How to prevent cellular modem from connecting using 3G

How to prevent cellular modem from connecting using 3G

The Sierra EM7565 modem available in many Nodegrid devices supports both 4G and 3G connectivity.  By default, the modem will first try to connect to relevant 4G networks available and only fall back to 3G when connecting via 4G fails.  The result is that locations with a solid 4G signal will not try to use 3G.  However, in locations where the 4G signal is less reliable, the modem may fallback to 3G.  Once this occurs, the modem must be reset before it will attempt to use 4G cellular connectivity again.

Many carriers have retired, or are in the process of retiring, their 3G networks.  We have observed that some of these networks will allow the modem to connect over 3G, but no network level traffic is allowed to pass.  This creates a confusing state where it appears the cellular connection is up even though the cellular network cannot be used.  Here is more information about the phase of various 3G cellular networks around the world:

If a Nodegrid device is in a location where the relevant carrier(s) for the installed SIM(s) have retired their 3G networks, it is recommended to remove 3G as an allowed mode.  Here are the steps:

Note: Only available on Nodegrid OS v5.4.13 or later, v5.6.4 or later, or 5.8.x or later.  The default value for this setting is 3G,4G.
  1. Navigate to Network :: Connections
  2. Click the existing Mobile Broadband GSM connection to update to edit its settings
  3. Alternately, this can be done when creating a new connecting using the Add button
  4. To update SIM-1:
    1. Select the dropdown for SIM-1 allowed modes: field
    2. Select 4G
  5. To update SIM-2:
    1. Select the dropdown for SIM-2 allowed modes: field
    2. Select 4G
  6. Click Save

Set the allowed modes setting in the CLI

Note: Only available on Nodegrid OS v5.4.13 or later, v5.6.4 or later, or 5.8.x or later.  The default value for this setting is 3g|4g.
  1. Log into the Nodegrid device CLI as an admin
  2. Navigate to the existing Mobile Broadband GSM connection to update to edit its settings
    1. Example network connection is named LTE
      1. Change LTE to correct name
    2. cd /settings/network_connections/LTE/
  3. To update SIM-1:
    1. set sim-1_allowed_modes=4g
  4. To update SIM-2:
    1. set sim-2_allowed_modes=4g
  5. Save the changes:
    1. commit

Set the allowed modes via root shell

For devices running Nodegrid OS v4.x:
  1. Run these two commands:
LTEBANDS="$(mmcli -m <index> | grep 'Bands.*supported:' | grep -Eo 'eutran-[a-z0-9]+,?' | tr ',\n' '|\0')"
mmcli -m <index> --set-current-bands="$LTEBANDS"

For devices running Nodegrid OS v5.x:
  1. Run this command to get the modem's current index number:
    1. mmcli -L
  2. Run this command to disable 3g:
    1. Example modem was index 0 indicated by output: /org/freedesktop/ModemManager1/Modem/0
      1. Change 0 to correct index number
    2. mmcli -m 0 --set-allowed-modes=4g

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