WIRELESS LOCAL AREA NETWORKS

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(No Transcript)
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WIRELESS LANs
Infrastructure Network
AP Access Point
AP
AP
wired network
AP
Ad-hoc Network
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Wireless LAN - IEEE 802.11 Reference Architecture

• The terminology and some of the specific features
  are unique to this standard and are not reflected
  in all commercial products.

• However, it is useful to be familiar with the
  standard since its features are representative of
  the Wireless LAN capabilities required.

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Reference Architecture of Wireless LANs

• Station (STA)
• terminal with access mechanisms to the wireless
  medium and radio contact to the access point
• Basic Service Set (BSS)
• group of stations using the same radio frequency
• Access Point
• station integrated into the wireless LAN and the
  distribution system
• Portal
• bridge to other (wired) networks
• Distribution System
• interconnection network to form one logical
  network (ESS Extended Service Set) based on
  several BSS

STA1
BSS1
Access Point
Access Point
BSS2
STA2
STA3
ESS
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Reference Architecture

• The smallest building block of a wireless LAN is
  a basic service set (BSS), which consists of some
  number of stations executing the same MAC
  protocol and competing for access to the same
  shared medium.
• A basic service set may be isolated or it may
  connect to a backbone distribution system through
  an access point.
• The access point functions as a bridge.
• The MAC protocol may be fully distributed or
  controlled by a central coordination function
  housed in the access point.

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Reference Architecture

• The basic service set generally corresponds to
  what is referred to as a cell in the literature.
• An extended service set (ESS) consists of two or
  more basic service sets interconnected by a
  distribution system.
• Typically, the distribution system is a wired
  backbone LAN.
• The extended service set appears as a single
  logical LAN to the logical link control (LLC)
  level.

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Reference Architecture

• The standard defines three types of stations
  based on mobility
• No transition A station of this type is either
  stationary or moves only within the direct
  communication range of the communicating stations
  of a single BSS.
• BSS transition This is defined as a station
  movement from one BSS to another BSS within the
  same ESS. In this case, delivery of data to the
  station requires that the addressing capability
  be able to recognize the new location of the
  station.
• ESS 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.

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Protocol Architecture
fixed terminal
mobile terminal
infrastructure network
access point
application
application
TCP
TCP
IP
IP
LLC
LLC
LLC
MAC
802.3 MAC
802.3 MAC
MAC
PHY
802.3 PHY
802.3 PHY
PHY
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Protocol Layers and Functions

• PLCP Physical Layer Convergence Protocol
• clear channel assessment signal (carrier sense)
• PMD Physical Medium Dependent
• modulation, coding
• PHY Management
• channel selection, MIB
• Station Management
• coordination of all management functions

• MAC
• access mechanisms, fragmentation, encryption
• MAC Management
• synchronization, roaming, MIB, power management

Station Management
LLC
DLC
MAC
MAC Management
PLCP
PHY Management
PHY
PMD
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Basics of Wireless LANs

• Coverage area, data rate, and battery
  consumption.
• Characterized by small coverage areas (200m),
  but relatively high bandwidths
• (data rates) (upto 50Mbps currently)
• Major standards
• WLAN IEEE 802.11 and HIPERLAN.
• WPAN IEEE 802.16 (Bluetooth) and HomeRF

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Advantages of WLANs

• Very flexible within the reception area
• Users can access high speed multimedia
  applications anywhere at anytime, with easy
  implementation, low cost, and wide user
  acceptance
• - Generally works in industrial, scientific,
  and
• medical (ISM) band, which is un-licensed and
• available for public.
• (Almost) no wiring difficulties (e.g. historic
  buildings, firewalls)

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WLANs Advantages

• Buildings with large open areas, such as
  manufacturing plants, stock exchange trading
  floors, and warehouses
• Historical buildings with insufficient twisted
  pair and where drilling holes for new wiring is
  prohibited
• Small offices where installation and maintenance
  of wired LANs is not economical

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Disadvantages of WLANs

• Typically very low bandwidth compared to wired
  networks (1-10 Mbit/s)
• Many proprietary solutions, especially for higher
  bit-rates, standards take their time.
• Products have to follow many national
  restrictions if working wireless, it takes a very
  long time to establish global solutions.
• Interference Problems

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Family of Wireless LAN (WLAN) Standards 802.11

• 802.11a - 5GHz- Ratified in 1999
• 802.11b - 11Mb 2.4GHz- ratified in 1999
• 802.11d - Additional regulatory domains
• 802.11e - Quality of Service
• 802.11f - Inter-Access Point Protocol (IAPP)
• 802.11g - Higher Data rate (20mBps) 2.4GHz
• 802.11h - Dynamic Frequency Selection and
  Transmit Power Control mechanisms
• 802.11i - Authentication and security

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WLANs Current Use

• Home wireless networks.
• Enterprise wireless networks.
• Public access.
• Hospitals.
• Warehouses.
• Consulting and audit teams
• Dynamic environments, ad agencies, etc.
• Universities
• Historic buildings, older buildings.
• Meeting rooms.
• Retail stores
• Restaurants and car rental agencies
• Data backup.

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In-Building Deployment Service Objectives

• Greater coverage
• High-speed rates
• Scalable and manageable bandwidth
• Enable new (high-end) services (and keep running
  the good old ones)
• Service differentiation
• Smooth deployment and low maintenance
• Interoperable systems
• Plug Play
• Extends the local area network
• Freedom to access the corporate network
• Comparable to those of wired networks
• Secure access to important information (e-mail,
  corporate data, Internet)

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Some Facts

• By 2005, more than 1/3rd of Internet users will
  have Internet connectivity through a wireless
  enabled device (750 million users)!!! (Source
  Intermarket group)
• By the end of 2001, more than half of the
  workforce in the US uses a wireless net device
  primarily cellular phones! (Source Cahners Intat
  Group)
• By the year 2004 revenue from wireless data will
  reach 34B, and by the year 2010 the number of
  wireless data subscribers will hit 1B!!

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Design Goals for Wireless LANs

• Global, seamless operation (must sell in all
  countries)
• Low power for battery use (power saving modes and
  power management functions)
• No special permissions or licenses needed to use
  the LAN
• Robust transmission technology (avoid
  interference)
• Simplified spontaneous cooperation at meetings
• Easy to use for everyone, simple management
• Protection of investment in wired networks
  (interoperable with wired LANs)
• Security (no one should be able to read my data),
  privacy (no one should be able to collect user
  profiles), safety (low radiation)

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Topologies- Single-Cell Wireless LAN
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Topologies- Single-Cell Wireless LAN

• In Figure there is a backbone wired LAN, such as
  Ethernet, that supports servers, workstations,
  and one or more bridges or routers to link with
  other networks.
• In addition, there is a control module (CM)
  (Access Point (AP) before) that acts as an
  interface to a wireless LAN. (CM AP)
• The control module includes either bridge or
  router functionality to link the wireless LAN to
  the backbone.
• In addition, it includes some sort of access
  control logic, such as a polling or token-passing
  scheme, to regulate the access from the end
  systems.
• Note that some of the end systems are stand-alone
  devices such as a workstation or a server.
• In addition, hubs or other user modules (UM)
  (PORTAL before) that control a number of stations
  off a wired LAN may also be part of the wireless
  LAN configuration.

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Topologies- Multiple Cell Wireless LAN
Figure 2
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Topologies- Multiple Cell Wireless LAN

• In this case there are multiple control modules
  interconnected by a wired LAN.
• Each control module supports a number of wireless
  end systems within its transmission range.
• For example, with an infrared LAN, transmission
  is limited to a single room therefore, one cell
  is needed for each room in an office building
  that requires wireless support.

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WLANs 802.11 Protocol Architecture
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IEEE 802.11- Physical Medium Specification

• Three Physical Media
• INFRARED
• Narrowband Microwave
• Spread Spectrum

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Infrared

• Infrared signals used to transmit data (similar
  to TV remotes!)
• Higher data rates possible (than spread
  spectrum)
• Line of sight point-to-point configuration
  required (or reflection surface that reflects
  signals)
• Too sensitive to obstacles, line-of-sight
  requirement, etc.
• 850-950 nm, diffuse light (to allow
  point-to-multipoint communication)
• 10 m maximum range with no sunlight or heat
  interfere

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Narrowband Microwave

• Typically used to link two WLANs together (for
  example, to link WLANs in two buildings)
• Microwave dishes required at both ends of link
• Unlike spread spectrum which operates in the
  unlicensed ISM band, narrowband microwave
  requires FCC licensing
• Exclusive license typically effective within a
  17.5 mile radius

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Spread Spectrum

• Distributed signals over multiple frequencies
  (to avoid eavesdropping or jamming)
• Frequency Hopping Spread Spectrum (FHSS)
• Sender transmits over a seemingly random series
  of frequencies
• Intended receiver aware of sequence of
  frequencies and hops accordingly
• Allows the coexistence of multiple networks in
  the same area by using different hopping
  sequences
• Direct Sequence Spread Spectrum (DSSS)
• Sender transmits redundant information called
  chips between actual data bits
• Intended receiver aware of spread removes
  redundant information accordingly
• Preamble and header of a frame is always
  transmitted with 1 Mbit/s, rest of transmission 1
  or 2 Mbit/s

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Wireless LAN Classification

• Infrared (IR) LANs
• An individual cell of an IR LAN is limited to a
  single room, since infrared light does not
  penetrate opaque walls.
• Spread Spectrum LANs
• In most cases these LANs operate in the ISM
  (industrial, scientific, and medical) bands, so
  no FCC licensing is required for their use in the
  United States.
• Narrowband Microwave LANs
• These LANs operate at microwave frequencies but
  do no use spread spectrum. Some of these
  products operate at frequencies that require FCC
  licensing others use one of the unlicensed ISM
  bands.
• Table 1 summarizes some of the key
  characteristics of these three technologies the
  details are explored in the next three
  subsections.

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Comparison Infrared vs. Radio Transmission

• Infrared
• uses IR diodes, diffuse light, multiple
  reflections (walls, furniture etc.)
• Advantages
• simple, cheap, available in many mobile devices
• no licenses needed
• Disadvantages
• interference by sunlight, heat sources etc.
• many things shield or absorb IR light
• low bandwidth
• Line of Sight Problem
• Example
• IrDA (Infrared Data Association) interface
  available everywhere PDAs, calculators, laptops,
  mobile phones...

• Radio
• typically using the license free ISM band at 2.4
  GHz
• Advantages
• experience from wireless WAN and mobile phones
  can be used
• coverage of larger areas possible (radio can
  penetrate walls, furniture etc.)
• Disadvantages
• very limited license free frequency bands
• shielding more difficult, interference with other
  electrical devices
• Example
• WaveLAN, HIPERLAN, Bluetooth

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Overview of WLAN Classification
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Wireless LAN MAC

• CSMA as Wireless MAC?
• Hidden and Exposed Terminal Problems make the
  use of CSMA an inefficient technique

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Hidden Terminal Problem
Collision
A
B
C

• A talks to B
• C senses the channel
• C does not hear As transmission (out of range)
• C talks to B
• Signals from A and B collide

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Exposed Terminal Problem
Not possible
A
B
C
D

• B talks to A
• C wants to talk to D
• C senses channel and finds it to be busy
• C stays quiet (when it could have ideally
  transmitted)

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Hidden and Exposed Terminal Problems

• Hidden Terminal
• More collisions
• Wastage of resources
• Exposed Terminal
• Underutilization of channel
• Lower effective throughput

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MACA - Collision Avoidance

• MACA (Multiple Access with Collision Avoidance)
  uses short signaling packets for collision
  avoidance
• RTS (request to send) a sender request the right
  to send from a receiver with a short RTS packet
  before it sends a data packet
• CTS (clear to send) the receiver grants the
  right to send as soon as it is ready to receive
• Signaling packets contain
• sender address
• receiver address
• packet size
• Variants of this method can be found in
  IEEE802.11 as DFWMAC (Distributed Foundation
  Wireless MAC)

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Hidden Terminal Revisited
RTS
A
B
C
CTS
CTS
DATA

• A sends RTS
• B sends CTS
• C overheads CTS
• C inhibits its own transmitter
• A successfully sends DATA to B

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Hidden Terminal Revisited

• How does C know how long to wait before it can
  attempt a transmission?
• A includes length of DATA that it wants to send
  in the RTS packet
• B includes this information in the CTS packet
• C, when it overhears the CTS packet, retrieves
  the length information and uses it to set the
  inhibition time

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Exposed Terminal Revisited
RTS
A
B
C
D
RTS
Tx not inhibited
CTS
Cannot hear CTS

• B sends RTS to A (overheard by C)
• A sends CTS to B
• C cannot hear As CTS
• C assumes A is either down or out of range
• C does not inhibit its transmissions to D

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Collisions

• Still possible RTS packets can collide!
• Binary exponential backoff performed by stations
  that experience RTS collisions
• RTS collisions not as bad as data collisions in
  CSMA (since RTS packets are typically much
  smaller than DATA packets)

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Drawbacks

• Collisions still possible if CTS packets cannot
  be heard but carry enough to cause significant
  interference
• If DATA packets are of the same size as RTS/CTS
  packets, significant overheads

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WLANs 802.11 Protocol Architecture
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IEEE 802.11- Medium Access Control

• Distributed Mode Distributed Coordination
  Function (DCF)
• Based on CSMA/CA protocol
• Uses a contention algorithm to provide access
  to all traffic.
• Ordinary asynchronous traffic uses DCF
  directly.
• Coordinated Mode Point Coordination Function
  (PCF)
• Supports real time traffic
• Based on polling which is controlled by a
  centralized point coordinator.
• Uses a centralized MAC algorithm and provides
  contention-free service.
• PCF is built on top of DCF and exploits
  features of DCF to assure access for its users.
• NOTE Both the DCF and PCF can operate
  concurrently within the same BSS to provide
  alternative contention and contention-free
  periods

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802.11 - MAC Layer Overview

• DFWMAC-DCF CSMA/CA (Mandatory)(Distributed
  Foundation Wireless Medium Access Control -
  Distributed Coordinated Function CSMA/CA)
• DFWMAC-DCF w/ RTS/CTS (Optional)
• Distributed Foundation Wireless MAC
• Avoids Hidden Terminal problem
• DFWMAC- PCF (Optional)
• Access point polls terminals according to a list

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802.11 - CSMA/CA Access Method DFWMAC-DCF CSMA/CA

• A station with a frame to transmit senses the
  medium.
• If the medium is idle, it waits to see if the
  medium remains idle for a time equal to IFS. If
  so, the station may transmit immediately.
• If the medium is busy (either because the station
  initially finds the medium busy or because the
  medium becomes busy during the IFS idle time),
  the station defers transmission and continues to
  monitor the medium until the current transmission
  is over.
• Once the current transmission is over, the
  station delays another IFS.
• If the medium remains idle for this period, the
  station backs off using a binary exponential
  backoff scheme and again senses the medium.
• If the medium is still idle, the station may
  transmit.

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802.11 - CSMA/CA Access Method I
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802.11 - CSMA/CA Access Method II Interframe
Spaces (IFS)

• Priorities
• Defined through different inter frame spaces
• SIFS (Short Inter Frame Spacing)
• highest priority, for ACK, CTS, polling response
• PIFS (PCF IFS) - Point Coordination Function
  Inter-Frame spacing
• medium priority, for real time service using PCF
• SIFS one slot time
• DIFS (DCF, Distributed Coordination Function IFS)
• lowest priority, for asynchronous data service
• SFIS two slot times

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Interframe Spaces (IFS)
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IEEE 802.11- Medium Access Control
In Figure we illustrate the use of these time
values.
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802.11 - CSMA/CA Access Method II

• Station has to wait for DIFS before sending data
• Receivers acknowledge at once (after waiting for
  SIFS) if the packet was received correctly (CRC))
• Automatic retransmission of data packets in case
  of transmission errors

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802.11 DFWMAC w/ RTS/CTS

• Station can send RTS (request to send) with
  reservation parameter after waiting for DIFS
  (reservation determines amount of time the data
  packet needs the medium)
• Every node receiving the RTS has to set its Net
  Allocation Vector (NAV) in accordance with the
  duration of the field (NAV specifies the earliest
  point at which the station can try to access the
  medium
• If receiver receives RTS, it sends CTS (Clear to
  Send) after SIFS. CTS again contains duration
  field and all stations receiving this packet need
  to adjust their NAV
• Sender can now send data after SIFS,
  acknowledgement via ACK by receiver after SIFS

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IEEE 802.11- Medium Access Control

• Clear to Send (CTS)
• A station can ensure that its data frame will get
  through by first issuing a small request to send
  (RTS) frame.
• The station to which this frame is addressed
  should respond immediately with a CTS frame if it
  is ready to receive.
• All other stations receive the RTS and defer
  using the medium until they see a corresponding
  CTS or until a timeout occurs.
• PIFS is used by the centralized controller in
  issuing polls and takes precedence over normal
  contention traffic.
• However, those frames transmitted using SIFS have
  precedence over a PCF poll.
• Finally, the DIFS interval is used for all
  ordinary asynchronous traffic.

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802.11 DFWMAC w/ RTS/CTS
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IEEE 802.11- Medium Access Control

• Point Coordination Function
• PCF is an alternative access method implemented
  on top of the DCF.
• The operation consists of polling with the
  centralized polling master (point coordinator).
• The point coordinator makes use of PIFS when
  issuing polls.
• Because PIFS is smaller than DIFS, the point
  coordinator can seize the medium and lock out all
  asynchronous traffic while it issues polls and
  receives responses.

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IEEE 802.11- Medium Access Control

• Point Coordination Function (Cont.)
• A wireless network is configured so that a number
  of stations with time-sensitive traffic are
  controlled by the point coordinator while
  remaining traffic contends for access using CSMA.
  
• The point coordinator could issue polls in a
  round-robin fashion to all stations configured
  for polling.
• When a poll issued, the polled station may
  respond using SIFS.
• If the point coordinator receives a response, it
  issues another poll using PIFS.
• If no response is received during the expected
  turnaround time, the coordinator issues a poll.

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IEEE 802.11- Medium Access Control

• Point Coordination Function (Cont.)
• Figure 18 illustrates the use of the superframe.
  

Figure 18
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IEEE 802.11- Medium Access Control

• Point Coordination Function (Cont.)
• At the beginning of a superframe, the point
  coordinator may optionally seize control and
  issues polls for a given period of time.
• This interval varies because of the variable
  frame size issued by responding stations.
• The remainder of the superframe is available for
  contention-based access.

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IEEE 802.11- Medium Access Control

• Point Coordination Function (Cont.)
• At the end of the superframe interval, the point
  coordinator contends for access to the medium
  using PIFS.
• If the medium is idle, the point coordinator
  gains immediate access and a full superframe
  period follows.
• However, the medium may be busy at the end of a
  superframe.
• In this case, the point coordinator must wait
  until the medium is idle to gain access this
  results in a foreshortened superframe period for
  the next cycle.

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DFWMAC-PCF I

• The access mechanisms presented so far cannot
  guarantee a maximum access delay or minimum
  transmission bandwidth.
• To provide a time bounded service, the standards
  specify a Point Coordination Function (PCF) on
  top of the DCF mechanisms.
• Using PCF requires an access point that can
  controls medium access and polls the single
  nodes. Ad Hoc networks cannot use this function.

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DFWMAC-PCF I

• At time t0 the contention-free period should
  start, but another station is transmitting data
• After the medium has been idle, the PCF has to
  wait for PIFS before accessing the medium.
• The point coordinator now sends data D1 to the
  first station. The station can answer after SIFS.
  After waiting for SIFS, the point coordinator can
  poll the second station by sending D2.
• The second station replies with U2

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DFWMAC-PCF I
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DFWMAC-PCF II

• Polling continues with the third node which has
  nothing to answer.
• After waiting for PIFS, the point coordinator can
  issue an end marker (CFend), indicating that the
  contention period may start again.
• The cycle starts again with the next superframe

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WLAN IEEE 802.11b

• Data rate
• 1, 2, 5.5, 11 Mbit/s, depending on SNR
• User data rate max. approx. 6 Mbit/s
• Transmission range
• 300m outdoor, 30m indoor
• Max. data rate 10m indoor
• Frequency
• Free 2.4 GHz ISM-band
• Security
• Limited, WEP (Wired Equivalent Privacy) insecure,
  SSID
• Availability
• Many products, many vendors

• Connection set-up time
• Connectionless/always on
• Quality of Service
• Typ. Best effort, no guarantees (unless polling
  is used, limited support in products)
• Manageability
• Limited (no automated key distribution, sym.
  Encryption)
• Special Advantages/Disadvantages
• Advantage many installed systems, lot of
  experience, available worldwide, free ISM-band,
  many vendors, integrated in laptops, simple
  system
• Disadvantage heavy interference on ISM-band
  (Industrial, Scientific, Medical band), no
  service guarantees, slow relative speed only

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WLAN IEEE 802.11a

• Connection set-up time
• Connectionless/always on
• Quality of Service
• Typ. best effort, no guarantees (same as all
  802.11 products)
• Manageability
• Limited (no automated key distribution, sym.
  Encryption)
• Special Advantages/Disadvantages
• Advantage fits into 802.x standards, free
  ISM-band, available, simple system, uses less
  crowded 5 GHz band
• Disadvantage stronger shading due to higher
  frequency, no QoS

• Data rate
• 6, 9, 12, 18, 24, 36, 48, 54 Mbit/s, depending on
  SNR
• User throughput (1500 byte packets) 5.3 (6), 18
  (24), 24 (36), 32 (54)
• 6, 12, 24 Mbit/s mandatory
• Transmission range
• 100m outdoor, 10m indoor
• E.g., 54 Mbit/s up to 5 m, 48 up to 12 m, 36 up
  to 25 m, 24 up to 30m, 18 up to 40 m, 12 up to 60
  m
• Frequency
• Free 5.15-5.25, 5.25-5.35, 5.725-5.825 GHz
  ISM-band
• Security
• Limited, WEP insecure, SSID
• Availability
• Some products, some vendors

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WLAN IEEE 802.11 Future Developments (08/2002)

• 802.11d Regulatory Domain Update completed
• 802.11e MAC Enhancements QoS ongoing
• Enhance the current 802.11 MAC to expand support
  for applications with Quality of Service
  requirements, and in the capabilities and
  efficiency of the protocol.
• 802.11f Inter-Access Point Protocol ongoing
• Establish an Inter-Access Point Protocol for data
  exchange via the distribution system.
• 802.11g Data Rates 20 Mbit/s at 2.4 GHz 54
  Mbit/s, OFDM ongoing
• 802.11h Spectrum Managed 802.11a (DCS, TPC)
  ongoing
• 802.11i Enhanced Security Mechanisms ongoing
• Enhance the current 802.11 MAC to provide
  improvements in security.
• Study Groups
• 5 GHz (harmonization ETSI/IEEE) closed
• Radio Resource Measurements started
• High Throughput started

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WLANs 802.11 Compatibility

• 802.11a and 802.11b share the same MAC layer
• Significant differences at the physical layer.
• 802.11b 2.4 GHz, ISM band,
• 802.11a 5 GHz, U-NII band
• possible to operate both on the same network
  concurrently (using the same access points)
• Interoperability
• WECA (Wireless Ethernet Compatibility Alliance)
  organization behind Wi-Fi that certifies products
  meeting the 802.11b specification

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WLANs Comparison of Technologies
67
WLANs Interference

• An important issue in all wireless systems
  because nearby users occupy same bandwidth and
  cause co-channel interference.
• For WLANs, in addition to co-channel
  interference, other types of interference exist
  mainly due to the use of unlicensed ISM band.
  Interference to WLANs comes from the following
  major sources
• Co-channel interference.
• Interference from non-wLAN devices in the same
  frequency band
• Interference between different wLANs in the same
  frequency band.

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WLANs Interference Reduction

• Regulatory and standards
• Change frequency segment of a channel (proposed
  by FCC for Bluetooth)
• Usage and practices
• When one wLAN is working, others are banned. Not
  practical. Modal operation of wLANs can be a good
  alternative
• Technical approaches.
• Driver layer software above the MAC layer can
  be installed for different types of wLANs. Thus,
  software switch from one wLAN to another wLAN is
  required.
• MAC layer more attractive but it is an on-going
  research topic.
• Physical layer signal processing techniques and
  anti-jamming schemes used

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WLANs Environmental Issues

• Has been proved that WLAN is safe for health
• Radiation used by this technology, fall well
  within the limits of safety guidelines (both in
  terms of frequency content and power level)
  specified by Radio Frequency Safety Standards and
  Recommendations.
• Radiation in this frequency range is non-ionizing
  (as they do not have enough energy to break the
  chemical bonds of genetic material of body
  cells).
• Vendors designing their products to operate
  within the power limit set by the Safety
  Standards.
• Others
• No wires to hide and maintain
• Looks much better and cleaner compared to the
  wired one.
• Positive impact on user psychology due to user
  mobility, reduced-cost of ownership,
  real-time-access to information,

70
WLANs Major Suppliers

• Three types of products in WLANs
• Access Point
• LAN Adapters and
• LAN Bridges.

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WLANs Access Point Products
72
WLANs LAN Adapter Products
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WLANs Bridge Products
74
WLANs Market Segment
by Wireless LAN Association (wLANA )
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WLANs Market Forecast

• Seen as "The Technology" of the future.
• Trend support Decrease of product price and
  increase of network speed,
• Apart from current sectors, more and more new
  markets are opening up for this technology. Some
  of these are shipping and receiving area,
  distribution center, cafeteria, home, train, bus,
  airport, sport complexes, trade shows, coffee
  shops, etc.
• Huge market potential
• Make WLAN as a viable option to connect the
  developing nations to the developed part of the
  world, making the concept "Global Village" a
  reality.
• Estimated a five-fold increase in its market by
  2005

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WLANs Technology Forecast

• WLAN will have higher speeds
• Wi-Fi5 for IEEE 802.11a up to 54Mbps
• 5.7-GHz band promises to allow for the next
  breakthrough data rate of 100 Mbps.
• Provide multimedia and access to 3G-4G Systems
• HIPERLAN/2 to provide high speed access (up to 54
  Mbit/s at PHY layer) to 3G mobile core networks,
  and Internet.
• More security guarantees.
• Enhancements to Wired Equivalent Privacy (WEP)

77
WLANs Technology Forecast

• Even more decreased size, cost, power consumption
• New approaches in handling network parameters
  dynamically to improve throughput.
• Improved reliability
• Efficient and concurrent uses of bandwidth via
  Wideband Orthogonal Frequency Division
  Multiplexing (W-OFDM)

78
WLANs Service Analysis

• Convergence for voice and data networks
• As voice, audio and video are shared among
  WLAN-enabled phones, MP3 players, web cameras,
  interactive TVs, etc, wireless applications will
  move beyond traditional computer networking.
• Replacement of proprietary cables.
• Portable access to wireless LAN.
• Multimedia over wireless networks.
• Wireless remote data access.
• Data Backup.

79
WLANs Network Design Plan Analysis

• Key parameters
• number of expected users
• area of coverage
• quality of service
• service types
• Network topology for WLAN can broadly be
  classified into
• Ad-Hoc WLAN
• Client-Server based WLAN

80
WLANs Performance Metrics

• Overall coverage area
• Can be evaluated in terms of received signal
  strength intensity (RSSI)
• Throughput
• Can be evaluated by measuring TCP connection
  throughputs since wLANs establish a client-server
  communication link via TCP connection,
• Implementations of handoff and dropping are the
  responsibility of manufacturers, since they vary
  according to different equipments

81
WLANs Network Security Aspects

• Service set identifier (SSID) (can be configured
  into 802.11 APs)
• Use VPN technologies built into or on top of WLAN
  products
• Wired equivalent privacy (WEP) of 802.11 or the
  common 128-bit extension
• Uses shared keys and a pseudo random number (PRN)
  as an initial vector (IV) to encrypt the data
  portion of network packets, but does not encrypt
  802.11b header
• Each station (clients and APs) has a number of
  keys to encrypt data before it is transmitted
• Each station can only receive a packet being
  encrypted with its appropriate key. Without
  proper key, the packet will be discarded
• Some vendors also provide key servers to
  implement centralized key management, such as
  Cisco.

82
WLANs Price Comparison
83
WLANs Total Cost

• Much smaller (around one year) payback period
• Even though initial capital cost for the WLAN
  may be more, but the running cost for the WLAN is
  much less
• Cost-effective large scale network deployment
• Example organizations for around 300 users
  benefited annual savings of up to 4.9 million,
  which corresponds to per user saving of
  15,989.00.
• Low initial installation cost (wiring)
• University of Akron, covered their four-story
  library with WLAN with a total cost of 80,000,
  using Cisco Airnet 350 series and the estimated
  cost for wired network for that was 800,000

84
Conclusions

• Users demand ubiquity mergence of the wireless
  communication services indoor and outdoor
• Greater demand for integration with Bluetooth,
  wLAN and cellular system
• Technology to meet these demand available today
• Some key issues
• interoperability between different wireless
  network systems (MORE WORK NEEDED)
• Security More work needed. An ideal solution
  combination of VPN and IPSec

85
Conclusions

• Since the needs from various enterprises and end
  users are quite different, the service providers
  should prepare various network deployments
• Many issues to be considered network capacity,
  the connectivity to wired network, QoS, security,
  price and performance.
• A competitive solution provides seamless
  end-to-end connectivity from mobile users to
  wired ones.
• A web-based, centralized network management is
  another consideration most customers want

86
WLANs - Challenging Issues

• Relatively low data rate.
• Some can achieve very high data rate, e.g., the
  rate of IEEE 802.11 WLANs can be as high as
  11Mbps, while some products such as Bluetooth can
  only achieve medium speed data rate.
• Lack of support for real time services.
• IEEE 802.11 products, which are based on the
  CSMA/CA protocol, are unable to provide QoS
  guarantees for voice, video, and other real time
  services. (IEEE 802.11 working group E is still
  working QoS enhancement)
• Interference between different types of WLANs
• Lack of Interoperability between WLANs