This book GSM-Network Switching Subsystem Engineering gives the main concepts, and models of GSM Systems Engineering at core network level. It responds to GSM- NSS Engineering practice for GSM Technicians, Engineers, Practitioners, Consultants, Reserchers and Managers. The book has thoroughly covered GSM protocol architecture in the context of GSM-Network Switching Subsystem Engineering which includes: GSM Evolution, GSM Network Architecture, The OSI Reference model, The A Interface, Signalling number 7, Telephony User Part, Signalling Connection Control Part (SCCP), ISDN User Part ISUP, Transaction Capabilities Part (TCAP), Intelligent Network Applications Part (INAP), Case Studies. This book fills the gap between texts in GSM that only treat constitution of protocol architecture in telecommunications engineering in a cursory manner and texts that are too broad in the coverage of GSM Core network engineering. It will therefore be good hands on text for GSM Technicians, Engineers, Practitioners, Consultants, Reserchers and Managers.