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9th International Linux System Technology Conference
September 4-6, 2002 in Cologne, Germany
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|Authors||Michael Finkenzeller, Andreas Kirstädter|
PDF: lk2002-finkenzeller.pdf (971512 Bytes)
Pushed by flat-rate Internet access and PSTN gateways IP Telephony (VoIP) becomes a more appealing alternative to "normal" telephony. Nevertheless easy-to-use stand-alone and affordable devices which provide the look and feel of common telephones are still rare.
To gain more experiences with the protocols involved and their interworking with IP quality of service and routing we decided to set up a flexible platform for VoIP experiments: As the first step a prototype of a stand-alone IP phone called "Voxilla-Internet-Phone" (VIP) with Ethernet and wireless-LAN interfaces was designed and integrated during a diploma thesis. The underlying hardware consists of a single-board PC (80468, 133 MHz, 32 MB RAM) with a PCMCIA module supporting the network interface card and a flash memory card serving as the "hard disk" of the system (all together fitting nicely into the case of a plain old telefone).
We didn't regret the decision to use Linux (in the form of "tomsrtbt", a very small distribution that fits on a single floppy) as the operating system: After some initial problems with the sound system and the boot process from the flash card the system integration went smoothly. For the VoIP application the software from the OpenH323 project was extended with some middleware. A user interface to meet the needs of a stand-alone phone with a four line LCD and a 12 button keyboard was added. By definition, the stack of the OpenH323 project conforms to the ITU recommendation H.323. To communicate with clients that use IETF's Session-Initiation-Protocol (SIP) it is possible to switch between H.323's signaling protocol H.245 and SIP.
One of our next steps will be to use VIP in larger wireless-LAN scenarios to study roaming and hand- over processes between different cells and the resulting implications on the achievable quality of the VoIP communications. Our presentation not only describes the system architecture but also discusses the lessons learned during system set up and integration.
|About the Authors||
Michael Finkenzeller received his Dipl.-Ing. Univ. degree in Electrical Engineering and Information Technology at the Technische Universität München (TUM), Germany, in 2000.
Since then he is working as Research Scientist for Siemens Corporate Technology in the field Networks and Multimedia Communication. In a first project he was involved in component development and setup of a testbed for Policy-Based-Networking and Quality-of-Service. At present his interests are on the area of Peer-To-Peer and ad hoc networking and the practical evaluation of these concepts in a testbed.
Andreas Kirstädter received the Dipl.-Ing., Dipl.-Wirtsch.-Ing., and Dr.-Ing degrees in Electrical Engineering and Economics from Munich University of Technology (TUM), Germany, in 1990, 1992, and 1997, respectively. From 1991 to 1997 he was with the Institute for Communication Networks at Munich University of Technology, where he worked on research topics in the area of high-speed networking, WDM networks, simulation, analytical modelling and high-speed hardware design. In 1997 he joined the "Networks and Multimedia Communications" department at Siemens Corporate Technology in Munich where he is responsible for the "High-Speed IP Networks" team. His current research interests include the hardware implementation of communication protocols, Internet quality of service concepts, MPLS networks, IP resilience, and mobility and multimedia concepts for the Internet. Since summer 2000 he gives a lecture on "Simulation of Communication Networks" in the framework of the Master of Science in Communication Engineering Program at Munich University of Technology.
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