A VoIP Implementation on an Embedded Platform

This thesis presents a method of building an open VoIP telephone using off-the-shelf hardware. VoIP has become an important area of study in computer science and engineering, but many of the pieces are expensive and proprietary. We discuss the process of building an open IP telephone, the design decisions and difficulties, a performance evaluation of the different pieces of the system, and methods and suggestions for improving the overall system. The IP telephone is built on the Freescale 68HC12 microcontroller because of its analog and digital capabilities and the Linksys WRT54GL router for its embedded simplicity and network capabilities. The lightweight Embedded Xinu operating system was selected to build up the VoIP capabilities on top of a functional network stack. Our results show that building this VoIP device is viable. The completed IP telephone establishes a call between two routers using UDP network transport and μ-law companding. The roundtrip latency is less than two milliseconds, and the phone has a PESQ MOS (voice quality) of 3.13