Communication Basics #16 PSTN Infrastructure: Hierarchy, Local Loop & SS7

Instructor: Dr. Süleyman Burak ÇELİK

This lesson opens the hood of the Public Switched Telephone Network (PSTN) and shows how the world's classic voice network is actually built. We start at the customer premises equipment (CPE) and the local loop, climb the five-level Class 1 to Class 5 switching hierarchy, look at the three node types — switching, transmission, and service — and meet Signaling System Number 7 (SS7) for out-of-band signaling. We close with a worked example that shows why a tandem switch dramatically reduces the number of trunks compared with a full mesh. Topics covered: - PSTN as the textbook example of circuit switching - customer premises equipment (CPE) and the local loop - 64 kbps PCM voice channel as the fundamental currency - Class 1 to Class 5 hierarchy (end office, toll, primary, sectional, regional center) - switching, transmission, and service nodes - Signaling System 7 (SS7), SSPs, STPs, SCPs and out-of-band signaling - worked example: full mesh vs tandem trunk count (5, 10, 100 exchanges) Part of the AcEdumy Communication Basics series.