USSD centre is a collection of hardware and software required to interconnect two or more disparate networks, including performing protocol conversion and is based upon the ability of the delivery agent or the source to send and receive USSD messages. It routes USSD messages from the signaling network to a service application and back and is often reffered to as „USSD gateway“.
USSD (Unstructured Supplementary Services Data) is a protocol used by GSM cellular telephones to communicate with the service provider's computers. USSD is session-based text communication protocol available on every GSM-enabled mobile device. Because there is no store-and-forward mechanism present with USSD (unlike SMS), the protocol is more practical for interactive communication, such as banking or education, establishing a real time session between mobile handset and application handling the service.