ieee 802.11 wireless lan standard -...
TRANSCRIPT
IEEE 802.11 Wireless LAN Standard
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Outline
n Wireless LAN Technology
n Medium Access Control for Wireless
n IEEE 802.11
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Wireless LAN Applications
n LAN Extensionn Cross-building interconnectn Nomadic Access
Ad hoc networkingn Ad hoc networking
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
LAN Extension
n Wireless LAN linked into a wired LAN on same premisesn Wired LAN
n Backbonen Backbonen Support servers and stationary workstations
n Wireless LANn Stations in large open areasn Manufacturing plants, stock exchange trading
floors, and warehouses
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Multiple-cell Wireless LAN
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Cross-Building Interconnect
n Connect LANs in nearby buildingsn Wired or wireless LANs
n Point-to-point wireless link is usedDevices connected are typically bridges n Devices connected are typically bridges or routers
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Nomadic Access
n Wireless link between LAN hub and mobile data terminal equipped with antennan Laptop computer or notepad computern Laptop computer or notepad computer
n Uses:n Transfer data from portable computer to
office servern Extended environment such as campus
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Ad Hoc Networking
n Temporary peer-to-peer network set up to meet immediate need
n Example:n Group of employees with laptops convene n Group of employees with laptops convene
for a meeting; employees link computers in a temporary network for duration of meeting
n Military applicationsn Disaster scenarios
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Wireless LAN Parametersn Throughputn Number of nodesn Connection to backbone LANn Service arean Battery power consumption
Wireless Networks Spring 2005
n Battery power consumptionn Transmission robustness and securityn Collocated network operationn License-free operationn Handoff/roamingn Dynamic configuration
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Wireless LAN Categories
n Infrared (IR) LANsn Spread spectrum LANsn Narrowband microwave
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Strengths of Infrared Over Microwave Radion Spectrum for infrared virtually unlimited
n Possibility of high data rates
n Infrared spectrum unregulatedn Equipment inexpensive and simplen Reflected by light-colored objects
Wireless Networks Spring 2005
n Reflected by light-colored objectsn Ceiling reflection for entire room coverage
n Doesn’t penetrate wallsn More easily secured against eavesdroppingn Less interference between different rooms
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Drawbacks of Infrared Medium
n Indoor environments experience infrared background radiationn Sunlight and indoor lightingn Ambient radiation appears as noise in an n Ambient radiation appears as noise in an
infrared receivern Transmitters of higher power required
n Limited by concerns of eye safety and excessive power consumption
n Limits range
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Spread Spectrum LANs
n Multiple cell arrangementn Most popular type of wireless LANn Two configurations:
Hub topology: infrastructure mode
Wireless Networks Spring 2005
n Hub topology: infrastructure moden Peer-to-peer topology: multi-hop ad hoc
network
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Spread Spectrum LAN configurations
n Hub topology: n Mounted on the ceiling and connected to backbonen Need MAC protocoln May act as multiport repeatern Automatic handoff of mobile stationsn Stations in cell either:n Stations in cell either:
n Transmit to / receive from hub onlyn Broadcast using omnidirectional antenna
n Peer-to-peer mode:n No hubn Need a distributed MAC protocol
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
IEEE 802 Protocol Layers
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Protocol Architecture
n Functions of physical layer:n Encoding/decoding of signals
n Preamble generation/removal (for synchronization)synchronization)
n Bit transmission/reception
n Includes specification of the transmission medium
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Protocol Architecture
n Functions of medium access control (MAC) layer:n On transmission, assemble data into a frame with
address and error detection fields
n On reception, disassemble frame and perform address recognition and error detectionrecognition and error detection
n Govern access to the LAN transmission medium
n Functions of logical link control (LLC) Layer:n Provide an interface to higher layers and perform flow
and error control
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Separation of LLC and MAC
n The logic required to manage access to a shared-access medium not found in traditional layer 2 data link control
n For the same LLC, several MAC options n For the same LLC, several MAC options may be provided
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
MAC Frame Format
n MAC controln Contains Mac protocol information
n Destination MAC addressn Destination physical attachment pointn Destination physical attachment point
n Source MAC addressn Source physical attachment point
n CRCn Cyclic redundancy check
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Logical Link Control
n Characteristics of LLC not shared by other control protocols:n Must support multiaccess, shared-medium
nature of the linknature of the link
n Relieved of some details of link access by MAC layer
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
LLC Servicesn Unacknowledged connectionless service
n No flow- and error-control mechanismsn Data delivery not guaranteed
n Connection-mode serviceLogical connection set up between two usersn Logical connection set up between two users
n Flow- and error-control provided
n Acknowledged connectionless servicen Cross between previous twon Datagrams acknowledgedn No prior logical setup
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Differences between LLC and HDLC
n LLC uses asynchronous balanced mode of operation of HDLC (type 2 operation)
n LLC supports unacknowledged connectionless service (type 1 operation) connectionless service (type 1 operation)
n LLC supports acknowledged connectionless service (type 3 operation)
n LLC permits multiplexing by the use of LLC service access points (LSAPs)
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
IEEE 802.11 Architecture
n Distribution system (DS)
n Access point (AP)
n Basic service set (BSS) n Stations competing for access to shared wireless n Stations competing for access to shared wireless
medium
n Isolated or connected to backbone DS through AP
n Extended service set (ESS) n Two or more basic service sets interconnected by DS
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
IEEE 802.11 Services
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Overview, 802.11 Architecture
STASTASTA
APAP
ESS
BSSBSS
Existing Wired LAN
STASTA
STA STA
BSS
BSSBSS
BSS
Infrastructure Network
Ad Hoc Network
Ad Hoc Network
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Distribution of Messages Within a DS
n Distribution servicen Used to exchange MAC frames from station in
one BSS to station in another BSS
n Integration servicen Integration servicen Transfer of data between station on IEEE
802.11 LAN and station on integrated IEEE 802.x LAN
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Transition Types Based On Mobility
n No transitionn Stationary or moves only within BSS
n BSS transitionn Station moving from one BSS to another BSS n Station moving from one BSS to another BSS
in same ESS
n ESS transitionn Station moving from BSS in one ESS to BSS
within another ESS
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Association-Related Services
n Associationn Establishes initial association between station and AP
n Reassociationn Enables transfer of association from one AP to another,
allowing station to move from one BSS to another
n Disassociationn Association termination notice from station or AP
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Access and Privacy Services
n Authenticationn Establishes identity of stations to each other
n Deathenticationn Invoked when existing authentication is n Invoked when existing authentication is
terminated
n Privacyn Prevents message contents from being read by
unintended recipient
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
IEEE 802.11 Medium Access Control
n MAC layer covers three functional areas:n Reliable data delivery
n Access control
n Securityn Security
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Reliable Data Deliveryn More efficient to deal with errors at the MAC
level than higher layer (such as TCP)n Frame exchange protocol
n Source station transmits datan Destination responds with acknowledgment (ACK)n Destination responds with acknowledgment (ACK)n If source doesn’t receive ACK, it retransmits frame
n Four frame exchangen Source issues request to send (RTS)n Destination responds with clear to send (CTS)n Source transmits datan Destination responds with ACK
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Access Control
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Medium Access Control Logic
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Interframe Space (IFS) Valuesn Short IFS (SIFS)
n Shortest IFSn Used for immediate response actions
n Point coordination function IFS (PIFS)Midlength IFSn Midlength IFS
n Used by centralized controller in PCF scheme when using polls
n Distributed coordination function IFS (DIFS)n Longest IFSn Used as minimum delay of asynchronous frames
contending for access
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
IFS Usagen SIFS
n Acknowledgment (ACK)n Clear to send (CTS)n Poll response
n PIFSn PIFSn Used by centralized controller in issuing pollsn Takes precedence over normal contention traffic
n DIFSn Used for all ordinary asynchronous traffic
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
MAC Frame Format
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
MAC Frame Fields
n Frame Control – frame type, control information
n Duration/connection ID – channel allocation time
n Addresses – context dependant, types include source and destinationsource and destination
n Sequence control – numbering and reassembly
n Frame body – MSDU or fragment of MSDU
n Frame check sequence – 32-bit CRC
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Frame Control Fields
n Protocol version – 802.11 version
n Type – control, management, or data
n Subtype – identifies function of frame
n To DS – 1 if destined for DSn To DS – 1 if destined for DS
n From DS – 1 if leaving DS
n More fragments – 1 if fragments follow
n Retry – 1 if retransmission of previous frame
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Frame Control Fields
n Power management – 1 if transmitting station is in sleep mode
n More data – Indicates that station has more data to send
n WEP – 1 if wired equivalent protocol is implemented
n Order – 1 if any data frame is sent using the Strictly Ordered service
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Control Frame Subtypes
n Power save – poll (PS-Poll)
n Request to send (RTS)
n Clear to send (CTS)
Acknowledgmentn Acknowledgment
n Contention-free (CF)-end
n CF-end + CF-ack
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Data Frame Subtypesn Data-carrying frames
n Datan Data + CF-Ackn Data + CF-Polln Data + CF-Ack + CF-Polln Data + CF-Ack + CF-Poll
n Other subtypes (don’t carry user data)n Null Functionn CF-Ackn CF-Polln CF-Ack + CF-Poll
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Management Frame Subtypes
n Association request
n Association response
n Reassociation request
Reassociation responsen Reassociation response
n Probe request
n Probe response
n Beacon
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Management Frame Subtypes
n Announcement traffic indication message
n Dissociation
n Authentication
Deauthenticationn Deauthentication
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Wired Equivalent Privacy
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Authentication
n Open system authenticationn Exchange of identities, no security benefits
n Shared Key authenticationShared Key assures authenticationn Shared Key assures authentication
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
Physical Media Defined by Original 802.11 Standardn Direct-sequence spread spectrum
n Operating in 2.4 GHz ISM bandn Data rates of 1 and 2 Mbps
n Frequency-hopping spread spectrumOperating in 2.4 GHz ISM bandn Operating in 2.4 GHz ISM band
n Data rates of 1 and 2 Mbps
n Infraredn 1 and 2 Mbpsn Wavelength between 850 and 950 nm
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net
IEEE 802.11a and IEEE 802.11bn IEEE 802.11a
n Makes use of 5-GHz bandn Provides rates of 6, 9 , 12, 18, 24, 36, 48, 54 Mbpsn Uses orthogonal frequency division multiplexing
(OFDM)(OFDM)n Subcarrier modulated using BPSK, QPSK, 16-QAM or
64-QAM
n IEEE 802.11bn Provides data rates of 5.5 and 11 Mbpsn Complementary code keying (CCK) modulation
scheme
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net