4.6 Dynamic model

26.5023GPP5G Multicast-Broadcast User Service ArchitectureRelease 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

4.6.1 MBS Distribution Session life-cycle

The life-cycle model for the MBS Distribution Session is depicted in figure 4.6.1‑1 below. The current state of a provisioned MBS Distribution Session is reflected in the state parameter of the information entities maintained by the MBSF and the MBSTF, and is exposed to the MBS Application Provider via the Nmbsf service.

Figure 4.6.1‑1: Life-cycle model for MBS Distribution Session

1. An MBS Distribution Session shall be in the INACTIVE state when it is first provisioned in the MBSF by the MBS Application Provider. The MBSF shall provision a corresponding MBS Distribution Session entity in the MBSTF. This replica of the MBS Distribution Session shall also be in the INACTIVE state.

If the provisioned end date–time of the parent MBS User Data Ingest Session is in the past, the MBS Distribution Session shall immediately expire and shall transition to a state in which it is no longer provisioned.

It is an error for the end date–time of the parent MBS User Data Ingest Session to be prior to the start date–time. The MBSF shall reject such a configuration at the time of provisioning.

2. Shortly before the provisioned start date–time of the parent MBS User Data Ingest Session (or immediately if the start date–time is in the past at the point of provisioning) the MBS Distribution Session shall transition into the ESTABLISHED state.

At this point:

a. The MBSF shall reserve resources for the MBS Distribution Session in the MBS System by interacting with the MB‑SMF at reference point Nmb1 using the procedures defined in clause 7.1.1 of TS 23.247 [5].

b. The MBSF shall establish the MBS Distribution Session in the MBSTF by invoking the MBS Distribution Session establishment procedure on the Nmbstf service at reference point Nmb2 using the procedures defined in clause 5.4 of the present document. As a result, the MBSTF shall attempt to establish an MBS User Data Ingest Session with the upstream data source at reference point Nmb8 and may commence ingesting data (but not distributing it).

NOTE: Successfully establishing the MBS User Data Ingest Session requires, in the case of the Object Distribution Method, successful retrieval of at least an initial object from the MBS Application Provider via reference point Nmb8. In the case of the Packet Distribution Method, successful establishment of the MBS User Data Ingest Session may require a data ingest tunnel to be established successfully with the MBS Application Provider at reference point Nmb8 and receipt of at least one data packet through that tunnel.

If either of these procedures fail, a suitable error shall be returned to the MBSF. Any successfully reserved resources in the MBS System shall be released and the MBS Distribution Session shall return to the INACTIVE state.

Otherwise, the MBSF shall advertise the successfully established MBS Distribution Session to MBSF Clients (either directly via MBS‑5, or indirectly via MBS‑8, depending on the provisioned advertisement mode) by means of an MBS User Service Announcement that it has compiled. An MBS Client in receipt of this advertisement may activate reception of the established MBS Distribution Session at this point (but will not yet receive any MBS data packets).

3. At the provisioned start date–time of the parent MBS User Data Ingest Session (or immediately if the start date–time is in the past at the point of provisioning) the MBS Distribution Session shall transition into the ACTIVE state.

The MBSF shall inform the MBSTF of this state transition by invoking the MBS Distribution Session activation procedure on the Nmbstf service at reference point Nmb2, as specified in clause 5.4 of the present document. As a result, the MBSTF shall commence sending MBS data packets to the MB‑UPF at reference point Nmb9, and any MBS Clients that have activated reception of the previously advertised MBS Distribution Session in step 2 above may start to receive MBS data packets at reference point MBS‑4‑MC.

4. If the MBSTF encounters any error conditions when the MBS Distribution Session is in the ACTIVE state it shall notify the MBSF by invoking the MBS Distribution Session notification procedure defined by the Nmbstf service at reference point Nmb2 per clause 5.4.

If the MBSF determines that the error is of such a severity that the MBS Distribution Session cannot continue, it shall transition to the DEACTIVATING state.

a. The MBSF shall stop advertising the MBS Distribution Session by means of an MBS User Service Announcement.

b. The MBSF shall inform the MBSTF of this state transition by invoking the MBS Distribution Session deactivation procedure on the Nmbstf service at reference point Nmb2 using the procedures defined in clause 5.4 of the present document. As a result, the MBSTF shall cease sending MBS data packets to the MB‑UPF at reference point Nmb9.

c. The MBSF shall release the MBS Distribution Session in the MBSTF by invoking the MBS Distribution Session release procedure on the Nmbstf service at reference point Nmb2 using the procedures defined in clause 5.4 of the present document. As a result, the MBSTF shall stop ingesting data at reference point Nmb8 from the upstream data source. As a result of this procedure, the MBSTF shall automatically transition to the INACTIVE state.

d. The MBSF shall release resources in the MBS System associated with the MBS Distribution Session by interacting with the MB‑SMF at reference point Nmb1 using the procedures defined in clause 7.1.1 of TS 23.247 [5]. As a result of this procedure, the MBSF shall automatically transition to the INACTIVE state.

5. At the provisioned end date–time of the parent MBS User Data Ingest Session (or immediately if the MBS Distribution Session or its parent MBS User Data Ingest Session are destroyed by the MBS Application Provider earlier than the provisioned end date–time) an MBS Distribution Session in the ACTIVE state shall transition into the DEACTIVATNG state and the deactivation procedure described in steps 4a to 4d inclusive shall be followed.

Once the deactivation procedure is complete, the expired MBS Distribution Session shall transition automatically to a state in which it is no longer provisioned.

4.6.2 Notification events

During the lifecycle of a MBS User Service Session, a number of notification messages may be sent by different Network Functions. The MBSF may modify event information when passing on notifications from other Network Functions to the MBS Application Provider (AF/AS) at reference point Nmb10 or (via the NEF) at reference point Nmb5.

The events may originate from different sources:

– If the event originates in the MB-SMF at reference point Nmb1 or in the PCF at reference point Nmb12, it is propagated to the MBS Application Provider (AF/AS) at reference point Nmb10 (or via the NEF at reference point Nmb5). The MBSF conditions the event payload for external usage.

– If the event originates in the MBSTF at reference point Nmb2, it is propagated to the MBS Application Provider (AF/AS) at reference point Nmb10 (or via the NEF at reference point Nmb5). The MBSF conditions the event payload for external usage.

– If the event originates in the MBSF itself, it is propagated directly to the MBS Application Provider (AF/AS) at reference point Nmb10 (or via the NEF at reference point Nmb5).

The notification events listed in table 4.6.2-1 below are used by the MBSF to notify the MBS Application Provider (AF/AS) or NEF. The relevant stimulating reference point is indicated in brackets in the final column of the table.

Table 4.6.2-1: Notification events

Event	Description	Applicable reference point(s)
Distribution Session established	The MBS Distribution Session is established.	Nmb10/Nmb5
Distribution Session service management failure	The MBS Distribution Session could not be started, for example because the necessary resources could not be allocated by the MBS System.	(Nmb1), (Nmb2), Nmb10/Nmb5
Distribution Session policy control failure	The MBS Distribution Session could not be started because of a policy authorization/control failure or rejection.	(Nmb12), Nmb10/Nmb5
Distribution Session activated	The MBS Distribution Session is activated successfully.	(Nmb2), Nmb10/Nmb5
Distribution Session deactivated	The MBS Distribution Session is deactivated.	(Nmb2), Nmb10/Nmb5
Distribution Session data ingest failure	The MBSTF is expecting ingest data for an active MBS Distribution session, but is not receiving data.	(Nmb2), Nmb10/Nmb5