CSE-538-Adaptive Clustering for Mobile Wireless networks by naukarimilgayi

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									Adaptive Clustering for Mobile
     Wireless networks
         Dr. R. B. Patel




                                 1
   Mobile Ad hoc Network (MANET)?

• A Mobile Ad hoc Network (MANET) is an autonomous
  system of nodes called mobile stations (MSs) connected by
  wireless links.
• A MANET does not necessarily need support from any
  existing network infrastructure like an Internet gateway or
  other fixed stations.
• The network’s wireless topology may dynamically change in
  an unpredictable manner since nodes are free to move.
• Information is transmitted in a store-and forward manner
  using multi hop routing.


                                                            2
                     Continued…

• Each node is equipped with a wireless transmitter and a
  receiver with an appropriate antenna.
• We assume that it is not possible to have all nodes within
  each other’s radio range.
• When the nodes are close-by i.e., within radio range, there
  are no routing issues to be addressed.
• At a given point in time, wireless connectivity in the form of
  a random multi-hop graph exists between the nodes.




                                                               3
                        Continued…


            MS2                             MS2

                                 MS4
     MS3                               Asymmetric link
                          MS5
Symmetric link                            MS7
                  MS1           MS6




                                                         4
    Characteristics of Ad Hoc Networks

• Dynamic topologies: Network topology may change
  dynamically as the nodes are free to move.
• Bandwidth-constrained, variable capacity links: Realized
  throughput of wireless communication is less than the
  radio’s maximum transmission rate. Collision occurs
  frequently.
• Energy-constrained operation: Some nodes in the ad hoc
  network may rely on batteries or other exhaustible means
  for their energy.
• Limited physical security: More prone to physical security
  threats than fixed cable networks.


                                                               5
                    Applications
• Virtual navigation: Data from a remote database is transmitted
  periodically in small relevant blocks using links present in the
  path of the automobile. This database may contain the
  graphical representation of streets, buildings, maps and the
  latest traffic information, which may be used by the driver to
  decide on a route.
• Tele-medicine: Conference assistance from a surgeon for an
  emergency intervention.
• Tele-Geo processing: Queries regarding location information
  of the users.
• Crisis-management: Natural disasters, where the entire
  communication infrastructure is in disarray.
• Education via the internet
                                                               6
         Routing in MANETS - Goals
• Provide the maximum possible reliability - use alternative routes
  if an intermediate node fails.
• Choose a route with the least cost metric.
• Give the nodes the best possible response time and throughput.
• Route computation must be distributed. Centralized routing in a
  dynamic network is usually very expensive.
• Routing computation should not involve the maintenance of
  global state.
• Every node must have quick access to routes on demand.
• Each node must be only concerned about the routes to its
  destination.
• Broadcasts should be avoided (highly unreliable)
• It is desirable to have a backup route when the primary route has
                                                                      7
  become stale.
Reactive On-demand Source-based Routing
               Schemes
•   Routes are created when necessary
•   Initiates a route discovery process
•   Route will be maintained until it is no longer needed.
•   Examples:
     – Ad Hoc On Demand Distance Vector (AODV) routing
        protocol
     – Dynamic Source Routing (DSR)
     – Temporary Ordered Routing Algorithm (TORA)




                                                             8
     A Highly Adaptive Distributed Routing
    Algorithm for Mobile Wireless Networks

•   Problems of routing in a mobile wireless
    – Nodes move about arbitrarily
    – Potentially rapid and unpredictable changing
      topology
    – Wireless links inherently have significantly
      lower capacity than hardwired links
    – More prone to congestion


                                                     9
       Temporally-Ordered Routing
          Algorithm (TORA)
• Highly adaptive, loop-free, distributed routing
  algorithm based on the concept of link reversal
• Proposed to operate in a highly dynamic mobile
  networking environment
• It is source initiated and provides multiple routes for
  any desired source/ destination pair
• This algorithm requires the need for synchronized
  clocks


                                                            10
                       Continued…

• TORA is a highly adaptive loop-free distributed routing
  algorithm based on the concept of link reversal.
• TORA decouples the generation of potentially far-reaching
  control messages from the rate of topological changes.
• The height metric is used to model the routing state of the
  network.




                                                           11
               Continued…
            Source

                            H=3




                            H=2



                            H=1



                            H=0

            Destination

Illustration of Tora height metric
                                     12
                 Continued…
•   The protocol can be separated into three
    functions:
    – Creating routes
      establishment of a sequence of directed links
      leading from node to dest.
    – Maintaining routes
      re-establish routes
    – Erasing routes
      upon detection of network partition, all links
      must be undirected to erase invalid routes

                                                       13
                Continued…
•   It accomplishes three functions through
    use of control packets:
    – Query (QRY) – used for creating routes
    – Update (UPD) – for both creating and
      maintaining routes
    – Clear (CLR) – for erasing routes




                                               14
                  Continued…
•   Creating Routes
    – Requires use of the QRY and UPD packets
    – QRY packet – dest-ID (did)
    – UPD – did and height of node I broadcasting
      the packet
    – Each node maintains a route-required (RR)
      flag, initially un-set
    – Node with no directed links and an un-set RR
      flag requires route to dest, it broadcasts a
      QRY packet, set RR flag
                                                     15
                   Continued…

• During the route creation and maintenance phases nodes
  use a height metric to establish a Directed Acyclic Graph
  (DAG) rooted at the destination.
• Thereafter links are assigned a direction based on the
  relative heights




                                                              16
                                     Continued…
                            2                                 7
                           (-,-)               5            (-,-)
                                              (-,-)
Source    1                   3                                           8        Destination
                             (-,-)
         (-,-)                                                           (0,0)
                                                           6
                                    4                    (-,-)
                                   (-,-)
                     Figure 13.6(a) – Propagation of the query message

                               2                                   7
                              (0,3)               5              (0,1)
                                                 (0,2)
  Source         1                  3                                          8      Destination
                                   (0,3)
              (0,3)                                                           (0,0)
                                                              6
                                       4                    (0,1)
                                      (0,2)
                 Node’s height updated as a result of the update message
                                                                                                 17
                     Continued…
• Provides multiple routes
• Minimizes algorithm’s reaction
    – Localization of control messages (close to topological
      change)
• Uses “height” metric to establish DAG
• If node other than destination is local minimum
    – full / partial reversal method



               S
                                          D
                                                               18
                     Continued…
• Provides multiple routes
• Minimizes algorithm’s reaction
    – Localization of control messages (close to topological
      change)
• Uses “height” metric to establish DAG
• If node other than destination is local minimum
    – full / partial reversal method



               S
                                          D
                                                               19
                     Continued…
• Provides multiple routes
• Minimizes algorithm’s reaction
    – Localization of control messages (close to topological
      change)
• Uses “height” metric to establish DAG
• If node other than destination is local minimum
    – full / partial reversal method



               S
                                          D
                                                               20
                     Continued…
• Provides multiple routes
• Minimizes algorithm’s reaction
    – Localization of control messages (close to topological
      change)
• Uses “height” metric to establish DAG
• If node other than destination is local minimum
    – full / partial reversal method



               S
                                          D
                                                               21
           Creating Routes

              QRY
              UPD     UPD
                      QRY
          A                 B
    UPD
    QRY                         UPD E
C
                UPD
                QRY
                  D                 G (DEST)


     F
                            H
          UPD
          QRY         UPD
                                               22
      Continued…
Route-required flag set




                          23
                  Route maintenance
• Full reversal
   – At each iteration each node other than the destination that
     has no outgoing link reverses the directions of all its
     incoming links.
• Partial reversal
   – Every node u other than the destination keeps a list of its
     neighboring nodes v that have reversed the direction of the
     corresponding link (u, v)
   – At each iteration each node u that has no outgoing link
     reverses the directions of the links (u; v) for all v which do
     not appear on its list, and empties the list. If no such v
     exists, node u reverses the directions of all incoming links
     and empties the list.
                                                                   24
          Continued…
                  UPD
          A             B
    UPD                     E
C
                  UPD
              D             G (DEST)
                  X
     F
                        H

                                       25
Continued…




             26
                    Continued…
•   Maintaining Routes performed only for nodes height > 0




                                                             27
                Erasing Routing
•   Following detection of a partition, node I
    sets its height and the height of neighbor
    to NULL
•   Update all entries in link-state array
•   Broadcast a CLR packet




                                                 28
             Continued…
Link (D,H) marked as failing




                               29
Continued…




             30
                  Performance
•   TORA is able to localize its reaction to
    topological changes
•   Best suited for relatively dense networks,
    only several nearby nodes involved in a
    reaction
•   Effect of localization – increased of
    scalability


                                                 31
               Comparative Study

Protocols               DSDV   DSR   AODV          TORA
Attributes


      Loop-free          Y      Y     Y     No, short lived loops



   Multiple routes       N      Y     N              Y


 Unidirectional links
                         N      Y     N              N
     supported


 Periodic Broadcast      Y     N      Y              Y




                                                                    32
          Advantages and Drawbacks:
• Advantages: provides loop free paths at all instants
  and multiple routes so that if one path is not available,
  other is readily available. It establishes routes quickly
  so that they may be used before the topology changes.
• Drawbacks: exhibits instability behavior similar to
  "count-to-infinity" problem in distance vector routing
  protocols.




                                                         33
                Concluding remarks
• TORA not designed to find shortest path
• TORA uses paths close to optimum when node mobility is low
• Proposed a highly adaptive distributed routing algorithm
  that well-suited in mobile wireless networks
• Decouple the generation of far-reaching control message
  propagation from the dynamics of the network topology
• Possible enhancement would be to periodically propagate
  refresh packets outwards from the dest.
• The refresh process permits intro of far-reaching control
  message propagation into the protocol independent of the
  network topology
                                                          34
Low-Energy Adaptive Clustering Hierarchy (LEACH)


• LEACH is a family of protocols containing both distributed
  and centralized schemes and using proactive updates.
• It utilizes randomized rotation of local cluster heads (CHs)
  to evenly distribute the energy load among sensors.
• It makes use of a TDMA/CDMA MAC scheme to reduce
  inter and intra-cluster collisions.




                                                            35
                 Reactive Network Protocol:TEEN


TEEN (Threshold-sensitive Energy Efficient sensor Network
  protocol)
• It is targeted at reactive networks and is the first protocol
  developed for such networks.
• In this scheme at every cluster change time, the CH
  broadcasts the following to its members:
   – Hard Threshold (HT): This is a threshold value for the
      sensed attribute.
   – Soft Threshold (ST): This is a small change in the value
      of the sensed attribute which triggers the node to switch
      on its transmitter and transmit.


                                                              36
                Reactive Network Protocol:TEEN


   Parameters                    Attribute > Threshold




Cluster Formation

  Cluster Change Time                     Cluster Head Receives Message




                        Time Line for TEEN

                                                                     37
                    TEEN (Cont’d)


• The nodes sense their environment continuously.
• The first time a parameter from the attribute set reaches its
  hard threshold value, the node switches on its transmitter
  and sends the sensed data.
• The sensed value is stored in an internal variable, called
  Sensed Value (SV).
• The nodes will transmit data in the current cluster period
  only when the following conditions are true:
   -- The current value of the sensed attribute is greater than
      the hard threshold.
   -- The current value of the sensed attribute differs from SV
      by an amount equal to or greater than the soft threshold.
                                                            38
                           TEEN


Important features:
• Suited for time critical sensing applications.
• Message transmission consumes more energy than data
  sensing. So the energy consumption in this scheme is less
  than the proactive networks.
• The soft threshold can be varied.
• At every cluster change time, the parameters are broadcast
  afresh and so, the user can change them as required.
• The main drawback is that if the thresholds are not reached,
  then the nodes will never communicate.


                                                             39
 Adaptive Periodic Threshold-sensitive Energy Efficient
         sensor Network protocol (APTEEN)
Functioning:
The cluster heads broadcasts the following parameters:
Attributes (A): This is a set of physical parameters which the
   user is interested in obtaining data about.
Thresholds: This parameter consists of a Hard Threshold (HT)
   and a Soft Threshold (ST).
Schedule: This is a TDMA schedule, assigning a slot to each
   node.
Count Time (CT): It is the maximum time period between two
   successive reports sent by a node.


                                                             40
  Adaptive Periodic Threshold-sensitive Energy Efficient
           sensor Network protocol (APTEEN)


    TDMA Schedule and
    Parameters
                                Slot for Node i




Cluster Formation
                                         Frame Time
  Cluster Change Time




                    Time line for APTEEN


                                                           41
                   APTEEN (Cont’d)


• The node senses the environment continuously.
• Only those nodes which sense a data value at or beyond the
  hard threshold transmit.
• Once a node senses a value beyond HT, it next transmits data
  only when the value of that attribute changes by an amount
  equal to or greater than the ST.
• If a node does not send data for a time period equal to the
  count time, it is forced to sense and retransmit the data.
• A TDMA schedule is used and each node in the cluster is
  assigned a transmission slot.



                                                           42
                      APTEEN (Cont’d)


Main features of the scheme:
• It combines both proactive and reactive policies.
• It offers a lot of flexibility by allowing the user to set the
  count-time interval (CT) and the threshold values for the
  attributes.
• Energy consumption can be controlled by changing the
  count time as well as the threshold values.
• The main drawback of the scheme is the additional
  complexity required to implement the threshold functions
  and the count time.


                                                                   43
                          Hierarchical Vs Flat topologies
           Hierarchical                                 Flat
Reservation-based scheduling          Contention-based scheduling
Collisions avoided                    Collision overhead present
Reduced duty cycle due to periodic Variable duty cycle by controlling sleep
sleeping                           time of nodes
                                      Node on multi-hop path aggregates
Data aggregation by cluster head
                                      incoming data from neighbors
Simple but non-optimal routing        Routing is complex but optimal
Requires global and local             Links formed on the fly, without
synchronization                       synchronization
Overhead of cluster formation         Routes formed only in regions that
throughout the network                have data for transmission
Lower latency as multi-hop network Latency in waking up intermediate
formed by cluster-heads is always nodes and setting up the multi-hop
available                          path                              44
    Adapting to the Inherent Dynamic Nature of Wireless Sensor
                             Networks


Certain objectives that need to be achieved are:
   – Exploit spatial diversity and density of sensors.
   – Build an adaptive node sleep schedule.
   – Explore the tradeoff between data redundancy and
      bandwidth consumption.
   – The nodes on deployment should create and assemble a
      network, adapt to device failure and degradation, manage
      mobility of sensor nodes and react to changes in task and
      sensor requirements.
   – Adaptability to traffic changes. Certain nodes may detect an
      event that could trigger a number of updates and at other
      times very little traffic may be present.
   – Allowing finer control over an algorithm rather than simply
      turning it on and off.                                    45

								
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