What is Unstructured Supplementary Service Data (USSD)?

Unstructured Supplementary Service Data (USSD), sometimes referred to as "Quick Codes" or "Feature codes", is a protocol used by Global System for Mobile (GSM) cellular telephones to communicate with the service provider's computers. USSD applications are accessed by user request, and make use of short codes or text strings to trigger certain services in a session-based communication. A typical USSD message starts with groups of digits (codes) comprising of an asterisk (*) followed by commands or data that may be further separated by additional asterisks then the message is terminated with a number sign (#). These codes could perform a function, request a snippet of information, or lead the user into a series of textual menus which are navigated through the corresponding menu numbers.

USSD can be used for Wireless Application Protocol (WAP) browsing, prepaid callback service, mobile-money services, location-based content services, menu-based information services, and as part of configuring the phone on the network. In Kenya, most mobile phone users use USSD to check airtime balance for example Safaricom *144# or Orange *131# and to load airtime, accessing news services, sports scores and fixtures, submission services, feedback and voting, advertising listings or directories among other codes with different functions depending on the Service Provider. USSD messages create a real-time connection during a USSD session. The connection remains open, allowing a two-way exchange of a sequence of data. This makes USSD more responsive than services that use SMS.

A USSD gateway is the automated system that bridges the gap between mobile handsets and IP based systems and finally connects to the portal which retrieves the information requested. When a user sends a message to the phone company network, it is received by a computer dedicated to USSD. The computer's response is sent back to the phone, generally in a basic format that can easily be seen on the phone display. Messages sent over USSD are not defined by any standardization body, so each network operator can implement whatever is most suitable for its customers.

Types of USSD modes:

Mobile-initiated mode

USSD/ PULL or USSD/ P2P - when the user dials a code, e.g. *139# from a GSM mobile handset

Network-initiated mode

USSD/ PUSH or USSD/A2P - when the user receives a push message from the network; primarily used for promotional services.

Advantages of USSD Services

Extremely low cost.
Real-time
Fast and responsive
Interactive navigation
Consumer driven
Can be used as payment method
Automated response
Allows mass-usage
Location-based, SIM and PUK-based and user selected customization and segmentation