The TKN Wireless Indoor Sensor network Testbed (TWIST), developed by the Telecommunication Networks Group (TKN) at the Technische Universität Berlin, is a scalable and flexible testbed architecture for experimenting with wireless sensor network applications in an indoor setting. It provides basic services like node configuration, network-wide programming, out-of-band extraction of debug data and gathering of application data, as well as several novel features:

• experiments with heterogeneous node platforms
• support for flat and hierarchical setups
• active power supply control of the nodes

The self-configuration capability, the use of hardware with standardized interfaces and open-source software makes the TWIST architecture scalable, affordable, and easily replicable. The TWIST architecture was published in this paper.

The TWIST instance deployed at the TKN group is one of the largest academic testbeds for indoor deployment scenarios. It spans the three floors of the FT building at the TU Berlin campus, resulting in more than 1500 square meters of instrumented office space. Currently the setup is populated with two sensor node platforms:

• 102 TmoteSky nodes, which are specified in detail here.
• 102 eyesIFXv2 nodes; this platform is an outcome of the EU IST EYES project. The platform is based on an MSP430 MCU and the TDA5250 transceiver, which operates in the 868 MHz ISM band using ASK/FSK modulation with data-rates up to 64 Kbps. A summary of the platform's hardware components is given, for example, in this paper.

In the small rooms, two nodes of each platform are deployed, while the larger ones have four nodes. The setup results in a fairly regular grid deployment pattern with intra node distance of 3m. The following shows the node placement on the 4th floor of the building (floors 3 and 2 have a very similar layout):

The testbed architecture can be divided into three tiers. The sensor nodes form the lowest tier, they are attached to the ceiling as visualized in the following figure, which shows a Tmote Sky and an eyesIFXv2 node in one of the office rooms:

Sensor nodes are connected via USB cabling and USB hubs to the testbed infrastructure. If TWIST only relied on the USB infrastructure, it would have been limited to 127 USB devices (both hubs and sensor nodes) with a maximum distance of 30 m between the control station and the sensor nodes (achieved by daisy-chaining of up to 5 USB hubs). Therefore the TWIST architecture includes a second tier: so-called "super nodes" which are able to interface with the previously described USB infrastructure. We are using the Linksys Network Storage Link for USB2.0 (NSLU2) device as super nodes as depicted in the following picture:

The third and last tier of the architecture is the server and the control stations which interact with the super nodes using the testbed backbone. The server, among other things, implements a PostgreSQL database that stores a number of tables including configuration data like the registered nodes. It also provides remote access via a webinterface. The following figure provides a general overview of the TWIST hardware architecture:

The hardware instantiation of the TWIST hardware architecture at the TKN group is shown in this figure: