Wireless Mesh Networks
Challenges and Opportunities


   Mihail L. Sichitiu
   Electrical and Computer Eng. Dept.
   NC St...
Outline

   Overview of the technology
   Opportunities
   (Research) Challenges
   Current state of the art
   Concl...
Overview
  Node Types                   Link Types
Wireless routers     Intra-mesh wireless links
Gateways
               ...
Gateways
   Multiple interfaces (wired &
    wireless)
   Mobility
       Stationary (e.g. rooftop) –
        most comm...
Wireless Routers
   At least one wireless interface.
   Mobility
    ●
        Stationary (e.g. rooftop)
    ●
        M...
Users
   Typically one interface.
   Mobility
       Stationary
       Mobile
   Connected to the mesh
    network th...
User – Wireless Router Links
   Wired
       Bus (PCI, PCMCIA, USB)
       Ethernet, Firewire, etc.
   Wireless
     ...
Router to Router Links
   Wireless
       802.11x
       Proprietary
   Usually multipoint to
    multipoint
       S...
Gateway to Internet Links
   Wired
       Ethernet, TV Cable,
        Power Lines
   Wireless
       802.16
       Pr...
How it Works
   User-Internet Data Flows
       In most applications the
        main data flows

   User-User Data Flo...
Taxonomy
                                                     Wireless
                                                   ...
Mesh vs. Ad-Hoc Networks
    Ad-Hoc Networks         Wireless Mesh Networks
   Multihop                   Multihop
   N...
Mesh vs. Sensor Networks
Wireless Sensor Networks          Wireless Mesh Networks
   Bandwidth is limited (tens       Ba...
Outline


   Overview of the technology
   Opportunities
       Applications
       Comparison with existing technolog...
Broadband Internet Access




                            15
Extend WLAN Coverage




    Source: www.meshdynamics.com




                                   Source: www.belair.com

 ...
Mobile Internet Access
   Direct competition
    with G2.5 and G3
    cellular systems.

                                ...
Emergency Response




              Source: www.meshdynamics.com

                                             18
Layer 2 Connectivity
   The entire wireless mesh
    cloud becomes one (giant)
    Ethernet switch
   Simple, fast insta...
Military Communications




                 Source: www.meshdynamics.com
                                                ...
Community Networks
   Grass-roots broadband
    Internet Access
   Several neighbors may
    share their broadband
    c...
Many Other Applications
   Remote
    monitoring and
    control
   Public
    transportation
    Internet access
   Mu...
Outline

   Overview of the technology
   Opportunities
       Applications
       Comparison with existing technologi...
Broadband Internet Access
                  Cable    WMAN       Cellular    WMN
                  DSL     (802.16)   (2.5-...
WLAN Coverage

         Source:
                            802.11       WMN
   www.meshdynamics.com




      Wiring     ...
Mobile Internet Access

                                  Cellular
                                  2.5 – 3G   WMN
   Sou...
Emergency Response

                                  Cellular    Walkie
                                  2.5 – 3G    Tal...
Layer 2 Connectivity

                   Ethernet          WMN

 Speed/Ease of    Slow/Difficult   Fast/Easy
  Deployment
...
Military Communications
                                   Existing
                                  System(s)    WMNs
  ...
Outline

   Overview of the technology
   Opportunities
       Applications
       Comparison with existing technologi...
Abstraction
   Users + routers = nodes
   Nodes have two functions:                                         =
          ...
Overview of Research Topics
   Physical Layer              Provisioning
       Smart Antennas
       Transmission Powe...
Physical Layer (PHY)
Wish list
   Performance                Extras
       Bandwidth                  Mobility (potent...
PHY - Modulation
   Existing modulations work well (OFDM,
    DSSS, FSK, etc.).
   UWB may be an interesting alternative...
PHY- Licensed vs. Unlicensed Spectrum
                          Licensed    Unlicensed
                          Spectrum ...
PHY – Smart Antennas
   Background                Omnidirectional
                                antenna
       Impleme...
PHY-Smart Antennas
Advantages
   Low power
    transmissions
       Battery not a big
        concern in many
        ap...
PHY-Smart Antennas
Advantages (cont)
   Punch-through links
       Better delays (?)
       Less packet loss (?)
     ...
PHY-Smart Antennas
Advantages (cont)
   Better SNR
       Better data rates
       Better delays
       Better error r...
PHY-Smart Antennas
Disadvantages
   Specialized
    hardware
   Specialized MAC
    (difficult to design)
   Difficult ...
PHY – Transmission Power Control



                GW          GW
   GW




  Too low     Too high     Just right


     ...
PHY – Transmission Power Control
(cont)
   Optimization Criteria
       Network capacity
       Delay
       Error rat...
Overview of Research Topics
   Physical Layer              Provisioning
       Smart Antennas
       Transmission Powe...
Medium Access Control (MAC)
   Scheduled
       Fix scheduled TDMA
       Polling
       Impractical due to lack of:
 ...
802.11 Compatibility
                       Proprietary     802.11
                          MAC        Compatible

Flexib...
MAC – Multichannel
What?
                                                   c
                                            ...
MAC – Multichannel
Why?
   Increases network capacity




                                                               ...
MAC – Multichannel
How?
        c
                      f


                          Standard MAC     Custom MAC
t       ...
MAC – Multichannel
Standard MAC – Single Radio
   Can it be done at all?
                                                ...
MAC – Multichannel
Standard MAC – Single Radio (cont)
   Channel assignment

                         GW                 ...
MAC – Multichannel
Custom MAC – Single Radio
   Easier problem than before
                                           IP
...
MAC – Multichannel
Standard MAC – Multiple Radios
   A node now can
    receive while
    transmitting
   Practical prob...
MAC – Multichannel
Custom MAC – Multiple Radios
   Nodes can use a
    control channel to
    coordinate and the rest
   ...
Overview of Research Topics
   Physical Layer              Provisioning
       Smart Antennas
       Transmission Powe...
Routing
   Finds and maintains
    routes for data flows
   The entire
    performance of the
    WMN depends on the
   ...
Routing – Wish List
   Scalability                         Flexibility
       Overhead is an issue in             Work...
Existing Routing Protocols
   Internet routing                              Ad-hoc routing
    protocols (e.g., OSPF,   ...
Routing - Optimization Criteria
   Minimum Hops
   Minimum Delays
   Maximum Data Rates
   Minimum Error Rates
   Max...
Routing – Cross-Layer Design
   Routing – Physical                Routing – MAC
       Link quality feedback is       ...
Routing – Cross-Layer Design (cont)
   Routing – Transport
       Choosing routes with
        low error rates may
     ...
Network Layer - Fairness
   Fairness
       Equal share of
        resources to all                   GW

        partic...
Fairness
Problem
                                   Unfair
  G        G
      2          1                 Inefficient
 ...
Network – Fairness
Problem Source
   Conflict between locally
    generated traffic and                                  ...
Fairness
Considered Topology and Node Model

                                                   f1
   4        3


       ...
Fairness
Separate Queue for Local Traffic
                                                                Unfair
        ...
Fairness
Weighted Queue for Local Traffic
                                  Unfair
      Separate Queue              Ine...
Fairness
Per-flow Queueing
                              Unfair
       Weighted Queue
                              Inef...
Fairness
Per-flow Queues + MAC Layer QoS
                               Fair
     Per-flow Queuing
                      ...
QoS
Support required at every layer
   Physical Layer                  Transport
       Robust modulation             ...
QoS
Flavors

    Guarantees                         Priorities
   Similar to RSVP in the         Similar to diffserv in ...
Network Layer QoS (Priorities)
        Per-flow Queues+
         MAC Layer QoS


                                 f1:f2:f3...
Overview of Research Topics
   Physical Layer              Provisioning
       Smart Antennas
       Transmission Powe...
TCP
Problems
   Efficiency – TCP                 Causes for missing
    assumes that a missing            ACKs in WMNs:
...
TCP
Efficiency Solutions
   Focus on eliminating the           End to end
    confusion between                      SA...
TCP
Problems (cont)
   Unfairness
       Due to network layer
        unfairness
                                    TCP...
Overview of Research Topics
   Physical Layer              Provisioning
       Smart Antennas
       Transmission Powe...
Provisioning
   Two related questions:
       How much bandwidth for
        each user?
       Where to place the next
...
Provisioning
802.11 Timing diagram for CSMA/CA

                              GW




                     DATA



        ...
Provisioning
802.11 Overhead


     LLC
     802.11(b)
                       M-HDR       MAC-SDU   FCS
                ...
Provisioning
TMT of 802.11 and 802.11b (CSMA/CA)




                                      80
Provisioning
TMT of 802.11b and 802.11a (CSMA/CA)




                                       81
Provisioning
Topology Modeling


                GW   GW        GW
     GW




                          GW
           GW
...
Provisioning
Intra-flow Interference & Chain Utilization

    Inter- and intra-flow interference        GW




          ...
Provisioning
   Chain Utilization
Time




                       Flow

                                GW


             ...
Provisioning
Collision Domains


       GW              GW                GW




    Symmetric MAC   Asymmetric MAC    Col...
Provisioning
Chain Topology



     G       G        G        G        G        G        G        G
                      ...
Provisioning
Arbitrary Topology
                                                                           G

      G     ...
Provisioning
Conclusion
   Non-trivial procedure                                                                         ...
Overview of Research Topics
   Physical Layer              Provisioning
       Smart Antennas
       Transmission Powe...
Security
   Authentication                    Reliability – protect:
       Prevent theft of service          Routing ...
Overview of Research Topics
   Physical Layer              Provisioning
       Smart Antennas
       Transmission Powe...
Network Management
   Monitor the “health” of
    the network
   Determine when is time
    to upgrade
       Either ha...
Overview of Research Topics
   Physical Layer              Provisioning
       Smart Antennas
       Transmission Powe...
Geolocation
What?


                Wireless
                Routers

                Users


              Monitoring
   ...
Geolocation
How?
   Measure ranges
    between mobile users
    and some known fixed
    points (wireless
    routers).
...
Outline

   Overview of the technology
   Opportunities
   (Research) Challenges
   Current state of the art
       C...
Companies
   Aerial Broadband           Motorola (ex. Mesh
   BelAir Networks             Networks)
   Firetide       ...
Aerial Broadband
   Tiny start-up in RTP, NC,
    USA in 2002
   Closed its doors shortly
    after its start
   Applic...
BelAir Networks
   Based in Ontario, Canada
   Application: 802.11b coverage
    of large zones
   Features:
       Th...
Firetide
   Based in Hawaii and Silicon
    Valley, USA
   Application: Layer 2
    connectivity (indoor and
    outdoor...
Intel
   Expressed interest in
    WMNs (since 2002).
   Research in:
       Low power – related
        with their wir...
Kiyon
   Based in La Jolla, CA,
    USA
   Applications: extended
    802.11 indoor coverage
   Features:
       Produ...
LamTech (ex. Radiant Networks)
   UK-based company
   Purchased by LamTech
    in 2004
   Applications: broadband
    I...
Locust World
   Based in UK
   Application: community
    networks
   Features:
       Free, open source
        softw...
Mesh Dynamics
   Based on Santa Clara, CA,
    USA                             Source: www.meshdynamics.com

   Applicat...
Microsoft
   Application: community
    networks
   Software
       Routing
                       Mesh Connectivity
  ...
Motorola – ex. MeshNetworks
   Based in Orlando, FL, USA
   Acquired by Motorola in Nov.
    2004
   Application: mobil...
Nokia Rooftop
   Acquisition of Rooftop
    Comm.
   Discontinued in 2003
   Application:
    broadband Internet
    ac...
Nortel Networks
   Applications: extended
    WLAN coverage
   Features:
       802.11a backhaul
       802.11b for us...
Packet Hop
   Based in Belmont, CA, USA
   Application: emergency
    response
   Product: software for mesh
    networ...
Ricochet Networks
   Based in Denver, CO, USA
   Application: Internet access
   Features:
       Mobile user support
...
SkyPilot Networks
   Based in Santa Clara, CA, USA
   Application: broadband Internet
    access
   Features:
       H...
Strix Systems
   Based in Calabasas, CA,
    USA
   Application: indoor and
    outdoor WLAN coverage,
    temporary net...
Telabria
   Based in Kent, UK
   Application: WLAN
    coverage
    (campus/city);
   Features:
       802.11 compatib...
Tropos Networks
   Based in Sunnyvale, CA, USA
   Ex – FHP wireless
   Applications: citywide 802.11b/
    g coverage
...
Outline

   Overview of the technology
   Opportunities
   (Research) Challenges
   Current state of the art
       C...
University Testbeds
   Georgia Tech - BWN-Mesh
   MIT - Roofnet
   Rutgers WinLab – Orbit
   SUNY Stonybrook – Hyacint...
Georgia Institute of Technology
BWN-Mesh
   15 IEEE 802.11b/g
    nodes
   Flexible configuration
    and topology
   C...
MIT Roofnet
   Experimental testbed
   40 nodes at the present
   Real users (volunteers)
   Focus on link layer
    m...
Rutgers Winlab
ORBIT
   Collaborative NSF project
    (Rutgers, Columbia,
    Princeton, Lucent Bell Labs,
    Thomson an...
SUNY Stonybrook
Hyacinth
   Multichannel testbed
    based on stock PCs
    with two 802.11a NICs.
   Research focus on:...
University of Utah
Emulab
   Three experimental environments
       simulated,
       emulated, and
          hundreds...
Outline

   Overview of the technology
   Opportunities
   (Research) Challenges
   Current state of the art
       C...
Standards related to WMNs
   IEEE 802.11s

   IEEE 802.15.1

   IEEE 802.15.4

   IEEE 802.15.5

   IEEE 802.16a
    ...
IEEE 802.11s
ESS Mesh Networking
   Started on May 13th, 2004
   802.11a/b/g were never intended to work multi-hop
   T...
IEEE 802.15.1
Bluetooth
   Low data rate (1Mbps bit-
    rate) PAN technology
   Targets wire replacement
   Has provis...
IEEE 802.15.4
Zigbee
   Lower data rate PAN
    (250,40,20kbps)
   Multi-months – years
    lifetime on small batteries
...
IEEE 802.15.5
Mesh Topology Capability in (WPANs).
   Standard applicable to all other
    WPANs
   Mesh networks have t...
IEEE 802.16a
WiMax
   Published April 1st 2003
   Enhances the original 802.16
    standard
   Original IEEE 802.16 spe...
Outline

   Overview of the technology
   Opportunities
   (Research) Challenges
   Current state of the art
       C...
Conclusion
   Relatively new technology
   Significant advantages for
    many applications
   Significant amount of re...
Acknowledgements and Disclaimer
      Special thanks to Jangeun
       Jun for practically all original
       artwork in...
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Transcript of "Wmn Tutorial"

  1. 1. Wireless Mesh Networks Challenges and Opportunities Mihail L. Sichitiu Electrical and Computer Eng. Dept. NC State University, Raleigh, NC, USA 1 © 2005,2006
  2. 2. Outline  Overview of the technology  Opportunities  (Research) Challenges  Current state of the art  Conclusion 2
  3. 3. Overview Node Types Link Types Wireless routers Intra-mesh wireless links Gateways Stationary client access Printers, servers Mobile client access Mobile clients Stationary clients Internet access links 3
  4. 4. Gateways  Multiple interfaces (wired & wireless)  Mobility  Stationary (e.g. rooftop) – most common case  Mobile (e.g., airplane, busses/subway)  Serve as (multi-hop) “access points” to user nodes GW  Relatively few are needed, (can be expensive) 4
  5. 5. Wireless Routers  At least one wireless interface.  Mobility ● Stationary (e.g. rooftop) ● Mobile (e.g., airplane, busses/subway).  Provide coverage (acts as a mini-cell-tower).  Do not originate/terminate data flows  Many needed for wide areas, hence, cost can be an issue. 5
  6. 6. Users  Typically one interface.  Mobility  Stationary  Mobile  Connected to the mesh network through wireless routers (or directly to gateways)  The only sources/destinations for data traffic flows in the network. 6
  7. 7. User – Wireless Router Links  Wired  Bus (PCI, PCMCIA, USB)  Ethernet, Firewire, etc.  Wireless  802.11x  Bluetooth  Proprietary  Point-to-Point or Point-to- Multipoint  If properly designed is not a bottleneck.  If different from router-to- router links we’ll call them access links 7
  8. 8. Router to Router Links  Wireless  802.11x  Proprietary  Usually multipoint to multipoint  Sometimes a collection of point to point  Often the bottleneck  If different from router- to-user links we’ll call them backbone links 8
  9. 9. Gateway to Internet Links  Wired  Ethernet, TV Cable, Power Lines  Wireless  802.16  Proprietary  Point to Point or Point- to-Multipoint  We’ll call them backhaul links  If properly designed, not the bottleneck 9
  10. 10. How it Works  User-Internet Data Flows  In most applications the main data flows  User-User Data Flows  In most applications a small percentage of data flows 10
  11. 11. Taxonomy Wireless Networking Single Multi-hop Hop Infrastructure-based Infrastructure-less Infrastructure-based Infrastructure-less (hub&spoke) (ad-hoc) (Hybrid) (MANET) 802.11 802.16 802.11 Bluetooth Cellular Car-to-car Networks Wireless Sensor Wireless Mesh Networks Networks Networks (VANETs) 11
  12. 12. Mesh vs. Ad-Hoc Networks Ad-Hoc Networks Wireless Mesh Networks  Multihop  Multihop  Nodes are wireless,  Nodes are wireless, possibly mobile some mobile, some fixed  May rely on  It relies on infrastructure infrastructure  Most traffic is user- to-user  Most traffic is user- to-gateway 12
  13. 13. Mesh vs. Sensor Networks Wireless Sensor Networks Wireless Mesh Networks  Bandwidth is limited (tens  Bandwidth is generous of kbps) (>1Mbps)  In most applications, fixed  Some nodes mobile, some nodes fixed  Energy efficiency is an  Normally not energy issue limited  Resource constrained  Resources are not an issue  Most traffic is user-to-  Most traffic is user-to- gateway gateway 13
  14. 14. Outline  Overview of the technology  Opportunities  Applications  Comparison with existing technologies  (Research) Challenges  Current state of the art  Conclusion 14
  15. 15. Broadband Internet Access 15
  16. 16. Extend WLAN Coverage Source: www.meshdynamics.com Source: www.belair.com 16
  17. 17. Mobile Internet Access  Direct competition with G2.5 and G3 cellular systems. Law enforcement Source: www.meshnetworks.com Intelligent transportation (now www.motorola.com). 17
  18. 18. Emergency Response Source: www.meshdynamics.com 18
  19. 19. Layer 2 Connectivity  The entire wireless mesh cloud becomes one (giant) Ethernet switch  Simple, fast installation  Short-term events (e.g., conferences, conventions, shows)  Where wires are not desired (e.g., hotels, airports)  Where wires are impossible (e.g., historic buildings) Internet 19
  20. 20. Military Communications Source: www.meshdynamics.com 20
  21. 21. Community Networks  Grass-roots broadband Internet Access  Several neighbors may share their broadband connections with many other neighbors  Not run by ISPs  Possibly in the disadvantage of the ISPs Source: research.microsoft.com/mesh/ 21
  22. 22. Many Other Applications  Remote monitoring and control  Public transportation Internet access  Multimedia home networking Source: www.meshnetworks.com (now www.motorola.com). 22
  23. 23. Outline  Overview of the technology  Opportunities  Applications  Comparison with existing technologies  (Research) Challenges  Current state of the art  Conclusion 23
  24. 24. Broadband Internet Access Cable WMAN Cellular WMN DSL (802.16) (2.5-3G) Bandwidth Very Very Limited Good Good Good Upfront Very High High Low Investments High Total Very High High Moderate Investments High Market Coverage Good Modest Good Good 24
  25. 25. WLAN Coverage Source: 802.11 WMN www.meshdynamics.com Wiring High Low Costs Bandwidth Very Good Good Number of APs As needed Twice as many Cost of APs Low High 25
  26. 26. Mobile Internet Access Cellular 2.5 – 3G WMN Source: www.meshnetworks.com (now www.motorola.com). Upfront High Low Investments Bandwidth Limited Good Geolocation Limited Good Upgrade High Low Cost 26
  27. 27. Emergency Response Cellular Walkie 2.5 – 3G Talkie WMN Source: www.meshdynamics.com Availability Reasonable Good Good Bandwidth Limited Poor Good Geolocation Poor Poor Limited 27
  28. 28. Layer 2 Connectivity Ethernet WMN Speed/Ease of Slow/Difficult Fast/Easy Deployment Bandwidth Very Good Good Mobile Users 802.11 needed Good Total Cost Low Moderate 28
  29. 29. Military Communications Existing System(s) WMNs Source: www.meshdynamics.com Very Coverage Good Good Bandwidth Poor Good Voice Support Very Good Good Covertness Poor Better Power efficiency Reasonable Good 29
  30. 30. Outline  Overview of the technology  Opportunities  Applications  Comparison with existing technologies  (Research) Challenges  Current state of the art  Conclusion 30
  31. 31. Abstraction  Users + routers = nodes  Nodes have two functions: = +  Generate/terminate traffic  Route traffic for other nodes Gateway 2 Gateway 2 y1 y1 Gatewa Gatewa Internet Internet 31
  32. 32. Overview of Research Topics  Physical Layer  Provisioning  Smart Antennas  Transmission Power  Security Control  MAC Layer  Network Management  Multiple Channels  Network Layer  Routing  Geo-location  Fairness and QoS  Transport Layer 32
  33. 33. Physical Layer (PHY) Wish list  Performance  Extras  Bandwidth  Mobility (potentially  Robust modulation high-speed)  Link adaptation  Sensitivity  Variable  Short preamble transmission power  Fast switch (details shortly) between channels  Multiple channels  Fast switch from  Link quality Tx/Rx and back feedback 33
  34. 34. PHY - Modulation  Existing modulations work well (OFDM, DSSS, FSK, etc.).  UWB may be an interesting alternative for short distances  Spread spectrum solutions are preferred as they tend to have better reliability in the face of  Fading (very important for mobile applications)  Interference (more of a factor than in any other wireless system) 34
  35. 35. PHY- Licensed vs. Unlicensed Spectrum Licensed Unlicensed Spectrum Spectrum Cost Expensive Free Controllable medium Yes No (i.e., no interference) Limits on Transmitted Power Some Lots 35
  36. 36. PHY – Smart Antennas  Background Omnidirectional antenna  Implemented as an array of Variable omnidirectional delay antennas Signal to transmit  By changing the Direction phase, beamforming changed by the delays can be achieved  The result is a software steered directional antenna Radiation Pattern 36
  37. 37. PHY-Smart Antennas Advantages  Low power transmissions  Battery not a big concern in many applications  Enables better spatial reuse and, hence, increased network capacity 37
  38. 38. PHY-Smart Antennas Advantages (cont)  Punch-through links  Better delays (?)  Less packet loss (?)  Better data rates (?)  Less power (?) 38
  39. 39. PHY-Smart Antennas Advantages (cont)  Better SNR  Better data rates  Better delays  Better error rates 39
  40. 40. PHY-Smart Antennas Disadvantages  Specialized hardware  Specialized MAC (difficult to design)  Difficult to track mobile data users 40
  41. 41. PHY – Transmission Power Control GW GW GW Too low Too high Just right 41
  42. 42. PHY – Transmission Power Control (cont)  Optimization Criteria  Network capacity  Delay  Error rates  Power consumption  The ideal solution will depend on  Network topology  Traffic load 42
  43. 43. Overview of Research Topics  Physical Layer  Provisioning  Smart Antennas  Transmission Power  Security Control  MAC Layer  Network Management  Multiple Channels  Network Layer  Routing  Geo-location  Fairness and QoS  Transport Layer 43
  44. 44. Medium Access Control (MAC)  Scheduled  Fix scheduled TDMA  Polling  Impractical due to lack of:  Central coordination point  Reasonable time synchronization  Random Access  CSMA – simple and popular  RTS/CTS – protects the receiver 44
  45. 45. 802.11 Compatibility Proprietary 802.11 MAC Compatible Flexible PHY/MAC Yes No Ease of upgrade Hard Easy Force clients to buy custom cards Yes/Yes No/No 45
  46. 46. MAC – Multichannel What? c f  Channels can be implemented by: t c f  TDMA (difficult due to lack of synchronization) c t  FDMA  CDMA (code f c t c assignment is an issue) s1 f t s2  SDMA (with directional t c f antennas) t s3 Combinations of the f  c above f t 46
  47. 47. MAC – Multichannel Why?  Increases network capacity Ch -1 1 Ch-1 2 1 Ch-1 2 3 Ch 2 -2 1 4 3 4 3 Ch-1 Ch-2 User bandwidth = B/2 User bandwidth = B Chain bandwidth = B B = bandwidth of a channel 47
  48. 48. MAC – Multichannel How? c f Standard MAC Custom MAC t (e.g.,802.11) Single Radio X X X X Multiple Radios 48
  49. 49. MAC – Multichannel Standard MAC – Single Radio  Can it be done at all? IP  Perhaps, if a new Multi- Channel Coordination Layer MCCL (MCCL) is introduced 802.11 between MAC and Network PHY  Must work within the constraints of 802.11 Ch -1 C h 1 Ch-1 2 3  May increase the 2 -2 capacity of the network 1 4 3 Ch-2 49
  50. 50. MAC – Multichannel Standard MAC – Single Radio (cont)  Channel assignment GW GW GW GW GW GW Gateway Loads = 4 : 1 : 1 Gateway Loads = 2 : 2 : 2 50
  51. 51. MAC – Multichannel Custom MAC – Single Radio  Easier problem than before IP  Common advantages and disadvantages associated Custom with custom MACs PHY  May further increase the capacity of the network GW GW  The problem of optimal channel assignment remains GW 51
  52. 52. MAC – Multichannel Standard MAC – Multiple Radios  A node now can receive while transmitting  Practical problems with GW GW antennas separation (carrier sense from nearby channel)  Optimal assignment – NP complete problem GW  Solutions ● Centralized ● Distributed 52
  53. 53. MAC – Multichannel Custom MAC – Multiple Radios  Nodes can use a control channel to coordinate and the rest to exchange data. GW GW  In some conditions can be very efficient.  However the control channel can be: GW ● an unacceptable overhead; ● a bottleneck; 53
  54. 54. Overview of Research Topics  Physical Layer  Provisioning  Smart Antennas  Transmission Power  Security Control  MAC Layer  Network Management  Multiple Channels  Network Layer  Routing  Geo-location  Fairness and QoS  Transport Layer 54
  55. 55. Routing  Finds and maintains routes for data flows  The entire performance of the WMN depends on the routing protocol  May be the main product of a mesh company  May be missing 55
  56. 56. Routing – Wish List  Scalability  Flexibility  Overhead is an issue in  Work with/without mobile WMNs. gateways, different topologies  Fast route discovery  QoS Support and rediscovery  Consider routes  Essential for reliability. satisfying specified criteria  Multicast  Mobile user support  Important for some  Seamless and efficient applications (e.g., handover emergency response) 56
  57. 57. Existing Routing Protocols  Internet routing  Ad-hoc routing protocols (e.g., OSPF, protocols (e.g., DSR, BGP, RIPv2) AODV, OLSR, TBRPF)  Well known and trusted  Newcomers by  Designed on the comparison with the assumption of seldom Internet protocols link changes  Designed for high rates  Without significant of link changes; hence modifications are perform well on WMNs unsuitable for WMNs in  May be further particular or for ad hoc Ad Hoc Networks optimized to account for networks in general. WMNs’ particularities Wireless Mesh Networks 57
  58. 58. Routing - Optimization Criteria  Minimum Hops  Minimum Delays  Maximum Data Rates  Minimum Error Rates  Maximum Route Stability  Minimum ETA  Use of multiple  Power Consumption routes to the same  Combinations of the gateway above  Use of multiple gateways 58
  59. 59. Routing – Cross-Layer Design  Routing – Physical  Routing – MAC  Link quality feedback is  Feedback on link loads shown often to help in can avoid congested selecting stable, high links → enables load bandwidth, low error balancing. rate routes.  Channel assignment  Fading signal strength and routing depend on can signal a link about each other. to fail → preemptive  MAC detection of new route requests. neighbors and failed  Cross-layer design routes may significantly essential for systems improve performance at with smart antennas. routing layer. 59
  60. 60. Routing – Cross-Layer Design (cont)  Routing – Transport  Choosing routes with low error rates may improve TCP’s throughput.  Especially important when multiple routes are used  Freezing TCP when a  Routing – Application route fails. ● Especially with respect of satisfying QoS constraints 60
  61. 61. Network Layer - Fairness  Fairness  Equal share of resources to all GW participants.  Special case of priority 1 2 based QoS.  Horizontal – nodes 1, 2  The MAC layer’s fairness ensures horizontal fairness. GW  Vertical – nodes 3, 4 3  MAC layer is no longer sufficient 4 61
  62. 62. Fairness Problem  Unfair G G 2 1  Inefficient GW S2 S1 Ideal Real 62
  63. 63. Network – Fairness Problem Source  Conflict between locally generated traffic and GW forwarded traffic.  At high loads the network layer queue fills up with local traffic and traffic to be Network layer forwarded arrives to a full queue. MAC layer  Consequence:  no fairness  poor efficiency Throughput  Solutions:  Compute the fair share for each user and enforce it generated  Local information based solution presented next forwarded Offered load 63
  64. 64. Fairness Considered Topology and Node Model f1 4 3 2 1 G G GW 2G 4G f2, f3 and f4 • Capacity of the network: G = B/8 • Assume unidirectional traffic for the clarity of explanation. 64
  65. 65. Fairness Separate Queue for Local Traffic  Unfair Single Queue f1  Inefficient Theoretically evaluated throughputs generated ( f1 ) forwarded ( f2-f4 ) f 2 , - f4 Offered load Separate Queue  Unfair  Inefficient f1:f2:f3:f4 = 4:1:2:1 65
  66. 66. Fairness Weighted Queue for Local Traffic  Unfair Separate Queue  Inefficient f1:f2:f3:f4 = 4:1:2:1 Weighted Queue  Unfair  Inefficient f1:f2:f3:f4 = 4:6:3:3 66
  67. 67. Fairness Per-flow Queueing  Unfair Weighted Queue  Inefficient f1:f2:f3:f4 = 4:6:3:3 Per-flow Queuing  Fair  Inefficient f1:f2:f3:f4 = 1:1:1:1 67
  68. 68. Fairness Per-flow Queues + MAC Layer QoS  Fair Per-flow Queuing  Inefficient f1:f2:f3:f4 = 1:1:1:1  Fair Per-flow Queues+ MAC Layer QoS  Efficient f1:f2:f3:f4 = 1:1:1:1 n1:n2:n3:n4 = 4:2:1:1 68
  69. 69. QoS Support required at every layer  Physical Layer  Transport  Robust modulation  Attempt end-to-end  Link adaptation recovery when possible  MAC Layer  Application  Offer priorities  Negotiate end-to-end and with lower layers  Offer guarantees (bandwidth, delay)  Adapt to changes in QoS  Network Layer  Select “good” routes  Offer priorities  Reserve resources (for guarantees) 69
  70. 70. QoS Flavors Guarantees Priorities  Similar to RSVP in the  Similar to diffserv in the Internet Internet  Has to implement  Offers classes of connection admission services control  Generalization of  Difficult in WMNs due fairness to:  A possible  Shared medium (see implementation on next provisioning section) slide  Fading and noise 70
  71. 71. Network Layer QoS (Priorities) Per-flow Queues+ MAC Layer QoS f1:f2:f3:f4 = 1:1:1:1 n1:n2:n3:n4 = 4:2:1:1 Per-flow Weighted Queues+ MAC Layer QoS f1:f2:f3:f4 = 1:2:3:4 n1:n2:n3:n4 = 4:2:1:1 71
  72. 72. Overview of Research Topics  Physical Layer  Provisioning  Smart Antennas  Transmission Power  Security Control  MAC Layer  Network Management  Multiple Channels  Network Layer  Routing  Geo-location  Fairness and QoS  Transport Layer 72
  73. 73. TCP Problems  Efficiency – TCP  Causes for missing assumes that a missing ACKs in WMNs: (or late) ACK is due to  Wireless transmission network congestion and error slows down:  Broken routes due to  to half if the missing mobility (both users and ACK shows up fast wireless routers) enough  Delays due to MAC  to zero if it times out contention  Interplay between MAC and TCP back-off mechanisms 73
  74. 74. TCP Efficiency Solutions  Focus on eliminating the  End to end confusion between  SACK congestion loss and all other  Explicit error notification reasons  Explicit congestion  Many approaches developed notification (e.g. RED) for single-hop wireless  Several solutions for multi- systems hop  Snoop  A-TCP  I-TCP  Freeze-TCP  M-TCP Applicability Trade-off Improvement in Clean Layering Efficiency Layer Violations 74
  75. 75. TCP Problems (cont)  Unfairness  Due to network layer unfairness TCP  Due to variation in round trip delays IP DLL  Likely both will be fixed if network layer fairness PHY is ensured 75
  76. 76. Overview of Research Topics  Physical Layer  Provisioning  Smart Antennas  Transmission Power  Security Control  MAC Layer  Network Management  Multiple Channels  Network Layer  Routing  Geo-location  Fairness and QoS  Transport Layer 76
  77. 77. Provisioning  Two related questions:  How much bandwidth for each user?  Where to place the next gateway?  Essential for QoS guarantees  Complicated by the shared medium and multi- hop routing 77
  78. 78. Provisioning 802.11 Timing diagram for CSMA/CA GW DATA ACK Repeated DIFS BO DATA SIFS ACK DIFS BO DATA Time 78
  79. 79. Provisioning 802.11 Overhead  LLC  802.11(b) M-HDR MAC-SDU FCS MAC-PDU  MAC Preamb P-HDR PLCP-SDU  PLCP  PMD PLCP-PDU Bit Stream (PMD-SDU) IFS [BO] Time 79
  80. 80. Provisioning TMT of 802.11 and 802.11b (CSMA/CA) 80
  81. 81. Provisioning TMT of 802.11b and 802.11a (CSMA/CA) 81
  82. 82. Provisioning Topology Modeling GW GW GW GW GW GW 82
  83. 83. Provisioning Intra-flow Interference & Chain Utilization  Inter- and intra-flow interference GW GW  Interference and topological models ` GW GW 83
  84. 84. Provisioning Chain Utilization Time Flow GW μ = 1/3 Time Flow GW μ = 1/4 84
  85. 85. Provisioning Collision Domains GW GW GW Symmetric MAC Asymmetric MAC Collision Domain (Symmetric MAC) 85
  86. 86. Provisioning Chain Topology G G G G G G G G GW G 2G 3G 4G 5G 6G 7G 8G 4G + 5G + 6G + 7G + 8G = 30 G Therefore, G ≤ B/30 86
  87. 87. Provisioning Arbitrary Topology G G G G G G G G G G G 2G 3G G GW 2G 3G 2G G G G 3G 2G G G G G G G G G 87
  88. 88. Provisioning Conclusion  Non-trivial procedure G Capacity depends on: G G  G  Network topology G G  Traffic load G G G G G 3G 2G G  Any practical algorithm 2G GW 3G 2G will trade-off: G 3G G G 2G  Responsiveness G G G G  Efficiency G G G G 88
  89. 89. Overview of Research Topics  Physical Layer  Provisioning  Smart Antennas  Transmission Power  Security Control  MAC Layer  Network Management  Multiple Channels  Network Layer  Routing  Geo-location  Fairness and QoS  Transport Layer 89
  90. 90. Security  Authentication  Reliability – protect:  Prevent theft of service  Routing data  Prevent intrusion by  Management data malicious users  Monitoring data  Prevent denials of  Privacy - user data is at service (very difficult at risk while on transit in the physical layer) the WMN due to:  Wireless medium  Multi-hop 90
  91. 91. Overview of Research Topics  Physical Layer  Provisioning  Smart Antennas  Transmission Power  Security Control  MAC Layer  Network Management  Multiple Channels  Network Layer  Routing  Geo-location  Fairness and QoS  Transport Layer 91
  92. 92. Network Management  Monitor the “health” of the network  Determine when is time to upgrade  Either hardware  New gateway  Detect problems  Equipment failures (often hidden by the self-repair feature of the network)  Intruders Source: www.meshdynamics.com  Manage the system 92
  93. 93. Overview of Research Topics  Physical Layer  Provisioning  Smart Antennas  Transmission Power  Security Control  MAC Layer  Network Management  Multiple Channels  Network Layer  Routing  Geo-location  Fairness and QoS  Transport Layer 93
  94. 94. Geolocation What? Wireless Routers Users Monitoring Station 94
  95. 95. Geolocation How?  Measure ranges between mobile users and some known fixed points (wireless routers).  Triangulate (same as cellular systems).  Since the “cells” are much smaller, much  Many improvements better precisions is possible as users can possible. talk to each other. 95
  96. 96. Outline  Overview of the technology  Opportunities  (Research) Challenges  Current state of the art  Companies  Universities  Standards  Conclusion 96
  97. 97. Companies  Aerial Broadband  Motorola (ex. Mesh  BelAir Networks Networks)  Firetide  Nokia Rooftop  Intel  Nortel Networks  Kiyon  Packet Hop  LamTech (ex. Radiant)  Ricochet Networks  Locust World  SkyPilot Networks  Mesh Dynamics  Strix Systems  Microsoft  Telabria  Tropos Networks 97
  98. 98. Aerial Broadband  Tiny start-up in RTP, NC, USA in 2002  Closed its doors shortly after its start  Application: broadband Internet access to apartment complexes  Features  802.11b-compatible product  Zero configuration  Layer 2 “routing” Source: www.aerialbroadband.com 98
  99. 99. BelAir Networks  Based in Ontario, Canada  Application: 802.11b coverage of large zones  Features:  Three radios on each wireless router; dynamically mapped on:  8 fixed directional antennas  Dynamic Tx power and data rate control  Routing based on PHY feedback, congestion, latency  Load balancing features Source: www.belairnetworks.com 99
  100. 100. Firetide  Based in Hawaii and Silicon Valley, USA  Application: Layer 2 connectivity (indoor and outdoor)  Features:  Proprietary routing protocol  2.4GHz and 5GHz products  AES, WEP security  Variable Tx Power  Management software Source: www.firetide.com 100
  101. 101. Intel  Expressed interest in WMNs (since 2002).  Research in:  Low power – related with their wireless sensor networks activities at Intel Research Berkeley Lab.  Traffic balancing  Together with Cisco active in 802.11s standardization process 101 Source: www.intel.com
  102. 102. Kiyon  Based in La Jolla, CA, USA  Applications: extended 802.11 indoor coverage  Features:  Products based on 802.11a/b/g  Custom routing (WARP)  Management software Source: www.kiyon.com 102
  103. 103. LamTech (ex. Radiant Networks)  UK-based company  Purchased by LamTech in 2004  Applications: broadband Internet access  MESHWORKTM  ATM switch in wireless router  90 Mbps  Directional links  4 mobile directional antennas  QoS - CBR & VBR-NR Source: www.radiantnetworks.com 103
  104. 104. Locust World  Based in UK  Application: community networks  Features:  Free, open source software  Off-the-shelf hardware + open source software  Monitoring software  Several deployments around the world Source: www.locustworld.com 104
  105. 105. Mesh Dynamics  Based on Santa Clara, CA, USA Source: www.meshdynamics.com  Application: 802.11 coverage (indoor, outdoor, citiwide), VoIP, video  Features:  802.11a/b/g compatible  Multiple radios options (1-4)  Dynamic channel selection  Dynamic tree topology  Management software  Radio agnostic control layer 105
  106. 106. Microsoft  Application: community networks  Software  Routing Mesh Connectivity  Link quality Layer (MCL  Routing based on DSR (named LQSR)  Transparent to lower and higher layers  Binaries for Windows XP Source: research.microsoft.com/mesh/ available at research. microsoft.com/mesh/ 106
  107. 107. Motorola – ex. MeshNetworks  Based in Orlando, FL, USA  Acquired by Motorola in Nov. 2004  Application: mobile broadband Internet access  Features:  Support for high speed mobile users  Proprietary routing protocol  Adaptive transmission protocol  Proprietary QDMA radio  Proprietary multichannel MAC  Proprietary geolocation feature Source: www.meshnetworks.com  Support for voice applications (now www.motorola.com)  Local testbeds 107
  108. 108. Nokia Rooftop  Acquisition of Rooftop Comm.  Discontinued in 2003  Application: broadband Internet access  Features:  Proprietary radio  Proprietary multi- channel MAC  Variable TX Power  Management and monitoring tools Source: www.rooftop.com 108
  109. 109. Nortel Networks  Applications: extended WLAN coverage  Features:  802.11a backhaul  802.11b for users  Management software Source: www.nortelnetworks.com Diagram and images and website hyperlink reproduced 109 with courtesy of Nortel Networks.
  110. 110. Packet Hop  Based in Belmont, CA, USA  Application: emergency response  Product: software for mesh networking  Features:  Works on 802.11a/b/g based hardware platforms  Security  Management software  Deployed testbed near Golden Gate Bridge in Feb. 2004 Source: www.packethop.com 110
  111. 111. Ricochet Networks  Based in Denver, CO, USA  Application: Internet access  Features:  Mobile user support  2 hop architecture  900 MHz user – pole top  2.4GHz pole top - WAP  Sell both hardware and service in Denver and San Diego  Speed: “up to 4 times the dial- up speed” Source: www.ricochet.net 111
  112. 112. SkyPilot Networks  Based in Santa Clara, CA, USA  Application: broadband Internet access  Features:  High power radio + 8 directional antennas  Proprietary routing (based on link quality and hop count)  Dynamic bandwidth scheduling (decides who transmits when)  Management software  Dual band (2.4GHz for users, 5GHz for backhaul) Source: www.skypilot.com 112
  113. 113. Strix Systems  Based in Calabasas, CA, USA  Application: indoor and outdoor WLAN coverage, temporary networks  Features:  Compatible with 802.11a/b/ g  Supports multiple (up to 6) radios  Management software  Soon to come testbeds Source: www.strixsystems.com 113
  114. 114. Telabria  Based in Kent, UK  Application: WLAN coverage (campus/city);  Features:  802.11 compatibility  Compatible indoor/outdoor products  Dual radio 802.11a/(b,g) (one for router-router, one for router-user traffic). Source: www.telabria.com 114
  115. 115. Tropos Networks  Based in Sunnyvale, CA, USA  Ex – FHP wireless  Applications: citywide 802.11b/ g coverage  Features:  Proprietary routing optimizing throughput  Support for client mobility  Security  Management software  Indoor/outdoor products  150 customers installed their products Source: www.tropos.com 115
  116. 116. Outline  Overview of the technology  Opportunities  (Research) Challenges  Current state of the art  Companies  Universities  Standards  Conclusion 116
  117. 117. University Testbeds  Georgia Tech - BWN-Mesh  MIT - Roofnet  Rutgers WinLab – Orbit  SUNY Stonybrook – Hyacinth  University of Utah - Emulab 117
  118. 118. Georgia Institute of Technology BWN-Mesh  15 IEEE 802.11b/g nodes  Flexible configuration and topology  Can evaluate routing and transport protocols for WMNs.  Integrated with the existing wireless sensor network testbed Source: http://users.ece.gatech.edu/~ismailhk/mesh/work.html 118
  119. 119. MIT Roofnet  Experimental testbed  40 nodes at the present  Real users (volunteers)  Focus on link layer measurements and routing protocols  Open source software runs on Intersil Prism 2.5 or Atheros AR521X based hardware Source: http://pdos.csail.mit.edu/roofnet/doku.php 119
  120. 120. Rutgers Winlab ORBIT  Collaborative NSF project (Rutgers, Columbia, Princeton, Lucent Bell Labs, Thomson and IBM Research)  Start date: September 2003  Emulator/field trial wireless system  400 nodes radio grid supporting 802.11x  Software downloaded for MAC, routing, etc.  Outdoor field trial Source: www.winlab.rutgers.edu 120
  121. 121. SUNY Stonybrook Hyacinth  Multichannel testbed based on stock PCs with two 802.11a NICs.  Research focus on:  interface channel assignment  routing protocol Source: http://www.ecsl.cs.sunysb.edu/multichannel/ 121
  122. 122. University of Utah Emulab  Three experimental environments  simulated,  emulated, and  hundreds of PCs (168 PCs in racks)  Several with wireless NICs (802.11 a/b/g)  wide-area network  50-60 nodes geographically distributed across approximately 30 sites  Smaller brothers at  U. of Kentucky  Georgia Tech Source: www.emulab.net 122
  123. 123. Outline  Overview of the technology  Opportunities  (Research) Challenges  Current state of the art  Companies  Universities  Standards  Conclusion 123
  124. 124. Standards related to WMNs  IEEE 802.11s  IEEE 802.15.1  IEEE 802.15.4  IEEE 802.15.5  IEEE 802.16a 124
  125. 125. IEEE 802.11s ESS Mesh Networking  Started on May 13th, 2004  802.11a/b/g were never intended to work multi-hop  Target application: extended 802.11 coverage  Will define an Extended Service Set (ESS), and a Wireless Distribution System (WDS)  Purpose: “To provide a protocol for auto-configuring paths between APs over self-configuring multi-hop topologies in a WDS to support both broadcast/multicast and unicast traffic in an ESS Mesh [...]”.  Status: 35 proposals will likely be submitted in July 2005.  Intel and Cisco are active in this area 125
  126. 126. IEEE 802.15.1 Bluetooth  Low data rate (1Mbps bit- rate) PAN technology  Targets wire replacement  Has provisions for multi- hop scatternets  Not a popular wireless mesh network platform due to:  the low bandwidth and  limited hardware support for scatternets. 126
  127. 127. IEEE 802.15.4 Zigbee  Lower data rate PAN (250,40,20kbps)  Multi-months – years lifetime on small batteries  Supports mesh topology – one coordinator is responsible for setting up the network  Characteristics suitable for wireless sensor networks rather than wireless mesh networks. 127
  128. 128. IEEE 802.15.5 Mesh Topology Capability in (WPANs).  Standard applicable to all other WPANs  Mesh networks have the capability to provide:  Extension of network coverage without increasing transmit power or receive sensitivity  Enhanced reliability via route redundancy  Easier network configuration  Better device battery life due to fewer retransmissions 128
  129. 129. IEEE 802.16a WiMax  Published April 1st 2003  Enhances the original 802.16 standard  Original IEEE 802.16 specifies only point to multipoint functionality – great for gateway to internet links  The extensions specifies user- user links using:  either centralized schedules,  or distributed schedules. 129
  130. 130. Outline  Overview of the technology  Opportunities  (Research) Challenges  Current state of the art  Companies  Universities  Standards  Conclusion 130
  131. 131. Conclusion  Relatively new technology  Significant advantages for many applications  Significant amount of research exist and, yet,  Significant improvements can be enabled by more research.  Impressive products from several companies  Multiple standardization activities are on the way 131
  132. 132. Acknowledgements and Disclaimer  Special thanks to Jangeun Jun for practically all original artwork in this presentation  Many thanks to all companies that graciously allowed the use of their artwork for this presentation Disclaimer All technical content, views, commentaries, positions and opinions expressed in this presentation are those of the author/presenter alone. The author and this presentation is not endorsed, sponsored or affiliated with the companies or products represented in it. Source: www.meshdynamics.com 132

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