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Rivier College
CS575: Advanced LANs
Chapter 10: Wireless LANs
Chapter 10
Wireless LANs
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Wireless LANs
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Wireless LANs Applications
Wireless LAN Requirements
Wireless LAN Technology
Infrared LANs: Transmission Techniques
Spread Spectrum Communications
Spread Spectrum LAN Design
Licensed and Unlicensed Narrowband RF Microwave LANs
Wireless LAN Standards:
* IEEE 802.11 Services
* Physical Medium Specification
* Medium Access Control
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Example 1: Single-Cell Wireless LAN Configuration
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Example 2: Multiple-Cell Wireless LAN Configuration
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Wireless LAN Configuration with Nomadic Access
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Wireless Ad hoc LAN Configuration
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Wireless LAN Requirements
0 Throughput: The medium access control protocol should make as
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efficient use as possible of the wireless medium to maximize capacity.
Number of nodes: Wireless LANs may need to support hundreds of
nodes across multiple cells.
Connection to backbone LAN: Interconnection with stations on a
wired backbone LAN is required. This is accomplished through the use
of Control Modules that connect to both types of LANs. Also it may be
accommodated for mobile users and ad hoc wireless networks.
Service area: A typical coverage area for a wireless LAN has a
diameter of 100 to 300 m.
Battery power consumption: Long-life battery-powered workstations
require wireless adapters.
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Wireless LAN Requirements (continued)
0 Transmission robustness and security: A wireless LAN may be interference
prone and easily eavesdropped. It must permit reliable transmission even in a
noisy environment and should provide some level of security from
eavesdropping.
0 Collocated network operation: Two or more wireless LANs can operate in the
same area and in some areas the interference between the LANs is possible. Such
interference may thwart the normal operation of a MAC algorithm and may allow
unauthorized access to a particular LAN.
0 License-free operation: Users would prefer to buy and operate wireless LAN
products without having to secure a license for the frequency band used by the
LAN.
0 Handoff-roaming: The MAC protocol used in the wireless LAN should enable
mobile stations to move from one cell to another.
0 Dynamic configuration: The MAC addressing and network management aspects
of the LAN should permit dynamic and automatic addition, deletion, and
relocation of end systems without disruption to other users.
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Wireless LAN Technologies
0 Infrared (IR) LANs: An individual cell of an IR LAN is limited to a single
room because infrared light does not penetrate opaque walls (providing secured
non-interfering communication). The unregulated world-wide IR spectrum is
virtually unlimited, which represents the possibility of achieving extremely high
data rates. IR equipment is inexpensive and simple. The ambient radiation (noise)
requires the use of higher-power transmitters.
0 Spread spectrum LANs: This type of LAN makes use of spread spectrum
transmission technology. They operate in the industrial, scientific, and medical
(ISM) bands so that no FCC licensing is required for their use in the United
States.
0 Narrowband microwave: These LANs operate at microwave frequencies but do
not use spread spectrum. Products operate at frequencies that require FCC
licensing, while others use one of the unlicensed ISM bands.
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Comparison of Wireless LAN Technologies
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General Model of Spread Spectrum Digital
Communication System
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Spread Spectrum Digital Communication:
Frequency-Hopping Principle
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Frequency-Hopping Spread Spectrum System
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Frequency-Hopping Spread Spectrum System
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Direct Sequence Spread Spectrum
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Direct Sequence Spread Spectrum System
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Direct Sequence Spread Spectrum System
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Wireless LAN Standards: IEEE 802.11 Architecture (1990)
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Wireless LAN Standards: Mobility Station Types
0 No transition: A station is either stationary or moves only within the
direct communication range of the communicating stations of a single
Basic Service Set (BSS).
0 BSS transition: This is defined as a station movement from one BSS to
another BSS within the same Extended Service Set (ESS). Delivery of
data to the station requires that the addressing capability be able to
recognize the new location of the station.
0 EES transition: This is defined as a station movement from a BSS in
one ESS to a BSS within another ESS. This case is supported only in the
sense that the station can move. Maintenance of upper-layer connections
supported by 802.11 cannot be guaranteed. Disruption of service is
likely to occur.
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IEEE 802.11 Services
0 Association: Establishes an initial association between a station and an access
point within a particular BSS. The access point can then communicate
information (station identity, its address) to other access points within the ESS to
facilitate routing and delivery of addressed frames.
0 Reassociation: Enables an established association to be transferred from one
access point to another, allowing a mobile station to move from one BSS to
another.
0 Disassociation: A notification from either a station or an access point that an
existing association is terminated.
0 Authentication: Used to establish the identity of stations to each other. The
standard does not mandate any particular authentication scheme, which could
range from insecure handshaking to public-key encryption schemes.
0 Privacy: Used to prevent the contents of messages from being read by other than
the intended recipient. The standard provides for the optional use of encryption to
assure privacy.
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IEEE 802.11 Physical Media
0 Infrared at 1 Mbps and 2 Mbps operating at a wavelength between 850
and 950 nm.
0 Direct-sequence spread spectrum operating in the 2.4 GHz ISM band.
Up to seven channels, each with a data rate of 1 Mbps and 2 Mbps, can
be used.
0 Frequency-hopping spread spectrum operating in the 2.4 GHz ISM
band, at data rates of 1 Mbps and 2 Mbps.
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IEEE 802.11 Protocol Architecture
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IEEE 802.11 MAC Timing: Basic Access Method
Distributed Coordination Function (DCF)
•Short InterFrame Space (SIFS)
•PIFS (Point coordination function IFS)
•DIFS (Distributed coordination function IFS)
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IEEE 802.11 MAC Timing: PCF Superframe Construction
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IEEE 802.11 MAC Frame Format
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