wireless lan full report

[seminar class]

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IEEE 802.11 Wireless Local Area Networks (RF-LANs)
 802.11 WLANs - Outline
 801.11 bands and layers
 Link layer
 Media access layer
 frames and headers
 CSMA/CD
 Physical layer
 frames
 modulation
 Frequency hopping
 Direct sequence
 Infrared
Security
 Implementation
 802.11 WLAN technologies
 IEEE 802.11 standards and rates
 IEEE 802.11 (1997) 1 Mbps and 2 Mbps (2.4 GHz band )
 IEEE 802.11b (1999) 11 Mbps (2.4 GHz band) = Wi-Fi
 IEEE 802.11a (1999) 6, 9, 12, 18, 24, 36, 48, 54 Mbps (5 GHz band)
 IEEE 802.11g (2001 ... 2003) up to 54 Mbps (2.4 GHz) backward compatible to 802.11b
 IEEE 802.11 networks work on license free industrial, science, medicine (ISM) bands:
Other WLAN technologies
 High performance LAN or HiperLAN (ETSI-BRAN EN 300 652) in the 5 GHz ISM
 version 1 up to 24 Mbps
 version 2 up to 54 Mbps
 HiperLAN provides also QoS for data, video, voice and images
Bluetooth
 range up to 100 meters only (cable replacement tech.)
 Bluetooth Special Interest Group (SIG)
 Operates at max of 740 kbps at 2.4 GHz ISM band
 Applies fast frequency hopping 1600 hops/second
 Can have serious interference with 802.11 2.4 GHz range network
802.11a
 Operates at 5 GHz band
 Supports multi-rate 6 Mbps, 9 Mbps,… up to 54 Mbps
 Use Orthogonal Frequency Division Multiplexing (OFDM) with 52 subcarriers, 4 us symbols (0.8 us guard interval)
 Use inverse discrete Fourier transform (IFFT) to combine multi-carrier signals to single time domain symbol
 IEEE 802.11a rates and modulation formats
IEEE 802-series of LAN standards
 802 standards free to
download from
http://standards.ieee.org
/getieee802/portfolio.html
 The IEEE 802.11 and
supporting LAN Standards
 See also IEEE LAN/MAN Standards Committee Web site
manta.ieeegroups/802/
IEEE 802.11 Architecture
 IEEE 802.11 defines the physical (PHY), logical page link (LLC) and media access control (MAC) layers for a wireless local area network
 802.11 networks can work as
 basic service set (BSS)
 extended service set (ESS)
 BSS can also be used in ad-hoc
networking
BSS and ESS
 In ESS multiple access points connected by access points and a distribution system as Ethernet
 BSSs partially overlap
 Physically disjoint BSSs
 Physically collocated BSSs (several antennas)
 802.11 Logical architecture
 LLC provides addressing and data page link control
MAC provides
 access to wireless medium
 CSMA/CA
 Priority based access (802.12)
 joining the network
 authentication & privacy
 Services
 Station service: Authentication, privacy, MSDU* delivery
 Distributed system: Association** and participates to data distribution
Three physical layers (PHY)
 FHSS: Frequency Hopping Spread
Spectrum (SS)
 DSSS: Direct Sequence SS
 IR: Infrared transmission
 802.11 DSSS
 Supports 1 and 2 Mbps data transport, uses BPSK and QPSK modulation
 Uses 11 chips Barker code for spreading - 10.4 dB processing gain
 Defines 14 overlapping channels, each having 22 MHz channel bandwidth, from 2.401 to 2.483 GHz
 Power limits 1000mW in US, 100mW in EU, 200mW in Japan
 Immune to narrow-band interference, cheaper hardware
 802.11 FHSS
 Supports 1 and 2 Mbps data transport and applies two level - GFSK modulation* (Gaussian Frequency Shift Keying)
 79 channels from 2.402 to 2.480 GHz ( in U.S. and most of EU countries) with 1 MHz channel space
 78 hopping sequences with minimum 6 MHz hopping space, each sequence uses every 79 frequency elements once
 Minimum hopping rate
2.5 hops/second
 Tolerance to multi-path,
narrow band interference,
security
 Low speed, small range
due to FCC TX power
regulation (10mW)
 How ring-network works
 A node functions as a repeater
 only destination copies
frame to it,
all other nodes
have to discarded
the frame
Unidirectional link
 Token ring
 A ring consists of a single or dual (FDDI) cable in the shape of a loop
 Each station is only connected to each of its two nearest neighbors. Data in the form of packets pass around the ring from one station to another in uni-directional way.
 Advantages :
 (1) Access method supports heavy load without degradation of performance because the medium is not shared.
 (2) Several packets can simultaneous circulate between different pairs of stations.
 Disadvantages:
 (1) Complex management
 (2) Re-initialization of the ring whenever a failure occurs
How bus-network works
 In a bus network, one node’s transmission traverses the entire network and is received and examined by every node. The access method can be :
 (1) Contention scheme : multiple nodes attempt to access bus; only one node succeed at a time (e.g. CSMA/CD in Ethernet)
 (2) Round robin scheme : a token is passed between nodes; node holds the token can use the bus (e.g.Token bus)
Advantages:
 (1) Simple access method
 (2) Easy to add or remove
stations
Disadvantages:
 (1) Poor efficiency with high
network load
 (2) Relatively insecure, due to
the shared medium
 MAC Techniques - overview
 Contention
 Medium is free for all