Spot Symposium 2009 Ksn Radio Stack

Markus Bestehorn Stephan KesslerAndreas Leppert Sven Meisinger

KSN Radio Stack:

pp g

KSN Radio Stack:Reliable Wireless Communication for Data-intensive Applications in Sensor Networksintensive Applications in Sensor NetworksSun SPOT Symposium 2009London

www.kit.edu

Data-Intensive Application in WSN?

Wireless Sensor Network (WSN)Large number of battery powered devices

IntroductionData-IntensiveS St k g y p

energy is valuable!Exchanging data using wireless communicationUser can access network through base station Sun SPOT

Sun Stack

KSN Radio StackDesign TargetsSHP User can access network through base station

Countless ApplicationsMedical Care, Environment Monitoring, Object Tracking…

Su S OSHPRoutingOther LayersDemo

What is data-intensive application in WSN?2 variations:Nodes generate Data

Comparison

KSNTeam g

Data must be transported to user / base stationAmount of data accumulates on the way

Base station has to distribute data to the whole network

AcitivitiesResearch

Q&A Base station has to distribute data to the whole network2 examples follow

Slide 2Markus Bestehorn

Example 1: Data Gathering

Data Gathering ApplicationsA large number of nodes

IntroductionData-IntensiveS St k g

Generating / Measuring data (continously)Sending measured data back to base station

Sun Stack

KSN Radio StackDesign TargetsSHPSHPRoutingOther LayersDemo

More Sensor Nodes

Base

Comparison

KSNTeam

D it C i /A ti

Base StationAcitivities

Research

Q&A Despite Compression/Aggregation: Messages of several KB have to transmitted reliablyLarge part of result is lost if 1 message is lost!


Example 2: Over-the-Air Deployment

TestbedsEvaluate your software

IntroductionData-IntensiveS St k y

Test and debug softwareSun Stack

KSN Radio StackDesign TargetsSHP Problem: Testing-Cycle very cumbersome

1. Connect SPOT to USB2. Put SPOTs into position

SHPRoutingOther LayersDemo u S O s o pos o

3. Start testing / evaluation1. Errors in software?2 Find error fix code

Comparison

KSNTeam 2. Find error, fix code

4. Collect SPOTs and start with step 1Solution:

AcitivitiesResearch

Q&AFixed infrastructure connected to nodes

Not possible/feasible or all deploymentsDistribute software over-the-air (OTA)

Slide 4

( )

Markus Bestehorn

Example 2: Over-the-air Deployment (cont‘d)

Requires large files / messages to be transmittedQuery Processor suite file ~500 KB

IntroductionData-IntensiveS St k Q y

Libraries ~700 KB„Large“ Number of Hops

I b d f 30 SPOT 9 H

Sun Stack

KSN Radio StackDesign TargetsSHP In our testbed of 30 SPOTs max. 9 Hops

Any testbed requires transmission of large

SHPRoutingOther LayersDemo Any testbed requires transmission of large

messages over multiple hopsComparison

KSNTeamAcitivitiesResearch

Q&A


Requirements of data-intensive Applications

Communication software (stack) mustDeliver messages reliably

IntroductionData-IntensiveS St k g y

Cope with relatively large messagesMultiple Hops between sender and receiver node

P ti l l h d i t k

Sun Stack

KSN Radio StackDesign TargetsSHP Particularly hard in sensor networks

Expect nodes to fail during transmissionReact to topology changes due to external influences, e.g.,

SHPRoutingOther LayersDemo p gy g g

WeatherClosing/Opening of doors

Comparison

KSNTeam

SPOTs are shipped with a communication stackWhy not use this stack?

AcitivitiesResearch

Q&A


Testing the Sun Stack (1)

Setup for evaluation2-5 nodes in a line, i.e., 1-4 hops

IntroductionData-IntensiveS St k , , p

1 specified node sends a message of varying sizeRadioStream was usedAfter sending node computes a hash value of the message

Sun Stack

KSN Radio StackDesign TargetsSHP After sending, node computes a hash value of the message

1 specified node receives messageWhen receiving completes, receiver computes hash value over received message

SHPRoutingOther LayersDemo received message

Transmission successful, if both hash values are equalCode can be obtained from our homepage:htt // i d i k l h d /KSN

Comparison

KSNTeam

http://www.ipd.uni-karlsruhe.de/KSNAcitivitiesResearch

Q&A

Sender Receiver


Sender Receiver

Testing the Sun Stack (2)

Evaluation was conducted with the „Blue“ release (current) IntroductionData-IntensiveS St kSun Stack

KSN Radio StackDesign TargetsSHPSHPRoutingOther LayersDemoComparison


Q&A


Motivation for a new stack

Sun stack is reliable and fast for small messagesAlmost no errors for message sizes below 1KB


Unreliable for large messages or high number of hopsMain reason: Design Goals for the Sun Stack

L P

Sun Stack

KSN Radio StackDesign TargetsSHP Low Power

Efficient usage of low bandwidth availableDesign not aimed at „data-intensive“ applications

SHPRoutingOther LayersDemo g „ pp

Messages are transmitted reliably 1 h

Comparison

KSNTeam

over 1 hop802.15.4 layer worksErrors must occur above

AcitivitiesResearch

Q&ADesign new stack above MAC


Agenda

Motivation: Why do we need another stack?What does „data-intensive“ in sensor networks mean

IntroductionData-IntensiveS St k „

Demo and reliability evaluation dataKSN Radio Stack

D i & ddi i l f

Sun Stack

KSN Radio StackDesign TargetsSHP Design targets & additional features

The core of the KSN StackOptional KSN stack layers

SHPRoutingOther LayersDemo p y

Possibilities for Optimization / ImprovementsReliability evaluation and Demo of the KSN stackComparison: Sun Stack vs KSN Stack

Comparison

KSNTeam Comparison: Sun Stack vs. KSN Stack

The KSN TeamProjects

AcitivitiesResearch

Q&AResearch Agenda


Design Targets - Reliability

Transmission of large messages over multiple hops must work reliably

IntroductionData-IntensiveS St k

yProblems encountered during transmission must be fixed inside the communication stack if possible

Handling of errors should not be mixed with application code

Sun Stack

KSN Radio StackDesignSHP Handling of errors should not be mixed with application code

Expect nodes to fail during transmissionExternal influences change communication behaviour of nodes

Weather

SHPRoutingOther LayersDemo Weather

Closing doors

Sender must know if transmission failed on intermediate

Comparison

KSNTeam

nodes End-to-End ACKAcitivitiesResearch

Q&A

Sender Receiver

ACK


Design Targets - Extendability

Different applications have different demandsRun Multiple Stacks parallely on one SPOT


p p yAdding / implementing new layersNetwork Management might require another stack than Query Processing

Sun Stack

KSN Radio StackDesignSHP Processing

Stack with less complex interfaces for student experiments, more sophisticated stack to gather the result of their experiments

SHPRoutingOther LayersDemo experimentsComparison


Q&A


Further Design Targets

Compatibility with 802.15.4Interface-Compatibility to Sun Stack

IntroductionData-IntensiveS St k Interface Compatibility to Sun Stack

Users have written applications using the Sun StackMigrating to our stack should not require rewriting the application

Sun Stack

KSN Radio StackDesignSHP application

Link-Quality-awarenessProbability for failures increases, as link quality decreases

SHPRoutingOther LayersDemo

Communication hardware on SPOTs allows estimations about link qualityExample: Quality-Aware Routing Layer

Comparison

KSNTeam p y g yAcitivitiesResearch

Q&A


Optimization is not a Design Target

Communication stacks for sensor nodes are usually optimized regarding energy usage


p g g gy gNodes are usually battery-powered

Reliability is the most important step towards efficiencyU t k t i i f ti

Sun Stack

KSN Radio StackDesignSHP Users query a sensor network to gain information

demand for information has to be satisfied (efficiently)If failures prevent delivery of information


Energy used to acquire information until failure occured is wasted!Users might retry Failure likely to occur again more waste!

Optimization is the step after functionality is ensured

Comparison

KSNTeam p p y

“We should forget about small efficiencies, say about 97% of th ti t ti i ti i th t f ll il ”

AcitivitiesResearch

Q&Athe time: premature optimization is the root of all evil.” (Donald Knuth)


Foundation for Reliable Communication

Basic Operation of 802.15.4:Sending a packet of 127 byte

IntroductionData-IntensiveS St k g p y

Receiver is a node within the radio range of the senderTwo variants of the Basic Operation:

B d R i dd i bl k“

Sun Stack

KSN Radio StackDesignSHP Broadcast: Receiver address is „blank“

No acknowledgementUnicast: Receiver address identifies node


If transmission of 127 byte was successful, acknowledgement is sentIf there was a failure, no acknowledgement is received and a i i

Comparison

KSNTeam

timeout expires.

Reliable communication is based on this basic operationFirst Step:

AcitivitiesResearch

Q&A First Step:Design communication protocol for messages larger than 127 byte


SHP – Single Hop Protocol

Single Hop Protocol (SHP) Layer provides interface forUnicast of messages of arbitrary size

IntroductionData-IntensiveS St k g y

Broadcast of messages of arbitrary sizePreparation for sending (unicast or broadcast)

L t M M h i f b b t

M

Sun Stack

KSN Radio StackDesignSHP Let Message M have a size of b bytes

Decompose M into f fragmentsAssign a sequence number s={1…p}

41 32SHPRoutingOther LayersDemo g p

to each fragmentCompute checksum C from M

Sending process for unicast and broadcast different

CComparison

KSNTeam Sending process for unicast and broadcast different

starting with broadcastAcitivitiesResearch

Q&A


Single Hop Protocol - Broadcast

Two types of packetsBroadcastData: Contains fragments


of 104 Byte, used for first f-1 fragmentsBroadcastEnd: Contains last fragmentwith sequence number s=f

Sun Stack

KSN Radio StackDesignSHP with sequence number s f

Possible failures:Unexpected sequence number


Timeout while waiting for next/lastfragment

Limitations (current implementation)

Comparison

KSNTeam ( p )

Sequence Number is 16-bit longmax. Broadcast ~ 6 MBsufficient for SPOTs

AcitivitiesResearch

Q&A


SHP – Possible Broadcast Improvement

Problem: Broadcast still inherently unreliableSender broadcasts f fragments to surrounding nodes

IntroductionData-IntensiveS St k f g g

Some receivers only receive k<f fragmentsReceiver has spent energy, but message is incomplete

receiver discards all received fragments energy wasted!

Sun Stack

KSN Radio StackDesignSHP receiver discards all received fragments, energy wasted!

Possible improvement (not yet implemented):Each receiver uses sequence numbers to determine, which k


fragments are missingIf k is sufficiently small compared to f, ask sender to resend missing fragments with unicast

Comparison

KSNTeam

Open questions:Caching mechanisms for broadcast messages on senderWhat is sufficiently small“?

AcitivitiesResearch

Q&A What is „sufficiently small ?


Single Hop Protocol - Unicast

SHP - Unicast Protocol1. Send UnicastRequest to receiver

IntroductionData-IntensiveS St k q

Contains Checksum CSize b of Message M in bytes

receiver can abort transfer

Sun Stack

KSN Radio StackDesignSHP

2. Send f fragments to receiverReceiver has to acknowledge each fragment

SHPRoutingOther LayersDemo g

Unacknowledged fragments are retransmitted after a timeout

3. Receiver checks if data is not

Comparison

KSNTeam

disrupted using checksum CAcitivitiesResearch

Q&A


SHP – Unicast Improvements

Evaluation has shown:Data rates with Sun stack higher than with KSN stack


Comparable only for small messages due to reliabilityReason for lower data rate:

A k l d f h f

Sun Stack

KSN Radio StackDesignSHP Acknowledgment for each fragment

congestionLess payload due to larger sequence numbers


Ideas for improvements: „TCP/IP-like ACK“Aggregate ackowledgements and send 1 packet to acknowledge several received fragments

Comparison

KSNTeam acknowledge several received fragments

Increase number of packets between ackowledgements depending on link quality

AcitivitiesResearch

Q&A


Summary Single Hop Protocol

SHP offers reliable delivery to 1-hop neighborsBroadcast


UnicastMessage size

B d d 6 MB f b d SPOT h

Sun Stack

KSN Radio StackDesignSHP Bounded to 6 MB for broadcast

Theoretically unbounded for unicastVM defines boundaries for max. array length

SPOT has 512KB ofRAM


Layer still not fine-tunedlarge room for improvements!

Comparison

KSNTeam

Design targets so far?Extendability not yet

AcitivitiesResearch

Q&A802.15.4 compatiblity doneReliability only 1 hop


Extendability – Multiple Stacks, 1 SPOT

All communication is based on reliable 1-hop communicationSHP usable as a foundation


Idea to allow multiple stacksEach Stack is assigned a globally unique ID

we used a simple byte value

Sun Stack

KSN Radio StackDesignSHP we used a simple byte value

max. 256 different stacksSpecial byte indicates stack IDE h d Di t h t


Each node uses a Dispatcher toPass incoming data to correct stack depending on stack IDPass outgoing data to SHP Layer

Comparison

KSNTeam

SHP Dispatcher has 4 functionsRegister / unregister new stack

AcitivitiesResearch

Q&ABroadcast / unicast datausing SHP


Extendability – More Stack-Layers

All new layers must implement LayerInterfaceMethods for broadcast / unicast of data from upper layers

IntroductionData-IntensiveS St k pp y

Method, which takes incoming data from lower layers or the SHP Level Dispatcher

Abstract Layer implementation is provided with our software

Sun Stack

KSN Radio StackDesignSHP Abstract Layer implementation is provided with our software

New Layers can be implemented with very few lines of codeExample of a AODV Routing Layer follows now

SHPRoutingOther LayersDemoComparison


Q&A


Example Layer – Multi-Hop Routing

Up to this point, only 1-hop communication coveredExample for a new Layer: Routing Layer


p y g yUsed Routing Mechanism: Ad-Hoc On Demand Distance Vector Routing (AODV) [2]

Sun Stack


Sun Stack also includes AODV implementation, butNo (working) End-to-End ACKs for Multi-Hop Unicasts

SHPRoutingOther LayersDemo ( g) p

Only 1 entry per Receiver no backup routesBoth problems affect reliability

Comparison

KSNTeam

will be addressed in the following

AcitivitiesResearch

Q&A


AODV Routing Mechanism

Basics of AODV: Sender S wants to send message to Receiver R


gS broadcasts Route Request (RREQ)Nodes receiving RREQs rebroadcast if

RREQ has not been broadcasted before

Sun Stack

KSN Radio StackDesignSHP RREQ has not been broadcasted before

Node already has a route to R stored in routing tableReceiver R receives the RREQ

Route Report (RREP) is sent back to S

SHPRoutingOther LayersDemo Route Report (RREP) is sent back to S

Message is sent through shortest / fastest-available routeComparison

KSNTeam

RREQRREQAcitivitiesResearch

Q&A

RREQRREQ RREQ RREPRREQACKACKACK


Sender Receiver

AODV – Routing Table Format

Routing Table without backup entries1 entry for each receiver R

IntroductionData-IntensiveS St k y

If transfer fails, new RREQ is broadcast by sender SProblem: RREQ very small message (1 packet)

might be transmitted reliably but larger messages fail

Sun Stack

KSN Radio StackDesignSHP might be transmitted reliably, but larger messages fail

same Route will be returnedtransfer might fail again for larger message energy

wasted!

SHPRoutingOther LayersDemo wasted!

Solution: Several entries for 1 receiver R

Comparison

KSNTeam

Use depth-first search to transmitlarger message to RCan be adapted to use

AcitivitiesResearch

Q&Aquality information!


AODV – End-to-End ACK

SHP sends ACK if message is transmitted correctlyProblem:

IntroductionData-IntensiveS St k Problem:

Intermediate node fails while sendingIntermediate node has sent ACK already, but message is lost!

Sun Stack

KSN Radio StackDesignSHP Solution: Receiver sends End-to-End ACK to sender

Sender waits for End-to-End ACKLength of timeout determined using hop count of routing table

SHPRoutingOther LayersDemo e g o eou de e ed us g op cou o ou g ab e

SHP-ACK

Comparison

KSNTeam

Design targets so far?Sender ReceiverEnd-to-End ACK

AcitivitiesResearch

Q&A g gExtendability done802.15.4 compatiblity doneReliability done

Slide 27

Reliability done

Markus Bestehorn

Other Layers

Reducing Data SizeCompression layer

IntroductionData-IntensiveS St k p y

Can be used with abitrary compression algorithmWe use a modified ZIP algorithm

Should be used above routing layer

Sun Stack

KSN Radio StackDesignSHP Should be used above routing layer

Avoids decompression on every hop

Protocol Dispatcher


Applications can use different protocols on top of single stack!Examples:

Comparison

KSNTeam p

PC-like with portsLowPan

AcitivitiesResearch

Q&A


KSN Radio Stack Demo

Message Size: 50 KBTested up to 1 MB with more than 10 hops

IntroductionData-IntensiveS St k p p

4 HopsOutput Power -30

Sun Stack

KSN Radio StackDesignSHP Difference to demo before

„Simulation“ of node failures by removing/exchanging nodesSimulated „failure“ will cause delay

SHPRoutingOther LayersDemo S u a ed „ a u e cause de ay

Message delivered despite topology changes„Application“ has not been changed

Comparison


Q&A

Sender Receiver


Comparison of both Stacks

Sun StackVery fast and efficient for small messages

IntroductionData-IntensiveS St k y g

use for experiments where „every second counts“Unreliable if

Messages become large

Sun Stack

KSN Radio StackDesignSHP Messages become large

Messages must be transmitted over a large number of hopsOther transmissions from other SPOTs run parallely

Was not shown here

SHPRoutingOther LayersDemo Was not shown here

IPv6 compatibleKSN Radio Stack

Comparison

KSNTeam

Reliable for large message sizes and large number of hopsUp to 1 MB And 15 hops tested without losing messages

AcitivitiesResearch

Q&AMore overhead slower

Use for experiments where „counting bytes“ is sufficientCurrently not IPv6 compatible

Slide 30

Currently not IPv6 compatible

Markus Bestehorn

Agenda

Motivation: Why do we need another stack?What does „data-intensive“ in sensor networks mean

IntroductionData-IntensiveS St k „

Demo and reliability evaluation dataKSN Radio Stack

D i & ddi i l f

Sun Stack

KSN Radio StackDesignSHP Design targets & additional features

The core of the KSN StackOptional KSN stack layers

SHPRoutingOther LayersDemo p y

Possibilities for Optimization / ImprovementsReliability evaluation and Demo of the KSN stackComparison: Sun Stack vs KSN Stack

Comparison

KSNTeam Comparison: Sun Stack vs. KSN Stack

The KSN TeamProjects

AcitivitiesResearch

Q&AResearch Agenda


Who is who @ KSN?

Stephan KesslerStudent Assistant


KSN Serialization & StackSun Stack

KSN Radio StackDesignSHP Andreas Leppert

Student AssistantKSN Stack, Query Dissemination

SHPRoutingOther LayersDemo S S ac , Que y sse a o

Sven Meisinger

Comparison

KSNTeam

Student AssistantKSN Serialization, Simulator

AcitivitiesResearch

Q&A

Markus BestehornPhD student

Slide 32

Project Head

Markus Bestehorn

KSN – Other Projects

Management ApplicationControlling large testbeds of SPOTs

IntroductionData-IntensiveS St k g g

Software deployment uses KSN StackSupport for experiments, e.g., collect data

S i li ti f SPOT

Sun Stack

KSN Radio StackDesignSHP Serialization for SPOTs

Serialization used in JDK to store/send objectsnot supported by Squawk VM


Pure Java serializationTestbed

30+ nodes deployed at the IPD

Comparison

KSNTeam 30+ nodes deployed at the IPD

Real network for experimentsAcitivitiesResearch

Q&AMany more…Homepage: www.ipd.uni-karlsruhe.de/KSN


KSN – Sensor Databases

Research Topic: Sensor DatabasesProblem: Every new application for WSN requires complete

IntroductionData-IntensiveS St k y pp q p

development processDesign & implement new hardwareDesign & implement new software

Sun Stack

KSN Radio StackDesignSHP Design & implement new software

very costlyIdea: Provide database-like interface for WSNAd t U ft f WSN li ti l

SHPRoutingOther LayersDemo Advantage: Use same software for new WSN application, only

change queryExample: SPOT 1 SPOT 2

Comparison

KSNTeam

Measurement stored distributedly in tables

Temp: 25.3°CHum.: 78%Light: 124

Temp: 23.4°CHum.: 77%Light: 120

AcitivitiesResearch

Q&A Measurement stored distributedly in tablesUse SQL to query data, e.g., SELECT nodeID, temp FROM Sensors

Slide 34

Size of result depends on query data-intensive!

Markus Bestehorn

KSN – Current Research Topics

Approximate Query ProcessingReduce result quality to save energy

IntroductionData-IntensiveS St k q y gy

Different quality parameters possiblePrecision of resultSecurity

Sun Stack

KSN Radio StackDesignSHP Security

Consistency

Query Distribution


Broadcast of query very energy consumingUse structure of query to choose distribution strategy

try to reach all relevant nodes, but not all nodes!

Comparison

KSNTeam

Spatio-Temporal query processing in WSNMoving object DBs provide operators to query object movement

Only for historical data stored in a DB server

AcitivitiesResearch

Q&A Only for historical data stored in a DB serverIdea: Try to provide these operators for object tracking in WSN


Thank you for your attention!

Questions?Introduction

Data-IntensiveS St k Questions?Sun Stack


References


No. Reference[1] MICA2 Sensor Node, http://www.xbow.com/

P ki R Ad h d d di t t ti M bil C ti

Comparison

KSNTeam

[2] Perkins, Royer: Ad-hoc on-demand distance vector routing; Mobile Computing Systems and Applications, 1999

AcitivitiesResearch

Q&A


Technology

Spot Symposium 2009 Ksn Radio Stack