11.3.8 Overview of signalling

3GPP43.069Release 17Stage 2TSVoice Broadcast Service (VBS)

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

In this overview, the messages required to implement the specified concept are identified, and brief details are given of each message.

A diagrammatic representation of the voice broadcast call message structure proposed and actions required are given in figures 2 to 4f.

In order to simplify the message flows for voice broadcast call establishment and call termination, the interaction between the MSC and the GCR is only shown for the MSC where the originator of the broadcast call is located or, for the case of a broadcast call originated by a dispatcher, only for the anchor MSC. In all cases, a similar interaction also takes place between the other MSC(s) and associated GCR(s) involved in the group call.

Summary of figures in this subclause:

Figure 2: voice broadcast call establishment by a service subscriber roaming in the anchor MSC area;

Figure 3: voice broadcast call establishment by a service subscriber roaming in the relay MSC area;

Figure 3a: voice broadcast call establishment by a service subscriber in a RANflex configuration;

Figure 3b: voice broadcast call establishment by a mobile dispatcher or fixed line dispatcher;

Figure 3c: Signalling information required for establishing voice broadcast calls by a service subscriber in a RANflex configuration with group call redundancy

Figure 4: termination of the broadcast call by the originating service subscriber;

Figure 4a: voice broadcast call establishment by a service subscriber using immediate setup;

Figure 4b: termination of the broadcast call by an entitled mobile dispatcher controlled by the anchor MSC;

Figure 4c: termination of the broadcast call by an entitled mobile dispatcher controlled by a visited MSC;

Figure 4d: termination of the broadcast call by an entitled fixed line dispatcher.

Figure 4e: A-interface link sharing used or broadcast call re-establishment by the BSS supported: Release after equipment failure (TRX, PCM, …) concerning a cell not serving the originating service subscriber;

Figure 4f: A-interface link sharing used or broadcast call re-establishment by the BSS supported: Release after equipment failure concerning the link between MSC and BSS;

MS’

MSs

BSS

MSC-A

VLR

GCR

FNT

MSC-R

SYSY_INFO (NCH allocated)]

<——-<———-

RACH (CHAN_REQ)

——————->

IMM_ASS

<——————-

SABM (SERV_REQ)

——————->

COM_L3_INFO

—————>

PROC_ACC_REQUIREMENT

UA (SERV_REQ)

——->

<——————-

PROC_ACC_ACK

Authentication & Ciphering

<——-

<—————————————->

SETUP

——————————————>

Txx

SEND_INFO_OUT

___

——->

COMPLETE_CALL

ASS_REQ

<——-

<—————

CH_MOD_MODFY

<——————-

CH_MOD_MODFY_ACK

——————->

ASS_COMP

—————>

GCR_INT

—————–>

GCR_INT_ACK

<—————–

SETUP (to FN)

VBS_ASS_REQ

————————————–>

<—————

VBS_AREA_CELL_INFO

PREPARE_GROUP_CALL

<—————

—————————————————>

PREPARE_GROUPCALL_ACK

<—————————————————

SETUP (to MSC-R)

—————————————————>

CONNECT (from MSC-R)

<—————————————————

MS’

MSs

BSS

MSC-A

VLR

GCR

FNT

MSC-R

VBS_ASS_RESULT

SEND GROUP CALL END SIGNAL

Tast

—————>

__|_

<—————————————————–

VBS_ASS_STATUS

—————>

NOTIFY_REQ (NCH)

<———-

NOTIFY_REQ FACCH)

CONNECT (from FN)

<———-

<————————————–

CONNECT

<——————————————

PERIODIC NOTIF_REQ (NCH)

<———-

Periodic SACCH Info

NOTE: MS’ calling service subscriber mobile station;
Mss destination service subscriber mobile stations
FNT fixed network user terminal
MSC-A anchor MSC;
MSC-R relay MSC.

Figure 2: Signalling information required for establishing voice broadcast calls
by a service subscriber roaming in the anchor MSC area

SYS_INFO (NCH allocated): Message used to indicate if the NCH is allocated on the CCCH in the cell.

Initial RACH CHAN_REQ: Standard message.

IMM_ASS: Standard message sent on the AGCH.

SERV_REQ (voice broadcast call): Modified form of the current call request message L3-MM CM SERVICE REQUEST sent on the allocated channel. Teleservice voice broadcast call is indicated.

UA (SERV_REQ): This message is used to acknowledge the layer 2 link and provide contention resolution of the service request.

COM_L3_INFO: The MSC is provided with initial information about the voice broadcast call.

NOTE 1: Messages flows for authentication and ciphering are not represented although performed as normal.

PROC_ACC_REQ: The MAP_PROCESS_ACCESS_REQUEST message is sent to the VLR to check the requested VBS teleservice against the subscription data.

PROC_ACC_ACK: The MAP_PROCESS_ACCESS_REQUEST ack message acknowledges the requested service.

Authentication & Ciphering: Authentication and Ciphering may be performed. Acknowledgement of the service request can also be performed by sending the CM SERVICE ACCEPT.

SETUP: The MSC is provided with details about the voice broadcast call.

NOTE 2: Alternatively, an IMMEDIATE_SETUP may have been send as the initial message including all details of the voice broadcast call. In this case no SETUP message must be sent.

SEND_INFO_OUT: The requested group ID is transferred to the VLR in the MAP_SEND_INFO_FOR_OUTGOING_CALL message.

COMPLETE_CALL: The VLR returns the MAP_COMPLETE_CALL confirming the use of the requested group ID.

ASSIGNMENT_REQUEST: Standard message.

CHAN_MOD_MODFY: Standard message to modify the channel mode in case of very early assignment.

CHAN_MOD_MODFY_ACK: Standard message to acknowledge the modification of the channel mode.

ASSIGNMENT_COMPLETE: Standard message.

NOTE 3: Alternatively, early assignment or OACSU procedures might be applied with the corresponding assignment messages not presented in figure 2.

GCR_INT: The broadcast attributes are requested from the GCR.

GCR_INT_ACK: The requested information is returned from the GCR.

VBS_ASSIGNMENT_REQ: This message is sent from the MSC to all affected BSCs, [one dedicated message for every requested channel in a cell] including the broadcast call reference, the channel type and possibly the call priority and details on the ciphering.

In case of AoIP this message shall contain call identifier, codec list and AoIP Transport layer address information.

NOTE 4: As an operator option the voice broadcast channels, the links to them and optionally also the links to dispatchers can already be established and permanently reserved in order to speed up the call set-up for emergency voice broadcast calls.

In case of A-interface link sharing this message shall contain a list of all cells in the group call area served by this BSC. If the entire list of cell identifiers does not fit into the message, one or more VBS AREA CELL INFO messages with additional cell identifier lists shall be sent. If the cell of origin is served by this BSC, the cell shall be included in the VBS ASSIGNMENT REQUEST message.

VBS_AREA_CELL_INFO: This message shall contain the cell IDs that did not fit into the VBS ASSIGNMENT REQUEST message in case of A-interface link sharing.

PREPARE_GROUP_CALL: The broadcast attributes are sent to every relay MSC and a Group Call number for call set-up to is requested.

PREPARE_GROUP_CALL_ACK: The Group Call number for call set-up is returned to the anchor MSC.

SETUP to MSC-R: The ISUP connection is set-up to the relay MSC.

CONNECT from MSC-R: Set-up of the ISUP connection to the relay MSC is confirmed.

SEND_GROUP_CALL_END_SIGNAL: Indicates to the anchor MSC that at least one downlink channel has been established in the relay MSC area.

VBS_ASSIGNMENT_RESULT: Acknowledgement message from the affected BSC in answer to the assignment request. If the assignment is not successful, a VBS_ASSIGNMENT_FAILURE message shall be sent instead.

In case of A-interface link sharing this message shall be sent as soon as a channel could be established to the cell of origin or, if the cell of origin is not served by this BSC, to any other cell. Then timer Tast shall be started.

In case of AoIP this message shall contain AoIP Transport layer address, call identifier and speech codec information.

Tast: In a network supporting A-interface link sharing timer Tast shall be used to measure the duration between periodic reports from the BSC to the MSC of Group Call Area cells for which channels have been assigned or released since the last periodic report. When timer Tast expires, if new cells in the Group Call Area have been established or existing ones have been released, pre-empted or failed, the MSC shall be informed of the changes (see subclause 7.1b). Timer Tast shall be started again to measure the period of time until the next report. The timer shall be stopped when the call is released.

VBS_ASSIGNMENT_STATUS: This message shall be sent in case of A-interface link sharing from the BSC to inform the MSC about the status of the channel establishment to the cells of a given VBS call. This message shall be sent after timer Tast expires and new channels are established or existing channels were released, pre-empted or failed. This message shall also be immediately sent, and Tast restarted, when all cells for a given group call area served by the BSC are established, indicating this.

SETUP to fixed network users: Based on the information determined about the users of external networks to be involved in the call, the MSC shall initiate calls to these users in the normal manner, depending on their mode of connection into the MSC, and shall connect them to the distribution function. Alternatively normal calls to GSM subscribers may be established for dispatchers being GSM subscribers which are not presented in the diagram.

Txx: Timer implemented in the MSC which is started with receipt of the SETUP message from the calling service subscriber. If the timer expires before the conditions for establishment have been met, as per subclause 11.3.1.1.2, then the call shall be released.

NOTIF_REQ (NCH): Messages for notification which contain the broadcast call reference, the priority of the call if eMLPP is applied, and possibly the channel description of the voice broadcast channel to which the mobile stations shall listen and the number of the group key used for ciphering.

NOTIF_REQ (FACCH): Message for notification sent on the FACCH to the mobile stations currently involved in other calls. The notification on the FACCH can include the broadcast call reference, and the priority level and may also include the channel description and the group ciphering key numbers.

Periodic NOTIF_REQ (NCH): The notifications are sent periodically so that mobile stations moving into the area can join the voice broadcast call.

Periodic SACCH Info: Periodic messages sent on SACCH. This message may include:

– information of changes of notifications;

– information used for cell reselection.

CONNECT: Information to the mobile station of the calling service subscriber that the VBS is established with the related broadcast call reference as the connected number. The CONNECT message is sent as soon as conditions for establishment are met, as per subclause 11.3.1.1.2.

MS’

MSs

BSS

MSC-R

VLR

GCR

MSC-A

SYSY_INFO (NCH allocated)]

<——-<———-

RACH (CHAN_REQ)

——————->

IMM_ASS

<——————-

SABM (SERV_REQ)

——————->

COM_L3_INFO

—————>

PROC_ACC_REQUIREMENT

UA (SERV_REQ)

——->

<——————-

PROC_ACC_ACK

Authentication & Ciphering

<——-

<—————————————->

SETUP

——————————————>

SEND_INFO_OUT

——->

COMPLETE_CALL

ASS_REQ

<——-

<—————

CH_MOD_MODFY

<——————-

CH_MOD_MODFY_ACK

——————->

ASS_COMP

—————>

GCR_INT

—————–>

GCR_INT_ACK

<—————–

SETUP (to MSC-A)

Txx

—————————————————>

___

PREPARE_GROUP_CALL

<—————————————————

GCR_INT

—————–>

GCR_INT_ACK

<—————–

ALLOCATE GROUP CALL NUMBER

——->

ALLOCATE GROUP CALL NUMBER ACK

<——-

PREPARE_GROUP_CALL_ACK

—————————————————>

MS’

MSs

BSS

MSC-R

VLR

GCR

MSC-A

SETUP (from MSC-A)

<—————————————————

RELEASE GROUP CALL NUMBER

——->

VBS_ASS_REQ

<—————

VBS_AREA_CELL_INFO

<—————

VBS_ASS_RESULT

Tast

—————>

CONNECT (to MSC-A)

—————————————————>

VBS_ASS_STATUS

_|_

—————>

NOTIFY_REQ (NCH)

<———-

NOTIFY_REQ FACCH)

SEND_GROUP_CALL_END_SIGNAL (IMSI)

<———-

—————————————————>

__|_

CONNECT (from MSC-A)

CONNECT

<—————————————————

<——————————————

PERIODIC NOTIF_REQ (NCH)

<———-

Periodic SACCH Info

NOTE: MS’ = calling service subscriber mobile station;
Mss = destination service subscriber mobile stations;
MSC-A = anchor MSC;
MSC-R = relay MSC.

Figure 3: Signalling information required for establishing voice broadcast calls
by a service subscriber roaming in the relay-MSC area

SYS_INFO (NCH allocated): Message used to indicate if the NCH is allocated on the CCCH in the cell.

Initial RACH CHAN_REQ: Standard message.

IMM_ASS: Standard message sent on the AGCH.

SERV_REQ (voice broadcast call): Modified form of the current call request message L3-MM CM SERVICE REQUEST sent on the allocated channel. Teleservice Voice broadcast call is indicated.

UA (SERV_REQ): This message is used to acknowledge the layer 2 link and provide contention resolution of the service request.

COM_L3_INFO: The MSC is provided with initial information about the voice broadcast call.

NOTE 5: Messages flows for authentication and ciphering are not represented although performed as normal.

PROC_ACC_REQ: The MAP_PROCESS_ACC_REQ message is sent to the VLR to check the requested VBS teleservice against the subscription data.

PROC_ACC_ACK: The MAP_PROCESS_ACC_ACK message acknowledges the requested service.

Authentication & Ciphering: Authentication and Ciphering may be performed. Acknowledgement of the service request can also be performed by sending the CM SERVICE ACCEPT.

SETUP: The MSC is provided with details about the voice broadcast call.

NOTE 6: Alternatively, an IMMEDIATE_SETUP may have been send as the initial message including all details of the voice broadcast call. In this case no SETUP message must be sent.

SEND_INFO_OUT: The requested group ID is transferred to the VLR in the MAP_SEND_INFO_FOR_OUTGOING_CALL message.

COMPLETE_CALL: The VLR returns the MAP_COMPLETE_CALL message confirming the use of the requested group ID.

ASSIGNMENT_REQUEST: Standard message.

CHAN_MOD_MODFY: Standard message to modify the channel mode in case of very early assignment.

CHAN_MOD_MODFY_ACK: Standard message to acknowledge the modification of the channel mode.

ASSIGNMENT_COMPLETE: Standard message.

NOTE 7: Alternatively, early assignment or OACSU procedures might be applied with the corresponding assignment messages not presented in this figure.

GCR_INT: The broadcast call attributes are requested from the GCR.

GCR_INT_ACK: The requested information (MSC-A address) is returned from the GCR.

SETUP to MSC-A: Based on information received from the GCR the relay MSC shall set-up a dedicated connection for the calling service subscriber to the anchor MSC. The VBS prefix plus broadcast call reference shall be sent as calling party number, and the address of the calling service subscriber’s relay MSC shall be sent as generic number parameter, with the number qualifier indicator set to "additional calling party number".

PREPARE_GROUP_CALL: The broadcast call attributes (parts) are received from the anchor MSC.

GCR_INT: The broadcast call attributes are requested from the GCR.

GCR_INT_ACK: The requested information (cell list) is returned from the GCR.

ALLOCATE GROUP CALL NUMBER: The Group Call number is requested from the VLR.

ALLOCATE GROUP CALL NUMBER ACK: The Group Call number is returned from the VLR.

PREPARE_GROUP_CALL_ACK: The Group Call number is sent to MSC-A.

SETUP from MSC-A: The ISUP connection is set-up between MSC-A and MSC-R.

RELEASE GROUP CALL NUMBER: The VLR is requested to release the Group Call number.

VBS_ASSIGNMENT_REQ: This message is sent from the MSC to all affected BSCs, [one dedicated message for every requested channel in a cell,] including the broadcast call reference, the channel type and possibly the call priority and details on the ciphering.

NOTE 8: As an operator option the voice broadcast call channels, the links to them and optionally also the links to dispatchers can already be established and permanently reserved in order to speed up the call set-up for emergency voice broadcast calls.

In case of AoIP this message shall contain call identifier, codec list and AoIP Transport layer address information.

VBS_AREA_CELL_INFO: This message shall contain the cell IDs that did not fit into the VBS ASSIGNMENT REQUEST message in case of A-interface link sharing.

VBS_ASSIGNMENT RESULT: Acknowledgement message from the affected BSC in answer to the assignment requests. If the assignment is not successful, a VBS_ASSIGNMENT_FAILURE message shall be sent instead.

In case of AoIP this message shall contain AoIP Transport layer address, call identifier and speech codec information.

Tast: In a network supporting A-interface link sharing timer Tast shall be used to measure the duration between periodic reports from the BSC to the MSC of Group Call Area cells for which channels have been assigned or released since the last periodic report. When timer Tast expires, if new cells in the Group Call Area have been established or existing ones have been released, pre-empted or failed the MSC shall be informed of the changes (see subclause 7.1b). Timer Tast shall be started again to measure the period of time until the next report. The timer shall be stopped when the call is released.

VBS_ASSIGNMENT_STATUS: This message shall be sent in case of A-interface link sharing from the BSC to inform the MSC about the status of the channel establishment to the cells of a given VBS call. This message shall be sent after timer Tast expires and new channels are established or existing channels are released, pre-empted or failed. This message shall also be immediately sent, and Tast restarted, when all cells for a given group call area served by the BSC are established, indicating this.

CONNECT to MSC-A: Set-up of the ISUP connection from the anchor MSC is confirmed.

SEND_GROUP_CALL_END_SIGNAL (IMSI): This message is sent by the relay MSC on receipt of the VBS ASSIGNMENT RESULT message for the cell in which the call was originated. The IMSI of the calling service subscriber who has established the voice broadcast call indicates to the anchor MSC that this message is sent by the relay MSC where the call was originated and that conversation can start.

If there is more than one relay MSC involved in the VBS call, all other relay MSCs send the SEND_GROUP_CALL_END_SIGNAL message to the anchor MSC when at least one downlink channel has been established in that relay MSC area. In these other SEND_GROUP_CALL_ END_SIGNAL messages no IMSI is included.

NOTIF_REQ (NCH): Messages for notification which contain the broadcast call reference, the priority of the call if eMLPP is applied, and possibly the channel description of the voice broadcast call channel to which the mobile stations shall listen and the number of the group key used for ciphering.

NOTIF_REQ (FACCH): Message for notification sent on the FACCH to the mobile stations currently involved in other calls. The notification on the FACCH shall include the broadcast call reference, and the priority level and may include also the channel description and the group ciphering key numbers.

Periodic NOTIF_REQ (NCH): The notifications are sent periodically so that mobile stations moving into the area can join the voice broadcast call.

Periodic SACCH Info: Periodic messages sent on the downlink of the SACCH. This message may include:

– information of changes of notifications;

– information used for cell reselection.

CONNECT (from MSC-A): Call set-up of the dedicated connection for the calling service subscriber is confirmed.

NOTE: MS’ = calling service subscriber mobile station;
MSs = destination service subscriber mobile stations;
MSC-A = anchor MSC;
MSC-R = relay MSC;
V-MSC = visited MSC

Figure 3a: Signalling information required for establishing voice broadcast calls
by a service subscriber in a RANflex configuration

SYS_INFO (NCH allocated): Message used to indicate if the NCH is allocated on the CCCH in the cell.

Initial RACH CHAN_REQ: Standard message.

IMM_ASS: Standard message sent on the AGCH.

SERV_REQ (voice broadcast call): Modified form of the current call request message L3-MM CM SERVICE REQUEST sent on the allocated channel. Teleservice Voice broadcast call is indicated.

UA (SERV_REQ): This message is used to acknowledge the layer 2 link and provide contention resolution of the service request.

COM_L3_INFO: The MSC is provided with initial information about the voice broadcast call.

NOTE 8a: Messages flows for authentication and ciphering are not represented although performed as normal.

PROC_ACC_REQ: The MAP_PROCESS_ACC_REQ message is sent to the VLR to check the requested VBS teleservice against the subscription data.

PROC_ACC_ACK: The MAP_PROCESS_ACC_ACK message acknowledges the requested service.

Authentication & Ciphering: Authentication and Ciphering may be performed. Acknowledgement of the service request can also be performed by sending the CM SERVICE ACCEPT.

SETUP: The MSC is provided with details about the voice broadcast call.

NOTE 8b: Alternatively, an IMMEDIATE_SETUP can be sent as the initial message including all details of the voice broadcast call. In this case no SETUP message is sent.

SEND_INFO_OUT: The requested group ID is transferred to the VLR in the MAP_SEND_INFO_FOR_OUTGOING_CALL message.

COMPLETE_CALL: The VLR returns the MAP_COMPLETE_CALL message confirming the use of the requested group ID.

SEND_GROUP_CALL_INFO: The MSC derives from the originating cell’s LAC the address of the group call serving MSC and sends MAP_SEND_GROUP_CALL_INFO to it, to retrieve the MSC-A address.

GCR_INT: The broadcast call reference and MSC-A address are requested from the GCR through the GCR Interrogation message sent by the MSC.

GCR_INT_ACK: The requested information (MSC-A address) is returned from the GCR in the GCR Interrogation Ack message.

SEND_GROUP_CALL_INFO_ACK: The requested information is returned to the visited MSC.

ASSIGNMENT_REQUEST: Standard message.

CHAN_MOD_MODIFY: Standard message to modify the channel mode in case of very early assignment.

CHAN_MOD_MODIFY_ACK: Standard message to acknowledge the modification of the channel mode.

ASSIGNMENT_COMPLETE: Standard message.

NOTE 8c: Alternatively, early assignment or OACSU procedures might be applied with the corresponding assignment messages not presented in figure 3a.

SETUP to MSC-A: Based on information received from the group call serving MSC the VMSC shall set-up a dedicated connection for the calling service subscriber to the anchor MSC. The VBS prefix plus broadcast call reference shall be sent as calling party number, and the address of the calling service subscriber’s group call serving MSC shall be sent as generic number parameter, with the number qualifier indicator set to "additional calling party number".

PREPARE_GROUP CALL: The broadcast call attributes (parts) are received from the anchor MSC.

GCR_INT: The broadcast call attributes are requested from the GCR through the GCR Interrogation message sent by the MSC.

GCR_INT_ACK: The requested information (cell list) is returned from the GCR in the GCR Interrogation Ack message.

ALLOCATE GROUP CALL NUMBER (not shown in figure 3a): MSC-R requests the group call number from its associated VLR

ALLOCATE GROUP CALL NUMBER ACK (not shown in figure 3a): The Group Call number is returned from the VLR.

PREPARE_GROUP_CALL_ACK: The Group Call number is sent to MSC-A.

SETUP from MSC-A: The ISUP connection is set-up between MSC-A and MSC-R.

RELEASE GROUP CALL NUMBER (not shown in figure 3a): The VLR is requested to release the Group Call number.

VBS_SETUP: This message is sent from the MSC to all affected BSCs, [one dedicated message for each BSC,] including the broadcast call reference with the eMLPP priority, and optionally the call priority.

VBS_SETUP_ACK: Acknowledgement message from the affected BSC in answer to the VBS_SETUP setup message. If the setup is not successful, a VBS_SETUP_REFUSE message shall be sent instead.

In case of AoIP this message shall contain call identifier, codec list and AoIP Transport layer address information.

NOTE 8d: As an operator option the voice broadcast call channels, the links to them and optionally also the links to dispatchers can already be established and permanently reserved in order to speed up the call set-up for emergency voice broadcast calls.

In case of AoIP this message shall contain AoIP Transport layer address, call identifier and speech codec information.

CONNECT to MSC-A: Set-up of the ISUP connection from the anchor MSC is confirmed.

SEND_GROUP CALL_END_SIGNAL (IMSI): This message is sent by the relay MSC on receipt of the VBS ASSIGNMENT RESULT message for the cell in which the call was originated. The IMSI of the calling service subscriber who has established the voice broadcast call indicates to the anchor MSC that this message is sent by the relay MSC where the call was originated and that conversation can start.

NOTIF_REQ (NCH): Messages for notification which contain the broadcast call reference, the priority of the call if eMLPP is applied, and possibly the channel description of the voice broadcast call channel to which the mobile stations shall listen and the number of the group key used for ciphering.

CONNECT (from MSC-A): Call set-up of the dedicated connection for the calling service subscriber is confirmed.

CONNECT: Information to the mobile station of the calling service subscriber that the VBS is established with the related broadcast call reference as the connected number.

Periodic NOTIF_REQ (NCH): The notifications are sent periodically so that mobile stations moving into the area can join the voice broadcast call.

Periodic SACCH Info: Periodic messages sent on the downlink of the SACCH informing mobile stations of:

– information of changes of notifications;

– information used for cell re-selection.

NOTE: DP = dispatcher;

MSs = destination subscriber mobile stations;
MSC-A = anchor MSC;
MSC-R = relay MSC;

V-MSC = visited MSC;

GMSC = Gateway MSC

Figure 3b: Signalling information required for establishing voice broadcast calls
by a mobile dispatcher or fixed line dispatcher

SETUP: Mobile dispatcher or fixed line dispatcher sets up a VGCS call. The visited MSC or the Gateway MSC receives the SETUP message with details about the voice broadcast call including the Group Call Reference within the MSISDN dialled by the originating dispatcher.

SETUP (IAM): The visited MSC or the Gateway MSC sends an IAM message to the anchor MSC of the group call based on the called party MSISDN number.

SETUP (Mobile dispatcher in anchor MSC area): If the originating mobile dispatcher is located in the anchor MSC area, the SETUP message with details about the voice broadcast call including the Group Call Reference within the MSISDN dialled by the originating dispatcher is received directly by the anchor MSC (further messages regarding the standard SETUP procedure are not drawn in the Fig.)

SEND_INFO_OUT: The requested group ID is transferred to the VLR in the internal MAP_SEND_INFO_FOR_OUTGOING_CALL message.

COMPLETE_CALL: The VLR returns the MAP_COMPLETE_CALL message confirming the use of the requested group ID.

GCR_INT: The group call attributes are requested from the GCR through the GCR Interrogation message sent by the MSC.

GCR_INT_ACK: The requested information is returned from the GCR in the GCR Interrogation Ack message.

VBS_SETUP: Anchor MSC sends to BSS’s a VBS SETUP message across VBS call controlling SCCP connection to initiate a VBS call set-up procedures.

VBS SETUP ACK: After receiving the VBS_SETUP message, BSS will allocate resources to the call and returns VBS SETUP ACK message to the MSC. This connection is established for the lifetime of the VBS call.

VBS_ASSIGNMENT_REQ: This message is sent from the MSC to all affected BSCs, [one dedicated message for every requested channel in a cell,] including the group call reference, the channel type and possibly the call priority and details on the ciphering. In case of AoIP this message shall contain call identifier, codec list and AoIP Transport layer address information.

PREPARE_GROUP CALL: The group call attributes are sent to every relay MSC and a Group Call number for call set-up to is requested.

PREPARE_GROUP CALL ACK: The Group Call number for call set-up is returned to the anchor MSC.

SETUP to MSC-R: The ISUP connection is set-up to the relay MSC.

VBS_SETUP: Relay MSC sends to BSSs a VBS SETUP message to initiate a VBS call set-up procedures.

VBS_ASSIGNMENT_REQ: This message is sent from the relay MSC to all affected BSCs, [one dedicated message for every requested channel in a cell,] including the group call reference, the channel type and possibly the call priority and details on the ciphering. In case of AoIP this message shall contain call identifier, codec list and AoIP Transport layer address information.

CONNECT from MSC-R: Set-up of the ISUP connection to the relay MSC is confirmed.

In case of AoIP this message shall contain AoIP Transport layer address, call identifier and speech codec information.

SEND_GROUP CALL_END_SIGNAL: Indicates to the anchor MSC that at least one voice broadcast call channel has been established in the relay MSC area.

Txx: Timer implemented in the anchor MSC which is started with receipt of the SETUP message from the dispatcher. If the timer expires before the conditions for establishment have been met, as per subclause 11.3.1.1.2, then the call shall be released.

NOTIF_REQ (NCH): Messages for notification which contain the group call reference, the priority of the call if eMLPP is applied, and possibly the channel description of the voice broadcast call channel to which the mobile stations shall listen and the number of the group key used for ciphering.

NOTIF_REQ (FACCH): Message for notification sent on the FACCH to the mobile stations currently involved in other calls. The notification on the FACCH shall include the group call reference; and the priority level and may also include the channel description and the group ciphering key numbers.

CONNECT: Information to the originating that the VBS is established with the related group call reference as the connected number.

Periodic NOTIF_REQ (NCH): The notifications are sent periodically so that mobile stations moving into the area can join the voice broadcast call.

Periodic SACCH Info: Periodic messages sent on SACCH. This message may include:

– information of changes of notifications;

– information used for cell re-selection.

Figure 3c: Signalling information required for establishing voice broadcast calls
by a service subscriber in a RANflex configuration with group call redundancy

See also figure 3a

1. SEND_GROUP_CALL_INFO: The V-MSC derives from the originating cell’s LAC the address of the group call serving MSC redundancy pool and sends MAP_SEND_GROUP_CALL_INFO to it, to retrieve the group call anchor MSC redundancy pool address. Network routing shall be configured so that the message is routed to one of the available MSCs within the redundancy pool. In this example MSC-R1 is selected. The message includes initial talker information.

2. GCR_INT: MSC-R 1 requests from its associated GCR the group call reference and group call anchor MSC redundancy pool address. The message may contain initial talker information.

3a. SYNC_GCR: Initial Talker Information is propagated to all GCRs associated to MSCs within the redundancy pool.

3b. GCR_INT_ACK: The requested information is returned from the GCR in the GCR Interrogation Ack message. To avoid glare cases GCR 1 may need to wait for message 5 before sending message 3b.

4. SEND_GROUP_CALL_INFO_ACK: The requested information is returned to the visited MSC.

5. SYNC_GCR_ACK: Successfull GCR synchronization is acknowledged.

6. SETUP to MSC-A: Based on information received from the group call serving MSC the VMSC shall set-up a dedicated connection for the calling service subscriber to the group call anchor MSC redundancy pool. Network routing shall be configured so that the message is routed to one of the available MSCs within the redundancy pool. In this example MSC-A1 is selected. The VBS prefix plus broadcast call reference shall be sent as calling party number. The address of the calling service subscriber’s group call serving MSC pool shall be sent as generic number parameter, with the number qualifier indicator set to "additional calling party number"; this shall be the same address as used to route message 1.

7. GCR_INT: MSC-A 1 requests from its associated GCR the broadcast call attributes and maks the broadcast call "on-going".

8a. SYNC_GCR: The "on-going" indication is propagated to all GCRs associated to MSCs within the redundancy pool.

8b. GCR_INT_ACK: The requested information is returned from the GCR in the GCR Interrogation Ack message. To avoid glare cases GCR 3 may need to wait for message 9 before sending message 8b.

9. SYNC_GCR_ACK: Successfull GCR synchronization is acknowledged.

10. PREPARE_GROUP_CALL: MSC-A 1 sends PREPARE_GROUP_CALL to the group call relay MSC redundancy pool. Network routing shall be configured so that the message is routed to one of the available MSCs within the redundancy pool. In this example MSC-R2 is selected.

11. GCR_INT: MSC-R 2 interrogates its associated GCR to retrieve the group call attributes and initial talker information and to mark the broadcast call "on-going" and to delete the initial talker information.

12a. SYNC_GCR: The "on-going" indication is propagated to all GCRs associated to MSCs within the redundancy pool.

12b. GCR_INT_ACK: The requested information is returned from the GCR in the GCR Interrogation Ack message.

13. SYNC_GCR_ACK: Successfull GCR synchronization is acknowledged.

ALLOCATE GROUP CALL NUMBER (not shown in figure 8a): MSC-R2 requests the Group Call number from its associated VLR

ALLOCATE GROUP CALL NUMBER ACK (not shown in figure 8a): The Group Call number is returned from the VLR.

14. PREPARE_GROUP_CALL_ACK: The Group Call number is sent to MSC-A1.

15. SETUP from MSC-A1: The ISUP connection is set-up between MSC-A1 and MSC-R2 using the Group Call number received in step 14.

RELEASE GROUP CALL NUMBER (not shown in figure 8a): The VLR is requested to release the Group Call number.

16a. CONNECT to MSC-A: Set-up of the ISUP connection from the anchor MSC is confirmed.

16b. SEND_GROUP CALL_END_SIGNAL (IMSI): Indicates to the anchor MSC that conversation can start. In addition the IMSI of calling service subscriber who has established the voice group call and who is allowed to terminate the call is included. After sending message 16b MSC-R2 deletes initial talker information (if any) as it may be invalid due to a lost race condition. Valid initial talker information (if any) may be received with message 17b.

17. CONNECT (from MSC-A): Call set-up of the dedicated connection for the calling service subscriber is confirmed.

MS’

MSs

BSS

MSC-A

GCR

FNT

MSC-R

TERMINATION REQUEST

Release

(NOTE 9)

——————————————>

<————————————-

(Specific DTMF message sequence for call termination (NOTE 9a))

(Specific DTMF tone sequence for call termination (NOTE 9b))

——————————————>

<—————————————————–

(Specific DTMF tone sequence for call termination (NOTE 9c))

<—————————————

TERMINATION

<——————————————

Release

(NOTE 10)

<—————————————————

CLEAR CMD

Dispatcher release

<—————

————————————–>

CHANNEL RELEASE

VBS_TERMIN

<——————-

—————–>

CHANNEL RELEASE

Release

<———-

—————————————————>

CLEAR COM

—————>

SEND_GROUP CALL_END_SIGNAL_ACK

SCCP_RLSD

—————————————————>

<—————

SCCP_RLC

—————>

CLEAR CMD

<—————

CLEAR COM

—————>

SCCP_RLSD

<—————

SCCP_RLC

—————>

Figure 4: Signalling required to disconnect the voice broadcast call

TERMINATION REQUEST: The calling service subscriber’s mobile station can send a TERMINATION REQUEST message to clear down the entire voice broadcast call.

NOTE 9: Alternatively an authorized dispatcher can terminate the voice broadcast call in which case a release message is received from the external network.

NOTE 9a: Alternatively an authorized mobile dispatcher can terminate the voice broadcast call by using a specific DTMF message sequence. If the mobile dispatcher is controlled by the anchor MSC, the specific DTMF message sequence is received by the anchor MSC (see figure 4b).

NOTE 9b: If the mobile dispatcher is controlled by a relay MSC, the specific DTMF message sequence is received by the relay MSC. The relay MSC converts the DTMF messages into DTMF tones and sends them towards the anchor MSC (see figure 4c).

NOTE 9c: Alternatively an authorized fixed line dispatcher can terminate the voice broadcast call by using a specific DTMF tone sequence. In this case, the specific DTMF tone sequence is received by the anchor MSC (see figure 4d).

NOTE 10: Alternatively the calling service subscriber currently served by the relay-MSC can terminate the call in which case a release message is received from the relay MSC on the dedicated connection.

CLEAR CMD: This message is sent from the MSC to the BSS via each Resource Controlling SCCP connection to clear radio and terrestrial resources.

VBS_TERMIN: The MSC informs the GCR that the voice broadcast call with the related broadcast call reference is terminated.

CHANNEL RELEASE: CHANNEL RELEASE messages are sent to the calling subscriber and on all downlink FACCH to the service subscribers. The CHANNEL RELEASE messages shall be repeated for a predefined period in order to provide a high probability that the listening mobile stations receive the message.

– CHANNEL RELEASE message is sent using I frame for the calling subscriber.

– CHANNEL RELEASE messages are sent using UI frames for listeners.

In addition, release messages are sent to all related dispatchers and relay MSCs.

SEND_GROUP CALL_END_SIGNAL_ACK: The dialogues to all relay MSCs are closed.

CLEAR COMPLETE: standard message.

SCCP_RLSD: standard message sent via resource controlling SCCP connection.

SCCP_RLC: standard message.

CLEAR CMD: This message is sent from the MSC to the BSS via the Call Controlling SCCP connection, after all the terrestrial resources associated with the BSS for this broadcast call have been released.

CLEAR COMPLETE: standard message.

SCCP_RLSD: standard message sent via call controlling SCCP connection.

SCCP_RLC: standard message.

MS		BTS		BSC		MSC
\|	*From the VBS call originator*	\|		\|		\|
\|		\|		\|		\|
\|	SYS_INFO (NCH allocated)	\|		\|		\|
\|		\|		\|		\|
\|		\|		\|		\|
\|	Channel_request	\|		\|		\|
\|		\|	channel_required	\|		\|
\|		\|		\|		\|
\|		\|	channel_activate(SDCCH)	\|		\|
\|		\|		\|		\|
\|		\|	channel_activate_ack	\|		\|
\|		\|		\|		\|
\|		\|	imm_assignment_command	\|		\|
\|	Imm_assignment	\|		\|		\|
\|		\|		\|		\|
\|	SABM(Immediate _setup)	\|		\|		\|
\|		\|	est_ind(Immediate _setup)	\|		\|
\|	UA(immediate_setup)	\|		\|	SCCP_CR((COMPLETE LAYER 3 INFORMATION (Immediate_setup)	\|
\|		\|		\|		\|
\|		\|		\|	SCCP_CC	\|
\|		\|		\|		\|
\|		\|		\|	assignment_req	\|
\|		\|	channel_activate(TCH)	\|		\|
\|		\|		\|		\|
\|		\|	channel_activate_ack	\|		\|
\|		\|		\|		\|
\|	assignment_command	\|	assignment_command	\|		\|
\|		\|		\|		\|
\|	SABM	\|		\|		\|
\|		\|	est_ind	\|		\|
\|	UA	\|		\|		\|
\|		\|		\|		\|
\|	assignment_comp	\|	assignment_comp	\|		\|
\|		\|		\|	assignment_comp	\|
\|		\|		\|		\|
\|		\|	RF_channel_release(SDCCH)	\|		\|
\|		\|		\|		\|
\|		\|	RF_channel_release_ack	\|		\|
\|		\|		\|		\|
\|		\|		\|		\|
\|		\|		\|	*For each BSC in the Group*	\|
\|		\|		\|		\|
\|		\|		\|	Same as Standard case	\|
\|		\|		\|		\|
\|		\|		\|	*For each cell in the Group*	\|
\|		\|		\|		\|
\|		\|		\|	Same as Standard case	\|

Figure 4a: Signalling information required for establishing voice broadcast calls
by a service subscriber using immediate setup

SYS_INFO (NCH allocated): Message used to indicate if the NCH is allocated on the CCCH in the cell.

Initial RACH CHAN_REQ: Standard message.

IMM_ASSIGNMENT: Standard message sent on the AGCH.

IMMEDIATE_SETUP: This message including all details of the broadcast call is sent by the MS to the network in order to set-up a broadcast call immediately, i.e. without previous establishment of an MM connection.

UA (IMMEDIATE_SETUP): This message is used to acknowledge the layer 2 link and provide contention resolution of the immediate setup.

NOTE 11: Authentication and/ or activation of Ciphering may be performed before or after sending a CONNECT message. If ciphering has not been activated before sending a CONNECT message, a CM_SERVICE ACCEPT may be sent before the CONNECT message by the MSC, however sending of the CM_SERVICE_ACCEPT is not mandatory.

Figure 4b: Signalling required for broadcast call termination by an entitled mobile dispatcher, if the mobile dispatcher is controlled by the anchor MSC of the broadcast call.

Figure 4c: Signalling required for broadcast call termination by an entitled mobile dispatcher, if the mobile dispatcher is controlled by a visited MSC (could be a relay MSC) of the broadcast call.

Figure 4d: Signalling required for broadcast call termination by an entitled fixed line dispatcher.

NOTE: The terrestrial resource for the broadcast call channel is not released.

Figure 4e: A-interface link sharing used or broadcast call re-establishment by the BSS supported: release after equipment failure (TRX, PCM …) concerning a cell that is not serving the originating service subscriber

If A-interface link sharing is used or broadcast call re-establishment by the BSS is supported, and a failure concerning a cell that is not serving the originating service subscriber was detected, the BSS shall send the VBS ASSIGNMENT STATUS message indicating that the connection to this cell is no longer established (see figure 4e). If A-interface link sharing is used, the VBS ASSIGNMENT STATUS message shall be sent on expiry of timer Tast.

Figure 4f: A-interface link sharing used or broadcast call re-establishment by the BSS supported: release after equipment failure concerning the link between MSC and BSS

If A-interface link sharing is used or broadcast call re-establishment by the BSS is supported, the BSC shall send the message CLEAR REQUEST with cause value "equipment failure" or another appropriate cause value, if a failure concerning the link between MSC and BSS was detected and the resources related to this connection shall be released (see figure 4f). After receipt of the CLEAR REQUEST message the MSC shall send a CLEAR COMMAND message for the respective connection and try to establish a new connection.