How to Access the AT Command Line via AT Over TCP on RobustOS Routers

How to Access the AT Command Line via AT Over TCP on RobustOS Routers

Overview

In industrial automation, devices like Ethernet PLCs often need to trigger cellular functions—such as sending SMS alarms—without a physical serial connection. The AT Over TCP feature allows these devices to encapsulate standard AT commands within TCP packets and send them over the local network to a Robustel gateway. The gateway, acting as a TCP server, parses the commands and executes them via its internal wireless module.


What You'll Need

Hardware:

  • 1x Robustel Gateway (e.g., R3000 series or similar) running RobustOS.
  • 1x Active SIM card with SMS service.
  • 1x PC for configuration and testing.

Software:

  • AT Over TCP APP (installed via the Robustel App Center).
  • TCP Client software (e.g., Hercules SETUP utility).

Step-by-Step Configuration Guide

Step 1: Configure Cellular WAN Connection

Ensure the gateway is online to allow the wireless module to process AT commands.

  1. Navigate to Interface > Link Manager.
  2. Set the Primary Link to your desired interface (e.g., WWAN1 for cellula) to ensure the device has an active network path.
  3. Verify the connection status under Status > Network to confirm the device has obtained an IP address.



Step 2: Configure the AT Over TCP APP

Once the APP is installed, you must enable the service and define the listening parameters.

  1. Browse to Services > AT Over TCP.
  2. Toggle the Enable switch to ON.
  3. Local IP: Enter the gateway's LAN IP address (e.g., 192.168.0.1). If left blank, the service typically listens on all available interfaces.
  4. Local Port: Define the TCP port for the service. The default is 8091 (Note: ensure this port is not blocked by any internal firewall).
  5. Enable Receive SMS: (Optional) Toggle to ON if you need the module to output incoming SMS data to the TCP client.
  6. Click Submit and then Save & Apply at the top of the page.


Verification & Testing

1. Establish TCP Connection

  1. Open the Hercules SETUP utility on your PC.
  2. Go to the TCP Client tab.
  3. Enter the Router IP (Router LAN IP) and the Port (e.g., 8091).
  4. Click Connect. The message "Connected to [IP]" should appear in the terminal.

2. Send SMS via AT Commands

Use the following sequence in the Hercules Send bar to trigger an SMS:

  • Set SMS Text Mode:
    • Command: AT+CMGF=1.
    • Expected Response: OK.
  • Specify Recipient:
    • Command: AT+CMGS="+[CountryCode][Number]" (e.g., AT+CMGS="+8618xxxxxx793").
    • Expected Response: >.

  • Send Content with Termination:
    • Enter your message followed by the hex code 1a (represents Ctrl+Z) to trigger the send.
    • Example: Alarm Test 123 1a.
    • Crucial: Check the HEX box in your client software for the content string to ensure 1a is sent correctly.
  • Mobile Phone succeeds to receive SMS content “123”.


Troubleshooting / FAQ

  • Q: The client connects but commands time out.
  • A: Verify that the gateway has a "Ready" SIM status and a valid cellular signal. Ensure the AT Over TCP service is enabled in the APP settings.

  • Q: How do I know the SMS was sent successfully?
  • A: The terminal should return a +CMGS: [index] message followed by OK. You should also verify receipt on the destination mobile phone.

Revision History

Version

Date

Author

Changes

1.0

2026-1-16

Steven

Initial verions


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