Unstructured Supplementary Service Data (USSD)

USSD service is mostly like SMS service. Read below to understand more:

  1. SMS deliver messages using store and forward technique:

A message is always first sent to short message service center (SMSC) before message get deliver to the recipient. The sender receives a deliver confirmation once message was  successfully received by SMSC. Message is not guaranteed to reach the destination user instantly.

  1. In USSD service, information is sent directly from sender to an application platform which handles USSD service. A real time session is started between sender and application. USSD platform then send requested data back to user and this continue till USSD service gets complete.
  2. USSD service is mostly used in balance enquiry and Top Up application.

Let’s take an example of balance enquiry to understand this clearly:

  1. A mobile user starts the USSD service by dialing *#678#.
  2. USSD application receives service request from the user and send back a menu of options.
  3. User responds by selecting a current balance option.
  4. The USSD application sends back details of the mobile current balance with option of top up also.
  5. User select option to exit.
  6. USSD application ends the session.

General telecom flow of USSD service is as below:

  1. Mobile send request to MSC.
  2. MSC send to VLR.
  3. VLR send to HLR.
  4. HLR invoke USSD Application or USSD Gateway.
  5. USSD application acts on service request.

USSD gateway is a GSM node that enables communication between users and USSD applications across the network. It enables communication between USSD applications and other network nodes like HLR, VLR and MSC.

USSD gateway and applications also generate log files to track sessions and also used in troubleshooting.

USSD gateway generates CDR at the end of every transaction.

Alarms are also generated for USSD gateway and USSD application. Alarms are sent to users via SMS/email.

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