8.3 MBMS Uu Signalling Flows

25.3463GPPIntroduction of the Multimedia Broadcast/Multicast Service (MBMS) in the Radio Access Network (RAN)Release 17Stage 2TS

8.3.1 Broadcast of MBMS System Information

Figure 8.3.1: Broadcast of MBMS system information.

This signalling flow is applicable for handling MBMS to UEs in PMM IDLE and PMM-CONNECTED mode.

The purpose of the signalling flow is for UTRAN to broadcast MBMS system information to UEs using the BCCH. The MBMS SYSTEM INFORMATION shall be repeatedly transmitted after its first transmission. Upon receiving the first MBMS SYSTEM INFORMATION, the UE shall establish the radio bearer carrying an MCCH.

The MBMS SYSTEM INFORMATION includes:

– MCCH schedule information (access info, repetition and modification periods)

– Configuration of a radio bearer carrying an MCCH

More information may be included in the MBMS SYSTEM INFORMATION.

8.3.2 MBMS Service Information

Figure 8.3.2: MBMS service information signalling flow

This signalling flow is applicable for handling MBMS to UEs in PMM IDLE and PMM-CONNECTED mode.

The purpose of the signalling flow is for RNC to inform UEs of all of MBMS services available in one cell. The MBMS SERVICE INFORMATION shall be transmitted periodically on MCCH to provide an indication of the status of the MBMS service in the cell and to support mobility.

The MBMS SERVICE INFORMATION contains MBMS service ids, optionally the MBMS Session ID, and an indication of the service status in the cell i.e. whether it is provided by p-t-m or p-t-p bearers or whether explicit release is indicated. The MBMS service ids indicate the MBMS services which are being served in the cell or the MBMS services which can be served if the UE requests it. P-t-m indication indicates that the MBMS service is on p-t-m in the cell, thus it informs the UE of the need of reception of the MBMS RADIO BEARER INFORMATION.

8.3.3 MBMS Radio Bearer Information

Figure 8.3.3: MBMS radio bearer information signalling flow

This signalling flow is applicable for handling MBMS to UEs in IDLE and PMM-CONNECTED mode.

The purpose of the signalling flow is for the RNC to inform UE(s) regarding the MTCH radio bearer information. MBMS RADIO BEARER INFORMATION is only available for p-t-m transmission. MBMS RADIO BEARER INFORMATION shall be transmitted periodically on MCCH to support mobility in the MBMS service.

MBMS RADIO BEARER INFORMATION includes MBMS Service Id, radio bearer, transport channel and physical channel information per MBMS service.

8.3.4 MBMS Access Information

Figure 8.3.4: MBMS Access Information signalling flow

This signalling flow is applicable for handling MBMS UEs in IDLE mode or URA_PCH, CELL_PCH, CELL_FACH state.

The purpose of the signalling flow is for the RNC to inform UE(s) with particular activated MBMS service of the potential need to make an MBMS Counting Response i.e. establish an RRC connection or make a cell update. The MBMS ACCESS INFORMATION is transmitted during counting and re-counting on MCCH. The MBMS ACCESS INFORMATION includes, for each service for which counting is required, the MBMS service identifier, probability factors for idle and connected modes and an indication of the connected mode states to which the signalling flow applies.

8.3.5 MBMS Neighbouring Cell Information

Figure 8.3.5: MBMS Neighbouring Cell Information signalling flow

This signalling flow is applicable for handling MBMS to UEs in PMM IDLE and CONNECTED mode.

The purpose of the MBMS NEIGHBOURING CELL INFORMATION signalling flow is for the UTRAN to inform to UEs of the MTCH configuration of the neighbouring cells which are available for selective combining. In case of partial soft combining, the MBMS NEIGBOURING CELL INFORMATION contains the L1-combining schedule, which indicates when the soft combining is applicable between the specific S-CCPCH of the cell and the specific S-CCPCH of the neighbouring cell. With MBMS NEIGHBOURING CELL INFORMATION the UE is able to receive MTCH transmission from neighbouring cell without reception of the MCCH of that cell. The MBMS NEIGHBOURING CELL INFORMATION shall be repeatedly transmitted on MCCH when selective or soft combining is utilized in the MBMS p-t-m transmission in the given cell group.

8.3.6 MBMS Joined Indication

Figure 8.3.6: MBMS joined indication signalling flow

This signalling flow is applicable for handling MBMS to UEs in RRC-Connected, PMM-IDLE state. The MBMS JOINED INDICATION is sent over the DCCH.

The signalling flow is initiated by the UE after entering RRC-Connected, PMM-IDLE state. The purpose of the signalling flow is to enable the UE to inform the SRNC that the user has joined at least one MBMS service. The SRNC requests the MBMS services the UE has joined from the SGSN as defined in subclause 8.2.10.

In SRNC relocation this information is transmitted from source RNC to target RNC.

NOTE: If SRNC has valid linking information the complete service list of activated services is also transmitted from source RNC to target RNC in SRNC relocation.

8.3.7 MTCH Scheduling Information

Figure 8.3.7: MTCH scheduling information.

This signalling flow is applicable for handling MBMS to UEs in PMM IDLE and CONNECTED mode.

The purpose of the signalling flow is to enable UEs to perform discontinuous reception of MTCH. The UE may discontinuously receive MTCH based on scheduling information indicated by the MTCH SCHEDULING INFORMATION. This signalling is transmitted on MSCH mapped on SCCPCH carrying MTCH. The MTCH SCHEDULING INFORMATION is signalled on each MSCH repetition period. The MSCH repetition period and the offset from the cell timing are indicated on MCCH. In case of soft combining, the MSCH repetition period is same for all soft combinable S-CCPCH. The scheduling information allows to cover different periods for different MBMS services.

The MTCH SCHEDULING INFORMATION includes for each service:

– MBMS service Id (the actual coding is defined in stage-3).

– Beginning and duration of MBMS data transmission (one contiguous block or more is defined in Stage-3).

– Duration can be infinite (no DTX). This option could be signalled in the MCCH (Stage-3 definition).

– Indication of no MBMS data transmission for either this period or several consecutive periods (a period is expressed in MSCH repetition period).

8.3.8 MBMS Change Information

Figure 8.3.8: MBMS change information.

This signalling flow is applicable for handling MBMS to UEs in PMM IDLE and CONNECTED mode. UTRAN should transmit this signalling flow in beginning of each modification period on MCCH and repeat it at least in every repetition period of that modification period. UE shall read this information flow when detecting that MICH bits set for a service that UE has activated, or periodically at the begin of each modification period when receiving MTCH.

The purpose of the signalling flow is to indicate MBMS services whose MCCH information is changed in that modification period. The content of MBMS CHANGE INFORMATIO shall be minimized, so that the MCCH reading time for the UEs, activated MBMS service whose MCCH information is not modified on that modification period, is minimized.

The MBMS CHANGE INFORMATION includes:

– The MBMS service Ids for which MCCH information is modified on that modification period.

8.3.9 MBMS P-T-P Modification Request

Figure 8.3.9: MBMS P-T-P Modification Request.

This signalling flow is applicable for handling UEs with an activated service that requires MBMS p-t-p RB in PMM IDLE and CONNECTED mode. In idle mode, URA_PCH and CELL_PCH states the UE may transmit this signalling flow to request the setup of a p-t-p MBMS RB after receiving the indication on MCCH that p-t-p transfer mode is utilised or, in CELL_DCH state, to request the release of the p-t-p MBMS RB due to higher priority MBMS service, or to indicate the frequency used for transmitting the higher priority service as specified in subclause 5.2.8. This signalling flow is transmitted on DCCH or on CCCH dependent upon UE state.

UEs in idle mode are required to perform RRC connection establishment for sending this information flow. UEs that are in URA_PCH or CELL_PCH state are required to make a cell update and UEs that are in CELL_DCH state transmit an MBMS MODIFICATION REQUEST message.

When UTRAN receives this message from the UE, the UTRAN may setup or release the p-t-p MBMS RB by normal RB release procedure or , in the case of a preferred frequency being indicated, it may perform inter-frequency HHO.

The MBMS P-T-P Modification Request message includes the identity of the MBMS service when the service appears in the list of MBMS Selected Services.

8.3.10 MBMS Counting Response

Figure 8.3.10: MBMS Counting Response.

This signalling flow is applicable for UEs passing the probability check in counting procedure in idle mode or URA_PCH, CELL_PCH or CELL_FACH state. For the UE in idle mode this signalling flow refers to the complete RRC connection establishment procedure. For UEs in URA_PCH, CELL_PCH and CELL_FACH state this signalling flow refers to cell update procedure.

The MBMS Counting Response message includes the identity of the MBMS service when the service appears in the list of MBMS Selected Services.

8.3.11 MBMS Selected Services Information

Figure 8.3.11: MBMS Selected Services Information.

This signalling flow is applicable for UEs entering CELL_DCH state. The purpose of the signalling flow is to enable the UE to inform the SRNC that the user requires the reception of MBMS Selected Services. When the SRNC is not the CRNC of the UE, this signalling flow may interact with the URA linking/de-linking described in subclause 5.1.10.

This signalling flow is also applicable for UEs in CELL_DCH states, when the list of MBMS Selected Services has been modified.

This signalling flow is also applicable for UEs in CELL_PCH, URA_PCH and CELL_FACH states when the list of MBMS Selected Services has been modified by the upper layers and the MBMS Service appears in the MCCH of the cell and the RNC has indicated in the MBMS GENERAL INFORMATION message that it should be notified of a change to this list. If an MBMS Service is contained in the list of MBMS Selected Services but is currently not available in the cell, when the service appears on the MCCH the UE does not perform this signalling flow.

The purpose of the signalling flow is to enable the UE to inform the CRNC that the list of MBMS Selected Services in the UE has been modified.