3.4.13 RR connection release procedure

3GPP44.018GSM/EDGE Radio Resource Control (RRC) protocolMobile radio interface Layer 3 specificationRelease 17TS

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

3.4.13.1 Normal release procedure

The release of the RR connection can be requested by upper layers.

The purpose of this procedure is to deactivate all the dedicated channels in use. When the channels are released and the mobile station is not IMSI attached for GPRS services (clause 4), the mobile station returns to the CCCH configuration, idle mode.

If the mobile station is IMSI attached for GPRS services the following four cases apply:

– If the mobile station has no radio resources (i.e., no temporary block flow) allocated on a PDCH, the mobile station returns to the PCCCH or CCCH configuration, packet idle mode;

– If the mobile station is operating in dual transfer mode when the RR connection is released, the radio resources allocated on a PDCH are released, the mobile station returns to the PCCCH or CCCH configuration, packet idle mode;

– If the mobile station is operating in dual transfer mode when the RR connection is released and the mobile station and the network support enhanced DTM CS release procedure, the mobile station may maintain its radio resources allocated on one or more PDCH(s) and enter packet transfer mode;

– Otherwise, if the mobile station has radio resources allocated on a PDCH, the mobile station enters packet transfer mode.

The channel release procedure can be used in a variety of cases, including TCH release after a call release, and DCCH release when a dedicated channel allocated for signalling is released.

In dedicated mode and group transmit mode, the channel release procedure is always initiated by the network.

3.4.13.1.1 Channel release procedure initiation in dedicated mode and in group transmit mode

The network initiates the channel release by sending a CHANNEL RELEASE message to the mobile station on the main DCCH, starts timer T3109 and deactivates the SACCH.

On receipt of a CHANNEL RELEASE message the mobile station starts timer T3110 and disconnects the main signalling link. When T3110 times out, or when the disconnection is confirmed, the mobile station deactivates all channels, considers the RR connection as released, and returns to CCCH idle mode, returns to PCCCH or CCCH packet idle mode or enters packet transfer mode.

NOTE 1: Data Links other than the main signalling link are disconnected by local end link release.

If case of dedicated mode, on the network side, when the main signalling link is disconnected, the network stops timer T3109 and starts timer T3111. When timer T3111 times out, the network deactivates the channels, they are then free to be allocated to another connection.

NOTE 2: The sole purpose of timer T3111 is to let some time to acknowledge the disconnection and to protect the channel in case of loss of the acknowledge frame.

If timer T3109 times out, the network deactivates the channels; they are then free to be allocated to another connection.

The CHANNEL RELEASE message will include an RR cause indication as follows:

#0: if it is a normal release, e.g. at the end of a call or at normal release of a DCCH.

#1: to indicate an unspecified abnormal release.

#2, #3 or #4: to indicate a specific release event.

#5: if the channel is to be assigned for servicing a higher priority call (e.g. an emergency call).

#65: if e.g. a handover procedure is stopped because the call has been cleared.

The CHANNEL RELEASE message may include the information element BA Range which may be used by a mobile station in its selection algorithm (see 3GPP TS 45.008 and 3GPP TS 23.022).

The CHANNEL RELEASE message may include the information element "Cell selection indicator after release of all TCH and SDCCH" which shall be used by the mobile station in its cell selection algorithm after release of all TCH and SDCCH (see 3GPP TS 45.008).

The CHANNEL RELEASE message may include Individual priorities IE to convey individual priorities information to the MS (see subclause 3.2.3.3). When the MS receives an Individual priorities IE it shall start an instance of timer T3230 with the value supplied in the Individual priorities IE.

If the network redirects a mobile station towards E-UTRAN, it proceeds as follows:

– The network shall use the information element "Cell selection indicator after release of all TCH and SDCCH" in the channel release message for redirection towards an EARFCN in the E-UTRAN band numbered less than 65.

– The network shall use the information element "individual priorities" in the channel release message for redirection towards an EARFCN in the E-UTRAN band numbered greater than 64.

Mobile stations not supporting VGCS or VBS listening shall ignore Group Channel Description (or Group Channel Description 2), Group Cipher Key Number, Cell Channel Description, Talker Identity and Talker Priority Status information elements if present in the message and perform the channel release procedure as normal.

For mobile stations supporting VGCS listening, the following procedures apply:

The CHANNEL RELEASE message may include the Group Channel Description, Group Channel Description 2, and possibly the Cell Channel Description information element(s). In this case, the mobile station shall release the layer 2 link, enter the group receive mode and give an indication to the upper layer. The BSS may provide the Group Channel Description 2 in the CHANNEL RELEASE message to the current talker only when the voice group call channel cannot be fully described by the Group Channel Description IE and the Cell Channel Description IE. If a CHANNEL RELEASE message with neither Group Channel Description, nor Group Channel Description 2, nor Cell Channel Description is received, or if those information elements do not properly specify a group channel, the normal behaviour applies.

If ciphering is applied on the VGCS or VBS channel, the network shall provide in the CHANNEL RELEASE message with the Group Cipher Key Number information element for the group cipher key to be used by the mobile station for reception of the VGCS or VBS channel. If this information element is not included, no ciphering is applied on the VGCS or VBS channel. When the group cipher key indicates that the group call is ciphered (ie group key is non zero), then the VGCS Ciphering Parameters Information Element shall be included to provide the VSTK_RAND and Cell_Global_Count. The MS shall adjust and maintain the Cell Global Count using the procedure described in sub-clause 3.3.3.1. The MS shall then calculate the ciphering keys as described in 3GPP TS 43.020. Also, the MS shall fetch from the USIM the identity of its ciphering algorithm to use on the VGCS or VBS channel, as described in 3GPP TS 43.020.

For mobile stations supporting VGCS talking, the following procedures apply:

If the VGCS talking subscriber is being pre-empted by a higher priority talker, then the network shall include the talker priority status information element. The network shall also include, when available, the talker identity associated with the new talker.

A mobile station not supporting the "GPRS" option shall consider the GPRS Resumption information element as an information element unknown in the CHANNEL RELEASE message and perform the RR connection release procedure as normal.

For a mobile station supporting the "GPRS" option, the following additional procedures also apply:

– The CHANNEL RELEASE message may include the information element GPRS Resumption. If the GPRS Resumption information element indicates that the network has resumed GPRS services, the RR sublayer of the mobile station shall indicate a RR GPRS resumption complete to the MM sublayer, see clause 4. If the GPRS Resumption information element indicates that the network has not successfully resumed GPRS services, the RR sublayer of the mobile station shall indicate a RR GPRS resumption failure to the MM sublayer, see clause 4.

– If the mobile station has performed the GPRS suspension procedure (see sub-clause 3.4.25) and the GPRS Resumption information element is not included in the message, the RR sublayer of the mobile station shall indicate a RR GPRS resumption failure to the MM sublayer, see clause 4.

– If the mobile station has not performed the GPRS suspension procedure and the GPRS Resumption information element is not included in the message, the mobile station shall perform the RR connection release procedure as normal.

3.4.13.1.1a Channel release procedure initiation in dual transfer mode

If the mobile station and the network support enhanced DTM CS release procedure, the network may delay the release of the RR connection until the mobile station has received the needed system information, in order to maintain the radio resources on the PDCH(s) after the release of the RR connection.

The network initiates enhanced DTM CS release procedure by sending the PACKET CS RELEASE INDICATION message as specified in 3GPP TS 44.060.

If the acquisition of system information is completed, the network shall send a CHANNEL RELEASE message on the main DCCH with the Enhanced DTM CS Release Indication field indicating that the mobile station is allowed to continue in packet transfer mode after the release of the RR connection. Upon receipt of the CHANNEL RELEASE message the mobile station starts timer T3110 and disconnects the main signalling link. When T3110 times out, or when the disconnection is confirmed, the mobile station deactivates all dedicated channels, considers the RR connection as released and enters packet transfer mode.

The network may for any reason send a CHANNEL RELEASE message on the main DCCH with the Enhanced DTM CS Release Indication field indicating that the mobile station is not allowed to continue in packet transfer mode after the release of the RR connection. Upon receipt of the CHANNEL RELEASE message the mobile station starts timer T3110 and disconnects the main signalling link. When T3110 times out, or when the disconnection is confirmed, the mobile station deactivates all channels, considers the RR connection as released, and enters packet idle mode.

3.4.13.1.2 Abnormal cases

Abnormal cases are taken into account in the main part of the description of the procedure.

3.4.13.2 Radio link failure in dedicated mode or dual transfer mode

The main part of these procedures concerns the "normal" cases, i.e. those without any occurrence of loss of communication means. A separate paragraph at the end of the description of each procedure treats the cases of loss of communication, called a radio link failure. In dedicated mode, in most of the cases the reaction of the mobile station or the network is the same. Those reactions are described in this sub-clause to avoid repetitions.

A radio link failure can be detected by several ways:

1) By analysis of reception at layer 1, as specified in 3GPP TS 45.008 and sub-clause 3.4.1.1.

2) By a data link layer failure as specified in 3GPP TS 44.006, on the main signalling link. A data link failure on any other data link shall not be considered as a radio link failure.

3) When a lower layer failure happens while the mobile station attempts to connect back to the old channels in a channel assignment procedure, handover procedure, DTM handover procedure or DTM assignment procedure with relocation of the RR connection.

4) In some cases where timers are started to detect the lack of answer from the other party, as described in clause 3.

The two first cases are known by the term "lower layer failure".

3.4.13.2.1 Mobile side

When a radio link failure is detected by the mobile station,

– the MS shall perform a local end release on all signalling links unless otherwise specified;

– the mobile station shall deactivate all dedicated channels;

– if the mobile station is in dual transfer mode, it shall abort the packet resources;

– the RR sublayer of the mobile station shall indicate an RR connection failure to the MM sublayer unless otherwise specified.

NOTE: Upper layers may decide on a re-establishment (see 3GPP TS 24.008).

When a mobile station which has performed the GPRS suspension procedure (sub-clause 3.4.25) detects a radio link failure, the RR sublayer of the mobile station shall indicate a RR GPRS resumption failure to the MM sublayer, see clause 4.

3.4.13.2.2 Network side

In dedicated mode, the reaction of the network to a lower layer failure depends on the context. Except when otherwise specified, it is to release the connection either with the channel release procedure as specified in sub-clause 3.5.1, or with the following procedure. The network starts timer T3109 and deactivates the SACCH (and hence to stop transmission on the SACCH). If the mobile station is in dual transfer mode, the network also aborts all the allocated packet resources.

When a radio link failure has been detected, an indication is passed to the upper Mobility Management sublayer on the network side.

When timer T3109 expires, the network can regard the channels as released and free for allocation.

This procedure relies on the fact that if a mobile station does not receive the SACCH for some time, it completely releases the channels (cf. 3GPP TS 45.008).

NOTE: The network should maintain for a while the transaction context in order to allow call re-establishment. The length of timer is for further study.

3.4.13.3 RR connection abortion in dedicated mode or dual transfer mode

The mobile station aborts the RR connection by initiating a normal release of the main signalling link, performing local end releases on all other signalling links, disconnecting all traffic channels, if any, and aborting all the packet resources, if any.

When a mobile station which has performed the GPRS suspension procedure (sub-clause 3.4.25) aborts the RR connection, the RR sublayer of the mobile station shall indicate a RR GPRS resumption failure to the MM sublayer, see 3GPP TS 24.008.

3.4.13.4 Uplink release procedure

If the uplink release is requested by the upper layer in group transmit mode, the mobile station shall send an UPLINK RELEASE message on the voice group call channel uplink, perform a release of the main signalling link and go back to the group receive mode.

If the uplink release is requested by the upper layer when the VGCS talker is on a dedicated channel, the mobile station shall send an UPLINK RELEASE message on the dedicated channel. When a mobile station receives a CHANNEL RELEASE message from the network, the mobile station shall perform a release of the main signalling link. The mobile station enters group receive mode if the CHANNEL RELEASE message includes the Group Channel Description (or Group Channel Description 2) and possibly the Cell Channel Description information element(s), otherwise it enters idle mode.

If the UPLINK RELEASE message is received from the network on the voice group call channel downlink, the MS shall perform a release of the main signalling link and go back to the group receive mode.

3.4.13.5 Radio link failure in group transmit mode

The main part of these procedures concerns the "normal" cases, i.e. those without any occurrence of loss of communication means. A separate paragraph at the end of the description of each procedure treats the cases of loss of communication, called a radio link failure. In group transmit mode, in most of the cases the reaction of the mobile station or the network is the same. Those reactions are described in this sub-clause to avoid repetitions.

A radio link failure can be detected by several ways:

1) By analysis of reception at layer 1, as specified in 3GPP TS 45.008 and sub-clause 3.4.1.1.

2) By a data link layer failure as specified in 3GPP TS 44.006, on the main signalling link. A data link failure on any other data link shall not be considered as a radio link failure.

3) When a lower layer failure happens while the mobile station attempts to connect back to the old channels in a channel assignment procedure or handover procedure.

4) In some cases where timers are started to detect the lack of answer from the other party, as described in clause 3.

The two first cases are known by the term "lower layer failure".

3.4.13.5.1 Mobile side

When a radio link failure is detected by the mobile station:

– the MS shall perform a local end release on all signalling links;

– the mobile station shall go back to idle mode and, when possible, to group receive mode;

– the RR sublayer of the mobile station shall indicate an RR connection failure to the MM sublayer unless otherwise specified.

3.4.13.5.2 Network side

When the uplink has been allocated and the network detects a lower layer failure, the network shall set the uplink free and provide an UPLINK FREE message on the main signalling channel, when appropriate.

When a radio link failure has been detected, an indication is passed to the upper Mobility Management sublayer on the network side.

3.4.13.6 RR connection abortion requested by upper layers

The purpose of this procedure is to abort the RR connection and bar the current cell. The procedure is requested by upper layers when they determine that the network has failed an authentication check (see 3GPP TS 24.008).

On request of the upper layers the MS shall locally abort the RR connection and behave as if a lower layer failure has occurred. The MS shall treat the current cell as barred (see 3GPP TS 23.022).