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Transcript of 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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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.
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8/10/2019 CWNA Chapter5
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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, for
example, outlines mesh networking. 802.11n proposesthroughput enhancements using MIMO technology.