Summary of the RAN procedures to acquire MCCH and MTCH:

  1. Obtain MIB
  2. Obtain SIB1 (points to SIB20)
  3. SIB20 contains configuration of MCCH
  4. Demodulation of MCCH (PDSCH) via PDCCH (with MCCH-RNTI = FFFD)
  5. MCCH contains MBSBroadcastConfiguration
  6. Obtain configuration of MTCH within MBSBroadcastConfiguration and G-RNTIs via mbs-SessionInfoList within MBSBroadcastConfiguration
  7. Demodulation of MTCH (PDSCH) with G-RNTI

Control Plane

RRC: MBS Broadcast

Acquisition of MBS Broadcast information via MCCH

  • Procedures in 3GPP TS 38.331 Clause 5.9
    • Acquisition of MCCH: via SIB20, included in SIBTypeInfo in SIB1. MCCH transmission indicated via PDCCH (MCCH-RNTI)
    • Configuration information in MCCH via MBSBroadcastConfiguration
  • SIB20 in 3GPP TS 38.331 Clause 6.2.2: SIB20 contains the information required to acquire the MCCH/MTCH configuration for MBS broadcast. Go to ASN.1.
  • MBSBroadcastConfiguration in 3GPP TS 38.331 Clause 6.2.2: The MBSBroadcastConfiguration message contains the control information applicable for MBS broadcast services transmitted via broadcast MRB. Go to ASN.1.
  • MBS information elements in 3GPP TS 38.331 Clause 6.3.6

Broadcast MRB configuration

  • Procedures in 3GPP TS 38.331 Clause 5.9.3
  • Broadcast MRB establishment in 3GPP TS 38.331 Clause 5.9.3.3
    • Upon a broadcast MRB establishment, the UE shall:
      • establish a PDCP entity and an RLC entity in accordance with MRB-InfoBroadcast for this broadcast MRB included in the MBSBroadcastConfiguration message and the configuration specified in 3GPP TS 38.331 Clause 9.1.1.7;
      • configure the MAC layer in accordance with the mtch-SchedulingInfo (if included);
      • configure the physical layer in accordance with the mbs-SessionInfoList, searchSpaceMTCH, and pdsch-ConfigMTCH, applicable for the broadcast MRB;
      • receive DL-SCH on the cell where the MBSBroadcastConfiguration message was received for the established broadcast MRB using g-RNTI and mtch-SchedulingInfo (if included) in this message for this MBS broadcast service;
      • if an SDAP entity with the received mbs-SessionId does not exist:
        • establish an SDAP entity as specified in 3GPP TS 37.324 clause 5.1.1.
        • indicate the establishment of the user plane resources for the mbs-SessionId to upper layers.
  • Broadcast MRB release in 3GPP TS 38.331 Clause 5.9.3.4
    • Upon broadcast MRB release for MBS broadcast service, the UE shall:
      • release the PDCP entity, RLC entity as well as the related MAC and physical layer configuration;
      • if the SDAP entity associated with the corresponding mbs-SessionId has no associated MRB:
        • release the SDAP entity, as specified in 3GPP TS 37.324 clause 5.1.2;
        • indicate the release of the user plane resources for the mbs-SessionId to upper layers.

PDCP: MBS Broadcast

  • Procedures in 3GPP TS 38.323 Clause 5
    • A PDCP entity associated with MRB can be configured by upper layers 3GPP TS 38.331 to use header compression.
    • Protocol data units, formats, and parameters in 3GPP TS 38.323 Clause 6
    • State variables, constants, and timers in 3GPP TS 38.323 Clause 7

RLC: MBS Broadcast

MAC: MBS Broadcast

User Plane

SDAP: MBS Broadcast

  • SDAP architecture in 3GPP TS 37.324 Clause 4.2
    • The SDAP sublayer is configured for MRBs by RRC. The SDAP sublayer maps MBS QoS flows to MRBs (mapping between an MBS QoS flow and an MRB for DL).
  • Data transfer DL in 3GPP TS 37.324 Clause 5.2.2
    • At the reception of an SDAP data PDU from lower layers for a QoS flow, the receiving SDAP entity shall:
      • if this SDAP data PDU is received from an MRB, retrieve the SDAP SDU from the DL SDAP data PDU as specified in 3GPP TS 37.324 Clause 6.2.2.1
  • Data PDU without SDAP header in 3GPP TS 37.324 Clause 6.2.2.1

PDCP: MBS Broadcast

Annex: RRC messages ASN.1

For definitions refer to 3GPP TS 38.331 Clause 6.2.2

SIB20 

-- ASN1START
-- TAG-SIB20-START

SIB20-r17 ::=	SEQUENCE {
    mcch-Config-r17                MCCH-Config-r17,
    cfr-ConfigMCCH-MTCH-r17        CFR-ConfigMCCH-MTCH-r17 OPTIONAL,  -- Need S
    lateNonCriticalExtension       OCTET STRING            OPTIONAL,
    ...
}

MCCH-Config-r17 ::= SEQUENCE {
    mcch-RepetitionPeriodAndOffset-r17   MCCH-RepetitionPeriodAndOffset-r17,
    mcch-WindowStartSlot-r17             INTEGER (0..79),
    mcch-WindowDuration-r17              ENUMERATED {sl2, sl4, sl8, sl10, sl20, sl40,sl80, sl160}     OPTIONAL, -- Need S
    mcch-ModificationPeriod-r17          ENUMERATED {rf2, rf4, rf8, rf16, rf32, rf64, rf128, rf256,
                                         rf512, rf1024, r2048, rf4096, rf8192, rf16384, rf32768, rf65536}
}

MCCH-RepetitionPeriodAndOffset-r17 ::= CHOICE {
    rf1-r17                                INTEGER(0),
    rf2-r17                                INTEGER(0..1),
    rf4-r17                                INTEGER(0..3),
    rf8-r17                                INTEGER(0..7),
    rf16-r17                               INTEGER(0..15),
    rf32-r17                               INTEGER(0..31),
    rf64-r17                               INTEGER(0..63),
    rf128-r17                              INTEGER(0..127),
    rf256-r17                              INTEGER(0..255)
}

-- TAG-SIB20-STOP
-- ASN1STOP

-- ASN1START
-- TAG-CFR-CONFIGMCCH-MTCH-START

CFR-ConfigMCCH-MTCH-r17 ::= SEQUENCE {
    locationAndBandwidthBroadcast-r17          LocationAndBandwidthBroadcast-r17  OPTIONAL,  -- Need S
    pdsch-ConfigMCCH-r17                       PDSCH-ConfigBroadcast-r17          OPTIONAL,  -- Need S
    commonControlResourceSetExt-r17            ControlResourceSet                 OPTIONAL   -- Cond NotSIB1CommonControlResource
}

LocationAndBandwidthBroadcast-r17 ::= CHOICE {
    sameAsSib1ConfiguredLocationAndBW          NULL,
    locationAndBandwidth                       INTEGER (0..37949)
}

-- TAG-CFR-CONFIGMCCH-MTCH-STOP
-- ASN1STOP

-- ASN1START
-- TAG-PDSCH-CONFIGBROADCAST-START

PDSCH-ConfigBroadcast-r17 ::= SEQUENCE {
    pdschConfigList-r17                    SEQUENCE (SIZE (1..maxNrofPDSCH-ConfigPTM-r17) ) OF PDSCH-ConfigPTM-r17,
    pdsch-TimeDomainAllocationList-r17     PDSCH-TimeDomainResourceAllocationList-r16                          OPTIONAL,   -- Need R
    rateMatchPatternToAddModList-r17       SEQUENCE (SIZE (1..maxNrofRateMatchPatterns)) OF RateMatchPattern   OPTIONAL,   -- Need R
    lte-CRS-ToMatchAround-r17              RateMatchPatternLTE-CRS                                             OPTIONAL,   -- Need R
    mcs-Table-r17                          ENUMERATED {qam256, qam64LowSE}                                     OPTIONAL,   -- Need S
    xOverhead-r17                          ENUMERATED {xOh6, xOh12, xOh18}                                     OPTIONAL    -- Need S
}

PDSCH-ConfigPTM-r17 ::= SEQUENCE {
    dataScramblingIdentityPDSCH-r17        INTEGER (0..1023)         OPTIONAL,   -- Need S
    dmrs-ScramblingID0-r17                 INTEGER (0..65535)        OPTIONAL,   -- Need S
    pdsch-AggregationFactor-r17            ENUMERATED {n2, n4, n8}   OPTIONAL    -- Need S
}

-- TAG-PDSCH-CONFIGBROADCAST-STOP
-- ASN1STOP

MBSBroadcastConfiguration 

-- ASN1START
-- TAG-MBSBROADCASTCONFIGURATION-START

MBSBroadcastConfiguration-r17 ::= SEQUENCE {
    criticalExtensions                CHOICE {
        mbsBroadcastConfiguration-r17     MBSBroadcastConfiguration-r17-IEs,
        criticalExtensionsFuture          SEQUENCE {}
    }
}

MBSBroadcastConfiguration-r17-IEs ::= SEQUENCE {
    mbs-SessionInfoList-r17               MBS-SessionInfoList-r17                                              OPTIONAL,   -- Need R
    mbs-NeighbourCellList-r17             MBS-NeighbourCellList-r17                                            OPTIONAL,   -- Need S
    drx-ConfigPTM-List-r17                SEQUENCE (SIZE (1..maxNrofDRX-ConfigPTM-r17)) OF DRX-ConfigPTM-r17   OPTIONAL,   -- Need R
    pdsch-ConfigMTCH-r17                  PDSCH-ConfigBroadcast-r17                                            OPTIONAL,   -- Need S
    mtch-SSB-MappingWindowList-r17        MTCH-SSB-MappingWindowList-r17                                       OPTIONAL,   -- Need R
    lateNonCriticalExtension              OCTET STRING                                                         OPTIONAL,
    nonCriticalExtension                  SEQUENCE {}                                                          OPTIONAL
}

-- TAG-MBSBROADCASTCONFIGURATION-STOP
-- ASN1STOP

-- ASN1START
-- TAG-MBS-SESSIONINFOLIST-START

MBS-SessionInfoList-r17 ::=      SEQUENCE (SIZE (1..maxNrofMBS-Session-r17)) OF MBS-SessionInfo-r17

MBS-SessionInfo-r17 ::=          SEQUENCE {
    mbs-SessionId-r17                TMGI-r17,
    g-RNTI-r17                       RNTI-Value,
    mrb-ListBroadcast-r17            MRB-ListBroadcast-r17,
    mtch-SchedulingInfo-r17          DRX-ConfigPTM-Index-r17                      OPTIONAL, -- Need S
    mtch-NeighbourCell-r17           BIT STRING (SIZE(maxNeighCellMBS-r17))       OPTIONAL, -- Need S
    pdsch-ConfigIndex-r17            PDSCH-ConfigIndex-r17                        OPTIONAL, -- Need S
    mtch-SSB-MappingWindowIndex-r17  MTCH-SSB-MappingWindowIndex-r17              OPTIONAL  -- Cond MTCH-Mapping
}

DRX-ConfigPTM-Index-r17 ::=          INTEGER (0..maxNrofDRX-ConfigPTM-1-r17)

PDSCH-ConfigIndex-r17  ::=           INTEGER (0..maxNrofPDSCH-ConfigPTM-1-r17)

MTCH-SSB-MappingWindowIndex-r17  ::= INTEGER (0..maxNrofMTCH-SSB-MappingWindow-1-r17)

MRB-ListBroadcast-r17 ::=            SEQUENCE (SIZE (1..maxNrofMRB-Broadcast-r17)) OF MRB-InfoBroadcast-r17

MRB-InfoBroadcast-r17 ::=            SEQUENCE {
    pdcp-Config-r17                      MRB-PDCP-ConfigBroadcast-r17,
    rlc-Config-r17                       MRB-RLC-ConfigBroadcast-r17,
    ...
}

MRB-PDCP-ConfigBroadcast-r17 ::=     SEQUENCE {
    pdcp-SN-SizeDL-r17                   ENUMERATED {len12bits}                   OPTIONAL, -- Need S
    headerCompression-r17                CHOICE {
        notUsed                              NULL,
        rohc                                 SEQUENCE {
            maxCID-r17                           INTEGER (1..16)               DEFAULT 15,
            profiles-r17                         SEQUENCE {
                profile0x0000-r17                    BOOLEAN,
                profile0x0001-r17                    BOOLEAN,
                profile0x0002-r17                    BOOLEAN
           }
        }
    },
    t-Reordering-r17                     ENUMERATED {ms1, ms10, ms40, ms160, ms500, ms1000, ms1250, ms2750}    OPTIONAL -- Need S
}

MRB-RLC-ConfigBroadcast-r17 ::=      SEQUENCE {
    logicalChannelIdentity-r17           LogicalChannelIdentity,
    sn-FieldLength-r17                   ENUMERATED {size6}                       OPTIONAL, -- Need S
    t-Reassembly-r17                     T-Reassembly                             OPTIONAL  -- Need S
}

-- TAG-MBS-SESSIONINFOLIST-STOP
-- ASN1STOP