Section: 4.3.33.5 Paging Timing Collision Control
Content: To avoid possible paging occasion collision and to enhance the likelihood that paging is received successfully for different USIMs, a Multi-USIM UE may provide, for at least one USIM, a Requested IMSI Offset value that is used for the determination of paging occasions. Upon reception of a Requested IMSI Offset value from UE in Attach Request or Tracking Area Update Request, a supporting MME provides an Accepted IMSI Offset value to the UE in the Attach Accept or Tracking Area Update Accept message to acknowledge it supports the feature and provide the accepted value. The Accepted IMSI Offset Value may be different from the Requested IMSI Offset provided by the UE. The Alternative IMSI value, determined as below, is stored in the UE context in the MME. If the UE does not provide any Requested IMSI Offset value in Attach Request or Tracking Area Request, the MME removes any stored Alternative IMSI value in the UE context. The UE and the network use the Accepted IMSI Offset to determine the paging occasion. The UE and MME use the Accepted IMSI Offset value to calculate the Alternative IMSI value that is determined based on UE's IMSI as follows: Alternative IMSI value = [MCC] [MNC] [(MSIN value + Accepted IMSI Offset) mod (MSIN address space)] where: the MCC, MNC and MSIN value are the fields of the UE's IMSI as defined in TS 23.003[ Numbering, addressing and identification ]  [9]. The MME uses the Alternative IMSI value to compute the UE Identity Index Value. The MME sends the UE Identity Index Value to RAN in the Paging message (see TS 36.413[ Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP) ]  [36]) for RAN to derive the paging occasions according to TS 36.304[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures in idle mode ]  [34]. The UE uses the Alternative IMSI value for the determination of paging occasions as specified in TS 36.304[ Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures in idle mode ]  [34]. NOTE 1: It is recommended to avoid excessive signalling load from UE due to this procedure. NOTE 2: The MME does not remove Alternative IMSI value if the Tracking Area Update Request is for periodic Tracking Area Update.