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EnviroTrack and JAM

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Title: EnviroTrack and JAM


1
EnviroTrack and JAM
  • Presented by Chien-Liang Fok

2
EnviroTrack
  • A entity-tracking middleware for sensor networks
  • Provides an single context label abstraction that
    is dynamically created and logically associated
    with an entity
  • Abstracts details of inter-node communication
  • Performs of group maintenance
  • Programmer interacts with context label rather
    than changing set of nodes

3
Context Label
  • A form of attribute-based naming
  • Serves as an address to the entity
  • Is distinguished by type (e.g., fire or car)
  • Contains aggregate state about the entity
  • Hosts application-defined tracking objects
  • Active elements that perform context-specific
    computation or action
  • Abstracts a group of nodes that can sense the
    entity

4
Problem Definition
  • Maintain context labels such that
  • Each entity has one context label
  • Context label follows the entity
  • Group management, leader maintenance
  • Approximate aggregate state is maintained
  • Freshness constraint, Le
  • Critical mass constraint, Ne
  • Simplify application development
  • Language support for defining context labels,
    aggregate state variables, and tracking objects
  • Directory service

5
Programming Model
6
Context Label Specification
  • To declare a context label of type e, the
    following must be provided
  • sensee() specifies a pattern in the environment
    to watch for
  • statee() the state data to be maintained within
    the context label
  • EnviroTrack provides a library of statee()
    functions
  • Accessible by all tracking objects
  • Which tracking objects to associate with the label

7
Group Maintenance
  • A group of sensors that detect the entity should
    produce a single context label for it
  • The algorithm must be lightweight and dynamic
  • All members of the group must satisfy sensee()
  • There is at most one majority leader within the
    group

8
Group Maintenance Algorithm
  • If a leader exists, the leader sends heartbeat
    containing e
  • Propagates h hops beyond group boundary
  • Tells member nodes leader is still present
  • Notifies non-members of the existence of context
    label e

9
G. M. Algorithm Cont.
  • When a member receives a heartbeat, it sets a
    timer. If timer expires before receiving another
    heartbeat, a leadership takeover protocol is
    triggered
  • This is a backup to the standard leadership
    handoff

10
G. M. Algorithm Cont.
  • When a non-member node receives a heartbeat, it
    sets a timer
  • If the entity is sensed before expiration, the
    node joins the group
  • If the entity is sensed after timer expires, the
    node creates a new group (and context label) and
    declares itself leader

11
Spurious Leaders
  • The group member algorithm may result in more
    than one leader
  • Solution
  • Each context labels leader contains a weight,
    initially zero
  • Increment weight each time data is received from
    the members
  • Weight is inherited during leadership handoff
  • Context label with greater weight wins
  • Unlikely for spurious leaders attain Ne

12
Approximate Aggregate State
  • The leader of the group maintains the approximate
    aggregate data state
  • Leader sends each member Le
  • The member periodically sends sensor data to
    leader with a period of Pe Le d
  • d network delay processing time
  • The leader performs aggregation every Pe
  • A valid flag is set if Ne is not met

13
Directory Service
  • Provides access to a particular type of context
    label
  • Use a hash function
  • context label type ? physical location (x,y)
  • Nodes within one hop of (x,y) are called
    directory object
  • Context labels periodically send their state and
    location to directory object

14
Language
  • EnviroTrack provides a language for declaring
    context labels and aggregate data state
  • Example code

15
Evaluation
  • Theoretical example scenario
  • A T-72 tank moves through a sensor field
  • Sensors can detect tank 100m away
  • Sensors arranged in grid 140m apart
  • At max speed, tank moves one hop every 11.2
    seconds (45km/h)
  • Actual test setup
  • 10001 model of the above scenario
  • 10s/hop (50km/h) and 15s/hop (33km/h)

16
Tracked tank trajectory
  • Nodes located at integer coordinates
  • Actual path y 0.5
  • Nodes have no notion of proximity

17
Leadership Handover
18
Communication Performance
  • System handles message loss
  • Message loss not due to link usage
  • Protocol uses very little bandwidth
  • Scalable to greater tracking difficulty

19
Maximum Trackable Speed
  • Affected most by heartbeat period
  • Best results when
  • Receive timer 2.1 HB
  • Time to take over leadership
  • Wait timer 4.1HB
  • Time to create new group

20
Maximum Trackable Speed
21
Communication Radius Sensing Radius Ratio
22
Conclusions
  • EnviroTrack is a middleware for tracking entities
  • Relieves applications from details of
  • Group management
  • Directory service
  • Data aggregation

23
JAM
  • A protocol that allows applications to view a
    jammed region as an entity rather than a
    collection of broken links and congested nodes
  • Allows data to be rerouted around a jammed region
    and other evasive actions

24
General Algorithm
  • Nodes within the jammed area notify nodes outside
    of the jammed area that they are jammed
  • Border nodes just outside jammed area coordinate
    to form groups of jammed nodes

jammed area
25
Architecture
26
Jam Detection
  • A node considers itself jammed when the utility
    of its communication link falls below a certain
    threshold
  • Based on local data (failed channel access,
    protocol violations, low SNR)
  • When a node considers itself jammed, it
    periodically sends a JAMMED message
  • Modify MAC to bypass carrier sense phase
  • Hopefully an un-jammed neighbor receives it

27
Mapping protocol
  • Border nodes receive a JAMMED messages from its
    jammed neighbors and calculates normal direction
    vector to the jammed nodes
  • These nodes are called mapping nodes
  • If it is not aware of a compatible group, it
    creates a new one with a random ID, waits a
    while, and broadcasts a BUILD message
  • Two groups are compatible if the angular
    difference between their direction vectors is
    below some threshold

28
Group Coalescing
  • If two groups are compatible, they are coalesced
    after a certain time
  • The group with the larger group ID dominates
  • Jammed nodes in the subordinate group is merged
    with the dominant group
  • Dominant groups BUILD message is augmented with
    subordinate group ID

29
BUILD Message
  • Contains
  • ID of original sender
  • Group ID
  • Sequence number
  • List of known jammed nodes
  • List of subordinate group IDs
  • When received
  • If a regular node, store data locally
  • If a mapping node, update the list of known
    jammed nodes and rebroadcast it

30
Eager Eavesdropping
  • JAM attempts to quickly diffuse knowledge of
    jammed region
  • Forward information diffusion As a BUILD message
    is relayed around mapping nodes, each node
    updates list of jammed nodes
  • Back Flooding When a a BUILD message is
    rebroadcasts, the single hop upstream mapping
    node processes it
  • Updates its list of jammed nodes
  • Does not relay it

31
Edge Nodes
  • A mapping node that does not have a neighbor left
    or right of the direction vector
  • If a neighbor is not discovered within some time,
    it periodically sends a PROBE message to detect
    neighboring mapping node(s) or form bridge nodes

jammed area
edge node
32
Bridge Nodes
  • Does not actually receive any JAMMED messages
  • Connects two edge nodes
  • Masks areas of low connectivity
  • A node becomes a bridge node when it detects a
    PROBE message from a group it knows about
  • A bridge nodes coalescing timer is longer to
    prevent spurious bridging nodes

33
Recovery
  • When a jammed node becomes un-jammed, it
    periodically sends an UNJAMMED message
  • When a mapping node receives it, it updates the
    list of jammed nodes and propagates an TEARDOWN
    message
  • The opposite of a BUILD message
  • When all of a mapping nodes jammed neighbors are
    un-jammed, the mapping node becomes a regular node

34
Example
1
2
3
4
35
Example (Cont.)
5
6
7
8
36
Simulation Methodology
  • GloMoSim simulator
  • 4000 x 4000 meter field
  • 400 nodes placed at 200m interval grid
  • Radio settings inbetween MICA2 and WaveLAN
  • MACA IEEE802.11 MAC layer
  • Jammed area ranged from 5-144 nodes
  • Connectivity
  • Low 4 neighbors
  • Moderate 8 and 12 neighbors

37
Simulation Results
  • Varying jammer range

38
Simulation Results Cont.
  • Time to map region, 12 neighbor case
  • 90 of mapping nodes know 1/3 of jammed region in
    0.5-3 seconds

39
Simulation Results Cont.
  • Node failure rate

40
Conclusions
  • JAM provides a protocol for mapping a jammed
    region
  • Loose group semantics and eager eavesdropping
  • Quick convergence and tolerance to failures when
    network is moderately connected
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