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technical document ref# IT006_wlan.html
issue date: 12 nov 2002
by techtolink technical division
 


Wireless LAN IEEE 802.11(x) Technology Basic



Wireless LAN 802.11b Technology

Technology

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 802.11“High Rate” amendment to the standard, which added new higher speeds (5.5 ... 55 Mbps) to 802.11.
With 802.11(x) 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). 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 802.11 are defined by the original 802.11 standard. The 802.11 specification affects only the physical layer, adding higher data rates and more robust connectivity.

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).
Figure 1 - Infrastructure Mode
The 802.11 standard defines two modes: infrastructure mode and ad hoc mode. In infrastructure mode (Figure 1), 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.
Figure 2 - Ad Hoc 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 2). 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).
 

 

 

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