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service ussd

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USSD stands for Unstructured Supplementary Service Data. It's a communication protocol used by GSM cellular telephones to communicate with the service provider's computers.

Let's break down USSD technically:

Basics:

  • Protocol: USSD is a text-based protocol, unlike SMS which is a store-and-forward service. This means that a USSD session is a real-time interaction between the mobile user and the application provider's computer.
  • Session-based: Each interaction (or session) in USSD is stateful. This means that once a USSD session is initiated, subsequent messages within that session are treated as part of the same conversation.

Technical Details:

  1. Channel: USSD uses the signaling channel of the GSM network to send and receive messages. This is different from SMS, which uses the dedicated message channels.
  2. Session Creation:
    • When a user dials a USSD code (e.g., *123#), a USSD session is initiated.
    • The GSM network establishes a connection with the service provider's USSD gateway.
  3. Message Format:
    • USSD messages are typically formatted as a series of 7-bit characters, allowing for a maximum of 182 characters per message. This character limit is determined by the GSM standard.
  4. Real-time Interaction:
    • Since USSD operates over the signaling channel, it facilitates real-time interaction between the mobile user and the application server. This makes USSD suitable for services that require immediate responses, like balance inquiries, prepaid top-ups, or interactive sessions.
  5. Security:
    • USSD sessions are encrypted between the mobile device and the service provider's network, ensuring a secure communication channel.
    • Moreover, since USSD sessions are short-lived and stateful, they inherently have a reduced exposure to security risks like session hijacking compared to other longer-lived protocols.
  6. Use Cases:
    • USSD is commonly used for:
      • Mobile banking services (e.g., checking balance, transferring funds).
      • Service activations or deactivations (e.g., activating a data pack).
      • Interactive campaigns (e.g., voting, surveys).
      • Prepaid top-ups and balance checks.
  7. Technical Flow:
    • When a user dials a USSD code, the GSM network forwards the request to the respective USSD gateway.
    • The USSD gateway processes the request and interacts with the necessary backend systems (like databases or application servers) to fetch or update information.
    • The USSD gateway then sends the response back to the user via the GSM network, and the session is terminated.

Advantages of USSD:

  • Widespread Availability: Since it operates over GSM networks, USSD is available on almost all GSM-enabled devices without requiring an internet connection.
  • Real-time Interaction: Provides immediate feedback and is suitable for time-sensitive operations.
  • Wide Range of Applications: From banking to mobile services, USSD serves various applications, making it versatile.