Programming Abstractionsin

Wireless Sensor Networks

Professor Jack StankovicDepartment of Computer

ScienceUniversity of Virginia

ImportanceImportance

• Raise the level of abstraction• Move out of the domain of HW and

embedded systems programmer• Amplify the applications addressed –

programmed by domain experts• More reliable

• One of the most important areas of research to make WSN widely used

ContextContext

System DevelopmentEnvironment

Analysis/Tools

Use of SystemSQL/Queries

Actual ProgrammingApplications prog.

Systems prog.

Programming Models (9)

Programming Models (9)• Environmental (domain specific ->

tracking, monitoring environment, medical…)– EnviroSuite

• Data/Database Centric - Queries– SQL, TinyBD, Cougar– Statistical and range queries

• Middleware APIs and Services– Group Management, Token machine language

(Regiment), Milan (QoS based), Agilla– Support for other models

• Components• Database• Event • Agent

Programming Models (9)

Programming Models (9)

• Components– nesC

• Virtual Machines– Mate

• Functional Macro-programming– Regiment (regions, streams)

• (Mobile) Scripts– SensorWare

• Extend TCL interpreter with support for commands such as query, send, wait, replicate, …

• Provides execution environment for Scripts

• Events– Publish/subscribe– DSWare, SNEDL, Impala

Programming Models (9)

Programming Models (9)

• Networks of Networks– Across the Internet

AbstractionsAbstractions

• Program as a whole – not individual nodes

• Hide details (which ones, expose what)– Single node decisions– Asynchrony– Race conditions– False alarms– Retries– Physical details (e.g., location, sensor characteristics,

…)– Faults– Scale– Storage locations

Environmental Paradigm

Environmental Paradigm

• Current Paradigms– Single node abstractions– Explicit interactions between nodes– Read sensor data; fuse data; move data– Set actuators

• Environmental Paradigm– Reflect the physical world directly– Virtual world of entities (fire, people, vehicles,

pesticide, velocity, location, areas, …)

EnviroSuiteEnviroSuite

• Way to think– Events – measurable environmental activities– Events mapped to programming objects– Computation is attached to these objects

• Report location, compute velocity, …

• Library provides protocols for sensor data processing, object maintenance, inter-object coordination, aggregation mechanisms, etc.

personevent

Base Station

vehicleevent

object type: VEHICLE object ID: vehicle01

method:report location to thebase station every 5seconds

attribute: location

object type: PERSON object ID: person01

method:turn on a nearby micro-phone if current locationis less than 1 mile awayfrom the base station

attribute: location

mapping

EnviroSuite

EnviroSuiteEnviroSuite

event-object VEHICLE { object_creation_condition = ferrous object && background sound object_resolution = 6; // minimal distance between // two events object_function = report.Location; object_function = report.Speed;}

ferrous object && background sound

This statement is supported by drivers in a library:

Level of Knowledge Required

Level of Knowledge Required

• Ferrous object– Which signal processing module?– What parameter specifications need to

be made?

– We are programming in an application that interacts with the environment – how divorced from that fact can the programmer be?

Programming ModelProgramming Model

TrackingObjects

Context Type: CarContext Label

Aggregate State

Variables

TrackingObjects

Context Type: PersonContext Label

Aggregate State

Variables

Network Abstraction Layer

ExternalEntity

Contexts and ObjectsContexts and Objects

• Contexts: Encapsulate entity state and tracking objects

• Tracking objects: Perform entity-specific computation, communication and sensing

HistoryEntity

ID

State

ContextAttached Tracking Objects

Programmer’sView

CommunicationCommunication

State

Context

Programmer’sView

Context

Attached Tracking Objects

Attached Tracking Objects

Objects may export methods for remote invocation

Attaching ObjectsAttaching Objects

HistoryEntity

ID

Programmer’sView

Sensee( ) = TRUELeader

Members

Statee( ) = average position

begin context tracker sense: magnetic() + motion(); state: location = avg (position,3,2);end

begin object reporter send (state, home);end

Attach

begin object mic turn-on microphone send (sound, home);end

SummarySummary

• Program in C++ or Java – like language

• Library supports domain specific abstractions– E.g., Java Swing supports programming

GUIs

• Pre-compiler maps programming abstractions to underlying “system”– E.g., could map to nesC and TinyOS

MiddlewareMiddleware

Middleware APIsMiddleware APIs

• Group Management– Create– Terminate– Merge– Join/Leave– Assign function

• Track target• Classify target• Map temperature region

– Consensus

Group ManagementGroup Management

IR Camera

Group ManagementGroup Management

IR Camera

Examples: Tracking and

Map Regions

Examples: Tracking and

Map Regions

Base Station

Group Management - APIGroup Management - API

– Create_Group(name,function,criterion,atleast,accuracy) - implicit and explicit

– Destroy_Group(name)– Join()– Leave()– Merge()– Move_COG()– Expand() -- to gain sensing confidence– Shrink() -- to save power– Commit(grp_ID) - to synchronize group re-

configurations

API for Other ServicesAPI for Other Services

• Naming• Directory• Location• Monitor• Configure• …

Virtual Machine - Mate Virtual Machine - Mate

TinyOS

Mate VM(interprets)

24 Instruction ProgramsEach instructionexecutes as task(slow)

Code capsules

Code CapsulesCode Capsules

• One capsule = 24 instructions• Fits into single TOS packet

– Energy efficient

• Atomic reception• Code Capsule

– Type and version information– Types: send, receive, timer, subroutine

• Larger programs – use several capsules

ValueValue

• Re-programmability– Re-task a network

• Parameter adjustment

• Self-replication– One of the special instructions on the

VM is forward (which supports a viral-like infection of the entire network)

• Incremental addition of new nodes

Propagation ExamplePropagation Example

Node Enters the NetworkNode Enters the Network

Instruction SetInstruction Set

One byte per instruction Three classes: basic, s-type, x-type

•basic: arithmetic, halting, LED operation•s-type: messaging system•x-type: pushc, blez

8 instructions reserved for users to define Instruction polymorphism

•Example: add(data, message, sensing)

User Defined Instructions User Defined Instructions

TinyOS

Mate VM(interprets)

24 Instruction Programs

Code capsules InstructionsUnderstood byMate

User defined

1 2 3 4

1 3

3

1

- Sound alarm

- Write to flash

Mate ArchitectureMate Architecture

0 1 2 3

Subroutines

Clock

Send

Receive

Events

gets/sets

0 1 2 3

Subroutines

Clock

Send

Receive

Events

gets/sets

Code

OperandStack

ReturnStack

PC

Code

OperandStack

ReturnStack

PC

Stack based architecture Operand stack Return address stack

Three events/execution contexts:•Clock timer•Message reception•Message send

Code Example(1)Code Example(1)

• Display Counter to LEDgets # Push heap variable on stackpushc 1 # Push 1 on stackadd # Pop twice, add, push resultcopy # Copy top of stacksets # Pop, set heappushc 7 # Push 0x0007 onto stackand # Take bottom 3 bits of valueputled # Pop, set LEDs to bit patternhalt #

Code Example(2)Code Example(2)

• Sense and Sendpushc 1 # Light is sensor 1sense # Push light reading on stackpushm # Push message buffer on stackclear # Clear message bufferadd # Append reading to buffersend # Send message using built-inhalt # ad-hoc routing system

TinyOS Sense and Send

TinyOS Sense and Sendevent result_t Timer.fired() {

if (state == IDLE && call Photo.sense()) {state = SENSE;}return SUCCESS;

}event result_t Photo.dataReady(uint16_t data) {

if (state == SENSE) {packet->reading = data;if (call SendMsg.send(packet, sizeof(DataBuf)) {

state = SENDING;} else {state = IDLE;}

}return SUCCESS;

}event result_t SendMsg.sendDone(TOS_MsgPtr msg) {

if (state == SENDING) {state = IDLE;}return SUCCESS;

}

Component BreakdownComponent Breakdown

• 7286 bytes code, 603 bytes RAM

SummarySummary

• Layer of software that can interpret programs

• Easy to download new programs• Power of VM will relate to ease of

programming– E.g., Java versus Mate

Networks of NetworksNetworks of Networks

BodyNetworks

Road and Street Networks

Battlefield Networks

VehicleNetworks

IndustrialNetworks

BuildingNetworks

Environmental Networks Heterogeneous

Networks withSensors and Actuators

(HNSAs)

Motivating ApplicationsMotivating Applications

Home

Home Application 1:Musical TrackingHome Application 2:

Alarm System

Motivating ApplicationsMotivating Applications

HomeForest

Forest Application 1:Temperature MonitoringForest Application 2:

Animal Tracking

Motivating ApplicationsMotivating Applications

Road

HomeForest

MESSAGE

Road Application 1:Traffic MonitoringRoad Application 2:

Traffic Law Enforcement

Motivating ApplicationsMotivating Applications

Road

HomeForest

Cross Network Application 1:Protection Against Wild Animals

Motivating ApplicationsMotivating Applications

Road

HomeForest

MESSAGECross Network Application 2:Wild Animal & Automobile Protection

System ArchitectureSystem Architecture

Internet

LocalTransportProtocol

LocalTransportProtocol

ProgrammingStation

Server Server

Nodes Nodes

System ArchitectureSystem Architecture

Internet

LocalTransportProtocol

LocalTransportProtocol

ProgrammingStation

Server Server

Nodes NodesInformation about

Services, InterfacesLocation

System ArchitectureSystem Architecture

Internet

ProgrammingStation

Server Server

Nodes Nodes

LocalTransportProtocol

LocalTransportProtocol

High levelProgramming

Language

EXE

High LevelVirtual Machine

High LevelVirtual Machine

Low LevelVirtual Machine

Low LevelVirtual Machine

System ArchitectureSystem Architecture

Internet

LocalTransportProtocol

LocalTransportProtocol

ProgrammingStation

Server Server

Nodes Nodes

Responsible forResource management

User access rights

System ArchitectureSystem Architecture

Internet

LocalTransportProtocol

LocalTransportProtocol

ProgrammingStation

Server Server

Nodes Nodes

Omnix PhysicalNetwork

Omnix PhysicalNetwork

The Physicalnet

SummarySummary

• Future Problem• Java-like language with different

levels of VMs

QuestionsQuestions

• What should a programmer see?– New language– New middleware– Services– Components– Abstract models– All the above– None of the above

QuestionsQuestions

• What would have made your life easier in doing the programming assignments?

• What makes it easier to get the system to work?– Debugging tools

• Initially (in programming environment)• On real platform

SummarySummary

• Very active area– It must be

• Solutions can have large impact– Applications programmers rather than

system experts

• Standard?– Analogy to real-time computing and

programming languages?• WSN-Java?