Transcript Sensor Networks: Directed Diffusion and other proposals ECE 256 Sensor Networking – Why ??  Data Collection – A basic need  Will the.

Sensor Networks:
Directed Diffusion and other proposals
ECE 256
Sensor Networking – Why ??
 Data Collection – A basic need
 Will the volcano erupt? Need temperature/gas signatures
 Are poles melting due to GW? Need ocean current data
 How many enemy tanks crossed through the jungle?
 Did anyone enter my house while I was away?
 Human monitoring
 Not always
possible/feasible ?
 Why not a sensor + RF? Why need
 Too much data
 In-network data distillation necessary
processor?
2
Sensor Networking -- Vision
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San Fransisco’s Moscone Center equipped with sensor network
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Sensor Hardware
(Glimpse)
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Sensor Nodes

Motivating factors for emergence




Applications
Moore’s Law in chips, MEMS
Advances in wireless technology
Challenges


Battery technology lagging
Canonical Sensor Node contains
1.
Sensor(s) to convert a energy form to an electrical impulse
–
2.
3.
4.
e.g., to measure temperature
Microprocessor
Communications link e.g., wireless
Power source e.g., battery
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Example: Berkeley “Motes” or “Smart Dust”
Laser diode
III-V process
Passive CCR comm.
MEMS/polysilicon
Analog I/O, DSP, Control
COTS CMOS
Power capacitor
Multi-layer ceramic
Sensor
MEMS/bulk, surface, ...
Solar cell
CMOS or III-V
Thick film battery
Sol/gel V2O5
1-2 mm
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Example Hardware

Size
 Golem Dust: 11.7 cu. mm
 MICA motes: Few inches

Everything on one chip: micro-everything
 processor, transceiver, battery, sensors, memory, bus
 MICA: 4 MHz, 40 Kbps, 4 KB SRAM / 512 KB Serial
Flash, lasts 7 days at full blast on 2 x AA batteries
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Examples
Spec, 3/03
•4 KB RAM
• 4 MHz clock
• 19.2 Kbps, 40 feet
• Supposedly $0.30
MICA: More recent (from xbow)
Similar i-motes by Intel
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Types of Sensors

Micro-sensors (MEMS, Materials, Circuits)
 acceleration, vibration, gyroscope, tilt, magnetic, heat, motion, pressure, temp,
light, moisture, humidity, barometric, sound

Chemical
 CO, CO2, radon

Biological
 pathogen detectors

Actuators too (mirrors, motors, smart surfaces, micro-robots)
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Berkeley Family of Motes
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Sensor Software
(TinyOS Glimpse)
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Programming TinyOS

Use a variant of C called NesC
 NesC defines components

A component is either
 A module
• A module can be a Clock or LED …
• Or an user-defined software module
 Or a configuration
• set of other components wired together
• Specifying the unimplemented methods invocation mappings

Complete NesC application - one top level configuration
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Steps in writing/installing your NesC app
(applies to MICA Mote)

On your PC





Write NesC program
Compile to an executable for the mote
Plug the mote into the parallel port through a connector board
Install the program
On the mote
 Turn the mote on, and it’s already running your application
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TinyOS component model
 Component specifies:
Internal Tasks
Commands
 Component invocation is event
 arising from hardware events
Internal State
Events
driven
 Static
allocation avoids run-time overhead
 Scheduling: dynamic
 Explicit interfaces accommodate different applications
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A Complete TinyOS Application
application
sensing application
Routing Layer
routing
messaging
packet
byte
bit
Messaging Layer
Radio Packet
Radio byte
RFM
photo
clocks
ADC
Temp
i2c
SW
HW
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Energy – a critical resource
Component
Rate
Startup time
Current consumption
CPU Active
4 MHz
N/A
4.6 mA
CPU Idle
4 MHz
1 us
2.4 mA
CPU Suspend
32 kHz
4 ms
10 uA
Radio Transmit
40 kHz
30 ms
12 mA
Radio Receive
40 kHz
30 ms
3.6 mA
2000 Hz
10 ms
1.235 mA
2 Hz
500 ms
0.150 mA
Pressure
10 Hz
500 ms
0.010 mA
Press Temp
10 Hz
500 ms
0.010 mA
500 Hz
500 ms
0.775 mA
Thermopile
2000 Hz
200 ms
0.170 mA
Thermistor
2000 Hz
10 ms
0.126 mA
Photo
I2C Temp
Humidity
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Sensor-node Operating System

Size of code and run-time memory footprint
 Embedded System OS’s inapplicable
 Need hundreds of KB ROM

Workload characteristics
 Continuous ? Bursty ?

Application diversity - Need to reuse sensor nodes

Energy consumption - Primary concern
 Computation, Communication must be energy-aware
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TinyOS: Summary
Matches both
 Hardware requirements
 power conservation, size
 Application requirements
 diversity (through modularity), event-driven, real time
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AdHoc and Sensors …
 Ad Hoc network lacking killer applications
 Difficult to force co-operation among HUMAN users
 Mobility/connectivity unreliable for a business model
 Difficult to bootstrap – critical mass required
 Sensor networks more realizable
 More defined applications
 Single owner/administration – easier to implement
 Sensing already an established process – just add
networking to it.
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However …
 Ad
Hoc and Sensor Networks are both multihop wireless architectures
 Thereby shares several technical issues and challenges
 Solutions in one domain often applicable to others.
 However, key differences exist
 Energy constraint in sensor networks
 Traffic models and characteristics
 Other issues like coverage, fault-tolerance, etc.
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This Talk …
 Directed Diffusion
 Focusing on the shift from the ad hoc paradigm
 The attention to energy conservation
 Other routing proposals
 SPIN, LEACH, Rumor Routing, etc.
 SMAC
 Energy-Aware Medium Access Control
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Directed Diffusion
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The Problem

A region requires eventmonitoring (harmful gas,
vehicle motion, seismic
vibration, temperature, etc.)


A sensor field
Sensor sources
Event
Deploy sensors forming a
distributed network
On event, sensed and/or
processed information
delivered to the inquiring
destination
Directed
Diffusion
Sensor sink
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The Proposal
 Proposes
an application-aware paradigm to
facilitate efficient aggregation, and delivery of
sensed data to inquiring destination
 Challenges:
 Scalability
 Energy efficiency
 Robustness / Fault tolerance in outdoor areas
 Efficient routing (multiple source destination pairs)
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IP or not to IP
 IP is the pivot of wired/wireless networks
 All networking protocol over and below IP
 Should
we stick to this model?
Comments ?
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Directed Diffusion
 Typical IP based networks
 Requires unique host ID addressing
 Application is end-to-end, routers unaware
 Directed diffusion – uses publish/subscribe
 Inquirer expresses an interest, I, using attribute values
 Sensor sources that can service I, reply with data
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Data Naming
 Expressing an Interest
 Using attribute-value pairs
 E.g., Type = Wheeled vehicle // detect vehicle location
Interval = 20 ms
Duration = 10 s
Field = [x1, y1, x2, y2]
// send events every 20ms
// Send for next 10 s
// from sensors in this area
 Other interest-expressing schemes
 E.g., hierarchical (different problem)
possible
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Gradient Set Up
 Inquirer (sink) broadcasts exploratory interest,
 Intended to discover routes between source and sink
 Neighbors
i1
update interest-cache and forwards i1
 Gradient for i1 set up to upstream neighbor
 No source routes
 Gradient – a weighted reverse link
 Low gradient  Few packets per unit time needed
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Exploratory Gradient
Exploratory Request
Gradient
Event
Low
Low
Low
Bidirectional gradients established on all links through flooding
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Event-data propagation
 Event e1 occurs, matches i1 in sensor cache
 e1 identified based on waveform pattern matching
 Interest reply diffused down gradient (unicast)
 Diffusion initially exploratory (low packet-rate)
 Cache filters suppress previously seen
 Problem of bidirectional gradient avoided
data
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Reinforcement
Event
A sensor field
Reinforced gradient
Reinforced gradient
Sink
 From
exploratory gradients, reinforce optimal
path for high-rate data download  Unicast
 By requesting higher-rate-i1 on the optimal path
 Exploratory gradients still exist – useful for faults
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Path Failure / Recovery
 Link failure detected by reduced rate, data loss
 Choose next best link (i.e., compare links based on
infrequent exploratory downloads)
 Negatively reinforce lossy link
 Either send i1 with base (exploratory) data rate
 Or, allow neighbor’s cache to expire over time
D
Event
M
Src
A
C
B
Sink
Link A-M lossy
A reinforces B
B reinforces C …
D need not
A (–) reinforces M
M (–) reinforces D
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Loop Elimination
P
D
Q
M
A
M
gets same data from both D and P, but P
always delivers late due to looping
 M negatively-reinforces (nr) P, P nr Q, Q nr M
 Loop {M  Q  P} eliminated
 Conservative
nr useful for fault resilience
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Simulation Setup & Metrics

ns2, 50 nodes in 160x160 sqm., range 40m
 Node density maintained, 802.11 MAC
 Random
5 sources in 70x70, random 5 sinks
 Average Dissipated Energy
 Per node energy dissipation / # events seen by sinks
 Average Delay
 Latency of event transmission to reception at sink
 Distinct event delivery ratio
 Ratio of # events sent to # events received by sink
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Average Dissipated Energy
flooding
Multicast
Diffusion
In-network aggregation reduces DD redundancy
 Flooding poor because of multiple paths from source to sink
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Delay
flooding
Diffusion
Multicast
DD finds least delay paths, as OM – encouraging
 Flooding incurs latency due to high MAC contention, collision
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Event Delivery Ratio under node failures
0%
10%
20%
Delivery ratio degrades with higher % node failures
 Graceful degradation indicates efficient negative reinforcement
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Conclusion
 Directed
diffusion, a paradigm proposed for
event monitoring sensor networks
 Energy efficiency achievable
 Diffusion mechanism resilient to fault tolerance
 Conservative negative reinforcements proves useful
 A careful
MAC protocol, designed for such
specifics, can yield further performance gains
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Questions?
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An Energy-Efficient MAC Protocol for
Wireless Sensor Networks (S-MAC)
Wei Ye, John Heidemann, Deborah Estrin
Major source of energy waste
 Collision
 Overhearing
 Control
 Idle
Overhead
Listening
 Listening to possible traffic that is not sent
 50%-100% energy drain compared with receiving
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Avenues to Reduce Energy Consumption
(1) Periodic listen and sleep
(2) Collision avoidance
(3) Overhearing avoidance
(4) Message passing
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(1) Periodic Listen and Sleep
 The
main idea
 Put nodes to sleep periodically
 Called “Duty Cycles”
 However, ensure that sleep/wake-up is synchronous
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Listen/Sleep Schedule Assignment
Choosing Schedule (1)
Listen
A
Go to sleep after time t
Listen for SYNC
Sleep
Broadcasts
Listen
B
td
Broadcasts
Go to sleep after time t- td
Sleep
Synchronizer
• Listen for a mount of time
• If hear no SYNC, select its
own SYNC
• Broadcasts its SYNC
immediately
Follower
• Listen for a mount of time
• Hear SYNC from A, follow
A’s SYNC
• Rebroadcasts SYNC after
random delay td
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Listen/Sleep Schedule Assignment
Choosing Schedule (2)
Listen
A
Go to sleep after time t1
Listen for SYNC
Broadcasts
B
Sleep
Listen
1. B receives A’s schedule and
rebroadcast it.
2. Hear different SYNC from C
3. Adapt both schedules
Sleep
td
Broadcasts
Only need to broadcast once
Nodes only rarely adopt
multiple schedules
Listen
C
Listen for SYNC
Go to sleep after time t2
Sleep
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Keeping Clocks in SYNC
 SYNC packets must not collide
 Reserve separate time window for SYNC transmission
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(2) Collision Avoidance
 Identical to 802.11
 RTS/CTS
 Virtual carrier sense (NAV)
 Physical carrier sense
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(3) Overhearing Avoidance
Neighbors go to sleepon overhearing RTS/CTS
A is talking to B
D receives CTS from B -> sleep
• D’s transmission will collide B’s
C receives RTS from A -> sleep
• C cannot receive CTS/DATA from E
All immediate neighbours of transmitting node sleep
How long should they sleep?
C and D update their NAV
Keeping sleeping until NAV count down to zero
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(4) Message Passing

How to transmit long message?



Transmitting one long message is inefficient
Many small packets with RTS/CTS/ACK for each
S-MAC: Divide into fragments, transmit in burst


RTS/CTS reserve medium for the entire sequence
Fragment-errors recovery with ACK
•
no control packets for fragments
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Acknowledgment to Pro. Jun Yang
Neighbors can sleep for whole message
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Message Passing
Advantages:

Energy saving:
 Neighbors go to sleep when sense transmissions
 Reduces control overhead by sending multiple ACK
Disadvantage:

Node-to-node fairness reduces
However, message-level latency reduces
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Experiment
Listen time: 300ms
Sleeping time: 1s
SYNC: every 13s (10 listen/sleep period)
A, B, C use the same schedule
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Energy save due
to periodic sleep
Energy save due to avoiding
overhearing by using message
passing
802.11
OA
SMAC
Heavy Traffic
Light Traffic
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OA: In light traffic status, nodes keep
listening for quite a long time
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SYNC overhead
Overhearing avoidance still benefit
Heavy Traffic
Light Traffic
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Questions?
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Energy Efficient Routing in Ad Hoc Disaster
Recovery Networks:
An Application Perspective
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Motivation
recovery – emerging application for
adhoc/sensor networks
 Disaster
 During Sep 11 attacks – survivors were detected
through mobile phone signals
 People often buried below earthquake disaster
 New RFID or smart badge technologies
 Each person wears a badge that is a transceiver
 Sends out very low rate signals about human location
 Information collected at peripheral central stations
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Problem
 Given some pkt generation rate at each badge
 Design routing strategy that maximizes network
lifetime
 Problem formulated as a LPP
 Maximize minimum lifetime
• subject to the flow constraints on each node
• Subject to the capacity constraints of the links
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Approach
 Existing
simplex techniques can be used to
solve the problem
 Computation intensive due to several iterations for
convergence
 Paper
proposes binary search on network
lifetime
 In plain words, a network lifetime (T) is chosen and
applied to see if there exists a feasible flow assignment
 If not, (T/2) is tried, else (2T) … until convergence
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Summary
 Complexity of O(n3logT)
 n3 for finding a feasible assignment of flows
 Log T for the binary search
 However, distributed version of this
 Only available for a single origin node
 For multiple badges  future work
protocol
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Other Research Challenges in Sensors
 Coverage
 Union of all sensing ranges need to cover entire region
 Time
synchronization
 Data Aggregation
 Calculating functions over a spatial distribution of sensors
 Data Dissemination
 Rumour routing, Ant colonies, swarm intelligence
 Motion
tracking, object guiding
 Sensors + Actuators  mobile robots !!!
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Questions?
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Message Complexity
Grid topology
N = 25
n = 5 Sources
m = 3 sinks
Nodes talk with
Adj. or diagonal
nodes
Flooding: Unrestricted broadcast
Each interest broadcast by each node  nN messages
A msg received twice over a link  total # receptions = 2n
(# of links)
Total msg. cost = nN + 4n(N – 1)(2N – 1) = O( nN )
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Message Complexity II
Omniscient Multicast: Multicast trees rooted at each source
(Cost of tree establishment not counted.)
Overhead of 2 receptions on each link of tree, Tj
Total msg. cost = 2 |{distinct links l: l  Uj = 1 to n (Tj)}|
Expressing all trees in terms of a common tree, T1, we get
Message Complexity = O(nN), asymptotically, and m «N
Directed Diffusion: Similar approach using rooted trees
Message Complexity = O(nN), asymptotically, and m «N
But, cost lower than OM, cause DD can perform duplicate
suppression on common link. More gain when more sources
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TinyOS design point



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Bursty dataflow-driven computations
Multiple data streams => concurrency-intensive
Real-time computations (hard and soft)
Power conservation
TinyOS:
– Event-driven execution (reactive mote)
 Size
 Accommodate diverse set of applications (plug n play)
Modular structure (components) and clean interfaces
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TinyOS Facts
 Software
Footprint 3.4 KB
 Power Consumption on Rene
 Transmission Cost: 1 µJ/bit
 Inactive State: 5 µA
 Peak Load: 20 mA
Platform
 Concurrency support:
 At peak load CPU is asleep 50% of time
 Events
propagate through stack <40 µS
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TinyOS: More Performance Numbers




Byte copy – 8 cycles, 2 microsecond
Post Event – 10 cycles
Context Switch – 51 cycles
Interrupt – h/w: 9 cycles, s/w: 71 cycles
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TinyOS: Size
Code size for ad hoc networking
application
3500
3000
Bytes
2500
2000
1500
1000
500
Interrupts
Message Dispatch
Initilization
C-Runtime
Scheduler: 144 Bytes code
Light Sensor
Totals: 3430 Bytes code
Clock
226 Bytes data
Scheduler
Led Control
Messaging Layer
Packet Layer
Radio Interface
Routing Application
Radio Byte Encoder
0
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Contribution
 Network addressing is data centric
 Probably correct approach for sensor type applications
 Application-awareness – a beneficial tradeoff
 Data aggregation can improve energy efficiency
 Better bandwidth utilization
 Notion of gradient
 Fault tolerance
(exploratory and reinforced)
 Implementation on Berkley
 Network API, Filter API
motes
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Critique
 Choice of path does not maximize aggregation
 Least delay path does not  max aggregation
 Exploratory paths improve fault tolerance
 But at the cost of additional msg./energy overhead
 Overhead analysis omits the exploratory paths
 Data overlap can be suppressed
 2 sources, reporting overlapping data can be combined
 Idle energy = 10% of receive, 5% of transmit
 Explains the poor energy performance of flooding
 Not realistic numbers – optimistic assumption
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Rumor Routing
LEACH
SPIN
Some other proposals for sensor routing
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Rumor Routing
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LEACH
 Proposes clustering of sensors + cluster leaders
 Can aggregate data in single (local) cluster
 Rotating cluster head balances energy consumption
 Cluster formation distributed and energy efficient
Cluster-head
always awake
Member nodes can
sleep when not Txing
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LEACH – The Protocol
 Time
is divided into rounds
 A node self-elects itself as the cluster head





Higher residual energy, higher probability to be head
Close-by sensors join this cluster-head
Cluster head does TDMA scheduling and gathers data
Gathered data compressed based on spatial correlation
Transmits data to Base Station (@ higher power)
 In
the next round, another cluster head elected
 Probabilistic load balancing
 Network lifetime can increase manifolds
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SPIN: Information Via Negotiation
 Flooding 
 Redundant
many sensors transmit same data
 Make
sensors disseminate spatially/temporally
disjoint data sets
 Name data with meta-data to define space/time property
 Sensors compare overheard data with self-sensed data
 Combine data to minimize overlap
 Make sensors resource-adaptive
 When low battery  perform minimum activities
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The SPIN 3-Step Protocol
A
B
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The SPIN 3-Step Protocol
A
B
Notice the color of the data packets sent by node B
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The SPIN 3-Step Protocol
A
B
SPIN effective when DATA sizes are large :
REQ, ADV overhead gets amortized
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