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Self Configuring

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Wireless Sensor Networks are used in applications where ... Specialized nodes must be adjacent to a router ... G selects the next best group H. 11/8/09 ... – PowerPoint PPT presentation

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Title: Self Configuring


1
Self Configuring Self Organizing Protocols
2
Outline
  • Background.
  • Taxonomy of Sensor Network Applications.
  • Policy Decisions Assumptions for the
    self-configuring architecture.
  • Terminology used.
  • Architecture for the self-configurable systems.
  • A Self-Organizing algorithm and its analysis.
  • References.

3
Background
4
Background
  • Why do we need self-organizing protocol?
  • Wireless Sensor Networks are used in
    applications where
  • They are deployed in large numbers (hundreds or
    thousands of sensor nodes).
  • They are deployed in remote/hostile environment.
  • Systems in which sensor nodes need to
    self-organize themselves into a network belong to
    the class of self configurable systems.

5
Terminology
6
Terminology
  • Sensor Motes
  • Sensor node that performs data discovery
  • Sink Node
  • Node with high processing capabilities and high
    capacity for data storage
  • Specialized Sensor
  • Sensor that performs specific data discovery
    operation (e.g. temperature sensors)
  • Router Sensor
  • Router sensor collects and transmits data to
    neighbors

7
Terminology
  • High-End System
  • Sink node
  • 2-Connected Graph
  • Topology in which there are two edge disjoint
    paths from every node to every other node
  • Broadcast Graph
  • Subset of edges in the network used for
    broadcasting data
  • Directed Acyclic Graph (DAG)
  • Graph with directed edges and no cycles

8
Taxonomy of Sensor Network Applications
9
Taxonomy of Sensor Network Applications
  • Classifying sensor network applications
  • Important Factors
  • Size of the system number of sensors used
  • Determine effort needed to configure the system
  • Maximum distance of the sensors to the wired
    infrastructure
  • Determines the amount of intelligence required at
    a sensor for routing to specific high processing
    nodes
  • Distribution of the sensor nodes
  • Deterministic administrator controls placement
    of sensor nodes and user performs remedial
    operations in case of faults
  • Non-deterministic fault-tolerance level depends
    on number of sensors deployed

10
Taxonomy of Sensor Network Applications
  • Three classifications of sensor network
    applications
  • Non-propagating systems
  • Sensor nodes are one hop to wired infrastructure
  • Wired infrastructure is the main connecting
    component
  • Nodes connected to the wired infrastructure route
    information to the end system

11
Taxonomy of Sensor Network Applications
Wired Nodes
12
Taxonomy of Sensor Network Applications
  • Deterministic routing systems
  • Sensor nodes route through a few hops to reach a
    wired infrastructure
  • Routes to the wired infrastructure are
    deterministic
  • Number of nodes in this system may be restricted

13
Taxonomy of Sensor Network Applications
14
Taxonomy of Sensor Network Applications
  • Self-configurable systems
  • Sensor nodes need to self-organize into a network
  • As long as the number of nodes in the system is
    small the systems are deterministic.
  • But when the number of nodes increase the systems
    become non-deterministic systems and they need to
    be self-configurable.(e.g. Security and Parking
    Lot networks)
  • Fault tolerance is achieved through
    re-configuring the system in the presence of new
    node and link failures

15
Taxonomy of Sensor Network Applications
16
Taxonomy of Sensor Network Applications
  • Non-Aggregating
  • Independent data
  • Transmitted separately
  • E.g. parking-lot systems
  • Aggregating
  • Data aggregating and transmitted along the
    network.
  • E.g. weather applications
  • Self-configuring sensor networks should include
    the functionality of performing aggregation too.

17
Policy Decisions Assumptions for the
Architecture of Self-configuring systems
18
Policy Decisions Assumptions
  • Heterogeneous nodes
  • Architecture should provide a common framework
  • Data Discovery Data Dissemination
  • Two orthogonal components
  • Nodes that perform data discovery
  • Nodes that perform data dissemination

19
Policy Decisions Assumptions
  • Memory and Power Constraints
  • All nodes have memory and power constraints
  • Attempt to reduce state stored at every node
  • Employ energy aware routing
  • Application Specific Infrastructure Requirements
  • Infrastructure components is dependent on
    application
  • Provide a wide variety of features to allow the
    application to make use of what is required

20
Policy Decisions Assumptions
  • Mobility/Immobility of nodes
  • Data discovery nodes are mobile
  • Data dissemination nodes are stationary
  • Previous Works
  • Multi-functional nodes
  • Cost more to implement
  • Routing in highly specialized nodes wasting
    energy
  • Storage of mass information
  • Data-Centric Networking
  • Critical nodes need to keep large amounts of
    state information
  • Cut nodes can cause the data to be lost

21
Policy Decisions Assumptions
  • Self-Configurable systems require one or more of
    the following
  • Naming/Addressing System
  • Routing
  • Required to pass information to sensors with
    specific functionality
  • Unique addresses to every node required
  • Broadcasting
  • Required to pass information to every sensor in a
    network (e.g. a wakeup message to all nodes in a
    security network)
  • Multicasting

22
Main Contribution of the Algorithm
23
Main Contribution of the Algorithm
  • Scalability
  • Every node has a O(log n) bit unique identifier
  • Reduction of State and Localized Operations
  • Maintain O(log n) O(N(v)) state information
    at each node
  • N - of nodes
  • V current node
  • N(v) - of neighboring nodes of v in network

24
Main Contribution of the Algorithm
  • Power Efficiency and Reliable Paths
  • Keeps track of the power requirements at every
    node to compute reliable and power efficient
    paths
  • Hierarchical Routing Architecture
  • Nodes reorder themselves in a hierarchical
    structure
  • Size of routing table is reduced to O(log n) at
    every node

25
Main Contribution of the Algorithm
  • Fault-Tolerant Broadcast Trees
  • Local Markov Loops (LML) technique is used to
    achieve fault tolerance
  • Reduce Frequency of Updates
  • Define discrete power levels to reduce the number
    of dynamic cost updates that need to be performed
    in the network

26
ComponentsInfrastructure
27
Components
  • Sensors
  • Specialized
  • Identifies itself with a class
  • Can communicate with other sensors either of its
    own class or with some other class
  • Can be Mobile
  • Routing
  • Form the backbone of the sensor network
  • Immobile
  • Performs data-dissemination

28
Components
  • Advantages
  • Separation of dissemination and discovery
  • Shorter network hops reduces power consumption
  • Cost decreased routing sensors are not
    specialized and may cost less
  • Large amounts of routers can increase the fault
    tolerance of the system

29
Components
  • Other components
  • Sink Nodes
  • High storage capacity high processing power
  • Can connect to WAN
  • Can activate specific actuators (through
    messaging) and broadcast important messages into
    the sensor net.
  • Aggregator Nodes
  • Nodes with the functionality of aggregation can
    be introduced in router nodes or specialized
    nodes
  • E.g. In weather monitoring application
    aggregation functionality is placed on all router
    nodes

30
Infrastructure Components
  • Functionalities provided by this architecture
  • Unique address for all nodes
  • Routing information between two nodes
  • Fault-Tolerant broadcasting infrastructure
  • Broadcasting information within a certain radius
  • Multicasting information to specialized nodes
  • Self-reorganization in the face of node failures
    and network partitions

31
Infrastructure Components
  • Scenarios in which these components are used
  • Security Sensors
  • Unique Addresses to pass critical information to
    that sensor
  • Routing Architecture to send messages to sink
    nodes
  • Multicasting infrastructure to coordinate actions
    of specialized sensors of a particular class
  • Broadcast infrastructure to alert all nodes
    within a radius to prepare to perform important
    actions

32
Infrastructure Components
  • Parking-Lot Networks
  • Unique Addressing to isolate a particular node
    controlling a particular spot
  • Routing Infrastructure for routing messages
  • Broadcast Infrastructure not generally required
    but may be utilized

33
Infrastructure
  • Addressing Infrastructure
  • If non-addressable nodes (e.g. traffic monitoring
    along a highway)
  • Self-configurable systems is an aggregating
    system
  • If addressing required - Local Unique Addressing
  • IP not appropriate global unique addressing
  • An alternative solution
  • An alternative solution for addressing - MAC
    Layer
  • Ensure that every node has a unique MAC address.

34
Infrastructure
  • Routing Infrastructure
  • Specialized nodes must be adjacent to a router
  • Transmits all messages to adjacent router with a
    message header
  • Indicates which node(s) to transmit the message
    to (whether to one node or broadcast or
    multicast)
  • Router acts as the proxy for the specialized
    node(s) i.e. every specialized node is addressed
    with the help of a router node.

35
Infrastructure
  • Broadcast and Multicasting Infrastructure
  • Sensor networks are more data centric
  • Require broadcasting and multicasting of data to
    all or groups of sensor nodes
  • Fault Tolerant Broadcast tree is created
  • Changes developing Local Markov Loops (LML)
  • Directed Acyclic Graphs (DAG) are used to support
    fault tolerance in paths
  • Participants
  • Router sensors self-configure
  • Specialized sensors keep track of the nearest
    router sensors

36
Self-Organizing Algorithm
37
Self-Organizing Algorithm
  • Phases of the algorithm
  • Discovery Phase
  • Organization Phase
  • Maintenance Phase
  • Self-Reorganization Phase

38
Discovery Phase
  • Each node discovers its set of neighbors and
    fixes its maximum radius of data transmission
  • Criteria
  • Nodes should not have too many neighbors
  • Specialized nodes n(x) 1
  • Router nodes, n(x) gt 1
  • where n(x) is the number of neighbors for node x
  • Maximum bound on transmission radius
  • Each node x picks a small radius r and broadcasts
    a Hello message indicating whether it is a router
    or a special node

39
Discovery Phase
  • Every node within radius r replies back with a I
    am Here message and their coordinates (determined
    by GPS)
  • If of replies lt minimum threshold n(x), x
    broadcasts Hello over radius kr, for k gt 1
  • Repeat until of nodes N that replies satisfies
  • n(x) ? N ? N(x) where n(x) and N(x) denote the
    min and max number of neighbors to node x.
  • Note that specialized nodes are only connected to
    routers only.

40
Discovery Phase
Hello
r
41
Discovery Phase
I am here
r
42
Discovery Phase
Hello
kr
43
Discovery Phase
I am here
kr
44
Organization Phase
  • Network is organized as follows
  • Nodes are aggregated into groups
  • Groups are aggregated into larger groups to form
    a hierarchy of groups which is height balanced
  • Each node is allocated an address based on its
    position in the hierarchy
  • A routing table of O(log n) is computed for each
    node
  • A broadcast tree and graph spanning all nodes is
    constructed
  • Graph is converted into a DAG based on the source
    node in the network

45
Organization Phase
  • Group formation
  • Routers form small basic groups with neighbors
    found
  • Group size is restricted to 8 and each node in a
    group is allocated a 3-bit address.
  • Each node belongs to one basic group
  • Each node maintains the distance and the next hop
    for reaching every other node in the group
  • If a node is unable to join a group
  • It forms a one node group with address 000
  • ? is the height difference parameter.

46
Organization Phase
  • Merging of Groups
  • Assume 2 groups G1 and G2 with m n bit
    address. For the formation of hierarchy set the
    value of ? to 3 equal to the height of a basic
    group.
  • If m-n ? ? the G1 and G2 are merged to G with
  • 0 appended to all node addresses in G1
  • 1 appended to all node addresses in G1
  • If m-n gt ? then
  • Consider node x in G1 with address (x1, x2, xm)
  • Consider subgroup Hi in G1 with 1st i bits equal
    to (x1, x2, xi) for i ? m-n-1.
  • All nodes in Hi are connected.

47
Organization Phase
  • Find if Hm-n-1 has a sub-branch where G2 can be
    added to hierarchy without affecting Height of
    Hm-n-1 or G2.
  • If not able to merge them at any value of i, then
    merge them according to the 1st method and mark
    the new graph as height imbalanced.
  • A boundary node is a node that connects to a node
    in another group

48
Organization Phase
  • Formation of hierarchy
  • Each Group G receives an advertisement from
    adjacent groups through its boundary nodes
  • Broadcast throughout the group
  • Contains size of adjacent group ( of address
    bits)
  • Each node concludes on an adjacent group G
  • G closest in size to G.
  • G has the maximum number of boundary nodes.
  • then node of G sends a join message to G.
  • If G decides to join G, the groups merge
  • Otherwise G selects the next best group H

49
Organization Phase
  • Continue until all groups merge into one
  • At any point, If a group is heavily imbalanced,
    then the group is reorganized with an increased
    value of ?new ?old 1
  • Theorem 1 Height of the hierarchy of the network
    will be O(log n) where n is the number of nodes
    in the graph

50
Organization Phase
  • Perform group reorganization if necessary
  • If height is unbalanced at multiple levels,
    reorganize
  • Group is broken into sub-groups
  • Regroup without affecting the state of the rest
    of the network
  • Some routing tales of nearby nodes will have to
    change addresses of neighbors
  • Generate addresses for all nodes
  • To give a general picture, if ? 3, then every
    node in a network of 10000 nodes will have a 16
    bit address.

51
Organization Phase
  • Routing table generation
  • Let every node have a m-bit group address
  • (x1,xm) is the m-bit address of a router node x
  • x maintains the least cost and next hop in the
    shortest path to the following destinations
  • x1, (x1, x2),,(x1,,xm-1,xm)
  • E G., Let m 4, x address 0011
  • Groups 1, 01, 000, and 0010 are maintained in the
    routing table for x
  • routing table of O(m) at each node

52
Organization Phase
  • Broadcast Trees and Graphs
  • Broadcast graphs are intended to provide multiple
    paths from the source
  • adding fault tolerance to the system
  • They are converted to DAG from the source
  • to remove any loops
  • To reduce power consumption
  • Certain links are indicated as primary and rest
    as secondary
  • Broadcast messages are sent through broadcast
    links
  • Only secondary links follow a 3-way handshake
    mechanism

53
Organization Phase
  • Broadcast Tree and Graph formation
  • After basic group formation, a broadcast tree and
    graph are constructed
  • Some nodes are labeled as primary nodes. They
    form the broadcast tree
  • After group merge (G H), two low cost edges
    (e1, e2) are selected that connect G and H
  • Let B(G), B(H), T(G), T(H) be broadcast graphs
    and trees of G and H
  • Let cost(e1) lt cost(e2)
  • Let P be the merged group
  • B(P) B(G) ? B(H) ? (e1, e2)
  • T(P) T(G) ? T(H) ? (e1)

54
Organization Phase
  • Theorem 2 The power consumed for broadcasting
    messages using this approach is
  • (n-1)E nE/2
    where
  • E is the mean power consumed for sending a long
    message along one hop
  • E is the mean power consumed for sending a
    request/ACK short message along one hop and
  • n is the number of nodes in the network
  • The SPIN protocol consumes (n-1)E 2eE..where
  • e is the number of edges in the graph
  • (n-1)E is the lower bound for broadcasting

55
Organization Phase
  • E.g., Sensors separated by 10 meters
  • It takes 150nJ per bit transmitted
  • 170nJ per bit received
  • 1 request/ACK requiring 8 bytes
  • E 20480nJ, in a network of 1000 nodes with
    average connectivity of 12
  • Berkleys self-organizing algorithm requires an
    extra 10mJ
  • SPIN requires an extra 240mJ
  • Hence our algorithm saves by a factor of 24.

56
Maintenance Phase
  • Active monitoring
  • Each node keeps track of its stored energy and
    constantly sends I Am Alive message to neighbors
    every 30 seconds
  • If a node does not receive a reply in 6
    consecutive intervals it sets the link as dead
    and reorganizes
  • Passive monitoring (energy saving)
  • A node sends an activate message to its neighbors
    only on demand and Alive nodes respond with a ACK

57
Maintenance Phase
  • Routing Metrics
  • Delay is not considered important in sensor
    networks
  • Perhaps not true in cases of security and maybe
    even weather patterns
  • Goal Keep network alive for a maximum amount of
    time

58
Maintenance Phase
  • Two Greedy metrics suggested
  • Always route along the path that has the minimum
    energy consumption per bit of information
    transmitted
  • Always transmit along the path that has the
    maximum capacity measured in terms of bits that
    can be transmitted
  • Capacity of the link between nodes A and B is
    given by, min(E(A)/E,E(B)/E), where E(A) and
    E(B) are the energies at A and B respectively and
    E and E are the energy consumed by A and B
    transmitting from A to B.

59
Maintenance Phase
  • Maintaining Routing Tables
  • Nodes inform their neighbors of their routing
    tables and their energy levels to their
    neighboring nodes (cost metric)
  • Count to infinity problem can be avoided by using
    the next hop entry for updating the routing table
    entry for a particular destination group
  • Maintaining Broadcast Infrastructure
  • Must detect node failures in advance by
    monitoring power requirements of a node
  • Only failures detected are those do to power
    failure

60
Maintenance Phase
  • Fault tolerant broadcast trees and graphs are
    maintained using LML
  • Node that is going to fail is a leaf node
  • Therefore, does not have any nodes to broadcast
    to
  • If node u is going to fail
  • Consider all edges (u,v)
  • Construct a LML by selecting a random edge (w,x)
    s.t. the edge (u,v) is part of a local loop
    formed by adding the edge (w,x) to the tree
  • Remove (u,v) from the tree
  • New tree with degree of u reduced by 1
  • Continue until u becomes the leaf node

61
Reorganization Phase
  • Detection of group partitions or node failures
  • Update routing table based on new topology
  • When all neighbors of a node fail
  • Node repeats discovery phase
  • When group partitions occur
  • Sub groups reorganize and join
  • Reorganization ensures hierarchy is balanced
  • Group and node discoveries are considered very
    rare

62
Reorganization Phase
  • Re-organization
  • Node Failures
  • Every neighbor of the node updates all the
    entries in their routing table where the next hop
    is the failed node
  • Link Failures
  • The routing table is changed accordingly at both
    nodes
  • If the edge is a primary edge, the secondary edge
    becomes primary and local loop is performed to
    find an alternate edge
  • Group Partitions
  • Disconnected pieces are reorganized into new
    groups and merge with other neighboring groups
  • Address of all the nodes in the groups change

63
Analysis of Algorithm
  • Node Rediscovery
  • Initial radius is set to the previous maximum
    radius of connectivity
  • Strengths
  • Hierarchy formed by algorithm is strictly
    balanced
  • Max difference between the left subtree and right
    subtree at any level is strictly les than or
    equal to ?
  • Routing state maintained at any router is O(log
    n)
  • Broadcast graph (2-connected) is incrementally
    computed

64
Analysis of Algorithm
  • LML performs a random walk on spanning trees of a
    graph providing tolerance to node and link
    failures
  • Broadcast graph can be oriented as a Directed
    Acyclic Graph from any node in a unique manner.
  • The property that every specialized sensor
    attaches to some router sensor allows these
    sensors to be mobile

65
Analysis of Algorithm
  • Weaknesses
  • Initial Organization phase and not on-demand
    organization
  • Forming a hierarchy in cases where there are a
    lot of cut nodes in the network increases the
    probability of applying reorganization
  • Protocol required for transmitting data from one
    node to another node is not addressed
  • Broadcast trees and graphs maintenance in the
    presence of failures undetected prior to failure
    is not addressed

66
References
67
References
  • S Subramanian, L. and Katz, R., An
    Architecture for Building Self-Configurable
    Systems, Dept. of EECS, U. C. Berkeley, 2000,
    pp. 63-73.
  • C. Chevallay, R. E. Van Dyck, T. A. Hall,
    Self-Organizing Protocols for Wireless Sensor
    Networks, NIST Gaithersburg, MD, 2002.
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