All GPRS-attached MSs, except A/Gb mode MSs in class B mode of operation engaged in CS communication, shall perform periodic RA updates. MSs that are IMSI-attached and not GPRS-attached shall perform periodic LA updates. Periodic RA updates are equivalent to intra SGSN routeing area updates as described in clause "Intra SGSN Routeing Area Update", with Update Type indicating periodic RA update. For MSs that are both IMSI-attached and GPRS-attached, the periodic updates depend on the mode of operation of the network:
If the network operates in mode I, periodic RA updates shall be performed, and periodic LA updates shall not be performed. In this case, the MSC/VLR shall disable implicit detach for GPRS-attached MSs and instead rely on the SGSN to receive periodic RA updates. If periodic RA updates are not received in the SGSN and the SGSN detaches the MS, the SGSN shall notify the MSC/VLR by sending an IMSI Detach Indication message.
If the network operates in mode II, both periodic RA updates and periodic LA updates shall be performed independently. RA updates are performed towards the SGSN, and LA updates are performed towards the MSC/VLR.
In A/Gb mode, the periodic RA update timer in the MS is stopped when an LLC PDU is sent since all sent LLC PDUs set the MM context state to READY. The periodic RA update timer is reset and started when the state returns to STANDBY.
In Iu mode, the periodic RA update timer in the MS is stopped when the MM context enters the PMM CONNECTED state. The periodic RA update timer is reset and started when the state returns to PMM IDLE state.
If the MS could not successfully complete the periodic RA update procedure after a retry scheme while the MS was in GERAN/UTRAN PS coverage, the MS shall wait a back-off time equal to the periodic LA update timer broadcast by the network before restarting the periodic RA update procedure.
The PS Handover procedure is used to handover an MS with one or more packet flows from a source cell to a target cell, when at least one of the cells is a GERAN cell. The source and target cells can be located within either the same BSS (Intra BSS HO), different BSSs within the same SGSN (Intra SGSN HO) or belonging to different SGSNs (Inter SGSN HO), or systems with different radio access types (Inter RAT HO, Inter mode HO).
While the MS is still in the source cell:
Radio resources in the target cell are allocated and signalled to the MS.
System information of the target cell needed for access in the target cell is signalled to the MS.
After handover between GERAN and UTRAN is complete, the RAU procedure is performed even if the RAI has not changed.
As specified in clause 188.8.131.52
, "Support for Non-IP data", with regard to CIoT EPS Optimisations, PDP Contexts of PDN Type "Non-IP" and PDN Connection to SCEF may need to be handled during the PS Handover Procedure. For an MS that is using a "Non-IP" connection to a GGSN/PGW, or a PDP Context to a SCEF, if these PDP Contexts cannot be supported by the target SGSN, the source SGSN does not attempt to handover those bearers and releases them upon successful completion of the handover. If the MS does not have any PDP Context other than Non-IP or SCEF ones that can be transferred, then the SGSN sends failure message to the source RAN node.
The complete PS Handover procedures are defined in TS 43.129
The complete Inter RAT HO between E UTRAN and GERAN procedures are defined in TS 23.401