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Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards. The 802 wireless family IEEE 802.11 The physical layer The MAC layer Quality of service: 802.11e MIMO: 802.11n Management tools. Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards.

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Redes inal mbricas tema 2 c wireless lans the ieee 802 11 standards

Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards

The 802 wireless family

IEEE 802.11

The physical layer

The MAC layer

Quality of service: 802.11e

MIMO: 802.11n

Management tools


Redes inal mbricas tema 2 c wireless lans the ieee 802 11 standards1

Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards

The 802 wireless family

IEEE 802.11

The physical layer

The MAC layer

Quality of service: 802.11e

MIMO: 802.11n

Management tools


Ieee 802 active working groups and study groups

IEEE 802 Active Working Groups and Study Groups

  • 802.1 HigherLayer LAN ProtocolsWorkingGroup

    • Link Security ExecutiveCommitteeStudyGroupisnowpart of 802.1

  • 802.3 Ethernet WorkingGroup

  • 802.11 Wireless LAN WorkingGroup

  • 802.15 Wireless Personal Area Network (WPAN) WorkingGroup

  • 802.16 BroadbandWireless Access WorkingGroup

  • 802.17 ResilientPacket Ring WorkingGroup

  • 802.18 Radio Regulatory TAG

  • 802.19 Coexistence TAG

  • 802.20 Mobile BroadbandWireless Access (MBWA) WorkingGroup

  • 802.21 Media IndependentHandoffWorkingGroup

  • 802.22 Wireless Regional Area Networks


Historical notes

Historical notes

  • The IEEE Working Group for WLAN Standards was created in 1997:

    • http://www.ieee802.org/11/index.shtml

  • Defines the MAC and 3 different physical layers that work at 1Mbps and 2Mbps:

    • Infrared (IR) in base band

    • Frequency hopping spread spectrum (FHSS), band de 2,4 GHz

    • Direct sequence spread spectrum (DSSS), band de 2,4 GHz

  • IEEE Std 802.11b (September 1999):

    • Extension of DSSS; Up to 11 Mbps

  • IEEE Std 802.11a (December 1999):

    • A different physical layer (OFDM): Orthogonal frequency domain multiplexing

    • Up to 54 Mbps

  • IEEE Std 802.11g (June 2003)

  • ...


Evolution of the ieee 802 11 standard

Evolution of the IEEE 802.11 standard

  • OFFICIAL IEEE 802.11 WORKING GROUP PROJECT TIMELINES

    • IN PROCESS  - Standards, Amendments, and RecommendedPractices

    • http://grouper.ieee.org/groups/802/11/Reports/802.11_Timelines.htm

  • 802.11p: Inter car communications

    • Communication between cars/road side and cars/cars

    • Planned for relative speeds of min. 200km/h and ranges over 1000m

    • Usage of 5.850-5.925GHz band in North America

  • 802.11s: Mesh Networking

    • Design of a self-configuring Wireless Distribution System (WDS) based on 802.11

    • Support of point-to-point and broadcast communication across several hops

  • 802.11r: Faster Handover between BSS

    • Secure, fast handover of a station from one AP to another within an ESS

    • Current mechanisms (even newer standards like 802.11i) plus incompatible devices from different vendors are massive problems for the use of, e.g., VoIP in WLANs

    • Handover should be feasible within 50ms in order to support multimedia applications efficiently


Evolution of the ieee 802 11 standard1

Evolution of the IEEE 802.11 standard

  • Other interesting groups

    • 802.11t: Performance evaluation of 802.11 networks

      • Standardization of performance measurement schemes

    • 802.11v: Network management

      • Extensions of current management functions, channel measurements

      • Definition of a unified interface

    • 802.11w: Securing of network control

      • Classical standards like 802.11, but also 802.11i protect only data frames, not the control frames. Thus, this standard should extend 802.11i in a way that, e.g., no control frames can be forged.

  • Note: Not all “standards” will end in products, many ideas get stuck at working group

  • Standards are available here: http://standards.ieee.org/getieee802/


Ieee 802 11 and wifi

IEEE 802.11 and WiFi

  • Wi-Fi is a set of standards for wireless networks based on IEEE 802.11 specifications.

  • Wi-Fi is a trademark of the Wi-Fi Alliance (formerly the Wireless Ethernet Compatibility Alliance), the trade organization that tests and certifies that equipments meet the IEEE 802.11x standards.

  • The main problem which is intended to solve through normalization is compatibility. This means that the user is assured that all devices having the seal Wi-Fi can work together regardless of the manufacturer of each.

  • A complete list of devices that have the certification Wi-Fi:

    • http://certifications.wi-fi.org/wbcs_certified_products.php?lang=en.


Redes inal mbricas tema 2 c wireless lans the ieee 802 11 standards2

Redes Inalámbricas – Tema 2.CWireless LANs: the IEEE 802.11 standards

The 802 wireless family

IEEE 802.11

The physical layer

The MAC layer

Quality of service: 802.11e

MIMO: 802.11n

Management tools


Spread spectrum transmission

Spread Spectrum Transmission


Comparison of wireless modulation schemes

Comparison of Wireless Modulation Schemes

  • FHSS transmissions less prone to interference from outside signals than DSSS

  • WLAN systems that use FHSS have potential for higher number of co-location units than DSSS

  • DSSS has potential for greater transmission speeds over FHSS

  • Throughput much greater for DSSS than FHSS

    • Amount of data a channel can send and receive


Orthogonal frequency division multiplexing ofdm

Orthogonal Frequency Division Multiplexing (OFDM)

  • With multipath distortion, receiving device must wait until all reflections received before transmitting

    • Puts ceiling limit on overall speed of WLAN

  • OFDM: Send multiple signals at same time

    • High number of low BW ‘modems’ are used, each on a different sub channel

    • The ‘slow’ sub channels are multiplexed into a ‘fast’ combined channel

    • Error correction is done with FEC and bit stripping

  • Avoids problems caused by multipath distortion

  • Used in 802.11a networks


Notion of a channel

Notion of a channel

Wireless communication is carried over a set of frequencies called a channel

Signal Power

Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison


Channels in wireless

Channels in Wireless

Available spectrum is typically divided into disjoint channels

Channel A

Channel B

Channel C

Channel D

Fixed Block of Radio Frequency Spectrum

Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison


Ideal spectrum usage

Ideal Spectrum Usage

  • Use entire range of frequencies spanning a channel

  • Usage drops down to zero right outside a channel

Channel A

Channel B

Power

Frequency

Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison


Realistic spectrum usage

Channel A

Channel B

Wastage of spectrum

Real Usage

Realistic Spectrum Usage

  • In reality, this is what communication circuits can achieve

  • Results in inefficient usage of spectrum

Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison


Realistic spectrum usage1

Channel A

Channel B

Wastage of spectrum

Real Usage

Realistic Spectrum Usage

Is it possible to eliminate such inefficiencies ?

Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison


Define a new channel

Channel A

Channel B

Channel A’

Define a new channel

  • Define a new channel as shown

  • Overlaps with neighboring two channels

  • Called a `partially overlapped’ channel

Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison


Define a new channel1

Channel A

Channel B

Channel A’

Define a new channel

  • Channel A’ would interfere with both A and B

  • Is it possible to get any gains from using A, A’ and B ?

Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison


802 11b channels

In the UK and most of EU: 13 channels, 5MHz apart, 2.412 – 2.472 GHz

Each channel is 22MHz

Significant overlap

Best channels are 1, 6 and 11

802.11b Channels


An 802 11 experiment

Link A Ch 1

Link B Ch 3

Link C Ch 6

Amount of Interference

An 802.11 Experiment

  • Can we use channels 1, 3 and 6 without interference ?

Ch 1

Ch 3

Ch 6

Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison


An 802 11 experiment1

Link A Ch 1

Link B Ch X

An 802.11 Experiment

35 meters

60 meters

Thanks to: Mishra, Shrivastava, Banerjee, and Arbaugh, The University of Wisconsin, Madison


Ieee 802 11b

IEEE 802.11b

  • Data rate

    • 1, 2, 5.5, 11 Mbit/s, depending on SNR

    • User data rate max. approx. 6 Mbit/s

  • Transmission range

    • 300m outdoor, 30m indoor

    • Max. data rate ~10m indoor

  • Frequency

    • Free 2.4 GHz ISM-band

  • Security

    • Limited, WEP insecure, SSID

  • Availability

    • Many products and vendors

  • Connection set-up time

    • Connectionless/always on

  • Quality of Service

    • Best effort, no guarantees (unless polling is used, limited support in products)

  • Manageability

    • Limited (no automated key distribution, sym. Encryption)

  • Pros

    • Many installed systems and vendors

    • Available worldwide

    • Free ISM-band

  • Cons

    • Heavy interference on ISM-band

    • No service guarantees

    • Relatively low data rate


Ieee 802 11a

IEEE 802.11a

  • Data rate

    • 6, 9, 12, 18, 24, 36, 48, 54 Mbit/s, depending on SNR

    • User throughput (1500 byte packets): 5.3 (6), 18 (24), 24 (36), 32 (54)

    • 6, 12, 24 Mbit/s mandatory

  • Transmission range

    • 100m outdoor, 10m indoor

      • E.g., 54 Mbit/s up to 5 m, 48 up to 12 m, 36 up to 25 m, 24 up to 30m, 18 up to 40 m, 12 up to 60 m

  • Frequency

    • Free 5.15-5.25, 5.25-5.35, 5.725-5.825 GHz ISM-band

  • Security

    • Limited, WEP insecure, SSID

  • Availability

    • Some products, some vendors

  • Connection set-up time

    • Connectionless/always on

  • Quality of Service

    • Best effort, no guarantees (same as all 802.11 products)

  • Manageability

    • Limited (no automated key distribution, sym. Encryption)

  • Pros

    • Fits into 802.x standards

    • Free ISM-band

    • Available, simple system

    • Uses less crowded 5 GHz band

    • Higher data rates

  • Cons

    • Shorter range


Ieee 802 11g

IEEE 802.11g

  • Ratified in June 2003 by the IEEE Standards Board

    • standard preliminary draft submitted in December 2001;

  • Uses the 2.4 GHz band

    • OFDM and codification PBCC

  • Backward compatibility IEEE 802.11b

    • They can co-exist in the same WLAN

  • New transmission speeds: 6, 9, 12, 18, 24, 36, 48 & 54 Mbps


Examples of the physical parameters of a real device al

Examples of the physical parameters of a real deviceal

  • DATA SHEET of a Cisco Aironet 802.11a/b/g CardBusWireless LAN ClientAdapter


Wifi and health

WiFi and health

RFR'sbiologicaleffects are measured in terms of specificabsorptionrate (SAR) -- howmuchenergyis absorbed intohumantissue -- whichisexpressed in Watts per kilogram (W/kg). A dangerouslevel (by U.S. standards) isconsideredtobeanythingabove 0.08 W/kg.Thusfar, RFR measurementsforWi-Fi, both at home and abroad, are a minute fraction of emissionsthatcouldamounttothislevel. Wi-Fi, in fact, emitslessthanothercommonsources of RFR likemicrowaves and mobilephones. Sincemobilephoneswererecentlycleared as a potentialcarcinogenby a comprehensive, long-termstudyconductedbytheDanishInstitute of CancerEpidemiology in Copenhagen, itseemsveryunlikelythatdevicesemitting a lower (and lessfrequent) levelcouldbe more dangerous.

  • ByNaomiGraychase, January 12, 2007

    • http://www.wi-fiplanet.com/news/article.php/3653711

  • More information:

    • http://www.fcc.gov/oet/rfsafety/


Redes inal mbricas tema 2 c wireless lans the ieee 802 11 standards3

Redes Inalámbricas – Tema 2.CWireless LANs: the IEEE 802.11 standards

The 802 wireless family

IEEE 802.11

The physical layer

The MAC layer

Quality of service: 802.11e

MIMO: 802.11n

Management tools


Available architectures

Available architectures

  • Independent Basic Service Set (IBSS)

    • is the simplest of all IEEE 802.11 networks in that no network infrastructure is required. As such, an IBSS is simply comprised of one or more Stations which communicate directly with each other.

    • Do not confuse it with ad hoc!!

  • infrastructure Basic Service Set (BSS)

    • Components:

      • Station (STA)

      • Access Point (AP)or Point Coordinator (PC)

    • Basic Service Set (BSS)

    • Extended Service Set (ESS)


The mac basics

Services with

contention

Services without

contention

Point CoordinationFunction (PCF)

MAC

Distributed Coordination Function (DCF)

DIFS

DIFS

Contention window

PIFS

busy medium

SIFS

defer access

slot

The MAC basics

CSMA/CA with binary exponential backoff

The protocol, at its minimum, consists of two frames: data and ack

The 5 timing values:

  • Slot time

  • SIFS: short interframe space (< slot time)

  • PIFS: PCF interframe space (=SIFS+1slot)

  • DIFS: DCF interframe space (=SIFS+2slots)

  • EIFS: extended interframe space


Dcf example

B1 = 25

B1 = 5

wait

data

data

wait

B2 = 10

B2 = 20

B2 = 15

DCF example

  • The backoff intervals are chosen within the contention window. That is in the interval [0, CW]

  • The CW can vary between 31 slots (CWmin) and 1023 slots (CWmax)

  • CW increases after a failed transmission and re-initialized after a successful transmission

  • B1 and B2 are the backoff intervals in STA 1 and 2

  • CW = 31


A couple of problematic configurations

Hidden node

Exposed node

A couple of problematic configurations

A

A

B

C

B

C

D


Hidden nodes situations

Hiddennodessituations

MU3 cannot hear MU1 or MU2 because of the distance

The obstacle prevents MU1 and MU2 from hearing one another


Rts cts mechanism

SIFS

SIFS

SIFS

RTS/CTS mechanism

  • Based on the network allocation vector (NAV)

DIFS+contention

source

data

RTS

destination

ACK

CTS

DIFS

Other STA

Contention window

NAV (RTS)

NAV (CTS)

defer access


Pcf point coordination function

PIFS

SIFS

SIFS

SIFS

PIFS

SIFS

SIFS

PC

Data+Poll

Data+Poll

Data+Poll

CF-End

Beacon

DATA+ACK

ACK

SIFS

(no response)

STA1

CP

Contention Free Period

CP

NAV

Reset

STA2

Station 2 sets NAV(Network Allocation Vector)

Station 3 is hidden to the PC, it does not set the NAV.

It continues to operate in DCF.

STA3

Time

PCF: Point Coordination Function

  • The beacons are used to maintain synchronization of the timers in the stations and to send control information

  • The AP generates the beacons at regular intervals

  • The stations know when the next beacon will arrive

    • the target beacon transmission time (TBTT) are announced in the previous beacon


Frames structure

Función

To DS

From DS

Addr. 1

Addr. 2

Addr. 3

Addr. 4

IBSS

0

0

RA = DA

SA

BSSID

-

From the AP

0

1

RA = DA

BSSID

SA

-

To the AP

1

0

RA = BSSID

SA

DA

-

Wireless DS

1

1

RA

TA

DA

SA

Frames structure

Types of addresses:

  • Source address (SA)

  • Destination Address (DA)

  • Transmitter Address (TA)

  • Receiver Address (RA)

  • BSS identifier (BSSID)

  • management (00)

  • control (01),

  • data (10),

  • reserved (11)


Addressing and ds bits

Función

To DS

From DS

Addr. 1

Addr. 2

Addr. 3

Addr. 4

IBSS

0

0

RA = DA

SA

BSSID

-

From the AP

0

1

RA = DA

BSSID

SA

-

To the AP

1

0

RA = BSSID

SA

DA

-

Wireless DS

1

1

RA

TA

DA

SA

Addressing and DS bits

DS

TA

RA (BSSID)

SA/TA

AP

AP

SA

RA

Client

AP

DA

Client

DA

Server

Server


Services

Services

  • The IEEE 802.11 architecture defines 9services

  • Station services:

    • Authentication

    • Deauthentication

    • Privacy  WEP

    • Data delivery

  • Distribution services:

    • Associationgenerate a connection between a STA and a PC

    • Disassociation

    • Reassociationlike association but informing the previous PC

    • Distribution

    • integration

Similar to plugging in and out in a regular network


State variables and services

State variables and services

In a IBSS there is no auth. nor ass. Data service is allowed

State 1:

unauthenticated,

unassociated

Class 1

frames

Successful authentication

Deauthentication notification

State 2:

authenticated,

unassociated

Class 1 & 2 frames

Deauthentication notification

Successful authenticationor reassociation

Disassociation notification

State 3:

authenticated,

associated

A STA can be authenticated by several AP but associated only with one AP

Class 1, 2 & 3 frames


Bssid y ssid

BSSID y SSID

  • BSSID (Basic Service Set Identity)

    • BSS: MAC address of the AP

    • Ad-Hoc: 46 bits random number

  • SSID (Service Set ID)

    • Known as the Network Name because it is basically the name that identifies the WLAN

    • Lenght: 0~32 octets

      • 0: it is the broadcast SSID

    • Used to distinguish WLAN among them

    • The access points and stations who want to connect to a single WLAN must use the same SSID


The extended service set ess

BSS

AP

WLAN

LAN

The Extended Service Set (ESS)

Distribution System (DS)

  • Inter-accespoint protocol (IAPP)


Iapp and the task group f

IAPP and the Task Group f

  • Scope of Project: to develop recommended practices for an Inter-Access Point Protocol (IAPP) which provides the necessary capabilities to achieve multi-vendor Access Point interoperability across a Distribution System supporting IEEE P802.11 Wireless LAN Links.

  • Purpose of  Project: ... including the concepts of Access Points and Distribution Systems. Implementation of these concepts where purposely not defined by P802.11 ... As 802.11 based systems have grown in popularity, this limitation has become an impediment to WLAN market growth. This project proposes to specify the necessary information that needs to be exchanged between Access Points to support the P802.11 DS functions. The information exchanges required will be specified for, one or more Distribution Systems; in a manner sufficient to enable the implementation of Distribution Systems containing Access Points from different vendors which adhere to the recommended practices

  • Status

    • The 802.11F Recommendation has been ratified and published in 2003.

    • IEEE 802.11F was a Trial Use Recommended Practice. The IEEE 802 Executive Committee approved its withdrawal on February 03, 2006


Wireless distribution system

Wireless Distribution System

  • IEEE 802.11, WDS means

    • Multiple wireless “ports” inside the access-point, to wirelessly interconnect cells (access-points connecting to other access-points)

  • pre-IEEE 802.11, did not support WDS:

    • Three ports exist in one access-point (one Ethernet, and two wireless cells)

    • One wireless backbone extension can be made (using two radio modules in the access-point)

  • WDS allows:

    • Extending the existing infrastructure with wireless backbone links

    • Totally wireless system without any wired backbones, needed in locations where large areas are to be covered and wiring is not possible


Wds examples

Bridgingtwowirednetworks

As a repeater to extend a network

WDS examples


Operational processes traffic flow wds operation

Bridge learn

table

Bridge learn

table

Packet for STA-2

ACK

ACK

Packet for STA-2

ACK

Packet for STA-2

Operational processesTraffic flow - WDS operation

AP-1000 or AP-500

STA-2

AP-1000 or AP-500

2

Avaya Wireless PC-Card

STA-1

2

STA-2

Association table

2

STA-2

Avaya Wireless PC-Card

STA-1

2

Association table

Wireless Backbone

WDS

Relay

STA-1

WDS

Relay

BSS-B

STA-2

STA-1

BSS-A


Linksys wireless g access point

Linksys Wireless-G Access Point


Linksys wireless g access point1

Linksys Wireless-G Access Point


Linksys wireless g access point2

Linksys Wireless-G Access Point


Linksys wireless g access point3

Linksys Wireless-G Access Point


Linksys wireless g access point4

Linksys Wireless-G Access Point


Linksys wireless g access point5

Linksys Wireless-G Access Point


Linksys wireless g access point6

Linksys Wireless-G Access Point


Linksys wireless g access point7

Linksys Wireless-G Access Point


Linksys wireless g access point8

Linksys Wireless-G Access Point


Linksys wireless g access point9

Linksys Wireless-G Access Point


Linksys wireless g access point10

Linksys Wireless-G Access Point


Redes inal mbricas tema 2 c wireless lans the ieee 802 11 standards4

Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards

The 802 wireless family

IEEE 802.11

The physical layer

The MAC layer

Quality of service: 802.11e

MIMO: 802.11n

Management tools


Limitations of the mac standard for qos

Limitations of the MAC standard for QoS

  • DCF (Distributed Coordination Function)

    • Only support best-effort services

    • No guarantee in bandwidth, packet delay and jitter

    • Throughput degradation in the heavy load

  • PCF (Point Coordination Function)

    • Inefficient and complex central polling scheme

    • Unpredictable beacon frame delay due to incompatible cooperation between CP and CFP modes

    • Transmission time of the polled stations is unknown


Overview of 802 11e

Overview of 802.11e

  • Task group e formed in Sep. 1999 and Approved in July 2005

    • Current version: IEEE P802.11e/D13.0

    • Backwardly compatible with the DCF and PCF

  • New QoS mechanism: HCF (Hybrid Coordination Function)

    • Contention-based channel access

      • EDCA (Enhanced Distributed Channel Access)

        • was Enhanced Distributed Coordination Function (EDCF)

    • Controlled channel access (includes polling)

      • HCCA (HCF controlled channel access)

  • The station that operates as the central coordinator for all other stations within the same QoS supporting BSS (QBSS) is called the hybrid coordinator (HC).

    • The HC reside inside an AP

  • A BSS that includes an 802.11e-compliant HC is referred to as a QBSS.


Edca parameters for ac

EDCA parameters for AC

  • 4 access categories (AC),

  • AIFS[AC] = SIFS + AIFSN[AC] *aSlotTime, AIFSN[AC]  2.


Edca and ac mapping

EDCA and AC Mapping


Hcf hybrid coordination function

HCF: Hybrid Coordination Function

  • During CFP

    • Poll STAs and give a station the permission to access channel

    • Starting time and maximum duration of each TXOP are specified by the HC

  • During CP

    • Can use the EDCA rules

    • HC can issue polled TXOPs in the CP by sending CF-Poll after a PIFS idle period

    • Controlled Contention

      • Allows STAs to request the allocation of polled TXOPs

      • STAs send resource request frames with the requested TC and TXOP duration

      • HC sends an ACK for resource request to the STA


Hcf superframes

HCF superframes


Performance

Performance


Qos 802 11e and wmm

QoS: 802.11e and WMM™

  • WMM (Wi-Fi Multimedia)

    • Prioritized QoS subset of 802.11e draft

    • Widely accepted by 802.11e members

    • Added to Wi-Fi certification in September 2004


Wmm for video

WMM™ for Video

Source: Wi-Fi Alliance


Redes inal mbricas tema 2 c wireless lans the ieee 802 11 standards5

Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards

The 802 wireless family

IEEE 802.11

The physical layer

The MAC layer

Quality of service: 802.11e

MIMO: 802.11n

Management tools

Thanks to: Paul Young / Bernie Rasenberger


What is wireless n

What is “Wireless N”?

  • 802.11n is the long anticipated update to Wi-Fi standards.

  • Ratified by IEEE in September 2009.

  • “Pre-N” wireless devices were available prior to ratification (Draft N) with speeds of up to 300Mb/s and range of up to 300 metres (300x300).

  • Increases channel utilisation through MAC aggregation (40MHz) and increased range & throughput through the use of MIMO (Multiple Input/Multiple Output) technology of 2+ antennas.

  • Will co-exist with 802.11b/g networks, but can degrade them because of channel overlap caused by MAC aggregation.

  • Same performance hit if you mix 802.11n clients with 802.11b clients, as you get with mixing 802.11g & 802.11b clients (OFDM).


What is wireless n1

What is “Wireless N”?


Why is it so fast

Why is it so fast?

  • Spatial multiplexing

  • With spatial multiplexing, the stream of data is split between 2 antennae and reassembled at the receiver. More data goes through in the same amount of time than when using a single antenna.


Why is it so fast1

Why is it so fast?

  • Support for 40Mhz Channels

  • So far each 802.11b/g channel only used 20MHz of the spectrum. With more spectrum available, more data can go through.


Wireless n is also more reliable

Wireless N is also more reliable

  • Through the use of Multipath we can achieve a more robust signal

  • Antennas cleverly combine the same signal which has travelled through different paths. Even if the environment changes and some of the signal is obstructed, enough can still go through.

  • This is how Wireless N achieves A ROBUST SIGNAL, less prone to interference and environmental changes.

Resulting signal

Receiver

Transmitter

Adjusted and combined signals

Multiple copies of signal received


Deployment considerations

Deployment Considerations

  • 802.11n can operate on 2.4 GHz or/and 5 GHz and is backward compatible with 802.11 a/b/g. Access Points can be set to support 11n only.

  • AP’s can be:

    • single radio (2.4GHz only or 5GHz only)

    • switchable dual radio (switchable between 2.4GHz and 5GHz)

    • concurrent dual radio (operates 2.4GHz and 5GHz at the same time)


Deployment considerations1

Deployment Considerations

  • When introducing 802.11n into existing 802.11a/b/g WLANs both bands (2.4GHZ and 5GHz) can have 802.11n enabled.

  • In case of dense AP architecture channel bonding for 2.4GHz should be disabled (set to 20MHz).

  • Or if there are other 2.4GHz networks in the area – disable channel bonding for 2.4GHz.

  • 802.11n can be offered to throughput-critical clients only which support 11n: 5GHz band can be set as “11n only”. Leaving 2.4GHz for the rest of the clients which will not interfere with the critical data (802.11b/g/n).

2.4GHz

5GHz

dual-radio 802.11n AP

802.11n only

802.11b/g/n

High Speed Wi-Fi

Legacy mixed Wi-Fi

802.11n client


The sting

The ‘Sting’

  • Increased channel spectrum from 22Mhz to 40Mhz, using MAC aggregation techniques;

  • Consumes 2 of 3 non overlapping 2.4Ghz channels;

  • Not an issue in “pure N” networks, but will cause issues in hybrid networks;

  • Uses OFDM, so if 802.11b clients on network performance degrades for all users.


Redes inal mbricas tema 2 c wireless lans the ieee 802 11 standards6

Redes Inalámbricas – Tema 2.C Wireless LANs: the IEEE 802.11 standards

The 802 wireless family

IEEE 802.11

The physical layer

The MAC layer

Quality of service: 802.11e

MIMO: 802.11n

Management tools


Wireshark ethereal

Wireshark / Ethereal

  • Wireshark is the world's foremost network protocol analyzer, and is the de facto (and often de jure) standard across many industries and educational institutions.

  • Wireshark development thrives thanks to the contributions of networking experts across the globe. It is the continuation of a project that started in 1998.


Wireshark features

WiresharkFeatures

  • Deepinspection of hundreds of protocols, with more beingaddedallthe time

  • Live capture and offline analysis

  • Standard three-panepacket browser

  • Multi-platform: Runson Windows, Linux, OS X, Solaris, FreeBSD, NetBSD, and manyothers

  • Capturednetwork data can bebrowsedvia a GUI, orviathe TTY-modeTSharkutility

  • RichVoIPanalysis

  • Read/writemanydifferent capture fileformats:

  • Capture files compressedwithgzip can bedecompressedonthefly

  • Live data can bereadfrom Ethernet, IEEE 802.11, PPP/HDLC, ATM, Bluetooth, USB, Token Ring, FrameRelay, FDDI, and others

  • Decryptionsupportformanyprotocols, includingIPsec, ISAKMP, Kerberos, SNMPv3, SSL/TLS, WEP, and WPA/WPA2

  • Output can beexportedto XML, PostScript®, CSV, orplaintext


Wireshark ethereal1

Wireshark / Ethereal


Kismet

Kismet

  • Kismet is an 802.11 layer2 wireless network detector, sniffer, and intrusion detection system. Kismet will work with any wireless card which supports raw monitoring (rfmon) mode, and can sniff 802.11b, 802.11a, and 802.11g traffic.

  • Kismet identifies networks by passively collecting packets and detecting standard named networks, detecting (and given time, decloaking) hidden networks, and infering the presence of nonbeaconing networks via data traffic.

  • Some of the features

    • Ethereal/Tcpdump compatible data logging

    • Built-in channel hopping and multicard split channel hopping

    • Hidden network SSID decloaking

    • Graphical mapping of networks

    • Manufacturer and model identification of access points and clients

    • Detection of known default access point configurations

    • Runtime decoding of WEP packets for known networks

    • Over 20 supported card types


Gkismet

gKismet


Network stumbler

Network Stumbler

  • Allows to save and export data in several different formats

  • Supports GPS and the ability to store GPS information in conjunction with other data


Redes inal mbricas tema 2 c wireless lans the ieee 802 11 standards

Network Stumbler

  • The graphical interface used is very intuitive and allows various types of analysis in a simple and direct form


Redes inal mbricas tema 2 c wireless lans the ieee 802 11 standards

Network Stumbler


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