- MBS User Services: provisioning through the MBSF, object and packet distribution by the MBSTF, User Service Announcement, post-session and in-session object repair, time synchronization, AL-FEC, security, location-dependent and multiplexed sessions, status notifications, eMBMS interworking and conformance profiles. Reception reporting and the QoS model are for further study.
- Each feature shows the clause that defines it and, folded, the services, APIs or procedures that realise it.
Provisioning of MBS User Services
Defined in TS 26.502 clauses 4.5 and 7.2 · procedure clause 5.3
The MBS Application Provider provisions an MBS User Service, then MBS User Data Ingest Sessions within it, each with one or more MBS Distribution Sessions. It does so at Nmb10, or through the NEF at N33 and Nmb5. The MBSF then creates an MBS Session in the MB-SMF and the Distribution Session in the MBSTF.
Services and APIs
| Reference point | Service | Operations | Stage 3 |
|---|---|---|---|
| Nmb10, Nmb5 | Nmbsf_MBSUserService | Create, Retrieve, Update, Destroy | TS 29.580 cl. 5.2 and 6.1 |
| Nmb10, Nmb5 | Nmbsf_MBSUserDataIngestSession | Create, Retrieve, Update, Destroy, StatusSubscribe, StatusUnsubscribe, StatusNotify, StatusSubscribeMod | TS 29.580 cl. 5.3 and 6.2 |
| N33 | Nnef_MBSUserService, Nnef_MBSUserDataIngestSession | the same, for an AF/AS outside the trusted data network | TS 29.522 (referred to by TS 26.502) |
| Nmb13 | Nmbsmf_TMGI_Allocate | optional TMGI pre-allocation by the provider | TS 23.247 cl. 9.1.2.2 |
| Nmb1 | Nmbsmf_TMGI_Allocate, Nmbsmf_MBSSession_Create | invoked by the MBSF | TS 23.247 cl. 9.1.2.2 and 9.1.3.6 |
Distribution Session control in the MBSTF
Defined in TS 26.502 clauses 4.3.3 and 7.3 · procedures clauses 4.6.1, 5.3 and 5.5
The MBSF creates, updates and destroys MBS Distribution Sessions in the MBSTF at Nmb2. The MBSTF mirrors the MBSF entity and notifies the MBSF of events.
Services and APIs
| Reference point | Service | Operations | Stage 3 |
|---|---|---|---|
| Nmb2 | Nmbstf_MBSDistributionSession | Create, Retrieve, Update, Destroy, StatusSubscribe, StatusUnsubscribe, StatusNotify, StatusSubscribeMod | TS 29.581 cl. 5.2 and 6.1 |
Object Distribution Method
Defined in TS 26.502 clause 6.1 · protocols TS 26.517 clause 6
Delivers discrete binary objects over an MBS Session, in four operating modes: single object, collection, carousel and streaming. With FLUTE, the MBSTF describes the objects currently transmitted with the Profiled FDT Schema of TS 26.346. The objects of the collection and carousel modes are listed in an object manifest.
Clauses
| Aspect | TS 26.502 | TS 26.517 |
|---|---|---|
| Operating modes OBJECT_SINGLE, OBJECT_COLLECTION, OBJECT_CAROUSEL, OBJECT_STREAMING | table 6.1-1 | cl. 6.2.3 |
| Object manifest | cl. 4.5.10 | cl. 6.1.2, annex D.1 |
| Pull-based and push-based ingest at Nmb8 | cl. 4.3.3.2 | cl. 8.2.1.3 |
| Use of FLUTE | cl. 6.2.1, 6.2.2 |
Packet Distribution Method
Defined in TS 26.502 clause 6.2 · protocols TS 26.517 clause 7
Delivers packet streams over an MBS Session. TS 26.502 states it is particularly useful for IP-based services whose content delivery protocols are defined outside the MBS specifications. The MBSTF may add packet sequence numbering and FEC redundancy. Two operating modes: forward-only (Layer 3 proxying) and proxy (Layer 4 proxying).
Clauses
| Aspect | TS 26.502 | TS 26.517 |
|---|---|---|
| Operating modes PACKET_FORWARD_ONLY, PACKET_PROXY | table 6.2-1 | cl. 7.2.1 |
| Packet ingest parameters | table 4.5.6-3 | |
| Session Description | cl. 7.2.3 |
User Service Announcement
Defined in TS 26.502 clauses 4.2.4, 4.5.7 and 4.5.8 · procedures clauses 5.3A and 5.4 · format TS 26.517 clause 5
The MBSF compiles an MBS User Service Announcement that describes the current Distribution Sessions. It reaches the MBS Client by unicast at MBS-5, in the MBS User Service Announcement Channel at MBS-4-MC (an MBS Distribution Session in OBJECT_CAROUSEL mode), or through the MBS Application Provider at MBS-8. The User Service Descriptions document is a JSON document, delivered with its dependent resources as a multipart/related bundle.
Reference points and APIs
| Reference point | API or delivery | TS 26.517 |
|---|---|---|
| MBS-5 | User Service Description retrieval API, exposed by the MBS AF | cl. 9, 5.3.3 |
| MBS-4-MC | Bundle in an object carousel (the Announcement Channel) | cl. 5.3.2 |
| MBS-1 | User Service Description retrieval API, exposed by the MBSF to the provider | cl. 8A |
| MBS-11, Nmb2 | Object manifest pulled from the MBS AF, or pushed by the MBSF | TS 26.502 cl. 4.3.3.2, 5.3A |
Object repair
Defined in TS 26.502 clauses 4.2.6 and 4.3.4 · procedures clauses 5.6.2 and 5.6.3 · protocols TS 26.517 clauses 6.2.4 and 10
With the Object Distribution Method, the MBS AS provides a byte-range Object Repair service to the MBSTF Client at MBS-4-UC. The MBSF decides whether to enable it. Post-session repair, with a randomised back-off, is defined. In-session repair, during the MBS Distribution Session, is added in Release 19: when the received object data is incomplete, the MBSTF Client requests from the MBS AS either enough data to repair the object or the entire object. To support repair, the MBS AS may be configured to ingest objects from the MBSTF at MBS-12, by pull or by push (added in Release 19). The MBSTF Client sends an HTTP GET, or a partial GET with byte ranges, for each damaged object.
Clauses
| Aspect | Clause |
|---|---|
| Post-session repair procedure | TS 26.517 cl. 6.2.4.2 |
| In-session repair procedure (Release 19) | TS 26.502 cl. 5.6.2; TS 26.517 cl. 6.2.4.3, 10.3 |
| Location of the repair object, byte ranges | TS 26.517 cl. 6.2.4.4, 6.2.4.5 |
| Back-off time | TS 26.517 cl. 10.2.2.3 |
| Repair requests and MBS AS requirements | TS 26.517 cl. 10.2.2.4, 10.2.3 |
| Repair parameters in the Distribution Session | TS 26.502 table 4.5.6-2 |
| Ingest by the MBS AS at MBS-12 (Release 19): Object repair exposure base URL, Object repair ingest base URL | TS 26.502 cl. 4.3.4, table 4.5.6-2; TS 29.581 cl. 6.1.6.2.5 |
Time synchronization
Defined in TS 26.502 clause 4.2.7 · format TS 26.517 clause 5.2.11 and annex C.3
Added in Release 19. The MBS Client is required to be time-synchronized with the 5G System with a precision of at least ±1 s to support certain MBS User Service functions. The network provides at least one of two options: NR SIB9, which conveys a UTC wallclock to an accuracy of 10 ms, or a time service hosted by the MBS AS. If both are offered, the MBS Client should preferably use SIB9. The Time Synchronization Parameters of a Distribution Session in the User Service Announcement indicate whether SIB9 is transmitted and list the time service endpoints, each identified by a DASH UTC timing scheme.
Application Layer FEC
Defined in TS 26.502 clauses 4.3.3.2 and 4.3.3.3, table 4.5.6-1
The MBSTF has an optional AL-FEC subfunction for both distribution methods. The FEC configuration of a Distribution Session identifies the scheme with a term from the RMT vocabulary of FEC Encoding IDs, and gives the overhead as a proportion of the MBS data.
Security
Defined in TS 26.502 clauses 4.3.4A and 4.8 · protocol TS 26.517 clause 11
Security protection of MBS traffic uses a control plane procedure, for multicast only, or a user plane procedure, for multicast and broadcast, as defined in TS 33.501 annex W. The MBSSF, co-located with the MBSF or the MBSTF, generates, manages and distributes the MBS Service Keys and MBS Traffic Keys. The MBS Application Provider requests protection with the Transport security protection flag of a Distribution Session. At MBS-10, the MBSF Client retrieves the MBS Service Key from the MBSSF with the protocol of TS 33.246 clause 6.3.
Service areas, location-dependent and multiplexed sessions
Defined in TS 26.502 clause 4.5.2 and table 4.5.6-1 · announcement TS 26.517 clause 5.2.9
A Distribution Session may specify target service areas, outside which MBS data is not transmitted. In the User Service Announcement, each target service area is expressed as a list of NR Cell Identifiers, a list of Tracking Area Identifiers or a list of polygon or circle shapes (added in Release 19). Location-dependent variants of a service share the same MBS Session Identifier with disjoint target service areas. With the Multiplexed service flag, Distribution Sessions with the same (or empty) target service areas are multiplexed onto one MBS Session. Target UE classes state whether a broadcast session is intended for reduced capability (RedCap) UEs, full capability UEs or both.
Status notifications
Defined in TS 26.502 clause 4.6.2, table 4.6.2-1
The MBSF notifies the MBS Application Provider, or the NEF, of events such as session started, Distribution Session established or activated, user data ingest failure and User Service advertisement. Events may originate in the MB-SMF, the PCF, the MBSTF or the MBSF itself.
Services
| Reference point | Service operation |
|---|---|
| Nmb10, Nmb5 | Nmbsf_MBSUserDataIngestSession_StatusSubscribe, StatusNotify, StatusSubscribeMod, StatusUnsubscribe |
| Nmb2 | Nmbstf_MBSDistributionSession_StatusSubscribe, StatusNotify, StatusSubscribeMod, StatusUnsubscribe |
Interworking with eMBMS
Defined in TS 26.502 clause 4.9 and informative annex D
A common TMGI is used in the MBS System and in the eMBMS System. The User Service Announcement can signal that the same service is also available over eMBMS, so a UE with both clients may choose either network and switch between them as reception conditions vary. An informative annex, added in Release 19, describes how to operate MBS User Services over eMBMS using Group Communication: the MBSF and the MBSTF additionally implement a subset of the GCS AS control plane and user plane functionality, at new reference points MB2′-C and MB2′-U towards a BM-SC.
Conformance profiles
Defined in TS 26.517 clause 12
Conformance profiles enable interoperability and signal which features a Distribution Session uses. The Baseline MBS Distribution Session Profile is identified by urn:3GPP:26517:17:baseline.
For further study
Reception reporting by the MBS Client (TS 26.502 clauses 4.2.5 and 4.5.4) and the use of the network QoS primitives by MBS User Services (clause 4.7) are for further study in Release 19.
Sources for this page
- MBS User Services: TS 26.502 V19.5.0, clauses 4.2.4 to 4.2.7, 4.3.3 to 4.3.4A, 4.5, 4.6, 4.7, 4.8, 4.9, 5.3 to 5.6, 6, 7 and annex D; TS 26.517 V19.2.0, clauses 5, 6, 7, 8.2.1.3, 8A, 9, 10, 11, 12 and C.3; TS 29.580 V19.6.0, clauses 5 and 6; TS 29.581 V19.3.0, clauses 5 and 6; TS 23.247 V19.3.0, clauses 9.1.2.2 and 9.1.3.6.