CWNA: Official Certification Guide
Unit 1
Introduction to Wireless LANs
Wireless LANs were once considered expensive and slow solutions to certain network connectivity issues. Wireless LAN sales are now exploding. A recent industry publication stated that wireless net-work sales are the only part of an otherwise depressed netnet-work solution market actually increasing in market share. Enterprise solution vendors such as Cisco Systems and Avaya Communica-tions, and small office/home office (SOHO) vendors, such as Link-sys and D-Link, all offer some type of wireless network solution. Wireless networks are finding their way into large enterprises, such as banks and hospitals, where they help solve network con-nectivity challenges such as extremely long distances between network nodes and mobile user communications. Small and mid-sized businesses can expand their existing networks quickly and inexpensively and can have a new network up and running in less than a day. Law enforcement, fire and rescue teams, ambulatory services, and other government agencies are finding wireless LANs useful in a Wireless Metropolitan Area Network (WMAN) configuration. Finally, home users who want to share a broad-band connection no longer have to pull wires or use the home electrical wiring as a networking medium.The knowledge of the history and evolution of wireless LAN tech-nology is an essential part of the foundational principles of wire-less LANs. A thorough understanding of the origins of wirewire-less LANs and the organizations and applications that helped the technology mature enables you to better apply wireless LAN tech-nologies to meet your organization’s or client’s needs.
Lessons
1. The Wireless LAN Market 2. Wireless LAN Applications
Terms
100BaseT—The group of proposed IEEE 802.3 Physical Layer specifications for 100-Mbps Ethernet (fast Ethernet) over various wiring specifications is referred to as 100BaseT. Fast Ethernet and the 100BaseT standard are synonymous. 100BaseT is the specifica-tion for twisted pair wiring in a Fast Ethernet environment.
802.11—802.11 is the IEEE standard that specifies medium access and Physical Layer specifications for 1 Mbps and 2 Mbps wireless connectivity between fixed, portable, and moving sta-tions within a local area.
802.11a—802.11a, a revision to the IEEE standard, operates in the unlicensed 5 GHz band. Most 802.11a products have data rates up to 54 Mbps and must support 6, 12, and 24 Mbps.
802.11b—802.11b is a revision to the IEEE standard for direct sequence wireless LANs. Most 802.11b products have data rates of up to 11 Mbps, even though the standard does not specify the techniques for achieving these data rates.
802.11g—IEEE 802.11g is a proposed wireless network standard designed to provide the bandwidth of 802.11a networks while maintaining backward compatibility with 802.11b networks. 802.11g operates in the 2.4-GHz ISM band.
Overview
access point—An access point is a Layer 2 (Data Link Layer) device that serves as an interface between the wireless network and a wired network and can control medium access using RTS/CTS. Access points combined with a distribution system (Ethernet, for example) support the creation of multiple radio cells (also called basic service sets [BSSs]) that enable roaming throughout a facility.
Asymmetric Digital Subscriber Line (ADSL)—ADSL is a rela-tively new technology used to deliver high-speed digital commu-nications across the local loop over standard local loop copper wire. ADSL data rates range from 128 Kbps to over 1.5 Mbps downstream, and 64 Kbps to over 640 Kbps upstream.
Asynchronous Transfer Mode (ATM)—ATM is connection-oriented cell relay technology based on (53-byte) cells. An ATM network consists of ATM switches that form multiple virtual cir-cuits to carry groups of cells from source to destination. ATM can provides high-speed transport services for audio, data, and video.
basic service set (BSS)—BSS is a set of 802.11-compliant sta-tions and an access point that operates as a fully connected wire-less network.
beamwidth—Beamwidth is the measure of the horizontal and vertical lobes of an antenna signal. An omnidirectional antenna has a 360-degree horizontal beamwidth, while a semidirectional antenna may only have a 30-degree beamwidth.
Carrier Sense Multiple Access with Collision Detection (CSMA/CD)—CSMA/CD is the technique Ethernet uses for con-trolling access to the shared transmission medium (the bus). In CSMA/CD, a node may not transmit unless the medium is idle (carrier sense). If the transmitting node detects (collision detec-tion) that another station (multiple access) has begun to transmit at the same time, both nodes stop, then wait a random time inter-val before attempting to retransmit.
Category 5 UTP data cable—Category 5 cabling is certified for data rates up to 100 Mbps, which facilitates 802.3 100BaseT (Ethernet) networks.
distribution layer—In a three-layer hierarchy network design, the distribution layer moves packets between the access layers, and passes information up to the core layer.
Ethernet—Ethernet technology, originally developed in the 1970s by Xerox Corporation in conjunction with Intel and DEC, is now the primary medium for LANs. The original Ethernet has 10-Mbps throughput and uses the CSMA/CD method to access the physical media. Fast Ethernet (100-Mbps Ethernet) and Giga-bit Ethernet (1,000-Mbps Ethernet) are also used.
Federal Communications Commission (FCC)—The FCC is an independent U.S. government agency, directly responsible to Congress. The FCC was established by the Communications Act of 1934 and is charged with regulating interstate and interna-tional communications by radio, television, wire, satellite, and cable. The FCC’s jurisdiction covers the 50 states, the District of Columbia, and U.S. possessions.
frame relay—Frame relay is a packet switching technology designed to move data across a WAN. Frame relay normally oper-ates at speeds of 56 Kbps to 45 Mbps.
Gigahertz (GHz)—A GHz is one billion cycles per second (hertz).
highly directional antenna—A highly directional antenna is one that tightly focuses the horizontal and vertical RF beam-widths to maximize the distance the propagated wave can travel.
Institute of Electrical and Electronic Engineers (IEEE)—IEEE is a United States-based standards organization participating in the development of standards for data transmission systems. IEEE has made significant progress in the establishment of standards for LANs, in particular, the IEEE 802 series of standards.
last mile—Last mile is a term used to describe the local loop. A local loop is the pair of copper wires that connects a customer’s telephone to the telephone company’s CO switching system.
megabits per second (Mbps)—Mbps identifies the rate at which information travels down a physical medium or through space (wireless). Mbps is equivalent to 1,000,000 bits per second. 1.544 Mbps is equivalent to 1,544,000 bits per second.
Overview
personal digital assistant (PDA)—PDAs are small, handheld devices that provide a subset of the operations of a typical PC. They are used for scheduling, electronic notepads, and small data-base applications.
point-to-point (PtP)—A PtP connection provides dedicated com-munications between two, and only two, endpoints.
point-to-multipoint (PtMP)—A PtMP connection connects a single point to multiple outlying points. Also known as hub-and-spoke, the hub is the focal point for communications between sev-eral adjacent networks. All communications center on the hub.
Request to Send/Clear to Send (RTS/CTS)—RTS/CTS is a vir-tual carrier sense protocol used on WLANs. When RTS/CTS is enabled on a wireless LAN, a station wishing to communicate effectively reserves the medium for a period of time. All other sta-tions then must wait for the communicasta-tions to end before they can use the medium.
semidirectional antenna—A semidirectional antenna is one where the antenna focuses most of the radio signal energy in one direction, while creating several smaller lobes around the edges of the major signal. Semidirectional antennas are well suited for short to medium range bridging between buildings, but can also be used indoors to better direct the radio signal down halls or around obstacles.
small office/home office (SOHO)—SOHO is a term used to describe data and voice communications workers who either work from their home, or work in a small office of 50 or fewer workers.
Token Ring—Token Ring is the IEEE 802.5-specified, ring-based, token-passing LAN topology. Each node on the ring acts as a repeater, passing the token from node to node as the token travels around the entire ring. Each node must wait its turn to transmit data and may only transmit when it controls the token.
Unlicensed National Information Infrastructure (UNII) bands—A segment of RF frequencies allocated by the FCC for unlicensed data communications, used by IEEE 802.11a, 802.11h, and HyperLAN2 wireless LANs; the three bands are: 5.15 to 5.25 GHz, 5.25 to 5.35 GHz, and 5.725 to 5.825 GHz.
Wireless Fidelity (Wi-Fi)—Wi-Fi is the WECA certification standard signifying interoperability among 802.11b products.
Wireless Internet Service Provider (WISP)—A WISP is an Inter-net service provider (ISP) that provides customers with access to the Internet over wireless networks. WISPs often operate in rural areas where the wired infrastructure is inadequate for providing any-thing but dialup Internet access.
Wireless LAN Association (WLANA)—The Wireless LAN Associa-tion (WLANA) is a nonprofit educaAssocia-tional trade associaAssocia-tion, com-prised of the leaders and technology innovators in the local area wireless technology industry. Through sponsor and affiliate mem-bers’ knowledge and experience, WLANA provides a clearing-house of information about wireless local area applications, issues, and trends. In addition, WLANA serves as an industry resource regarding wireless LAN and PAN products, as well as to industry press and analysts.
Lesson 1—The Wireless LAN Market
Lesson 1—The Wireless LAN Market
The market for wireless local area networks (WLANs) seems to be evolving similarly to the networking industry as a whole, starting with the early adopters using whatever technology was available. The market has moved into a rapid growth stage, for which popu-lar standards are providing the catalyst. The big difference between the networking market as a whole and the wireless LAN market is the rate of growth. The flexible implementation of wire-less LANs makes it clear why they are outpacing every other mar-ket sector.
Objectives
At the end of this lesson you will be able to: • Explain the general history of wireless LANs • Identify standards specific to today’s wireless LANs
History of Wireless LANs
Spread spectrum wireless networks, like many technologies, came of age under the military’s guidance. The military needed a sim-ple, easily implemented, and secure method of exchanging data in a combat environment.
As the cost of wireless technology decreased and the quality increased, it became cost-effective for enterprise companies to integrate wireless segments into their network. Wireless technol-ogy offered a relatively inexpensive way for corporate campuses to connect buildings to one another without laying copper or fiber cabling. Today, the cost of wireless technology enables most busi-nesses to implement wireless segments on their network. Many companies have converted completely to wireless networks, saving time and money while allowing the flexibility of roaming.
Key
Households are also benefiting from the low cost and subsequent availability of wireless LAN hardware. Many people are now installing cost-effective wireless networks that take advantage of the convenience of mobility and creating home offices or wireless gaming stations.
As wireless LAN technology improves, the cost of manufacturing (and therefore purchasing and implementing) the hardware con-tinues to fall, and the number of installed wireless LANs contin-ues to increase. The standards that govern wireless LAN operation increasingly stress interoperability and compatibility. As the num-ber of users grows, lack of compatibility may render a network useless, and the lack of interoperability may interfere with the proper operation of other networks.
Today’s Wireless LAN Standards
Because wireless LANs transmit using radio frequencies, the same types of regulations that govern such things as AM/FM radios reg-ulate wireless LANs. The Federal Communications Commission (FCC) regulates the use of wireless LAN devices. In the current wireless LAN market, several accepted operational standards and drafts in the United States are created and maintained by the Institute of Electrical and Electronic Engineers (IEEE).
Groups of people that represent many different organizations, including academics, business, military, and the government cre-ate these standards. Because IEEE standards can have a significant impact on the development of technology, the standards can take many years to be created and agreed upon. You may even have an opportunity to comment on these standards at certain times dur-ing the creation process.
Wireless LAN Specific Standards
The standards specific to wireless LANs are covered in greater detail in further reading on wireless LAN organizations and stan-dards. Because these standards are the basis upon which the latest wireless LANs are built, a brief overview is provided here:
• IEEE 802.11—the original wireless LAN standard that speci-fies the slowest data transfer rates in both spread spectrum RF and infrared transmission technologies.
Lesson 1—The Wireless LAN Market • IEEE 802.11a—describes much faster data transfer rate than IEEE 802.11b (but lacks backwards compatibility), and uses the 5 GHz UNII frequency bands.
Activities
1. Which of the following reasons explain why wireless LANs have recently grown in popularity? (Choose three.)
a. They provide increased speed over wired network solutions. b. They provide an inexpensive way to connect buildings on
a corporate campus.
c. They enable users to build home networks without install-ing network cables.
d. They save time and money when building new network segments.
2. Which of the following wireless LAN standards specifies the lowest data transfer rate?
a. 802.11 b. 802.11a c. 802.11b d. 802.11g
3. Which of the following organizations creates and maintains the U.S. wireless LAN standards?
a. FCC b. WECA c. IEEE d. IETF
4. Which of the following wireless LAN standards specifies data rates higher than, but remains backward compatible with, 802.11b?
Lesson 1—The Wireless LAN Market 5. Which of the following organizations promotes 802.11b
as Wi-Fi? a. FAA b. WECA c. IEEE d. IETF
Extended Activities
1. Research the history of spread spectrum wireless LANs, from their military origins to their current applications. How do the military applications differ from today’s use of the tech-nology? How are they the same?
