How does the Unstructured Supplementary Service Data (USSD) protocol enhance GSM services?

The Unstructured Supplementary Service Data (USSD) protocol is a communication protocol used in GSM (Global System for Mobile Communications) networks to provide session-based communication between a mobile device and a service application. USSD allows the exchange of text-based messages between the user and the application, offering a simple and interactive way to access services. Here are the technical details of how the USSD protocol enhances GSM services:

1. Session Initiation:
   • USSD sessions are initiated by the mobile user through the entry of a specific USSD code on their device. These codes typically begin with a "*," followed by a numerical sequence, and end with a "#". For example, "*123#" might be used to check account balance.
2. USSD Code Structure:
   • USSD codes consist of a service code and optional parameters. The service code indicates the specific service or operation requested by the user. Parameters, if present, provide additional information needed for the service.
3. Interactive Communication:
   • USSD allows interactive communication between the mobile user and the application. Unlike SMS, which is store-and-forward, USSD sessions are real-time and session-based, providing a dynamic and responsive user experience.
4. Stateful Sessions:
   • USSD sessions can be stateful, meaning that the user's interaction with the service is maintained throughout the session. Each interaction can influence subsequent interactions, allowing for dynamic and personalized service delivery.
5. Service Requests and Responses:
   • When a user initiates a USSD session by entering a code, a USSD request is sent to the USSD Gateway or USSD application server. The server processes the request and sends a USSD response back to the user's mobile device.
6. Network Signaling:
   • USSD messages are transported over the signaling channel of the GSM network, allowing for real-time communication without the need for a dedicated data connection. This makes USSD a cost-effective solution for both users and service providers.
7. Service Delivery and Interaction:
   • USSD services cover a wide range of applications, including balance inquiries, mobile banking, prepaid top-up, service activations, and more. Users can interact with the service by entering responses to prompts presented by the USSD application.
8. Secure Transactions:
   • USSD sessions are considered secure as they operate over the GSM signaling channel, which is encrypted. This makes USSD suitable for transactions that require a higher level of security, such as mobile banking or authentication.
9. Efficient Use of Resources:
   • USSD is a session-based protocol that is efficient in terms of resource usage. Sessions are short-lived, reducing the load on the network compared to persistent connections required by other data services.
10. Compatibility with Basic Phones:
    • USSD is compatible with basic mobile phones that may not have advanced data capabilities. This ensures that a wide range of mobile users, including those with basic feature phones, can access USSD services.
11. Real-time Balance Updates:
    • USSD is commonly used for real-time balance inquiries in prepaid mobile services. Users can quickly check their account balance by entering the appropriate USSD code, and the response provides the up-to-date balance information.
12. Emergency Services:
    • USSD can be used for emergency services, allowing users to quickly access important information or request assistance by entering specific codes.

In summary, the USSD protocol enhances GSM services by providing an interactive and real-time communication channel between mobile users and service applications. Its session-based nature, compatibility with basic phones, efficient use of resources, and secure operation make USSD a valuable tool for a variety of services, ranging from mobile banking to emergency assistance.