Sends radio-frequency signals between your computers
An access point which is a wired controller that receives and transmits data to
the wireless adapters installed in each computer
• communicates on a frequency of 2.45 gigahertz, which has been set aside
by international agreement for the use of industrial, scientific and medical
• spread-spectrum frequency hopping -a device will use 79 individual,
randomly chosen frequencies within a designated range, changing from
one to another on a regular basis.
• Transmitters change frequencies 1600 times every second, meaning that
more devices can make full use of a limited slice of radio spectrum
• create a personal-area network (PAN), or piconet, that may fill a room or
may encompass no more distance than that between the cell phone on a
belt-clip and the headset on your head
• Once a piconet is established, the members randomly hop frequencies in
unison so they stay in touch with one another and avoid other
• Bluetooth can send data at more than 64,000 bits per second in a full-
• The devices in a piconet share a common communication data channel.
The channel has a total capacity of 1 megabit per second (Mbps). Headers
and handshaking information consume about 20 percent of this capacity.
• In the United States and Europe, the frequency range is 2,400 to 2,483.5
MHz, with 79 1-MHz radio frequency (RF) channels. In practice, the range
is 2,402 MHz to 2,480 MHz. In Japan, the frequency range is 2,472 to 2,497
MHz with 23 1-MHz RF channels.
• A data channel hops randomly 1,600 times per second between the 79 (or
23) RF channels.
• Each channel is divided into time slots 625 microseconds long.
• A piconet has a master and up to seven slaves. The master transmits in
even time slots, slaves in odd time slots.
• Packets can be up to five time slots wide.
• Data in a packet can be up to 2,745 bits in length.
• There are currently two types of data transfer between devices: SCO
(synchronous connection oriented) and ACL (asynchronous
• In a piconet, there can be up to three SCO links of 64,000 bits per second
each. To avoid timing and collision problems, the SCO links use reserved
slots set up by the master.
• Masters can support up to three SCO links with one, two or three slaves.
• Slots not reserved for SCO links can be used for ACL links.
• One master and slave can have a single ACL link.
• ACL is either point-to-point (master to one slave) or broadcast to all the
• ACL slaves can only transmit when requested by the master.
• Infrared Data Association
• communicate using infrared light pulses
• is a standard for devices to communicate using infrared light pulses;
depend on direct line of sight
• data speeds up to 4 megabits per second (Mbps)
• downside is need access points in each room because need direct line of
Institute of Electrical and Electronics Engineers (IEEE) original standard
wireless-Ethernet specification IEEE 802.11 designated 2 ways of communicating
between devices allowed for speeds up to 2Mbps
Direct-sequence spread spectrum (DSSS)
Frequency-hopping spread spectrum (FHSS)
• Both use frequency-shift keying (FSK) technology
• Both based on spread-spectrum radio waves in 2.4 gigahertz (GHz) range
Spread-spectrum = data is sent in small pieces over a number of discrete
frequencies available for use at any time in the specified range
• communicate by splitting each byte of data into several parts and sending
them concurrently on different frequencies
• uses lot of available bandwidth, about 22megahertz (MHz)
• send a short burst of data, shift frequencies (hop), and then send another
• devices using FHSS agree on frequencies to hop to, and use each
frequency for short period of time (less than 400 milliseconds) before
moving on, several independent FHSS networks can exist in same
physical area without interfering with each other
• use only 1MHz or less of available bandwidth
• less prone to interference than DSSS because use any given frequency for
such short period of time
• FHSS-based devices are easier and cheaper to produce
HomeRF (radio frequency) and SWAP
HomeRF is alliance of businesses that developed standard called Shared
Wireless Access Protocol (SWAP)
• Includes 6 voice channels bases on Digital Enhanced Cordless
Telecommunications (DECT) and 802.11 wireless-Ethernet specification
• SWAP devices make 50 hops per second
• Transmit at 1 Mbps
• Can get up to 2Mbps if very little interference
Advantages of SWAP:
Here are the advantages of SWAP:
* It's inexpensive ($70 to $200 per device).
* It's easy to install.
* It requires no additional wires.
* It has no access point.
* It uses six full-duplex voice channels and one data channel.
* It allows up to 127 devices per network.
* It allows multiple networks in the same location.
* You can use encryption to make your data secure.
Here are the disadvantages of SWAP:
* It's not very fast (normally 1 Mbps).
* It has a limited range (75 to 125 ft / 23 to 38 m).
* It's not compatible with FHSS devices.
* Physical obstructions (walls, large metal objects) can interfere with
* It's difficult to integrate into existing wired networks.
WECA and Wi-Fi
Wireless Ethernet Compatibility Alliance (WECA)
• Targeted more at office use than home networks
• Wi-Fi stands for “wireless fidelity” like hi-fi for “high fidelity”
• Compliant with IEEE 802.11b
• Specification drops FHSS and focuses on DSSS because of higher data rate
• Speed of 11Mbps whenever possible
Here are the advantages of Wi-Fi:
* It's fast (11 Mbps).
* It's reliable.
* It has a long range (1,000 ft / 305 m in open areas, 250 to 400 ft / 76 to 122
m in closed areas)
* It's easily integrated into existing wired-Ethernet networks.
* It's compatible with original 802.11 DSSS devices.
Here are the disadvantages:
* It's expensive.
* It requires an access point.
* It can be difficult to set up.
• Speed can fluctuate significantly.
Airport has to be connected to an Apple computer, but will accept signals from
any 802.11b-compatible wireless-network card
Tyson, Jeff. “How Wireless Networking Works.” Marshall Brain’s HowStuffWorks.
Franklin, Curtis. “How Bluetooth Works” Marshall Brain’s HowStuffWorks. pp.
Gast, Matthew S. 802.11 Wireless Networks: The Definitive Guide.
Advantages of wireless networks ---
• Ease and speed of deployment – no need to mess with wires
• Cost – “Over time, point-to-point wireless links are far cheaper than
leasing capacity from the telephone company.”(p. x)
• 1997 802.11 standard
• speeds increased from 2 – 11 – 54 Mbps
• network medium is a form of electromagnetic radiation
o infrared light – limitations – easily blocked by walls, partitions, and
other office construction
o radio waves – can penetrate most office obstructions and offer
---most use radio wave physical layer!!
ISM (Industrial, Scientific, and Medical) – frequency bands (microwave oven) –
where 802.11 devices operate
802.11b devices specifically in S-band ISM – license-free!!
802.11 1 & 2 Mbps, 2.4 GHz, first standard (1997) – both frequency-hopping and
direct-sequence modulation techniques
802.11a up to 54 Mbps 5 GHz, second standard (1999), but products not released
until late 2000
802.11b 5.5 & 11 Mbps, 2.4 GHz, third standard, but second wave of products
and most common equipment
802.11g up to 54 Mbps, 2.4 GHz, not yet standardized
IEEE 802 focus on lowest 2 layers of OSI model
802.11b HR/DSSS physical layer – High Rate, Direct-sequence Layer
802.11a OFDM physical layer – Orthogonal Frequency Division Multiplexing
access point --- “If one mobile station in an infrastructure BSS needs to
communicate with a second mobile station, the communication must make 2
hops. First, the originating mobile station transfers the frame to the access point.
Second, the access point transfers the frame to the destination station.”(p. 11)
so all mobile stations must maintain a distance to the access point – useful
because otherwise physical layer complexity would be increased due to the need
for maintenance of neighbor relationships (without access point)
stations must associate with an access point – association is the process by which
mobile stations join 802.11 network
802.11 sometimes called “wireless Ethernet” because core elements similar
o stations id by 48-bit MAC address
o frames are delivered based on MAC address
o frame delivery is unreliable
o distribution – access point
o integration – with non-IEEE 802.11 network
o association –mobile stations register or associate with access points
o reassociation –if moving around, and station finds access point with
o disassociation—detach from network
o authentication—security measure
o privacy—Wired Equivalency Protocol (WEP), encrypts frames as they go
o MSDU delivery—MAC Service Data Unit delivery service
Uses Carrier Sense Multiple Access (CSMA) scheme, but instead uses Collision
Avoidance (not Collision Detection, because waste valuable transmission
Chapter 5, Wired Equivalency Protocol
Security has haunted wireless deployments since standardization. Clause 8.2 of
802.11 includes optional WEP standard…which can be used by stations to protect
data as it traverses the wireless medium, but it provides no protection past the
“WEP was initially marketed as the security solution for wireless LANs, though
its design was so flawed as to make that impossible”. p. 86
problem with cryptographic cipher used by WEP
o RC4 cipher (symmetric (secret-key) stream cipher)
o Uses stream of bits, keystream, and combined with message to produce
o To recover original text, receiver processes ciphertext w/ identical
o Key length only 40 bits
Confidentiality, integrity, authentication
WEP – frame body encryption = confidentiality; integrity check sequence =
integrity; shared-key authentication=authentication
IN REALITY, WEP falls short on all 3:
o RC4 cipher compromises confidentiality
o Integrity check poorly designed
o Authentication is to MAC addresses, not to users themselves
Type keys into your device drivers or access points BY HAND, which is the most
non-scalable protocol in use
o Keys cannot be considered secret, as they are statically entered
o WEP cannot protect against authorized insiders who also have the key
o Published keys for large organizations
Problems with WEP
Design flaws – Internet Security, Applications, Authentication and Cryptography
o Manual key mgmt
o 40 bit secret key
o stream ciphers vulnerable when key stream reused
o decryption dictionaries – due to infrequent rekeying
o CRCs not cryptographically secure, so because of frame retransmissions,
an attacker could replace a legitimate frame with something else
o Access point
Some vendors offer proprietary approaches that allow stronger public-key
authentication and random session keys
IETF’s Extensible Authentication Protocol (EAP) – Cisco’s lightweight EAP,
LEAP, is based on EAP
-802.11 does not provide a way to guarantee the authenticity and integrity of any
frames on the wireless network
O’Hara, Bob and Al Petrick. IEEE 802.11 Handbook: A Designer’s Companion.
IEEE 802.11 WLAN was designed to look and feel like any IEEE 802 wired LAN
Data carried by WLAN is not private, broadcast for all to hear…
Vagaries of electromagnetic propagation
o Both radio and infrared everything is either a reflector or an attenuator of
the signal carrying the LAN data
No simple way to deal with the change of a layer-3 network address should the
mobile station cross from one part of the network to another that is connected by
a router…solutions today using DHCP and Mobile-IP
“notions such as the nearest network printer must be defined in a different way,
when the physical location of network user may be constantly changing.” p. 5
1997 IEEE first standard for WLANs, IEEE Std. 802.11-1997
o Medium access control (MAC) sublayer
o MAC mgmt protocols and services
o 3 physical layers – infrared (IR) baseband PHY, a frequency hopping
spread spectrum (FHSS) radio in the 2.4 GHz band, and a direct sequence
spread spectrum (DSSS) radio in the 2.4 GHz band
o both 1 & 2 Mbps operation
o developing 2 new PHY layers – IEEE Std 802.11a is orthogonal frequency
domain multiplexing (OFDM) radio in the UNII bands, delivering up to
54 Mbps data rates; IEEE Std 802.11b is extension of DSSS PHY in the 2.4
GHz band, delivering up to 11Mbps data rates
o most decision-making distributed to mobile stations
o flexible to support small, transient networks and large semipermanent or
o deep power-saving modes of operations (because mobile stations run on
AP – provides buffering of traffic for a mobile station while that station is
operating in very low power state
ESS (Extended Service Set)
DS – Distribution System may be wired or unwired
MAC (Medium Access Control) supplies the functionality required to provide a
reliable delivery mechanism for user data over noisy, unreliable wireless media
WEP – “The level of encryption chosen approximates the level of protection data
might have on a wired LAN in a building with controlled access that prevents
physically connecting to the LAN wiring without authorization.” p. 19
o CSMA/CA with binary exponential backoff – “listen before talk”
o Unusual for wireless devices to receive and transmit simultaneously (why
uses collision avoidance)
o Unusual for all wireless devices in a LAN to be able to communicate
directly with all other devices
o Implements Network Allocation Vector (NAV) that is a value indicates to
a station the amount of time that remains before the medium will become
o NAV kept current by duration values transmitted in all frames
IEEE 802.11 different from others because has very specific management frame
802.11 MAC can fragment its frames in an attempt to increase the probability that
they will be delivered without errors induced by interference (microwaves)
WEP is an encryption mechanism that takes the content of a data frame, its frame
body, and passes it through an encryption algorithm---SO only frame body is
data frames is encrypted
o So WEP provides protection for content of data frames
o Does not protect against other security threats, such as traffic analysis
RC4 developed by Ron Rivest of RSA Data Security, Inc. (RSADSI, which is now
part of Network Associates, Inc.
Is symmetric stream cipher that supports variable length key
Symmetric stream cipher is one that uses the same key and algorithm for both
encryption and decryption
Kanellakis, Kelly. “White Paper: Enterasys on Standard’s Confusion.” 802.11
Planet.com. February 26, 2002 .
Originally the plan was (for most vendors and customers) to move
from an 802.11b technology to 802.11a technology. The new
technology would deliver increased bandwidth (from 11Mbps to
54Mbps) and at the same time allow wireless data transmission to
move to a less crowded area of the radio spectrum (from the
crowded 2.4 GHz band to the less crowded 5 GHz band)
In reality, WEP was designed to provide only the same level of
privacy as a wired network.
As part of the Wi-Fi standard, wireless networks can advertise
(literally broadcast) their network names to make them easy to find
and join. This advertisement is called the SSID. The first step in
providing some form of security would be to not broadcast this
name. Then it would be smart to choose a name which cannot
easily be guessed. Many organizations that set up wireless
networks do not turn on any sort of security, and they allow the
name of their network to be broadcasted to anyone who wants to
listen for it.
TEN different options for wireless data transmission outside of
Other Wireless Technologies
The next set of technologies that should be examined are ones that,
while they still exist and are being promoted, can really be
considered fringe technologies at this point. They are considered
fringe technologies for the enterprise data network because they
lack many of the features that an enterprise data network requires.
These technologies include the likes of HyperLAN 1 and 2,
Bluetooth, Ultra-Wideband, Wide Band Frequency Hopping and
HomeRF. While none of these technologies have a presence in the
mainstream wireless market - with the possible exception of
Bluetooth (and even that is a stretch) - each one is trying to gain
wireless market share. Yet, all of these technologies have some
technical merit, and may be a good solution in some cases. The
problem is that because there are so many of them, they add to the
confusion in the market. It is not expected that any of these will
ever gain significant market share, although they will continue to
exist in the market.
Security concerns are being addressed by 802.11i committee, which can been
seen as the security solution for 802.11a (which became a standard in 1999, but
no hardware was built until now)
802.11i will probably use some form of widely accepted
encryption like AES or something just as strong. For 802.11a to be
truly accepted as a technology to be for use in the enterprise it
must include 802.11i to provide a standards-based and strong
security capability. The IEEE should ratify 802.11i sometime in
the summer of 2002 timeframe.
Interoperability – will be promoted by Wireless Ethernet
Compatibility Alliance (WECA), which was the group responsible
for the Wi-Fi specification for 802.11b, and now has specification
for 802.11a (called Wi-Fi5)
o Should be at least 2 chip manufacturers
o Should be at least 3 vendor solutions
Your solution (in this case 802.11a) needs to be able to detect these
other radios and react by lowering its power output in order to keep
them from interfering with each other.
Brown, Bruce. “802.11a—Fast Wireless Networking”.
Extremetech. December 3, 2001.
we found 802.11a to be almost five times faster than 802.11b (the current
hands down wireless network standard) at short distances
802.11a and b aren’t compatible because operate at different frequencies,
2.4 GHz for 802.11b, 5 GHz for 802.11a
Wireless networking wasn't accepted initially for three reasons: throughput
(1Mbps/2Mbps) was much too slow compared to the most prevalent
(10Mbps) wired Ethernet standard; wireless adapters and access points
were significantly more expensive than wired NICs and switches; and the
first wireless products didn't work well together with wireless products from
Wi-Fi was probably the most significant, since it assured large volume
enterprise buyers that they wouldn't be stuck with proprietary, dead-end
isn't perfect. 802.11b has three major problems: limited bandwidth, radio
interference from other devices and networks, and security concerns.
can cut the actual throughput to 4 to 7Mbps (in our testing we measured
actual file transfer performance below 3Mbps for 802.11b
Bluetooth and 802.11b both use the 2.4GHz radio spectrum, as do
microwave ovens and the most powerful widely available cordless phones,
also legacy wireless devices and home control devices that use the X-10
both specifications were published in 1999 by the IEEE standards body -
but 802.11b made it to market faster.
Major advantage of a over b are higher throughput rates and increased
channel support (both of which result in higher bandwidth)
Nominal speed is 54Mbps, but with overhead actual max should range
802.11b's speeds are 11, 5.5, 2, and 1Mbps. 802.11a has a maximum
rated speed of 54Mbps but drops back to 48, 36, 24, 18, 12, 9, and 6Mbps.
A second reason for additional overall bandwidth with 802.11a is channel
support. With 802.11b, three channels are available for simultaneous
operation in the 2.4 to 2.4835GHz frequency band (there are eleven center
frequencies specified 2.412, 2.417, 2.422, 2.427, 2.432, 2.437, 2.442,
2.447, 2.452, 2.457, and 2.462 GHz, but because there is a required
25MHz spacing between active channels, only three are typically used at
one time). In 802.11a, however, eight channels can operate
simultaneously in the two lower bands of the 5GHz spectrum used in the
U.S., 5.15 to 5.25GHz and 5.25 to 5.35GHz. The center points for the eight
channels, each of which is 20MHz wide and can support 52 carrier signals,
are 5.18, 5.2, 5.22, 5.24, 5.26, 5.28, 5.30, and 5.32 GHz. The high band of
the unlicensed 5GHz spectrum (5.725 to 5.825GHz), is available, but is
more commonly used for building-to-building wireless applications.
Brown, Bruce. “Wireless Standards Up in the Air”. Extremetech. Dec. 3,
one of the most anticipated proposed standards, 802.11e, the standard
that promises to bring QoS (quality of service - essential for multimedia) to
the 802.11 world, is still in committee
November 15th (2001) the 802.11g specification was granted tentative
approval based on a compromise between proposed specifications from
Intersil and Texas Instruments.
Today 802.11b is the clear winner in business wireless networking.
Operating in the 2.4GHz frequency range, 802.11b (aka Wi-Fi) has a
nominal maximum data rate of 11Mbps, with the potential of three
simultaneous channels. 802.11b has a great advantage in that it is
accepted worldwide. One of the more significant disadvantages of 802.11b
is that the frequency band is crowded, and subject to interference from
other networking technologies, microwave ovens, 2.4GHz cordless phones
(a huge market), and Bluetooth. There are drawbacks to 802.11b,
including lack of interoperability with voice devices, and no QoS provisions
for multimedia content. Interference and other limitations aside, 802.11b is
the clear leader in business and institutional wireless networking and is
gaining share for home applications as well.
802.11a, which has just started to ship, is much faster than 802.11b, with a
54Mbps maximum data rate (actually increased to 72Mbps or 108Mbps in
a non-standard double-speed mode depending on the chipset vendor and
component manufacturer). 802.11a (and its recently announced
interoperability standard called Wi-Fi5) operates in the 5GHz frequency
range and allows eight simultaneous channels. One big advantage to
802.11a is that it isn't subject to interference from Bluetooth or any of the
other 2.4GHz frequency denizens. One big disadvantage is that it is not
directly compatible with 802.11b, and requires new bridging products that
can support both types of networks--although if you don't mind spending
the money for access points for both 11a and 11b, you can plug them into
hubs or better yet, switches on your network and they'll work just fine.
Other clear disadvantages are that 802.11a is only available in half the
bandwidth in Japan (for a maximum of four channels), and it isn't approved
for use in Europe, where HiperLAN2 is the standard. Another IEEE group,
802.11h, is working on technologies that will tweak 802.11a to work around
some of the 5GHz channels used by military in Europe. Like 802.11b,
802.11a has no provisions to optimize voice or multimedia content.
At first glance 802.11g, which operates in the 2.4GHz frequency with
mandatory compatibility with 802.11b but with a maximum data rate of
54Mbps, would be an obvious step in the race to improve wireless
networking performance while maintaining compatibility with Wi-Fi, but
there's more to the story. Far from a rubber-stamping, the 802.11g
proposal met significant resistance and many predicted it would be tossed
out, leaving the field for high-speed wireless networking to 802.11a. But
the compromise worked out last month based on proposals from Intersil
and TI is moving things along. Note that it's still a tentatively approved
specification (it won't have final approval until working versions are tested
and 90% of the voting body votes affirmatively--that's when it gets actual
So here's the deal on 802.11g technology. The standard operates entirely
in the 2.4GHz frequency, but uses a minimum of two modes (both
mandatory) with two optional modes. The mandatory modulation/access
modes are the same CCK (Complementary Code Keying) mode used by
802.11b (hence the compatibility with Wi-Fi) and the OFDM (Orthogonal
Frequency Division Multiplexing) mode used by 802.11a (but in this case in
the 2.4GHz frequency band). The mandatory CCK mode supports 11Mbps
and the OFDM mode has a maximum of 54Mbps. There are also two
modes that use different methods to attain a 22Mbps data rate--TI's
PBCC-22 (Packet Binary Convolutional Coding, rated for 6 to 54Mbps) and
Intersil's CCK-OFDM mode (with a rated max of 33Mbps).
The obvious advantage of 802.11g is that it maintains compatibility with
802.11b (and 802.11b's worldwide acceptance) and also offers faster data
rates comparable with 802.11a (at least on paper, since working silicon
isn't available). The number of channels available, however, is not
increased, since channels are a function of bandwidth, not radio signal
modulation - and on that score, 802.11a wins with its eight channels,
compared to the three channels available with either 802.11b or 802.11g.
Another disadvantage of 802.11g is that the 2.4GHz frequency will get
even more crowded. 802.11g also gives up roughly one year to 802.11a--
products for the latter are already beginning to reach the market, although
many products (those based on chipsets from companies other than
Atheros) won't be out until mid year. Companies that want faster
performance now may not have any choice but to upgrade to, or augment
existing networks with 802.11a, which could make it harder for 802.11g to