Content Overview This module introduces wireless LANs (WLANs). WLANs comprise an access technology which has an increasing significance for network access in offices, factories, hotels, airports, and at home. This module explains the differences between wired and wireless LANs, describes WLAN topologies, and teaches you how to implement Cisco WLAN solutions.
Content 6.1 Introducing Wireless LANs 6.1.1 Wireless Data Technologies There are many different types of wireless data communications, and each has its own particular characteristics in regards to range, data rate, and cost. Figure describes the characteristics of various types of wireless data technologies. The different wireless technologies also provide different coverage. The following list starts with the networks that provide the smallest coverage area:
Content 6.1 Introducing Wireless LANs 6.1.2 Wireless LANs Wireless LANs (WLAN) are similar to Ethernet networks in many ways. A WLAN is a shared network. The access point is a shared device and functions like a shared Ethernet hub. In the wireless cell, only one station can transmit at any time; all other stations listen. A station that wants to transmit must wait until the wireless media is not in use by another station. This transmission setup is similar to that of a coaxial cable or half-duplex Ethernet and an Ethernet hub. The average data rate per station is total bandwidth divided by the number of stations. The actual data throughput experienced by the wireless clients is even less because of wireless-specific issues. In WLANs, data is transmitted over radio waves. WLAN signals use the same frequency for transmitting and receiving (half-duplex); therefore, a station cannot receive while it is transmitting. This is similar to coaxial cable Ethernet. The WLAN evolution started in the 1980s using 900-MHz Direct Sequence Spread Spectrum (DSSS) technology. The 900-MHz systems were fairly easy to deploy, because one access point could cover large areas and no licenses were required in the approved countries. However, only a few countries allowed the technology. As time progressed, the need for faster speeds, open standards, and global acceptance forced the manufacturers of WLAN products to engineer new products for the 2.4-GHz band. The move to 2.4 GHz in the 1990s put WLAN products into a “cleaner” radio frequency (RF) environment, making it possible to deploy data collection systems without interference from 900-MHz transmissions. The 2.4-GHz technology was also well received because the throughput grew from 860 kbps to 1 Mbps and 2 Mbps. When frequency and speeds are increased, coverage distances are decreased, but the new data collection opportunities that the faster throughput helped to create justified the extra access points that were needed. However, end users were still concerned about using a proprietary system. In 1992, the IEEE began drafting the 802.11 standard to eliminate the issue of proprietary technology and design an open standard for WLANs. In July 1997, the IEEE ratified the 2.4-GHz standard that included DSSS technology at the physical layer. This standard specified 1 Mbps as the standard speed and 2 Mbps as a “turbo” mode. In September 1999, the IEEE ratified the 802.11a standard (54 Mbps at 5 GHz) and the 802.11b standard (11 Mbps at 2.4 GHz). In June 2003, the IEEE ratified the 802.11g standard (54 Mbps at 2.4 GHz). This standard is backward compatible with 802.11b systems, because both standards use the same 2.4-GHz frequency band.
Content 6.1 Introducing Wireless LANs 6.1.3 WLANs and Other Wireless Technologies WLANs are designed for a local network, not a WAN. They are intended for in-building wireless networks, line-of-sight outdoor bridging applications, or a combination of the two. They are not designed for citywide wireless networks. Most countries do not require a license for the WLAN. A WLAN is not a cellular phone network and does not provide packet data transmission for cellular phone networks.
Content 6.1 Introducing Wireless LANs 6.1.4 WLANs and LANs Wireless LANs fall under the IEEE 802 standards. However, the data in WLANs is sent over radio waves. In wired LANs, the data is sent over wires. However, for the user, the WLAN network interface looks similar to wired LANs. Both WLANs and wired LANs define the physical and data link layers and use MAC addresses. The same protocols and applications can be used over LANs and WLANs. Examples of protocols are IP and IP Security (IPSec) for virtual private networks (VPNs). Examples of applications are Web, FTP, and Simple Network Management Protocol (SNMP) management. WLANs differ from LANs in the following ways: