the next generation of wireless local area networks mark ciampa

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 e-mail, 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

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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

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Wireless Changing All Sectors

Finance Health Care Manufacturing Retail Logistics Government Military Construction Education

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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

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Wireless LANsSame function of standard LAN

but without wiresBased on IEEE standardsAlso called Wi-FiTypical range 150-375 feet Typical bandwidth 11-54 Mbps

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Standard WLAN

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Wireless LAN Cells

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IEEE WLAN Standards

802.11 (1997) – 2 Mbps 802.11b (1999) – 11 Mbps802.11a (2001) – 54 Mbps802.11g (2003) – 54 Mbps

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802.11b11 MbpsDirect Sequence Spread

Spectrum (DSSS)3 non-overlapping channels2.4 GHzRange 375 feet

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802.11a54 MbpsOrthogonal frequency-division

multiplexing (OFDM)8 non-overlapping channels5 GHzRange 150 feet

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802.11g54 Mbps Orthogonal frequency-division

multiplexing (OFDM)3 non-overlapping channels2.4 GHzRange 375 feet

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Limitations 802.11a/b/g

Speed – Only 11 to 54 MbpsCoverage area – Limited Interference – Most popular

802.11b/g 2.4 GHz crowdedSecurity – Useless WEP and

weak WPA

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Next Generation WLAN

Speed – Up to 600 MbpsCoverage area – Double

indoor range, triple outdoor range

Interference – Use either 2.4 GHz or 5 GHz

Security – Require WPA2

IEEE 802.11n-2009

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Next Generation WLAN

Development of 802.11n802.11n PHY layer802.11n MAC layer802.11n SecurityDeployment strategies


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-2009IEEE 802.11n-2009 ratified Sep 11 2009Amendment to IEEE 802.11-2007 802.11n significantly improved over

previous standardsMajor 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 channelsData encodingData streamsSpatial MultiplexerAggregationBlock ACKTransmission opportunity


802.11n-2009 PHY Layer

OSI Model

OSI vs. IEEE

PHY Enhancements

Multiple-Input Multiple-Output (MIMO)

Spatial MultiplexingChannel width



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

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)



Spatial Multiplexing

Multiple Antenna TechniquesAdding 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 DiversitySpatial 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 LossRadio 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

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Absorption

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Reflection

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Scattering

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Refraction

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Diffraction

Spatial DiversitySpatial diversity can address RF lossEach spatial stream sent from own

antenna using its own transmitterBecause some space (10 centimeters)

between each antennae, each signal follows slightly different path to receiver

Spatial diversity can address RF loss

Spatial MultiplexingSpatial 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

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

Notation - 2x3:22 - Maximum number of transmit

antennas that can be used by the radio3 - Maximum number of receive

antennas that can be used by the radio2 - 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 802.11n802.11n allows up to 4x4:4Common configurations of 11n

devices are 2x2:2, 2x3:2, 3x3:23x3:3 is becoming common

because higher throughput due to additional data stream

Improvements beyond 3x3 are small



Channels

40 MHz Channel Width802.11a/b/g channel widths 20 MHz802.11n 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 Guards11 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


802.11n-2009 MAC Layer

MAC Enhancements

AggregationBlock acknowledgementTransmission opportunity

802.11a/b/g Operation



Aggregation

AggregationAggregation 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

AggregationAggregation 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



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 A-

MSDU (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



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


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


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


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


802.11n-2009 Security

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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

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AES Security

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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

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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

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802.1x

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 TKIPDoing 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


Deployment Strategies & Summary

Operation Modes

3 modes of operationNon-HT = Follows 802.11a/b/g

modeGreenfield = No backward

compatibilityMixed = 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 2007Covers both 20 MHz and 40 MHz wide channelsMaximum 2 spatial streamsMaximum 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.”

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Wi-Fi Certificate

Device CategoriesLow (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 antennas20% - Double width channels of 40 MHz 40% - Tweaking coding to reduce overhead.

Yet many devices may not have 4 antennasUp to 3 antennas are commonly supported by

NICsExpected that clients will tend to have fewer

antennas for space and power reasons, while APs will tend to have more antennas for performance reasons


Mark Ciampa

[email protected]

the next generation of wireless local area networks mark ciampa

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