How to ensure proper device interworking with a Multi-IMSI SIM solution?
- Device should have a 3 minute minimum active period:
- IMSI rotation may fail if this isn’t ensured. Sleep mode (or disabling modem) in between will disrupt the IMSI rotation sequence.
- This minimum threshold may be higher for devices which need to scan different NB-IoT/LTE-M bands. In this case, we recommend fine tuning your device by reducing the number of bands scanned.
- Device (terminal and modem) should support SIM Toolkit Application protocol:
Release 99 implementation is mandatory, in order to ensure successful applet logic.
IMSI rotation will fail if support of this application is not guaranteed.
What is Multi-IMSI solution?
Multi-IMSI stands for Multiple International Mobile Subscriber Identities. A SIM card containing multiple IMSIs enables subscribers to switch carriers as required and connect to significantly more networks: the applet will trigger an IMSI swap if the current IMSI does not have an available roaming agreement with a local network operator.
It is therefore an essential feature for global deployments of IoT solutions.
What is STK?
STK stands for SIM Toolkit Application. This protocol is specified by:
- 3GPP TS 11.14 (v8 / Rel99).
- 3GPP TS 31.111 (includes USIM Application Toolkit for 3/4G networks).
STK support in devices is mandatory to handle Multi-IMSI solutions.
Which commands within the STK are used for the Multi-IMSI solution?
Multi-IMSI applet is relying on the following standard STK Proactive commands:
- Setup Menu
- Provide Location Info
- Timer Management
- Refresh
Full details of the functioning of commands above can be found in both specifications 3GPP TS 11.14 and 3GPP TS 31.111.
Under which conditions will the Multi-IMSI applet will trigger an IMSI rotation?
Device will be forced to reboot and use a new IMSI identity after a 2 minute period when:
- Network attach is rejected by all networks with the current IMSI (e.g. none of the available networks in this location are allowed in the Roaming Profile with the current IMSI).
- Device lands in a new country where the priority IMSI isn’t currently active .
- The SIM card being notified that the network has “Limited Service” (timeouts during the Authentication procedure or poor coverage for a extended period of time).
What is the forbidden PLMN list and how does it impact network searching?
The forbidden PLMN list is dynamically stored in the SIM and maintained by the device. When a device attempts to connect to a network and is denied, it will insert that network to the fPLMN list, thus preventing it from attempting to connect to the same network again.
If all available networks are added to the fPLMN list, the only way to ensure the modem will keep trying to connect will be to either make manual registration attempts (possible in phones but very unlikely in IoT devices) or clean the content of the fPLMN list.
Our Multi-IMSI applet will clear the fPLMN list content after every IMSI rotation.
Which network will my device choose to connect to?
The first time a SIM attempts to connect in a country, if no other preferences are explicitly set, a device will choose based on the signal strength coming from all the available networks. If the strength is better than -85 dBm, a network will be chosen randomly, if the signal strength is lower, the network with the highest signal strength will be selected.
Remark: Networks contained in the forbidden PLMN list will be ignored by the modem during this phase.
For subsequent connections, the SIM will normally instruct the device to register under the last used network (and with the same technology), minimizing the registration time.
Inside a country, CityKinect is not steering to any specific networks, apart from the screening based on the customer’s Roaming Profile or blacklisting.
Within the default Roaming Profile inherited from CityKinect, SFT customer has the possibility to customize their own profiles, removing/blacklisting any of those networks.
How to optimize the network scanning?
Band scanning for LWPA technologies as NB-IoT/LTE-M is very time consuming, at 2 minutes per band. In order to optimize the network registration, it is recommended to pre-configure the device by reducing the scanned bands to the minimum required needed for the region:
- Asia: B3,B8
- Europe: B3, B20
- North America: B4,B12
- South America: B4,B28
- Africa: B3,B8
- Oceania: B3,B28
It is also possible to prioritize a RAT over the others via the device configuration.
Why is the initial attach to NB-IoT sometimes taking very long?
Some devices (i.e. Quectel BG95/96), while being configured to search only for NB-IoT radio access, are experiencing long delays to perform the initial network attach. This may happen within auto-selection network mode, when a SIM card isn’t instructed to connect to a specific network.
If the outcome of the required connectivity tests is showing this misbehaviour, it is recommended to use a manual network selection setup, while taking into consideration the static nature of NB-IoT devices and that coverage offered by BICS is subject to change.
What is a LPWAN device?
LPWAN Devices are made to optimise battery consumption, meaning they will trigger sleep mode to minimize the time a device is active.
Sleep mode will be initiated not only by PSM/eDRX modes inside the network, but also by the upper application on the device.
In order to ensure that network registration can occur, a device should stay active for at least 3 minutes after the initial registration to the network.
My device is up and running but it’s not trying to connect to any network
This can be caused by one of following reasons:
- Full fPLMN list.
- To solve this situation, it’s highly recommended to have means on the device to clear the forbidden PLMN list periodically, like this new registration attempts will occur, and eventual IMSI rotation will be triggered.
- Out of coverage.
- Stuck on an IMSI without available networks.
My device is attached but it cannot exchange any data
This can be caused by one of following reasons:
- APN isn’t configured, hence data session isn’t created.
- APN in the device isn’t aligned with the APNs present in the APN group.
- Network interface isn’t associated to the EPS bearer.
- Under NB-IoT/LTE-M, can be due to VPMN policies.
My device is connected but it doesn’t receive SMS
In order to be capable of receiving an SMS the device needs to be attached via the proper leg (MSC/VLR). This is guaranteed for all smartphones but not for all IoT devices. Scenarios where this won’t happen are listed below:
- The device doesn't support SMS and is made to be data-only.
- LTE-M/NB-IoT devices without 2G support (SMS via SGd interface towards MME isn’t yet a reality for the vast majority of networks)
- Per configuration, the device is in datacentric mode (PS attach only). Please ensure then that CS/PS attach is configured
A2P SMS Coding schema: device isn’t reacting properly to commands
Some IoT devices aren’t supporting all coding schemas for SMS, meaning that the text inside an SMS may not be properly interpreted. Therefore, one should bear in mind that currently, A2P campaigns towards an endpoint are following the approach depicted below:
- A2P SMS tool in SFT Portal will use per default UCS2 schema.
- A2P SMS API will provide enough flexibility to choose specific coding schema among 7 bit alphabet (GSM), 8-bit data and 16 bit (UCS2).
My device is unable to switch IMSIs
This can be caused by one of following reasons:
- Active period of the device is shorter than 3 minutes.
- Unexpected STK call flow between device and applet.
- Modem is not supporting STK or debugging mode is active.
What is the Samsung Regional block?
Some Samsung devices don’t allow SIMs to function which belong to a different region to the one they are trying to operate in. A call (longer than 5 mins) using a different SIM provider (as BICS SIMs do not support voice service) will unblock the device.