WLAN Fundamentals by linxiaoqin


									WLAN Fundamentals
  By Marc-André Léger
    DESS, MASc, PHD(candidate)

                                 Fall 2007
           Save the forest
• Please do not print out more than one
  module at a time as it may evolve…
Module 2
         Session objectives
• Description and review of the various
  components which make up a wireless
                WLAN Design Issues
• THROUGHPUT: Factors that affect throughput include airwave
  congestion (number of users), range, the type of WLAN system used, as well as
  bottlenecks on the wired portions of the WLAN.

• COVERAGE: Function of product design including transmitted power
  and receiver design and the propagation path, especially in indoor environments.

• INTEROPERABILITY: Interconnection with wired systems.

• RELIABILITY: Radio interference can cause degradation.
          Costs issues of
        WLAN implementations
• Initial investment
    •   Network Interface Cards
    •   Access Points
    •   WLAN Management Software
    •   Test and Evaluation Costs

• On-going operation & Support
    • User Training, guides and policies
    • On-going IT training
    • License and Service Contract Fees (Hardware & Software)
    • Infrastructure maintenance
    • Network and Security monitoring
Six critical planning challenges

1. Defining data needs, capacity and
   coverage requirements
2. Service Levels and Quality
3. Threats and Risk
4. Project planning
5. Choosing the right standard and vendor
6. Educating users
             WLAN Applications
• Home Usage: Wireless networks save time and money.
• Small business: entrepreneurs focus on growing their
  businesses, the WLAN can grow with them.
• Services industry: Wireless internet access for customers
• Enterprise: Larger corporations and manufacturing facilities find
  benefits in having a portion of their network wireless, combined with
  RFID and GPS it can be an agent of change.
• Urban access: Wireless hotspots create a public space.
• LAN to LAN Bridging: WLAN are a quick and reliable solution
  to link a campus WAN.
     WLAN infrastructure networks


             wired network

AP= Access Point
 Infrastructure-based networks
• Infrastructure networks provide access to other networks.
• Communication typically takes place only between the
  wireless nodes and the access point, but not directly
  between the wireless nodes.
• The access point does not just control medium access,
  but also acts as a bridge to other wireless or wired
• Several wireless networks may form one logical wireless
  – The access points together with the fixed network in between can
    connect several wireless networks to form a larger network
    beyond actual radio coverage.
    Infrastructure-based networks
• Network functionality lies within the access point
  (controls network flow), whereas the wireless clients can
  remain quite simple.
• Use different access schemes with or without collision.
   – Collisions may occur if medium access of the wireless nodes
     and the access point is not coordinated.
       • If only the access point controls medium access, no collisions are
           – Useful for quality of service guarantees (e.g., minimum bandwidth for
             certain nodes)
           – The access point may poll the single wireless nodes to ensure the data
• Infrastructure-based wireless networks lose some of the
  flexibility wireless networks can offer in general:
   – They cannot be used for disaster relief in cases where no
     infrastructure is left.
Ad hoc networks
    Ad Hoc network definition
• A network made up exclusively of wireless
  nodes without any access points operating
  in peer-to-peer configuration, grouped
  together in a temporary manner.
         Ad hoc WLAN networks
• No need of any infrastructure to work
  – greatest possible flexibility
• Each node communicate with other nodes, so no access
  point controlling medium access is necessary.
  – The complexity of each node is higher
     •   implement medium access mechanisms, forwarding data
• Nodes within an ad-hoc network can only communicate if
  they can reach each other physically
  – if they are within each other’s radio range
  – if other nodes can forward the message
     Sensor network definition
• A sensor network is a collection of
  collaborating sensor nodes (ad hoc tiny
  nodes with sensor capabilities) forming a
  temporary network without the aid of any
  central administration or support services.
• Sensor nodes can collect, process,
  analyze and disseminate data in order to
  provide access to information anytime and
       Sensor network features
•   Large number of sensors
•   Low energy use
•   Efficient use of the small memory
•   Data aggregation
•   Network self-organization
•   Collaborative signal processing
•   Querying ability
Wireless LAN Topologies
         Wireless LAN Topologies

•   Without a wireless alternative, organizations frequently resort to wide
    area networking (WAN) technologies to link together separate facilities.
•   Contracting for leased-line or other wide-area services often presents a
    variety of drawbacks:
    • Installation is typically expensive and rarely immediate
    • Monthly fees are often quite high for bandwidth
•   A wireless bridge can typically be purchased and installed in a day with
    no recurring charges.
WLAN Devices
       WLAN Devices
•   Access points
•   Wireless bridges
•   Wireless Workgroup bridges
•   Wireless routers
•   WLAN Client devices
•   Wireless Gateways
•   Enterprise gateways
•   WLAN Switches WLAN Mesh routers
•   PoE
Access points

                (CWNA Ch7-p220)
          Access Point
Different vendors
  • Cisco
  • D-Link
  • Linksys
  • Nortel
  • Symbol
  • and more…
           Access Point
Different shape and size but all share
 similar options
  • Fixed or detachable antennas
  • Advanced filtering capabilities
  • Removable radio cards
  • Variable output power
  • Variable types of wired connectivity
     – 10BaseTx, 10/100BaseTx, 100BaseTx,
       100BaseFx, and more
           Typical Application of AP

                  Access                                   Wireless
   Wireless        Point                                    Laptop
                               PC with
    Laptop                  Wireless Card


                                        Point      PC with
                 Wireless                       Wireless Card
               AP Modes
– Root mode
– Repeater Mode
– Bridge Mode
  •   Root
  •   Non-root
  •   Repeater
  •   Access-point

– Additional topologies
  •   System redundancy
  •   Added bandwidth
               AP Wireless root mode

                CHANNEL 1      CHANNEL 6

LAN Backbone

                AP             AP

                  Root           Root
                  Mode           Mode
      AP Wireless Repeater Mode
•   The repeater’s Ethernet port does not forward packets
•   The repeater must be within reach of the root
•   The repeater is a client to the root like any other STAs
•   Reduction of throughput !!!
                           CHANNEL 1   CHANNEL 1

         LAN Backbone

                             Root       Repeater
                             Mode        Mode
     AP Wireless Bridge Mode
– 4 modes supported
  • Root, Non-Root, Repeater, Access-Point
– In bridge mode no STAs are allowed
  • Except in Access-Point mode                             ntA
                                                      g  me


                                                                                n   tC
                                                                          g  me
                                   Bridge                         LA
       Wireless Workgroup Bridge
• Aggregates multiple wired clients over a common
  wireless link
  – Clients’ MAC will not be seen behind the workgroup bridge
• The workgroup bridge is a client to the AP
• The AP can associate with other STAs
• Useful for mobile setups
                         ntA                              ntB
                      me                            g  me
                s   eg                            se
             AN                               N
           L                                LA

              Root               Bridge
              Mode                Mode
  AP Modes (cont’d)
Distances Limited by the 802.11 Specification

            1.6km @ any Data Rate

              AP to any client

               40km @ 2Mbps
               18km @11Mbps

            Bridge to any client
Hot standby Redundancy Topology
  •   One AP acts as a backup for a root AP
  •   Provides redundancy when one AP fails
  •   Standby AP must associate to the Root AP as a client
  •   Root and Standby APs communicate through radio and Ethernet

      LAN Backbone

                          Active AP       Standby AP
        Added Bandwidth Topology
• Used in crowded workplace
• More than 1 channel (3 maximum) covering an area
• Provides different AP to associate with

LAN Backbone

               CHANNEL 1
                           CHANNEL 6
Wireless bridges

                   (CNWA Ch7-p243)
   Wireless Bridge Applications

Wireless Bridge
     Types of WLAN Bridges
• Basic Ethernet-to-Wireless
• Workgroup Bridges
• Access Point / Wireless Bridge
Wi-Fi bridge
    •A device used to add desktop
    computers and printers in remote
    locations to the network without
    having to string cables and without
    having to equip each one with a Wi-
    Fi adapter.
    •Has a built-in LAN switch for
    plugging in several devices, and
    does not require line-of-site.
    •Can be set up almost anywhere
    and transmit over the air to another
    Wi-Fi bridge or access point that is
    wired to the main network.
            Wireless Bridge

    A wireless bridge is
 used to span buildings
  or areas where laying
cable or leasing lines is
   Wireless Workgroup bridges
• A Wireless bridge +
  an AP in a box

                         (CNWA Ch7-p253)
Wireless routers
WLAN products
              See also
• http://www.tigerdirect.ca/
• http://
WLAN Client devices

                  (CNWA Ch7-p257)
           Client Adapters
• For all types of computer in all WLAN
• External or directional antennas can
  provide extra distance, special
• This is covered in-depth in the RF
             WLAN Switch
• Wireless vendors such as Airespace (now
  Cisco) offer an alternative wireless LAN
  infrastructure that includes a wireless
  switch in addition to the access points.
• In this case, a company installs the
  wireless switch instead of using existing
  infrastructure. The switch concentrates the
  intelligence of the wireless network,
  enabling the access points to be less
  intelligent ("thin").
           WLAN Switch
• The WLAN switch offers a centralized
  hardware platform for supporting the
  access points without tying up an
  existing wired network.
• The WLAN switch continually
  monitors the access points and
  physically disables an access point if
  it doesn't have a configuration that
  matches the company's security
           WLAN Switch
• The switch is smart enough to shut off
  the electrical power to suspicious
  access points via a power-over-
  Ethernet (PoE) connection.
• In addition, wireless switches
  incorporate designs that offer very
  fast handoffs as users roam from one
  access point to another. This results
  in smooth operation of Voip WLAN
             Cable and Accessories

Low Loss Cable
Antenna Mounts
Wireless IP Phone
     Consumer wireless products

•   There is a real difference in functionality and administrative
    capabilities between Business-class and Consumer
    wireless products.
Wireless Gateways

                    (CNWA Ch7-p271)
    WLAN Residential Gateways
• ‘All-in one’ single device solution
• Built to connect a small number
  of STAs to a single device
  offering more than WLAN
  WLAN Residential Gateways
• They generally offer:
     • Ethernet connectivity both wired and wireless.
     • Built-in hub or switch
     • WAN port facing the Internet that may be connected through
       one of the following: Cable modem, xDSL modem, Analog
       modem, Satellite modem
     • Point-to-Point Protocol over Ethernet (PPPoE)
     • Network Address Translation (NAT)
     • Port Address Translation (PAT)
     • Ethernet switching
     • Print Services
     • Routing
     • Virtual Private Networks (VPNs)
     • Dynamic Host Configuration Protocol (DHCP) Server
     • Firewall
      Linksys - SOHO Wireless Devices

  WAP54G          WRT54G      WRT300N           WAP4400N
  Wireless-G     Wireless-G   Wireless-N    Wireless-N Access
 Access Point    Broadband    Broadband    Point with Power Over
                   Router      Router             Ethernet

WMP54G          WUSB54GC      WPC54G            WPC300N
Wireless-G        Compact     Wireless-G   Wireless-N Notebook
   PCI           Wireless-G   Notebook           Adapter
 Adapter        USB Adapter    Adapter
Enterprise gateways
  WLAN Enterprise Gateways
• Supports:
  – many APs
  – a variety of WLAN and WPAN technologies such as:
     • 802.11 standard, Bluetooth, HomeRF and more
  – SNMP and allow enterprise-wide simultaneous user
    profiles upgrades
  – RADIUS, LDAP, Windows NT authentication
    databases, and data encryption using industry-
    standard VPN tunnel types
    WLAN Enterprise Gateways
• Provides specialised authentication and
  connectivity for wireless clients

        Cisco Wireless Devices

 Aironet   1200         Aironet                    1300 Series
     Series              1100 Series                  Bridge
  Access-Point          Access-Point

                                          Diversity               Yagi mast
                                       omnidirectional              or wall
                                        ceiling mount               mount
                                           Antenna                 Antenna

                              dipole                     Omnidirectional
Cisco Client Adapters        antenna                      mast mount
WLAN Switches

                (CNWA Ch7-p280)
          WLAN Switches
• Creates virtual or logical WLANs
• Can segregate WLAN for security
• Still evolving – bleeding edge
           WLAN Mesh routers

     Wireless Mesh Networks are anticipated to
resolve the limitations and to significantly improve
   the performance of ad hoc networks, wireless
 local area networks (WLANs), wireless personal
       area networks (WPANs), and wireless
      metropolitan area networks (WMANs).
                                        (CNWA Ch7-p286)
               Mesh routers
• Wireless mesh networks (WMNs) consist of
  mesh routers and mesh clients, where mesh
  routers have minimal mobility and form the
  backbone of WMNs.
• They provide network access for both mesh and
  conventional clients.
• The integration of WMNs with other networks
  such as the Internet, cellular, IEEE 802.11, IEEE
  802.15, IEEE 802.16, sensor networks, etc., can
  be accomplished through the gateway and
  bridging functions in the mesh routers.
             Mesh routers
• Mesh clients can be either stationary or
  mobile, and can form a client mesh
  network among themselves and with mesh
• They are undergoing rapid progress and
  inspiring numerous deployments.
• WMNs will deliver wireless services for a
  large variety of applications in personal,
  local, campus, and metropolitan areas.
Wireless Mesh backbone

      (CNWA Ch7-p290)
     Power over Ethernet (PoE)
• Use to place radio near antenna to avoid cost and
  loss of a long antenna cable
  – PoE injector at base
  – Run Cat 5E Ethernet cable to 24 VDC conditioned power
    tap by radio
• Can be means to meet specifications requiring PoE
  support – PoE injectors / taps not too costly

          PoE Regulated Tap
Diagnostics devices
Handheld Spectrum Analyzer
    & 802.11 Analyzers
                 Key terms
•   Bridge mode
•   Mesh router
•   PoE
•   Root mode
•   Wireless routers

                             (CNWA Ch7-p297)
802.11 Alphabet Soup
                  802.11a & b
– 802.11a
    High rate PHY, 6 to 54 Mb/s
    5 GHz UNII band
    OFDM (Orthogonal Frequency Division

– 802.11b
    High rate PHY, 5.5 and 11 Mb/s
    2.4 GHz ISM band (83 MHz, 22 MHz channel)
    CCK (Complementary Code Keying)
              802.11c & d
– 802.11c
 •   Bridging operation procedures
     between APs
 •   Used by AP manufacturers to insure
 •   Approved in 1998

– 802.11d
 •   Extending operations to new
     regulatory domains
 •   Specifically 5 GHz
                   802.11e - QoS
– QoS and improved efficiency of 802.11 MAC
– 8 priority levels
– Remember 802.11 as media access control protocol
  •   DCF based on CSMA/CA
  •   PCF based on polling
– Problem: DCF and PCF don’t differentiate traffic
             802.11e – QoS
– Enhanced DCF (EDCF)
   • Arbitration Interframe Space (AIFS)
      – High priority traffic have a shorter AIFS
      – STA’s with lower priority wait longer before accessing the
   • To avoid collision within a traffic category
   • STA’s countdown additional random number of time slots
     (contention window)
   • If STA 1 transmit before countdown ended, STA 2 waits next
     idle period and continues countdown where it left off
– NO guarantees of service are provided, just a
  mechanism to allocate bandwidth based on traffic
                     802.11f & g
– 802.11f - Inter AP Protocol
  •   Higher layer protocol
  •   Communication between APs
  •   Roaming between multi vendor APs
  •   Fast hand off
– 802.11g – 54Mbps for 2.4 GHz ISM band
  •   > 20 Mb/s (max 54 Mb/s)
  •   Backward compatibility with 802.11b (through
      CCK and RTS/CTS)
  •   CCK and OFDM mandatory
  •   Other optional modulation schemes
                     802.11h, i & j
– 802.11h
    •   Use of 802.11a in 5 GHz band in Europe
    •   Include dynamic frequency selection (DFS) and
        transmit power control (TPC)
–   802.11i
    •   Enhanced security and authentication in 802.11
    •   WEP not enough
    •   Solution leveraging existing 802.1x standard
– 802.11j
    •   Use of 802.11a in the Japanese 4.9 GHz band
   High throughput PHY and MAC
   108 to 320 Mb/s
   Reduced overhead
   Year 2005/2006
                            Acronym List
•16QAM    16 Level Quadrature Amplitude Modulation    •CTS     Clear To Send
•2GFSK    2nd Gaussian Frequency Shift Keying         •DBPSK   Differential Binary Phase Shift Keying
•3G       Third Generation Cellular Mobile            •DA      Destination Address
Communications                                        •DC      Direct Current
•4GFSK    4th Gaussian Frequency Shift Keying         •DCF     Distribution Coordination Function
•64QAM    64 Level Quadrature Amplitude Modulation    •DFS     Dynamic Frequency Selection
•AC       Alternating Current                         •DHCP    Dynamic Host Configuration Protocol
•ACK      Acknowledgement                             •DIFS    Distributed Coordination Function
•ADSL     Asymmetric Digital Subscriber Loop (Line)            Interframe Space
•AIFS     Arbitration Interframe Space                •DQPSK   Differential Quadratic Phase Shift Keying
•AM       Amplitude modulation                        •DRS     Dynamic Rate Shifting
•AP       Access Point                                •DS      Distribution System
•ARS      Adaptive/Automatic Rate Shifting            •DSSS    Direct Sequence Spread Spectrum
•ATIM     Adhoc Traffic Indication Map                •EDCF    Enhanced Distribution Coordination Function
•ATM      Asynchronous Transfer mode                  •ESS     Extended Service Set
•BPSK     Binary Phase Shift Keying                   •FAQ     Frequently Asked Question
•BSS      Basic Service Set                           •FCC     Federal Communications Commission
•CCA      Clear Channel Assessment                    •FCS     Frame Check Sequence
•CCK      Complementary Code Keying                   •FHSS    Frequency Hopping Spread Spectrum
•CDMA     Code Division Multiple Access               •FM      Frequency Modulation
•CP       Contention Period                           •FSK     Frequency Shift Keying
•CRC      Cyclic Redundancy Check                     •GHz     Gigahertz
•CRTC     Canadian Radio Television Committee         •GPS     Global Positioning System
•CSMA     Carrier Sense Multiple Access               •HCF     Hybrid Coordinator Function
•CSMA/CA Carrier Sense Multiple Access/Collision      •HEC     Header Error Check
Avoidance                                             •IBSS    Independent Basic Service Set
•CSMA/CD Carrier Sense Multiple Access/Collision
                               Acronym List
•IEEE      Institute of Electrical and Electronic Engineers   •PHY    Physical
•IFS       Interframe Space                                   •PIFS   Point Coordination Function Interframe
•IIT       International Institute of Telecommunications              Space
•IP        Internet Protocol                                  •PLCP   Physical Layer Convergence Procedure
•IR        Infra Red                                          •PMD    Physical Medium Dependent
•ISM       Industrial Scientific Medical                      •PPDU   PLCP Protocol Data Unit
•ISP       Internet Service Provider                          •PRE    Preamble
•LAN       Local Area Network                                 •PSDU   Physical Layer Service Data Unit
•LBT       Listen Before Talk                                 •PSK    Phase Shift Keying
•LEN       Length                                             •PSP    Power Save Polling
•LLC       Logical Link Control                               •PTMP   Point To Multipoint
•MAC       Media Access Control                               •PTP    Point To Point
•Mbps      Mega Bits per Second                               •QAM    Quadrature Amplitude Modulation
•MHz       Mega Hertz                                         •QoS    Quality of Service
•NAV       Network Allocation Vector                          •QPSK   Quadratic Phase Shift Keying
•NetBIOS   Network Adapter Basic Input Output System          •RF     Radio Frequency
•NIC       Network Interface Card                             •RTS    Request To Send
•OFDM      Orthogonal Frequency Division Multiplexing         •SA     Source Address
•OSI       Open System Interconnection                        •SDLC   Synchronous Data Link Control
•PAD       Padding                                            •SFD    Start Frame Delimiter
•PAN       Personal Area Network                              •SIFS   Shortest Interframe Space
•PAR       Project Authorisation Request                      •SOHO   Small Office Home Office
•PCF       Point Coordination Function                        •SSID   Service Set IDentification
•PCS       Personal Communication Services                    •STA    Station
•PDA       Personal Digital Assistant                         •SYNC   Synchronisation
                                                              •TG     Task Group
                            Acronym List
•TIM          Traffic Indication Map
•UNII         Unlicensed National Information
•VLAN         Virtual Local Area Network
•VoIP         Voice over IP
•VPN          Virtual Private Network
•WECA         Wireless Ethernet Compatibility Alliance
•WEP          Wired Equivalency Privacy
•WG           Working Group
•Wi-Fi        Wireless Fidelity
•WISP         Wireless Internet Service Provider
•WLAN         Wireless Local Area Network
•WLANA        Wireless Local Area Network Association
•WLIF         Wireless LAN Interoperability Forum
•XOR          eXclusive OR

•For more Acronyms
Questions ?
End of Module 2
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