5 MBS User Service Announcement

26.5173GPP5G Multicast-Broadcast User ServicesProtocols and FormatsRelease 17TS

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

5.0 Overview

MBS User Service Announcement is needed in order to advertise MBS User Services in advance of, and potentially during, the MBS User Service Sessions described. MBS User Service Announcement (as defined in clauses 4.5.7 and 4.5.8 of TS 26.502 [3]) is provided by means of an MBS User Service Description, the syntax of which is defined in this clause.

5.1 MBS User Service Description data model

5.1.1 General

An MBS User Service Description is described by a set of metadata documents that are delivered as described in clause 4.3.2 of TS 26.502 [3]. The data model defined in this clause subdivides the parameters defined in [3] and groups them into a set of metadata documents.

Each metadata document is divided into metadata units. A metadata unit is a single uniquely identifiable block of metadata. The metadata itself describes details of services. An obvious example of a metadata unit would be a single SDP document [8].

The metadata consists of:

– An MBS User Service Bundle Description metadata unit (see clause 5.2.2) describing a bundle of one or more MBS User Services, and containing one or more:

– MBS User Service Description metadata unit (see clause 5.2.3) describing an MBS User Service Session that is associated with:

– One or more MBS Distribution Session Description metadata units (see clause 5.2.4), each of which references a Session Description document [8] that may be packaged with the MBS User Service Bundle Description, and each of which may optionally reference an Object Repair Parameters document (see clause 5.2.7) describing the object repair parameters for the MBS Distribution Session.

– Zero or more MBS Application Service Description metadata units (see clause 5.2.5), each of which references an Application Service Entry Point document that may be packaged with the MBS User Service Bundle Description. Additional resources referenced by the entry point document may also be packaged with the MBS User Service Bundle Description.

– Zero or one MBS Schedule Description metadata unit (see clause 5.2.6) advertising the delivery schedule for the MBS User Service Session.

Figure 5.1‑1 illustrates the relationships between these metadata units using UML for a single MBS User Service Bundle.

NOTE: “N” means any number in each instance.

Figure 5.1-1: User Service Data Model simple description

An MBS User Service Bundle Description document shall contain one or more instances of the MBS User Service Description metadata unit, each of which describes a single MBS User Service Session within the MBS User Service Bundle.

Each instance of the MBS User Service Description metadata unit shall include at least one MBS Distribution Service Description metadata unit describing the set of MBS Distribution Sessions currently associated with the MBS User Service Session.

– The MBS Distribution Session Description metadata unit shall refer to one Session Description document.

– Each MBS Distribution Session Description metadata unit may contain a reference to an Object Repair Parameters document.

Each instance of the MBS User Service Description metadata unit may include zero or more MBS Application Service Description metadata units, each one referencing an Application Service Entry Point document (e.g. a DASH MPD, HLS Master Playlist or HTML document) which describes the root of the Application Service associated with this MBS User Service. When multiple Application Service Entry Point documents are referenced, an MBS Client shall select only one on the basis of a distinct MIME content type indicated in the Application Service Description.

Each instance of the MBS User Service Description metadata unit may include an MBS Schedule Description metadata unit. If included, the MBS Schedule Description shall refer to a Schedule Description document, and the UE can expect to receive MBS User Service data during the time periods described in the Schedule Description document.

In the case of the Object Distribution Method, the Schedule Description document may include an object transmission schedule for objects associated with the MBS User Service Session. The UE may select which objects to receive based on the object transmission schedule information published in the Schedule Description document.

5.2 Semantics

5.2.1 General

The following description in this clause presumes XML encoding of the metadata units comprising the MBS User Service Announcement.

5.2.2 MBS User Service Bundle Description metadata unit

The root element of the MBS User Service Bundle Description metadata unit is bundleDescription. This element is of type bundleDescriptionType. The bundleDescription element contains one or several userService‌Description child elements.

5.2.3 MBS User Service Description metadata unit

The root element of the MBS User Service Description metadata unit is the userServiceDescription element. Each userServiceDescription element shall signal a unique identifier in its @serviceId attribute and this shall be of URI format.

The userServiceDescription element may contain one or more name child elements. The purpose of a name element is to communicate a human-readable title of the MBS User Service. For each name element, the language shall be specified according to XML datatypes (XML Schema Part 2 [9]).

The userServiceDescription element may contain one or more serviceLanguage child elements. Each serviceLanguage element represents the available languages of the MBS User Service. The language shall be specified according to XML datatypes (XML Schema Part 2 [9]) using the xml:lang attribute.

5.2.4 MBS Distribution Session Description metadata unit

Each MBS User Service Description metadata unit shall reference at least one MBS Distribution Session Description.

The distributionSessionDescription element shall contain a @conformanceProfile attribute indicating the set of features that the MBS Distribution Session conforms to and which the MBS Client needs to support in order to fully receive the MBS Distribution Session. The value of this attribute shall be a fully-qualified term identifier URI from the controlled vocabulary defined in annex C.

The distributionSessionDescription element shall contain a @sessionDescriptionURI attribute which references a Session Description document. The element may also contain an @objectRepairParametersURI attribute referencing an Object Repair Parameters document.

The distributionSessionDescription element may contain a @dataNetworkName attribute indicating a Data Network Name (DNN) as defined in TS 23.003 [10]. When this attribute is present, the MBS Client shall use the given DNN for interactions with the MBSF at reference point MBS‑5 and with the MBS AS at reference point MBS‑4‑UC. If this attribute is not present, the MBS UE shall use a default PDU Session for these network interactions.

The userServiceDescription element may include an availabilityInfo child element providing additional information pertaining to the availability of the MBS Distribution Session within the 5G Network. If present, the availabilityInfo element shall include one or more infoBinding child elements. The infoBinding element shall contain the child elements serviceArea, mbsFSAId and radiofrequency:

– The serviceArea element declares the one or more service areas in which the MBS Session corresponding to this MBS Distribution Session is currently available.

– In the case of a broadcast MBS Session corresponding to this MBS Distribution Session, the mbsFSAId element identifies a preconfigured area within which, and in proximity to, the cell(s) announce the MBS FSA ID and its associated frequency.

NOTE: This is used to guide frequency selection by the UE for a broadcast MBS Session.

– The radioFrequency element indicates the one or more radio frequencies in the NG-RAN downlink which transmit the MBS Session corresponding to this MBS Distribution Session in the service area(s) identified by the serviceArea element.

5.2.5 Session Description metadata unit

The @sessionDescriptionURI attribute of the MBS User Service Bundle Description references a Session Description metadata unit. Each Session Description metadata unit shall describe one MBS Distribution Session. The Session Description metadata unit is conveyed in a Session Description document that shall be formatted according to RFC 8866 [8]. The Session Description document may be packaged in the same MBS User Service Bundle.

– The session description for the MBS Object Distribution Method is specified in clause 6.2.3

– The session description for the MBS Packet Distribution Method is specified in clause 7.2.3.

5.2.6 MBS Application Service Description metadata unit

In order to support application services in MBS, the MBS User Service Bundle Description metadata unit shall contain an appServiceDescription element referencing an Application Service Entry Point document which contains the descriptive information of the resources delivered via MBS and/or unicast distribution. That Application Service Entry Point document shall be formatted according to the value of the @mimeType attribute.

If the MBS User Service Description contains a reference to an Application Service Entry Point document, then:

1) At least one MBS Distribution Session Description of type Object Distribution Method shall be present, i.e. the MBS User Service Description shall include at least one distributionSessionDescription element referencing a Session Description Document that describes an Object Distribution Method as defined in clause 7.

2) When multiple MBS Distribution Session Descriptions of type Object Distribution Method are present, the appServiceDescription element shall define a mapping between the Application Service Entry Point document and the associated MBS Distribution Session.

3) The MBS Distribution Session described by the Session Description document shall deliver objects that are directly or indirectly referenced by the Application Service Entry Point document.

4) When the Application Service Entry Point document is a DASH MPD, then all of the following shall hold:

a) The MBS Distribution Session shall deliver the objects such that the last packet of the delivered object is available to the MBS Client by no later than its availability time as announced in the DASH MPD.

b) The Content-Location element in the FLUTE File Delivery Table for the delivered object shall match the URL in the DASH MPD.

Editor’s Note: Bullets 4 and 5 should be moved to Clause 7.

4) If an update to the Application Service Entry Point document is delivered as a FLUTE transmission object then the Content-Location element in the FLUTE File Delivery Table for the delivered object shall match the URL of the referenced Application Service Entry Point document.

In the case of 3GP-DASH formatted content, the appServiceDescription element may refer to a unified media manifest document which describes Representations available for both MBS reception and unicast retrieval, and this shall be used by MBS Clients compliant with this specification. In practical deployments, different subsets of the Representations described by the unified manifest document and referenced by such appServiceDescription may be specified for:

– Availability via MBS delivery only,

– Availability via both unicast and MBS delivery,

– Availability via unicast only, and the Representation is redundant in MBS area coverage, i.e. the usage of these resources does not provide an improved user experience. As an example, this may be a lower bitrate Representation of a media component for which a higher bitrate is available over MBS distribution, and

– Availability always via unicast, and the Representation is supplementary in MBS area coverage, i.e. even in MBS area coverage these resources provide an improved user experience. As an example, this may be a secondary language that is only accessible over unicast.

All resources that are directly or indirectly referenced in the Application Service Entry Point document of this metadata unit that are expected to be retrieved by HTTP GET shall be delivered by at least one of the MBS Distribution Sessions associated with the MBS User Service Description.

5.2.7 MBS Schedule Description metadata unit

Availability of the Schedule Description metadata unit is indicated by the presence of the scheduleDescription element in the MBS User Service Bundle Description metadata unit. The URI of the Schedule Description instance document is provided by the @scheduleDescriptionURI attribute in the scheduleDescription element.

A Schedule Description instance document describes the distribution schedule of the MBS Distribution Session and the availability of content via unicast delivery for an MBS User Service in terms of:

– Start/stop lists,

– Recurrence information,

– The service ID or service class to which the schedule may apply,

An MBS User Service containing multiple content components may be carried on a single MBS Distribution Session, or on multiple MBS Distribution Sessions. The MBS Client can expect to receive MBS data during the described time period(s) when at least one of the MBS Distribution Sessions for the MBS User Service is active.

A Schedule Description instance document may also include a schedule of when the objects are intended to be transmitted as part of an MBS Distribution Session using the Object Distribution Method. The object schedule information is defined in terms of:

– The service ID or service class to which the object schedule applies,

– An object transmission schedule listing for each object:

– Object URI,

– A list of start and end times for distribution of the object via MBS,

A Schedule Description instance document may be delivered to the MBS Client:

– prior to the MBS Distribution Session as part of the MBS User Service Announcement along with the Session Description metadata unit (out-of-band of that session); or

– in band within an MBS Distribution Session; or

– via an MBS Distribution Session dedicated to the transport of Schedule Description instance documents.

The most recently delivered Schedule Description instance document shall take priority, such that schedule parameters received prior to – and out-of-band of – the MBS Distribution Session they apply to are regarded as "initial defaults", and schedule parameters received in-band with the MBS Distribution Session overwrite the earlier received schedule parameters.

The Schedule Description instance document is clearly identified using a URI, to enable cross-referencing by the MBS Client of instance documents delivered in band and out of band.

The session schedule and object transmission schedule are described in the Schedule Description instance document respectively by the sessionSchedule and objectSchedule elements.

– The start and stop time of a single sessionSchedule is specified by the start and stop elements.

– The start and stop time of a single objectSchedule is specified by the @start and @end attributes.

In both cases the time is specified as the absolute date and UTC time. The duration may be determined by subtracting the start time from the stop time.

The MBS Distribution Session shall be available to the MBS Client during the time interval(s) announced by the session schedule (i.e. scheduleDescription/serviceSchedule/sessionSchedule element of the Schedule Description instance document), for either unicast or MBS reception. In particular, for unicast reception, the Schedule Description is indicative of the time availability for unicast access of an MBS User Service while the TMGI for the MBS Distribution Session is not activated, as well as for unicast fallback reception when the MBS Client is not located in the MBS coverage area for the service.

The MBS Client may activate reception of that MBS Distribution Session only within the sessionSchedule (and the objectSchedule if present) time window.

When an objectSchedule element is present in a serviceSchedule element, then:

– The MBS Client should not expect that an object described by an objectSchedule will be updated during a time window instance, defined by @start and @end attributes, within a deliveryInfo element of that objectSchedule.

– There shall be only one object version (as defined in the @File-ETag attribute in the FLUTE File Delivery Table) transmitted in a time window defined by the @start and @end attributes within a deliveryInfo element for a given objectSchedule element.

– If objectETag attribute is not present, the objects transmitted in the time windows from different deliveryInfo elements in an objectSchedule should not be expected to be the same object version.

– If the @objectETag attribute is present, there shall be only one object version transmitted in all of the time windows delimited by the start and end attributes of each of the one or more deliveryInfo elements.

– In-band Schedule Description instance document updates can be used to provide a dynamic schedule update to override the existing delivery schedule, such as using the @cancelled attribute mechanism specified in this clause.

– A sessionSchedule element in the same serviceSchedule element shall be present, and its start and stop elements shall specify a time window that completely overlaps the time windows specified in each of the objectSchedule elements of the same serviceSchedule.

When a sessionSchedule is present and there are no objectSchedule child elements in a serviceSchedule, then the MBS Client should download each new object, independently of whether the MBS Distribution Session uses the MBS Object Distribution Method or the MBS Packet Distribution Method.

The objectSchedule element specifies details about the objects to be delivered during an MBS Distribution Session. The @sessionId attribute, if present, identifies the MBS Distribution Session for each object. If not present, an MBS Client shall instead determine the MBS Distribution Session by examining the Session Description metadata unit for the MBS Distribution Session. The @objectETag attribute of the objectSchedule element is the version identifier of the object. If present, the purpose of this entity tag is to enable an MBS Client to determine if an object has changed since a prior reception without having to download the object.

The scheduleUpdate element specifies a time after which MBS Client shall seek to update its schedule information by acquiring the latest available Schedule Description instance document.

An @index attribute is included as a child of the sessionSchedule element. If the sessionSchedule does not describe any session reoccurrence, then the index corresponds to the single session occurrence. If the sessionSchedule describes one or more reoccurrences the @index is the starting index of the first session occurrence with the index value increased by one for each session reoccurrence.

A @cancelled attribute is defined as a child of the objectSchedule/objectURI element.

– If the @cancelled attribute is set to "true" or "1", then the transmission of the object identified by the objectURI element is cancelled, and the MBS Client shall cancel any applicable repair and/or reception reporting procedures for that object.

If this object schedule-level cancellation indication in the updated schedule description is received after the associated object has already been delivered, then any related repair or reception reporting for that object (associated with its parent service), either in progress or yet to occur, shall be aborted.

– If the @cancelled attribute is set to "false" or "0" or is absent, then normal object transmission and associated delivery procedures, if applicable, shall occur.

A sessionScheduleOverride element is defined as a child of the serviceSchedule element. If present, the sessionScheduleOverride element indicates either the cancellation of the session occurrence, or schedule override, as follows:

– If the @cancelled attribute (a child of sessionScheduleOverride element) is set to "true" or "1", then the transmission of the MBS Distribution Session identified by the index attribute (a child of sessionScheduleOverride element) is cancelled, and the MBS Client shall cancel any applicable repair and/or reception reporting for all objects belonging to that MBS Distribution Session.

If this session schedule-level cancellation indication in the updated schedule description is received after any of the associated objects have already been delivered, then any related repair or reception reporting for those objects (associated with their parent service(s)), either in progress or yet to occur, shall be aborted.

– If the @cancelled attribute (a child of sessionScheduleOverride element) is set to "false" or "0" or is absent, then the start and stop time elements (children of sessionScheduleOverride element) shall override the nominal start and stop time of the transmission schedule of the session as identified by the @index attribute (a child of sessionScheduleOverride element).

The value of the @index attribute in the sessionScheduleOverride element corresponds to any of the value of the index element in the reoccurenceStartStopType in the sessionSchedule element.

Schedule information received in the Schedule Description metadata unit shall take precedence over timing information that may have been received in the Session Description metadata unit (t and/or r lines in the SDP).

5.2.8 MBS Object Repair Parameters metadata unit

An Object Repair Parameters document for the object repair procedures may be delivered to MBS Clients:

– Prior to the MBS Distribution Session becoming active, along with the MBS Distribution Session Description metadata unit (out of band of that session); or

– in band within an MBS Distribution Session.

The most recently delivered Object Repair Parameters document shall take priority, such that configuration parameters received prior to – and out-of-band of – the MBS Distribution Session they apply to are regarded as "initial defaults", and configuration parameters received during – and in band with – the MBS Distribution Session, override the earlier received parameters. Thus, a method to update parameters dynamically on a short timescale is provided but, as would be desirable where dynamics are minimal, is not mandatory.

During the User Service Discovery/Announcement Procedure, the Object Repair Parameters document is clearly identified using a URI, to enable UE cross-referencing by the MBS Client of instance documents delivered in band and out of band.

5.3 Delivery of Service Announcement

Editor’s Note: Specify delivery envelope for User Service Bundles.

The MBS User Service Announcement provides information needed by the MBS Client to discover and activate the reception of one or more MBS User Services. User Service Announcement information may be delivered via MBS Distribution Sessions or via a regular PDU Session.