Support for Multi-SIM devices for LTE/NR

Aug 08, 2022

The Multi-(U)SIM work item specifies solutions to address the paging occasion collision issue for single-Rx/single-Tx Multi-USIM (MUSIM) User Equipment (UE), and to notify network A of its switch from network A for MUSIM purpose, and to support indicating to the MUSIM UE whether an incoming paging is for voice service.

860063

Support for Multi-SIM devices for LTE/NR

LTE_NR_MUSIM

RP-212610

The following schemes were introduced as part of the Work Item:

Paging collision objective: To solve paging occasion collision problem, the MUSIM UE can trigger a new 5G-GUTI reallocation in the 5G System (5GS) or an IMSI offset assignment in the EPS to modify the timing of the paging occasions. In 5GS, the UE obtains a new 5G-GUTI by performing a MRU without any specific indication. In EPS, the UE can provide a requested IMSI offset value in Attach Request or TAU Request, which triggers the MME to provide an accepted IMSI Offset value in the Attach Accept or TAU Accept message. The MME and UE use the alternative IMSI (calculated based on the IMSI and the accepted IMSI offset) for the determination of paging occasion.
Network notification objective: AS-based network switching for leaving RRC_CONNECTED and network switching without leaving RRC_CONNECTED (i.e., requesting/configuring MUSIM gaps) were introduced. Both schemes can be configured by the network separately.

- When determining it needs to leave RRC_CONNECTED, the UE sends the UEAssistanceInformation message, which indicates the UE’s preferred RRC state when leaving RRC_CONNECTED for MUSIM purpose. gNB may release the UE to RRC IDLE/INACTIVE when receiving this UAI. The UE is allowed to enter RRC_IDLE if it does not receive response message from network within a certain configured time.

- When determining it needs the MUSIM gaps, the UE sends the UEAssistanceInformation message, which indicates the UE’s preference on the MUSIM gaps. The UE can request at most a single aperiodic MUSIM gap and two periodic MUSIM gaps. The MUSIM gap is per UE level.

Paging cause objective: a paging cause field with only one codepoint voice was introduced in the NR/LTE Uu paging message, S1AP/NGAP paging message, and XNAP/F1AP paging message. The network provides this field for the upcoming paging triggered by IMS voice, only if the UE indicates the paging cause feature is supported to the network. In order to enable NG-RAN to deliver the paging cause in RAN paging for the UE in RRC-INACTIVE, the AMF provides an indication indicating the Paging Cause Indication for Voice Service feature is supported to the NG-RAN. The NG-RAN node knows the downlink data which triggers the RAN Paging message is related to voice service based on the Paging Policy Indicator, in the header of the received downlink data.

The latest Status report for the Work Item (RP-220603) reported on agreements approved at 3GPP TSG RAN meeting #95e (November 06-17, 2021), on detailed work from RAN2, RAN3 and RAN4 Working Groups.

See a list of related CRs: select "TSG Status = Approved" in: https://portal.3gpp.org/ChangeRequests.aspx?q=1&workitem=860063,860163

Acronyms:

5G-GUTI	Globally Unique Temporary Identifier
5GS	5G System
AMF	Access and Mobility management Function
AS	Access Stratum
EPS	Evolved Packet System - Comprising the Evolved UTRAN and the Evolved Packet Core
F1AP	NG-RAN; F1 Application Protocol
gNB	gNodeB. 5G wireless base station
IMSI	International mobile subscriber identity
MME	Mobility Management Entity
MRU	Mobility Registration Update
NGAP	NG Application Protocol
RRC	Radio Resource Control
S1AP	S1 Application Protocol
TAU	Tracking Area Update
XNAP	NG-RAN; Xn Application Protocol

3GPP Work Plan:

See a listing of all work & study items here: https://www.3gpp.org/ftp/Information/WORK_PLAN/ and search for ‘MUSIM’ in the acronym field of the Excel sheet there.

The text above is largely taken from the Release 17 description document TR21.917 (clause 10), which is a summary based on RP -220604 (LTE_NR_MUSIM).