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TR 22.834
Study on support for
Multi-USIM Devices

V17.2.0 (Wzip)  2019/12  17 p.
Rapporteur:
Dr. Liao, Ellen C.Intel

Content for  TR 22.834  Word version:  17.2.0

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1  ScopeWord‑p. 6

The present document examines several use cases in support of UE with multiple USIMs (MUSIM UE) provided by same or different MNOs and identifies new potential service requirements for emergency services and normal services among USIMs.

2  References

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
  • References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific.
  • For a specific reference, subsequent revisions do not apply.
  • For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
[1]
TR 21.905: "Vocabulary for 3GPP Specifications".
[2]
GSMA Requirements for Multi SIM Devices Version 5.0: https://www.gsma.com/newsroom/wp-content/uploads//TS.37-v5.0.pdf
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3  Definitions, symbols and abbreviations

3.1  Definitions

For the purposes of the present document, the terms and definitions given in TR 21.905 and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905.
MUSIM UE:
An ME with multiple USIMs that are in operation at the same time.
Passive:
the device contains two SIMs, but only one can be selected for use at any given time [2].
Dual SIM Dual Standby (DSDS):
both SIMs can be used for idle-mode network connection, but when a radio connection is active the second connection is disabled. As in the passive case, the SIMs in a DSDS device share a single transceiver. Through time multiplexing two radio connections are maintained in idle mode. When in-call on network for one SIM it is no longer possible to maintain radio connection to the network of the second SIM, hence that connection is unavailable for the duration of the call. Registration to the second network is maintained [2].
Dual SIM Dual Active (DSDA):
both SIMs can be used in both idle and connected modes. Each SIM has a dedicated transceiver, meaning that there are no interdependencies on idle or connected mode operation at the modem level [2].
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3.2  Abbreviations

For the purposes of the present document, the abbreviations given in TR 21.905 and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905.
MUSIM
Multiple USIMs

4  OverviewWord‑p. 7

With the growing demand in the consumer market, many commercially deployed devices support more than one USIM (typically two) in which the USIMs may be from the same or from different MNOs. The 3GPP system performance and user experiences are greatly impacted in the following two facts:
  • Currently, support for multi-USIM is handled in an implementation-specific manner without any support from 3GPP specifications, resulting in a variety of implementations and UE behaviours.
  • A multi-USIM device implementation typically uses common radio and baseband components that are shared among the multiple USIMs. For example, while actively communicating with the first system associated with USIM A, the UE needs to occasionally check the other system associated with USIM B, e.g. to monitor the paging channel, perform signal measurements, or read the system information, and determine if it needs to respond to a paging request from the other system.
The aim of this study is to study aspects indicated in objectives agreed in FS_MUSIM SID in the following use cases and provide corresponding service requirements for enabling multi-USIM devices supports in 3GPP system:
  • Enabling the support for terminal with multiple USIMs
  • Supporting Mobile-Terminated Service
  • Handling of emergency calls and sessions
The modes of operation for the MUSIM UE is indicated in [2].
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5  Use cases

5.1  Use case 1: Support for ME with Multiple USIMs

5.1.1  Description

When a device supports multiple USIMs provided by the same or different PLMNs, it is important for the 3GPP system to specify how it can support these terminals with multiple USIMs that are registered at the same time in terms of service priorities and terminal capabilities.

5.1.2  Pre-conditions

This is the use case about Peter Parker and Mary Jane, Part I.
Mary Jane moved to London and Peter follows her to give her a surprise.
Peter's mobile phone supports multiple UICCs. After he landed at Heathrow airport, he bought a travel SIM card from vending machine.

5.1.3  Service flows

Step 1:
Peter installed the travel SIM card in the second UICC slot of his mobile phone.
Step 2:
When the mobile phone detects multiple UICCs, it requests for user's inputs from Peter for user preferences on service prioritizations on both USIMs.
Step 3:
When Peter completes user's inputs, the UE registers to the network using the travel USIM installed in the second UICC slot.

5.1.4  Post-conditions

Peter is able to start using his travel USIM for local phone call and data connection services in London and receive the phone call and SMS from his first USIM simultaneously.

5.1.5  Existing features partly or fully covering the use case functionalityWord‑p. 8

According to TS 22.101, clause 13.3, the following use case is currently supported in EPS/5GS.
  • A single terminal may support the use of multiple UICCs and only one UICC shall be active (registered) at a time to access a PLMN.
  • Each UICC can contain one or more than one USIMs.
However, according to the current requirements in TS 22.101, it is not yet possible to have multiple active (registered) USIMs.
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5.1.6  Potential New Requirements needed to support the use case

[PR.5.1.6-1]:
The 3GPP system shall support ME with multiple USIMs (on the same UICC or on different UICCs) that are registered at the same time.
[PR.5.1.6-2]:
A MUSIM UE should allow the user to configure the user's preference for the same or different services among multiple USIMs provided by the same or different MNOs.
[PR.5.1.6-3]:
The 3GPP system shall prevent one operator from restricting the use of another operator's USIM for any services if the USIMs are provided by different MNOs.
[PR.5.1.6-4]:
The 3GPP system may support network resources utilization efficiently when the network operator is able and permitted (e.g. due to privacy regulations) to ascertain that multiple USIMs in a MUSIM UE are registered with that network operator's PLMN.
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5.2  Use case 2: Support of Mobile Terminated Services for Multi-USIM Devices

5.2.1  Description

Currently, support for devices with multi-USIM is handled in an implementation-specific manner resulting in a variety of implementations and UE behaviours. When using common radio and baseband components that are shared among the multiple USIMs, the UE needs to occasionally check the other system associated with USIM B while actively communicating with the first system associated with USIM A, e.g. to monitor the paging channel, perform signal measurements, or read the system information. In order to preserve the quality of established communications while avoiding the potential loss of calls, it would be beneficial if the network were able to assist the UE in deciding e.g. whether or not to respond to a paging request from the other system associated to another active USIM. The exact UE behaviour could also be further assisted by configuring service prioritization policies in the UE.
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5.2.2  Pre-conditions

This is the use case about Peter Parker and Mary Jane, part II. Peter's mobile phone supports multiple USIMs and he has started using his travel USIM card for local phone call and data connection services in London, and his first USIM to receive phone calls and SMS simultaneously.
Peter, using Non-IMS voice service associated to travel USIM, calls Mary to let her know he has arrived in London. At the same time in New York, NYPD is dealing with an international crime and the suspects are escaping to London. NYPD decides to phone Peter for help.
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5.2.3  Service flowsWord‑p. 9

Step 1:
the first network initiates mobile terminated Non-IMS or IMS voice service to Peter's UE via his phone number associated to the first USIM.
Step 2:
the first network found the UE is in idle state so it initiates paging procedure towards the UE and includes assistance information in the paging message regarding the service type that triggered the paging.
Case 1: For UE with single RX and voice for the first USIM:
Step 3:
based on UE capability, Peter's phone having single RX does not monitor the activity on the first USIM when Peter is using voice call with Mary.
Step 4:
the paging procedure is failed due to no response from the first USIM on the Peter's UE. NYPD has to deal with the crime on their own.
Case 2: For UE with dual RX:
Case 2A:
Step 3A:
Peter configures his phone with the service prioritization settings, in which he sets voice call from first USIM is allowed while having voice or any other service associated to the travel USIM.
Step 4A:
Peter's phone having dual RX monitors the activity of the first USIM. When receiving the paging message for voice call on the first USIM, the UE determines to present a MT call notification to Peter based on the service type indicated in the assistance information sent along with the paging message, as well as based on the user's preferences and UE configuration.
Step 5A:
When Peter decides to pick up the call on the first USIM, the UE sends a message to the network associated to the travel USIM and requests for the suspension of the connection.
Case 2B:
Step 3B:
Peter configures his phone with the service prioritization settings, in which he sets voice call from first USIM is NOT allowed while having voice or any other service associated to the travel USIM.
Step 4B:
based on user's preference, Peter's phone having dual RX does not monitor the activity on the first USIM when Peter is using voice call with Mary.
Step 5B:
the paging procedure is failed due to no response from the first USIM on the Peter's UE. NYPD has to deal with the escaping criminals on their own.
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5.2.4  Post-conditions

For case 1 and case 2B, Peter is happy to have a date with Mary when talking to Mary without being interrupted by the voice call from the first USIM.
For case 2A, Peter picks up the phone call from NYPD and prepares to catch the criminals in London. Mary is back on the call when the network resumes the call based on the UE request. Peter manages to defeat the criminals in London and have a date out with Mary.

5.2.5  Existing features partly or fully covering the use case functionality

N/A

5.2.6  Potential New Requirements needed to support the use case

[PR.5.2.2-1]:
The 3GPP system shall be able to indicate to the UE as part of the paging procedure the type of traffic that triggered the paging. This information may be used by a user or MUSIM UE to determine whether it needs to respond to a mobile terminated call on one registered USIM while the UE is engaged in active communication on another USIM. The granularity of the paging information shall discriminate between the following service categories;
  • IMS and non-IMS based Voice service.
  • IMS and non-IMS based SMS or USSD
  • IMS service other than voice or SMS
  • Other service not listed above e.g. data services including video.
[PR.5.2.2-2]:
The 3GPP system shall be able to suspend an active communication, e.g. when the UE needs to perform activity associated with another USIM.
[PR.5.2.2-3]:
The 3GPP system shall be to resume a suspended communication, e.g. when the UE has completed activity associated with another USIM.
[PR.5.2.2-4]: The 3GPP system shall be able to minimize paging collision for paging related to multiple USIMs in the UE.
[PR.5.2.2-5]:
The 3GPP system shall provide a mechanism to minimize signalling overhead for services associated to multiple USIM of a MUSIM UE.
[PR.5.2.2-6]:
The 3GPP system shall be able to minimize the impacts of services associated to one USIM to services associated to another USIM for a MUSIM UE.
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5.3  Use case 3: Support of Emergency services for Multi-USIM DevicesWord‑p. 10

5.3.1  Description

With the support of multi-USIM devices, it is important for the 3GPP system to specify service requirements to ensure emergency services provisioning and avoid conflicting behaviour among multiple USIMs for originating emergency call and terminating emergency call-back.

5.3.2  Pre-conditions

This is the use case about Peter Parker and Mary Jane, part III.
When Peter is on the way to meet Mary, Mary is kidnapped by the criminals to an abandoned factory and calls for help from Peter. Peter makes his way to the factory and tries to rescue Mary.
When Peter is fighting with criminals, Mary grabs Peter's phone, which has a first USIM and travel USIM installed, and dials IMS emergency voice call to London police.

5.3.3  Service flows

Case 1: one of the USIM is normal service
Step 1:
The UE detects that the travel USIM is in limited service state and the first USIM is camping on a normal cell which also supports IMS emergency service.
Step 2:
The UE chooses the first USIM to make the first emergency call attempt.
Case 2: both of the USIM are in normal service
Step 1:
The UE detects that both USIMs are registered, the UE is in normal service state on both and both camped-on cells support IMS emergency voice service.
Step 2:
The UE uses the first USIM to originate IMS emergency voice call based on UE configuration that was made by Peter.
Case 3 both of the USIM are in normal service, but the travel SIM is data only
Step 1:
The UE detects that both USIMs are registered, the UE is in normal service on both and both camped-on cells support IMS emergency voice service.
Step 2:
The UE uses the first USIM to originate IMS emergency voice call because the travel SIM is for "data only" services.
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5.3.4  Post-conditionsWord‑p. 11

Peter successfully beats up the criminals and saves Mary's life. They are happily reunited. London police officers arrive right on time to catch the criminals.

5.3.5  Existing features partly or fully covering the use case functionality

N/A

5.3.6  Potential New Requirements needed to support the use case

[PR.5.3.6-1]:
A MUSIM UE shall be able to select a USIM to originate an emergency call in the following priority:
  • USIM in normal service
  • USIM in limited service state
[PR.5.3.6-2]:
The MUSIM UE shall avoid interruptions of emergency call procedures of one USIM by other services of other USIM.

5.4  Use Case 4: Incoming call for one USIM while having a call for another USIM

5.4.1  Description

Many commercially deployed devices support more than one USIM (typically two). For cost efficiency reasons, a multi-USIM device implementation typically uses common radio and baseband components that are shared among the multiple USIMs. This use case enables that a user using a device with two USIMs with such implementation can have an incoming call associated with one USIM while having a call associated with another USIM. The two USIMs may be from the same or from different MNOs.

5.4.2  Pre-conditions

User A has a mobile phone with two USIMs, i.e. USIM 1 and USIM 2. The two USIMs may be from the same or from different MNOs.
The mobile phone uses common radio and baseband components that are shared between the two USIMs.

5.4.3  Service Flows

  1. User A has a call associated with USIM 1.
  2. During the call, user B calls USIM 2 of user A.
  3. The mobile phone of user A rings and informs user A that there is an incoming call associated with USIM 2.
  4. User A hangs up the call from user B for USIM 2 and continue the first call for USIM 1.
  5. Or User A decides to answer the call from user B, User A answers this call and hangs up the first call for USIM 1.
  6. When the call from user B ends, user A resume the first call for USIM 1.

5.4.4  Post-conditions

None.

5.4.5  Existing features partly or fully covering the use case functionality

None.

5.4.6  Potential New Requirements needed to support the use caseWord‑p. 12

[PR.5.4.6-1]:
The 3GPP system shall provide means to allow a MUSIM UE to receive and switch over to an incoming call originally associated with one USIM when a call associated with another USIM is on-going.

5.5  Use Case 5: Simultaneous voice service for one USIM and data service for the other USIM

5.5.1  Description

Many commercially deployed devices support more than one USIM (typically two). For cost efficiency reasons, a multi-USIM device implementation typically uses common radio and baseband components that are shared among the multiple USIMs. This use case enables that a user using a device with two USIMs with such implementation can have voice service associated with one USIM and data service associated with the other USIM simultaneously. The two USIMs may be from the same or from different MNOs.

5.5.2  Pre-conditions

User A has a mobile phone with two USIMs, i.e. USIM 1 and USIM 2. The two USIMs may be from the same or from different MNOs.
The mobile phone uses common radio and baseband components that are shared between the two USIMs.

5.5.3  Service Flows

  1. User A is using the multi-USIM smartphone to play the game via the data connection associated with USIM 1.
  2. User B calls USIM 2 of user A.
  3. The mobile phone of user A rings and informs user A that there is an incoming call associated with USIM 2.
  4. User A answers the call from user B and keeps playing the game. And the call will not impact the gaming experience, i.e., will not cause lag or packet loss.

5.5.4  Post-conditions

After the call from user B ends, user A can keep playing the mobile game.

5.5.5  Existing features partly or fully covering the use case functionality

None.

5.5.6  Potential New Requirements needed to support the use case

[PR.5.5.6-1]:
The 3GPP system shall be able to allow a MUSIM UE to provide voice from one USIM and data services from another USIM simultaneously.
[PR.5.5.6-2]:
The 3GPP system shall be able to minimize the impact for a MUSIM UE, for the on-going data service associated with one USIM while the users is answering a call associated with another USIM simultaneously.

5.6  Use case 6: Efficient Support of Mobile Terminated Services for Multi-USIM Devices

5.6.1  Description

Without any additional support MUSIM UEs in DSDS mode may operate in such a way as to reduce User experience due to interruptions in service when paging collision occurs.
This use case seeks to avoid this degradation of service experienced by the user as well as, if possible, wasted resources in the system. Examples of waste in the system are: additional signalling (of any kind) between the UE and the network, unnecessary paging, unnecessary interruptions of service on the UE to respond to paging.
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5.6.2  Pre-conditionsWord‑p. 13

J has a MUSIM UE in DSDS mode.
J uses services associated with one USIM.

5.6.3  Service flows

J has a MUSIM UE in DSDS mode.
J uses data download services (e.g. streaming music) associated with one USIM.
J receives a mobile terminated call associated with another USIM, and speaks to the caller.

5.6.4  Post-conditions

J's user experience is excellent.
The use of MUSIM in DSDS mode has resulted in a minimum of wasted signalling and resources.

5.6.5  Existing features partly or fully covering the use case functionality

N/A

5.6.6  Potential New Requirements needed to support the use case

[PR.5.6.2-1]:
The 3GPP system shall be able to minimize unnecessary signaling and use of resources for a MUSIM UE in DSDS mode.
[PR.5.6.2-2]:
Suspension and resumption for a specific set of services should be possible for each PLMN that a MUSIM UE in DSDS mode is registered in.

5.7  Use Case 7: Security Risks with Multi-USIM Devices

5.7.1  Description

Dual SIM mobile phones, one form of multi-USIM devices, have become mainstream since late 2000s in many countries, which refer to mobile phones that support use of multiple UICCs [GSMA TS.37]. So far switching between multiple USIMs / UICCs is achieved by terminal side implementations while remaining transparent to mobile networks. With the current implementations, a Dual SIM phone either allows users to switch between two separate mobile network services manually, has hardware support for keeping both connections in a "standby" state for automatic switching, or has individual transceivers for maintaining both network connections at once. Enabling 3GPP system support of multi-USIM devices has benefits, while it also introduces some potential security risks.
Separating personal and business uses
Dual SIM Phone is one of the options that allow the user to have both a personal and business phone number within the same phone. Users can place their 'work' USIM or a UICC in the phone alongside a personal USIM or a UICC, so that they only have to carry one handset.
Many business phones would enable the remote control / management from the (owner) company. Security guarantee for both personal use and business use is essential. Data privacy is crucial in many regions based on regulatory requirements. Therefore, it is very important that personal usage to be separated / isolated from business usage. In addition, separation of the associated subscriptions/preferences with different UICCs/USIMs is also necessary.
Efficiency
Dual SIM phones make it easier for tariff hopping. For example, a user may want a separate UICC/USIM for data services only, and Dual SIM phones would allow the user to carry both subscriptions in one single phone without repeated UICC replacement. This keeps the primary number contactable with the addition of data only UICC/USIM for use on the go.
In this use case these two UICCs/USIMs have subscriptions for different services, for example the primary UICC/USIM for phone calls while the additional UICC/USIM for data services. In addition to security and data privacy guarantee for each UICC/USIM, clear separation between the associated subscriptions/preferences becomes more important.
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5.7.2  Existing features partly or fully covering the use case functionalityWord‑p. 14

The following definitions captured in TR 21.905 are applicable.
UICC:
a physically secure device, an IC card (or 'smart card'), that can be inserted and removed from the terminal. It may contain one or more applications. One of the applications may be a USIM.
Universal Subscriber Identity Module (USIM):
An application residing on the UICC used for accessing services provided by mobile networks, which the application is able to register on with the appropriate security.
Concerning the related service principles specified in TS 22.101, some are still applicable while some may require careful review, for example
In TS 22.101, clause 13.3 "Terminals and Multiple UICCs" --
A single terminal may support the use of multiple UICC (e.g. with applications like USIM and/or banking, credit card, ...). Only one UICC shall be active at a time to access a PLMN.
In TS 22.101, clause 13.1.4 "Multiple USIMs per UICC" --
The standard shall support more than one USIM per UICC even when those USIMs are associated with different home environments. Only one of the USIMs or the SIM shall be active at a given time. While the UE is in idle mode, it shall be possible for the user to select/reselect one USIM application amongst those available on the UICC. At switch on, the Last Active USIM shall be automatically selected. The Last Active USIM shall be stored on the UICC. By default if there is no Last Active USIM defined in the UICC, the user shall be able to select the active USIM amongst those available on the UICC.
The standard must not prevent the coexistence of USIM applications, each associated with different home environments on the same UICC, so long as the security problems which arise from such a coexistence are solved.
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5.7.3  Potential New Requirements needed to support the use case

[PR.5.7.3-1]
The 3GPP system shall enable the secure support of an MUSIM UE with multiple USIMs from the same or different MNOs on the same UE.
[PR.5.7.3-2]
The 3GPP system shall provide appropriate security mechanisms to prevent interference between operator's service preferences of one USIM and the operator's service preferences of the other USIM.
[PR.5.7.3-3]
Each USIM shall appear as a separate device to the 3GPP system.

6Void

7  Additional considerations

8  Consolidated potential requirements

This section provides consolidated potential requirements for consideration to include in the normative specifications.

8.1  Support of Terminal with Multiple USIMsWord‑p. 15

[CPR.8.1-1]:
The 3GPP system shall support ME with multiple USIMs (on the same UICC or on different UICCs) that are registered at the same time.
[CPR.8.1-2]:
The 3GPP system shall provide appropriate security mechanisms to prevent interference between operator's service configuration of one USIM and the operator's service configuration of the other USIM.
[CPR.8.1-3]:
The 3GPP system shall treat each registration from these USIMs of a MUSIM UE independently. Each registerred USIM in a MUSIM UE shall be associated with a dedicated IMEI/PEI.
[CPR.8.1-4]:
The 3GPP system may support network resources utilization efficiently when the network operator is able and permitted (e.g. due to privacy regulations) to ascertain that multiple USIMs in a MUSIM UE are registered with that network operator's PLMN.
The mapping between consolidated service requirements and the recommendation for normative specification is as follows:
Consolidate Potential Service Requirements Recommendation for normative in TS 22.101
[CPR-8.1-1]Y
[CPR-8.1-2]N
[CPR-8.1-3]Y
[CPR-8.1-4]N
 
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8.2  Support Mobile Terminated Services for Multi-USIM Devices

[CPR.8.2-1]:
The 3GPP system shall enable the end user to select the mobile terminated services that can take priority over ongoing communications associated with another USIM.
[CPR.8.2-2]:
The 3GPP system shall enable a MUSIM UE in coordination with the network to pause and continue an active communication for efficient use of resources.
[CPR.8.2-3]:
Void.
[CPR.8.2-4]:
The 3GPP system shall be able to effectively page MUSIM UEs in order to reduce missed paging.
[CPR.8.2-5]:
Void.
[CPR.8.2-7]:
The 3GPP system shall provide means to allow a MUSIM UE to respond to an incoming mobile terminated service associated with one USIM when the MUSIM UE has an on-going service associated with another USIM.
[CPR.8.2-8]:
The 3GPP system should be able to allow a MUSIM UE to provide voice from one USIM and data services from another USIM simultaneously.
[CPR.8.2-9]:
The 3GPP system shall provide a means to support a MUSIM UE with minimal signalling overhead and impact to services associated with the different USIMs.
The mapping between consolidated service requirements and the recommendation for normative specification is as follows:
Based on Consolidate Potential Service Requirements (clause 8.2) Recommendation for normative in TS 22.278
[CPR-8.2-1]Y
[CPR-8.2-2]Y
[CPR-8.2-3]Void
[CPR-8.2-4]Y
[CPR-8.2-5]Void
[CPR-8.2-6]Void
[CPR-8.2-7]N
[CPR-8.2-8]N
[CPR-8.2-9]N
 
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8.3  Support of Emergency Services for Multi-USIM DevicesWord‑p. 16

[CPR.8.3-1]:
A MUSIM UE shall be able to select a USIM to originate an emergency call in the following priority:
  • USIM in normal service
  • USIM in limited service state
[CPR.8.3-2]:
The MUSIM UE shall avoid interruptions of emergency call procedures of one USIM by other services of other USIM.
[CPR.8.3-3]:
The MUSIM UE shall allow call-backs (e.g. from a PSAP) to the same user credentials which originated an emergency call within a certain time period.
The mapping between consolidated service requirements and the recommendation for normative specification is as follows:
Consolidate Potential Service Requirements Recommendation for normative in TS 22.101
[CPR-8.3-1]Y
[CPR-8.3-2]Y
[CPR-8.3-3]Y
 
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$  Change historyWord‑p. 17


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