This paper covers the topic of implementing voice services in packet-switched Voice Over IP (VoIP) and circuit-switched (traditional telephony) networks using Linux and commodity hardware. It contains a short introduction into general telephony, VoIP, and Public Switched Telephony Networks (PSTN). It also provides an overview of VoIP services, including the open-source software packages used to implement them, and the kernel interfaces they include. It explains kernel support for connecting Public Switched Telephony Networks using digital interfaces (E1/T1) via the Zaptel framework, and user-space integration issues. The conclusion examines current trends in Linux-based and open-source telephony.
A basic understanding of networking concepts is helpful for understanding this presentation.