What’s New in Wireless LANs: The IEEE

A wireless LAN (WLAN) is a data transmission system designed to provide location-independent network access between computing devices by using radio waves rather than a cable infrastructure. In the corporate enterprise, wireless LANs are usually implemented as the final link between the existing wired network and a group of client computers, giving these users wireless access to the full resources and services of the corporate network across a building or campus setting.

WLANs are on the verge of becoming a mainstream connectivity solution for a broad range of business customers. The wireless market is expanding rapidly as businesses discover the productivity benefits of going wire-free. According to Frost and Sullivan, the wireless
LAN industry exceeded $300 million in 1998 and will grow to $1.6 billion in 2005. To date,
wireless LANs have been primarily implemented in vertical applications such as manufacturing
facilities, warehouses, and retail stores. The majority of future wireless LAN growth is expected in healthcare facilities, educational institutions, and corporate enterprise office spaces. In the corporation, conference rooms, public areas, and branch offices are likely venues for WLANs.

The widespread acceptance of WLANs depends on industry standardization to ensure product compatibility and reliability among the various manufacturers. The Institute of Electrical and Electronics Engineers (IEEE) ratified the original 802.11 specification in 1997 as the standard for wireless LANs. That version of 802.11 provides for 1 Mbps and 2Mbps data rates and a set of fundamental signaling methods and other services.

The most critical issue affecting WLAN demand has been limited throughput. The data rates supported by the original 802.11 standard are too slow to support most general business requirements and have slowed adoption of WLANs. Recognizing the critical need to support higher data-transmission rates, the IEEE recently ratified the 802.11b standard (also known as 802.11 High Rate) for transmissions of up to 11 Mbps. Global regulatory bodies and vendor alliances have endorsed this new high-rate standard, which promises to open new markets for WLANs in large enterprise, small office, and home environments. With 802.11b, WLANs will be able to achieve wireless performance and throughput comparable to wired Ethernet.

Outside of the standards bodies, wireless industry leaders have united to form the Wireless Ethernet Compatibility Alliance (WECA). WECA’s mission is to certify cross-vendor
interoperability and compatibility of IEEE 802.11b wireless networking products and to
promote that standard for the enterprise, the small business, and the home. Members
include WLAN semiconductor manufacturers, WLAN providers, computer system vendors,
and software makers—such as 3Com, Aironet, Apple, Breezecom, Cabletron, Compaq, Dell, Fujitsu, IBM, Intersil, Lucent Technologies, No Wires Needed, Nokia, Samsung, Symbol Technologies, Wayport, and Zoom.

IEEE 802.11 and 802.11b Technology

As the globally recognized LAN authority, the IEEE 802 committee has established the standards that have driven the LAN industry for the past two decades, including 802.3 Ethernet, 802.5 Token Ring, and 802.3z 100BASE-T Fast Ethernet. In 1997, after seven years of work, the IEEE published 802.11, the first internationally sanctioned standard for wireless
LANs. In September 1999 they ratified the 802.11b “High Rate” amendment to the standard, which added two higher speeds (5.5 and 11 Mbps) to 802.11.

With 802.11b WLANs, mobile users can get Ethernet levels of performance, throughput, and availability. The standards-based technology allows administrators to build networks that seamlessly combine more than one LAN technology to best fit their business and user needs.

Like all IEEE 802 standards, the 802.11 standards focus on the bottom two levels of the ISO model, the physical layer and data link layer (Figure 1 on page 4). Any LAN application, network operating system, or protocol, including TCP/IP and Novell NetWare, will run on an 802.11-compliant WLAN as easily as they run over Ethernet.

The basic architecture, features, and services of 802.11b are defined by the original 802.11 standard. The 802.11b specification affects only the physical layer, adding higher data rates and more robust connectivity.

Figure 1. 802.11 and the OSI Model

802.11 Operating Modes

802.11 defines two pieces of equipment, a wireless station, which is usually a PC equipped with a wireless network interface card (NIC), and an access point (AP), which acts as a bridge between the wireless and wired networks. An access point usually consists of a radio, a wired network interface (e.g., 802.3), and bridging software conforming to the 802.1d bridging standard. The access point acts as the base station for the wireless network, aggregating access for multiple wireless stations onto the wired network. Wireless end stations can be 802.11 PC Card, PCI, or ISA NICs, or embedded solutions in non-PC clients (such as an 802.11-based telephone handset).

The 802.11 standard defines two modes: infrastructure mode and ad hoc mode. In infrastructure mode (Figure 2), the wireless network consists of at least one access point connected to the wired network infrastructure and a set of wireless end stations. This configuration is called a Basic Service Set (BSS). An Extended Service Set (ESS) is a set of two or more BSSs forming a single subnetwork. Since most corporate WLANs require access to the wired LAN for services (file servers, printers, Internet links) they will operate in infrastructure
mode.

Ad hoc mode (also called peer-to-peer mode or an Independent Basic Service Set, or IBSS) is simply a set of 802.11 wireless stations that communicate directly with one another without using an access point or any connection to a wired network (Figure 3). This mode is useful for quickly and easily setting up a wireless network anywhere that a wireless infrastructure does not exist or is not required for services, such as a hotel room, convention center, or airport, or where access to the wired network is barred (such as for consultants at a client site).