Service subscribers can become group members on a PLMN wide basis to one or more groups pre-defined in the network by a corresponding group identification (group ID). The membership enables them to initiate or receive voice group calls associated with that group ID. Certain dispatchers connected to external networks also require the capability to initiate or receive voice group calls.
A prefix can be used together with the group ID to define a subset of the group members and to restrict the group of service subscribers able to receive a voice group call to this subset.
In addition to subscriber details in the HLR, it is necessary for the mobile station to be aware of its group membership by storing details on the SIM/USIM. This is required because it shall respond to notification messages which include only the group ID (i.e. no IMSI or TMSI details).
Having become a group member, each service subscriber can set to active state or deactive state the group ID or any one out of his several group IDs on the SIM/USIM. In active state the subscriber can initiate voice group calls to that group. When in deactive state the subscriber can not make voice group calls to the group and the mobile station ignores any notification for that group.
If no NCH is defined in the cell, mobiles shall assume VGCS service is not available on that cell.
A group call area can be restricted to a single MSC area or can exceed one MSC area. In a RANflex configuration (with or without group call redundancy) a group call area can be restricted to a single pool area or can exceed one pool area.
A voice group call shall be initiated by a calling service subscriber by a related input function, e.g. via MMI, specifying the selected service and the group ID dialled or by a calling dispatcher by the MSISDN address (see subclause 9.2). As an option, a calling service subscriber may add a prefix to the group ID. As an option, the request of the calling service subscriber to set up a voice group call may specify information to be sent as originator-to-dispatcher information to the network; in this case the originator to dispatcher information is included in the signalling for call setup from the mobile station to the network. It is the responsibility of the input function to ensure that the originator-to-dispatcher information has a correct format (in particular, an allowed length).
As a further option, the request of the calling subscriber may indicate one of the following talker priorities, listed in ascending order of talker priority:
normal subscriber;
privileged subscriber;
emergency subscriber.
A mobile station supporting the use of talker priorities shall check with the SIM/USIM whether the subscriber is allowed to use the requested talker priority for the respective group ID before signalling the talker priority to the network.
On reception of a VGCS setup request with a talker priority different from "normal subscriber", the MSC shall check with the VLR whether the subscriber has a subscription to use this talker priority. If the subscriber is not allowed to use the requested talker priority, the MSC shall reduce the talker priority to a value the subscriber is allowed to use. In any case the talker priority used by the MSC shall be signalled back to the calling service subscriber in the Connect message.
If a VGCS setup request with talker priority "emergency subscriber" is received by the network and the subscription check is successful, the network shall set the emergency mode for this voice group call. The emergency mode may be reset during the voice group call (see subclause 4.2.2.1).
If a prefix is added to the group ID, the MSC shall ignore the prefix when performing the subscription check.
The MSC in which a voice group call is initiated obtains the group call attributes by requesting the Group Call Register (GCR, see clause 5). Without a RANflex configuration or in a RANflex configuration (with or without group call redundancy), if visited MSC and group call serving MSC are identical, the MSC performs a local GCR interrogation.
The local GCR interrogation after call initiation also determines whether the MSC shall act as anchor or as relay MSC. If the MSC is not the anchor MSC then the call will be "forwarded" from the relay to the respective anchor MSC (information also delivered by GCR) and further "call-establishment" is done by the anchor MSC as described in the following.
In a RANflex configuration the VMSC in which a voice group call is initiated may be different from the group call serving MSC of the voice group call initiating subscriber's location area. In this case the VMSC derives the identity of the group call serving MSC from the initiating subscriber's LAC and requests the group call anchor MSC address from the group call serving MSC by means of the SEND_GROUP_CALL_INFO MAP service. The call is then "forwarded" from the VMSC to the anchor MSC and further "call-establishment" is done by the anchor MSC as described in the following.
In a RANflex configuration with group call redundancy the VMSC in which a voice group call is initiated may not belong to the group call serving MSC redundancy pool of the voice group call initiating subscriber's location area. In this case the VMSC derives the identity of the group call serving MSC redundancy pool from the initiating subscriber's LAC and requests the group call anchor MSC redundancy pool address from the group call serving MSC by means of the SEND_GROUP_CALL_INFO MAP service. The call is then "forwarded" from the VMSC to the anchor MSC redundancy pool and further "call-establishment" is done by the selected anchor MSC as described in the following.
When a calling service subscriber or calling dispatcher initiates a voice group call, one voice group call channel shall be established in each cell of the group call area and notifications for that call shall be sent in each of these cells. As an alternative, voice group call channels may only be established in cells in reaction to responses received from mobile stations on the notifications using notification response procedure. At the same time standard connections to dispatchers in the mobile network or in an external network shall be established. If originator-to-dispatcher information has been received in the signalling for call setup from the mobile station to the network and if the originating MSC supports processing of originator to dispatcher information, this information is transformed into user-to-user information and sent to the dispatchers as UUS1 when setting up the standard connections.
A voice group call channel shall consist of a combined uplink/downlink. The uplink will be used exclusively by the presently talking service subscriber. All mobile stations of the listening service subscribers in one cell shall only listen to the same common downlink.
During call establishment there are different options for the network to allocate a speech channel for the calling service subscriber:
In the first option, the calling service subscriber shall have its dedicated standard connection during call establishment and for the first period when he will be the talking service subscriber up to the time when the network decides that he shall join the voice group call channel. The mobile station of the calling service subscriber shall then go to the voice group call channel and the dedicated standard connection shall be released.
In the second option, the network shall allocate a dedicated signalling channel (e.g. SDCCH) to be used by the mobile station up to the time when the voice group call channel in the originating cell is established and the network decides that the mobile station shall join the voice group call channel.
Only one voice group call channel shall be established in each cell for any given voice group call, although there may be a number of simultaneous voice group calls within the same cell.
Destination service subscribers shall be notified on the voice group call in each cell. These voice group call notification messages shall be broadcast on the Notification CHannel (NCH).
The notification messages use the group ID rather than individual TMSIs/IMSIs. If the length of the group ID is less than 8 decimal digits , then the group call area ID is used in order to enable a resolution in the case of overlapping group call areas. A service subscriber's mobile station needs to be able to recognise notification messages for those group IDs subscribed to and presently activated. If the mobile station supports the use of prefixes with group IDs and has stored prefixes for a group ID, it shall take these prefixes into account following detection of a match of the group ID.
The network may also send messages on appropriate voice group call channel FACCHs, in order to notify group call members who may participate in other voice group calls. In addition, also paging information messages for standard calls may be sent in order to inform group call members on actually paged point-to-point calls.
Further the network may provide notification on the voice group call to service subscribers who have subscribed to the paged group ID and which are in dedicated mode. The process of broadcasting messages on NCHs is to be carried out throughout the call in order to provide the "late entry" facility whereby group members entering the area can join the call.
If the emergency mode is set for a voice group call, the network shall include an emergency mode indication in the voice group call notification messages sent on the NCH, the group call channel FACCHs of all other ongoing voice group calls, voice broadcast calls, and the FACCHs associated with dedicated channels.
On receiving notification of a voice group call a group call member's mobile station shall adjust to the nominated channel to receive the voice group call if this channel was described in the notification message and receive the information on the downlink. Whilst receiving, the mobile station shall not transmit on the uplink SACCH. This group receive mode is different to the normal idle mode or dedicated mode. If no channel description was provided in the notification message, the mobile station shall establish a dedicated connection by use of the notification response procedure in order to respond to the notification. The network may then provide the mobile station with a channel description for the voice group call.
As a further mobile station option, the mobile station may read its paging subchannel in the current cell while in group receive mode or in group transmit mode in order to receive paging messages for mobile terminated calls.
Completion of links into congested cells where pre-emption did not occur is required.
On receiving details of a voice group call the user may choose to move to the notified call or the mobile station may automatically move to the notified call if the new call is of higher priority than the existing call and automatic acceptance applies for this priority level.
Within each voice group call starting from the instant where the calling service subscriber first becomes a listening service subscriber, one service subscriber has the access at any one time to the uplink of the voice group call channel and his speech is then broadcast on all voice group call channel downlinks accordingly. The mobile station of the talking service subscriber who uses the uplink of the voice group call channel can be commanded by the network to mute or unmute the downlink of the voice group channel when needed. The mobile station is commanded:
to mute the downlink in order to avoid non intelligible echoes (in this case, the talking service subscriber can not hear dispatcher's voice); and
to unmute the downlink in order to hear dispatcher's voice .
Either DTMF or the signalling option specified in ETSI TS 103 389 [19] shall be used by dispatchers to trigger network signalling to mute and un-mute the downlink of a talking service subscriber as described in subclause 11.3.7.2.
If more than one service subscriber applies for the uplink, contention resolution shall be performed in the network. Contention resolution shall be performed in the group call anchor MSC.
Additionally, in order to speed up the uplink access procedure, the BSS may grant the uplink prior to contention resolution being performed by the group call anchor MSC. This would mean that more than one service subscriber may access to the uplink and the respective speech may be combined in the group call bridge and broadcast onto all voice group call downlink channels during a transitional period. The anchor MSC shall then select one of the talking subscribers and pre-empt the uplink use of the other talking subscribers.
Dispatchers' voice involved shall be broadcast on the voice group call channel downlink at any time. Mobile dispatchers are provided with a standard link and thus with a dedicated permanent uplink different from the voice group call channel.
All non-dispatcher group call members are provided with an indication on the voice group call channel of whether the uplink is in use. If a network supports the use of talker priorities, it shall indicate the talker priority of the current talking service subscriber together with this uplink busy indication, and repeat the uplink busy indication periodically. When the uplink is not in use, any non-dispatcher group call member can request access to the uplink. Any speech from dispatchers is combined with any speech from a talking service subscriber.
The talker priorities specified in subclause 4.2.1.1 can be included by the mobile station in the uplink access message or priority uplink request message and used by the network to prioritize between different uplink requests or between an uplink request and the priority of the current talker. A mobile station shall not include a talker priority different from "normal subscriber" in the uplink access message and shall not send a priority uplink request message, if the network has indicated in the uplink busy message that talker priorities are not supported.
An uplink request with talker priority "normal subscriber" is signalled as an uplink request without talker priority.
If a subscriber requests for the uplink while the uplink is in use, a mobile station supporting the use of talker priorities shall signal the request to the network only if:
the subscriber is allowed to use the requested talker priority for the respective group ID;
the network supports the use of talker priorities. The mobile station shall assume that the network supports talker priorities, until the mobile station receives an uplink busy indication containing no talker priority information; and
the requested talker priority is higher than the talker priority of the current talking service subscriber. The mobile station shall consider the talker priority of the current talking service subscriber to be "normal subscriber", until it receives an uplink busy indication indicating the actual talker priority.
If the BSS receives an uplink access message with a talker priority different from "normal subscriber", a BSS supporting the use of talker priorities shall delay the sending of the uplink request message to the MSC, until the MS identity, IMSI or TMSI, is received from the MS with the subsequent layer 3 message talker indication. The BSS shall then include in the uplink request message the layer 3 message, the requested talker priority, and the cell identity of the cell where the uplink access message was received.
If the BSS receives a layer 3 message priority uplink request, it shall include the MS identity received from the MS in the uplink request message. The BSS shall also include, in the uplink request message, the requested talker priority and the cell identity of the cell where the priority uplink request message was received.
The BSS shall send the uplink request message to the MSC only if the uplink is free or if the talker priority included in the uplink access is higher than the talker priority of the current talking service subscriber. If the layer 3 message is transmitted in the uplink request message, the BSS may omit the sending of the uplink request confirm message.
In a RANflex configuration (with or without group call redundancy), if the group call serving MSC receives an uplink request message it shall check by analysing the NRI of the requesting subscriber's TMSI whether it is the requesting subscriber's VMSC. If it is not, the group call serving MSC shall retrieve the IMSI and information about subscribed talker priorities from the VLR of the VMSC by means of the MAP service SEND_GROUP_CALL_INFO. During this MAP operation the VMSC shall check the subscription for the group ID.
In any configuration, if the MSC receives a talker request with a talker priority different from "normal subscriber" from the BSS, the MSC shall check whether the subscriber has a subscription to use this priority:
if the subscriber is allowed to use the requested priority, the network shall disconnect the uplink allocated to the current talking service subscriber and assign the uplink to the requesting service subscriber;
otherwise, the network shall reject the uplink request with cause value "requested option not authorized".
If a talker request with talker priority "emergency subscriber" is received from a subscriber who has a subscription to use this priority, the network shall additionally set the emergency mode and signal the emergency mode indication
to the listeners of the group call, and
to the other group members in the group call area with the group ID active, regardless whether they are in idle mode or dedicated mode, or participate in a different group call,
until the emergency mode is reset by a subscriber with a specific subscription to do this. If the uplink is busy then the indication to the listeners shall be given periodically every T1 seconds. The emergency mode indication has no influence on the talker priority handling.
If a subscriber requests to reset of the emergency mode, a mobile station supporting the use of talker priorities shall send an uplink access message or priority uplink request message indicating "emergency mode reset request" only if
the subscriber has a subscription for this request for the respective group ID; and
the network indicates that the emergency mode is set.
If the BSS receives an uplink access message with an "emergency mode reset request", a BSS supporting the use of talker priorities shall wait until the MS provides the MS identity, IMSI or TMSI, with the subsequent layer 3 message talker indication. Then the BSS shall send an emergency reset indication to the MSC including the layer 3 message and the cell identity of the cell where the uplink access message was received.
If the BSS receives a layer 3 message priority uplink request, it shall include the MS identity received from the MS in the emergency reset indication. The BSS shall also include, in the emergency reset indication message, the cell identity of the cell where the priority uplink request message was received.
If the MSC receives an emergency reset indication from the BSS, the MSC shall check whether the subscriber has a subscription for this request. If so, the network shall:
stop sending the emergency mode indication; and
set the talker priority to "normal subscriber", if the uplink status is uplink busy with talker priority "emergency subscriber".
If the subscriber has no subscription for the request or if the emergency mode is not set, then the MSC shall discard the request.
The receipt of an "emergency mode reset request" does not trigger a talker change.
If more than one service subscriber applies for the uplink, the one with the highest talker priority shall be accepted. An uplink access message or priority uplink request message with an "emergency mode reset request" shall be treated with higher priority than any uplink request with talker priority "normal subscriber", "privileged subscriber" or "emergency subscriber". If several requests with the same highest priority are received, contention resolution between these requests shall be performed in the network. For the ranking of uplink access messages by the BSC, if the network additionally supports the transfer of time-critical application-specific data, see subclause 4.2.8.2.2 a.
Contention resolution shall be performed by the BSC, relay MSC or anchor MSC which is the first to detect that more than one request with the same highest priority was received. An MSC performing contention resolution shall select the service subscriber whose request was received first by the MSC and pre-empt the uplink use of the other service subscribers. For contention resolution performed by the BSC see subclause 11.3.7.1.
Mobile stations shall support the reception of additional information related to the current talking service subscriber. The transmission of additional information is optional for the network. If additional information is provided, then it is periodically repeated by the network as long as the current talking service subscriber keeps the uplink. The additional information consists of a string of up to 17 octets and is stored in the HLR as part of the subscription data of the subscriber. The contents and the encoding of the additional information is operator specific.
The release of the uplink is triggered by the user and indicated by the mobile station to the network. The network shall then indicate to the listening mobile stations that the uplink is free.
Mobile stations in group receive mode use the group receive mode procedure (see TS 43.022) to "camp-on" in a new cell to be able to listen to the group call channel. The mobile station may find the voice group call channel details of a new cell on the related NCH.
A network may decide not to establish voice group call channels in all cells. Instead, notifications containing no channel description may be provided. If a mobile station moves to such a cell, it must establish a dedicated connection and respond to the notification by use of the notification response procedure in order to receive the voice group call. The network may then establish a voice group call channel and inform the mobile station on the channel position.
If the uplink reply procedure is applicable for the voice group call, the network may obtain knowledge on whether mobile stations are listening in a cell by sending an uplink access request (perform uplink reply procedure) in an uplink free message on the voice group call channel downlink when no talking service subscriber is present in the cell. Mobile stations receiving such a request shall use uplink reply procedure and send uplink access bursts on the voice group call channel uplink with the establishment cause "reply on uplink access request". If no uplink access bursts are received by the network, the network may decide to release the voice group call channel in that cell and then provide notifications containing no channel description.
The network may decide to reconfigure an existing voice group call's physical channel configuration, frequencies and/or hopping sequences as well as the cell channel description. For the cell in which the group call is being reconfigured, the network informs any listeners in group receive mode and any talker in group transmit mode of the change in VGCS channel description by using the VGCS reconfiguration procedure (see TS 44.018). Mobile stations on receipt of the VBS/VGCS reconfiguration messages shall remain on the existing group channel until indicated starting time and then apply the new configuration to the VGCS call that the mobile station is currently involved in.
When a talking subscriber's mobile station loses contact with the network, the network must detect this loss and set the uplink free so that other mobile stations may access the uplink. The talking subscriber's mobile station which has lost the contact with the network shall return immediately to the group receive mode.
If a mobile station in group receive mode indicates a failure due to radio link time-out, the mobile station shall behave as specified in TS 45.008 and go back to idle mode, possibly in another cell, as determined by the cell re-selection algorithm. If a notification is received for the same call, the mobile station shall try to reconnect.
