TCP socket systematically closed by HL7800 during tower handover

We are deploying a product using the HL7800 (it is a battery-powered portable IoT device).
The device is periodically sending data to a server using a unique TCP socket (AT+KTCPSND command)

When the device is static (physically not moving) the connection is stable and almost no disconnection occurs.

But when we start moving, we systematically see a socket disconnection when a tower switch event occurs. The sequence is the following:

  1. An AT+KTCPSND command is sent to the module
  2. HL7800 answers with “CONNECT”
  3. Data to send are transferred to the HL7800 (ended with the “–EOF–Pattern–”)
  4. After 4-6 seconds, the HL7800 answers with the following sequence (with no delay between the messages):



This looks like the socket is closed (apparently by the HL7800 because the server doesn’t see anything) exactly at the same time when the tower switch event occurs.

Could you please confirm that this behavior is normal? Theoretically, the socket should be kept active even if the cell tower is changed over the time…

We are using the latest available version of the HL7800 firmware (release in June 2023).

Using an older version of this firmware, the HL7800 behaves differently. The disconnection is not systematic, but sometimes the module doesn’t ACK the data sending command (no “OK” message at all)…

If anyone can help us to understand if we are doing something wrong? any help very much appreciated.
Thanks for your feedback and support,

Hi @mfournier,

Welcome to our community!

Please provide the complete AT Command log starting from when the HL7800 device begins to move.