Hardware Platform

Each node needs a piece of hardware that handles the wireless signal and provides IP routing. Currently Intel Pentium I class PC machines with a PCI bus are used. The wireless interface cards are standard cards using the Intersil PRISM series chip set and a PCI bus, such as the Linksys WMP11 or Compaq WL200. The PCs used are often found as surplus machines or are donated. Due to the different hardware configurations of the machines it is difficult to standardize the hardware and improve the reliability. To overcome these problems different options are evaluated. Commercial wireless nodes (e.g. the Nokia rooftop systems) are not an option as they are often not ``open'' and far too expensive. Often they use proprietary adaptations from the 802.11 standard and are not accessible to the developers in the community to develop the hard- and software further.

Embedded systems based on i486 or better processors with at least one Ethernet interface and at least 2 slots for connecting wireless network cards are a good alternative. When using an Intel i486 or better processor most of all software developments can be reused.

Embedded boards are available in various different flavors. At this moment we are testing the Soekris Engineering embedded boards. These boards use an i486 compatible processor (AMD Elan SC 520) running at 133 MHz, 64 Mbytes of RAM, a Compact Flash slot, a mini PCI slot and two PCMCIA slots. Figure 5 shows a block diagram of this board when used as wireless network node. For the PCMCIA and Mini PCI solution wireless cards based on the PRISM 2 reference design (e.g. SENAO) are used. This adds software compatibility with the PRISM 2.5 based PCI cards that are used in the PC design. The Soekris board is a commercial product and will run either Linux or a flavor of BSD without problems, freeing the developments in the node software from the hardware developments. Other industrial Intel based boards often use various bus standards (e.g. PC 104), which add additional costs in connecting (standard) cards for wireless networking. Self-designing a board level solution is not an option due to lack of resources and money.

Figure 5: A Soekris based node.

At a price higher than the price of the donated PC machines these embedded systems will add reliability and standardization to the node base. The intention is to migrate the core network nodes from PC's to embedded systems.