TWIST: A Scalable and Reconfigurable Testbed for Wireless Indoor Experiments with Sensor Networks Vlado Handziski, Andreas K ¨ opke, Andreas Willig, Adam Wolisz Telecommunication Networks Group Technische Universit¨ at Berlin, Germany {handzisk,koepke,willig,wolisz}@tkn.tu-berlin.de ABSTRACT We present TWIST, a scalable and flexible testbed archi- tecture for indoor deployment of wireless sensor networks. The design of TWIST is based on an analysis of typical and desirable use-cases. It provides basic services like node configuration, network-wide programming, out-of-band ex- traction of debug data and gathering of application data, and also introduces several novel features. Firstly, TWIST supports experiments with heterogeneous node platforms. Secondly, it supports active power supply control of the nodes. This enables easy transition between USB-powered and battery-powered experiments, dynamic selection of topologies as well as controlled injection of node failures into the system. Thirdly, TWIST supports creation of both flat and hierarchical sensor networks. For this we introduce a layer of “super nodes” that on one hand form a part of the testbed infrastructure but can also play a role as elements of the sensor network. The self-configuration capability, the use of hardware with standardized interfaces and open-source software makes the TWIST architecture scalable, affordable, and easily repli- cable. To demonstrate its usefulness, we present our ex- periences with building and using a specific realization of TWIST that spans three floors of our office building and supports over one hundred sensor nodes. Categories and Subject Descriptors D.2.5 [Testing and Debugging]: Distributed Debugging; C.4 [Performance of Systems]: Measurement Techniques General Terms Design, Experimentation, Measurement Keywords wireless sensor networks, testbeds, power supply control, TinyOS Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. REALMAN’06, May 26, 2006, Florence, Italy. Copyright 2006 ACM 1-59593-360-3/06/0005 ...$5.00. 1. INTRODUCTION Wireless Sensor Networks (WSNs) are large-scale distrib- uted embedded systems incorporating small, energy- and resource-constrained sensor nodes communicating over wire- less media [11]. Because of their massively distributed na- ture, the design, implementation and evaluation of sensor network applications, middleware and communication pro- tocols is a difficult task. The first design steps can often be made with the help of simulations, however, they frequently force the designer to make artificial assumptions about traf- fic, failure patterns and topologies. The later steps of im- plementation and evaluation of application performance as well as assessment of error resilience and other nonfunctional properties, require the use of real hardware, realistic envi- ronments and realistic experimental setups. Unfortunately, real experiments with distributed systems like sensor networks quickly become very cumbersome if the number of nodes exceeds a few dozens. In fact, all the phases of the experiment: deployment of the nodes in the desired, possibly heterogeneous and hierarchical, configuration; mak- ing changes in the software of individual nodes; and last but not least, conducting experiments which include both data processing and self-reconfiguration of the network are very, very difficult without a targeted, specialized support. For all but the smallest experiments a dedicated infrastructure supporting the above listed steps is necessary. This infras- tructure – from now on referred to as testbed – makes it possible to create, modify and observe the target configura- tion (both hardware and software) in its whole complexity including nodes, communication protocols, middleware and application. We will refer to this target configuration as the System under Examination (SUE). In this paper we describe a novel solution for sensor net- work tesbeds called TKN Wireless Indoor Sensor network Testbed (TWIST). Its design evolved out of our experiences with an early WSN testbed [14] deployed at TKN (Telecom- munication Networks group at Technical University Berlin) in the framework of the EU IST EYES project. We went through the full development cycle of TWIST: from design, deployment of a full instance at our premises, as well as its usage for first experiments. TWIST is based on cheap off- the-shelf hardware and uses open-source software. It is thus a cost-effective and open solution which can be reproduced by others. The rest of the paper is organized as follows: Section 2 contains an analysis of the requirements that a sensor net- work testbed should fulfill. The TWIST architecture is ex- plained in Section 3, while in Section 4 we reflect on how