IMS emergency sessions over emergency access via packet core are supported for UTRAN access as well as inter-RAT handover between UTRAN and E-UTRAN. Support for Packet Core (GPRS and EPS) emergency bearer services over GERAN networks is not included in this Release and thus PS handover to GERAN access should not be performed when IMS emergency sessions over EPS or GPRS using emergency bearer services are active.
The MS shall signal a cause specific for emergency as defined in TS 25.331
when it requests an RRC connection in relation to an emergency session. Specific situations that require setting the RRC establishment cause to emergency are described in TS 24.008
An emergency attached MS when its periodic RA update timer expires shall not initiate a periodic RAU procedure but enter PMM- DETACHED state. The SGSN assigns the periodic RAU timer value to emergency attached MS. This timer keeps the MS emergency attached after change to PMM-IDLE state to allow for a subsequent emergency service without a need to emergency attach again. For emergency attached MS the SGSN runs a mobile reachable timer with a similar value to the MS's periodic RAU timer. Any time after expiry of this timer the SGSN may change the PMM state of an emergency attached MS to PMM- DETACHED.
When Emergency Services are supported and local regulation requires Emergency Sessions to be provided regardless of mobility or access restrictions, regional subscription restrictions or access restrictions (see TS 23.221
and TS 23.008
) e.g. CSG restrictions, should not be applied to MSs receiving emergency services. When the RABs for emergency bearers are established, the ARP value for emergency bearer services indicates the usage for emergency services to the UTRAN.
During handover, the source UTRAN and source SGSN ignore any MS related restrictions during handover evaluation when there are active emergency bearers. UTRAN shall not initiate handover to GERAN PS domain. During handover to a CSG cell, if the UE is not a CSG member of the target CSG cell and has emergency bearer services, the target RNC only accepts the emergency bearers and the target SGSN releases the non-emergency bearers that were not accepted by the target RNC according to clause 188.8.131.52
. Such UEs behave as emergency attached.
During Routing Area Update procedures, including a RAU as part of a handover, the target SGSN ignores any mobility or access restrictions for MS with emergency bearer services where required by local regulation. Any non emergency bearer services are deactivated, according to clause 184.108.40.206
, by the target SGSN when not allowed by the subscription for the target location. Such MSs behave as emergency attached. To allow the emergency attached MS to get access to normal services after the emergency session has ended and when it has moved to a new area that is not stored by the MS as a forbidden area, the MS may explicitly detach and reattach to normal services without waiting for the emergency PDN connection deactivation by the PDN GW or GGSN.
This functionality applies to all mobility procedures.