The Beginning of the PSTNUnderstanding PSTN BasicsAnalog and Digital SignalingDigital Voice SignalsLocal Loops, Trunks, and Interswitch CommunicationPSTN SignalingUser-to-Network SignalingNetwork-to-Network SignalingPSTN Services and ApplicationsPSTN Numbering PlansNANPITU-T International Numbering PlanDrivers Behind the Convergence Between Voice and Data NetworkingDrawbacks to the PSTNPacket Telephony Network DriversStandards-Based Packet Infrastructure LayerOpen Call-Control LayerVoIP Call-Control ProtocolsH.323MGCP (Evolution from SGCP and IPDC)SIPH.248/MEGACOOpen Service Application LayerNew PSTN Network Infrastructure ModelSummary