The Next Generation of Wireless
Local Area Networks
Mark Ciampa
“Disruptive Technology”
 Disruptive technology - A radical technology
or innovation that fills a new role that an
existing device or technology could not
 Examples: steamships, telephones,
automobiles, word processors, and the
Internet replacing sailing ships, telegraphs,
horses, typewriters, and libraries
 Disruptive technologies proven have
profound impact upon society and how
people live, work, and play
Wireless
 Today’s disruptive technology changing our world:
wireless
 Although wireless voice started revolution in 1990s,
wireless data communications driving force in 21st
century
 Wireless data communications replacing need be
tethered by cable to a network to surf Web, check email, or access inventory records
 Wireless made mobility possible to degree never
before possible or rarely even imagined: users
access same resources walking across college
campus as can sitting at desk
Wireless In Travel
 Airlines - All domestic air carriers (except
Allegiant Air and Spirit) offer or will offer
wireless in 2010
 Airports - All 219 US airports (except
Fairbanks, Van Nuys, Yampa Valley Regional,
5 Hawaii) offer wireless
 Hotels - Over 25,000
 Trains - San Francisco Bay Area Rapid
Transit (BART), Massachusetts Bay
Transportation Authority (MBTA)
 Limousine - Multiple major US metropolitan
 Washington State Ferry system
4
Wireless Changing All Sectors
 Finance
 Health Care
 Manufacturing
 Retail
 Logistics
 Government
 Military
 Construction
 Education
5
Wireless By The Numbers
Number of locations where wireless
data services are available increasing
40% annually
By 2011 over 250 million wireless data
devices will be sold (up from 22 million
in 2003 and zero in 1999)
Virtually all laptop computers sold
today have wireless data capabilities as
standard equipment
6
Wireless LANs
Same function of standard LAN
but without wires
Based on IEEE standards
Also called Wi-Fi
Typical range 150-375 feet
Typical bandwidth 11-54 Mbps
7
Standard WLAN
8
Wireless LAN Cells
9
IEEE WLAN Standards
802.11 (1997) – 2 Mbps
802.11b (1999) – 11 Mbps
802.11a (2001) – 54 Mbps
802.11g (2003) – 54 Mbps
10
802.11b
11 Mbps
Direct Sequence Spread
Spectrum (DSSS)
3 non-overlapping channels
2.4 GHz
Range 375 feet
11
802.11a
54 Mbps
Orthogonal frequency-division
multiplexing (OFDM)
8 non-overlapping channels
5 GHz
Range 150 feet
12
802.11g
54 Mbps
Orthogonal frequency-division
multiplexing (OFDM)
3 non-overlapping channels
2.4 GHz
Range 375 feet
13
Limitations 802.11a/b/g
Speed – Only 11 to 54 Mbps
Coverage area – Limited
Interference – Most popular
802.11b/g 2.4 GHz crowded
Security – Useless WEP and
weak WPA
14
Next Generation WLAN
Speed – Up to 600 Mbps
Coverage area – Double
indoor range, triple outdoor
range
Interference – Use either 2.4
GHz or 5 GHz
Security – Require WPA2
15
IEEE 802.11n-2009
Next Generation WLAN
Development of 802.11n
802.11n PHY layer
802.11n MAC layer
802.11n Security
Deployment strategies
17
The Next Generation of Wireless
Local Area Networks
Development of 802.11n-2009
IEEE Standard Bodies
 WLAN standards set by Institute of Electrical
and Electronics Engineers (IEEE)
 IEEE uses 2 different internal groups
 Working groups (WG), such as 802.3 (Ethernet),
802.15 (WPANs), WLANs (802.11)
 Task Groups (TG), designated by a letter following
number of WG (802.11b)
 Function TG to produce draft standard standard,
recommended practice, guideline, or supplement
to present to WG
 After TG’s work made public by creating a
publication, function of TG complete and
charter expires
IEEE 802.11-2007
 Since 1997 IEEE approved 4 standards for WLANs (IEEE
802.11, 802.11b, 802.11a, 802.11g) and several amendments
(802.11d, 802.11h, etc.)
 To reduce “alphabet soup” in 2007 combined standards and
amendments into 1 single standard
 IEEE 802.11-2007, called the IEEE Standard for Information
Technology—Telecommunications and information exchange
between systems—Local and metropolitan area network—
Specific requirements—Part 11: Wireless LAN Medium Access
Control (MAC) and Physical Layer (PHY) specifications
 Document officially retires all previous standards (802.11,
802.11a, 802.11b, 802.11d, 802.11g, 802.11h, 802.11i, 802.11j,
802.11e)
 Combines into 1 comprehensive document
IEEE 802.11 TGn
 Sep 11 2004 IEEE formed Task Group n (TGn) begin
work on dramatically new WLAN standard that
increase speed, range, and reliability
 Original estimate 802.11n ratified 2006
 TGn initially evaluated 62 different proposals
 Due to delay Wi-Fi Alliance in Jun 2007 began
certifying vendor products based Draft 2.0 and
certified 500+ products including 80+ enterprise
products in 2 years (not same as “Pre-n”)
 “Anticipated” that products based on final 802.11n
standard be backward compatible with Draft 2.0
devices
IEEE 802.11n-2009
IEEE 802.11n-2009 ratified Sep 11 2009
Amendment to IEEE 802.11-2007
802.11n significantly improved over
previous standards
Major impact is increase in maximum
raw data rate from 54 Mbps to of 600
Mbps using multiple techniques
802.11n-2009 Features
Multiple-input multiple-output (MIMO)
40 MHz channels
Data encoding
Data streams
Spatial Multiplexer
Aggregation
Block ACK
Transmission opportunity
The Next Generation of Wireless
Local Area Networks
802.11n-2009 PHY Layer
OSI Model
OSI vs. IEEE
PHY Enhancements
Multiple-Input
Multiple-Output (MIMO)
Spatial Multiplexing
Channel width
The Next Generation of Wireless
Local Area Networks
802.11n-2009 PHY Layer
Multiple-Input Multiple-Output
(MIMO)
Tenn Genetic Defect
Multiple-Lane Road
SISO
 SISO (Single-Input Single-Output) - Uses 1
transmit (TX) antenna and 1 receive (RX)
antenna
 IEEE 802.11a/b/g access points (APs) choose
best antenna to send or receive a packet, but
still uses 1 antenna at a given moment
Best Antenna
SISO
MIMO
 Long been known that multiple receive (RX)
antennas can improve reception through selection of
stronger signal or combination of individual signals
at receiver
 In mid-1990s research predicted large performance
gains from using multiple antennas at both transmit
(TX) and receive (RX), called MIMO (Multiple-Input
Multiple-Output)
 Using multiple antennas at receiver and transmitter
has revolutionized wireless communications
 Most high-rate wireless systems use MIMO
technologies (802.11n, 4G mobile phone technology
LTE, WiMAX)
MIMO
The Next Generation of Wireless
Local Area Networks
802.11n-2009 PHY Layer
Spatial Multiplexing
Multiple Antenna Techniques
Adding antennas can increase capacity
even though antennas transmit and
receive on same frequency band
simultaneously
Changes fundamental relationship
between power and capacity per
second per Hz
2 techniques can be used to take
advantage of multiple streams
Spatial Diversity
 Spatial diversity techniques increase
reliability and range by sending/receiving
redundant streams in parallel along
different spatial paths between transmit
and receive antennas
 Use of extra paths improves reliability
because unlikely all of the paths will be
degraded at the same time
 Spatial diversity can also improve range
and some performance increase (gather
larger amount of signal at receiver)
Spatial Diversity
RF Loss
 Radio Frequency (RF) signals bounce
impacted by types of objects and surfaces
encounter
 Many copies of the signal arrive at the
receiver at different times having traveled
along many different paths
 Delay is enough cause significant
degradation of signal at a single antenna
because all copies interfere with first
signal to arrive
Absorption
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Reflection
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Scattering
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Refraction
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Diffraction
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Spatial Diversity
Spatial diversity can address RF loss
Each spatial stream sent from own
antenna using its own transmitter
Because some space (10 centimeters)
between each antennae, each signal
follows slightly different path to
receiver
Spatial diversity can address RF loss
Spatial Multiplexing
 Spatial multiplexing techniques increase
performance by sending independent
streams in parallel along the different
spatial paths between transmit and
receive antennas
 It multiplexes multiple independent data
streams, transferred simultaneously
within one spectral channel of bandwidth
 Improves performance because
independent streams not slow down
streams that are already being sent
Spatial Multiplexing
SISO vs. MIMO
Spatial Multiplexing
 Independent paths between multiple
antennas can be used to much greater
effect than simply for diversity to
overcome RF loss
 Spatial multiplexing uses independent
spatial paths to send independent
streams of information at same time over
the same frequencies
 Streams will become combined as pass
across channel
 Receiver will separate and decode
Spatial Multiplexing
Notation - 2x3:2
2 - Maximum number of transmit
antennas that can be used by the radio
3 - Maximum number of receive
antennas that can be used by the radio
2 - Maximum number of data spatial
streams the radio can use
Radio that can transmit on 2 antennas
and receive on 3 but can only send or
receive 2 data streams
IEEE 802.11n
802.11n allows up to 4x4:4
Common configurations of 11n
devices are 2x2:2, 2x3:2, 3x3:2
3x3:3 is becoming common
because higher throughput due to
additional data stream
Improvements beyond 3x3 are
small
The Next Generation of Wireless
Local Area Networks
802.11n-2009 PHY Layer
Channels
40 MHz Channel Width
 802.11a/b/g channel widths 20 MHz
 802.11n doubles channel width to 40 MHz
channels by using 2 adjacent 20 MHz
channels merged into 1 40 MHz channel
 Can be enabled in the 5 GHz mode or
within the 2.4 GHz if there is knowledge
that it will not interfere with any other 2.4
GHz (Bluetooth) system using same
frequencies
Channel Guards
 11 channels (carrier) divided into 64
subcarriers of 312.5 kHz each, such that
each subcarrier can be thought of as its
own narrowband channel
 802.11a/g - 48 data subcarriers, 4 pilot
tones for control, 6 unused guard
subcarriers at each edge of the channel
 802.11n - only 4 guard subcarriers at each
edge of the channel
 Different modulation schemes (BPSK,
QPSK, QAM-16 and QAM-64)
802.11 PHY Comparison
The Next Generation of Wireless
Local Area Networks
802.11n-2009 MAC Layer
MAC Enhancements
Aggregation
Block acknowledgement
Transmission opportunity
802.11a/b/g Operation
The Next Generation of Wireless
Local Area Networks
802.11n-2009 MAC Layer
Aggregation
Aggregation
Aggregation combines multiple data
packets from upper layer into 1 larger
aggregated data frame for transmission
Overhead in multiple frame
transmissions reduced since header
overhead and interframe time is saved
Aggregation
 Aggregation of MAC Service Data Units
(MSDUs) at top of the MAC (MSDU
aggregation or A-MSDU)
 Aggregation of MAC Protocol Data Units
(MPDUs) at bottom of the MAC (MPDU
aggregation or A-MPDU)
 Aggregation packs multiple MSDUs or
MPDUs together to reduce overheads and
average them over multiple frames to
increase data rate
A-MSDU & A-MPDU
A-MSDU is composed with multiple
MSDUs
Created when MSDUs are received by
the MAC layer
Multiple MPDUs are aggregated into a
A-MPDU
A-MPDUs are created before sending to
PHY layer for transmission.
Aggregation
The Next Generation of Wireless
Local Area Networks
802.11n-2009 MAC Layer
Block Acknowledgement
Block ACK
 A-MPDU aggregation requires the use of block
acknowledgment (BlockACK) which was first introduced in
802.11e
 Block ACK mechanism in 802.11n is modified to support
multiple MPDUs in an A-MPDU
 When A-MPDU from 1 station received and errors are found in
some of aggregated MPDUs, receiving node sends a block ACK
only acknowledging those correct MPDUs
 Sender only retransmit non-acknowledged MPDUs
 Block ACK mechanism only applies to A-MPDU but not AMSDU (when MSDU is incorrect entire A-MSDU needs to be
transmitted)
Block ACK
Compressed Block ACK
 Original Block ACK message in 802.11e contains Block
ACK field with 64 × 2 bytes (2 bytes record fragment
number of the MSDUs to be acknowledged)
 Fragmentation MSDU is not allowed in 802.11n A-MPDU
 2 bytes can be reduced to 1 byte, and the block ACK
bitmap is compressed to 64 bytes
 Called compressed block ACK (overhead of block ACK is
reduced)
 Maximum number of MPDUs in 1 A-MPDU limited to 64 (1
block ACK can only acknowledge maximum 64)
 Station transmitting multiple data frames can request
one block ACK for all frames instead of using legacy
acknowledgments to each frame
The Next Generation of Wireless
Local Area Networks
802.11n-2009 MAC Layer
Transmission Opportunity (TXOP)
(Reverse Direction)
CSMA/CA
 802.11 standard uses Carrier Sense Multiple Access
with Collision Avoidance (CSMA/CA) that attempts to
avoid collisions
 The time most collisions occur is immediately after a
station completes its transmission, because all other
stations wanting to transmit have been waiting to for
medium to clear
 Once medium is clear they all try to transmit at same
time, which results in more collisions and delays
 CMSA/CA has all stations wait a random amount of
time (backoff interval) after medium is clear (slot
time)
Transmission Opportunity
 Transmission opportunity (TXOP) defines
period of time for station accessing
channel to transmit multiple data frames
 During TXOP period, station can transmit
multiple data frames without entering
backoff procedure
 Reduces overhead due to contention and
backoff and enhances efficiency of
channel utilization
TXOP & Block ACK
Transmission Opportunity
 Reverse direction mechanism allows holder of
TXOP to allocate the unused TXOP time to its
receivers to enhance the channel utilization and
performance of reverse direction traffic flows
 2 types of stations are defined: RD initiator and RD
responder.
 RD initiator is station that holds TXOP and has the
right to send Reverse Direction Grant (RDG) to RD
responder
 RDG is marked in the 802.11n header and is sent
with the data frame to the RD responder
Transmission Opportunity
 When the RD responder receives the data
frame with RDG, it responds with RDG
acknowledgement if it has data to be sent (or
without RDG if no data)
 If acknowledgement marked with RDG, the RD
initiator will wait for transmission from RD
responder, which will start with SIFS or
Reduced InterFrame Spacing (RIFS) interframe
time after the RDG acknowledgement is sent
 If there is still data to be sent from the RD
responder, it can mark RDG in the data frame
header to notify the initiator
TXOP & Block ACK
Transmission Opportunity
 The RD initiator still has the right to accept the
request
 To reject the new RDG request, the initiator just
ignores it
 The major enhancement in reverse direction
mechanism is the delay time reduction in reverse
link traffic
 Reverse direction data packets do not need to wait
in queue until the station holds TXOP but can
be transmitted immediately when the RD
responder is allocated for the remaining TXOP
 This feature can benefit a delay-sensitive service
like VoIP
The Next Generation of Wireless
Local Area Networks
802.11n-2009 Security
Wi-Fi Protected Access 2 (WPA2)
 Wi-Fi Alliance introduced Wi-Fi Protected
Access 2 (WPA2) in Sep 2004
 WPA2 based on the final IEEE 802.11i
 WPA2 uses AES for data encryption and
supports authentication server or PSK
technology
 WPA2 allows both AES and TKIP clients to
operate in the same WLAN; IEEE 802.11i
only recognizes AES
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AES
 AES algorithm processes blocks of 128 bits, yet the
length of the cipher keys and number of rounds can
vary, depending upon the level of security that is
required
 Available key lengths are of 128, 192 and 256 bits,
and the number of available rounds are 10, 12, and
14
 Only the 128-bit key and 128-bit block are mandatory
for WPA2
 It is recommended that AES encryption and
decryption be performed in hardware because of the
computationally intensive nature of AES
85
AES Security
86
802.1x
 IEEE 802.11i authentication and key
management uses IEEE 802.1x (originally
developed for wired networks)
 802.1x port security (device requests access
to network prevented from receiving any
traffic until its identity can be verified)
 802.1x blocks all traffic on port-by-port basis
until the client is authenticated using
credentials stored on authentication server
87
802.1x Authentication
 The supplicant is device which requires secure
network access and sends request to an
authenticator that serves as an intermediary device
(authenticator can be an access point on a wireless
network or a switch on a wired network)
 The authenticator sends request from supplicant to
authentication server, which accepts/rejects the
supplicant’s request and sends that information
back to the authenticator, which in turn grants or
denies access to the supplicant
 Strength of the 802.1x protocol is that supplicant
never has direct communication with authentication
server
88
802.1x
89
802.11n Security
 All 802.11n products are required to support WPA2
 Advanced Encryption Standard (AES)
 Pre-shared key (PSK) or 802.1X authentication
 Caveat
 WLANs that must support both 802.11a/b/g and
802.11n clients may be forced to permit TKIP
 Doing so makes it possible for older non-AES
clients to connect securely.
 802.11n prohibits high-throughput data rates
when using TKIP
Adding Clients
 3 new methods for securely adding clients to
802.11n network
 Shifts security setup responsibility from the
user to the network itself
 Avoids end-user configuration of security
parameters reduces confusion and error
 Can eliminate the need for manual WLAN
configuration interfaces
 Called Wi-Fi Protected Setup (WPS)
Personal Information Number
(PIN)
 All devices are associated with a unique number
printed on device or its packaging, or displayed by
device
 To enroll a device, its PIN is entered into a "WPS
registrar“ (usually configuration page on AP)
 Registrar and device complete a secure over-the-air
WPS handshake, during which registrar assigns
random PSK to the device
 The device then self-enables WPA2-PSK, using
those WPS-supplied SSID and PSK values
Push-Button Configuration
(PBC)
 Physical WPS buttons must be pushed
simultaneously on AP and device to be
registered
 For a short period, the AP listens for and
accepts any nearby device requesting WPS
enrollment
 Method eliminates PIN entry but creates a
brief window of opportunity during which
unauthorized devices might conceivably be
added
Near-Field Communication
(NFC)
 When NFC-enabled client device is placed
within 10 centimeters of the NFC "target
mark" on AP, the WPS registrar uses NFC
communication to read client's identity from
a token embedded in device
 Once approved, that device is given the SSID
and PSK that it needs to complete automated
WPA2-PSK setup and join the WLAN
The Next Generation of Wireless
Local Area Networks
Deployment Strategies &
Summary
Operation Modes
3 modes of operation
Non-HT = Follows 802.11a/b/g
mode
Greenfield = No backward
compatibility
Mixed = Addresses compatibility
with legacy 802.11a/b/g devices
Mixed Mode
 Backward compatibility with existing 802.11a/b/g devices
that allows older devices to understand information
necessary to allow 802.11n devices to operate in same
area
 Mixed mode protection mechanism for 802.11n similar to
protection mechanism of 802.11g
 802.11n transmits a radio preamble and signal field
(control frame) in 20 MHz can be decoded by 802.11a/g
and gives enough information allow a/g to know another
transmission on air and how long transmission will last
 After sending this legacy preamble and signal field
802.11n device sends remaining information using
802.11n rates and its multiple spatial streams, including
an 802.11n preamble and signal field
 Performance impact on 802.11n devices
Wi-Fi Draft 2 Certification
 IEEE ratified 802.11n standard Sep 2009
 Wi-Fi Alliance certifying products based on Draft 2.0
since 2007
 Covers both 20 MHz and 40 MHz wide channels
 Maximum 2 spatial streams
 Maximum throughputs of 144.4 Mbps for 20 MHz
and 300 Mbps for 40 MHz
 “Wi-Fi CERTIFIED n products must be backward
compatible . . . However, keep in mind that Wi-Fi
CERTIFIED 802.11n draft 2.0 devices may not include
some of the advanced features included in Wi-Fi
CERTIFIED n products.”
Wi-Fi Certificate
99
Device Categories
 Low (under $90) - Don't need maximum
performance, but who can benefit from
802.11n's improved range and speed
 Midrange ($90-$150) – Fast wireless
speeds and Gigabit Ethernet
 High ($150-$200) - Dual-band routers that
support both 2.4GHz and 5GHz for
networked multimedia devices that need
uncluttered bandwidth to stream media
Deployment Strategies
 To achieve maximum output pure 802.11n 5 GHz
network is recommended (has substantial capacity
due to many non-overlapping radio channels and
less radio interference)
 Yet 802.11n-only network may be impractical
because requires replacement of 802.11b/g
wireless NIC adapters
 May be more practical in short term to operate
mixed wireless network
 Use 802.11n dual-band router and put older
802.11b/g traffic on 2.4 GHz and newer 802.11n
traffic on 5 GHz
Throughput Increases
 Highest data rate in 802.11a/g is 54 Mbps vs.
highest data rate in 802.11n is 600 Mbps
 Increase of a factor of 11
 40% - Use of 4 antennas
 20% - Double width channels of 40 MHz
 40% - Tweaking coding to reduce overhead.
 Yet many devices may not have 4 antennas
 Up to 3 antennas are commonly supported by
NICs
 Expected that clients will tend to have fewer
antennas for space and power reasons, while APs
will tend to have more antennas for performance
reasons
Range
The Next Generation of Wireless
Local Area Networks
Mark Ciampa
Mark.Ciampa@wku.edu