SIM800L + Arduino TCP disconnect issue

[Leon_P-S]

Okay so I am currently using an arduino-uno to send AT commands to a SIM800l module. I am running a basic TCP socket server on my computer and the SIM800L is initially able to connect to it fine and send a message. After a seemingly random period of time on my serial monitor “NUL” is then displayed at which I am unable to send messages.
(So it is working initially however it seems to suddenly just stop mid process)

bool connectionProcedure()
{
  bool result = false;
  if(sendATcommand("AT+CIPSHUT", "SHUT OK", 200) == 1)
  {
    Serial.println("Proceed: AT+CIPMUX=0");
    if(sendATcommand("AT+CIPMUX=0", "OK", 1000)  == 1 )
    {
      Serial.println("Proceed: AT+CGATT=1");
      if(sendATcommand("AT+CGATT=1", "OK", 1000)  == 1 )
      {
        Serial.println("Proceed: AT+CSTT=\"gifgaff.com\",\"gifgaff\"");
        if(sendATcommand("AT+CSTT=\"gifgaff.com\",\"gifgaff\"", "OK", 1000)  == 1 )
        {
          Serial.println("Proceed: AT+CIICR");
          if(sendATcommand("AT+CIICR", "OK", 60000)  == 1 )
          {
            Serial.println("Proceed: AT+CIFSR");
            if(sendATcommand("AT+CIFSR", ".", 5000)  == 1 )
            {
              Serial.println("Proccess Success!");
              result = true;
            }
            else
            {
              Serial.println("Error: AT+CIFSR");
            }
          }
          else
          {
            Serial.println("Error: AT+CIICR");
          }
        }
        else
        {
          Serial.println("Error: AT+CSTT=\"gifgaff.com\",\"gifgaff\"");
        }
      }
      else
      {
        Serial.println("Error: AT+CGATT=1");
      }
    }
    else
    {
      Serial.println("Error: AT+CIPMUX=0");
    }
  }
  else
  {
   Serial.println("Error: CIPSHUT");
  }
  return result;
}

– This is then called to check for a connection to the network

void awaitGSMConnection()
{
  while( sendATcommand2("AT+CREG?", "+CREG: 0,1", "+CREG: 0,5", 1000) == 0 );
}

– Now the more useful stuff…

void initTCPConnection()
{
    unsigned long previous;
    unsigned int timeout = 10000;
 
    Serial.println("Starting TCP Connection!");
    if(sendATcommand("AT+CIPSTART=\"TCP\"," + tcpIp + "," + tcpPort, "OK", 10000) == 1)
    {
        Serial.println("Connection Success: Checking for stable connection before handshake!");
 
        String expected = "CLOSED";
        uint8_t x=0,  answer=0;
        char response[100];
 
        memset(response, '\0', 100);
        while( mySerial.available() > 0) mySerial.read();
        x = 0;
        previous = millis();
 
         // Loop waits for the response from SIM800L
        do {
            if(mySerial.available() != 0) {
                response[x] = mySerial.read();
                x++;
                // check if the desired answer 1  is in the response of the module
                if (strstr(response, expected.c_str()) != NULL)
                {
                    answer = 1;
                }
            }
        }
        while((answer == 0) && ((millis() - previous) < timeout));
 
        if(answer == 0)
        {
            Serial.println("No Apparent ISSUE sending handshake!");
            if(sendATcommand("AT+CIPSEND", ">", 4000) == 1)
            {
                Serial.println("SEND-HANDSHAKE");
                sendMessage("Handshake");
                //sendATcommand("AT+CIPCLOSE","OK",2000);
            }
            else
            {
                Serial.println("Error: AT+CIPSEND");
            }
        }
        else
        {
            Serial.println("Connection test failed: Attempting to RECONNECT!");
        }
    }
    else
    {
        Serial.println("Connection Error!");
    }  
}

Serial Monitor - Output

Here is the “NUL” I am talking about, this seems to appear completely randomly sometime during the connection. Random messages being sent from me from the server and being received.

No Apparent ISSUE sending handshake!
AT+CIPSEND
>
SEND-HANDSHAKE
 Handshake␚
SEND OK
HELLO
AWESOME
COOL
INSANE
STILL WORKING!!!!
␀

Thanks in advance!