peer connections between two dual role devices, with each device in its host role managing a separate wireless USB channel (called the default and reverse links) over a common MAC layer channel. DRDs can also be connected to one or more wireless USB channels as a device while at the same time providing a wireless USB channel for other devices as a host. An example of this combination scenario would be a wireless USB printer acting as a device to a laptop computer and as a host to a digital camera. Although wireless USB devices are still under development, several features of the specification, particularly of the MAC layer, point to some important characteristics that will have practical implications. The WiMedia PHY and MAC have features that allow the distance between devices to be determined by measurement of the two-way transfer time (TWTT) of a message between devices. Simple MAC to MAC transactions will allow devices to exchange measurement frames and pass a distance calculation up to the application layer. With several devices distributed in 3D, triangulation can then be used to establish the spatial location of each device. This can be put to a variety of uses, from the trivial (helping to find a lost PDA) to more significant location specific services. Current and Future Developments Although wireless USB is still in its infancy, it seems likely that, building on the foundation established by wired USB and the MBOA UWB radio platform (which is likely to be common to several other technologies including W1394), wireless USB will quickly become established as a Wireless PAN Standards standard for wireless interconnection of PC peripherals and other consumer electronic devices. The wireless USB architecture and protocol are scalable to higher data rates and, as the MBOA UWB radio platform evolves, data rates of 1 Gbps and beyond are likely to be achieved. ZigBee (IEEE 802.15.4) Origins and Main Characteristics ZigBee is a standards based technology addressing the needs of remote monitoring and control, and 