Wireless LAN Technology

Wireless Local Area Networks

Wireless LAN Technologies

By: Shane A. Neff

ICS 620

Fall 2001

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1.1 Introduction....................................................................................................................32.1 The Need to Disconnect.................................................................................................43.1 Wireless LAN History...................................................................................................54.1 How it works..................................................................................................................6

4.2 The 802.11 Standard..................................................................................................74.3 The 802.11b Standard................................................................................................94.4 The 802.11a Standard..............................................................................................104.5 The 802.11g Standard..............................................................................................11

5.1 What is needed to implement a WLAN?.....................................................................126.1 The future.....................................................................................................................15References..........................................................................................................................17

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1.1 IntroductionOur global economy and consciousness have switched from an industrial to an

informational mindset. This change in focus has far reaching implications. Clear evidence

of this shift in consciousness is in the numbers of Americans that own personal

computers. The Census Bureau reports that 51% of all American households have at least

one personal computer, a figure which has risen 9% since 1998. (Newburger, 2001)

Computers have become an integral part of our everyday lives.

Most of these computers are part of some type of network; either Wide Area

Networks (WAN), Local Area Networks (LAN), or the internet. Being a part of a

network allows end-users to share resources such as printers and file servers. Computer

networks also make possible the exchange of information and data from distances that

can span continents in an instant. The use of the World Wide Web has grown to include

almost half of American households. A recent Census Bureau report indicates that 41.5%

of American homes have internet access. (Newburger, 2001) Computers that are a part of

a network are becoming an increasingly important component of the education process. A

Newsweek Magazine article on electronic classrooms recently reported, “95% of schools

had Internet access and 63% of public-school classrooms were wired.” (Spencer, 2000)

Student’s access to the internet is not limited to the classroom. "Studies show that 94

percent of high-school seniors have Internet access." (Begun, 2000)

Many homes have multiple computers and are beginning to feel the pains that

businesses have experienced trying to connect their collective resources to form a LAN.

Cisco’s Dictionary of Internetworking Terms and Acronyms defines a LAN as:

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Local-area network. High-speed, low-error data network covering a relatively small geographic area (up to a few thousand meters). LANs connect workstations, peripherals, terminals, and other devices in a single building or other geographically limited area. LAN standards specify cabling and signaling at the physical and data link layers of the OSI Model.

The most crucial component of a LAN is the media (coaxial cables, twisted-pair cables,

and other types of cables) that carry and transmit the digital data from its source, to its

destination. One of the primary concerns (and limitations) of a LAN has been its

dependence on hard-wired cabling, switching closets, hubs, and the restrictions that

require its close proximity to the signal source or a repeater that increases the signal’s

source.

2.1 The Need to DisconnectMany corporations do not own the building that their business occupies. The

spaces that are leased are often portable in nature as the business expands, contracts, or

finds a need to move to a new facility. The installation of the cable media necessary to

implement a LAN is not only expensive to install, but a trained technician is needed to be

sure that it is done correctly. In order to install a traditional LAN, the physical

modification of the structure and office design features become more permanent in

nature. If an office layout needs to be adapted at a later time, the physical wiring

infrastructure often limits, or restricts the ability to easily adapt architectural facilities to

accommodate change.

In addition to the physical limitations imposed by traditional hard-wired LANs,

there are often legal and financial restrictions that can prohibit an organization from

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utilizing the full potential that a LAN can afford. City ordinances, private ownership of

utility poles, and often the shear expense of wiring buildings can stop a planned LAN

implementation in its tracks. Facilities such as schools, churches, and other non-profit

organizations have a real need to bring together all the buildings of their campuses into

their local area networks. These limitations not only affect corporate LANs, but they can

also be foreboding enough to force those wishing to implement home networks to seek-

out slower, but more affordable network options. As the ownership of personal computers

becomes more common, the market that enables users to share resources such as internet

access and printers will increase correspondingly.

3.1 Wireless LAN HistoryTo discuss the history of wireless LAN technology without mentioning its

foundations in radio technology would be impossible. Guglielmo Marconi’s research in

1894 of ‘Hertzian Waves’ (researched and produced in Heinrich Hertz lab) enabled him

the produce and detect the waves over great distances. These were the foundations of

what we know today as the radio. Guglielmo applied for, and received a patent for his

radio, and in 1896 he started the Wireless Telegraph and Signal Company Limited; the

world’s first radio company. In 1905 the first transatlantic signals were sent and received.

(Johns Hopkins, 1996)

Throughout the history of telecommunications, the military has often been

responsible for technical innovations as they modify existing technology to serve the

defensive needs of the United States- radio is no different. During World War II, the

military’s use and modification of radio technology was critical in the allies’ victory over

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Germany and Japan. Encryption technology was a crucial tool that enabled military

personnel to discuss plans in a secure environment.

The first wireless LAN was the result of a research project of Norman Abramson;

an engineering and computer science professor at the University of Hawaii. This project

became known as ALOHANET, and was implemented in 1970. It was the first packet

radio network based upon a star topology that operated at 9600 bits per second

throughput capacity. The network connected seven computers on 4 of the Hawaiian

Islands. Many consider Abramson’s network to be the world’s first modern network. In

1971, ALOHANET was connected to the ARPAnet on the mainland. (Perry, 2000) The

Aloha network protocol was one of the outcomes of this research. Webopedia, the online

technical glossary defines Aloha as:

A protocol for satellite and terrestrial radio transmissions. In pure Aloha, a user can transmit at any time but risks collisions with other users' messages. "Slotted Aloha" reduces the chance of collisions by dividing the channel into time slots and requiring that the user send only at the beginning of a time slot. Aloha was the basis for Ethernet, a local area network protocol. (Webopedia, 2001)

From ALOHANET, wireless LAN technology stagnated with few new

developments until the 802.11 standard was approved by the IEEE in the

1990s.

4.1 How it worksThere are three primary methods for wireless LAN (WLAN) products to

communicate with one another: narrowband microwave, infrared, and spread spectrum.

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Narrowband microwave is a “line of sight” technology. This means that both sending and

receiving towers must maintain a consistent line of sight between them; with no

obstructions. This method requires an FCC license and is primarily used for intra-

building networks. Infrared technology is another line of sight wireless technology. The

signal cannot be obstructed by walls or objects and does not require an FCC license. The

most popular method is a radio-based technique called spread spectrum. This process was

developed by the United States military. As was discussed in the previous section, this

technique enabled military troops to encrypt radio transmissions. There are two types of

spread spectrum technologies. Frequency hopping spread spectrum (FHSS), and direct

sequence spread spectrum (DSSS). FHSS involves the signal being sent over frequencies

that are continuously hopping around the available bandwidth at select time intervals,

while the receiver is synchronized to switch frequencies in order to receive the signals

being sent. FHSS uses 1 Mhz subchannels and uses the entire bandwidth of available 2.4

Ghz bandwidth to send these small “usages” through the signal. With DSSS technology

different portions of the data signal are sent on different frequencies along the available

bandwidth, and are then reassembled at their destination. Neither of these two spread

spectrum techniques require an FCC license and are not compatible with one another.

(Townes & Brecker, 2001)

4.2 The 802.11 StandardWireless technology made major strides in the early 1990’s. The Institute of

Electrical and electronic engineers (IEEE) 802.11 standard was proposed by the Federal

Communications Commission, and implemented in 1997. The goal of this standard was

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to standardize wireless technology products so that these devices would operate together,

regardless of the manufacturer. Originally, this standard was designed to use one of the

frequencies that were part of the Industrial, Scientific, and Medicine (ISM) frequency

bands. These frequencies are 902-928 MHz, 2400-2483.5 MHz and 5725-5850 MHz and

are unlicensed by the FCC (as long as the devices they use meet certain FCC

specifications). Since these frequencies are unlicensed, that portion of the frequency band

is experiencing growing by the recent influx of many devices such as Bluetooth devices,

wireless LAN devices, mobile phones, and microwaves. The 802.11 standard uses the 2.4

Ghz portion of the unlicensed frequency and has 1Mbps and 2Mbps maximum data rates.

802.11 used two techniques to modulate. One is Binary shift keying (BPSK), and the

other is Quadrature phase shift keying. QPSK is the more advanced of the two techniques

and doubles the data rate (1Mbps) found in BPSK and illustrates the maximum

throughput of an 802.11 compliant device. (PulseWan, 2000). The 802.11 standard

incorporates both the FHSS and DSSS methods of radio-based data transfer. There are

also two modes, or types of networks that can be established using an 802.11 compliant

wireless device: infrastructure or ad hoc. A recent PulseWan online article explained how

these two wireless network types differ.

The 802.11 standard defines two modes: infrastructure mode and ad hoc mode. In infrastructure mode (Figure 2), 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.

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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 3). 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). (PulseWan, 2000)

4.3 The 802.11b StandardThe 802.11b standard was approved by the IEEE in September 1999. This

standard has many marked improvements over the 802.11 standard. The only OSI layer

that is affected by the improved standard is the physical layer. The 802.11b standard is

backwards compatible and will still support the 1-2 Mbps data speeds that were found in

the 802.11 standard- if the FHSS technology is disabled on legacy 802.11 equipment, as

FHSS was abandoned in the 802.11b standard. The data speed range of WLAN products

that are IEEE 802.11b compatible are from 1-2 Mbps to 5.5-11Mbps. Since 11Mbps

speeds are only possible within 150 feet of the access point (AP), the lower data speeds

will be experienced as the distance increases, while the higher data transfer speeds can be

found closer to the access point..

There are other notable differences between the 802.11 and 802.11b standards

besides the increased data transfer speed. The 802.11b standard eliminates the FHSS

technology and uses DSSS exclusively. Using DSSS, divides the 2.4 Ghz band into

fourteen 22 Mhz channels. Each channel overlaps the others partially and 3 are

completely non-overlapping. This technique is partially responsible for the increase of

speed and the ability to correct many of the data transfer errors it encounters; thus

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eliminating the need to resend corrupted data. The original 802.11 standard used an 11-

bit “chipping” technique called a Barker sequence. A major improvement found in the

802.11b standard is the use of an 8-bit chipping technique called Complementary Code

Keying (CCK), which is the second improvement that improved data transfer speeds with

the new standard. (PulseWan, 2001)

The future of the 802.11b standard is unclear, but it is currently able to match

closely the data speeds found in traditionally wired networks. The 802.11b standard

allows many small organizations to implement a wireless network simply and affordably.

The market for 802.11b compliant hardware is one of the few computer hardware

markets that are experiencing growth in the shrinking computer market. Faulkner

Information Services reports that, “In the first quarter of 2001, 802.11b’s sales increased

15 percent to $234.1 million.” (Townes & Brecker, 2001)

4.4 The 802.11a StandardOne of the major differences between the 802.11b and 802.11a standards that are

likely to be noticed first be even the most common observer is the switch from the 2.4

Ghz frequency range to the 5 Ghz range on the UNII (Unlicensed National Information

Infrastructure). One major benefit of the frequency change (aside from increased

throughput) will be taking WLANs off of the same frequency as microwaves, mobile

phones and Bluetooth devices. One problem the frequency change might cause when

implementing the new standard might be compatibility issues with 802.11 and 802.11b

standards. It is important to note that these two standards are not compatible with one

another. The 802.11a standard was approved the same year (1999) as 802.11b. The

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maximum data transfer speeds have been increased from 1-2 Mbps with 802.11, to 5.5-11

Mbps with 802.11b to an astonishing 54 Mbps. In a recent Network World article, the

modulation technique called Coded Orthogonal Frequency Division Multiplexing

(COFDM) and how it is used to dramatically increase data throughput is explained.

“COFDM breaks the ceiling of the data bit rate by 1) sending data in a massively parallel

fashion, and 2) slowing the symbol rate down so each symbol transmission is much

longer than the typical delay spread. A guard interval (sometimes called a cyclic prefix)

is inserted at the beginning of the symbol transmission to let all delayed signals "settle"

before the baseband processor demodulates the data.” (Anderson, 2001) Despite the

incompatibility issues between the 2.4 Ghz and the 5 Ghz networks, momentum for the

802.11a standard is growing. In a recent Intel press release, the company disclosed its

plan to release their PRO/Wireless 5000 product line in November; based upon the

802.11a standard. Initially critics believed the 802.11a standard would be priced out of

the range of most consumers. Intel also released its pricing structure in the same press

release. “The suggested list prices for the Intel PRO/Wireless 5000 LAN CardBus

Adapter, the Intel PRO/Wireless 5000 LAN Access Point and the Intel PRO/Wireless

5000 LAN PCI Adapter are $179, $449, and $229 respectively.” (Intel, 2001)

4.5 The 802.11g StandardThis is a proposed standard that has been locked in IEEE litigation for nearly a

year. It would operate on the crowded 2.4 Ghz frequency and would also provide

backwards compatibility with 802.11 and 802.11b standards. It also uses the same

modulation technique employed by 802.11a, but has a maximum throughput of 22 Mbps

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which is less than half of the maximum data transfer rate of 802.11a. The litigation and

debate exists between Texas Instruments and Intersil Corporation. In recent

developments, Texas Instrument’s Packet Binary Convolution Coding (PBCC)

technology was taken out of the running by the IEEE 802.11g committee. Intersil’s

OFDM failed to secure the needed 75% vote to approve it. The committee at IEEE will

vote again in late September to ratify Intersil’s modulation as the core 802.11g

technology, but even they are considering that the ruling may be a moot point. Even

Intersil plans to begin releasing 802.11a equipment by the second quarter of 2002.

(Nobel, 2001)

5.1 What is needed to implement a WLAN?Before beginning to procure the equipment that is needed to set-up a wireless

LAN, some planning should be considered and a needs assessment performed. Whether

someone is implementing a WLAN at home, or an office environment, each of the

802.11x standards has its advantages and disadvantages. Data transfer speed, frequency

used, hardware expense, distance constraints, and encryption methods all need to be

examined so that the most appropriate technology is selected for any organization’s

needs.

Once the standard that is suitable for the system’s needs has been chosen, a close

look at what various hardware venders have to offer should be carried out. There are

multitudes of WLAN hardware manufacturers, which is helping to bring down the price

of the technology, while increasing the quality. For the purposes of this paper, an

overview of consumer WLAN hardware will be performed.

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Typically, a WLAN fits into one of four configuration types: base-to-remote,

microcellular, peer-to-peer, personal area network, or satellite bridging. Most home

networks and small office use the base-to-remote configuration. W.E. Lutz describes the

base-to-remote WLAN architecture.

With base-to-remote, workstations and PCs are linked to a central base workstation. Because the base workstation is the hub of the LAN, excellent signal propagation, range and high security levels are required. As part of the nature of distributed networks, more demanding network management functions are required. For commercial uses, such as those found within a single building or integrated set of buildings in close proximity to each other. Base-to-remote LAN systems work well either as a standalone wireless LAN or as an extension to a wired LAN. (Lutz, 2001)

There are two important hardware components that are needed to employ the base-to-

remote configuration: the access point (AP) and a wireless NIC that is capable of

receiving the radio frequency (RF) transmitted by the AP. Many commercial APs can

support 32 simultaneous users, and is capable of transmitting data up to a distance of 100

feet indoors at 11 Mbps, and 500 feet outdoors at 11 Mbps. The access point is typically

the most expensive component involved in implementing a WLAN with costs ranging

from $199- to $2,000.

The list of WLAN hardware providers grows daily, and the names that appear on

that list read like a who’s who in computer manufacturing. The multitude of choices that

is available to the consumer in WLAN technology point to the fact that there is a growing

interest in this media as a method available to deliver digital data. One article predicts

that there will be a 25 percent growth in the WLAN industry peaking in 2004 at $2.2

billion in worldwide sales. (Lutz, 2001)

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Some of the commercially available WLAN components are: 3Com, AT&T,

Buslink, Cisco, Compaq, Dlink, Intel, Linksys, Lucent, Netgear, Proxim, Sony, Symbol,

Xircom, and Zoom. There are many qualities and specifications that set these products

apart. Different APs will support different numbers of users, broadcast their signals

alternate distances, and vary greatly in cost. WLAN network cards come in four formats:

PCI for desktop computers, PCMCIA for laptop computers, USB which is designed for

both, and compact flash (CF) which is designed for personal data assistants (PDAs).

PCI adapter for desktop computers PCMCIA adapter for laptop computers

USB adapter for plug and play Compact Flash adapter for PDA devices

Figure 5.1 Various adapter cards for WLANs

Aside from cost and hardware format, drivers for varying operating systems (OS) are not

supported by all hardware manufacturers. Without these appropriate drivers, these cards

will not work. As a result of these implications, it is important when selecting a card to

take note of the operating systems that are supported by its manufacturer. Most current

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commercially available WLAN hardware is based on the 802.11b standard. However, it

is important to make sure that all hardware that is purchased and installed into an existing

WLAN configuration be compatible. Therefore, determining early in the planning

process which standard will be used is crucial. With the anticipated popularity of the

802.11a standard, network administrators will be faced with decisions that may involve

adopting the new standard at the expense of the old; as the two are incompatible.

6.1 The futureWhile it is difficult to determine just where this technology will go, it is surely

here to stay. Aside from the freedom that results from unplugging your networked

computers, the overall savings involved in implementing a WLAN over a traditional

LAN where each workstation is tied to a physical connection to the network can be

astonishing. Recently Johns Hopkins School of Public Health in Baltimore Maryland

performed a cost analysis comparing the implementation of both types of networks in

their aging buildings. Their findings speak volumes about the recent rise in the popularity

of this technology.

WIRED • Fiber Connection $3k • Hubs $2k • Raised floor – $10k • In-room wiring - $3k

$18k per room

WIRELESS • Data Connections & Power - $1500 • Access Point - $1500 ($750 per

unit) $3k per room

Figure 6.1 Johns Hopkins School of Public Health Cost Comparison

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For Johns Hopkins to implement a network based on hard-wiring their aging buildings

was projected to have cost $720,000 while installing a wireless network was estimated to

cost $210,000 (Johns Hopkins, 1996) With costs falling and the speed of the technology

increasing, it is clear that WLANs will cause network engineers and administrators to

consider seriously the costs and benefits involved in employing this new technology.

Many organizations (including Ball State University) with existing network

infrastructures are realizing the potentials associated with a wireless network. WLANs

empower people and free the individual to use the computer network in ways that are

reminiscent of people’s dependence of calculators and textbooks. Instant access to the

corporate intranet or the World Wide Web can occur anywhere a WLAN has been put in

place. Students are not restricted to busy computer labs, and employees are not

constrained to their cubicles. WLAN technology moves our information-based society

one step closer to the personal computer resembling a common household appliance or a

personal tool that can be put into the hands of anyone for the common good of everyone.

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References

Anderson, Fred. (January 29, 2001). 802.11a speeds wireless LANs. NetworkWorld, 24.

Johns Hopkins School of Public Health. (1996). History of Wireless. Retrieved

September 8, 2001 from the World Wide Web: http://wireless.jhsph.

edu/history.html

Johns Hopkins School of Public Health. (1996). Wireless LAN: Cost Comparison.

Retrieved September 18, 2001 from the World Wide Web:http://wireless.

jhsph.edu/edusite/default_files/frame.htm

Bret B. (October 30, 2000). Campus Tours 1.0. Newsweek, 97.

Dictionary of Internetworking Terms and Acronyms: Cisco Systems Official

Internetworking Dictionary. (2001). Indianapolis: Cisco Press.

Intel. (September 11, 2001). Intel Introduces Advanced Technologies for Wireless

Networks: Intel Unveils Next Generation 802.11a Products Along With Enhanced

802.11b Family and Innovative Software. Retrieved September 14, 2001 from the

World Wide Web: http://www.intel.com/pressroom/archive/releases/

20010911net.htm

Lutz, W.E. (2001). Wireless LAN Technologies. Retrieved September 15, 2001 from the

World Wide Web: http://products.faulkner.com/products/faccts/00014337.htm

Newburger, Eric C. (September, 2001). Home Computers and

Internet Use in the United States: August 2000. Retrieved September 4, 2001

from the World Wide Web: http://www.census.gov/prod/2001pubs/p23-207.pdf

Nobel, Carmen. (August 24, 2001). Speedy 802.11a gains momentum. Retrieved

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September 8, 2001 from the World Wide Web: http://www.zdnet.com/

eweek/stories/general/ 0,11011,2807757,00.html

Perry, Emma. (2000, April). Norman Abramson and ALOHANET: The First Packet

Radio Network. Retrieved September 8, 2001 from the World Wide Web:

http://www.rit.edu/~elp7807/imm/project3/index.html

Spencer J. (September 18, 2000). E-turning to the Classroom. Newsweek, 74J.

Townes, Kay & Andrew Brecker. (2001). Wireless LANs Comparison & Selection

Guide. Retrieved September 14, 2001 from the World Wide Web:

http://products.faulkner.com/products/faccts/00016888.htm

Webopedia. (September, 2001). Aloha Protocol Definition. Retrieved September 10,

2001 from the World Wide Web:

http://www.webopedia.com/TERM/A/Aloha.html

PulseWan, (2000). What is 802.11 & 802.11B ? Retrieved September 14, 2001 from the

World Wide Web: http://www.pulsewan.com/data101/802_11_b_basics.htm

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