3.4.15 Group receive mode procedures
3GPP44.018GSM/EDGE Radio Resource Control (RRC) protocolMobile radio interface Layer 3 specificationRelease 17TS
Only applicable for support of VGCS listening or VBS listening.
3.4.15.1 Mobile station side
3.4.15.1.1 Reception of the VGCS or VBS channel
3.4.15.1.1.1 General
In group receive mode, the mobile station receives the downlink of the voice broadcast channel or voice group call channel for which the channel description was provided within the notification message or in the related command message. The mobile station should also listen to the CCCH of the serving cell. Moreover, it measures the received levels on the serving cell and on the neighbour cells to assess the need for a cell reselection as specified in 3GPP TS 45.008. The general cell reselection procedure for the mobile station in group receive mode is described in 3GPP TS 23.022. If the group call is ciphered then the MS on cell reselection shall recalculate the cipher keys and obtain the identity of its ciphering algorithm as described in sub-clause 3.4.15.1.1.2.
Information on neighbour cells used for cell reselection and reception of the VGCS or VBS channel in the neighbour cells may be provided on the downlink messages (see sub-clause 3.4.15.1.2). If no such information is provided or information is missing, the mobile station shall try to read this information on the BCCH and NCH of the neighbour cells.
3.4.15.1.1.2 Reception on ciphered VGCS or VBS channel
The MS shall derive the group cipher key using the following parameters:
– VSTK_RAND – obtained via the notification message;
– CELL_GLOBAL_COUNT – obtained via the NCH, Notification/FACCH or Paging Request Type 1;
– CGI – obtained via System Information 3 or 4;
– Group Cipher Key Number – obtained via the group call reference.
The derivation of the key from the above parameters is explained in 3GPP TS 43.020.
The MS shall obtain the identity of its ciphering algorithm from its USIM, as described in 3GPP TS 43.020.
3.4.15.1.2 Monitoring of downlink messages and related procedures
Mobile stations in group receive mode shall monitor messages related to the following procedures on the VGCS or VBS channel downlink and act appropriately in order to be able to keep receiving the VGCS or VBS channel downlink.
All messages for mobile stations in group receive mode shall be sent in UI format on the VGCS or VBS channel downlink. Mobile stations in group receive mode shall ignore all messages which are not sent in UI format or which are not related to the following mentioned procedures.
The mobile should also monitor messages on the PCH or NCH of the current cell.
3.4.15.1.2.1 (void)
3.4.15.1.2.2 (void)
3.4.15.1.2.3 Channel mode modify procedure
The mobile station shall receive CHANNEL MODE MODIFY messages. The mobile station shall use the new channel mode but shall not transmit any response to the network.
3.4.15.1.2.4 Notification and paging information
The mobile station shall monitor messages related to notification and paging procedures.
The RR entity shall provide indications on all received notifications for voice group calls or voice broadcast calls to the upper layer. The indication shall include the notified group or broadcast call reference and, if provided, and if the mobile station supports eMLPP the related priority.
On request by the upper layer to join another voice broadcast call or voice group call for which a corresponding notification has been received on the VGCS or VBS channel downlink, the RR entity shall read the corresponding notification on the NCH.
If the mobile station has received a paging message with its own mobile station identity on the PCH or on the voice broadcast channel or voice group call channel downlink, the RR entity shall provide an indication to the upper layers, together with the related priority, if applicable.
When a paging message that contains an indication of the paging cause (mobile terminating call or short message) is received on the VBS or VGCS channel, this indication shall also be passed to the upper layer. If no paging cause is present in the paging message the VBS/VGCS mobile station shall assume that the paging is for a mobile terminating call.
3.4.15.1.2.4.1 Use of Reduced NCH monitoring
This sub-clause applies to mobile stations which are in group receive mode or group transmit mode of dedicated mode and which in addition want to receive notification messages for other voice broadcast calls or voice group calls and which aim at reducing the reception load.
When the MS in group receive mode or group transmit mode enters a cell, it may read the NCH until it has received at least two messages on the NCH indicating NLN, with the two last received NLN being identical. Then it may stop reading the NCH until it receives on the SACCH an NLN(SACCH) different from the last previously received NLN.
For this, a parameter is provided on the SACCH in the SYSTEM INFORMATION TYPE 6 message:
– NLN(SACCH): Notification List Number.
If a mobile station receives on the SACCH an NLN(SACCH) different from the last received NLN it may read the NCH until it has received at least two messages on the NCH indicating NLN with the two last received NLN being identical.
If a message in the SACCH is not received correctly the MS may read the NCH until it has received at least two messages on the NCH indicating NLN, with the two last received NLN being identical.
3.4.15.1.2.5 Uplink status messages
Mobile stations supporting VGCS talking shall monitor the VGCS uplink control related messages UPLINK FREE and UPLINK BUSY.
3.4.15.1.2.6 Channel release message
The mobile station shall receive CHANNEL RELEASE messages. On receipt of a CHANNEL RELEASE message, the RR entity shall go to idle mode and give an indication to the upper layer. (See also sub-clause 3.4.15.1.4.1, 4th paragraph.)
3.4.15.1.2.7 Information on paging channel restructuring
On receipt of a SYSTEM INFORMATION TYPE 6 message indicating that paging channel restructuring has taken place, if the mobile station wants to be able to read its paging subchannel while in group receive mode or group transmit mode, the mobile station should read the related messages on the BCCH to know the position of its paging group.
3.4.15.1.3 Uplink reply procedure
In Group Receive mode, on receipt of an UPLINK FREE message with an uplink access request indication from the network on the voice group call channel downlink or voice broadcast channel downlink, the mobile station shall send two UPLINK ACCESS messages on the voice group call channel uplink or voice broadcast channel uplink with establishment cause "Reply on uplink access request" and then stop immediately transmitting on the uplink.
The first UPLINK ACCESS message shall be transmitted by the mobile station with a random delay between 0 and 20 ms. The second UPLINK ACCESS messages shall be repeated after a further period of 100 ms plus a random delay between 0 and 20 ms. The UPLINK ACCESS messages shall be sent unciphered.
If an uplink identity code (UIC) of the current cell has been provided by the network in the UPLINK FREE message, the mobile station shall use this UIC for the coding of the UPLINK ACCESS messages. If no UIC is provided, the mobile station shall use the BSIC received of the serving cell, for instance as received from the initial synchronization.
3.4.15.1.4 Leaving the group receive mode
3.4.15.1.4.1 Returning to idle mode
If the mobile station enters a new cell in which:
– notifications for the current group or broadcast call are sent; but
– no VGCS or VBS channel description for the current group or broadcast call is provided,
the mobile station shall go to idle mode and give an indication to the upper (sub-)layers.
NOTE: Upper (sub-)layers then can request the establishment of an RR connection in order to be informed about the channel description by the network.
If the mobile station enters a cell in which notifications for the current group or broadcast call are not sent, the mobile station shall disconnect locally the TCH, go to idle mode and give an indication to the upper (sub-)layers.
On request by the upper layer in order to respond to a paging message the RR entity shall go to the idle mode in order to establish a dedicated RR connection.
On receipt of a CHANNEL RELEASE message in UI format from the network the RR entity shall go to idle mode and give an indication to the upper layer.
If the upper layer requests to abort the group receive mode, the mobile station shall go back to idle mode.
3.4.15.1.4.2 Going to group transmit mode
Only applicable for mobile stations supporting VGCS talking.
If the upper layer requests an uplink access, the mobile station shall perform the uplink investigation procedure as defined in sub-clause 3.3.1.2.1.1 and 3.3.1.2.1.1a.
If the uplink investigation procedure is not successful, the mobile station shall give an indication to the upper layers and remain in group receive mode.
If the uplink investigation procedure is successful, the uplink access procedure as defined in sub-clause 3.3.1.2.1.2 and 3.3.1.2.1.2a or the priority uplink request procedure as defined in sub-clause 3.3.1.2.1.2b is initiated.
If the uplink access procedure or priority uplink request procedure is successful, the mobile station shall give an indication to the upper layers and enter the group transmit mode.
If the uplink access procedure or priority uplink request procedure is not successful, the mobile station shall give an indication to the upper layers and remain in group receive mode.
3.4.15.2 Network side
3.4.15.2.1 Provision of messages on the VGCS or VBS channel downlink
3.4.15.2.1.1 General
The network shall provide all messages directed to mobile stations in group receive mode (see sub-clause 3.4.15.1.2) in unacknowledged mode. Those messages which are also sent to the mobile station in group transmit mode in acknowledged mode have therefore to be repeated in addition as UI messages on the VGCS channel downlink if they shall also be received by mobile stations in group receive mode.
When the VGCS/VBS call is ciphered the BSS shall derive the ciphering keys from the following parameters, as described in 3GPP TS 43.020:
– Short term key as supplied at group call setup in the cell
– CELL_GLOBAL_COUNT
– Cell Global Identifier (CGI)
The ciphering key needs to be recalculated whenever CELL_GLOBAL_COUNT changes.
The ciphering algorithm is specified at resource assignment.
3.4.15.2.1.2 Provision of general information messages
In the case where the group call area exceeds one cell, the network should provide the SYSTEM INFORMATION TYPE 6 message on the SACCH related to the voice broadcast channel or voice group call channel.
In addition, if the group call area exceeds one cell, the network should provide SYSTEM INFORMATION TYPE 5 (possibly together with TYPE 5bis and 5ter) on the SACCH related to the voice broadcast channel or voice group call channel.
– The SYSTEM INFORMATION TYPE 5, TYPE 5bis and TYPE 5ter messages provide information on the BCCH frequency of the neighbour cells.
– The SYSTEM INFORMATION TYPE 6 message provides information on the location area of the current cell, possibly the status of the NCH (see conditions in sub-clause 3.3.3), and an indication of whether paging channel restructuring has taken place, and an indication of the AMR codec configuration if AMR is being used on the VGCS/VBS group channel.
– $(ASCI)$ The SYSTEM INFORMATION TYPE 10 message provides information for cell re-selection in group receive mode.
The network may also provide layer 3 messages for notification on the VGCS or VBS channel downlink FACCH.
The network may in addition provide SYSTEM INFORMATION TYPE 10bis messages on the SACCH of a voice group call channel to describe the location of the group call channel in neighbour cells. In such a case, if the description of the group call channel for a neighbour cell (including frequency parameters) does not fit in a SYSTEM INFORMATION TYPE 10bis message, the network shall send in addition a SYSTEM INFORMATION TYPE 10ter message for that neighbour cell.
In case the information in a SYSTEM INFORMATION TYPE 10bis (or TYPE 10ter) becomes invalid, the network shall immediately send a VGCS Neighbour Cell Information message on the FACCH of the group call channel. This shall indicate which parameters are now invalid for which neighbour cells, and shall include as much replacement information as possible.
A mobile station in group receive mode shall consider any information relating to a neighbour cell received in a SYSTEM INFORMATION TYPE 10bis (respectively TYPE 10ter) message with sequence number n or in a VGCS Neighbour Cell Information message with sequence number n as valid unless:
– a VGCS Neighbour Cell Information message is received which explicitly indicates that the information for that cell is invalid, or
– any SYSTEM INFORMATION TYPE 10bis or TYPE 10ter message is received with sequence number m (where m = (n + 1) mod 4 ) and a VGCS Neighbour Cell Information message has not been received which explicitly indicates that the information in the SYSTEM INFORMATION TYPE 10bis (respectively TYPE 10ter) message with sequence number n for that cell remains valid, or
– a SYSTEM INFORMATION TYPE 10bis (respectively TYPE 10ter) message is received containing information for that cell with sequence number m (where m > n mod 4 ), or
– any SYSTEM INFORMATION TYPE 10bis or TYPE 10ter message is received with sequence number m (where m > (n + 1) mod 4 ).
3.4.15.2.1.3 Provision of messages related to the voice group call uplink channel
Only applicable for the support of VGCS talking.
The network shall provide UPLINK FREE messages on the main signalling link of all voice group call channels when the uplink is set free. The provision of UPLINK FREE messages shall be repeated as long as no uplink is granted to a mobile station. When talker priority is supported by the network, the UPLINK FREE message shall indicate the status of the emergency mode.
The network shall provide an UPLINK BUSY message on the main signalling link of all voice group call when the uplink has been granted to a mobile station. When talker priority is supported by the network, the UPLINK BUSY message shall indicate the current talker priority and the status of the emergency mode. When validation of PRIORITY UPLINK REQUEST messages is required, the UPLINK BUSY message shall also include a token (see subclause 3.3.1.2.2b.2.4).
When the network supports uplink access option (i), as defined in 3GPP TS 43.068, and performs a handover of the talking service subscriber the network 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;
– 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.
The network may send UPLINK FREE messages containing an uplink access request on the main signalling channel of the VGCS channels in order to obtain knowledge on whether any listening mobile is present in a cell or not. If there is no UPLINK ACCESS message, responding to the uplink access request or for the uplink access procedure, received by the network, the network may decide to clear the VGCS channel in that cell.
3.4.15.2.1.4 Provision of messages related to the voice broadcast uplink channel
The network may send UPLINK FREE messages containing an uplink access request on the main signalling channel of the VBS channels in order to obtain knowledge on whether any listening mobile is present in a cell or not. If there is no mobile station responding to the uplink access request, the network may decide to clear the VBS channel in that cell.
3.4.15.2.2 Release of the VGCS or VBS Channels
If a release request for a voice group call is received from the upper layer, the network, after having released the RR connection with the mobile station in group transmit mode, shall stop the notification procedures for that voice group call and clear all related voice group call channels.
If a release request for a voice broadcast call is received from the upper layer, the network shall stop the notification procedures for that voice broadcast call and locally disconnect any channel related to the voice broadcast call.
3.4.15.2a VBS/VGCS reconfiguration procedure
3.4.15.2a.1 Normal behaviour
This procedure is used by the network to indicate a change in Group Channel Description, and if required, in the Cell Channel Description, at a given time for VBS and VGCS listeners in group receive mode and the VGCS talker in group transmit mode. The VBS/VGCS RECONFIGURE and VBS/VGCS RECONFIGURE2 messages are sent in unacknowledged mode (to mobile stations in group receive mode) or acknowledged mode (to mobile stations in group transmit mode) on the main DCCH of a VBS or VGCS channel.
The network sends a VBS/VGCS RECONFIGURE message containing the new group channel description together with a starting time indication. If the Cell Channel Description is to be changed then the Additional Segment field in the VBS/VGCS RECONFIGURE message shall indicate that the VBS/VGCS RECONFIGURE2 message is to follow. If the Cell Channel Description is unchanged then the Additional Segment field is set to ‘0’ and no VBS/VGCS RECONFIGURE2 message is sent. The VBS/VGCS RECONFIGURE2 message shall be sent on the main DCCH with the same starting time as indicated in the VBS/VGCS RECONFIGURE message.
Optionally, the VBS/VGCS RECONFIGURE and VBS/VGCS RECONFIGURE2 messages may be resent multiple times before starting time on the main DCCH of a VBS or VGCS channel.
On receiving the VBS/VGCS RECONFIGURE message with Additional Segment set to ‘0’ the mobile station shall wait until starting time before applying the new physical channel configuration, frequencies and/or hopping sequences to the VBS or VGCS call that the mobile station is currently listening to. If the mobile station was in group transmit mode and received the message in an I frame, it shall then, in addition, re-establish the main signalling link by sending a SABM containing a Talker Indication message (see sub-clause 3.1.5).
On receiving the VBS/VGCS RECONFIGURE message with Additional Segment set to ‘1’ the mobile station shall wait to receive the VBS/VGCS RECONFIGURE2 message with the same starting and then wait until starting time to apply the new physical channel configuration, frequencies and/or hopping sequences using the new Cell Channel Description to the VBS or VGCS call that the mobile station is currently listening to. If the mobile station was in group transmit mode and received the message in an I frame, it shall then, in addition, re-establish the main signalling link by sending a SABM containing a Talker Indication message (see sub-clause 3.1.5).
On receiving only the VBS/VGCS RECONFIGURE2 message the mobile station shall wait to receive the VBS/VGCS RECONFIGURE message with the same starting time and then wait until starting time to apply the new physical channel configuration, frequencies and/or hopping sequences using the new Cell Channel Description to the VBS or VGCS call that the mobile station is currently listening to. If the mobile station was in group transmit mode and received the message in an I frame, it shall then, in addition, re-establish the main signalling link by sending a SABM containing a Talker Indication message (see sub-clause 3.1.5).
If the Starting Time in the VBS/VGCS RECONFIGURE message indicates a time that has elapsed with Additional Segment set to ‘0’, then the mobile station shall switch to the new Group Channel Description immediately.
NOTE: The network implementation should take into account the possible presence of mobiles which do not recognize the VGCS/VBS RECONFIGURE or VBS/VGCS RECONFIGURE2 messages. An appropriate message (e.g. Channel Release) should be sent to indicate to such mobiles that the current group call channel is no longer in use. Such mobiles must determine the new location of the group channel by reading the NCH.
3.4.15.2a.2 Abnormal cases
If the starting time in the VBS/VGCS RECONFIGURE has elapsed with Additional Segment set to ‘1’ and the mobile has not received the VBS/VGCS RECONFIGURE2 message, then the mobile station shall locally abort the radio connection and search all possible channel positions on the current cell and the neighbour cells for which a channel description is known for that call.
If the starting time in the VBS/VGCS RECONFIGURE2 message has elapsed and the mobile has not received the VBS/VGCS RECONFIGURE message, then the mobile station shall locally abort the radio connection and search all possible channel positions on the current cell and the neighbour cells for which a channel description is known for that call.
If the starting times in the received set of VBS/VGCS RECONFIGURE and VBS/VGCS RECONFIGURE2 messages are different then the mobile station shall ignore both of the messages.
3.4.15.3 Failure cases
If the mobile station loses the voice group call channel or voice broadcast channel, the mobile station shall search all possible channel positions on the current cell and the neighbour cells for which a channel description is known for that call.
3.4.15.3a Additional Information procedure
In group receive mode, the network sends the talker’s details on the main DCCH in either a VGCS ADDITIONAL INFORMATION or an UPLINK BUSY message. The VGCS ADDITIONAL INFORMATION message is sent in unacknowledged mode on the main DCCH of the voice group channel. In addition the transmission of the VGCS ADDITIONAL INFORMATION message is repeated every T3153 seconds on the SACCH, until the talker is released.
The MS shall pass the information to the upper layers.
3.4.15.3b SMS to on going group call procedure
The network may send VGCS mobile stations that are in group receive mode or group transmit mode a short message by sending it one or more RP-Data messages (see 3GPP TS 24.011). An RP-Data message is sent to the mobile stations by using one or more instances of the VGCS SMS Information message. Each VGCS SMS Information message contains an SMS reference number that identifies a particular RP-Data message. The VGCS SMS Information message is sent in unacknowledged mode on the SACCH of the group channel to the VGCS mobile stations that are in group receive mode and any VGCS talking subscriber that is using the uplink of the group channel. When the talker is on a dedicated channel the VGCS SMS Information message is sent in unacknowledged mode on the SACCH of this channel. The network may retransmit an SMS Information message for a period of up to 30s (including the initial transmission).
The network shall insert an SMS reference number in the VGCS SMS Information message to identify the particular RP-Data message. In the case that the RP-Data message has to be segmented over multiple VGCS SMS Information messages, the network shall insert a segment number in each message segment to identify the segment. The first segment shall contain a segment number of zero, with the segment number incremented by one in each subsequent segment.
The VGCS mobile station shall start an instance of T3112 for the RP-Data message when it first receives a segment of the message. The instance of timer T3112 relating to the message shall be stopped when:
– the MS receives the complete RP-Data message;
– the MS receives a VGCS SMS Information message with an SMS reference number which is more than 4 higher (modulo 16) than that of this message;
– the MS changes its channel;
– the voice group call is cleared.
If T3112 is stopped and the RP-Data message has not been completely received, the VGCS mobile station shall discard the segments of the RP-Data message.
The VGCS mobile station shall (as far as possible) pass correctly received RP-Data messages to the upper layers in order of increasing SMS reference number. The MS shall store the parameter V(G) which is the SMS reference number of the message which is to be delivered next to the upper layer. The MS initialises the value of V(G) to the value in the first received segment on the current channel.
If an RP-Data message is completely received which has an SMS reference number equal to V(G) it is passed to the upper layer, and V(G) is incremented by one (mod 16).
If an RP-Data message is completely received which has an SMS reference number which is not equal to V(G) then the MS shall start timer T3114 for that message. Timer T3114 is stopped when the message is passed to the upper layer.
On expiry of the timer T3114 for a message, each message (or any segments thereof) which has a sequence number between V(G) (inclusive) and the SMS reference number of the message for which timer T3114 expired (inclusive) shall be:
discarded and the corresponding timer T3112 stopped, if the message has not been completely received, or
passed to the upper layers in order, and the corresponding timer T3114 stopped, if it has been completely received.
V(G) shall then be set to the SMS reference number of the message for which timer T3114 expired plus one modulo 16.
All messages for which T3114 is running shall be passed to the upper layers, in order of increasing SMS reference number and the corresponding instances of timer T3114 stopped, if:
– the MS changes its channel, or
– the voice group call is cleared
NOTE: The delivery of the RP-Data message to the group call is not guaranteed. No confirmation is sent of the receipt of the RP-Data message by the VGCS mobile station.