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Complex
Network Integration
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What is a wireless LAN? In the simplest of terms, a wireless LAN (WLAN) does exactly what the name implies. It provides all the features and benefits of traditional LAN technologies such as Ethernet and Token Ring, but without the limitations of wires or cables. Thus, WLANs redefine the way the industry views LANs. Connectivity no longer implies attachment. Local areas are measured not in feet or meters, but in miles or kilometers. An infrastructure need not be buried in the ground or hidden behind walls. An infrastructure can be moved and changed based on the needs of an organization. A WLAN, just like a LAN, requires a physical medium through which transmission signals pass. Instead of using twisted-pair or fiber-optic cable, WLANs use infrared light (IR) or radio frequencies (RFs). The use of RF is far more popular for its longer range, higher bandwidth, and wider coverage. WLANs use the 2.4-gigahertz (GHz) and 5-GHz frequency bands. These portions of the RF spectrum are reserved in most of the world for unlicensed devices. Wireless networking provides the freedom and flexibility to operate within buildings and between buildings.
No more wires? Wireless systems are not completely wireless. Wireless devices are just one part of the traditional wired LAN. These wireless systems, designed and constructed using standard microprocessors and digital circuits, connect to traditional wired LAN systems. Furthermore, wireless devices must be powered to provide energy to encode, decode, compress, decompress, transmit, and receive wireless signals. The first generation WLAN devices, with their low speeds and lack of standards, were not popular. Modern standardized systems are now able to transfer data at acceptable speeds. The IEEE 802.11 committee and the Wi-Fi Alliance have diligently worked to make wireless equipment standardized and interoperable. Wireless technology will now support the data rates and interoperability necessary for LAN operation. Also, the cost of the new wireless devices has decreased greatly. WLANs are now an affordable option to wired LAN connectivity. In most countries these devices do not require special governmental licensing.
Why wireless? Current wired Ethernet LANs operate at speeds around 100 Mbps at the access layer, 1 Gbps at the distribution layer, and up to 10 Gbps at the core layer. Most WLANs operate at 11 Mbps to 54 Mbps at the access layer and are not intended to operate at the distribution or core layers. The cost of implementing WLANs is competitive with wired LANs. So why install a system that is at the lower end of the current bandwidth capabilities? One reason is that in many small LAN environments, the slower speeds are adequate to support the application and user needs. With many offices now connected to the Internet by broadband services such as DSL or cable, WLANs can handle the bandwidth demands. Another reason is that WLANs allow users to roam a defined area with freedom and still remain connected. During office reconfigurations, WLANs do not require rewiring and its associated costs. WLANs have numerous benefits for home offices, small businesses, medium businesses, campus networks, and larger corporations. The environments that are likely to benefit from a WLAN have the following characteristics:
WLANs do not eliminate the need for Internet Service Providers (ISPs). Internet connectivity will still require service agreements with local exchange carriers or ISPs for Internet access. There is a current trend for ISPs to provide wireless
Internet service. These ISPs are referred to as Wireless Internet Service Providers (WISPs). Furthermore, WLANs do not replace the need for traditional wired routers, switches, and servers in a typical LAN. Even though WLANs are primarily designed as LAN devices, they can be used to provide site-to-site connectivity at distances up to 40 km (25 miles). The use of WLAN devices is much more cost effective than using WAN bandwidth or either installing or leasing long fiber runs. For instance, the cost of installing a WLAN between two buildings will incur a one-time cost of several thousand U.S. dollars. A dedicated leased T1 link, which only provides a fraction of the bandwidth of a WLAN, will easily cost hundreds of U.S. dollars per month or more. Installing fiber across a distance of more than 1.6 km (1 mile) is difficult and would cost much more than a wireless solution.
Evolution of wireless LANs The first wireless LAN technologies defined by the 802.11 standard were low-speed proprietary offerings of 1 to 2 Mbps. Despite these shortcomings, the freedom and flexibility of wireless allowed these early products to find a place in technology markets. Mobile workers used hand-held devices for inventory management and data collection in retail and warehousing. Later, hospitals applied wireless technology to gather and deliver patient information. As computers made their way into the classrooms, schools and universities began installing wireless networks to avoid cabling costs, while enabling shared Internet access. Realizing the need for an Ethernet-like standard, wireless vendors joined together in 1991 and formed the Wireless Ethernet Compatibility Alliance (WECA). WECA proposed and built a standard based on contributed technologies. WECA later changed its name to Wi-Fi. In June 1997, the IEEE released the 802.11 standard for wireless local-area networking. Just as the 802.3 Ethernet standards allows for data transmission over twisted-pair and coaxial cable, the 802.11 WLAN standard allows for transmission over different media. Specified media include the following:
Spread spectrum is a modulation technique that was developed in the 1940s. It spreads a transmission signal over a broad range of radio frequencies. This technique is ideal for data communications because it is less susceptible to radio noise and creates little interference. The Future of Wireless Local-Area Networking
There will be many improvements to come. For example, many weaknesses have been found in the basic security settings of WLANs, and stronger security in all future products is a priority. Versions such as 802.11g will offer 54 Mbps like 802.11a, but also will be backward compatible with 802.11b. This course will cover the general technologies behind 802.11a and 802.11b WLANs, including radio technologies, WLAN design, site preparation, and antenna theory. Detailed coverage of the Cisco Aironet products and accessories will also be presented. Students should be able to apply their knowledge at the completion of the course to design WLANs using products from one or multiple vendors.
Networking Media 1. Physical layer media
A
solid foundation must be used for building either a wired or wireless
LAN. As shown Figure This section introduces different types of networking media that are used at the physical layer, including:
Radio waves are the medium used by wireless technologies. When designing and building networks, it is important to comply with all applicable fire codes, building codes, and safety standards. Established performance standards should be followed to ensure optimal network operation. Because of the wide variety of options that are currently available in networking media, compatibility and interoperability should also be considered. 2. Atmosphere: the wireless medium Wireless signals are electromagnetic waves, which can travel through space. No physical medium is necessary for wireless signals, which travel as well in the vacuum of space as they do through the air in an office building. The ability of radio waves to pass through walls and cover great distances makes wireless a versatile way to build a network. The waves differ only in their frequency. Power waves, radio waves, microwaves, Infrared light waves, visible light waves, ultraviolet light waves, x-rays, and gamma rays share some very important characteristics:
The interactive calculator can be used for the following activities:
Wireless Applications
Components and Topologies 1. Client adapters Client adapters give users the freedom, flexibility, and mobility of wireless networking. Figure illustrates the three types of the wireless client adapters, which are PCMCIA-based (PC card), LM, and PCI-based card. PC card adapters give users with laptop or notebook PCs the ability to move freely throughout a campus environment, while maintaining connectivity to the network. Wireless PCI adapters allow users to add desktop PCs to the WLAN. All adapters feature antennas that provide the range required for data transmission and reception in large indoor facilities.
The Mini-PCI (Client Adapter is an embedded solution, available only to manufacturers, Based on direct sequence spread spectrum (DSSS) technology operating in the 2.4 GHz band, the MPI350 client adapter complies with the IEEE 802.11b standard, ensuring interoperability with other compliant WLAN products. The Mini-PCI small form factor and lightweight design are ideally suited for PC notebooks, Internet appliances, and other mobile devices. Drivers are supported for all popular operating systems, including Windows 95, 98, NT 4.0, Windows 2000, Windows ME, Windows XP, Mac OS Version 9.x, and Linux. 2. Access points An access point (AP) contains a radio transceiver. It can act as the center point of a stand-alone wireless network or as the connection point between wireless and wired networks. In large installations, the roaming functionality provided by multiple APs allows wireless users to move freely throughout the facility, while maintaining seamless, uninterrupted access to the network.
APs come with varied technology, security, and management features. Some APs are dual-band and support both 2.4-GHz and 5-GHz technologies, while others only support a single band. If an AP has a nonvolatile FLASH ROM to store firmware and configurations, it is easier to update firmware and change configurations. Any AP can be used as a repeater, or extension point, for the wireless network.
3. Antennas A variety of optional 2.4 GHz and 5 GHz antennas are available for Cisco wireless devices. Antennas should be chosen carefully to ensure that optimum range and coverage is obtained.
Each antenna has different gain and range capabilities, beam widths, coverage, and form factors. Coupling the right antenna with the right AP allows for efficient coverage in any facility, as well as better reliability at higher data rates.
4. Cables and accessories Every WLAN deployment is different. When engineering an in-building solution, varying facility sizes, construction materials, and interior divisions raise a host of transmission and multipath considerations. When implementing a building-to-building solution, distance, physical obstructions between facilities, and number of transmission points involved must be accounted for.
WAN provides a complete solution for any WLAN deployment including cables, mounting hardware, and accessories. First, low-loss cable extends the length between any bridge and the antenna. Low-loss cable provides installation flexibility without a significant sacrifice in range. Next, a bulkhead extender is a flexible antenna cable that extends AP cabling typically within an enclosure. In addition to cables, a Yagi articulating mount adds swiveling capability to mast-mounted Yagi antennas. Finally, it is important to prevent damage to the network by using a lightning arrestor which helps prevent damage due to lightning-induced surges or static electricity. Wireless LAN Topologies WLAN technology can either take the place of a traditional wired network or extend its reach and capabilities. Much like the wired counterparts, in-building WLAN equipment consists of client adapters and APs, which perform functions similar to wired networking hubs. For small or temporary installations, a WLAN can be arranged in a peer-to-peer (also referred to as ad hoc) topology using only client adapters. For added functionality and range, APs can be incorporated to act as the center of a star topology, as shown in Figure. The AP can also function as a bridge to an Ethernet network.
Adopting wireless technology enables computing that is both mobile and connected within a building. Users can move freely within a facility, while maintaining access to the network. Applying WLAN technology to desktop systems provides an organization with flexibility that is impossible to attain with a traditional LAN. Desktop client systems can be located in places where running cable is impractical or impossible. Desktop PCs can be redeployed anywhere within a facility as frequently as needed. This makes wireless ideal for temporary workgroups and fast-growing organizations.
Building-to-Building WLANs
Without a wireless alternative, organizations frequently resort to wide area networking (WAN) technologies to link together separate facilities. Contracting for leased-line or other wide-area services often presents a variety of drawbacks:
A wireless bridge can typically be purchased and installed in a day. Once the investment is made there are no recurring charges. Modern wireless bridges provide the bandwidth one would expect from a technology rooted in data communication rather than voice communications.
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, this
foundation is referred to as Layer 1 or the physical layer in the OSI
reference model. The physical layer is the layer that defines the
electrical, mechanical, procedural, and functional specifications for
activating, maintaining, and deactivating the physical link between end
systems. 
