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Describe the process of USSD communication.

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USSD (Unstructured Supplementary Service Data) is a communication protocol used by GSM (Global System for Mobile Communications) and other cellular networks to enable real-time interaction between a mobile device and a service provider's computer. USSD is typically used for quick, session-based interactions, such as checking your prepaid balance or topping up mobile credit. Here's a technical description of the process of USSD communication:

1. Initiation:

  • USSD sessions are initiated by dialing a special USSD code on a mobile device. These codes typically start with a * (star) and end with a # (hash) and are often relatively short (e.g., *123#).

2. Network Signaling:

  • When a user dials a USSD code and presses the call button, the mobile device sends a request to the mobile network's USSD gateway.

3. USSD Gateway:

  • The USSD gateway within the mobile network receives the request and routes it to the appropriate service provider's application server.

4. Service Request:

  • The USSD request is forwarded to the specific USSD application or service on the server that corresponds to the dialed code. This application handles the user's request.

5. Server Response:

  • The server processes the user's request and generates a response. This response can be a menu of options, a text message, or any other relevant information.

6. Session-Based Interaction:

  • USSD sessions are typically session-based, meaning that the user interacts with the server one step at a time, responding to the server's prompts. This interaction allows the user to navigate through a series of menu options and select the desired service or information.

7. Real-Time Communication:

  • USSD communication is real-time, and the user receives immediate responses to their inputs. This makes USSD suitable for services that require instant feedback, such as checking balances or making mobile payments.

8. Responses and Options:

  • The server can present the user with various options, and the user selects the desired option by inputting a corresponding number or code on their mobile device's keypad.

9. Data Transfer:

  • USSD messages are transmitted using a signaling channel separate from voice and SMS. This allows for the transmission of data without an active data connection. USSD is more like a direct communication channel between the mobile device and the service provider's server.

10. Temporary Session:

  • USSD sessions are temporary and have a predefined lifespan. If there is no user activity for a certain period or the session reaches its predefined duration, the session is terminated.

11. Response Delivery:

  • The server sends responses to the user's input back to the mobile device using USSD. The responses can include account information, service confirmations, or menu options.

12. Session Termination:

  • Once the USSD session is complete, either due to user request or timeout, the session is terminated, and the user is disconnected from the USSD service.

13. Billing and Charging:

  • Mobile operators may charge users for USSD services, and billing information is typically exchanged between the service provider's server and the mobile operator's billing system.

In summary, USSD communication is a real-time, session-based interaction between a mobile device and a service provider's application server. It is initiated by dialing a short code, and users navigate through a series of menu options, receiving immediate responses to their inputs. USSD is suitable for quick, interactive services that do not require a continuous data connection, making it a cost-effective and efficient way to provide information and services to mobile users.