FAQ

Question 1: Why should I configure APN?

APN is a required parameter when a terminal device connects to the network. The APN determines which method the terminal device uses to access the network. Each operator has its specific APNs. Usually, the base stations of operators have the APN automatic correction feature. When a terminal device connects to the network without APN configuration or with an incorrect APN, the base station will automatically correct it and send the correct APN to the device. The device will accept and use the corrected APN to continue connecting to the network. However, there are some special cases where you must manually configure APN for the device to connect to the network, as listed below.

• Some base stations in certain areas do not have the APN automatic correction feature. In this case, if the terminal device does not configure APN or configures incorrect APN, the device will fail to connect to the network. You are recommended not to rely on the APN automatic correction feature of base stations because it is hard to know whether a base station has the APN automatic correction feature in advance.
• For some special SIM cards, such as dedicated network cards, if the APN is not configured, the terminal device will fail to connect to the network and will be rejected when initiating an attach request in the cell. These special SIM cards must be configured with APN first.
• There is another type of special SIM card that can connect to both public networks (such as the Internet) and dedicated networks. The connection to different networks is achieved by configuring different APNs.

In summary, you are recommended to manually configure APN regardless of the type of SIM card you are using.

Question 2: How can I find out the APN information for the SIM card I am using?

You can get the information from your operator.

Question 3: Why can the NIC be activated successfully even without APN configuration or with an incorrect APN?

Because the base stations of some operators have the APN automatic correction feature. When a terminal device connects to the network without APN configuration or with an incorrect APN, the base station will automatically correct it and send the correct APN to the device. The device will accept and use the corrected APN to continue connecting to the network.

Currently, in most areas within China, most base stations have the APN automatic correction feature, but some do not. You are recommended not to rely on the APN automatic correction feature of base stations and manually configure the correct APN because it is hard to know whether a base station has the APN automatic correction feature in advance.

Question 4: Why can the SIM card be recognized but fail to register on the network?

This situation is relatively complex. Please refer to [Module Network Registration Failure](./exception-handling.html#Module Network Registration Failure) in the Handle Network Exceptions chapter for details. Here are some common reasons:

• The RF antenna is not connected or the RF antenna performance is poor.
• The SIM card requires APN configuration to register to the network, but no APN is configured.
• The SIM card is bound to a specific device. You need to contact the operator to unbind the SIM card or replace it with a new SIM card.
• The testing location is not covered by the network of the SIM card operator.
• The SIM card only supports specific frequency bands.
• The SIM card only supports specific network modes.
• There are hardware issues with the device, such as interference caused by hardware design flaws, or damaged RF components.

Question 5: Why cannot the NIC perform network services after being activated successfully?

• Your SIM card is in arrears. The module can register on the network and activate the NIC successfully even when the SIM card inserted is in arrears, but the operator will restrict the module from network communication.

• Your SIM card supports access to a special network through a specific APN and you have configured the APN for accessing the special network. In this case, your device can only access the special network instead of the Internet. If you try to access the Internet, the access will fail.

Question 6: When the automatic reconnection of the NIC is enabled, do Socket, HTTP, and MQTT need to be reinitialized after the NIC is re-connected to the network if the network connection is disconnected due to some reasons during the normal operation of the module?

You should know that the IP address of the NIC will be changed as long as the NIC is automatically re-connected to the network after disconnecting from the network due to network exceptions. In this case, you need to perform the following steps for Socket, HTTP, and MQTT features.

• Socket

  When creating a socket object, the system automatically binds it to the current IP address of the cellular NIC. When the IP address of the cellular NIC changes, the previous socket becomes invalid and you need to close the previous socket and create a new socket object.

• HTTP

  HTTP is a short connection service based on socket. Each time an HTTP API is called, a new socket object is created. Therefore, the automatic reconnection feature does not affect the HTTP functionality, and you can continue to use the HTTP feature.

  The socket object created in the HTTP API will be automatically closed by the system after you obtain the response (response.text & response.content & response.json). If you do not obtain the response, you need to manually call response.close() to close the connection and close the socket object.

• MQTT

  The MQTT client in QuecPython solution has the automatic reconnection feature. When the MQTT client detects that the cellular NIC is automatically reconnected to the network after a network disconnection, the MQTT client will be automatically initialized and automatically subscribe to the relevant topics according to the previous subscription information. Therefore, after the cellular NIC is automatically reconnected, you do not need to reinitialize the MQTT client and can continue to use the MQTT feature.