3.7 DTM Handover procedure

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

3.7.1 General

In dual transfer mode an intercell change of dedicated and packet data channel(s) can be requested by the network RR sublayer. This change may be performed using the DTM handover procedure.

This procedure is optional and is only applicable in dual transfer mode when both the mobile station and the network support DTM handover. The mobile station shall indicate its support for DTM handover in the Mobile Station Classmark 3 IE and the MS Radio Access Capability IE. The purpose of the procedure is to handover the dedicated channel and one or more of the packet resources while in dual transfer mode when a cell is changed. The DTM handover procedure is a combination of the handover procedure for circuit switched handover, defined in sub-clause 3.4.4, and the procedure for packet switched handover, defined in 3GPP TS 44.060.

NOTE: The decision to initiate a DTM handover and the choice of the new cell is out of the scope of this technical specification.

The DTM handover procedure is always initiated by the network.

3.7.2 DTM Handover from GERAN A/Gb mode to GERAN A/Gb mode procedure

The DTM handover procedure includes:

– The suspension of normal operation except for RR management (layer 3).

– The disconnection of the main signalling link, and of the other links via local end release (layer 2), and the disconnection of the TCH.

– The mobile station suspension of the packet resources used in the old cell (see 3GPP TS 44.060) until the MS determines the DTM handover procedure to be successfully completed at which point these packet resources are released.

– The mobile station disconnection and deactivation of the dedicated channel used in the old cell (see 3GPP TS 44.018) until the MS determines the DTM handover procedure to be successfully completed at which point the dedicated channel is released (at layer 1).

– The activation of the new channels, and their connection if applicable.

– The triggering of the establishment of data link connection for SAPI = 0 on the new channels.

– The activation of the new PDCH(s) and the resumption of the packet resources (see 3GPP TS 44.060).

For the circuit switched domain the requirements and procedures listed in sub-clauses 3.4.4.1, 3.4.4.2 and 3.4.4.3 are valid with the following exceptions:

– Handover of VGCS is not supported by the DTM handover procedure.

– MBMS service information sending completion is not supported by the DTM handover procedure.

– The DTM HANDOVER COMMAND message applies instead of the HANDOVER COMMAND message and is sent on the PACCH (see 3GPP TS 44.060).

– Sending of DTM Information is not needed.

For the packet switched domain the requirements and procedures described for PS handover in 3GPP TS 44.060 are valid with the following exceptions:

– The synchronisation of the physical channels is not performed in the PS domain, i.e. the mobile station shall not send the PS HANDOVER ACCESS message.

– The target BSS considers the DTM handover procedure to be successfully completed upon receiving a HANDOVER COMPLETE message on the main DCCH according to sub-clause 3.4.4.3.

– Timer T3216 shall not be started for DTM handover.

– The DTM HANDOVER COMMAND message applies instead of the PS HANDOVER COMMAND message.

3.7.2.1 Abnormal cases

The failure cases and actions defined in sub-clause 3.4.4.4, shall apply for DTM handover from GERAN A/Gb mode to GERAN A/Gb mode with the following exceptions:

– The DTM HANDOVER COMMAND message applies instead of the HANDOVER COMMAND message and is sent on the PACCH.

In addition, a mobile station operating in A/Gb mode shall consider the DTM handover to A/Gb mode to have failed if the DTM HANDOVER COMMAND message:

a) violates the mobile station’s DTM multislot capabilities; or

b) does not include at least one uplink TBF; or

c) provides one or more downlink TBFs with PFIs that are different from those currently allocated; or

d) provides one or more uplink TBFs with PFIs that are different from those currently allocated except when there are no ongoing uplink TBFs in which case a single uplink TBF with a PFI that indicates signalling shall be allocated.

If these additional error cases occur, the mobile station shall remain in DTM in the old cell and return a HANDOVER FAILURE message on the current main DCCH with the PS Cause IE set as follows:

– in case a) above, "DTM multislot capabilities violated"; or

– in case b) above, "No uplink TBF"; or

– in case c) above, "Too many TBFs"; or

– in case d) above, "Too many TBFs".

If there are no errors in the DTM HANDOVER COMMAND message related to the CS domain and there are no common errors then the RR Cause IE shall indicate "Normal Event". Any error that is common to both the CS domain and the PS domain shall be reported in the RR Cause IE.

The transmission of a HANDOVER FAILURE message terminates the DTM handover procedure in the mobile station.

After terminating the DTM handover procedure the mobile station shall resume all uplink and downlink TBFs that were ongoing in the old cell prior to receiving the DTM HANDOVER COMMAND message and for which T3180 (uplink TBFs) and T3190 (downlink TBFs) are still running (see 3GPP TS 44.060).

For each TBF that is resumed the corresponding RLC state machine shall reflect its state when the last RLC data block was transmitted for that TBF in the old cell (uplink TBFs) and the last RLC data block was received for that TBF in the old cell (downlink TBFs) (see 3GPP TS 44.060).

3.7.3 DTM Handover from GERAN A/Gb mode to UTRAN procedure

For the successful case of DTM Handover from GERAN A/Gb mode to UTRAN, the behaviour of the MS in the old cell is as specified for DTM Handover from GERAN A/Gb mode to GERAN A/Gb mode (see sub-clause 3.7.2). The behaviour of the MS in the new cell is as specified for Inter-RAT Handover to UTRAN in 3GPP TS 25.331. The behaviour of the old BSS is as specified in sub-clause 3.7.2.

The definition of abnormal cases for the mobile is specified in 3GPP TS 25.331. If the UE/MS receives a HANDOVER TO UTRAN COMMAND message, which contains a protocol error causing the variable PROTOCOL_ERROR_REJECT to be set to TRUE (see 3GPP TS 25.331), the MS sends a HANDOVER FAILURE message on the main DCCH to the old cell. The appropriate cause shall be included (see sub-clause 3.4.4a.3).

The definition of abnormal cases for the old BSS and the behaviour of the old BSS in such cases (including on receipt of a HANDOVER FAILURE) is as specified in sub-clause 3.7.2.1.