Why dial-ups through a 3G Cellular interface always fail

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The problem is caused by the following reasons in general:

- The 3G data card is not recognized by the network, or the 3G data card is not included in the supported data card list of the device.
- Some authentications or negotiations fail during the dial-up process because the 3G data card does not match local networks, resulting in dial-up failures. (For example, some special authentications may need to be performed in local networks, if the authentications are not enabled on a 3G data card or a USIM/SIM card, the card does not match the local networks.)
- The 3G data card is not registered to an available network, manifesting as poor signal strength. You can run the display cellular command to check the status of 3G signal. In the displayed output information, the value of the Current Service Status field must be Service available, and the signal strength must be normal.
- The mode of the 3G data card is not properly configured. For example, The network connection method of a 3G data card in which a SIM card is inserted is set to wcdma-only.
- The USIM/SIM card is not available.
- The status of the USIM/SIM card is abnormal. You can run the display cellular command to check whether the status of the USIM/SIM card is normal. The status of the USIM/SIM card must be OK but not Not insert.
- The USIM/SIM card does not subscribe to 2G/3G services (services are not subscribed).
- The fund of the USIM/SIM card is insufficient.
- Check whether the 3G configurations are correct, including the dial-up character string. If you want to dial up to the CDMA2000 network, confirm whether a PPP authentication needs to be performed to access the network.
- The profile is not configured or incorrectly configured.
- Check whether you disable the 3G Cellular interface by running the shutdown command.

Other related questions:
What is the default dial-up mode of the 3G cellular interface
On-demand dial-up.

Why does dialup often fail on a 3G cellular interface

The possible causes are as follows:

  • The 3G data card cannot be identified on the current network or is not supported on the AR.
  • The 3G data card does not match the current network. For example, authentication or service required on the current network is not enabled on the data card or USIM/SIM card. As a result, authentication or negotiation fails in dialup.
  • The 3G data card is not registered with available networks, due to weak signal strength or other reasons. Run the display cellular command to check information about 3G signals. The Current Service Status field must be displayed as "Service available", and the signal strength must be in the allowed range.
  • An incorrect connection mode is configured on the 3G data card. For example, the 3G data card has a SIM card installed but its connection mode is set to WCDMA-only.
  • The USIM/SIM card is not properly installed.
  • The 2G/3G services are not enabled on the USIM/SIM card.
  • The account balance of the USIM/SIM card is insufficient.
  • The USIM/SIM card works incorrectly. Run the display cellular command to check whether the USIM/SIM card is in correct state. The status of the USIM/SIM card must be Ok not Not insert.
  • Check whether 3G configurations, including the dialer number are correct. Check whether PPP authentication is required when the 3G cellular interface accesses a CDMA2000 network.
  • No profile is configured or a profile is incorrectly configured.
  • The 3G cellular interface is shut down using the shutdown command.

Why the physical interface status of a 3G cellular interface is Down

If the physical status of a 3G cellular interface (cellular interface) is Down, no 3G link is established and data service has not been transmitted yet. That is, no dialup is triggered or dialup fails on the 3G link.

NOTE:

If no dialup is triggered or dialup fails on a 3G link, the physical interface status is still Down even if a 3G data card (3G modem) is installed.


Why is the dialer interface still Up when the physical status of the dialer interface is Down
When the physical interface that is not connected to a cable is Down, the dialer interface displays Snoofing Up. This situation is normal. You can run the dialer number 1 autodial command so that the dialer interface changes as the physical interface.

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