A Decentralized Directory Service for Peer-to-Peer-Based Telephony - Cloud, Grid and High Performance Computing: Emerging Applications - page 332

Chapter 21
A Decentralized Directory
Service for Peer-to-Peer-
Based Telephony
Fabian Stäber
Siemens Corporate Technology, Germany
Gerald Kunzmann
Technische Universität München, Germany 1
Jörg P. Müller
Clausthal University of Technology, Germany
ABSTRACT
IP telephony has long been one of the most widely used applications of the peer-to-peer paradigm.
Hardware phones with built-in peer-to-peer stacks are used to enable IP telephony in closed networks
at large company sites, while the wide adoption of smart phones provides the infrastructure for software
applications enabling ubiquitous Internet-scale IP-telephony.
Decentralized peer-to-peer systems fit well as the underlying infrastructure for IP-telephony, as they
provide the scalability for a large number of participants, and are able to handle the limited storage
and bandwidth capabilities on the clients. We studied a commercial peer-to-peer-based decentralized
communication platform supporting video communication, voice communication, instant messaging, et
cetera. One of the requirements of the communication platform is the implementation of a user directory,
allowing users to search for other participants. In this chapter, we present the Extended Prefix Hash Tree
algorithm that enables the implementation of a user directory on top of the peer-to-peer communication
platform in a fully decentralized way. We evaluate the performance of the algorithm with a real-world
phone book. The results can be transferred to other scenarios where support for range queries is needed
in combination with the decentralization, self-organization, and resilience of an underlying peer-to-peer
infrastructure.