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The Physical SIM

Not all Sims are the same. When you are supplying the voice market then using a consumer SIM makes sense. It keeps the cost down and usually a phone is kept away from very cold and very hot situations since they tend to be with the owner, protected from the cold say by being in a phone inside a jacket. In M2M the hardware can be far more exposed. Roadside cabinets very often are not heated or cooled and can suffer from a wide variety of temperatures just in one day. The fast growing area of climate monitoring  is very often in exposed locations and has even less ambient heating than a roadside cabinet. Here as in automotive, extreme cold can result in deformation of the plastic substrate of the SIM resulting in catastrophic failure of the unit as the SIM tears itself free of the SIM holder and possibly the PCB it is attached to.

But there are other forms of failure which those involved in long term M2M projects are aware of. The SIMs can fill with SMS messages, some hardware doesn’t have a command to delete SMS so that eventually the card has to be replaced in the field.The network will make small changes throughout the life of the product. The SIM holds a small amount of non-volatile memory on board to allow the SIM to keep up with the updates. EEPROM generally supports around 100,000 read/write cycles before the individual memory cells start to fail. The end result is the SIM fails and will have to be replaced.

Mobius has always provided a more robust specification SIM designed for industrial applications. That means that the SIMs we shipped 8 or 9 years ago are still in the field with an average 87 parts per million failure rate compared to an industry average of nearly 10%.

SIM Technical specification

  • Combined 2G SIM, 3G & 4G USIM
  • Plug-in UICC form factor according to ETSI TS 102.221
  • 62 Kbytes of available operator memory
  • Long life – high use
  • Temp range: -35°C to +85°C
  • High stress memory (HSM) supports >2M E/W cycles per file
  • Data retention: >10 years at -35°C to 85°C
  • Outside of HSM 500k E/W cycles

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