedures clauses 7.2.4 and 7.3.4
A local MBS service is provided in one MBS service area: only UEs in it receive the content. A location dependent MBS service distributes different content to different MBS service areas, with the same MBS Session ID and a different Area Session ID for each area (TS 23.247 V20.0.0 clause 6.2.2; TS 23.247 V20.0.0 clause 6.2.3; TS 23.247 V20.0.0 clause 6.2.1).
Service control and policy
QoS and policy control
Applies to: MBS Broadcast and MBS Multicast · Defined in TS 23.247 clauses 6.6 and 6.10 · services clause 9.2
The network supports QoS control per MBS session, with one or more GBR or non-GBR QoS flows. The policy and charging control framework of TS 23.503 applies, for example MBS Session binding and QoS Flow binding.
Services
| Service | Operations | Consumers |
|---|---|---|
| Npcf_MBSPolicyControl | Create, Update, Delete | MB-SMF (TS 23.247 V20.0.0 clause 9.2.1) |
| Npcf_MBSPolicyAuthorization | Create, Update, Delete | AF, NEF, MBSF (TS 23.247 V20.0.0 clause 9.2.1) |
Authorisation and identifiers
Applies to: MBS Broadcast and MBS Multicast · Defined in TS 23.247 clauses 6.1, 6.4 and 6.5 · services clauses 9.1.2 and 9.4.2
The 5G Core authorises a UE for multicast: whether it may use the Multicast service in the PLMN, and whether it may receive a given session. A Multicast MBS session may be open to any UE. An MBS session is identified by a TMGI (broadcast and multicast) or by a source specific IP multicast address (multicast only) (TS 23.247 V20.0.0 clause 6.1.2; TS 23.247 V20.0.0 clause 6.5.1). From V20.0.0 (Release 20), the MBS subscription data can also list the VPLMNs where the UE may use a multicast MBS service provided by the VPLMN (TS 23.247 V20.0.0 clause 6.4.2).
Services
| Service | Operations | Consumers |
|---|---|---|
| Nmbsmf_TMGI | Allocate, Deallocate | NEF, MBSF, AF (TS 23.247 V20.0.0 clause 9.1.1) |
| Nnef_MBSTMGI | Allocate, Deallocate, ExpiryNotify | AF (TS 23.247 V20.0.0 clause 9.4.1) |
Service announcement and pre-configuration
Applies to: MBS Broadcast and MBS Multicast · Defined in TS 23.247 clause 6.11 · TS 24.575 clause 4
The service announcement describes the services delivered in an MBS session. It may be encoded as defined in TS 26.517 or in an application-specific format. A UE may also be pre-configured, per PLMN, with the information to discover and receive services. The UE pre-configuration work item UEConfig5MBS, Release 18, defines the management object of TS 24.575, whose first version is V18.0.0, and a USIM file for the same purpose (TR 21.918 clause 12.3).
Security
Applies to: MBS Broadcast and MBS Multicast · Defined in TS 23.247 clause 6.13
The MBS security function is implemented in the MBSF and MBSTF, so it applies only with configuration options 2 and 3 (TS 23.247 V20.0.0 clause 6.13).
Device and network
Power saving
Applies to: MBS Broadcast and MBS Multicast · Added in Release 18 · Defined in TS 23.247 clause 6.16 · procedures clauses 7.2.10 and 7.3.8
UEs that use power saving functions wake up at coordinated times. The service announcement gives them a start time and/or scheduled activation times of the MBS session (TS 23.247 V20.0.0 clause 6.16).
Resource sharing in network sharing
Applies to: MBS Broadcast · Added in Release 18 · Defined in TS 23.247 clause 6.18 · NG-RAN TS 38.300 clause 16.10.6.8
When the AF creates broadcast MBS sessions with the same content through several core networks, the shared NG-RAN allocates radio resources for only one of them (TS 23.247 V20.0.0 clause 6.18; TS 38.300 V19.4.0 clause 16.10.6.8). The AF identifies such sessions with an Associated Session ID, which TS 29.532 and TS 29.580 carry (feature 5MBS2, TS 29.580 V20.0.0 clause 6.2.8). Clause 6.18 is in TS 23.247 V18.8.0 and not in V17.12.0 (TR 21.918 clause 12.2).
Access to MBS of the VPLMN while roaming
Applies to: MBS Broadcast and MBS Multicast · Added in Release 20 · Defined in TS 23.247 clauses 6.22 and 6.23
A roaming UE may request to join a multicast MBS session provided by the VPLMN with a local breakout PDU session, using the DNN and S-NSSAI of the service announcement or of its configuration for the VPLMN. The UE needs a permission, stored in its subscription data in the UDM, and may be configured with the VPLMNs where it can join multicast sessions. For a session open only to selected UEs, the AF in the VPLMN provisions the authorisation through a NEF in the HPLMN of the user, with the VPLMN ID. The SMF in the VPLMN authorises the join from the subscription data and the policies of the VPLMN. A roaming UE may receive a broadcast session of the VPLMN based on the service announcement (TS 23.247 V20.0.0 clauses 6.22 and 6.23). The change request is CR 0389 "MBS Roaming", approved at SA#113 (TS 23.247 V20.0.0 change history). TS 23.247 V19.3.0 clause 4.1 states that MBS for roaming is not supported. Release 20 is open, and no TR 21.920 was available to confirm the work item.
Service area, reliability, mobility and mixed traffic
Applies to: MBS Broadcast and MBS Multicast
How is the coverage area of a service determined?
For both Multicast and Broadcast Services, individual cells may be added to or removed from the service area (TS 23.247 V20.0.0 clause 3.1 (MBS service area, note 2)). The Multicast Service is transmitted only in cells within the multicast service area in which there are UEs that have joined an MBS session (TS 23.247 V20.0.0 clause 4.3; TS 38.300 V19.4.0 clause 16.10.5.2, 16.10.5.3.2). Cells within the broadcast service area transmit the Broadcast Service regardless of whether the service is requested or not (TS 23.247 V20.0.0 clause 3.1 (note 1), 4.2.2).
For broadcast, the MCS is indicated in the DCI that schedules the transmission, from the MCS table configured for MCCH or MTCH (TS 38.212 V19.4.0 clause 7.3.1.5.1; TS 38.214 V19.5.0 clause 5.1.3.1; TS 38.300 V19.4.0 clause 16.10.6.6).
How is reliability of reception managed?
For multicast, provision of UE feedback and support of retransmissions using PTP or PTM, among other mechanisms, ensure reliability (TS 38.300 V19.4.0 clause 16.10.1, 16.10.5.6, 16.10.5.7). For broadcast, services are delivered with no guarantee of reception (TS 23.247 V20.0.0 clause 3.1 (note 1); TS 38.300 V19.4.0 clause 16.10.6.6), however data repetition (slot-level) is possible for improved performance (TS 38.300 V19.4.0 clause 16.10.6.6).
How are mobility and service continuity managed?
For multicast, service continuity across cells is supported by handover between the base stations a UE traverses (TS 38.300 V19.4.0 clause 16.10.5.3.2, 16.10.5.3.3; TS 23.247 V20.0.0 clause 6.3.1). For broadcast, neighbour-cell information and cell-reselection mechanisms are available but may not ensure lossless handover (TS 38.300 V19.4.0 clause 16.10.6.5.1; TS 23.247 V20.0.0 clause 6.3.2).
Since Release 18, a UE receiving multicast in RRC_INACTIVE state can also continue when changing cells by cell reselection, without resuming the RRC connection, if it can acquire the PTM configuration of the new cell (TS 38.300 V19.4.0 clause 16.10.5.3.5; TS 23.247 V18.8.0 clause 6.17). See the multicast procedures, moving between cells in RRC_INACTIVE.
Can MBS services be transmitted together with other types of traffic on the 5G network?
Mixed radio carriers can deliver multicast and/or broadcast services alongside other unicast data on the same cell (TS 38.214 V19.5.0 clause 5.1; TS 38.300 V19.4.0 clause 16.10.5.6, 16.10.6.7).
Sources for this page
- MBS: TS 23.247 V20.0.0, clauses 4.2, 4.3, 5.2, 6.1 to 6.20, 7.1.1, 7.2, 7.3, 7.5 and 9; TS 38.300 V19.4.0, clauses 16.10.1, 16.10.5 and 16.10.6; TS 38.413 V19.4.0, clauses 8.17 and 8.18; TS 38.331 V19.4.0, clauses 5.9, 5.10 and 6.3.1, and TS 38.331 V18.11.0 compared with TS 38.331 V17.17.0 for the Release 18 addition; TS 24.575 V19.0.0, clause 4.
- Broadcast over NR NTN: TS 23.247 V20.0.0, clause 6.21; TS 38.300 V19.4.0, clauses 7.3.1 and 16.14.12; TS 38.331 V19.4.0, clauses 5.9.3.2 and 6.3.1 (SIB27). Compared with TS 23.247 V18.8.0 and TS 38.300 V18.11.0, which have neither.