What is USSD in IoT?

A summary of USSD

USSD (Unstructured Supplementary Service Data) is a communication protocol that allows mobile phones to interact directly with a service provider’s systems using short codes like *123#. In the context of IoT (Internet of Things), USSD serves as a lightweight, real-time method for sending and receiving data over GSM networks, particularly in areas where internet access (via 4G, 5G, or Wi-Fi) is unavailable, unstable, or too costly.

USSD remains widely used today, especially in regions with limited internet connectivity or where basic feature phones are common.

How USSD works

USSD (Unstructured Supplementary Service Data) lets mobile phones and GSM-enabled IoT devices communicate directly with a network operator’s system using short codes like *123#. When a code is dialed, it initiates a real-time, interactive session between the device and the server. The server processes the request and instantly returns a response.

Unlike SMS, USSD does not rely on internet connectivity. It operates over 2G GSM signaling channels, making it ideal for quick, low-bandwidth interactions in areas with limited or no internet access.

USSD in action:

·       A GSM-enabled device sends a USSD code.

·       The code reaches the operator’s server or a linked application.

·       The server processes the request and responds with data (e.g., a status update or command confirmation).

USSD message format

A USSD message typically starts with an asterisk symbol (*) or a hash symbol (#) and is terminated with a hash symbol. For example *995#

Types of USSD Codes

Benefits of USSD in IoT

1. No internet required

• Works entirely over GSM signaling channels, making it ideal for offline or low-connectivity environments.

• Useful in rural or remote areas without mobile data coverage.

2. Low cost

• USSD is generally cheaper than data or SMS-based communication.

• Reduces the need for expensive data plans or high-end modems in IoT devices.

3. Real-time communication

• USSD sessions are interactive and immediate, allowing for quick command execution and response (unlike SMS, which can be delayed).

4. Wide network coverage

• Operates over 2G networks, which are still widely available in developing countries and rural regions.

• Can extend IoT reach to places where newer technologies like 4G, 5G, or LPWAN are not yet available.

5. Simple implementation

• USSD is relatively easy to integrate in basic GSM-enabled devices using AT commands.

• Doesn’t require complex protocols or heavy computing resources, making it ideal for low-power, low-capability devices.

6. No need for special apps or interfaces

• USSD doesn't require custom software or apps on the end-user side, reducing the development burden.

• This simplicity benefits systems where field operators or local users need to interact with IoT devices using feature phones.

7. Secure by isolation

• Since it doesn't rely on internet exposure, USSD can be less prone to internet-based attacks, though it's not encrypted by default.

Use cases

Smart Agriculture

Farmers use USSD-enabled feature phones to query sensor data from remote farms (e.g., soil moisture levels) or control irrigation systems.

Energy Metering

Prepaid energy meters can be topped up via USSD codes without internet, using basic phones.

Asset Tracking

Low-end GPS trackers use USSD to send location updates when no data connection is available.

Remote Device Management

USSD commands can trigger specific actions like restarting a device or sending diagnostics.

USSD versus SIMs: A Comparison

What is the difference between USSD and SMS?

Key challenges of USSD in IoT

1. Limited data capacity

• USSD messages can only carry 182 characters per message, which restricts the complexity and richness of the data.

• Not suitable for sending sensor logs, images, or bulk telemetry.

2. Lack of encryption

• USSD is not inherently secure. Data sent over USSD is typically unencrypted, making it vulnerable to interception.

• Security must be added at the application level, increasing complexity.

3. Session-based communication

• USSD is session-oriented and synchronous, meaning it only supports real-time, two-way interaction.

• It doesn't support asynchronous or push-based communication (unlike MQTT or HTTP).

4. No guaranteed delivery

• Unlike SMS, USSD has no store-and-forward mechanism. If a session is interrupted (e.g., due to poor signal), the communication fails without retries.

5. Carrier dependence

• USSD heavily relies on telecom operator infrastructure, which varies by country and provider.

• Not all operators support custom USSD services or provide APIs for integration.

6. Device limitations

• IoT devices must include a GSM modem capable of handling USSD requests.

• Many modern IoT modules are optimized for IP-based communication (e.g., NB-IoT, LTE-M), not USSD.

7. Poor developer tooling and support

• Compared to IP-based protocols, USSD lacks mature libraries, SDKs, or open-source support for IoT platforms.

• Development and testing are often done manually or via telecom APIs.

8. User interaction required (in some models)

• Traditional USSD is designed for human interaction, not machine-to-machine communication.

• In automated IoT systems, implementing USSD requires creative workarounds (e.g., scripted AT commands).

Future outlook for USSD

USSD remains relevant in specific IoT scenarios, especially in:

Emerging markets

Where 2G coverage is still strong and smartphone/internet penetration is low.

Rural deployments

Where power, infrastructure, and network conditions are basic.

Cost-sensitive applications

Where device simplicity, energy efficiency, and low operational costs are critical.

Why USSD May Decline

Decline in usage of 2G and 3G networks

2G and 3G networks are being phased out in many regions (e.g., the US, Europe, Australia).

Development of modern solutions

Modern LPWAN technologies (NB-IoT and LTE-M) offer better scalability, lower power, and security.

IP-based protocols with higher levels of proficiency

IP-based protocols like MQTT and CoAP are more suited for advanced, large-scale IoT deployments.

Why USSD Might Persist

Reliance upon 2G and USSD infrastructure

In parts of Africa, South Asia, and Latin America, 2G networks and USSD-based mobile infrastructure are still essential.

USSD is affordable and accessible

Basic feature phones and GSM modules are affordable and widespread.

USSD as a reliable backup to existing systems

For mission-critical fallback or redundancy, USSD might serve as a backup control channel.

USSD: pros vs cons

Using USSD in IoT comes with trade-offs. It provides wide network coverage and low-cost connectivity, making it useful in areas with limited infrastructure. However, it also has significant limitations, such as low data capacity, lack of built-in security, and poor scalability.

USSD is best suited for simple, low-data applications in environments where internet access is unavailable or unreliable. It’s especially valuable in niche or transitional use cases where modern connectivity technologies (NB-IoT, LTE-M) are not yet accessible or practical.

What is USSD’s expected lifespan for the future?

USSD is expected to remain relevant in the near future, especially in regions with limited internet access, as it supports essential services like mobile banking and airtime purchases. However, its long-term lifespan is declining as smartphones, mobile apps, and digital wallets gain dominance. Over the next decade, USSD will likely persist in emerging markets but gradually phase out in favor of internet-based and app-driven solutions.

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