Learn Telephony & WebRTC
A free, structured course on how phone calls actually work, from the basics of a phone number up to enterprise carrier interop. Plain English throughout, every concept paired with a real tool you can try yourself. No signup, no paywall.
Start at the beginning
The course is ordered beginner to advanced across seven modules, browsable any time in the sidebar. If you are not sure where to start, start here.
Start with: How a phone call works →What is in the course
Seven modules, each building on the last. The Basics covers what a call, a number, and a network actually are. How Calls Travel and SIP In Depth take you through the protocol underneath most phone systems. WebRTC covers how browser calls connect without an app. Call Quality explains why calls sometimes sound bad, and how to measure it. Trust & Security covers spoofing, STIR/SHAKEN, and spam. Carrier Interop goes further, into SBCs, ITSPs, and how platforms like Microsoft Teams and Webex Calling actually reach the phone network.
Learn by doing, not just reading
Every guide in this course links to a free, working tool: trace a real SIP call, watch your own browser gather ICE candidates, decode a SIP error code, check a number for spam. Reading explains the idea. The tool lets you see it on your own connection.