Design and Implementation of A Packet-Switched Phone Server

The goal of the Packet-Switched Phone Server (PPS) project is to build a gateway between the public telephone network and a packet switching network such as the In-ternet, so that end users can make long-distance telephone calls using existing analog phone sets rather than the computer interface. This paper describes the design and implementation of an operational PPS prototype built in State University of New York at Stony Brook, which is developed on a PentiumPro 200 machine running Windows NT 4.0 with oo-the-shelf computer telephony hardware from Dialogic. In particular, we present the bandwidth estimation algorithm used in PPS that allows speech encoding to adapt to the available network bandwidth, and the packet buuering scheme that minimizes the end-to-end latency. The paper also focuses on the implementation details of the prototype, the development experiences, and the performance measurements and analysis. The current PPS prototype can support at least 9 concurrent phone conversations using LPC-10 compression algorithm, with the worst-case end-to-end voice packet latency being 222 msec over an Internet connection between Stony Brook, New York and Orlando, Florida.