6.7 MS behaviour in heterogeneous networks

3GPP43.055Dual Transfer Mode (DTM)Release 17Stage 2TS

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

6.7.1 General

The support of DTM in a network is not likely to be homogeneous. Network operators normally have more that one infrastructure supplier and different manufacturers will support DTM with different time scales. In addition, the rollout of a product release from a certain manufacturer is not performed simultaneously across the network.

It is therefore difficult to avoid the fact that some cells in a network support DTM whereas others do not, making necessary to ensure a consistent behaviour of a DTM mobile station in such scenario. The existing GPRS Suspension and Resume procedures are reused for this purpose.

Table 5 contains the four possible combinations when the mobile station is handed over between two cells, where each of them may or not support DTM.

Table 5: Modification to CS handover to ensure a correct DTM behaviour
when DTM is not always supported

			Support of DTM in new cell
			No	Yes
Support of DTM in old cell	No		The MS waits for the reception of the SI 6 message indicating whether the cell supports DTM. If DTM is supported, the same message contains the RAC.
			Normal CS handover.	When the SI6 message is received, the MS performs the Resume procedure: it performs the RR Packet Request procedure for the GMM RA Update procedure.
	Yes	MS in DM	The MS waits until the reception of the SI 6 message indicating that the cell does not support DTM. Then, if GPRS is supported, the MS performs the GPRS suspension procedure.	The MS waits for the reception of the SI 6 message indicating that the cell supports DTM and containing the RAC. When the SI6 message is received, the MS performs the Cell Update (MS in READY), the RA Update procedure (change of RA) or none of both (MS in STANDBY and both cells in the same RA).
		MS in DTM		The network sends the DTM Information message (implicitly implying the support of DTM) containing the RAC and any other information needed to perform the Packet Request procedure.

6.7.1 Suspension procedure

The GPRS Suspension procedure is defined in the standards to be used when a mobile station in mode of operation B and in packet transfer mode is paged for circuit switched services.

The GPRS Suspension procedure can be used without modifications when:

– a DTM mobile in dedicated or dual transfer mode is handed over from a cell that supports DTM to one that does not; or

– a DTM mobile in packet transfer mode on a cell that does not support DTM is paged for circuit switched services.

The GPRS Suspension procedure is initiated by the mobile station by sending a GPRS SUSPENSION REQUEST message to the BSS after it has entered dedicated mode.

6.7.2 Resume procedure

The Resume procedure is used for the resumption of GPRS service when the conditions for suspension have disappeared (e.g. a suspended class B mobile station has cleared the resources allocated for the circuit switched service). The procedure is initiated:

a) by the BSS, when it detects the change of conditions: the BSS indicates the resumption to the SGSN and then the mobile station;

b) by the mobile station, when it detects the change of conditions and the BSS has not resumed GPRS: the mobile station performs a RA Update procedure that resumes GPRS with the SGSN.

For the two new causes for GPRS suspension, there is no message from the BSS to the mobile station and, thus, the Resume procedure is initiated by the mobile station (b).