Tutorial on draft D3.0 of IEEE P802.11
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Tutorial on draft D3.0 of IEEE P802.11

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03/08/96doc.: IEEE P802.11-96/49BMarch 1996802.11 Tutorial March 96802.11 ArchitectureCopyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change 1802.11 Tutorial March 96What is unique about wireless?• Difficult media– interference and noise– quality varies over space and time– shared with “unwanted” 802.11 devices– shared with non-802 devices (unlicensedspectrum, microwave ovens)• Full connectivity cannot be assumed– “hidden node” problem• Multiple international regulatory requirementsCopyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change 2Submission 1 Greg Ennis, Symbol Technologies* 1103/08/96doc.: IEEE P802.11-96/49BMarch 1996802.11 Tutorial March 96Medium VariationsCopyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change 3802.11 Tutorial March 96Uniqueness of Wireless (continued)• Mobility– variation in link reliability– battery usage: requires power management– want “seamless” connections• Security– no physical boundaries– overlapping LANsCopyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change 4Submission 2 Greg Ennis, Symbol Technologies* 2203/08/96doc.: IEEE P802.11-96/49BMarch 1996802.11 Tutorial March 96Requirements• Single MAC to support multiple PHYs.– Support single and multiple channel PHYs.– PHYs with different ...

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Reads 12
Language English
1
March 1996
03/08/96
*
1
doc.: IEEE P802.11-96/49B
Submission
1
Greg Ennis, Symbol Technologies
802.11 Tutorial
1
March
96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
802.11 Architecture
802.11 Tutorial
2
March
96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
What is unique about wireless?
• Difficult media
–interference and noise
–quality varies over space and time
–shared with “unwanted” 802.11 devices
–shared with non-802 devices (unlicensed
spectrum, microwave ovens)
• Full connectivity cannot be assumed
–“hidden node” problem
• Multiple international regulatory requirements
2
March 1996
03/08/96
*
2
doc.: IEEE P802.11-96/49B
Submission
2
Greg Ennis, Symbol Technologies
802.11 Tutorial
3
March
96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
Medium Variations
802.11 Tutorial
4
March
96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
Uniqueness of Wireless (continued)
• Mobility
– variation in link reliability
– battery usage: requires power management
– want “seamless” connections
• Security
– no physical boundaries
– overlapping LANs
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Submission
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Greg Ennis, Symbol Technologies
802.11 Tutorial
5
March
96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
Requirements
• Single MAC to support multiple PHYs.
– Support single and multiple channel PHYs.
– PHYs with different “Medium Sense” characteristics.
• Should allow overlap of multiple networks in the
same area and channel space.
• Need to be “Robust for Interference”.
– Microwave, other non-802.11 interferers.
– Co-channel interference.
• Need mechanisms to deal with “Hidden Nodes”.
• Need provisions for Time Bounded Services.
802.11 Tutorial
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March
96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
Architecture Overview
• One MAC supporting multiple PHYs
– currently Frequency Hopping, Direct Sequence and
Infrared PHYs
• Two configurations
– “Independent” (ad hoc) and “Infrastructure”
• CSMA/CA (collision avoidance) with optional
“point coordination”
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Submission
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Greg Ennis, Symbol Technologies
802.11 Tutorial
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March
96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
802.11 Protocol Entities
MAC
Sublayer
PLCP Sublayer
PMD Sublayer
MAC Layer
Management
PHY Layer
Management
Station
Management
LLC
MAC
PHY
802.11 Tutorial
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March
96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
802.11 Protocol Architecture
• MAC Entity
– basic access mechanism
– fragmentation
– encryption
• MAC Layer Management Entity
– synchronization
– power management
– roaming
– MAC MIB
• Physical Layer Convergence Protocol (PLCP)
– PHY-specific, supports common PHY SAP
– provides Clear Channel Assessment signal (carrier
sense)
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Submission
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Greg Ennis, Symbol Technologies
802.11 Tutorial
9
March
96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
802.11 Protocol Architecture
(cont.)
• Physical Medium Dependent Sublayer (PMD)
– modulation and encoding
• PHY Layer Management
– channel tuning
– PHY MIB
• Station Management
– interacts with both MAC Management and PHY
Management
802.11 Tutorial
10
March
96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
802.11 Configurations - Independent
• Independent
– one “Basic Service Set”, BSS
– “Ad Hoc” network
– direct communication
– limited coverage area
Station
AH3
Station
Station
AH1
AH2
Ad Hoc Network
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Submission
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Greg Ennis, Symbol Technologies
802.11 Tutorial
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96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
802.11 Configurations - Infrastructure
• Infrastructure
–Access Points and stations
• Distribution System
interconnects Multiple Cells
via Access Points
to form a single Network.
–extends wireless coverage area
Station
Station
Station
Station
A1
A2
B1
B2
BSS-A
BSS-B
A
AP
AP
B
Server
DISTRIBUTION SYSTEM
802.11 Tutorial
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96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
Distribution System
• Used to interconnect wireless cells
– multiple BSS connected together form an ESS, Extended
Service Set
– Allows mobile stations to access fixed resources
• Not part of 802.11 standard
– could be bridged IEEE LANs, wireless, other networks …
– Distribution System Services are defined
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Submission
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Greg Ennis, Symbol Technologies
802.11 Tutorial
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March
96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
Access Points
• Stations select an AP and “associate” with it
• Support roaming
• Provide other functions
– time synchronization (beaconing)
– power management support
– point coordination function
• Traffic typically (but not always) flows through AP
– direct communication possible
802.11 Tutorial
14
March
96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
802.11 Defines the Airwaves IF
• The airwaves interface between stations
(including that between station and AP) is
standardized
– PHY and MAC
• No exposed MAC/PHY interface specified
• No exposed interface to Distribution System
– required DS services are defined
• Internals of Distribution System not defined
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doc.: IEEE P802.11-96/49B
Submission
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Greg Ennis, Symbol Technologies
802.11 Tutorial
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March
96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
MAC Services
• Asynchronous MSDU Data Delivery
– provided to LLC (2304 octet maximum)
• Time Bounded Services
– optional point coordination function
• Security Services
– confidentiality, authentication, access control
• Management Services
– scanning, joining, power management
802.11 Tutorial
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96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
MAC Functionality
• Independent and Infrastructure configuration
support
– Each BSS has a unique 48 bit address
– Each ESS has a variable length address
• CSMA with collision avoidance
– MAC-level acknowledgment
– allows for RTS/CTS exchanges
» hidden node protection
– MSDU fragmentation
– “Point Coordination” option
» AP polling
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doc.: IEEE P802.11-96/49B
Submission
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Greg Ennis, Symbol Technologies
802.11 Tutorial
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March
96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
MAC Functionality (continued)
• Roaming support within an ESS
– station scans for APs, association handshakes
• Power management support
– stations may power themselves down
– AP buffering, distributed approach for IBSS
• Authentication and privacy
– Optional support of “Wired Equivalent Privacy” (WEP)
– Authentication handshakes defined
802.11 Tutorial
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Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
PHY Layer Services
• PHY_DATA transfers
– multiple rates
• Clear Channel Assessment (CCA)
– carrier sense
• PHY Management
– channel tuning
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doc.: IEEE P802.11-96/49B
Submission
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Greg Ennis, Symbol Technologies
802.11 Tutorial
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March
96
Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change
Three PHYs
• Frequency Hop Spread Spectrum
– 2.4 GHz band, 1 and 2 Mbps transmission
– 2GFSK, 4GFSK
– hop over 79 channels (North America)
• Direct Sequence Spread Spectrum
– 2.4 GHz band, 1 and 2 Mbps transmission
– DBPSK, DQPSK
– 11 chip Barker sequence
• Baseband IR
– Diffuse infrared
– 1 and 2 Mbps transmission, 16-PPM and 4-PPM