TOSSIM: Accurate and Scalable Simulation of Entire TinyOS

Applications

Philip Levis UC Berkeley

Intel Berkeley

Nelson Lee UC Berkeley

Stanford

Matt Welsh Harvard

University

David Culler UC Berkeley

Intel Berkeley

11/7/03 SenSys 2003 1

A Lesson from History

•  Simulation can provide –  The ability to inexpensively explore ideas –  A controlled environment –  Support for extensive observation

•  Examples –  SimOS –  SimpleScalar –  ns-2

•  Accelerated research in their domains

But…

Capturing the essential elements of their domains was

critical to the utility of these simulators.

11/7/03 SenSys 2003 4

Mote Sensor Network Domain?

33m: 111 32m: 110

30m: 109,108,107

20m: 106,105,104

10m: 103, 102, 101

•  Many tiny devices •  Embedment •  Non-deterministic •  Application-specific •  System interactions

11/7/03 SenSys 2003 5

What Do We Need to Capture?

•  Bridging –  Implementations, not just algorithms

•  Completeness –  Spectrum of low-level protocols to applications –  Applications adapt to their environment –  Capture the cross-layer interactions

•  Fidelity –  Capture these interactions at a very fine grain

•  Scalability –  Examine behavior in dense or large networks

11/7/03 SenSys 2003 6

Our Approach: TOSSIM

•  Simulator for TinyOS programs •  Compiles directly from TinyOS code

–  Executes code from many system layers •  Provides a flexible framework for adjusting

fidelity –  Based on TinyOS programming model

•  Can scale to large numbers

11/7/03 SenSys 2003 7

Outline

•  Introduction •  TOSSIM architecture •  Evaluation •  Conclusion

11/7/03 SenSys 2003 8

Outline

•  Introduction •  TOSSIM architecture •  Evaluation •  Conclusion

11/7/03 SenSys 2003 9

Standard TinyOS Program (what we start with)

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM CLOCK

Hardware

Component Graph

11/7/03 SenSys 2003 10

TOSSIM Adds Five Things

•  Alternative compilation target •  Hardware component re-implementations •  Discrete event queue •  Radio and sensor models •  Communication services

11/7/03 SenSys 2003 11

Multiple Component Graphs

Component Graph

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM CLOCK

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM CLOCK

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM CLOCK

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM CLOCK

s

11/7/03 SenSys 2003 12

Compiler Support

•  “Simulator” target added to ncc compiler •  Rewrites all state declarations and accesses

–  Arrays of variables –  Index into array based on current node

ncc app.c (avr-gcc)

TinyOS Files

11/7/03 SenSys 2003 13

Compiler Support

•  “Simulator” target added to ncc compiler •  Rewrites all state declarations and accesses

–  Arrays of variables –  Index into array based on current node

ncc

app.c (native gcc)

app.c (avr-gcc)

TinyOS Files

11/7/03 SenSys 2003 14

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM CLOCK

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM CLOCK

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM CLOCK

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM CLOCK

Component Graphs

11/7/03 SenSys 2003 15

Component Re-implementations

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM CLOCK

Component Graphs

Component Re-implementations

11/7/03 SenSys 2003 16

Event Queue

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

Component Graphs

Event Queue

CLOCK

ADC Event

Component Re-implementations

11/7/03 SenSys 2003 17

Timer Clock Clock.setRate()

Clock.fire()

outp(interval, OCR0)

INTERRUPT(COMPARE2)

Hardware

Mapping TinyOS into TOSSIM

•  TOSSIM events trigger TinyOS components –  Each event is for a specific mote and has a time

•  TinyOS calls can enqueue TOSSIM events •  Hardware-level components re-implemented

–  This boundary can change

11/7/03 SenSys 2003 18

Timer Clock Clock.setRate()

INTERRUPT(COMPARE2) Clock.fire()

Event Queue enqueue(clock_event);

Mapping TinyOS into TOSSIM

•  TOSSIM events trigger TinyOS components –  Each event is for a specific mote and has a time

•  TinyOS calls can enqueue TOSSIM events •  Hardware-level components re-implemented

–  This boundary can change

11/7/03 SenSys 2003 19

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

Component Graphs

Event Queue

CLOCK

ADC Event

Component Re-implementations

11/7/03 SenSys 2003 20

Radio Model

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

Component Graphs

Event Queue

CLOCK

ADC Event

Component Re-implementations

11/7/03 SenSys 2003 21

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

Component Graphs

Event Queue

CLOCK

Sensor Model

ADC Event

Component Re-implementations

Sensor Model

11/7/03 SenSys 2003 22

Radio Model

•  Inter-node interaction •  Transmit and receive events

–  Who can hear whom graph –  Receive radio state –  Resolution function –  Individual radio clocks (based on TinyOS code)

•  Standard model: directed graph of bit error rates –  Boil complex models to a connectivity graph

•  Standard model: signal is the OR of transmissions –  All transmissions have uniform strength –  Hidden terminal problem

11/7/03 SenSys 2003 23

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

Component Graphs

Event Queue

CLOCK

Sensor Model

ADC Event

Component Re-implementations

11/7/03 SenSys 2003 24

Actuation and Monitoring

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

APP

AM PHOTO TEMP

CRC

BYTE

ADC RFM

Component Graphs

Event Queue

CLOCK

Sensor Model

Communication Services ADC Event

Component Re-implementations

11/7/03 SenSys 2003 25

Actuation and Monitoring

•  Programs can actuate and monitor running simulations –  Inject events, log messages –  Change simulation state (loss rates, sensors)

•  Keeps models external to TOSSIM –  API to integrate models through sockets –  TinyViz application

11/7/03 SenSys 2003 26

TinyViz

11/7/03 SenSys 2003 27

Outline

•  Introduction •  TOSSIM architecture •  Evaluation •  Conclusion

11/7/03 SenSys 2003 28

What Do We Need to Capture? (revisited)

•  Bridging –  Implementations, not just algorithms

•  Completeness –  Spectrum of low-level protocols to applications –  Applications adapt to their environment –  Capture the cross-layer interactions

•  Fidelity –  Capture these interactions at a very fine grain

•  Scalability –  Examine behavior in dense or large networks

11/7/03 SenSys 2003 29

Evaluation

•  Bridging –  Compiles directly from TinyOS code

•  Fidelity –  Mote networking

•  Completeness –  Complete applications –  Unanticipated behavior

•  Scalability –  Tension between fidelity and scalability

11/7/03 SenSys 2003 30

Fidelity: Mote Networking

•  Generated a loss model from empirical data –  Map empirical data to TOSSIM loss rates

•  Start symbol failure, CRC checks, acknowledgement false negatives/positives

•  Ran empirical experiment in TOSSIM Simulated Data

0%20%40%60%80%

100%

0 10 20 30 40 50

Distance (feet)

Loss

Rat

e

Empirical Data

0%20%40%60%80%

100%

0 10 20 30 40 50

Distance (feet)

Loss

Rat

e

11/7/03 SenSys 2003 31

Completeness

•  Network interactions –  Hidden terminal problem, link asymmetry –  Discovered bugs in the Surge application

•  System-level race conditions –  Network stack for mica: ChannelMonM start

symbol detection and packet transmission •  Testing at low levels

–  State machine rene stack implementation •  Application-level logic driving simulation

–  Maté, TinyDB

11/7/03 SenSys 2003 32

Scalability

•  10 virtual seconds •  Scales to thousands of nodes •  ~30 network active nodes in real time

–  40,000 radio events per second for each mote

0.001

0.01

0.1

1

10

100

1000

10000

1 2 4 8 16 32 64 128

256

512

1024

2048

4096

8192

Motes

Tim

e (s

econ

ds)

BusyQuietInactive

11/7/03 SenSys 2003 33

Scalability Continued

•  30 nodes * 40,000 events = 1.2 million TOSSIM events/second

•  Bit-level simulation is the bottleneck –  But we can move the re-implementation line…

11/7/03 SenSys 2003 34

Outline

•  Introduction •  TOSSIM architecture •  Evaluation •  Conclusion

11/7/03 SenSys 2003 35

Some Cautionary Notes

•  Non-preemptive execution –  Handlers execute instantaneously

•  Signal strength –  Results and assumptions

•  Independent bit errors •  Perfect channel sense •  TOSSIM has not been validated

–  A basis for comparison, but not the basis

11/7/03 SenSys 2003 36

Extensions (help appreciated!)

•  Changing the re-implementation boundary –  Packet level simulation –  Talking to real motes

•  Heterogeneous networks –  Additional compiler support –  Compelling applications?

•  Power modeling –  Source annotation for CPU timing –  Component power state transitions

11/7/03 SenSys 2003 37

Concluding Thoughts

•  Event-driven OS maps to event-driven simulation •  TOSSIM as a TinyOS development environment

–  Validate with deployment •  Simulate at the lowest level

–  More than what you think you need –  Capture the unanticipated problems

•  Capture the mess, but not reality –  Model the observed behavior, not the phenomena that

cause that behavior –  Do we understand these systems well enough yet?

11/7/03 SenSys 2003 38

Questions

11/7/03 SenSys 2003 39

Backup Slides

11/7/03 SenSys 2003 40

Why Not ns-2?

•  Not designed for application interaction •  Algorithms, not implementations •  Need a TinyOS simulator, not just the

network

11/7/03 SenSys 2003 41

Surge

•  Empirically, Surge protocol showed poor performance –  Users added TinyDB attribute to monitor protocol –  Everything looked fine

•  Tested Surge application in TOSSIM –  Observed traffic surges –  Send queue overflow

•  TOSSIM revealed the problem –  Cycles + acks + retransmission policy –  Lose TinyDB query results indicating the problem

11/7/03 SenSys 2003 42

Surge, Continued

0

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Time (Simulated Seconds)

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eue

Dep

th

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Time (Simulated Seconds)

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eue

Dep

th

Fixed Algorithm

Observed Behavior

11/7/03 SenSys 2003 43

Radio Example

A B C

D

1 1

11/7/03 SenSys 2003 44

Radio Example

A B C

D

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11/7/03 SenSys 2003 45

Radio Example

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11/7/03 SenSys 2003 46

Radio Example

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11/7/03 SenSys 2003 47

Radio Example

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Radio Example

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11/7/03 SenSys 2003 49

Radio Example

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11/7/03 SenSys 2003 50

Radio Example

A B C

D

01101001011 1010110010 10111100101 01101101011

11111101111

01001001011 01001001011