GSM HLR Unstructured Supplementary Service Data (USSD) service

Abstract: The Unstructured Supplementary Service Data (USSD) provides a service additional to GSM main service (teleservices and bearer services). Similar to its counterparts, Mobile Station (MS) user and entities of GSM network operator  act as main roles in order to establish communication in which the message traffic is transparent for the mentioned actors. USSD service uses real-time, session-oriented communication of messages. There are two possibilities in order to establish the USSD dialog: one is MS initiated (MI) and the other one is Network Initiated (NI). In this thesis, the target is to develop the Home Location Register (HLR) part of USSD service using Erlang. The project consisted of a large amount of team work, large scale programming and testing in Telecommunications. The development was required to be based on Erlang projects including Mobile Arts' USSD Gateway (USSDGW) unit and Uppsala university Project CS 2011-a prototype  of GSM voice call service-. Hence, the USSD Handler of HLR was built and accommodated according to handlers in USSDGW and MSC/VLR. The system was defined to be run and tested over SS7/SIGTRAN stack as the Signaling Transport underlying network used for routing and end-to-end delivery of packets. Thus, it was also required to setup, configure, and make the SIGTRAN stack up and running in a server. A cluster of Virtual Machines (VM) of different network nodes interconnected  over SIGTRAN were used in order to verify the message passing while system testing. The message passing was checked through Wireshark and also MS display interface either over MI or NI USSD single operation or multiple operations. The thesis gives both the identification of developed USSD services in HLR according to 3GPP specifications and the necessary integration with USSD Gateway along with the demonstration of rightness of Erlang intrinsic features using processes' message passing as the core functionality over the network and also functional programming. The thesis can be extended towards HLR specific Operation, Administration and Operation support, Charging support, Product documentation, and also Supplementary Service management(service activation, deactivation, registration, erasure, interrogation and invocation)