MBSF: Configure service announcement channel

[davidjwbbc]

Introduction

The VIA_MBS_DISTRIBUTION_SESSION Service Announcement Mode uses an OBJECT_CAROUSEL distribution operating mode Distribution Session to transmit the service announcements. See TS 26.517 Clause 5.3.2.

The MBSF needs to configure this service announcement channel if one or more active MBS User Services have the VIA_MBS_DISTRIBUTION_SESSION Service Announcement Mode.

Initial implementation

Since the 5G-MAG Reference Tools MBSTF currently does not support the CAROUSEL operating mode (see issue 5G-MAG/rt-mbs-transport-function#51), we will initially use SINGLE mode to test the carousel configuration. Once Carousel mode is available this can be reverted to CAROUSEL operating mode.

The following configuration values will be found in the MBSF YAML configuration file:

mbsf:
  serviceAnnouncementChannel:
    ssm:
      source: <ip>
      destination: <ip>
      port: <port>
    repetitionRate: <seconds>
    mbr: <bit-rate>
#Optional
    distributionBaseUrl: <URL>

The MBSF will first configure an MBS Session with the MB-SMF at a bit rate equal to the configured mbsf/serviceAnnouncementChannel/mbr value, the SSM equal to the mbsf/serviceAnnouncementChannel/ssm object, and request a TMGI and UDP tunnel. This will be remembered as a special service announcement MBS Service.

The MBSF will then configure, on an available MBSTF, a Distribution Session using the following parameters:

• PUSH acquisition mode
• SINGLE operating mode
• the UPF UDP tunnel from the special service announcement MBS Session
• the mbsf/serviceAnnouncementChannel/ssm/destination and mbsf/serviceAnnouncementChannel/ssm/port configuration values as the upTrafficFlowInfo.
• Once MBSF: Add Source IP and TSI to MBSTF configuration API #27 has been implemented this shall use TSI = 1 and the source address from mbsf/serviceAnnouncementChannel/ssm/source configuration value in the upTrafficFlowInfo.
• If available in the MBSF YAML configuration, the mbsf/serviceAnnouncementChannel/distributionBaseUrl value will be used to set objDistributionData.objDistributionBaseUrl.

This Distribution Session will be remembered as a special case Distribution Session that is not accessible via the normal User Data Ingest Session APIs.

The Application Provider will be expected to use the same SSM and TSI = 1 for subscription to the service announcement channel in their app.

Once the Distribution Session for the service announcement channel is configured, the MBSF will PUSH the carousel description containing all URLs for service announcements belonging to MBS User Services which have the VIA_MBS_DISTRIBUTION_SESSION Service Announcement Mode present (See #26). See TS 26.517 Clause 6.1.2 for details of the carousel manifest format. The repetition rate for each service announcement will be taken from the mbsf/serviceAnnouncementChannel/repetitionRate configuration value.

The MBSF will also check that the the sum of the bit sizes of the User Service Description Bundles divided by the repetitionRate does not exceed the mbr setting. An error will be raised in the log for operator attention if it does and the repetitionRate in the carousel description will be extended to fit the data within the mbr.