Remote Control: Using AT over Telnet for Your Industrial Router

In the world of industrial IoT, devices are often deployed in remote, unmanned locations like power substations, water treatment plants, or on top of a wind turbine. In my experience, these are the places where on-site maintenance isn't just expensive; it’s often impossible at a moment's notice. So, what happens when a critical event occurs? How do you get an immediate alert without a costly on-site visit?

This is where the power of AT over Telnet comes in. It’s a feature that allows you to manage a router's cellular module remotely. You can do this by using a Telnet client to connect to the router's AT port and send commands as if you were sitting right in front of it. This capability is a game-changer for machine-to-machine (M2M) communication and remote troubleshooting in the field.

At its core, AT over Telnet is a simple yet effective concept. It takes the AT command interface, a standard for controlling modems, and makes it accessible over an IP network. This allows an external user or a script to send AT commands to a device, such as a Robustel R1520 router, via a Telnet connection.

Here’s a quick breakdown of how it works:

• The Connection: First, a PC running Telnet software like SecureCRT connects to the router over a cellular network .
• The Command: The user types AT commands directly into the Telnet session . These commands are then interpreted by the router's cellular module.
• The Result: The router executes the command. For example, you can send an AT command to instruct the device to send an SMS message to a mobile phone .

This powerful feature allows for seamless remote control, making it possible to manage and diagnose devices without ever being on-site.

Let's walk through a common scenario where this feature is invaluable. I've seen clients use this to set up automated alerts for critical events.

Imagine you have a water pump in a remote area. The pump has a sensor that monitors water pressure, which is connected to your industrial router. You need to be notified instantly if the pressure exceeds a dangerous threshold.

1. Event Source: The router’s digital input (DI) is configured to monitor the pump’s sensor . Alternatively, you could be monitoring Modbus data or an SNMP trap.
2. Trigger Rule: On the router’s management interface, you configure a rule that says, “When the pump pressure exceeds 100 psi, trigger an event.”
3. Automated Action: The event is configured to automatically initiate a script. This script opens a Telnet session to the router's AT port and sends the necessary AT commands to send an SMS alert. The router sends the message "DI 1 ON, Alarm on" to a pre-set phone number .
4. Remote Notification: An engineer receives an SMS alert on their phone, letting them know about the high-pressure situation in real time. They can then take action without needing to be physically present.

This entire process happens automatically, turning what could have been a costly and dangerous situation into a manageable, remote event.

• Cost Savings: Reduces the need for expensive, time-consuming on-site visits for simple tasks like sending alerts or re-configuring modem parameters .
• Enhanced Reliability: Provides a separate, reliable channel for M2M communication, ensuring critical events are reported even if the primary network connection is unstable.
• Remote Automation: Enables the automation of tasks, allowing devices to self-report and send alerts based on pre-defined triggers from a variety of industrial sensors.