The paging procedure is used by the network to request the establishment of a NAS signalling connection to the UE. The NAS signalling connection thus established can also be used to transport cdma2000® signalling messages to the UE. Another purpose of the paging procedure is to prompt the UE to reattach if necessary as a result of a network failure. If the UE is not attached when it receives a paging for EPS services, the UE shall ignore the paging. Additionally, the network can use the paging procedure to initiate the mobile terminating CS fallback procedure.
- Paging for EPS services through E-UTRAN using S-TMSI
The network shall initiate the paging procedure for EPS services using S-TMSI with CN domain indicator set to "PS" when NAS signalling messages, cdma2000® signalling messages or user data is pending to be sent to the UE when no NAS signalling connection exists. Upon reception of a paging indication, the UE responds to the paging with a SERVICE REQUEST message.
- Paging for EPS services through E-UTRAN using IMSI
Paging for EPS services using IMSI is an abnormal procedure used for error recovery in the network. The network may initiate paging for EPS services using IMSI with CN domain indicator set to "PS" if the S-TMSI is not available due to a network failure.
Upon reception of a paging for EPS services using IMSI, the UE shall locally deactivate any EPS bearer context(s) and locally detach from EPS. Additionally the UE shall delete the following parameters: last visited registered TAI, TAI list, GUTI and KSIASME. The UE shall set the EPS update status to EU2 NOT UPDATED and change the state to EMM-DEREGISTERED.
After performing the local detach, the UE shall then perform an attach procedure. If the UE is operating in CS/PS mode 1 or CS/PS mode 2 of operation, then the UE shall perform a combined attach procedure.
-Paging for CS fallback to A/Gb or Iu mode
The network may initiate the paging procedure for non-EPS services when the UE is IMSI attached for non-EPS services. To initiate the procedure when no NAS signalling connection exists, the EMM entity in the network requests the lower layer to start paging. The paging message includes a CN domain indicator set to "CS" in order to indicate that this is paging for CS fallback.
To notify the UE about an incoming mobile terminating CS service when a NAS signalling connection exists, the EMM entity in the network shall send a CS SERVICE NOTIFICATION message. This message may also include CS service related parameters (e.g. Calling Line Identification, SS or LCS related parameters).
Upon reception of a paging indication, the UE shall respond with an EXTENDED SERVICE REQUEST. If the paging is received in EMM-IDLE mode, the UE shall respond immediately. If the paging is received as NAS CS NOTIFICATION message in EMM-CONNECTED mode, the UE may request upper layers input i.e. to accept or reject CS fallback before responding with an EXTENDED SERVICE REQUEST. The response is indicated in the CSFB response information element in the EXTENDED SERVICE REQUEST message in both EMM-IDLE and EMM-CONNECTED modes.