chapter 14. wireless lans
DESCRIPTION
Chapter 14. Wireless LANs. IEEE 802.11 Bluetooth. Basic Service Set (BSS). BSS The building block of a wireless LAN BSS with an AP Access Point (AP): central base station BSS without an AP Stand-alone network Cannot send data to other BSSs Ad hoc architecture BSS with an AP - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 14. Wireless LANs
1. IEEE 802.11
2. Bluetooth
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Basic Service Set (BSS)
• BSS
– The building block of a wireless LAN
• BSS with an AP
– Access Point (AP): central base station
• BSS without an AP
– Stand-alone network
– Cannot send data to other BSSs
– Ad hoc architecture
• BSS with an AP
– Called an infrastructure network
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BSS
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Extended Service Set (ESS)
• BSSs are connected through a distribution system: infrastructure network (usually wired LAN)
• Station Types: No-transition, BSS-transition, and ESS-transition mobility
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MAC Sublayer
• Two MAC sublayers: DCF and PCF
• DCF uses CSMA/CA as the access method
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CSMA/CA Flow Chart
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CSMA/CA and NAV
• Network allocation vector (NAV) shows how much time must pass before these stations are allowed to check the channel for idleness
• Collision During handshaking
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Point Coordination Function (PCF)• An optional access method that can be implemented in an AP• A centralized, contention-free polling access method• To give priority to PCF over DCF, another set of interframe spaces has
been defined: PIFS and SIFS• PIFS (PCF IFS) is shorter than the DIFS AP using PCF has priority• Repetition interval starts with a special control frame, called a beacon
frame
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MAC Layer Frame Format
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Frame Types
• Three categories of frames• Management frames for initial communication between stations and APs• Control frames for accessing the channel and acknowledging frames• Data frame for carrying data and control information
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Addressing Mechanism
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Hidden Station Problems
• The CTS frame in CSMA/CA handshake can prevent collision from a hidden station.
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Exposed Station Problems
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Physical Layer
• Industrial, scientific, and medical (ISM) band which defines three unlicensed bands in three ranges 902-928 MHz, 2.400-4.835 GHz, and 5.725-5.850 GHz
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Physical Layer• IEEE 802.11 FHSS
• IEEE 802.11 DSSS
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Physical Layer• IEEE 802.11 Infrared
• IEEE 802.11a OFDM– Common data rates are 18 Mbps (PSK) and 54 Mbps (QAM)
• IEEE 802.11b DSSS– High-rate direct sequence spread spectrum (HR-DSSS)
– Similar to DSSS method except for the encoding method called complementary code keying (CCK), Four data rates; 1, 2, .5, 11 Mbps
• IEEE 802.11g– Forward error correction and OFDM using 2.4 GHz ISM, 22- or 54-Mbps data rate
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Bluetooth: Piconet
• Bluetooth is a wireless LAN technology designed to connect devices oBluetooth is a wireless LAN technology designed to connect devices of different functions such as telephones, notebooks, computers, cameraf different functions such as telephones, notebooks, computers, cameras, printers, coffee makers, and so on. A Bluetooth LAN is an ad hoc nes, printers, coffee makers, and so on. A Bluetooth LAN is an ad hoc network, which means that the network is formed spontaneouslytwork, which means that the network is formed spontaneously
• Bluetooth network is called piconet, or a small net
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Bluetooth: Scatternet
• Piconet can be combined to form what is called a scatternet.Piconet can be combined to form what is called a scatternet.
• Bluetooth device has a built-in short range radio transmitter with 2.4 GHz bandwidth. A Bluetooth device has a built-in short range radio transmitter with 2.4 GHz bandwidth. A possibility of interference with IEEE 802.11bpossibility of interference with IEEE 802.11b
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Bluetooth Layers
• Radio layer
– 2.4 GHz ISM band divided into 79 channels of 1 MHz each
– FHSS: Bluetooth hops 1600 times per second, dwell time is 625 μsec (= 1/1600 sec)
– Modulation: GFSK (FSK with Gaussian bandwidth filtering)
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Bluetooth Layers
• Baseband layer
– TDD-TDMA (time division duplex TDMA): half-duplex communication
– Single-secondary communication
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Bluetooth Layers
• Baseband layer
– TDD-TDMA: multiple-secondary communication
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Bluetooth Layers• Physical links
– SCO (synchronous connection-oriented)
– ACL (asynchronous connectionless link)
• Frame format
• L2CAP (Logical Link Control and Adaptation Protocol)
– Multiplexing, segmentation and reassembly, QoS, group management