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					 Towards Efficient and Robust
Multihop Wireless Networks with
     Real-Time Media-Rich
      Application Support

      Ph.D. Dissertation Proposal

                Kimaya Mittal
     Department of Computer Science
   University of California, Santa Barbara
                   Introduction
• Popularity of wireless networks
     – Homes, offices, universities, airports, malls
     – Largely access-point-based at present

                       Access point


                                                         Internet
Wireless user
  devices
                                  Wireline
                                connectivity

                  Kimaya Mittal, Ph.D. Dissertation Proposal
                       Introduction
• Multihop wireless networks gaining attention

                                                      Wireline
                                                    connectivity
                                                                   Internet




Stand-alone (Ad hoc)        Extending Internet connectivity (Mesh)

                  Kimaya Mittal, Ph.D. Dissertation Proposal
                 Introduction
• Multihop wireless networks
  – Benefits:
     •   Easy to deploy/extend
     •   Self-configuring
     •   Adaptive
     •   Cost-effective
  – Tremendous potential to be technology of
    choice for ubiquitous Internet access

                Kimaya Mittal, Ph.D. Dissertation Proposal
               Introduction
• Popularity of real-time media-rich applications
  – VoIP, video streaming, gaming, video-
    conferencing, media-rich messaging
• Must be supported by Internet access
  technology
• Strict requirements
  – Minimum required throughput
  – Maximum tolerable delay and jitter


              Kimaya Mittal, Ph.D. Dissertation Proposal
              Our Vision

           Multihop wireless networks
                     provide
        ubiquitous Internet connectivity
       and support diverse applications,
         including real-time media-rich
        applications, in an efficient and
                 robust manner

Our focus is on 802.11 and IP-based networks

           Kimaya Mittal, Ph.D. Dissertation Proposal
                    Challenges
• Differences between wireless and wired networks
   – Shared medium
        • Nodes sharing medium may be unable to communicate
   –   High link error rates
   –   Significantly lower capacity
   –   Resource-constrained devices
   –   Mobility and dynamic topology
   –   Easily accessible to malicious attackers
• Wired network solutions not always applicable

                  Kimaya Mittal, Ph.D. Dissertation Proposal
Wireless Transmission
   Characteristics
                                          V
  T                  R
                                                   W
                 P                  Q
       U

                                               X
                          S



      Kimaya Mittal, Ph.D. Dissertation Proposal
     Wireless Transmission
        Characteristics
Transmission range of P
                                                   V
           T                  R
                                                            W
                          P                  Q
                U

                                                        X
                                   S



               Kimaya Mittal, Ph.D. Dissertation Proposal
        Wireless Transmission
           Characteristics
  Transmission range of P
                                                       V
              T                   R
                                                                W
                              P                  Q
                    U

                                                            X
                                       S

Carrier-sense range of P

                   Kimaya Mittal, Ph.D. Dissertation Proposal
        Wireless Transmission
           Characteristics
                                                       V
              T                   R
                                                                W
                              P                  Q
                    U

                                                            X
                                       S

Carrier-sense range of P                              Carrier-sense range of Q

                   Kimaya Mittal, Ph.D. Dissertation Proposal
                  Our Focus
• Focus on addressing three key challenges
  – Shared medium
  – Significantly lower capacity
  – Easily accessible to malicious attackers
• Motivation
  – Very important for realization of our vision
  – Previously-proposed solutions lacking
  – Significant scope for improvement



               Kimaya Mittal, Ph.D. Dissertation Proposal
               Shared Medium
•   Medium shared with carrier-sense neighbors (CSN)
•   Not all CSN can directly communicate
•   Potentially different view of medium at each CSN
•   Medium management challenging
•   Challenge for realization of vision: How can
    requirements of real-time media-rich applications be
    met?                                     V
                                         T         R
           Transmission range                    P         Q W
                                             U
           Carrier-sense range
                                                                X
                                                       S
                   Kimaya Mittal, Ph.D. Dissertation Proposal
               Low Capacity
• Wireless bandwidth limited and shared
• Multiple hops along path contend for medium
  access
  – Significant capacity drop
• Hidden terminal and exposed terminal
  problems
• Challenge for realization of vision: How can
  diverse applications be efficiently supported?


               Kimaya Mittal, Ph.D. Dissertation Proposal
    Accessibility to Malicious
           Attackers
• Any device within range can gain access
   – Can become part of routing infrastructure
• Security vulnerabilities in several protocols
   – Popular routing protocols (AODV, DSR)
• Can be exploited for non-optimal
  performance and denial of service
   – Compromise of the routing protocol can have far-
     reaching effects on entire network
• Challenge for realization of vision: How can
  network be made robust?
               Kimaya Mittal, Ph.D. Dissertation Proposal
        Dissertation Goals
• To contribute to the realization of our
  vision in the following areas:
  – Real-time media-rich application support
  – Efficient utilization of capacity
  – Robustness to malicious behavior




            Kimaya Mittal, Ph.D. Dissertation Proposal
               Contributions
• Real-time media-rich application support
   – Perceptive Communication [Tridentcom 06]
   – PRP and RRT: Protocols for intra-flow contention
     calculation [Broadnets 04, MONET 06]
• Efficient utilization of capacity
   – Improvement of 802.11 capacity utilization
     (Remaining work)
   – Leveraging mobility [Mobiquitous 04, WCMC
     Journal (submitted)]
• Robustness to malicious behavior
   – Analysis of security vulnerabilities of popular
     routing protocols + secure routing protocol (ARAN)
     [ICNP 02, JSAC 05]
               Kimaya Mittal, Ph.D. Dissertation Proposal
VISION
    Multihop wireless networks provide
    ubiquitous Internet connectivity and
        support diverse applications,
       including real-time media-rich                                             GOALS
      applications, in an efficient and            Real-time
               robust manner                                              Efficient     Robustness
                                                   media-rich
                                                                       utilization of   to malicious
                                                   application
                                                                          capacity        behavior
                                                     support

  CONTRIBUTIONS

                                           Leveraging
           Intra-flow contention                                   Authenticated
                                              user
                calculation                                           routing
                                             mobility
         Network Layer



                           Perceptive               Improvement of 802.11
                         communication                capacity utilization

         MAC Layer



                          Kimaya Mittal, Ph.D. Dissertation Proposal
VISION
    Multihop wireless networks provide
    ubiquitous Internet connectivity and
        support diverse applications,
       including real-time media-rich                                             GOALS
      applications, in an efficient and            Real-time
               robust manner                                              Efficient     Robustness
                                                   media-rich
                                                                       utilization of   to malicious
                                                   application
                                                                          capacity        behavior
                                                     support

  CONTRIBUTIONS

                                           Leveraging
           Intra-flow contention                                   Authenticated
                                              user
                calculation                                           routing
                                             mobility
         Network Layer



                           Perceptive               Improvement of 802.11               Remaining
                         communication                capacity utilization                Work
         MAC Layer



                          Kimaya Mittal, Ph.D. Dissertation Proposal
 Perceptive Communication:
         Motivation
• Medium-related operations at a node
  depend on/affect medium state at CSN
• Need for communication among CSN
                                                             V
                                 T            R
 Transmission range
                                            P            Q   W
 Carrier-sense range                  U
                                                                 X
                                                   S

                Kimaya Mittal, Ph.D. Dissertation Proposal
   Examples of Need for
 Communication Among CSN
• Support of real-time media-rich
  applications requires
  – Admission control
  – Prioritized medium access
• Need to share information such as
  bandwidth consumption and priorities of
  existing flows with CSN


            Kimaya Mittal, Ph.D. Dissertation Proposal
    Potential Approaches to
   Communicate Among CSN
• Direct communication
   – Impossible (CS range > Tx range)
• High-power transmission [Yang 03]
   – More energy, less spatial reuse
• Multihop forwarding [Yang 03]
   – Requires relay node
• Lower rate transmission code
   – May not be supported, may not reach all CSN


               Kimaya Mittal, Ph.D. Dissertation Proposal
    Potential Approaches to
   Communicate Among CSN
• Direct communication                         CS range
   – Impossible (CS range > Tx range)               Tx range
• High-power transmission [Yang 03]       T      R
   – More energy, less spatial reuse            P       Q
• Multihop forwarding [Yang 03]              U

   – Requires relay node                      S
• Lower rate transmission code
   – May not be supported, may not reach all CSN


                Kimaya Mittal, Ph.D. Dissertation Proposal
    Potential Approaches to
   Communicate Among CSN
• Direct communication                         CS range
   – Impossible (CS range > Tx range)               Tx range
• High-power transmission [Yang 03]       T      R
   – More energy, less spatial reuse            P       Q
• Multihop forwarding [Yang 03]              U

   – Requires relay node                      S
• Lower rate transmission code                      High power
                                                     Tx range
   – May not be supported, may not reach all CSN


                Kimaya Mittal, Ph.D. Dissertation Proposal
    Potential Approaches to
   Communicate Among CSN
• Direct communication                         CS range
   – Impossible (CS range > Tx range)               Tx range
• High-power transmission [Yang 03]       T      R
   – More energy, less spatial reuse            P       Q
• Multihop forwarding [Yang 03]              U

   – Requires relay node                      S
• Lower rate transmission code
   – May not be supported, may not reach all CSN


                Kimaya Mittal, Ph.D. Dissertation Proposal
    Potential Approaches to
   Communicate Among CSN
• Direct communication                         CS range
   – Impossible (CS range > Tx range)               Tx range
• High-power transmission [Yang 03]      T       R
   – More energy, less spatial reuse            P      Q
• Multihop forwarding [Yang 03]              U

   – Requires relay node                     S
• Lower rate transmission code                      Lower rate
                                                     Tx range
   – May not be supported, may not reach all CSN


                Kimaya Mittal, Ph.D. Dissertation Proposal
  Perceptive Communication
• During transmission, change in carrier signal
  perceived by CSN
• Certain characteristics can be detected
  – Duration of transmission
  – Silence between transmissions
• Information encoded in perceivable
  characteristics
  – Can be inferred by CSN by monitoring carrier
    signal, packet need not be decoded
              Kimaya Mittal, Ph.D. Dissertation Proposal
     Detection of Perceptive
         Characteristics
• Node records received signal strength
  (RSS) continuously (i.e. in every time
  slot)
• Tracks signal strength over time
• Identifies transmissions and silences
  from this information
• Measures their durations

            Kimaya Mittal, Ph.D. Dissertation Proposal
   Detection of Transmission
           Duration
• Idealized graph of
                                          RSS
  signal strength vs.
  time
• Packet Y sensed, not
                                RxThresh
  decoded
• Duration of packet Y                                X
  (Ty) perceived                CSThresh
                                                            Y
• Information encoded
  in and inferred from
                                                                 time
  Ty                                                        Ty

               Kimaya Mittal, Ph.D. Dissertation Proposal
 Detection of Silence Duration
• Every transmission
                                       RSS         Pre-frame
  preceded by pre-
                                                     Inter-frame space
  frame
                                                        Packet
• Inter-frame space
  perceived, duration         RxThresh                      Inter-packet space
  (Ts) detected
• Ts < Tdifs (inter-          CSThresh
  packet space)                                             Y
• Information encoded
  in and inferred from
                                                                         Time
  Ts                                                  Ts        Tdifs

               Kimaya Mittal, Ph.D. Dissertation Proposal
   Application of Perceptive
       Communication
• Application-specific codebook
  – Maps transmission durations or inter-frame
    space durations to meanings
• Examples
  – Communication of identity through size of
    Hello messages
    • Size modified by appending ‘tail’
  – Communication of packet priority through
    duration of inter-frame space
             Kimaya Mittal, Ph.D. Dissertation Proposal
         Testbed Evaluation
• Motivation
  – Do actual graphs of signal strength vs. time
    resemble ideal graphs?
  – How accurately can perceptive characteristics be
    measured on wireless hardware?
• Implementation
  – Prototype implementation on Mica2 mote
     • Only platform with API for per-slot RSS
  – RSSI sampling in alternate time slots

                Kimaya Mittal, Ph.D. Dissertation Proposal
       Simple Test Scenario
• Single transmitter
  – Placed within few inches of receiver
  – Transmits 100 packets
     • 10 packets per second
     • 20 bytes payload
• Single receiver
  – Samples RSS in every time slot
  – Processes RSS readings to identify transmissions
     • Simplistic algorithm
  – Infers payload size from detected transmission
    duration
                Kimaya Mittal, Ph.D. Dissertation Proposal
Plot of RSSI vs. Time
                                                 Ack

                                                 Data




                                                 Noise




    Kimaya Mittal, Ph.D. Dissertation Proposal
Payload Size Detection in Simple
         Test Scenario




        Kimaya Mittal, Ph.D. Dissertation Proposal
                   Analysis
• All packets detected within +/- 2 bytes
• 2-byte detection error unavoidable
  – RSSI sampling in alternate slots
  – Time slots of receiver and transmitter not
    perfectly synchronized
• In remaining results, detection within +/-
  2 bytes considered correct
• Silence detection results similar
             Kimaya Mittal, Ph.D. Dissertation Proposal
     Experiment: Effect of
   Received Signal Strength

• Experiment setup similar to simple test
  scenario
• Magnitude of RSS varied by changing
  transmit power of sender



            Kimaya Mittal, Ph.D. Dissertation Proposal
Effect of Received Signal Strength




         Kimaya Mittal, Ph.D. Dissertation Proposal
  Perceptive Communication:
         Conclusions
• Perceptive communication among CSN
  feasible and effective on wireless
  hardware
• Some error in detection unavoidable
  – Should be accounted for in protocol design
• More sophisticated detection algorithm
  can further improve accuracy

            Kimaya Mittal, Ph.D. Dissertation Proposal
  Perceptive Communication:
            Impact
• Powerful mechanism
• Creates new possibilities for managing
  wireless medium
• Several potential applications in
  prioritized MAC, admission control,
  bandwidth estimation, channel
  assignment, power control, etc.

            Kimaya Mittal, Ph.D. Dissertation Proposal
  Determination of Intra-Flow
    Contention: Motivation
• Network capacity limited, may not be
  able to support all flows requesting
  access
• Admission control necessary
• Need to estimate bandwidth
  consumption of new flow for admission
  control decision
• Non-trivial due to intra-flow contention
            Kimaya Mittal, Ph.D. Dissertation Proposal
         What is Intra-Flow
           Contention?
• Nodes along a multihop path may lie within
  each other’s carrier-sense range
• This leads to intra-flow contention
                                             Carrier-sensing range
                                                   of node Y
                        Z
             Y                     Packets of flow F contend for medium
     W                                 access at nodes W, X and Y
         X
                                 Flow F
                 Kimaya Mittal, Ph.D. Dissertation Proposal
          What is Intra-Flow
            Contention?
• Due to intra-flow contention, bandwidth
  consumption of a flow at a node becomes a
  multiple of that requested by the application
                                             Carrier-sensing range
                                                   of node Y
                        Z
             Y                        Bandwidth consumed by flow F at
     W                                nodes W, X, Y each is 3 times the
         X                                 single-hop bandwidth

                                 Flow F
                 Kimaya Mittal, Ph.D. Dissertation Proposal
         Contention Count
• Contention Count (CC) at a node =
     Intersection of (set of carrier-sensing
     neighbors) with (set of nodes on multihop
     path) + 1
• Bandwidth consumption of flow =
     CC x (single-hop bandwidth consumption)
• To estimate bandwidth consumption, CC
  must be calculated


             Kimaya Mittal, Ph.D. Dissertation Proposal
   Calculation of Contention
             Count
• Previous approaches
  – Contention-Aware Admission Control (CACP)
    [Yang et al. 03]
     • High power transmissions to communicate with CSN
• Our approaches
  – Pre-Reply Probe (PRP) and Route Request Tail
    (RRT)
  – Use our perceptive communication techniques
    to communicate with CSN
  – Integrated with reactive route discovery

               Kimaya Mittal, Ph.D. Dissertation Proposal
Comparison of PRP/RRT with
          CACP
• Main benefits
  – Reduced energy consumption
  – Reduced network overhead
• Main drawback
  – Error in CC calculation when collisions
    occur (No more than +/- 1 in our
    simulations)


             Kimaya Mittal, Ph.D. Dissertation Proposal
Remaining Work: Improving
Capacity Utilization of 802.11

• Hidden terminal and exposed terminal
  problems well-known artifacts of CSMA
  protocols
• Result in wasted network capacity



           Kimaya Mittal, Ph.D. Dissertation Proposal
What are Hidden Terminals?
                      Carrier-sense range

                                              Nodes P and R
                                              cannot carrier
   P   Q                                      sense each other
                                              and transmit
       S             R
                                              simultaneously,
                                              causing collisions
                                              at one or both
                                              receivers


       Kimaya Mittal, Ph.D. Dissertation Proposal
What are Exposed Terminals?
                                                   Carrier-sense range


      Q               S                          Nodes P and R
                                                 cannot transmit
                                                 simultaneously due
      P               R
                                                 to carrier sensing,
                                                 even though their
                                                 transmissions do
                                                 not mutually
                                                 interfere


          Kimaya Mittal, Ph.D. Dissertation Proposal
Hidden and Exposed Terminals
• Hidden terminals waste capacity through
  collisions
• Exposed terminals waste capacity through
  missed opportunities to transmit
• Prevalence of hidden and exposed terminals
  depends on topology and carrier sense range
  – Large CS range => More exposed terminals
  – Small CS range => More hidden terminals
  – Inherent tradeoff


               Kimaya Mittal, Ph.D. Dissertation Proposal
 Alleviation of Hidden and Exposed
     Terminals: Previous Work
• RTS/CTS
  – Does not address exposed terminals
• Adjusting CS range
  – Eliminating hidden terminals [Chakeres 04,
    Fuemmeler 04]
  – Reducing exposed terminals [Vasan 05]
  – Achieving optimal balance [Zhai 06, Zhu
    06]

            Kimaya Mittal, Ph.D. Dissertation Proposal
      Proposed Contribution
• Can a solution be designed to eliminate both
  hidden and exposed terminals
  simultaneously?
  – Adjustment of CS range clearly not enough
• Proposed Approach
  – Set CS range to sufficiently large value to
    eliminate hidden terminals
  – Modify protocol to discover and alleviate exposed
    terminals


              Kimaya Mittal, Ph.D. Dissertation Proposal
               Challenges
• Detection of exposed terminals
  – Distance-based assumptions naïve
• Keeping information up-to-date
  – Interference characteristics may vary with
    time
• Coordination of simultaneous
  transmissions

             Kimaya Mittal, Ph.D. Dissertation Proposal
             Potential benefit
• Qualnet simulation of random topology of 20
  nodes in a 600m x 600m area shows 90 pairs
  of mutually exposed links
  – This is without increasing CS range to avoid
    hidden terminals
  – Hardware limitations currently prevent testbed
    evaluation
• Indicates potential benefit of proposed
  approach

              Kimaya Mittal, Ph.D. Dissertation Proposal
VISION
     Multihop wireless networks
               provide
         ubiquitous Internet
      connectivity and support
        diverse applications,                                GOALS
   including real-time media-rich
     applications, in an efficient
         and robust manner             Real-time
                                                                                 Conclusions
                                                      Efficient   Robustness
                                       media-rich
                                       application
                                                   utilization of to malicious   • Dissertation
                                                     capacity       behavior
                                        support                                    contributes
                                                                                   towards solving
 CONTRIBUTIONS                                                                     important
                                                                                   problems
                                                                                   towards
      Intra-flow contention
                                 Leveraging
                                                  Authenticated
                                                                                   realization of our
                                    user
           calculation
                                   mobility          routing                       vision
      Network Layer                                                              • Significantly
                                                                                   advances state-
                                                                                   of-the-art
                    Perceptive
                  communication
                                          Improvement of 802.11
                                            capacity utilization
                                                                                 • Creates new
                                                                                   avenues for
      MAC Layer                                                                    further research

                                     Kimaya Mittal, Ph.D. Dissertation Proposal
  Thank You!


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posted:7/30/2012
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