WAND Protocol Development Environment
Packet broadcast networks are in widespread use in modern wireless communication systems. Medium Access Control (MAC) is a key functionality within such technologies. Substantial research effort has been and continues to be invested into the study of existing protocols and the development of new and specialised ones. Academic researchers are restricted in their studies by an absence of suitable wireless MAC protocol development methods.
The WAND Protocol Development Environment (WPDE) provides a framework for the design and evaluation of wireless link-layer protocols. It consists of software and hardware elements which aim to support a large span of the protocol design lifetime. These can be divided into four main regions: specification; simulation; implementation; and measurement.
Typical wireless MAC protocols are concurrent distributed real-time systems, and therefore benefit from use of formal methods in the design phase. The Specification and Description Language (SDL) provides a semi-formal representation with a graphical variant which is generally intuitive for network protocol engineers providing a short learning curve.
The first element of the WPDE is a tool which provides automated translation of an SDL protocol description into C++ which can be readily used in simulation and implementation environments.
Simulation is an integral part of protocol design and evaluation. It allows a link-layer protocol to be tested in presence of specific traffic and channel characteristics at early stages of the design process.
The WPDE includes an SDL testbench providing for basic simulation at the earliest stages of design. A wrapper allows incorporation of C++ models automatically generated from SDL into the popular network simulator ns-2. This gives access to a powerful simulation environment with a wide range of traffic models.
Though simulation provides advantages in terms of accessibility and flexibility, accurate models are required in order to achieve useful results. Simulation model detail is often traded-off against the need for reduced simulation execution time. Often the effects of this reduced detail on the metrics of interest are not well understood. Measurement of an implementation in the real world provides a means of developing and validating simulation models.
The Wireless Analysis and Generation (WAG) device provides for implementation and measurement of new and existing protocols. This Mini-PCI form-factor card incorporates an FPGA with embedded Power-PC microprocessor, a quantity of Static-RAM, and an IEEE 802.11b transceiver and baseband modem. The FPGA allows custom protocols to be implemented using a combination of configurable hardware and embedded software.
A hardware framework described in VHDL allows MAC protocols automatically generated from SDL as discussed above to be implemented using the facilities provided by the FPGA (incorporating the Power-PC core). This architecture affords the designer flexibility in hardware/software co-design decisions.
A customisable Linux device driver allows the card to be used in standard Linux-based PCs. The Mini-PCI form factor allows the use of low-power single-board computers for maximum flexibility.
Given an implementation, measurement allows troubleshooting or evaluation of that protocol against design objectives.
Measurement in wireless networks typically involves passive capture of network traffic either by a third party wireless receiver located in range of the network under investigation, or by a wired receiver on a link adjacent to the wireless network. Using these approaches much inference is often required in order to gain an understanding of link-layer protocol operation.
The WAG card allows measurement elements to be incorporated into a working network node. This ensures that captured physical layer events are consistent with those seen by the associated MAC entity. Accurate timing within the FPGA allows correlation of these with internal MAC state and host interface activity.
By providing for distributed measurement a complete picture of network operation can be developed. The WAG card supports distributed measurement by incorporating an RS-422 receiver to allow time synchronisation of WAG cards through the Global Positioning System (GPS) enabling the accurate correlation of measurements taken at physically separate locations.