11.3.8 Overview of signalling

3GPP43.068Release 17Stage 2TSVoice Group Call Service (VGCS)

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 group call message structure proposed and actions required are given in figures 2 to7j.

In order to simplify the message flows for voice group call establishment and call termination, the interaction between the MSC and the GCR is only shown for the MSC where the originator of the group call is located or, for the case of a group 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 group call establishment by a service subscriber roaming in the anchor MSC area;

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

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

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

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

Figure 4: uplink access request in the anchor MSC area without talker priority (uplink free);

Figure 4a: uplink access request in the anchor MSC area with talker priority "privileged subscriber" (uplink free, subsequent talker on dedicated channel);

Figure 4b: uplink access request in the anchor MSC area with talker priority "emergency subscriber" (uplink busy, access via group call channel uplink, subsequent talker on dedicated channel);

Figure 4c: uplink access in the anchor MSC area with "emergency mode reset request" (uplink busy, access via group call channel uplink);

Figure 4d: uplink access request in the anchor MSC area with talker priority "privileged subscriber" (uplink busy, access via RACH, subsequent talker on group call channel uplink);

Figure 4e: uplink access in the anchor MSC area with "emergency mode reset request" (uplink busy, access via RACH);

Figure 5: uplink access request in the relay MSC area without talker priority (uplink free);

Figure 5a: uplink access request in the relay MSC area with talker priority "privileged subscriber" (uplink busy, access via RACH, subsequent talker on group call channel uplink);

Figure 5b: dispatcher indicates wish to speak, talker attached to the anchor MSC;

Figure 5c: dispatcher indicates wish to speak, talker attached to the relay MSC;

Figure 5d: mobile dispatcher roaming in a non-Anchor MSC area indicates wish to speak, talker attached to the anchor MSC;

Figure 6: uplink release requested by the network;

Figure 6a: uplink release requested by the network; preemption of the current talker by a privileged talker;

Figure 6b: uplink release, talker on a dedicated link (normal case);

Figure 6c: uplink release, talker on a dedicated link (loss of radio contact or equipment failure (TRX, PCM, …));

Figure 6d: uplink release, talker on group call channel (normal case);

Figure 6e: uplink release, talker on group call channel (loss of radio contact);

Figure 6f: uplink release, talker on group call channel (equipment failure (TRX, PCM, …)), group call re-establishment by the BSS not supported;

Figure 6g: release after equipment failure (TRX, PCM, …) concerning a cell not serving the talker, group call re-establishment by the BSS not supported;

Figure 6h: A-interface link sharing used or group call re-establishment by the BSS supported: Uplink release for the talker on group call channel after equipment failure (TRX, PCM …)

Figure 6i: A-interface link sharing used or group call re-establishment by the BSS supported: Release after equipment failure (TRX, PCM, …) concerning a cell not serving the talker;

Figure 6j: A-interface link sharing used or group call re-establishment by the BSS supported: Release after equipment failure concerning the link between MSC and BSS;

Figure 7: termination of the group call by the calling service subscriber;

Figure 7a: voice group call establishment by a service subscriber using immediate setup;

Figure 7b: signalling for DTMF digit entry by an entitled mobile dispatcher controlled by the anchor MSC;

Figure 7c: signalling for DTMF digit entry by an entitled mobile dispatcher controlled by a visited MSC;

Figure 7d: signalling for DTMF digit entry by an entitled fixed line dispatcher;

Figure 7e: Validation of Priority Uplink Requests for a ciphered group call;

Figure 7f: A listener in the anchor MSC area sends application-specific data to the other group call members, while the group call channel uplink in the cell is free;

Figure 7g: A talker in the anchor MSC area sends application-specific data to the other group call members;

Figure 7h: A listener in a relay MSC area sends application-specific data to the other group call members, while the group call channel uplink in the cell is free;

Figure 7i: After receiving application-specific data, a service subscriber in the anchor MSC area sends a confirmation for the received data to the other group call members, while the group call channel uplink in the cell is free;

Figure 7j: A listener in the anchor MSC area sends application-specific data that is not time-critical via RACH to the other group call members, while the talker is using the group call channel uplink in the same cell.

MS’

MSs

BSS

MSC-A

VLR

GCR

FNT

MSC-R

[SYS_INFO (NCH allocated)]

<——-<———-

RACH (CHAN_REQ)

——————->

IMM_ASS

<——————-

SABM (SERV_REQ)

——————->

COM_L3_INFO

—————>

PROC_ACC_REQ

UA (SERVICE_REQ)

——->

<——————-

PROC_ACC_ACK

Authentication & Ciphering

<——-

<—————————————->

SETUP

——————————————>

Txx

SEND_INFO_OUT

——->

COMPLETE_CALL

<——-

GCR_INT

—————–>

GCR_INT_ACK

<—————–

ASS_REQ

<—————

CH_MOD_MODFY

<——————-

CH_MOD_MODFY_ACK

——————->

ASS_COMP

—————>

SETUP (to FN)

VGCS_SETUP

————————————–>

<—————

VGCS_SETUP_ACK

PREPARE_GROUP_CALL

—————>

—————————————————>

VGCS_ASS_REQUEST

PREPARE_GROUP CALL_ACK

<—————

<—————————————————

VGCS_AREA_CELL_INFO

<—————

SETUP (to MSC-R)

—————————————————>

CONNECT (from MSC-R)

<—————————————————

MS’

MSs

BSS

MSC-A

VLR

GCR

FNT

MSC-R

VGCS_ASS_RESULT

SEND GROUP CALL END SIGNAL

Tast

—————>

_|_

<———————————————–

..|

FORWARD_GROUP_CALL_SIGNALLING (IMSI, add info)

VGCS_ASS_STATUS

_|_

—————>

———————————————–>

NOTIFY_REQ (NCH)

<———-

CONNECT (from FN)

<————————————–

NOTIFY_REQ (FACCH)

<———-

UPLINK_SEIZED_CMD

<—————

UPLINK_BUSY

<———-

CONNECT

<——————————————

VGCS_ADD_INFO

<—————

ADD_INFO

<———-

Periodic ADD_INFO (SACCH)

<———-

PERIODIC NOTIF_REQ (NCH)

<———-

Periodic SACCH Info

UPLINK_RELEASE (NOTE 4a)

——————->

UPLINK_RELEASE_IND

—————>

FORW._GROUP CALL_SIGNAL. (uplink rel ind)

———————————————->

CHAN_RELEASE

CLR_CMD

<——————-

<————-

CLR_COMP

DISC

————->

——————->

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 group 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 group call): Modified form of the current call request message L3-MM CM SERVICE REQUEST sent on the allocated channel. Teleservice Voice group 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 group call.

NOTE 1: 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 VGCS teleservice against the subscription data.

PROC_ACC_ACK: The MAP_PROCESS_ACC_ACK message acknowledges the requested service.

Authentication and 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 group call. Optionally this message may contain a talker priority.

NOTE 2: Alternatively, an IMMEDIATE_SETUP may have been send as the initial message including all details of the voice group 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. The VLR also returns additional information about the calling service subscriber, if available.

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.

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.

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

VGCS_SETUP_ACK: Acknowledgement message from the affected BSC in answer to the VGCS_SETUP message. If the setup is not successful, a VGCS_SETUP_REFUSE message shall be sent instead.

VGCS_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.

NOTE 4: As an operator option the voice group 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 group 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 VGCS 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 VGCS ASSIGNMENT REQUEST message.

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

VGCS_ASSIGNMENT RESULT: Acknowledgement message from the affected BSC in answer to the assignment requests. If the assignment is not successful, a VGCS_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.

VGCS_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 VGCS 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 into the conference bridge. Alternatively normal calls to GSM subscribers may be established for dispatchers being GSM subscribers which are not presented in the diagram.

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.

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 voice group call channel has been established in the relay MSC area.

FORWARD_GROUP_CALL_SIGNALLING (IMSI, additional info): The IMSI of the service subscriber who has established the voice group call and who is allowed to terminate the call is sent to every relay MSC. If the network supports the use of talker priorities, the message includes also the talker priority. Furthermore, the message provides additional information about the current talking service subscriber, if available.

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 group call reference, the priority of the call if eMLPP is applied, and possibly the channel description of the voice group 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.

UPLINK_SEIZED_CMD: If the network supports the use of talker priorities, this message informs the BSS about the talker priority of the current talking service subscriber and about the status of the emergency mode. The MSC may also include additional information about the current talking service subscriber, if the information is available when sending this message.

UPLINK_BUSY: If the network supports the use of talker priorities, this connectionless RR message is sent on the downlink FACCH to inform all mobile stations about the talker priority of the current talking service subscriber and about the status of the emergency mode. The network may also include additional information about the current talking service subscriber, if the information is available when sending this message and there is sufficient space available in the message. The message is repeated on the FACCH every T1 seconds.

VGCS_ADD_INFO: The MSC sends additional information about the current talking service subscriber to all BSCs, unless the information was already included in the UPLINK_SEIZED_CMD message.

ADD_INFO: The BSCs broadcast the additional information on the FACCH to all listeners. , unless the information was already included in the UPLINK_BUSY message

Periodic ADD_ INFO (SACCH): The message is repeated on the SACCH every T2 seconds.

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

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

– information of changes of notifications;

– information used for cell re-selection.

CONNECT: Information to the mobile station of the calling service subscriber that the VGCS is established with the related group 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. If the SETUP message from the calling subscriber contained a talker priority, the MSC returns the talker priority used by the network. This will be lower than the requested talker priority, if the subscription check for the requested talker priority was unsuccessful.

UPLINK_RELEASE: When the calling service subscriber wants to become a listening service subscriber for the first time, a message indicating release of the uplink is required to be sent from the MS to the BSS in order to set the uplink free.

NOTE 4a: For different cases of uplink release and the related message flows refer to Figure 6.b to 6.g.

UPLINK_RELEASE_INDICATION: The BSS informs the MSC on the uplink release.

FORWARD_GROUP_CALL_SIGNALLING (uplink release indication): This message is sent to every relay MSC to indicate that the uplink is free.

CLEAR COMMAND : The MSC requests the BSS to clear radio and terrestrial resources associated with originator dedicated link if not already done.

CHAN_RELEASE: The BSS sends a channel release message to the calling service subscriber’s mobile station including the channel description of the voice group call channel to which the mobile station shall tune to.

NOTE 5: Alternatively, if no UPLINK_RELEASE has been sent to the network by the mobile station, the network may transfer the mobile station to the voice group call channel by the channel mode modify procedure or by an assignment procedure or by a handover procedure.

DISC: Two layer 2 disconnect messages shall be sent by the mobile station to the network.

MS’

MSs

BSS

MSC-R

VLR

GCR

MSC-A

[SYS_INFO (NCH allocated)]

<——-<———-

RACH (CHAN_REQ)

——————->

IMM_ASS

<——————-

SABM (SERV_REQ)

——————->

COM_L3_INFO

—————>

PROCEDURE_ACC_REQUIREMENT

UA (SERV_REQ)

——->

<——————-

PROC_ACC_ACK

Authentication & Ciphering

<——-

<—————————————->

SETUP

——————————————>

SEND_INFO_OUT

——->

COMPLETE_CALL

<——-

GCR_INT

—————–>

GCR_INT_ACK

<—————–

ASS_REQ

<—————

CH_MOD_MODFY

<——————-

CH_MOD_MODFY_ACK

——————->

ASS_COMP

—————>

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

——->

VGCS_SETUP

<—————

VGCS_SETUP_ACK

—————>

VGCS_ASS_REQ

<—————

VGCS_AREA_CELL_INFO

<—————

VGCS_ASS_RESULT

Tast

—————>

CONNECT (to MSC-A)

—————————————————>

VGCS_ASS_STATUS

_|_

—————>

NOTIFY_REQ (NCH)

<———-

NOTIFY_REQ (FACCH)

SEND_GROUP CALL_END_SIGNAL

<———-

(IMSI, add info)

—————————————————>

_|_

UPLINK_SEIZED_CMD

<—————

UPLINK_BUSY

<———-

CONNECT (from MSC-A)

CONNECT

<—————————————————

<——————————————

PERIODIC NOTIF_REQ (NCH)

<———-

Periodic SACCH Info

VGCS_ADD_INFO

<—————

ADD_INFO

<———-

Periodic ADD_INFO (SACCH)

<———-

UPLINK_RELEASE (NOTE 9a)

——————->

UPLINK_RELEASE_IND

—————>

PROCESS_GROUP CALL_SIGNAL. (uplink rel ind)

—————————————————>

RELEASE (from MSC-A)

<—————————————————

CHAN_RELEASE

CLR_CMD CMP

<——————-

<————

DISC

CLR_COMP

—————–>

————->

—————–>

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 group 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 group call): Modified form of the current call request message L3-MM CM SERVICE REQUEST sent on the allocated channel. Teleservice Voice group 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 group call.

NOTE 6: 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 VGCS 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 group call. Optionally this message may contain a talker priority.

NOTE 7: Alternatively, an IMMEDIATE_SETUP may have been send as the initial message including all details of the voice group 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.

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 (MSC-A address) is returned from the GCR in the GCR Interrogation Ack message.

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

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 VGCS prefix plus group 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 group call attributes (parts) are received from the anchor MSC.

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 (cell list) is returned from the GCR in the GCR Interrogation Ack message.

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.

VGCS_SETUP_ACK: Acknowledgement message from the affected BSC in answer to the VGCS_SETUP setup message. If the setup is not successful, a VGCS_SETUP_REFUSE message shall be sent instead.

VGCS_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.

NOTE 9: As an operator option the voice group 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 group calls.

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

VGCS_ASSIGNMENT_RESULT: Acknowledgement message from the affected BSC in answer to the assignment requests. If the assignment is not successful, a VGCS_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.

VGCS_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 VGCS 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, additional info): 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. If the network supports the use of talker priorities, the message includes also the talker priority. Furthermore, the message provides additional information about the current talking service subscriber, if available.

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 include also the channel description and the group ciphering key numbers.

VGCS_ADD_INFO: The MSC sends additional information about the current talking service subscriber to all BSCs, unless the information was already included in the UPLINK_SEIZED_CMD message.

ADD_INFO: The BSCs broadcast the additional information on the FACCH to all listeners, unless the information was already included in the UPLINK_BUSY message.

Periodic ADD_ INFO (SACCH): The message is repeated on the SACCH every T2 seconds.

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

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

NOTE 9a: For different cases of uplink release and the related message flows refer to Figure 6.b to 6.g.

UPLINK_RELEASE_INDICATION: The BSS informs the MSC on the uplink release.

PROCESS_GROUP_CALL_SIGNALLING (uplink release indication): To indicate to the anchor MSC that the uplink is free.

CLEAR_COMMAND: The MSC requests the BSS to clear radio and terrestrial resources associated with originator dedicated link if not already done.

NOTE 10: Alternatively, if no UPLINK_RELEASE has been sent to the network by the mobile station, the network may transfer the mobile station to the voice group call channel by the channel mode modify procedure or by an assignment procedure or by a handover procedure.

DISC: Two layer 2 disconnect messages shall be sent by the mobile station to the network.

RELEASE from MSC-A: The dedicated connection for the calling service subscriber is released with cause ‘normal, unspecified’.

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 group 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 group call): Modified form of the current call request message L3-MM CM SERVICE REQUEST sent on the allocated channel. Teleservice Voice group 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 group call.

NOTE 10a: 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 VGCS 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 group call. Optionally this message may contain a talker priority.

NOTE 10b: Alternatively, an IMMEDIATE_SETUP may have been send as the initial message including all details of the voice group 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.

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. The message may also contain talker priority and additional info.

GCR_INT: The group 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 10c: 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 VGCS prefix plus group 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 group call attributes (parts) are received from the anchor MSC.

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 (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.

VGCS_SETUP_ACK: Acknowledgement message from the affected BSC in answer to the VGCS_SETUP setup message. If the setup is not successful, a VGCS_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 10d: As an operator option the voice group 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 group 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, additional info): 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. If the network supports the use of talker priorities, the message includes also the talker priority. Furthermore, the message provides additional information about the current talking service subscriber, if available.

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 include also the channel description and the group ciphering key numbers.

VGCS_ADD_INFO: The MSC sends additional information about the current talking service subscriber to all BSCs.

ADD_INFO: The BSCs broadcast the additional information on the FACCH to all listeners.

Periodic ADD_ INFO (SACCH): The message is repeated on the SACCH every T2 seconds.

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

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 VGCS is established with the related group call reference as the connected number. If the SETUP message from the calling subscriber contained a talker priority, the MSC returns the talker priority used by the network. This will be lower than the requested talker priority, if the subscription check for the requested talker priority was unsuccessful.

NOTE 10e: For different cases of uplink release and the related message flows refer to Figure 6.b to 6.g.

UPLINK_RELEASE_INDICATION: The BSS informs the MSC of the uplink release.

PROCESS_GROUP CALL_SIGNALLING (uplink release indication): To indicate to the anchor MSC that the uplink is free.

CLEAR COMMAND: The MSC requests the BSS to clear radio and terrestrial resources associated with originator dedicated link if not already done.

NOTE 10f: Alternatively, if no UPLINK_RELEASE has been sent to the network by the mobile station, the network may transfer the mobile station to the voice group call channel by the channel mode modify procedure or by an assignment procedure or by a handover procedure.

DISC: Two layer 2 disconnect messages shall be sent by the mobile station to the network.

RELEASE from MSC-A: The dedicated connection for the calling service subscriber is released.

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 group 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 group 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 group 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.

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

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

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.

VGCS_SETUP: Relay MSC sends to BSS’s a VGCS SETUP message to initiate a VGCS call set-up procedures.

VGCS_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 group 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.

FORWARD_GROUP CALL_SIGNALLING (uplink release indication): The anchor MSC indicates to all relay MSCs that the uplink is free. On receipt of the uplink free indication the relay MSC shall send an UPLINK RELEASE message to every BSS of the group call area to indicate that the uplink free.

UPLINK_REL_CMD and UPLINK_FREE: After having received the VGCS SETUP ACK, the MSC sends to BSCs the UPLINK RELEASE CMD in order to indicate that the call has been initiated by a dispatcher. As a consequence, UPLINK FREE is sent on the common channel(s). Then a service subscriber can request the uplink by using Uplink Request procedure.

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 VGCS 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 group 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 group 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 VGCS prefix plus group 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 group call attributes and maks the group 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 group 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, additional info): 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. If the network supports the use of talker priorities, the message includes also the talker priority. Furthermore, the message provides additional information about the current talking service subscriber, if available. 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.

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

17b. FORWARD_GROUP_CALL_SIGNALLING: Initial Talker Information is propagated from MSC-A to MSC-R.

BSS

MSC-A

MSC-R

UPLINK_FREE

<—————————

UPLINK_ACCESS

—————————>

UPLINK_REQUEST

——————–>

VGCS_UPLINK_GRANT

<—————————

UPLINK_BUSY

<—————————

SABM(L3msg)

—————————>

UA (L3msg)

FORW._GROUP CALL_SIGN.

<—————————

UPLINK_REQ_ACK

(uplink seized command)

<——————–

—————————–>

UPLINK_ REQ_CONF (L3msg)

———————>

Retrieve additional info fromLR

from the VLR (NOTE12a)

VGCS_ADD_INFO

FORW._GROUP CALL_SIGN.

<——————–

(add_info)

—————————–>

Conversation proceeds

<——————————————————->

UPLINK_RELEASE (NOTE 12b)

—————————>

UPLINK_RELEASE_IND

———————>

UPLINK_FREE

FORW._GROUP CALL_SIGN.

<—————————

(uplink release indication)

——————————>

Figure 4: Signalling information required for the voice group call uplink access
in the anchor MSC without talker priority (normal case, without contention resolution)

UPLINK_FREE: This connectionless RR message is repeatedly sent by the BSS on the main signalling link (FACCH) to inform all mobile stations of the voice group call members that the uplink is free.

UPLINK_ACCESS: This is sent on the uplink of the voice group call channel using random access procedures. The UPLINK_ACCESS message is similar to a channel request but sent on the group call channel uplink. The establishment cause for subsequent talker uplink request as defined in 3GPP TS 44.018 shall be used for this purpose. The mobile station may send repeated UPLINK_ACCESS messages (see 3GPP TS 44.018).

UPLINK_REQUEST: The request for the uplink is indicated to the MSC. Only one request per BSC shall be forwarded.

VGCS_UPLINK_GRANT: The reply to the uplink request sent on the voice group channel downlink containing information for synchronisation of the mobile station to the network and uplink access contention resolution. The VGCS_UPLINK_GRANT message shall therefore include a request reference (reflecting the UPLINK_ACCESS) and the physical information required for transmission on the voice group call channel uplink. On receipt of a VGCS_UPLINK_GRANT, the related mobile station can start to send speech directly.

NOTE 11: UPLINK_FREE messages are stopped immediately.

UPLINK_BUSY: This connectionless RR message is sent on the downlink FACCH to inform all mobile stations that the uplink is now busy.

NOTE 12: The order of UPLINK_BUSY and SABM message is independent.

SABM(L3msg): The layer 2 link is set up and layer 3 information on classmark and mobile station identity included.

UA(L3msg): The layer 2 link is acknowledged and the layer 3 information reflected for contention resolution.

UPLINK_REQUEST_ACKNOWLEDGE: The anchor MSC acknowledges the uplink to one BSC. If uplink requests have been made by more than one BSC or MSC-R, all remaining uplink requests shall be rejected by an UPLINK_REJECT_CMD which is not presented in figure 4. On reception of an UPLINK_REJECT_CMD the BSS shall send an UPLINK_REL to the related mobile station, followed by an UPLINK_BUSY to indicate to the mobile stations that the uplink is in use. The MSC shall send to other BSCs which did not send an uplink request an UPLINK_SEIZED_CMD message which is not presented in figure 4. On reception of an UPLINK_SEIZED_CMD the BSS shall send an UPLINK_BUSY to indicate to the mobile stations that the uplink is in use.

FORWARD_GROUP CALL_SIGNALLING (uplink seized command): This message is sent to all relay MSCs, to inform all mobile stations roaming in parts of the group call area which are controlled by relay MSCs, that the uplink is now busy.

UPLINK_REQUEST_CONFIRM: The BSS confirms the uplink use to the MSC together with the mobile station identity.

NOTE 12a: In a RANflex configuration (with or without group call redundancy) the uplink requesting subscriber’s VMSC may be different from his current location area’s group call serving MSC. In this case the retrieval of info from the (distant) VLR is done by means of the MAP service SEND_GROUP_CALL_INFO.

VGCS_ADD_INFO: The MSC sends additional information about the new talking service subscriber to all BSCs. The BSCs broadcast ADD_INFO messages containing the additional information to all listeners (not shown in figure 4).

FORWARD_GROUP CALL_SIGNALLING (additional info): This message is sent to all relay MSCs to provide information about the new talking service subscriber.

Conversation proceeds: Once the mobile station has control of the uplink, it shall be able to communicate directly. The two-way nature of the conference bridge will ensure that they are already connected to all appropriate downlink channels.

UPLINK_RELEASE: When the service subscriber who has access to the uplink wants to release the channel, then a message indicating release of the uplink is required to be sent from the MS to the BSS on the FACCH.

NOTE 12b: For different cases of uplink release and the related message flows refer to Figure 6.b to 6.g.

UPLINK_RELEASE_INDICATION: The BSS informs the MSC on the uplink release.

BSS

MSC-A

MSC-R

UPLINK_FREE

<—————————

UPLINK_ACCESS

(privileged subscriber

request)

—————————>

VGCS_UPLINK_GRANT

<—————————

UPLINK_BUSY

(privileged subscriber)

<—————————

UPLINK_REQUEST

SABM(L3msg)

(L3msg,

—————————>

privileged subscriber)

MSC-A checks

UA (L3msg)

(NOTE 16)

subscription for group ID

<—————————

——————–>

and talker priority and

retrieves additional info

from VLR (NOTE 16a)

FORW._GROUP CALL_SIGN.

(uplink seized command,

UPLINK_REQ_ACK

privileged subscriber,

(privileged subscriber)

add info)

<——————–

—————————–>

VGCS_ADD_INFO

<——————–

Conversation proceeds with talker priority

"privileged subscriber"

<——————————————————->

ASS_REQ

Dedicated channel

ASSIGNMENT_CMD

<——————–

Assignment

<—————————

ASSIGNMENT_COMP

—————————>

ASS_COMP

——————–>

UPLINK_RELEASE (NOTE 18)

(privileged subscriber)

UPLINK_RELEASE_IND

—————————>

(privileged subscriber)

———————>

UPLINK_FREE

FORW._GROUP CALL_SIGN.

<—————————

(uplink release indication)

——————————>

NOTE: The figure describes the handling, if MSC decides to have a subsequent talker on a dedicated channel.

Figure 4a: Signalling information required for the voice group call uplink access
in the anchor MSC with talker priority "privileged subscriber" (normal case, without contention resolution, subsequent talker on dedicated channel)

UPLINK_ACCESS: This is sent on the uplink of the voice group call channel using random access procedures. The UPLINK_ACCESS message is similar to a channel request but sent on the group call channel uplink. The establishment cause for a privileged subscriber request as defined in 3GPP TS 44.018 shall be used for this purpose. The mobile station may send repeated UPLINK_ACCESS messages (see 3GPP TS 44.018).

NOTE 13: UPLINK_FREE messages are stopped immediately.

NOTE 14: The order of UPLINK_BUSY and SABM message is independent.

SABM(L3msg): The layer 2 link is set up and layer 3 information on classmark and mobile station identity included.

UA(L3msg): The layer 2 link is acknowledged and the layer 3 information reflected for contention resolution.

NOTE 15: Dedicated signalling connection on the main DCCH needs to be established.

UPLINK_REQUEST: The request for the uplink containing the MS identity and the talker priority is indicated to the MSC. Only one request per BSS shall be forwarded.

NOTE 16: As the BSS supports the use of talker priorities and receives from the MS a talker priority different from "normal subscriber", the BSS delays the sending of the UPLINK_REQUEST message to the MSC, until SABM(L3msg) with the MS identity is received from the MS. Then the BSS includes the layer 3 message, the talker priority, and the cell identity of the cell where the UPLINK_ACCESS message was received in the UPLINK_REQUEST message. In this case the UPLINK_REQUEST_CONFIRM message may be omitted by the BSS.

NOTE 16a: In a RANflex configuration (with or without group call redundancy) the uplink requesting subscriber’s VMSC may be different from his current location area’s group call serving MSC. In this case the retrieval of info from the (distant) VLR is done by means of the MAP service SEND_GROUP_CALL_INFO.

UPLINK_REQUEST_ACKNOWLEDGE: The anchor MSC acknowledges the uplink to one BSC. If uplink requests have been made by more than one BSC or MSC-R, all remaining uplink requests shall be rejected by an UPLINK_REJECT_CMD which is not presented in figure 4a. On reception of an UPLINK_REJECT_CMD the BSS shall send an UPLINK_REL to the related mobile station, followed by an UPLINK_BUSY to indicate to the mobile stations that the uplink is in use. The MSC shall send to other BSCs which did not send an uplink request an UPLINK_SEIZED_CMD message which is not presented in figure 4a. On reception of an UPLINK_SEIZED_CMD the BSS shall send an UPLINK_BUSY to indicate to the mobile stations that the uplink is in use.

The anchor MSC may also include additional information about the new talking service subscriber in the UPLINK_REQUEST_ACKNOWLEDGE, UPLINK_REJECT_CMD and UPLINK_SEIZED_CMD messages, if the information is available when sending these messages. The BSS may include the additional information in the UPLINK_BUSY messages, if the information is available when sending these messages and there is sufficient space available in the messages.

FORWARD_GROUP CALL_SIGNALLING (uplink seized command, privileged subscriber, additional info): This message is sent to all relay MSCs, to inform all mobile stations roaming in parts of the group call area which are controlled by relay MSCs that the uplink is now busy for a talker with talker priority "privileged subscriber". Furthermore, the message provides additional information about the new talking service subscriber, if available.

UPLINK_REQUEST_CONFIRM: The BSS confirms the uplink use to the MSC together with the mobile station identity.

ASS_REQ: This message contains details of the resource(s) required for the dedicated connection.

ASSIGNMENT_CMD: This message contains details of the resource(s) required and triggers the assignment procedure of the dedicated channel at the MS.

ASSIGNMENT_COMP: Standard message.

ASS_COMP: Standard message.

VGCS_ADD_INFO: The MSC sends additional information about the new talking service subscriber to all BSCs, unless the information was already included in the UPLINK_REQUEST_ACKNOWLEDGE, UPLINK_REJECT_CMD and UPLINK_SEIZED_CMD messages. The BSCs broadcast ADD_INFO messages containing the additional information to all listeners (not shown in figure 4a) , unless the information was already included in the UPLINK_BUSY messages.

NOTE 17: For different cases of uplink release and the related message flows refer to Figure 6b to 6g.

UPLINK_RELEASE_INDICATION: The BSS informs the MSC of the uplink release.

BSS

MSC-A

MSC-R

Conversation proceeds with talker priority

"normal subscriber"

<——————————————————->

UPLINK_ACCESS

Emergency (em

ergency mode reset request)

(emergency subscriber

request)

—————————>

VGCS_UPLINK_GRANT

<—————————

UPLINK_BUSY

(emergency subscriber)

<—————————

UPLINK_REQUEST

SABM(L3msg)

(L3msg,

—————————>

emergency subscriber)

UA (L3msg)

(NOTE 20)

<—————————

——————–>

MSC-A checks

subscription for group ID

and talker priority and

UPLINK_REQ_ACK

retrieves additional info fromLR

UPLINK_BUSY

(emergency subscriber,

from VLR (NOTE 20a)

(emergency subscriber,

emergency mode

indication)

<——————–

<—————————

FORW._GROUP CALL_SIGN.

(uplink seized command,

emergency subscriber,

add info)

—————————–>

Distribution of the

VGCS_ADD_INFO

additional info to the

<——————–

listeners

VGCS_ADD_INFO

and

<——————–

to the previous talker

Conversation proceeds with talker priority

"emergency subscriber"

<——————————————————->

ASS_REQ

Dedicated channel

ASSIGNMENT_CMD

<——————–

assignment for the new

<—————————

talker

ASSIGNMENT_COMP

—————————>

ASS_COMP

——————–>CLR_CMD

CHAN_RELEASE

(emergency subscriber,

emergency mode

CLR_CMD

Indication, add info)

<——————–

Release of the dedicated

<—————————

CLR_COMP

channel of the previous

DISC

——————–>

talker

—————————>

SCCP_RLSD

<——————–

SCCP_RLC

——————–>

NOTE: The figure describes the handling, if the MSC decides to have a subsequent talker on a dedicated channel.

Figure 4b: Signalling information required for the voice group call uplink access in the anchor MSC with talker priority "emergency subscriber" and pre-emption of the current talker (normal case, subsequent talker on dedicated channel, without contention resolution)

UPLINK_ACCESS: This is sent on the uplink of the voice group call channel using random access procedures. The UPLINK_ACCESS message is similar to a channel request but sent on the group call channel uplink. The establishment cause for an emergency subscriber request as defined in 3GPP TS 44.018 shall be used for this purpose. The mobile station may send repeated UPLINK_ACCESS messages (see 3GPP TS 44.018).

UPLINK_BUSY: This connectionless RR message is sent on the downlink FACCH to inform all mobile stations that the uplink is now busy. UPLINK_BUSY indicates the talker priority "emergency subscriber" of the new talking service subscriber to all listening service subscribers.

NOTE 18: The order of UPLINK_BUSY and SABM message is independent.

SABM(L3msg): The layer 2 link is set up and layer 3 information on classmark and mobile station identity included.

UA(L3msg): The layer 2 link is acknowledged and the layer 3 information reflected for contention resolution.

NOTE 19: Dedicated signalling connection on the main DCCH needs to be established.

UPLINK_REQUEST: The request for the uplink containing the MS identity and the talker priority is indicated to the MSC. Only one request per BSS shall be forwarded.

NOTE 20: As the BSS supports the use of talker priorities and receives from the MS a talker priority different from "normal subscriber", the BSS delays the sending of the UPLINK_REQUEST message to the MSC, until SABM(L3msg) with the MS identity is received from the MS. Then the BSS includes the layer 3 message, the talker priority, and the cell identity of the cell where the UPLINK_ACCESS message was received in the UPLINK_REQUEST message. In this case the UPLINK_REQUEST_CONFIRM message may be omitted by the BSS.

NOTE 20a: In a RANflex configuration (with or without group call redundancy) the uplink requesting subscriber’s VMSC may be different from his current location area’s group call serving MSC. In this case the retrieval of info from the (distant) VLR is done by means of the MAP service SEND_GROUP_CALL_INFO.

UPLINK_REQUEST_ACKNOWLEDGE: The anchor MSC acknowledges the uplink to one BSC, including the talker priority and the emergency mode indication. If uplink requests have been made by more than one BSC or MSC-R, all remaining uplink requests shall be rejected by an UPLINK_REJECT_CMD with an emergency mode indication (not presented in figure 4b). On reception of an UPLINK_REJECT_CMD the BSS shall send an UPLINK_REL to the related mobile station, followed by an UPLINK_BUSY to indicate to the mobile stations that the uplink is in use. The MSC shall send to other BSCs which did not send an uplink request an UPLINK_SEIZED_CMD message with an emergency mode indication (not presented in figure 4b). On reception of an UPLINK_SEIZED_CMD the BSS shall send an UPLINK_BUSY to indicate to the mobile stations that the uplink is in use.

UPLINK_BUSY: This connectionless RR message is sent on the downlink FACCH to inform all mobile stations that the uplink is now busy with talker priority "emergency subscriber" and that the emergency mode is set in the network. The message is repeated on the FACCH every T1 seconds.

FORWARD_GROUP CALL_SIGNALLING (uplink seized command, emergency subscriber, add info): This message is sent to all relay MSCs, to inform all mobile stations roaming in parts of the group call area which are controlled by relay MSCs, that the uplink is now busy for a talker with talker priority "emergency subscriber" and that the emergency mode indication shall be signalled. Furthermore, the message provides additional information about the new talking service subscriber, if available.

ASS_REQ: This message contains details of the resource(s) required for the dedicated connection.

ASSIGNMENT_CMD: This message contains details of the resource(s) required and triggers the assignment procedure of the dedicated channel at the MS.

ASSIGNMENT_COMP: Standard message.

ASS_COMP: Standard message.

VGCS_ADD_INFO: The MSC sends additional information about the new talking service subscriber to all BSCs, unless the information was already included in the UPLINK_REQUEST_ACKNOWLEDGE, UPLINK_REJECT_CMD and UPLINK_SEIZED_CMD messages. The BSCs broadcast ADD_INFO messages containing the additional information to all listeners (not shown in figure 4b) , unless the information was already included in the UPLINK_BUSY messages.Additionally, the MSC sends the additional information on the dedicated connection for the previous talker, before this connection is released.

CLEAR COMMAND: The MSC requests the BSS to clear radio and terrestrial resources associated with previous talker.

CLEAR_COMP: Standard message.

CHAN_RELEASE: The BSS sends a channel release message to the previous talker’s mobile station including the channel description of the voice group call channel to which the mobile station shall tune to. Additionally the BSS includes the talker priority of the new talker and the additional information, if available, and the emergency mode indication, if applicable.

DISC: Two layer 2 disconnect messages shall be sent by the mobile station to the network.

SCCP_RLSD: Standard message.

SCCP_RLC: Standard message.

BSS

MSC-A

MSC-R

Conversation proceeds with talker priority

"emergency subscriber",

"emergency mode" is set

<——————————————————->

UPLINK_ACCESS

(emergency mode reset

request)

—————————>

VGCS_UPLINK_GRANT

<—————————

SABM(L3msg)

EMERGENCY_

—————————>

RESET_IND

UA (L3msg)

(L3msg)

<—————————

——————–>

MSC-A checks

subscription for group ID

UPLINK_RELEASE

and talker priority (NOTE

<—————————

21a)

DISC

EMERGENCY_

FORW._GROUP CALL_SIGN

—————————>

RESET_COMMAND

(emergency mode reset command)

<——————–

—————————–>

UPLINK_BUSY

(normal subscriber)

<—————————

Conversation proceeds with talker priority

"normal subscriber"

<——————————————————->

Figure 4c: Signalling information required for the voice group call uplink access
in the anchor MSC with "emergency mode reset request"

UPLINK_ACCESS: This is sent on the uplink of the voice group call channel using random access procedures. The UPLINK_ACCESS message is similar to a channel request but sent on the group call channel uplink. The establishment cause for emergency mode reset request as defined in 3GPP TS 44.018 shall be used for this purpose.

EMERGENCY_RESET_IND: The reception of an emergency mode reset request is indicated to the MSC. Only one request per BSC shall be forwarded.

NOTE 21: The BSS delays the sending of the EMERGENCY_RESET_IND message to the MSC, until SABM(L3msg) with the MS identity is received from the MS. Then the BSS includes the layer 3 message and the cell identity of the cell where the UPLINK_ACCESS message was received in the EMERGENCY_RESET_IND message.

NOTE 21a: In a RANflex configuration (with or without group call redundancy) the uplink requesting subscriber’s VMSC may be different from his current location area’s group call serving MSC. In this case the retrieval of info from the (distant) VLR is done by means of the MAP service SEND_GROUP_CALL_INFO.

SABM(L3msg): The layer 2 link is set up and layer 3 information on classmark and mobile station identity included.

UA(L3msg): The layer 2 link is acknowledged and the layer 3 information reflected for contention resolution.

UPLINK_RELEASE: When the BSS has forwarded the emergency mode reset request it releases the layer 2 link. A message indicating release of the uplink is required to be sent from the BSS to the MS on the FACCH.

EMERGENCY_RESET_COMMAND: The anchor MSC commands all BSCs involved in the voice group call to reset the emergency mode. If the BSC receives an EMERGENCY_RESET_COMMAND message, it changes the content of the NCH to indicate "no emergency mode" and the talker priority of the current talking service subscriber to "normal subscriber", if the previous uplink status was uplink busy with talker priority "emergency subscriber".

FORWARD_GROUP CALL_SIGNALLING (emergency mode reset command): This message is sent to all relay MSCs, to inform all BSCs controlled by relay MSCs that the emergency mode indication shall not be sent any longer and that the talker priority of the current talking service subscriber is changed to "normal subscriber", if the previous uplink status was uplink busy with talker priority "emergency subscriber".

Conversation proceeds: The conversation of the current talker is not interrupted.

BSS

MSC-A

MSC-R

Conversation proceeds with talker priority

"normal subscriber"

< —————————————————– >

MS leaves the group call

RACH(CHAN_REQ)

—————————>

IMM_ASS

<—————————

SABM(Priority Uplink Request)

—————————>

UPLINK_REQUEST

(

UA(Priority Uplink Req)

privileged subscriber)

<—————————

——————–>

CHAN_RELEASE

<—————————

DISC

—————————>

<—————————

MS rejoins the group call

UPLINK_REQ_ACK

(privileged subscriber)

< ———————

Retrieve additional info

UPLINK_RELEASE

From the VLR (NOTE

<—————————

Current Talker

21b)

DISC

Released:

FORW. GROUP CALL SIGNAL (uplink seized command, privileged subscriber, add info)

—————————>

<—————————

VGCS_UPLINK_GRANT

—————————–>

<—————————

UPLINK_BUSY

<—————————

SABM(L3msg)

—————————>

UA (L3msg)

<—————————

UPLINK_ REQ_CONF (L3msg)

——————–>

VGCS ADD INFO

< ——————–

Conversation proceeds with talker priority

"privileged subscriber"

<——————————————————->

Figure 4d: Signalling information required for the voice group call uplink request via RACH with talker priority "privileged subscriber" in the anchor MSC and pre-emption of the current talker (normal case, without contention resolution)

RACH(CHAN_REQ): Standard message to request an SDCCH.

IMM_ASS: Standard message sent on the AGCH.

SABM (PRIORITY_UPLINK_REQ): L3 message PRIORITY_UPLINK_REQ sent on the allocated channel.

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

UPLINK_BUSY (not presented in figure 4d): If validation of Priority Uplink Requests applies for the group call, the BSS, on receipt of a valid Priority Uplink Request, shall send an UPLINK_BUSY on the downlink FACCH to inform all mobile stations that a priority request has been made and to provide a new token. The message is sent on Tbb expiry.

CHAN_RELEASE: The BSS sends a channel release message to the service subscriber’s mobile station.

DISC: Standard message to release the layer 2 link.

UA: Standard message to acknowledge release of the layer 2 link.

UPLINK_REQUEST: The request for the uplink containing the MS identity and the talker priority is indicated to the MSC. Only one request per BSS shall be forwarded.

UPLINK_REQUEST_ACKNOWLEDGE (privileged subscriber): The anchor MSC acknowledges the uplink to one BSC. If uplink requests have been made by more than one BSC or MSC-R, all remaining uplink requests shall be rejected by an UPLINK_REJECT_CMD which is not presented in figure 4d. On reception of an UPLINK_REJECT_CMD the BSS shall send an UPLINK_REL to the related mobile station, followed by an UPLINK_BUSY to indicate to the mobile stations that the uplink is in use. The MSC shall send to other BSCs which did not send an uplink request an UPLINK_SEIZED_CMD message which is not presented in figure 4d. On reception of an UPLINK_SEIZED_CMD the BSS shall send an UPLINK_BUSY to indicate to the mobile stations that the uplink is in use.

UPLINK_RELEASE: Upon receipt of an UPLINK_REQUEST_ACKNOWLEDGE, UPLINK_REJ or UPLINK_SEIZED_CMD indicating the talker priority of the new talker, the BSC releases the current talker from the uplink by sending a message requesting release of the uplink to the mobile station on the FACCH.

DISC: Standard message to release the layer 2 link.

UA: Standard message to acknowledge release of the layer 2 link.

NOTE 21b: In a RANflex configuration (with or without group call redundancy) the uplink requesting subscriber’s VMSC may be different from his current location area’s group call serving MSC. In this case the retrieval of info from the (distant) VLR is done by means of the MAP service SEND_GROUP_CALL_INFO.

FORWARD_GROUP CALL_SIGNALLING (uplink seized command, privileged subscriber, add info): This message is sent to all relay MSCs, to inform all mobile stations roaming in parts of the group call area which are controlled by relay MSCs, that the uplink is now busy for a talker with talker priority "privileged subscriber". Furthermore, the message provides additional information about the new talking service subscriber, if available.

VGCS_UPLINK_GRANT: The reply to the priority uplink request sent on the voice group channel downlink containing information for synchronisation of the mobile station to the network and uplink access contention resolution. The VGCS_UPLINK_GRANT message shall therefore include a request reference (reflecting the PRIORITY_UPLINK_REQUEST) and the physical information required for transmission on the voice group call channel uplink. On receipt of a VGCS_UPLINK_GRANT, the related mobile station can start to send speech directly.

UPLINK_BUSY: This connectionless RR message is sent on the downlink FACCH to inform all mobile stations that the uplink is now busy. If the network supports talker priorities, then the UPLINK_BUSY indicates the talker priority of the current talking service subscriber to all listening service subscribers and additionally, if the emergency mode is set in the network, the emergency mode indication. The message is repeated on the FACCH every T1 seconds. If validation of Priority Uplink Requests applies each periodic UPLINK_BUSY message shall include a new token (i.e. a new token is broadcast every T1 seconds).

NOTE: The order of UPLINK_BUSY and SABM message is independent.

SABM(L3msg): The layer 2 link is set up and layer 3 information on classmark and mobile station identity included.

UA(L3msg): The layer 2 link is acknowledged and the layer 3 information reflected for contention resolution.

UPLINK_REQUEST_CONFIRM: The BSS confirms the uplink use to the MSC together with the mobile station identity, classmark information and optionally the CKSN.

VGCS_ ADD_ INFO: The MSC sends additional information about the new talking service subscriber to all BSCs, unless the information was already included in the UPLINK_REQUEST_ACKNOWLEDGE, UPLINK_REJECT_CMD and UPLINK_SEIZED_CMD messages. The BSCs broadcast ADD_INFO messages containing the additional information to all listeners (not shown in figure 4d) , unless the information was already included in the UPLINK_BUSY messages.

BSS

MSC-A

MSC-R

Conversation proceeds with talker priority

"emergency subscriber"

<——————————————————->

MS leaves the group call

RACH(CHAN_REQ)

—————————>

IMM_ASS

<—————————

SABM(Priority Uplink Request)

—————————>

EMERGENCY_RESET_IND
————————— >

UA(Priority Uplink Req)

<—————————

MSC-A checks subscription for group ID and talker priority

CHAN_RELEASE

<—————————

(NOTE 21c)

DISC

—————————>

<—————————

MS rejoins the group call

EMERGENCY_RESET_COMMAND

FORW. GROUP CALL SIGNAL (emergency mode reset command)

UPLINK_BUSY

< ——————–

<—————————

—————————–>

Conversation proceeds with talker priority “normal subscriber”
<——————————————————->

Figure 4e: Signalling information required for the voice group call uplink request via RACH with "emergency mode reset request" in the anchor MSC (normal case, without contention resolution)

RACH(CHAN_REQ): Standard message to request an SDCCH.

IMM_ASS: Standard message sent on the AGCH.

SABM (PRIORITY_UPLINK_REQ): L3 message PRIORITY_UPLINK_REQ sent on the allocated channel.

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

CHAN_RELEASE: The BSS sends a channel release message to the service subscriber’s mobile station.

DISC: Standard message to release the layer 2 link.

UA: Standard message to acknowledge release of the layer 2 link.

UPLINK_BUSY (not presented in figure 4e): If validation of Priority Uplink Requests applies for the group call, the BSS, on receipt of a valid Priority Uplink Request, shall send an UPLINK_BUSY on the downlink FACCH to inform all mobile stations that a priority request has been made and to provide a new token. The message is sent on Tbb expiry.

EMERGENCY_RESET_IND: The reception of an emergency mode reset request is indicated to the MSC. Only one request per BSS shall be forwarded.

NOTE 21c: In a RANflex configuration (with or without group call redundancy) the uplink requesting subscriber’s VMSC may be different from his current location area’s group call serving MSC. In this case the retrieval of info from the (distant) VLR is done by means of the MAP service SEND_GROUP_CALL_INFO.

UPLINK_BUSY: This connectionless RR message is sent on the downlink FACCH to inform all mobile stations that the voice group call is no longer in emergency mode and that the talker priority was changed to "normal subscriber", if the previous uplink status was uplink busy with talker priority "emergency subscriber". The message is repeated on the FACCH every T1 seconds. . If validation of Priority Uplink Requests applies each periodic UPLINK_BUSY message shall include a new token (i.e. a new token is broadcast every T1 seconds).

Conversation proceeds: The conversation of the current talker is not interrupted.

BSS

MSC-R

MSC-A

UPLINK_FREE

<—————————

UPLINK_ACCESS

—————————>

UPLINK_REQUEST

(NOTE 22)

——————–>

PROCESS GROUP CALL SIGN.

VGCS_UPLINK_GRANT

(uplink request)

<—————————

——————————>

UPLINK_BUSY

<—————————

SABM (L3msg)

—————————>

UA (L3msg)

FORWARD GROUP CALL_SIGN.

<—————————

UPLINK_REQ_ACK

(uplink request ack)

<——————–

<—————————–

UPLINK_REQ_CONF (L3msg)

(NOTE 26)

———————>

Retrieve additional info fromLR

form VLR (NOTE 26a)

VGCS_ADD_INFO

PROCESS GROUP CALL_SIGN.

<——————–

(add_info)

—————————–>

Conversation proceeds

<——————————————————->

UPLINK_RELEASE (NOTE 28)

—————————>

UPLINK_RELEASE_IND

———————>

UPLINK_FREE

PROCESS_GROUP CALL_SIGN.

<—————————

(uplink release indication)

——————————>

Figure 5: Signalling information required for the voice group call uplink access
in the relay MSC without talker priority (normal case, without contention resolution)

UPLINK_REQUEST: The request for the uplink is indicated to the MSC. Only one request per BSC shall be forwarded.

NOTE 22: If the BSS supports the use of talker priorities and receives from the MS a talker priority different from "normal subscriber", the BSS delays the sending of the UPLINK_REQUEST message to the MSC, until SABM(L3msg) is received from the MS. Then the BSS includes the layer 3 message, the talker priority, and the cell identity of the cell where the UPLINK_ACCESS message was received in the UPLINK_REQUEST message. In this case the UPLINK_REQUEST_CONFIRM message may be omitted by the BSS.

NOTE 23: UPLINK_FREE messages are stopped immediately.

UPLINK_BUSY: This connectionless RR message is sent on the downlink FACCH to inform all mobile stations that the uplink is now busy.

NOTE 24: If the BSS supports the use of talker priorities, then it indicates the talker priority of the current talking service subscriber and the status of the emergency mode in the UPLINK_BUSY message and repeats the message on the FACCH every T1 seconds.

NOTE 25: The order of UPLINK_BUSY and SABM message is independent.

SABM (L3msg): The layer 2 link is set up and layer 3 information on classmark and mobile station identity included.

UA (L3msg): The layer 2 link is acknowledged and the layer 3 information reflected for contention resolution.

PROCESS_GROUP CALL_SIGNALLING (uplink request): This message is sent to the anchor MSC, to indicate that the uplink is requested by a subscriber roaming in the relay MSC area.

NOTE 26: If the UPLINK_REQUEST message contained the layer 3 message, the message provides additional information about the new talking service subscriber, if available.

FORWARD_GROUP CALL_SIGNALLING (uplink request ack): This message is sent to the relay MSC, to indicate that the uplink is granted to the mobile station roaming in parts of the group call area which are controlled by relay MSC.

UPLINK_REQUEST_ACKNOWLEDGE: The relay MSC acknowledges the uplink to one BSC. If uplink requests have been made by more than one BSC, all remaining uplink requests shall be rejected by an UPLINK_REJECT_CMD which is not presented in figure 5. On reception of an UPLINK_REJECT_CMD the BSS shall send an UPLINK_REL to the related mobile station, followed by an UPLINK_BUSY to indicate to the mobile stations that the uplink is in use. The MSC shall send to other BSCs which did not send an uplink request an UPLINK_SEIZED_CMD message which is not presented in figure 5. On reception of an UPLINK_SEIZED_CMD the BSS shall send an UPLINK_BUSY to indicate to the mobile stations that the uplink is in use. If the BSS supports the use of talker priorities, then it indicates the talker priority of the current talking service subscriber and the status of the emergency mode in the UPLINK_BUSY message and repeats the message on the FACCH every T1 seconds.

UPLINK_REQUEST_CONFIRM : The BSS confirms the uplink use to the MSC together with the mobile station identity.

NOTE 26a: In a RANflex configuration (with or without group call redundancy) the uplink requesting subscriber’s VMSC may be different from his current location area’s group call serving MSC. In this case the retrieval of info from the (distant) VLR is done by means of the MAP service SEND_GROUP_CALL_INFO.

PROCESS_GROUP CALL_SIGNALLING (additional info): This message is sent to the anchor MSC to provide information about the new talking service subscriber. The anchor MSC forwards the message to all other relay MSCs.

NOTE 27: This message is omitted, if the additional info was already included in the PROCESS_GROUP CALL_SIGNALLING (uplink request) message.

NOTE 28: For different cases of uplink release and the related message flows refer to Figure 6.b to 6.g.

UPLINK_RELEASE_INDICATION: The BSS informs the MSC on the uplink release.

PROCESS_GROUP CALL_SIGNALLING (uplink release indication): The relay MSC indicates to the anchor MSC that the uplink is free.

BSS

MSC-R

MSC-A

Conversation proceeds with talker priority

"normal subscriber"

<——————————————————->

MS leaves the group call

RACH(CHAN_REQ)
(privileged subscriber request)

—————————>

IMM_ASS

<—————————

SABM(Priority Uplink Request)

—————————>

UPLINK_REQUEST

(

UA(Priority Uplink Req)

privileged subscriber)

<—————————

——————–>

PROCESS GROUP

Retrieve additional info

CALL SIGNAL (uplink

From the VLR

request, privileged

(NOTE 28a)

subscriber, add info)

CHAN_RELEASE

—————————–>

<—————————

DISC

—————————>

<—————————

MS rejoins the group call

FORWARD GROUP CALL SIGNAL (uplink request ack)

UPLINK_REQ_ACK

< ——————————

UPLINK_RELEASE

< ———————

<—————————

DISC

—————————>

<—————————

VGCS_UPLINK_GRANT

<—————————

UPLINK_BUSY

<—————————

SABM(L3msg)

—————————>

UA(L3msg)

<—————————

UPLINK_ REQ_CONF (L3msg)

——————–>

VGCS ADD INFO

< ——————–

Conversation proceeds with talker priority

"privileged subscriber"

<——————————————————->

Figure 5a: Signalling information required for the voice group call uplink request via RACH with talker priority "privileged subscriber" in the relay MSC (normal case, without contention resolution)

RACH(CHAN_REQ): Standard message to request an SDCCH.

IMM_ASS: Standard message sent on the AGCH.

SABM (PRIORITY_UPLINK_REQ): L3 message PRIORITY_UPLINK_REQ sent on the allocated channel.

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

CHAN_RELEASE: The BSS sends a channel release message to the service subscriber’s mobile station.

DISC: Standard message to release the layer 2 link.

UA: Standard message to acknowledge release of the layer 2 link.

UPLINK_BUSY (not presented in figure 5a): If validation of Priority Uplink Requests applies for the group call, the BSS, on receipt of a valid Priority Uplink Request, shall send an UPLINK_BUSY on the downlink FACCH to inform all mobile stations that a priority request has been made and to provide a new token. The message is sent on Tbb expiry.

UPLINK_REQUEST: The request for the uplink is indicated to the MSC. Only one request per BSS shall be forwarded.

NOTE 28a: In a RANflex configuration (with or without group call redundancy) the uplink requesting subscriber’s VMSC may be different from his current location area’s group call serving MSC. In this case the retrieval of info from the (distant) VLR is done by means of the MAP service SEND_GROUP_CALL_INFO.

PROCESS_GROUP_CALL_SIGNALLING (uplink request, privileged subscriber, add info): This message is sent to the anchor MSC, to indicate that the uplink is requested by a subscriber with talker priority "privileged subscriber" roaming in the relay MSC area. Furthermore, the message provides additional information about the service subscriber requesting the uplink, if additional information is available.

FORWARD_GROUP_CALL_SIGNALLING (uplink request ack): This message is sent to the relay MSC, to indicate that the uplink is granted to the mobile station roaming in parts of the group call area which are controlled by the relay MSC.

UPLINK_REQUEST_ACKNOWLEDGE: The relay MSC acknowledges the uplink to one BSC. If uplink requests have been made by more than one BSC, all remaining uplink requests shall be rejected by an UPLINK_REJECT_CMD which is not presented in figure 5a. On reception of an UPLINK_REJECT_CMD the BSS shall send an UPLINK_REL to the related mobile station, followed by an UPLINK_BUSY to indicate to the mobile stations that the uplink is in use. The MSC shall send to other BSCs which did not send an uplink request an UPLINK_SEIZED_CMD message which is not presented in figure 5a. On reception of an UPLINK_SEIZED_CMD the BSS shall send an UPLINK_BUSY to indicate to the mobile stations that the uplink is in use.

UPLINK_RELEASE: Upon receipt of an UPLINK_REQUEST_ACKNOWLEDGE, UPLINK_REJECT_CMD or UPLINK_SEIZED_CMD indicating the talker priority of the new talker, the BSC releases the current talker from the uplink by sending a message requesting release of the uplink to the mobile station on the FACCH.

DISC: Standard message to release the layer 2 link.

UA: Standard message to acknowledge release of the layer 2 link.

NOTE: The order of UPLINK_BUSY and SABM message is independent.

SABM (L3msg): The layer 2 link is set up and layer 3 information on classmark and mobile station identity included.

UA (L3msg): The layer 2 link is acknowledged and the layer 3 information reflected for contention resolution.

UPLINK_REQUEST_CONFIRM: The BSS confirms the uplink use to the MSC together with the mobile station identity, classmark information and optionally the CKSN.

VGCS_ ADD_ INFO: The MSC sends additional information about the new talking service subscriber to all BSCs, unless the information was already included in the UPLINK_REQUEST_ACKNOWLEDGE, UPLINK_REJECT_CMD and UPLINK_SEIZED_CMD messages. The BSCs broadcast ADD_INFO messages containing the additional information to all listeners (not shown in figure 5a) , unless the information was already included in the UPLINK_BUSY messages.

Figure 5b: Signalling information required when the talker is attached to the Anchor MSC and a dispatcher sends DTMF signals

Conversation proceeds: The talker is in control of the uplink (see figure 4) and is attached to the Anchor MSC. The mobile station’s downlink is muted to prevent any distracting echo being heard by the mobile station user.

DTMF Tones (start_talking) or DTMF message (start_talking): This signalling indicates the dispatcher’s unmute request to the MSC. DTMF Tones are used by a fixed line dispatcher while the DTMF message is used by a mobile dispatcher.

Grant Tone: The Anchor MSC may optionally play an in-band tone to the dispatcher to indicate that the dispatcher’s request is recognized and that the downlink of the talking service subscriber will be unmuted The attributes of the grant tone (e.g. frequency and duration) are network operator specific..

Set Parameter (D-ATT = TRUE): The Anchor MSC sends this message to the mobile station to unmute the downlink so that the user can hear what the dispatcher says.

NOTE 29: This message is sent only when the downlink of the talker is muted.

DTMF Tones (end_talking) or DTMF message (end_talking): This signalling indicates the dispatcher’s mute request to the MSC. DTMF Tones are used by a fixed line dispatcher while the DTMF message is used by a mobile dispatcher.

Set Parameter (D-ATT = FALSE): Once the dispatcher indicates that he has finished speaking, the Anchor MSC mutes the talker’s downlink.

NOTE 30: This message is only sent when all dispatchers who have sent the unmuting request have finished their talk.

Figure 5c: Signalling information required when the talker is attached to a Relay MSC and a dispatcher sends DTMF signals

Conversation proceeds: The talker is in control of the uplink (see figure 4) and is attached to a Relay MSC. The mobile station’s downlink is muted to prevent any distracting echo being heard by the mobile station user.

DTMF Tones (start_talking or DTMF message (start_talking): This signalling indicates the dispatcher’s unmute request to the MSC. DTMF Tones are used by a fixed line dispatcher while the DTMF message is used by a mobile dispatcher.

Grant Tone: The Anchor MSC may optionally play an in-band tone to the dispatcher to indicate that the dispatcher’s request is recognized and that the downlink of the talking service subscriber will be unmuted. The attributes of the grant tone (e.g. frequency and duration) are network operator specific.

FORWARD_GROUP_CALL_SIGNAL: This message is sent to the Relay MSC when anchor MSC wants to change the mute/unmute status of the talking service subscriber. In this case stateAttributes::DA = TRUE, is set.

Set Parameter (D-ATT = TRUE/FALSE): The Relay MSC sends this message to the talker when a FORWARD GROUP CALL SIGNAL containing a STATE_ATTRIBUTES information element is received. The D-ATT field is set as received in STATE_ATTRIBUTES element.

FORWARD_GROUP_CALL_SIGNAL: This message is sent to the Relay MSC when the anchor MSC wants to change the mute/unmute status of the talking service subscriber. In this case stateAttributes::DA = FALSE is set.

Set Parameter (D-ATT = FALSE): Once the dispatcher indicates that he has finished speaking, the MSC mutes the talker’s downlink again.

Figure 5d: Signalling information required when the talker is attached to the Anchor MSC and a mobile dispatcher who is roaming in a non-Anchor MSC area sends DTMF signals

DTMF message (start_talking): This signalling indicates the mobile dispatcher’s unmute request to visited MSC. On reception of the DTMF message, the visited MSC will convert it into DTMF tones and send these DTMF tones through the network to the anchor MSC.

Grant Tone: The Anchor MSC may optionally play an in-band tone to the dispatcher to indicate that the dispatcher’s request is interpreted as a request to talk and that the downlink of the talking service subscriber will be unmuted. The attributes of the grant tone (e.g. frequency and duration) are network operator specific.

Set Parameter (D-ATT = TRUE): The Anchor MSC sends this message to the talker to force his mobile station to unmute its downlink so that the user can hear what the dispatcher says.

DTMF message (end_talking): This signalling indicates the mobile dispatcher’s mute request to the MSC.

Set Parameter (D-ATT = FALSE): Once the dispatcher indicates that he has finished speaking, the Anchor MSC mutes the talker’s downlink.

BSS

MSC


Conversation proceeds
<——————————————————->

	UPLINK_REL_CMD
		<——————–

UPLINK_RELEASE
<—————————
UPLINK_FREE
<—————————

Figure 6: Signalling information required for the voice group call uplink release
requested by the network

UPLINK_REL_CMD: When the network wants to release the uplink for any reason, except when a service subscriber with a higher priority has seized the uplink, then a message requesting release of the uplink is required to be sent from the network to the mobile station on the FACCH.

BSS

MSC

Conversation proceeds with talker priority

"normal subscriber"

<——————————————————->

UPLINK_SEIZED CMD (privileged subscriber)

<——————–

UPLINK_RELEASE

<—————————

UPLINK_BUSY

(privileged subscriber)

<—————————

Figure 6a: Signalling information required for the voice group call uplink release
requested by the network; preemption of the current talker by a privileged service subscriber

UPLINK_SEIZED_CMD: When the network wants to release the uplink because a service subscriber with a higher priority has seized the uplink in another BSS area, an UPLINK_SEIZED_CMD indicating the talker priority of the new talking service subscriber is sent by the MSC. If the BSS has sent an UPLINK_REQUEST to the MSC, the MSC will either send UPLINK_REQUEST_ACKNOWLEDGE or UPLINK_REJECT instead of the UPLINK_SEIZED_CMD.

The following figures 6.b to 6.g show the message flows applicable for the uplink release in normal and error cases, dependent on whether the talker is

– on a dedicated link (e.g. the talker is the originator); or

– on the group call channel (e.g. the talker is a subsequent talker).

NOTE: The messages CLEAR CMD, CLEAR COM, etc., are used to release the dedicated connection of the talker.

Figure 6.b: Uplink release for the talker on a dedicated link: normal case

NOTE: The messages CLEAR CMD, CLEAR COM, etc., are used to release the dedicated connection of the talker. The same message flow applies for all cause values different from "call control".

Figure 6.c: Uplink release for the talker on a dedicated link: loss of radio contact or equipment failure (TRX, PCM …)

Figure 6.d: Uplink release for the talker on group call channel: normal case

Figure 6.e: Uplink release for the talker on group call channel: loss of radio contact

NOTE: The messages CLEAR CMD, CLEAR COM, etc., are used to release the radio and terrestrial resources for the cell serving the talker. The same message flow applies for all cause values different from "call control", and "radio interface failure".

Figure 6.f: Uplink release for the talker on group call channel after equipment failure (TRX, PCM …), group call re-establishment by the BSS not supported

The BSC shall send the message UPLINK RELEASE INDICATION with cause value "equipment failure" or another appropriate cause value, if a failure concerning the cell that is serving the talker was detected and the radio and terrestrial resources related to this cell shall be released (see figure 6.5). After receipt of the UPLINK RELEASE INDICATION message the MSC shall send a CLEAR COMMAND message for the respective cell. The BSC does not send CLEAR REQUEST in addition to UPLINK RELEASE INDICATION in order to avoid conflicts.

NOTE: The messages CLEAR CMD, CLEAR COM, etc., are used to release the radio and terrestrial resources for the cell not serving the talker. The same message flow applies also for all other cause values.

Figure 6.g: Release after equipment failure (TRX, PCM …) concerning a cell that is not serving the talker, group call re-establishment by the BSS not supported

The BSC shall send the message CLEAR REQUEST with cause value "equipment failure" or another appropriate cause value, if a failure concerning a cell not serving the talker was detected and the resources related to this cell shall be released (see figure 6.g). After receipt of the CLEAR REQUEST message the MSC shall send a CLEAR COMMAND message for the respective cell.

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

Figure 6.h: A-interface link sharing used or group call re-establishment by the BSS supported:
Uplink release for the talker on group call channel after equipment failure (TRX, PCM …)

If A-interface link sharing is used or group call re-establishment by the BSS is supported, the BSC shall send the message UPLINK RELEASE INDICATION with cause value "equipment failure" or another appropriate cause value, if a failure concerning the cell that is serving the talker was detected. In addition the BSC shall send the VGCS ASSIGNMENT STATUS message indicating that the connection to this cell is no longer established (see figure 6.h). If A-interface link sharing is used, the VGCS ASSIGNMENT STATUS message shall be sent on expiry of timer Tast.

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

Figure 6.i: A-interface link sharing used or group call re-establishment by the BSS supported: Release after equipment failure (TRX, PCM …) concerning a cell that is not serving the talker

If A-interface link sharing is used or group call re-establishment by the BSS is supported, and a failure concerning a cell that is not serving the talker was detected, the BSS shall send the VGCS ASSIGNMENT STATUS message indicating that the connection to this cell is no longer established (see figure 6.i). If A-interface link sharing is used, the VGCS ASSIGNMENT STATUS message shall be sent on expiry of timer Tast.

Figure 6.j: A-interface link sharing used or group 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 group 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 6.h). 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.

MS’

MSs

BSS

MSC-A

GCR

FNT

MSC-R

TERMINATION REQUEST

Release (NOTE 31)

——————————————>

<————————————-

(Specific DTMF messages sequence for call termination (NOTE 32))

(Specific DTMF tone sequence for call termination (NOTE 33))

——————————————>

<————————————————————–

(Specific DTMF tone sequence for call termination (NOTE 34))

<————————————————-

TERMINATION

<——————————————

PROCESS_GROUP CALL_SIGN. (release call) (NOTE 35)

<————————————————————–

Release (normal call clearing)(NOTE 35)

<————————————————————–

CLEAR CMD

Dispatcher release

<—————

————————————–>

CHANNEL

RELEASE

VGCS_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 7: Signalling required to disconnect the group call

TERMINATION REQUEST: An authorized mobile station can send a TERMINATION REQUEST message to clear down the entire voice group call. To do this, the mobile station must have access to the uplink. The network has to check the IMSI to verify the calling service subscriber. If the IMSI of the mobile station which has uplink access is presently not known to the network, the network shall send an identity request to the mobile station

NOTE 31: Alternatively an authorized dispatcher can terminate the voice group call in which case a release message is received from the external network.

NOTE 32: Alternatively an authorized mobile dispatcher can terminate the voice group 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 7b).

NOTE 33: 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 7c).

NOTE 34: Alternatively an authorized fixed line dispatcher can terminate the voice group call by using a specific DTMF tone sequence or other applicable signalling. In case DTMF is used, the specific DTMF tone sequence is received by the anchor MSC (see figure 7d).

NOTE 35: Alternatively an authorized mobile station currently served by a relay MSC can clear down the entire group call in which case either a Release (normal call clearing) is received from the relay MSC (for the case when the calling service subscriber still has the initial dedicated connection to MSC-A) or a PROCESS_GROUP CALL_SIGNALLING message indicating call release is received from the relay MSC (when the calling service subscriber is on the group call channel or has a dedicated connection to the relay MSC).

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

VGCS_TERMIN: The MSC informs the GCR that the voice group call with the related group call reference is terminated.

CHANNEL RELEASE: CHANNEL RELEASE messages are sent 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 talker.

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

In addition, release messages are sent to all related dispatchers and relay MSCs. If the group call termination is initiated by an entitled dispatcher, and there is a dedicated connection for the calling service subscriber between the anchor MSC and the relay MSC, the anchor MSC shall release this connection with cause ‘normal call clearing’.

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 group 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 VGCS 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 7a: Signalling information required for establishing voice group 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 voice group call is sent by the MS to the network in order to set-up a group 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 36: 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 7b: Signalling required for communication of DTMF digit entry by an entitled mobile dispatcher, if the mobile dispatcher is controlled by the anchor MSC of the group call.

Figure 7c: Signalling required for communication of DTMF digit entry by an entitled mobile dispatcher, if the mobile dispatcher is controlled by a visited MSC (could be a relay MSC) of the group call.

Figure 7d: Signalling required for communication of DTMF digit entry by an entitled fixed line dispatcher in case DTMF tone is used.

MS	Unciphered SDCCH	MSSs	Ciphered Group Channel	BSS		MSC
\|		\|		Token	Timers	\|
1.		\|	UPLINK BUSY (Token = A)	A	Start T1	\|
\|		\|	<————————————–	A		\|
\|		\|		:		\|
\|		\|		A	T1 Expires	\|
\|	Periodic UPLINK BUSY (Token = B)			A,B	Start T1, Start Ttv	\|
\|	🡨——————————————–			A,B	Ttv Expires T4	\|
\|	Priority Uplink Request (‘Emergency’, GCRef, Token=B)			B	Stop T1	\|
\|	————————————————————————————————–>			√	Run Tbb	\|
\|		\|	UPLINK BUSY (Token = C)	C	Reset & Restart T1	\|
\|		\|	<————————————–	C		\|
\|		\|		C		\|
\|		\|		C		\|
2.	Priority Uplink Request (‘Emergency’, GCRef, Token=C)			C	Stop T1	\|
\|	————————————————————————————————–>			√	Run Tbb	\|
\|		\|	UPLINK BUSY (Token = D)	D	Reset & Restart T1	\|
\|		\|	<————————————–	D		\|
\|		\|		D		\|
\|		\|		D		\|
\|		\|		D		\|
3.	Priority Uplink Request(Emergency Reset, GCRef, Token=D)			D	Stop T1	\|
\|	————————————————————————————————–>			√	Run Tbb	\|
\|		\|	UPLINK BUSY (Token = E)	E	Reset & Restart T1	\|
\|		\|	<————————————–	E		\|
\|		\|		E		\|
4.	Priority Uplink Request (‘Privilege’, GCRef, Token =P)			E		\|
\|	————————————————————————————————–>			X – discard msg		\|
\|				E		\|
\|		\|	Periodic	E	T1 Expires	\|
\|		\|	UPLINK BUSY (Token = F)	E,F	Start T1, Start Ttv	\|
\|		\|	<————————————–	E,F	Ttv Expires	\|
\|		\|		F		\|
5.	Priority Uplink Request (‘Privilege’, GCRef,)			F		\|
\|	————————————————————————————————–>			X – discard msg		\|
\|				F		\|
\|		\|	Periodic	F	T1 Expires	\|
\|		\|	UPLINK BUSY (Token = G)	F,G	Start T1, Start Ttv	\|
\|		\|	<————————————–	F,G	Ttv Expires	\|
\|		\|		G		\|
6.	Priority Uplink Request (‘Privilege’, GCRef, Token=G)			G	Stop T1	\|
\|	————————————————————————————————–>			√	Run Tbb	\|
\|		\|	UPLINK BUSY (Token = H)	H	Reset & Restart T1	\|
\|		\|	<————————————–	H		\|
\|	Priority Uplink Request (‘Emergency’, GCRef, Token=G)			H		\|
\|	————————————————————————————————–>			X – discard msg		\|
\|	Priority Uplink Request (‘Emergency’, GCRef, Token=H)			H	Stop T1	\|
\|	————————————————————————————————–>			√	Run Tbb	\|
\|		\|	UPLINK BUSY (ID Value = I)	I	Reset & Restart T1	\|
\|		\|	<————————————–	I		\|
\|		\|		I		\|
\|		\|		I		\|
7.	Uplink Release			I		\|
\|	————————————————————————————————–🡪			I	Stop T1	\|
\|		\|				\|
\|		\|	UPLINK FREE			\|
\|		\|	<————————————–			\|
\|		\|				\|
\|		\|	UPLINK ACESS			\|
8.		\|	————————————–>			\|
\|		\|				\|
\|		\|	VGCS UPLINK GRANT			\|
\|		\|	<————————————–			\|
\|		\|	UPLINK BUSY (Token = J)	J	Reset and Restart T1	\|
\|		\|	<————————————–	J		\|
\|		\|		J		\|
\|		\|		J		\|
\|		\|		:		\|
\|		\|				\|

Figure 7e: Validation of Priority Uplink Requests for ciphered group calls

NOTE:
MS = service subscriber requesting priority access to the uplink
MSs = all service subscribers in the group, in this BSS area
Token (A, B…J) = 32bit random number, generated by the BSS. Broadcast in UPLINK BUSY messages on the ciphered group channel downlink (FACCH)

Figure 7e Scenarios:

1. For a service subscriber originated group call, if the call is ciphered, the BSS includes a token in the first UPLINK BUSY message sent on the group channel downlink. For a dispatcher originated group call, if the call is ciphered, the BSS includes a token in the first UPLINK BUSY message sent after the first successful uplink access by a service subscriber. A new token is sent in each periodic UPLINK BUSY message, every T1 seconds. If the old token has not been used it remains valid for a further Ttv seconds along with the new token. Once Ttv expires only the new token is valid. (If, within Ttv seconds, a Priority Uplink Request is received with the old token, the request is accepted, the old and new tokens are invalidated and an UPLINK BUSY, with another new token and the priority of the accepted request, is sent after Tbb ms on the group channel downlink.)

2. Subscriber on the group call with ‘Privilege’ or ‘Emergency’ subscription requests the uplink. Token matches in BSS. A new token, and the priority of the accepted request, are sent after Tbb ms in an UPLINK BUSY on the group channel downlink to ensure higher priority requests can still be made in the cells covered by this BSS. Timer T1 is reset and restarted.

3. Subscriber on the group call with ‘Emergency Mode Reset’ subscription requests an ‘Emergency Mode Reset’. Token matches in BSS. A new token is sent after Tbb ms in an UPLINK BUSY on the group channel downlink. Timer T1 is reset and restarted.

4. User not on the group call makes fraudulent uplink request. Token does not match in BSS. BSS discards message. BSS continues to broadcast tokens in periodic UPLINK BUSY messages.

5. Subscriber on the group call with a ‘Privilege’, ‘Emergency’ or ‘Emergency Mode Reset’ subscription requests the uplink. No token included in the request. BSS discards message. BSS continues to broadcast tokens in periodic UPLINK BUSY messages.

6. Subscriber with a ‘Privilege’ subscription requests the uplink. Token matches in BSS. A new token, and the priority of the accepted request (i.e. ‘Privilege’), are sent after Tbb ms in an UPLINK BUSY on the group channel downlink, however a subscriber with an ‘Emergency’ subscription requests the uplink before the new token has been received by the MS (use of the old token, causes the message to be discarded by BSS). On receipt of the UPLINK BUSY with new token and priority ‘Privilege’, the MS resends the Priority Uplink Request (‘Emergency’) with the new token.

7. When a subscriber releases the uplink, timer T1 is stopped and the BSS broadcasts UPLINK FREE. A token is not broadcast while the uplink is free.

8. A subscriber requests the uplink by sending an UPLINK ACCESS on the group channel uplink. The BSS grants the uplink and a UPLINK BUSY including a new token, and the current talker priority, is sent on the group channel downlink. A new token and the current talker priority is also sent in UPLINK BUSY on the group channel downlink if the uplink becomes busy because it is granted in another BSS or MSC area and an UPLINK_REJECT_CMD or UPLINK_SEIZED_CMD is received by the BSS.

Figure 7f: A listener in the anchor MSC area sends application-specific data to the other group call members, while the group call channel uplink in the cell is free

UPLINK_ACCESS (Establishment_cause=UL Request for sending application-specific data): This message is sent on the uplink of the voice group call channel using random access procedures. The UPLINK ACCESS message is similar to a channel request but sent on the group call channel uplink.

VGCS_UPLINK_GRANT: The BSS grants the uplink of its group call channel immediately. The reply to the uplink request sent on the voice group channel downlink containing information for synchronisation of the mobile station to the network and uplink access contention resolution. The VGCS_UPLINK_GRANT message shall therefore include a request reference (reflecting the UPLINK_ACCESS) and the physical information required for transmission on the voice group call channel uplink.

SABM (DATA_INDICATION (Application_data)): The MS sends a SABM message with its mobile station identity and the Application data to the BSS.

UA(DATA_INDICATION (Application_data)): This message is used to acknowledge the layer 2 link and provide contention resolution of the data indication.

NOTIFY_APPLICATION_DATA (Application_data): If the network option of immediate distribution of application-specific data by the BSS is activated, on receiving the application data sent from the MS, the BSS broadcasts the application data immediately to the cells within the BSC area in a notification message on the FACCH. Optionally, the NOTIFY_APPLICATION_DATA message for application-specific data is repeated on the group call channel downlink. As a prerequisite for the immediate distribution, during the establishment phase of the voice group call the BSC stored the cell identities of the cells belonging to the group call area and served by the BSC.

UPLINK_APPLICATION_DATA (CID, IDI, DATA_INDICATION): The BSS adds the sender’s cell identifier (CID) and passes the L3 information (DATA_INDICATION) via the UPLINK_APPLICATION_DATA message to the MSC. If the BSC has immediately distributed the application data to its BSC area, the BSC shall additionally include the Immediate Distribution Indicator (IDI).

UPLINK_RELEASE: The BSS immediately releases the uplink by sending this message to the MS on the FACCH.

DISC: Standard message to release the layer 2 link.

UA: Standard message to acknowledge release of the layer 2 link. The mobile station returns to group receive mode.

FORWARD_GROUP CALL_SIGNALLING (NOTIFICATION_DATA): On receipt of the UPLINK_APPLICATION_DATA message, the anchor MSC shall put the application data and optionally the mobile subscriber’s MSISDN into the BSSMAP message NOTIFICATION_DATA and distribute the message towards all relay MSCs.

Editor’s note: The condition for including the MSISDN in the BSSMAP message NOTIFICATION_DATA is ffs.

NOTIFICATION_DATA: The MSC sends NOTIFICATION_DATA messages with the application data to all BSSs in their MSC area involved in the group call. If the originating BSC has immediately distributed the application data to its BSC area, the MSC shall not send the NOTIFICATION DATA message to the originating BSC.

NOTIFY_APPLICATION_DATA (Application_data): The BSS broadcasts the application data to all listeners and the talker, if any, in a notification message on the FACCH. Optionally the NOTIFY_APPLICATION_DATA message for application-specific data is repeated on the group call channel downlink. (The broadcast of the application data by the other BSSs is not shown in figure 7f.)

Figure 7g: A talker in the anchor MSC area sends application-specific data to the other group call members.

DATA_INDICATION (Application_data): Since the talker has the uplink and a layer 2 link is established, the MS can send the application data to the BSS.

For the meaning of the other messages see figure 7f. The option of immediate distribution of the application-specific data by the BSC can be applied also in figure 7g, although it is not shown in the message flow (for details see figure 7f).

Figure 7h: A listener in a relay MSC area sends application-specific data to the other group call members, while the group call channel uplink in the cell is free.

In the following only the messages different from figure 7f are explained:

PROCESS_GROUP CALL_SIGNALLING (NOTIFICATION_DATA): On receipt of the UPLINK_APPLICATION_DATA message the relay MSC shall put the application data and optionally the mobile subscriber’s MSISDN into the BSSMAP message NOTIFICATION_DATA and send the message to the anchor MSC.

Editor’s note: The condition for including the MSISDN in the BSSMAP message NOTIFICATION_DATA is for FFS.

FORWARD_GROUP CALL_SIGNALLING (NOTIFICATION_DATA): On receipt of the NOTIFICATION_DATA, the anchor MSC shall forward the message to all relay MSCs except the relay MSC from which the NOTIFICATION_DATA was received. The relay MSCs shall send the NOTIFICATION_DATA messages with the application data to all BSSs in their MSC area involved in the group call. The BSSs shall broadcast the data to all listeners.

For the meaning of the other messages see figure 7f. The option of immediate distribution of the application-specific data by the BSC can be applied also in figure 7h, although it is not shown in the message flow (for details see figure 7f).

UPLINK_ACCESS (Establishment_cause=UL Request for sending application-specific data): This message is sent on the uplink of the voice group call channel using random access procedures. The UPLINK_ACCESS message is similar to a channel request but sent on the group call channel uplink.

VGCS_UPLINK_GRANT: The BSS grants the Uplink of its group call channel immediately. The reply to the uplink request sent on the voice group channel downlink containing information for synchronisation of the mobile station to the network and uplink access contention resolution. The VGCS_UPLINK_GRANT message shall therefore include a request reference (reflecting the UPLINK_ACCESS) and the physical information required for transmission on the voice group call channel uplink.

SABM (DATA_INDICATION (Application_data)): The MS sends a SABM message with its mobile station identity and the Application_data to the BSS. For the purpose of identifying the received data, the data_id which was received in the message that contained the application data that is being confirmed shall be included in the message.

For the meaning of the other messages see figure 7f. The option of immediate distribution of the application-specific data by the BSC can be applied also in figure 7i, although it is not shown in the message flow (for details see figure 7f).

Figure 7j: A listener in the anchor MSC area sends application-specific data that are not time-critical via RACH to the other group call members, while the talker is using the group call channel uplink in the same cell.

RACH (CHAN_REQ): The network supports uplink access option (i) as defined in subclause 7.2, and the talker is on the group call channel in the same cell as the mobile station of the listener; therefore, the "uplink access indication for data" in the uplink busy message instructs the mobile station to use the RACH when application-specific data is to be sent.

The mobile station leaves the group receive mode and sends the CHANNEL_REQUEST message with an appropriate establishment cause via the RACH to request an SDCCH.

IMM_ASS: Standard message sent on the AGCH.

SABM (DATA_INDICATION_2 (Application_data)): The MS sends a SABM message with its mobile station identity and the Application_data to the BSS on SDCCH. The network determines from the group call reference included in the message which group call is addressed by this message.

UA (DATA_INDICATION_2 (Application_data)): This message is used to acknowledge the layer 2 link and provide contention resolution of the data indication 2.

NOTE 1: Optionally, on receipt of the UA (DATA_INDICATION_2 (Application_data) the mobile station performs a local release of the layer 2 link, i.e. without exchange of DISC/UA, and returns to group receive mode.

NOTIFY_APPLICATION_DATA (Application_data): If the network option of immediate distribution of application-specific data by the BSC is activated, on receiving the application data sent from the MS, the BSS broadcasts the application data immediately to the cells within the BSC area in a notification message on the FACCH. Optionally, the NOTIFY_APPLICATION_DATA message for application-specific data is repeated on the group call channel downlink. As a prerequisite for the immediate distribution, during the establishment phase of the voice group call the BSC stored the cell identities of the cells belonging to the group call area and served by the BSC.

UPLINK_APPLICATION_DATA (CID, IDI, DATA_INDICATION_2): The BSS adds the sender’s cell identifier (CID) and passes the L3 information (DATA_INDICATION_2) via the UPLINK_APPLICATION_DATA message to the MSC. If the BSC has immediately distributed the application data to its BSC area, the BSC shall additionally include the Immediate Distribution Indicator (IDI).

CHANNEL_RELEASE: The BSS immediately releases the uplink by sending this message to the MS on the SDCCH including the channel description of the voice group call channel to which the mobile station shall tune to. The mobile station returns to group receive mode.

NOTE 2: If the mobile station performed a local release of the layer 2 link, the following two messages will not be exchanged. Instead T3109 in the BSS will expire and the BSS will release the channel.

DISC: Standard message to release the layer 2 link.

UA: Standard message to acknowledge release of the layer 2 link. The mobile station returns to group receive mode.

For the meaning of the other messages see figure 7f.