GSM MSC/VLR Unstructured Supplementary Service Data (USSD) Service

Abstract: Although the Unstructured Supplementary Service Data (USSD) service is one of the most used GSM services such as checking the balance of prepaid cards, it is not well known by subscribers and it is so often confused with a popular GSM service, Short Message Service (SMS). While SMS is based on the characteristics of storing and forwarding data, USSD is session based and real-time. Technically, USSD service allows the Mobile Station (MS) user and a Public Land Mobile Network (PLMN) operator  defined application to communicate in a way which is transparent to the MS and to intermediate network entities.[6] This master thesis specifies all the phases in the development of USSD service in Mobile Switching Center (MSC)/Visitor Location Register (VLR) and its integration with an USSD Gateway. Meanwhile, it shows how a message passing functional programming language (Erlang) fits to develop a highly concurrent, available, fault-tolerant and distributable telecommunication system.