ABSTRACT In this article, we focus on the use of radio frequency wireless LANs, as opposed to infrared wireless systems. For radio frequency wireless LANs, the availability of unlicensed spectrum is a significant enabler. In the United States, it was the Federal Communications Commission's rule change, first published in 1985 (modified in 1990) allowing unlicensed spread spectrum use of the three industrial, scientific, and medical (ISM) frequency bands, that encouraged the development of a number of wireless technologies. Today, unlicensed wireless LAN products are available in all three of the ISM bands at 902-928 MHz,' 2.400-2.4835 GHz, and 5.725-5.850 GHz. As described later, the IEEE 802.11 committee makes use of the 2.4 GHz ISM band. The discussion that follows treats several types of emerging standards which impact wireless LAN systems. We begin with a description of two influential physical-and data-link-layer standards, IEEE 802.11 and HIPERLAN. Following this, we briefly examine some developments concerning the U.S. personal communication services (PCS) bands, future spectrum allocations, and wireless asynchronous transfer mode (ATM) systems. After describing these physical-and link-layer developments, we focus on the network layer. We discuss the extensions being made to the widely used Internet Protocol (IP) t o deal with mobility (wired or wireless). Finally, we describe some emerging standards for wireless link management in which interfaces are specified to provide wireless link information to protocol stacks and applications on the mobile client. In the conclusion, we speculate on future directions of wireless LAN systems. IEEE 802.1 1 WIRELESS LAN STANDARD he IEEE 802.11 committee has been working on the estab-T lishment of a standard for wireless LANs. Having begun its work in 1990, the 802.11 committee is nearing completion of the standard, which is expected to be finalized in mid-1996 Much of the standard appears to have reached final form at the current time (early 1996), so we can describe the main features of the architecture, the multiple physical layers, and the common medium access control (MAC) sublayer [1]. ARCHITECTURE We introduce the general architecture and terminology defined by the 802 11 committee [l]. As shown in 8
