A solid foundation must be used for building either a wired or wireless LAN. As shown Figure , 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.
This section introduces different types of networking media that are used at the physical layer, including:
-shielded twisted-pair cable
-unshielded twisted-pair cable
-coaxial cable
-fiber-optic cable
-propagated radio waves
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.
Physical Layer Media
The Future of Wireless Local-Area Networking
Current WLAN technologies offer increasing data rates, better reliability and dependability, and decreasing costs. Data rates have increased from 1 Mbps to 54 Mbps, interoperability has become a reality with the introduction of the IEEE 802.11 family of standards, and prices have dramatically decreased. As WLANs become more popular, manufacturers can increasingly leverage economies of scale.
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.
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.
Evolution of Wireless LAN
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 standard 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:
-Infrared light
-Three types of radio transmission within the unlicensed 2.4-GHz frequency bands:
Frequency hopping spread spectrum (FHSS)
Direct sequence spread spectrum (DSSS)
Orthogonal frequency-division multiplexing (OFDM) 802.11g
-One type of radio transmission within the unlicensed 5-GHz frequency bands:
Orthogonal frequency-division multiplexing (OFDM) 802.11a
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.
Just as the 802.3 Ethernet standard 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:
-Infrared light
-Three types of radio transmission within the unlicensed 2.4-GHz frequency bands:
Frequency hopping spread spectrum (FHSS)
Direct sequence spread spectrum (DSSS)
Orthogonal frequency-division multiplexing (OFDM) 802.11g
-One type of radio transmission within the unlicensed 5-GHz frequency bands:
Orthogonal frequency-division multiplexing (OFDM) 802.11a
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.
Wireless LAN (WLANs)
What is Wireless LAN
In the simplest of terms, a wireless local-area network (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 move and change 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.
In the simplest of terms, a wireless local-area network (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 move and change 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 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 level. 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:
-Require standard Ethernet LAN speeds
-Benefit from roaming users
-Reconfigure the physical layout of the office often
-Expand rapidly
-Utilize a broadband Internet connection
-Face significant difficulties installing wired LANs
-Need connections between two or more LANs in a metropolitan area
-Require temporary offices and LANs
-Require standard Ethernet LAN speeds
-Benefit from roaming users
-Reconfigure the physical layout of the office often
-Expand rapidly
-Utilize a broadband Internet connection
-Face significant difficulties installing wired LANs
-Need connections between two or more LANs in a metropolitan area
-Require temporary offices and LANs
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.
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.
Subscribe to:
Posts (Atom)