CWNA Chapter5

8/10/2019 CWNA Chapter5

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Chapter 5-802.11 standards Alphabet Soup!


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Exam Essentials Know the defined spread spectrum technologies of the original 802.11standard and the subsequent 802.11-2007 standard. Although the original 802.11 standard defend infrared, FHSS, and DSSS, later

amendments that are now incorporated in the 802.11-2007 standard also defineHR-DSSS, OFDM, and ERP.

Remember both the required data rates and supported data rates ofeach PHY. DSSS and FHSS require and support data rates of 1 and 2 Mbps. Other PHYs

offer a wider support for data rates. For example, OFDM and ERP-OFDMsupport data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps, but only the rates of6, 12 and 24 Mbps are mandatory. Please understand that data rates are speedsand not aggregate throughput.

Know the frequency bands used by each PHY as defined by the

802.11-2007 standard. OFDM equipment operates in the 5 GHz UNII bands. DSSS, FHSS, HR-DSSS,

and ERP devices transmit and receive in the 2.4 GHz ISM band.

Explain the three vendor operational modes of ERP (802.11g) and theconsequences of each mode. An 802.11g access point may be configured as B-only mode, G-only mode, or

B/G mixed mode. The three modes support different spread spectrum

technologies and have different aggregate throughput results.


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Exam Essentials Know the mandatory and optional technologies used in an ERPWLAN. ERP (802.11g) defines two mandatory PHYs, ERP-OFDM and ERP-

DSSS/CCK. The two optional PHYs are ERP-PBCC and DSSS-OFDM.

Define transmit power control and dynamic frequencyselection. TPC and DFS are often mandated for use in the 5 GHz band. Both

technologies are used as a means to avoid interference with radartransmissions.

Explain the defined wireless security standards both pre-802.11i and post-802.11i.

Before the passage of 802.11i, WEP encryption and either OpenSystem or Shared Key authentication were defend. The 802.11iamendment calls for the use of CCMP/AES for encryption. Forauthentication, 802.11i defines either an 802.1X/EAP solution or the useof preshared keys.


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Exam Essentials Define the Inter-Access Point Protocol and why it wasoriginally proposed. IAPP is a vendor interoperability roaming protocol that is

outlined in the 802.11F recommended practice.

Explain the purpose of the 802.11e amendment and themedium access methods it requires. The 802.11e amendment addresses quality of service (QoS)

issues by mandating the use of Enhanced Distributed ChannelAccess (EDCA) and Hybrid Coordination Function (HCF).

Understand the purpose of each 802.11 draft proposal. Each draft has a specific intended goal. The 802.11s draft, forexample, outlines mesh networking. 802.11n proposesthroughput enhancements using MIMO technology.


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Overview of IEEE 802.11 802.11 task group and subcommittees

Revising and amending the MAC and PHY

standards Media Access

Physical

Draft standards are not official yet Sometimes they are adopted by vendors as

pre 802.11x

Pg 155


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Overview of IEEE 802.11 Two sets of definitions

The original alphabet soup

The 802.11-2007 and clauses Need to know the technologies, clauses,

and letters

802.11 original in 1997Also known as 802.11 Prime

Pg 155


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Overview of IEEE 802.11 802.11-2007 rolled up ratified amendments

IEEE Std 802.11-1999 (R2003)

IEEE Std 802.11a-1999

IEEE Std 802.11b-1999

IEEE Std 802.11d-2001

IEEE Std 802.11g-2003

IEEE Std 802.11h-2003 IEEE Std 802.11i-2004

IEEE Std 802.11j-2004

IEEE Std 802.11e-2005

Pg 155


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Overview of IEEE 802.11 Original Physical layer options Infrared (IR)

Infrared (IR) technology uses a light-based medium. Although aninfrared medium was indeed defined in the original 802.11 standard,the implementation is obsolete. More information about modernimplementations of infrared technology can be found at the InfraredData Associations website, at www. irda. org. The scope of thisbook focuses on the 802.11 RF mediums. Infrared devices areknown as clause 16devices.

Frequency hopping spread spectrum (FHSS) Radio frequency signals can be defined as narrowband signals or

as spread spectrum signals. An RF signal is considered spreadspectrum when the bandwidth is wider than what is required to carrythe data. Clause 14

Direct sequence spread spectrum (DSSS) Direct sequence spread spectrum (DSSS) is another spread

spectrum technology that is frequently used and easiest toimplement. DSSS 802.11 radio cards are often known as clause 15

devices. Pg 155


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802.11Prime FHSS and DSS were originally specified for 2.4 Ghz ISMband 2.4 Ghz to 2.4835 Ghz

Older equipment is much less common now

DSS cannot work with FHSS Most early implementations were FHSS

Original speeds were 1 Mbps or 2 Mbps This is bandwidth, not throughput

Used Barker Keying

Pg 156


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802.11 Ratified Amendments 802.11 b 802.11 a

802.11 g

802.11d 802.11 F

802.11 h

802.11 I

802.11 j

802.11 e

802.11 k

802.11 r Pg 157


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802.11 b HR-DSSS Backward compatible with any DSSS

implementations of 802.11 prime Not common

Clause 18

2.4 Ghz

CCK modulation 1, 2, 5.5, 11 Mbps

5.5 and 11 are HR-DSSS

Pg 157


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802.11 a For the new 5 Ghz UNII band Less crowded than 2.4 Ghz

Clause 17

Orthogonal Frequency Division Multiplexing (OFDM) Required rates

6, 12, 24

Also supports 6, 9, 12, 18, 24, 36, 48, 54

Different vendors can choose different implementations

Not compatible with earlier standards But can coexist because no overlap

Pg 159


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802.11 g Clause 19

2.4 Ghz

Extended Rate Physical-ERP

Enhance the 802.11b speeds

Two PHY

ERP-OFDM

ERP-DSSS/CCK

Backward compatible with 802.11b OFDM

Pg 160


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802.11 g Required Speeds

6, 12, 24

For backward compatibility, ERP-DSSS/CCKsupports 1, 2, 5.5, 11

Optional

6, 9, 12, 18, 24, 36, 48, 54 Also had ERP-PBCC and DSS-OFDM

Not used much

Pg 160


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802.11 g Due to backward compatibility, multiple

implementations

B-only mode G-Only Mode

b/g mode

Supports both, but when a 802.11b signal isdetected, all stations are forced to protection

Causes degradation of throughput to support older

ratesPg 160


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802.11 Amendments

Pg 162


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Other Amendments 802.11 d To support other countries

Beacon and probes to support countryspecific power levels

802.11 F

Recommended practice

Roaming standard Like cell phones

IAPP is now a recommendation Intervendor roaming isnt great

Pg 163


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Roaming


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Roaming


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Inter Access Point Protocol (IAPP) Recommended practice

Never specified how to implement in 802.11

802.11F never ratified If vendors support IAPP, you should be

able to roam between vendors

Pg 164


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802.11 h The dynamic frequency selection (DFS) service providesfor the following: An AP will allow client stations to associate based on the

supported channel of the access point. The term associate

means that a station has become a member of the APs wirelessnetwork.

An AP can quiet a channel to test for the presence of radar.

An AP may test a channel for the presence of radar before usingthe channel.

An AP can detect radar on the current channel and otherchannels.

An AP can cease operations after radar detection to avoidinterference.

When interference is detected, the AP may choose a different

channel to transmit on and inform all the associated stations. Pg 166


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802.11 h TPC provides

Designation of the maximum transmit power

levels permitted on a channel, as permitted byregulations.

An AP can specify the transmit power of any

or all stations that are associated with the

access point.An AP can change transmission power on

stations based on factors of the physical RF

environment such as path loss.Pg 167


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802.11 i Data privacy

Authentication

Replaced WEP WEP was a poorly implemented solution

Pg 167


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Wireless Security Open System Authentication

Verified identity regardless

No authentication Shared Key Authentication

If you had the key, you were authenticated

Pg 168


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802.11 i Defined the Robust Security Network

(RSN)

Better hide data broadcast on an unboundedmedium

Bigger guard at the door to the network

Data Privacy Authentication

Pg 168


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802.11 i-Data Privacy Counter Mode with Cipher Block Chaining

Message Authentication Code Protocol

(CCMP)Advanced Encryption Standard (AES)

algorithm

AES/CCMP or CCMP

Also supports Temporal Key Integrity

Protocol with RC-4 stream cipher

More like WEP, but much betterPg 168


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802.11 i-Authentication 802.1X Implements Extensible Authentication

Protocol (EAP)

Method of authentication not specified

Commonly used with existing authenticationsystems

RADIUS KERBEROS

Pre-Shared Key

Uses a passphrase/Key as the starting pointPg 168


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802.11 i-Robust Security Network Defines the methods for establishing

authentication, negitiating security and

generating keys WiFi Alliance-WPA2 matches the 802.11i

Pg 168


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802.11 j Japanese Market approval

Different frequencies and bands

Pg 168


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802.11 e Layer 2 MAC methods for providing QOS

for time sensitive applications

Voice Over technologies 802.11 prime had some methods for

controlling network

Distributed Coordination Function (DCF) Random

Point Coordination Function

Access point takes control and polls clients

Pg 169


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802.11 e 802.11e defines Hybrid Coordination Function(HCF)

Enhanced Distributed Channel Access (EDCA)

Extends DCF-allows for prioritization of frames

Create an EZ-PASS lane for higher need traffic

Hybrid Coordination Function Controlled Channel

Access (HCCA) extends PCF

Allows AP to allow certain stations to transmit first

Matches to the WiFi Alliance Wi-Fi Multimedia

(WMM)

Pg 169


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802.11 k Radio Resource Measurements Ability to gather information about the network for better control

Layer 1 and Layer 2

Data gathered by stations and processed by AP or

WLAN controller Transmit power control (TPC)

The 802.11h amendment defined the use of TPC for the 5 GHzband to reduce interference. Under 802.11k, TPC will also beused in other frequency bands and in areas governed by otherregulatory agencies.

Client statistics Physical layer information such as signal-to-noise ratio, signal

strength, and data rates can all be reported back to the accesspoint or WLAN controller. MAC information such as frametransmissions, retries, and errors may all be reported back tothe access point or WLAN controller as well.

Pg 170


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802.11 k Channel statistics Clients may gather noise-floor information based on any RF

energy in the background of the channel and report thisinformation back to the access point. Channel load informationmay also be collected and sent to the AP. The access point or

WLAN controller may use this information for channelmanagement decisions.

Neighbor reports Mobile Assisted Handover (MAHO) is a technique used by digital

phones and cellular systems working together to provide betterhandover between cells. 802.11k gives access points or WLANcontrollers the ability to direct stations to perform the sort oftasks that a cellular network requires its handhelds to do whenusing MAHO.

Clients will keep table of access points and makedecisions on when to roam

Pg 170


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802.11 r Fast basic service set transition Fast secure roaming

Proposed for VoIP and other real time

applications

Needed because security takes extra time

Since Authentication takes time, 802.11 r

manages authentication before doing the switchbetween access points to limit delay.

Not part of the 802.11 2007

Pg 171


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802.11 Draft Amendments Test is focused on 802.11n, which is nowa standard

Pg 171


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802.11 n 2.4 Ghz AND 5 Ghz High Throughput-HT

Both PHY and MAC enhanced for 100 Mbps MIMO technology with OFDM

Increased throughput and greater range

Pg 172


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802.11 Draft Amendments 802.11 m housekeeping

802.11 n

New HT standard

802.11 p Wireless Access in Vehicles

802.11 s Wireless Distribution System-Mesh Networks

802.11 T metrics

Pg 172


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802.11 Draft Amendments 802.11 u Internetworking to other standards

802.11 v Wireless centralized control

802.11 w Secure management frames

802.11 y New frequencies

802.11 z Direct Link Setup

802.11 aa Robust audio and video streaming

Pg 175


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Exam Essentials Know the defined spread spectrum technologies of the original 802.11standard and the subsequent 802.11-2007 standard. Although the original 802.11 standard defend infrared, FHSS, and DSSS, later

amendments that are now incorporated in the 802.11-2007 standard also defineHR-DSSS, OFDM, and ERP.

Remember both the required data rates and supported data rates of

each PHY. DSSS and FHSS require and support data rates of 1 and 2 Mbps. Other PHYs

offer a wider support for data rates. For example, OFDM and ERP-OFDMsupport data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps, but only the rates of6, 12 and 24 Mbps are mandatory. Please understand that data rates are speedsand not aggregate throughput.

Know the frequency bands used by each PHY as defined by the

802.11-2007 standard. OFDM equipment operates in the 5 GHz UNII bands. DSSS, FHSS, HR-DSSS,

and ERP devices transmit and receive in the 2.4 GHz ISM band.

Explain the three vendor operational modes of ERP (802.11g) and theconsequences of each mode. An 802.11g access point may be configured as B-only mode, G-only mode, or

B/G mixed mode. The three modes support different spread spectrum

technologies and have different aggregate throughput results.


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Exam Essentials Know the mandatory and optional technologies used in an ERPWLAN. ERP (802.11g) defines two mandatory PHYs, ERP-OFDM and ERP-

DSSS/CCK. The two optional PHYs are ERP-PBCC and DSSS-OFDM.

Define transmit power control and dynamic frequency

selection. TPC and DFS are often mandated for use in the 5 GHz band. Both

technologies are used as a means to avoid interference with radartransmissions.

Explain the defined wireless security standards both pre-802.11i and post-802.11i.

Before the passage of 802.11i, WEP encryption and either OpenSystem or Shared Key authentication were defend. The 802.11iamendment calls for the use of CCMP/AES for encryption. Forauthentication, 802.11i defines either an 802.1X/EAP solution or the useof preshared keys.


41/41

Exam Essentials Define the Inter-Access Point Protocol and why it wasoriginally proposed. IAPP is a vendor interoperability roaming protocol that is

outlined in the 802.11F recommended practice.

Explain the purpose of the 802.11e amendment and themedium access methods it requires. The 802.11e amendment addresses quality of service (QoS)

issues by mandating the use of Enhanced Distributed ChannelAccess (EDCA) and Hybrid Coordination Function (HCF).

Understand the purpose of each 802.11 draft proposal. Each draft has a specific intended goal. The 802.11s draft, for

example, outlines mesh networking. 802.11n proposesthroughput enhancements using MIMO technology.

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CWNA Chapter5