Example scenario details:

• We have 3 devices with RS232 serial ports (configured to 115200,8,N,1 and HW flow control) which need to be monitored from a PC with internet access from a Central Control station.

• You need to be able to access the RS232 devices at any time so the modems connected to the devices’ serial ports must stay GPRS connected 100% of the time, waiting for a connection from the remote PC. The modems wait for incoming connections via the TCP 20010 port.

• SIM cards with a fixed IP address will be used in each of the modems.

Proposed solution with  MTX-65i + MTXTunnel:

MTX-65i + MTXTunnel configuration file for the proposed solution above:

You have to enter this into the modem’s configuration file to be able to run the application as described in the scenario:

COMM_baudrate: 115200 Serial port baud rate
COMM_bitsperchar: 8 8 data bits
COMM_autocts: on CTS hardware flow control activated
COMM_autorts: on RTS hardware flow control activated
COMM_stopbits: 1 1 stop bit
COMM_parity: none No parity
GPRS_apn: internetestatico.movistar.es GPRS APN provided by GSM operator 
GPRS_login: MOVISTAR GPRS Login provided by GSM operator
GPRS_password: MOVISTAR GPRS Password provided by GSM operator
GPRS_timeout: 0 The modem is permanently GPRS connected when value is 0
MTX_PIN: 0000 If the SIM card doesn’t have a PIN, leave it as 0000
MTX_model: MTX65i MTX65i is the chosen model for RS232
MTX_mode: server TCP server mode
MTX_urc: off We don’t need URC information messages
MTX_rssiLevel: 10 The MTX65i’s coverage LED is activated
TCP_port: 20010 The MTX’s TCP port that waits for IP connections
FIREWALL_enabled: off Firewall disabled to accept connections from any IP

Comments




The example shown below is similar to Example 1 but this time we are using SIM cards with a dynamic IP address instead of paying for SIM cards with a fixed IP address. This is because the GPRS connection will not be permanent with the modems, it will only be used for remote maintenance tasks when we need to access a remote device’s RS232 port.

Here is the example scenario in a little more detail:

• We have 3 devices with RS232 ports (configured to 9600,8,N,1 and without flow control) which need to be monitored from a central control station via a GPRS-Serial tunnel.

• We occasionally need to access the RS232 serial devices for remote maintenance purposes, therefore the modems don’t need to be permanently GPRS connected.

• A modem must be connected to GPRS for ten minutes when it receives a missed call or an SMS with the text “mtxtunnel on” from a phone number. In order to connect to GPRS, the modem has to send an SMS with the IP address (obtained by the GSM operator) to the phone number that sent the SMS or made the missed call.  For those ten minutes, the modem will keep waiting for incoming connections via the 20010 TCP port.

• For security reasons, the modems should only respond to activation SMS messages or missed calls from authorized telephone numbers 666123456 and 666123457. Additionally, MTXTunnel only allows IP connections to be established from the central office’s IP which is 200.101.102.103

Proposed solution with MTX-65i + MTXTunnel


MTX-65i + MTXTunnel configuration file for the proposed solution above:

You have to enter this into the modem’s configuration file to be able to run the application as described in the scenario:

COMM_baudrate: 9600 Serial port baud rate 
COMM_bitsperchar: 8 8 data bits
COMM_autocts: off CTS hardware flow control deactivated
COMM_autorts: off RTS hardware flow control deactivated
COMM_stopbits: 1 1 stop bit 
COMM_parity: none No parity
   
GPRS_apn: movistar.es  GPRS APN provided by GSM operator 
GPRS_login: MOVISTAR  GPRS Login provided by GSM operator
GPRS_password: MOVISTAR  GPRS Password provided by GSM operator
GPRS_timeout: 10  The modem will stay GPRS connected for 10 minutes if there is no data
   
MTX_PIN: 0000  If the SIM card doesn’t have a PIN, leave it as 0000
MTX_model: MTX65i  The MTX65i is the chosen MTX model (MTX65IND for RS485)
MTX_mode: server  The modem is configured as TCP server
MTX_urc: off  We don’t need URC information messages
MTX_rssiLevel: 10  The MTX65i’s coverage LED is activated
   
TCP_port: 20010  The MTX’s  TCP port that waits for IP connections
   
FIREWALL_enabled: off  Firewall disabled to accept connections from any IP 
   
SMS_allPhones: off All phone numbers are NOT authorized 
SMS_sendIP: on We will send the IP to the authorized phone number that makes the missed
call or sends the SMS with the text “mtxtunnel on”
SMS_validPhone1: 666123456 Authorized phone number 1
SMS_validPhone2: 666123457  Authorized phone number 2 
   

The difference with the previous example lies in enabling/disabling the firewall. We only accept incoming connections from an authorized IP address (200.101.102.103) and we allow authorized phone numbers 666123456 and 666123457 to send the string “mtxtunnel on” or make a missed call in order to activate a GPRS connection for just ten minutes (GPRS_timeout) so that remote maintenance is possible.

Comments