The paper is organized as follows: Section 2 describes
the theoretical background of GSM system architecture and
network Architecture with necessary block diagrams. Section
3 discusses the open-source software tools and hardware
used to capture downlink packet data. Section 4 describes
analysis of GSM protocol stack by amalgamation of RTLSDR,
GNU Radio and Wireshark. In Section 5, the results
captured by Wireshark and GNU Radio are analysed and
verified with the designated test phone. The future scope on
security enhancement and more research required on software
front is discussed in section 6. Lastly, the paper ends with
conclusion.