MBMS Advanced Signalling Examples

MBMS Service Activation

The following scenario gives an example message flow for UE joining an MBMS service. The example chosen is the one where the UE is in DRNC in state Cell-DCH receiving possible other services. This is the first UE joining the MBMS service in SRNC and DRNC.

  1. UE performs NAS procedure for MBMS Service Activation or having activated the service previously goes into PMM connected state. UE is in a cell in the DRNC. There is no MBMS context for this service in the DRNC.
  2. The Core Network initiates the MBMS UE Linking procedure by sending RANAP MBMS UE Linking Request message to provide the SRNC with the list of MBMS Service Ids activated by this UE. (Parameters: TMGIs, PTP RB id)
  3. RNC sends an RANAP MBMS UE Linking Response message to Core Network after RNC updates the MBMS Service Context.
  4. As the SRNC has no MBMS context for this service, it does not know the IP Multicast address or APN for this service. The SRNC request these from the SGSN using the connectionless RANAP Uplink Information Exchange Request message. (Parameters: TMGI.)
  5. SGSN responds with RANAP Uplink Information Exchange Response message. (Parameters: TMGI, IP Multicast Address and APN.)
  6. UE linking in the DRNC is performed using the RNSAP MBMS Attach Command message over the Iur interface. (Parameters: TMGIs)
  7. As the DRNC has no MBMS context for this service, it does not know the IP Multicast Address and APN for this service. The DRNC request these from the SRNC using the connectionless RNSAP Information Exchange Initiation Request message. (Parameters: MBMS Bearer Service List)
  8. SRNC responds with RNSAP Information Exchange Initiation Response message (Parameters: TMGI, IP Multicast Address and APN)
  9. An MBMS Service Context for the service is created in the DRNC.
  10. The DRNC informs the Core Network that it would like to receive MBMS Session Start Request messages by sending an RANAP MBMS Registration Request message. (Parameters: Registration Request type, TMGI, IP Multicast Address, APN, Global RNC id.)
  11. Core Network replies with an RANAP MBMS Registration Response message.



MBMS Session Start

The following is an example scenario for an MBMS Session Start. The RNC decides to perform counting and offer the service over PTM bearer. The UE is receiving a lower priority MBMS service over a PTP bearer. The UE capability does not allow reception of PTP and PTM bearers simultaneously.

  1. When the MBMS session starts the SGSN informs all RNCs that is connected to this SGSN of the availability of data and requests the establishment of the User plane bearer using RANAP MBMS Session Start message . This also establishes the SCCP connection for the MBMS service. (Parameters: TMGI, Session id, Repetition number, Bearer Service type, Iu signaling connection id, RAB parameters, PDP type, Session Duration, Service Area, Frequency layer convergence flag, RA list of idle mode UEs, Global CN-id)
  2. The RNC responds with an RANAP MBMS Session Start Response message. Since there are UEs in this RNC that have joined the service, it sets up the RAB for the MBMS service. (Parameters: Iu transport layer information)
  3. CRNC updates the MICH using NBAP MBMS Notificaiton Update Command. This message is updated for every change in MICH. (Parameters: C-ID, Common Physical Channel ID, Modification Period, MICH CFN, NI Information.)
  4. RNC is in the Service Area for the service. The RNC notifies the UE(s) about the start of the MBMS service by updating the RRC MBMS Modified Services Info message on the MCCH. This is sent on DCCH for UEs in Cell-DCH and on MCCH for other UEs. (Parameters: TMGI, Session id, UE action required, MBMS preferred frequency, Continued MCCH reading)
  5. RNC takes a decision to perform UE counting in order to evaluate what is the optimal method for MBMS delivery.
  6. RNC requests UE to set up PMM connection using RRC MBMS Access Info message on MCCH. (Parameters: TMGI and probability factor.)
  7. A fraction of (or all) UEs who have joined the MBMS service establishes PMM connection towards CN. UE linking is done by the CN when Iu-ps connection is established for these UEs.
  8. After counting, CRNC has enough information to make PTP/PTM decision. In this scenario there were enough UEs to exceed the threshold to justify ptm transmission.
  9. The CRNC establishes the S-CCPCH and FACH which will carry the MTCH by using the Common Transport Channel Setup procedure.
  10. CRNC informs UE of the MTCH channel used for the MBMS service in the cell and its neighbouring cells using the RRC MBMS Common P-T-M RB Info, MBMS Current Cell P-T-M RB Info, MBMS Neighbouring Cell P-T-M RB Info messages on MCCH. (Parameters: TMGI, MBMS UTRAN Cell Group Identifier, logical channel, transport channel, physical channel information, MSCHInformation per MBMS service.)
  11. UE is receiving a lower priority MBMS service on a PTP bearer. UE capability does not allow reception of a PTP and PTM bearer simultaneously.
  12. UE requests the release of the PTP bearer for the other lower priority service using RRC MBMS Modification Request message. (Parameters: RB to be released.)
  13. RNC releases the PTP RB of the other lower priority MBMS service.
  14. MBMS data transmission for this service on the PTM bearer.
  15. RNC may request the release of the Iu connection for the UEs that were moved to PMM connected state during the counting process.



MBMS Session Start for UE in Cell-DCH in DRNC

The following is an example scenario for an MBMS Session Start for a UE in Cell-DCH in a DRNC. The DRNC decides to offer the service in PTM mode. The UE capability does not allow reception of PTP and PTM bearers simultaneously. The UE prioritises to receive MBMS service over the dedicated service.

  1. When the MBMS session starts the SGSN informs all registered RNCs of the availability of data and requests the establishment of the User plane bearer using RANAP MBMS Session Start message . This also establishes the SCCP connection for the MBMS service.
    Parameters: TMGI, Session id, Repetition number, Bearer Service type, Iu signaling connection id, RAB parameters, PDP type, Session Duration, Service Area, Frequency layer convergence flag, RA list of idle mode UEs, Global CN-id
  2. The RNCs responds with an RANAP MBMS Session Start Response message. Since there are UEs in this RNC that have joined the service, it sets up the RAB for the MBMS service.
    Parameters: Iu transport layer information
  3. CRNC makes PTP/PTM decision. In this scenario the CRNC makes a PTM decision.
  4. The CRNC as DRNC sends MBMS Channel Type Reconfiguration Indication for all the cells for which it is the DRNC to the SRNCs.
    Paramaters: DRNC-ID, C-ID, TMGI, Transmission mode (PTM)
  5. SRNC notifies users in Cell-DCH over DCCH using MBMS Modified Services information.
    Parameters: TMGI, MBMS required UE action (acquire PTM RB Info), MBMS preferred frequency
  6. PTM Radio beares are set up by CRNC.
  7. UE decides that it wants to receive MBMS service. In this scenario, the UE is not capable of receiving both PTM and dedicated services.
  8. UE invokes NAS procedures to request the release of the dedicated services.



MBMS UE Mobility from a PTP to PTM cell

This example shows a UE receiving MBMS service over a PTP bearer in the SRNC moving into DRNC area where the service is available over a PTM bearer.

  1. MBMS Service has been activated and is currently ongoing. UE is receiving the MBMS traffic using a PTP bearer. SRNC makes the decision that to add a cell in the DNRC to the active set. The Cell already has PTM bearer for the MBMS service.
  2. UE Linking is performed via using RNSAP Radio Link Setup Request message to add the radio link in the new cell.
    Parameters: MBMS Bearer Service List,
  3. MBMS service context in the DRNC is updated.
  4. DRNC responds with RNSAP RL set up response message.
    Parameters: Active MBMS Bearer Service List
  5. NBAP RL Set up procedure to set up the RL on the NodeB
  6. RRC Active Set Update to the UE to add the PTP radio link on the new cell to the active set.
  7. When the cell in the DRNC is good enough to provide MBMS service to UE, the SRNC deletes the PTP radio bearer. The RRC Radio Bearer Release message includes the "MBMS RB list released to change transfer mode" IE to indicate that the release is due to transfer mode change, i.e. PTM availability.
    Parameters (only MBMS specific ones listed): MBMS FLC capability, MBMS RB list released to change transfer mode
  8. UE is able now to read information regarding the MBMS Service on the MCCH and picks up MTCH.



MBMS UE Mobility from PTM cell to PTP cell

This example shows an example scenario for the case when the UE moves from a cell in the SRNC with PTM bearer for the MBMS service to another cell in the DRNC. The DRNC chooses PTP transmission for the service.

  1. MBMS Service has been activated and is currently ongoing. UE is in URA-PCH state in the DRNC coverage area and is receiving the MBMS traffic using a PTM bearer. UE performs cell re-selection to a cell where there is no PTM bearer for the MBMS service within the same URA.
  2. UE reads the RRC Modified Services Info and Unmodified Services Info messages on MCCH and identifies that there is no PTM bearer for the service in this cell.
  3. UE sends a RRC Cell Update message.
    Parameters: Cause Value set to MBMS reception.
  4. DRNC relays the Cell update to the SRNC in RNSAP Uplink Signalling Transfer Indication message. Since this is the first access in the DRNC for this UE (UE linking information is not available in the DRNC), the DRNC cannot include the channel type indication to the SRNC.
  5. SRNC sends MBMS ATTACH COMMAND to create a UE link in the DRNC, using the connection oriented service of the signalling bearer.
    Parameters: MBMS Bearer Service List, D-RNTI if UE in Cell_FACH/Cell_PCH or SRNC-ID+URA-ID if UE in URA-PCH.
  6. SRNC sends the RRC Cell Update Confirm message to the UE.
  7. SRNC sets up PTP bearer for all the ongoing MBMS services that the user has subscribed to and that the SRNC is not aware as being offered PTM in the cell. The RNSAP RL set up Request message also performs UE linking. UE starts to receive MBMS service over PTP bearer.
  8. DRNC is aware of activated MBMS service(s) for the UE and sends the connectionless RNSAP MBMS Channel Type Reconfiguration Indication message indicating PTP bearer type. This message includes the transmission mode for all the ongoing UE linked MBMS services.
    Parameters: DRNC-id, C-ID, TMGI, Transmission mode, S-RNTI of affected UE.
  9. SRNC releases the PTP bearers for those services that it is now aware as being offered PTM in the cell. UE starts to receive MBMS service over PTP bearer.



MBMS Session Stop and Service termination

The following example shows a scenario for MBMS session ends followed by a termination of the MBMS service.

  1. In this scenario it is assumed that an MBMS Session is ongoing with UE in DRNC receiving MBMS service over PTM bearers.
  2. End of MBMS data session;
  3. CN invokes RANAP MBMS Session Stop message towards all RNC that are explicitly or implicitly registered with the CN. RAB resources and Iu signaling connection are released.
    Parameters: MBMS CN De-registration
  4. RNCs send RANAP MBMS Session Stop Response messagess back to SGSN.
  5. DRNC as CRNC also update and remove all relevant information related to the MBMS Service on the MCCH: RRC Modified Services Info message on MCCH. Parameters: TMGI, Release PTM RB; and all RB info on the PTM bearer for the service on RRC. Common PTM RB Info, Current Cell PTM RB Info, Neighbouring Cell PTM RB Info
  6. UE releases the Radio Bearer for the MBMS service.
  7. Iub bearer is released using NBAP Common Transport Bearer release procedure.
  8. MBMS services terminates.
  9. SGSN sends a RANAP CN De-Registration Request message to all RNCs registered with the CN in order to inform the RNC that a certain MBMS Service is no longer available.
    Parameters: TMGI, Global CN-id.
  10. RNCs replies with a RANAP CN De-Registration Response message back to the SGSN.
  11. RNCs removes this MBMS service contexts and De-links all UEs from this service.



RAU during MBMS Session

The following scenario gives an example message flow for an Idle mode UE receiving MBMS service over PTM bearer crossing an RA boundary and performing a RAU update. The RA filtering option is used in the network.

  1. UE in idle mode receiving MBMS service over PTM crosses RA boundry.
  2. UE moves to connected mode and performs RA update. CN releases Iu connection on completion of RA udpate procedure. If the CN does not release Iu connection immediately, it must perform UE linking.
  3. This is first UE in the RA.
  4. Core Network sends an RANAP MBMS Session Update message to RNC after updating the RA list containing UEs.
    Parameters: Session Update ID, Delta RA list of Idle mode UEs.
  5. RNC responds with RANAP MBMS Session Update Response message. MBMS Iu bearer was already set up earlier.
    Parameters: Session update Id.
  6. RNC sends NBAP MBMS Notification Update Command to update the MICH in all the cells that is part of both the MBMS Service Area and one of the RNCīs RAs indicated in the RA to be added List IE, if this IE is included in the Delta RA List of Idle Mode UEs IE group.
    Parameters: C-ID, Common Physical Channel ID, Modification Period, MICH CFN, NI Information.
  7. SRNC as CRNC updates the MCCH using RRC MBMS Modified Services Info message on MCCH in all the cells indicated in step 6 to request UE to establish PMM connection. As this is the first UE in the RA, the SRNC does not need to peform counting.
    Parameters: MBMS Transmission id, MBMS Required UE action, Continue MCCH reading.
  8. UE establishes PMM connection. CN performs UE linking.
  9. SRNC sets up PTP radio bearer. UE starts to receive data over PTP radio bearer.








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