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ELS61T falling off the grid in remote location | Thales IoT Developer Community

February 13, 2022 - 8:25pm, 2137 views

Hello everybody,

I have a serious issue on my hands and would appreciate any helpful insights.
I have a fleet of so far 50 ELS61T-E2 LAN modules deployed at hard-to-reach locations since 3-5 months in a wide area IoT system.
All the SIM cards are in roaming **** and connect to various mobile operators in multiple countries. Some locations barely have enough signal to manage the connection. All access technologies are enabled (2G, 3G and LTE).

The problem:
In the initial period after installations in the field (from a week to a couple of months), all terminals were working OK, sending sensor data to the central system every minute.
In the next two months. we lost all communication with more than 10 terminals. They were all working OK up to a certain point, then all comms were cut instantly, the devices just fell off the grid.

These are remote locations and service intervals are scarce, so it took two months to organize a visit to these locations. From the mobile provider side, all that was said was that they are not registered to the network.
A physical inspection, performed last week on ten locations, revealed the same status everywhere:
All terminals were powered on (green LED), but were attempting to register to the network (orange LED blinking each second).

In an attempt to fix the situation, several options were explored:

  1. power off/on - NO IMPROVEMENT
  2. SIM card taken out, wiped, reinserted - NO IMPROVEMENT
  3. a new SIM from the same provider inserted - NO IMPROVEMENT
  4. terminal replaced with a spare one (using original SIM card)- NORMAL COMMS ESTABLISHED!!!

This procedure was tried on all ten locations with the same outcome - 10 terminals were replaced to restore the funcionality.
Of course, this is by far not the end of the story. In the following days, most of the serviced locations fell of the grid again in the same manner that was observed previously.

The replaced terminals, uninstalled from the visited locations, were tested locally. All but one are fully operational!
In the mean time, 30+ terminals continue to work without issues.

I'm asking for suggestions, where and what to debug in this situation:

  • measuring cabinet conditions
  • network operator
  • device settings
  • firmware

Please, ask if more specific info is needed.

thanks in advance...