11.3.7 Uplink and Downlink management

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

11.3.7.1 Uplink transmission management

The downlink FACCH channel shall be used to indicate whether the uplink is in use.

If a request to talk is made by the user and the uplink has been free the mobile station shall start to transmit UPLINK_ACCESS messages as defined in the 3GPP TS 44.018.

If the network supports the use of talker priorities, a mobile station supporting the use of talker priorities may

– send a request to talk even if an uplink busy indication is received, if the talker priority of the new request is higher than the talker priority of the current talking service subscriber; or

– send an emergency mode reset request, if the emergency mode indication is signalled by the network.

If a VGCS_UPLINK_GRANT message is received by the mobile station with a different request reference than that of the access made by the mobile station, the mobile station shall not signal for a further 1 s.

If in this time the uplink becomes busy, and the network does not support the use of talker priorities, the mobile station shall indicate to the user that the access has been denied.

If in this time the uplink becomes busy, and the network indicates in the UPLINK_BUSY message a talker priority equal or higher than the talker priority used by the mobile station in the UPLINK_ACCESS message or PRIORITY_UPLINK_REQUEST message, the mobile station shall indicate to the user that the access has been denied; otherwise, it shall resend the UPLINK_ACCESS message or PRIORITY_UPLINK_REQUEST message, respectively.

The user shall be provided with a short indication immediately after the reception of the VGCS_UPLINK_GRANT which indicates that he can speak. Contention caused by simultaneous access messages on the uplink of the voice group call channel shall be resolved as for standard random access procedures. If the uplink access is rejected a further indication shall be provided to the user to inform him that his access attempt was not successful.

The network then shall send an UPLINK_BUSY message on the FACCH of the voice group call channel downlink in all cells involved in the group call.

Signalling messages for call establishment and termination on the voice group call channel shall then only apply for the mobile station currently using the uplink. All other mobile stations shall not respond to this downlink signalling. Once the request to talk is over, this shall be indicated to the network by the mobile station, an UPLINK_FREE message is broadcast on all FACCHs in the group call area.

If the network supports the use of talker priorities, the BSS shall include the priority of the current talker in the UPLINK_BUSY message and shall repeat the message on the FACCH every T1 seconds.

If the network supports uplink access option (i) as defined in subclause 7.2, the BSS shall indicate in the UPLINK_BUSY message which channel shall be used by service subscribers for an uplink request in the current cell. The UPLINK_BUSY message can contain two different indications. The mobile station of the service subscriber shall act:

– according to the "uplink access indication for talker priority" when signalling an uplink request with talker priority higher than "normal subscriber" or an "emergency mode reset request; or

– according to the "uplink access indication for data" when signalling an uplink request for sending application-specific data.

If both indications are included in the UPLINK_BUSY message, they should be set to the same value.

If the "talker channel parameter" is used and indicates that the network shall always establish and maintain a dedicated channel for the talking service subscriber, then the BSS shall set any uplink access indication included in the uplink busy message (i.e. "uplink access indication for data", "uplink access indication for talker priority", or both) to "group call channel uplink access".

Otherwise, the BSS shall apply the following procedures:

If the talking service subscriber uses the group call channel uplink in the current cell, the BSS shall indicate in the UPLINK_BUSY message that the RACH shall be used; otherwise it shall indicate that the group call channel uplink shall be used. The BSS shall immediately send an updated UPLINK_BUSY message:

– in the handover target cell when the BSS allocates the resources for a handover of the talking service subscriber to the voice group call channel in the target cell;

– in the handover target cell when BSS releases the resources allocated for the handover of the talking service subscriber to the voice group call channel in the target cell, because handover failed;

– in the handover source cell after reception of a HANDOVER SUCCEEDED message;

– in the current cell after the talking service subscriber has been switched within the cell from the group call channel to a dedicated channel or vice versa.

When the BSS receives an indication from the MSC that the emergency mode is set in the network, the BSS shall immediately send an UPLINK_BUSY message on the FACCH and include also the "emergency mode indication".

If the BSS receives a VGCS Additional Info message from the MSC, an ADDITIONAL_INFO message is broadcasted on the FACCHs of the voice group call channel downlink in all cells involved in the current group call. If the BSS receives the additional information in the UPLINK_SEIZED_CMD, UPLINK_REQUEST_ACKNOWLEDGE or UPLINK_REJECT_CMD message then the BSS may include the information in the UPLINK BUSY message instead of sending it in a separate ADDITIONAL_INFO message on the group call channel downlink. The BSS shall repeat the ADDITIONAL_INFO message on the SACCHs of the respective voice group call channels every T2 seconds, until the uplink is released, or the BSS receives an Uplink Release Command message or Uplink Seized Command message for the respective voice group call from the MSC.

If the BSS receives a VGCS Additional Info message from the MSC and the current talker on a dedicated channel is pre-empted by another service subscriber with a higher talker priority, the BSS shall transmit the additional information about the new talker also to the current talker when releasing his dedicated channel.

11.3.7.1a Transfer of a talking service subscriber to a dedicated connection

The network may decide to switch a talking service subscriber’s mobile station from the voice group call channel to a dedicated standard uplink/downlink at any time. The talking subscriber’s voice group call channel and the dedicated channel may belong to different cells within the group call area, i.e. the network may request the talker to perform a handover. The dedicated connection shall then be maintained up to the instance where the network decides that the mobile station shall join the voice group call channel again.

If the "talker channel parameter" is used and indicates that the network shall always establish and maintain a dedicated channel for the talking service subscriber, a dedicated traffic channel shall be allocated to the talking service subscriber. If there are not sufficient radio resources to allocate a suitable dedicated channel in a cell within the group call area, the MSC shall release the uplink of the voice group call channel used by the talking service subscriber.

11.3.7.1b Release of the dedicated transmission means of a talking service subscriber

For the release of the dedicated transmission means of a talking service subscriber the procedures specified in subclause 11.3.1.1.3 apply accordingly.

11.3.7.2 Mute/Unmute downlink of the talker

This subclause applies to networks where the talking service subscriber may use the voice group call channel. The handling of the Mute/Unmute requests by the anchor MSC is shown in Figure 1a.

The mobile station of the talking service subscriber shall mute the downlink to avoid non intelligible echoes when it is commanded by the network to mute the downlink. On request of the dispatcher, the network can command the mobile station of talking service subscriber to mute or unmute the downlink.

If a dispatcher originates a VGCS call, he is allowed to talk immediately when the VGCS call is established. If a dispatcher joins or re-joins an ongoing VGCS call, he is allowed to talk to the ongoing VGCS call at any time without need to indicate this by any kind of signalling. If there is a talking service subscriber using the uplink of the group call channel, he will not be able to hear the dispatcher’s voice.

If a dispatcher wishes to talk to the talking service subscriber and all members of the ongoing group call, he shall indicate his wish by means of an operator-defined operation. If the dispatcher has finished speaking, he shall indicate this by means of another operator-defined operation. These operations (via DTMF or the signalling option specified in ETSI TS 103 389 [19]) will trigger the network to command the talking service subscriber’s MS to mute or unmute the downlink of voice group call channel.

When the network has detected a valid unmute request from a dispatcher it may optionally indicate the recognition of this request by playing a “grant tone” to be received by the requesting dispatcher only. The grant tone will be sent in-band. The attributes of the grant tone (e.g. frequency and duration) are network operator specific.

A dispatcher can be a mobile subscriber or a fixed line subscriber. The dispatcher uses out-of-band DTMF messages if it is a mobile dispatcher. The dispatcher uses DTMF tones or the signalling option specified in ETSI TS 103 389 [19], if it is a fixed line dispatcher. In case of a mobile dispatcher, the out-of-band messages START_DTMF(X) and STOP_DTMF are sent via the radio interface towards the network. If the out-of-band DTMF messages are sent by a mobile dispatcher who is not controlled by the anchor MSC, the DTMF messages will be converted by the controlling MSC (e.g. visited MSC) into DTMF tones and these DTMF tones will be sent through the network to the anchor MSC. If a fixed line dispatcher initiates DTMF tones, the DTMF tones will be sent through the network to the anchor MSC.

NOTE: The transport of DTMF tones within the network is detailed in figures 7b, 7c and 7d.

Both for mobile and fixed line dispatchers the anchor MSC is responsible for the detection and collection of the out-of-band or inband DTMF signals. After the evaluation of the received information, the anchor MSC shall trigger the appropriate action (i.e. send/not send the SET_PARAMETER message according to previous paragraphs, playing of the optional grant tone).

The DTMF sequences used for signalling are implementation specific. These two DTMF sequences shall not be the same.

Figure 1a: Handling of Mute/Unmute Requests in Anchor MSC (Sheet 1 of 3)

Figure 1a: Handling of Mute/Unmute Requests in Anchor MSC (Sheet 2 of 3)

Figure 1a: Handling of Mute/Unmute Requests in Anchor MSC (Sheet 3 of 3)

Figure 1b: Handling of Mute/Unmute Requests in Relay MSC (Sheet 1 of 2)

Figure 1b: Handling of Mute/Unmute Requests in Relay MSC (Sheet 2 of 2)