Environment
SIM type: SoftSIM
Device: SoftSIM-supported modules
Question
Why is SoftSIM taking longer to attach than physical SIM?
Is it normal to observe noticeable increase in attach times when using SoftSIM?
Answer
This is normal and expected.
Physical SIM hardware has its own computing power to perform certain operations.
SoftSIM does not come with dedicated hardware.
SoftSIM's performance is reliant on computing power of the module processor and other components, which are also responsible for other services, applications and processes that need to be timed and scheduled.
This may impact connection times.
Cause
The SoftSIM codebase/app (onomondo-uicc) is a lean and generic UICC implementation written in C programming language.
The application needs to be compiled and hosted on some processing unit that would otherwise interact with a USIM interface.
Physical UICCs (SIMs) are, in fact, custom developed processors with secure data storage and hardware-accelerated cryptographic operations performed by the SIM itself.
Such hardware architecture, found within a SIM, is designed and optimized to do one job and one job only: hosting the SIM codebase/app (onomondo-uicc).
With SoftSIM, we are moving this application out of the dedicated hardware component and carrying it over into "any" hardware (for now - only when supported by hardware manufacturers). This new hosting environment of the SIM application (onomondo-uicc) is no longer optimized for SIM operations nor does it guarantee to have hardware-accelerated cryptographic operations that match the requirements of a SIM. Most often, like in case of the nRF91 Series SiP the architecture match those of a physical SIM. But nevertheless, we are now sharing the processor with other services, applications and processes that need to be timed and scheduled.
Having more than one application hosted on e.g. the nRF91 Series SiP, will allow developers to conflict and interfere with the workflow and scheduling of the SoftSIM, which might be experienced as "the SIM is slow at attaching to a network" - but might be caused by, e.g. a delay by some other process running on the same processor.
Simply put, since we are utilizing a non-specifc SIM processor to perform SIM functionality (that is not that complex, by default) we would always expect performance differences between a dedicated physical SIM and SoftSIM. Most often it might be that SoftSIM is a little slower, but it could theoretically also be quicker when run on the right processes.
Specifically for the nRF91 Series SiP, the attachment times using SoftSIM will not take more than a few seconds more than what might be measured with a physical SIM.