 for the personal devices associated with a particular user. The user is concerned with electronic devices in his or her possession, or within his or her vicinity, rather than with any particular geographic or network location. The term personal area network was coined to describe this different kind of network connection. The untethered version of this concept is the WPAN (wireless personal area network). A WPAN can be viewed as a personal communications bubble around a person. Within this bubble, which moves as a person moves around, personal devices can connect with one another. These devices may be under the control of a single individual or several people's devices may interact with each other. Communicating devices may not be within line-of-sight of each other. For this reason, WPANs may employ radio-frequency (RF) technologies to provide added flexibility to communicate with hidden devices. The IEEE 802.15 standard presents a WPAN using RF techniques based on Bluetooth wireless technology. The 802.15 WPAN technology will serve as an adjunct to a metropolitan area network and is not meant to serve as a backbone protocol as IEEE 802.16. 13.5.1 Differences Between 802.11 and 802.15 At first blush, 802.11 and 802.15 seem very similar. Their objectives of operation and method of operation seem very similar. However, we point up three major differences: 1. Power levels and coverage 2. Control of the media 3. Lifespan of the network 13.5.1.1 Power Levels and Coverage. RF power levels of 802.15 devices run from 1 mW to 2.5 mW and up to "high power" of 100 mW. Coverage is roughly in the range of 10 m. Modulation is Gaussian FSK. 13.5.1.2 Control of the Media. Control of a medium usually refers to the allocation of bit rate capacity. The medium can remain contention-free by means of a "master-slave" relationship with a master polling incumbent slaves. 13.5 IEEE 802.15 STANDARD 13.5.1.3 Lifespan of the Network. WLAN and WPAN networks must be distin- guished. WLANs do not have an inherent or implied lifespan. They hav