Incremental Network Programming for Wireless Sensors

NEST Retreat June 3rd, 2004

Jaein Jeong

UC Berkeley, EECS Introduction Background – Mechanisms of XNP First Approach – Fixed Block Comparison Optimization – Using Rsync for diff generation Optimization – Using Rsync with split decode. Related Work Conclusion and Future Work

Introduction – Programming Wireless Sensors In-System Programming (ISP)

A sensor node is plugged to the serial / parallel port. But, it can program only one sensor node at a time.

Network Programming Delivers the program code to multiple nodes over the air with a

single transmission. Saves the efforts of programming each individual node.

Host Machine

ProgramCode

Sensor Node

ParallelCable

Host Machine

ProgramCode

Sensor Node

RadioChannel

Sensor Node Sensor Node…

In-system programming Network programming

Introduction – Network Programming for TinyOS

Network programming for TinyOS (XNP) Has been available since release 1.1 Originally made by Crossbow and modified by UCB. Provides basic network programming capability. Has some limitations.

No support of multi-hop delivery. No support of incremental update.

Goal: Fast code delivery by incremental update Multihop delivery (Deluge (UCB), MOAP(UCLA))

Background – Mechanisms of XNP

(1) Host: sends program code as download msgs.(2) Sensor node: stores the msgs in the external flash.(3) Sensor node: calls the boot loader. The boot loader

copies the program code to the program memory.

User appSREC file

ExternalFlash

NetworkProgrammingHost Program

Bootloader User

ApplicationSection

Program

Memory

Boot loaderSection

Network

ProgrammingModule

RadioPackets

Host Machine Sensor Node

(2)

(3)(1)

First Approach – Fixed Block Comparison(Difference Generation)

The host program Generates the difference of the two program versions. Compares the corresponding blocks of the two program

images. Sends “copy” for the matching blocks, “download” for

the unmatched ones.

B bytesB bytes

B bytes

B bytes

Remaining

CurrentProgram

Image

PreviousProgram

Image

B bytes

B bytes

=? A copy command

or

The block fromthe current program image

First Approach – Fixed Block Comparison(Storage Organization and Code Rebuild)

The sensor node Keeps new and previous sections in the external flash. For “copy”, copies the records from the prev section to new

section. For “download”, stores the code bytes in the new section.

PreviousProgram

Image

CurrentProgram

Image

copy

download

copy

Copy

DownloadDownload

Copy

DifferenceMessage

download

Experiment Setup

Test Applications Wrote simple network programmable applications, XnpBlink and XnpCount.

XnpBlink and XnpCount are modifications of TinyOS applications Blink and CntToLedsAndRfm for network programming.

Test Scenarios Case 1: Changing a constant (XnpBlink) Case 2: Modifying implementation file (XnpCount) Case 3: Major change (XnpBlink XnpCount) Case 4 and 5: Modifying configuration file (XnpCount)

Experiment Setup – Test Scenarios

Case 1: Changing a constant (XnpBlink)

Case 2: Modifying implementation file (XnpCount)

Experiment Setup – Test Scenarios

Case 3: Major change (XnpBlink XnpCount)

Case 4: Modifying configuration file (XnpCount) Commented out IntToLeds

component.

Case 5: Modifying configuration file (XnpCount) Commented out IntToRfm component.

Code Comparison Compared the two program images in different

block sizes.The level of sharing in bytes is much higher than

that in blocks.

However, using smaller block size means more copy messages – increasing xmit time.

Block Size Case 1 Case 2 Case 3

Flash page256 Bytes

97.2 % ( = ) 21.9 % ( = ) 2.7 % ( = )

SREC record16 Bytes

98.3 % ( = ) 40.8 % ( = ) 12.0 % ( = )

byte1 Byte

100.0 % ( = ) 98.3 % ( = ) 90.5 % ( = )

72

70

1139

1120

18190

18185

73

16

73

2

1167

476

1167

140

18636

1832018636

16866

Results – Fixed Block Comparison We compared the transmission time (T) with the non-

incremental delivery time (Txnp). There is almost no speed up except when we modified

the constant in the source code (case 1).

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

Case 1 Case 2 Case 3 Case 4 Case5

Sp

eed

up

Estimated Speed Up (Fixed)

Measured Speed Up (Fixed)

Results – Fixed Block Comparison In most cases (other than case 1), much of program

code is sent as download messages rather than copy and this contributes the not-so-good performance.

Optimizing Difference Generation using Rsync algorithm Needs an algorithm that can capture the

shared data even when the program is shifted. We use Rsync algorithm to compare the two

program images at an arbitrary byte position. Rsync was originally made to transfer the

incremental update of arbitrary binary file over a low bandwidth Internet connection.

Difference Generation using Rsync algorithm (Diff Generation)(1) Build the hash table for the previous image.

CurrentProgram

Image

PreviousProgram

Image

(R0, H0)(R1, H1)

(Checksum, Hash)

(R2, H2)

(R5, H5)(R6, H6)

(R4, H4)

Hash Table

(R3, H3)

Insert hashLook up hash

CopyCopy

Download

CopyCopy

Copy

matching

nonmatching

Copy

Difference

……

……

……

……

Calculate the checksum pair (checksum, hash) for each block. The checksum is for the fast match. The hash is for more accurate match.

Difference Generation using Rsync algorithm (Diff Generation)

CurrentProgram

Image

PreviousProgram

Image

(R0, H0)(R1, H1)

(Checksum, Hash)

(R2, H2)

(R5, H5)(R6, H6)

(R4, H4)

Hash Table

(R3, H3)

Insert hashLook up hash

CopyCopy

Download

CopyCopy

Copy

matching

nonmatching

Copy

Difference

……

……

……

……

Calculate the checksum for the block at each byte. Calculate the hash only if the checksum matches. Moves to the next byte and recalculates the checksum if the block doesn’t

match.

(2) Scan the current image and find the matching block.

Difference Generation using Rsync (Rebuilding the code image) Storage Organization

Two sections (current & previous) in the external flash memory. Building the program image using the difference

Download: data bytes are written to the current program section. Copy: lines of the prev section are copied to the current section. Copy blocks are set as multiple of SREC lines to avoid additional

flash memory read/write due to partial SREC lines.PreviousProgram

Image

CurrentProgram

Image

copy

download

copy

Copy

DownloadDownload

Copy

DifferenceMessage

download

Results – Using Rsync The performance got better than Fixed Block Comparison. Speed up of 2 to 2.5 for a small change.

2.5 for adding a few lines in implementation file (case 2). 2.0 for commenting out IntToLeds in the configuration file (case 4).

Still limited speed up for big changes. Major change (case 3). Commenting out IntToRfm (case 5).

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

Case 1 Case 2 Case 3 Case 4 Case5

Sp

ee

d u

p

Estimated Speed Up (Fixed)

Measured Speed Up (Fixed)

Estimated Speed Up (Rsync)

Measured Speed Up (Rsync)

Problems – Using Rsync Sends a number of copy messages even though the two

program images are very close. The maximum block size of a copy message is limited. This is to bound the running time of a copy message.

Inefficient handling of missing packets. The script commands are not stored. Checks the rebuilt program image for verification. In case a copy message is lost, it requests the retransmission of

each missing record rather than the copy message itself.

Optimizing Difference Delivery

(1) The network programming module stores the difference script first.

PreviousProgram

Image

CurrentProgram

Image

CMD_DOWNLOADINGCopy

DownloadDownload

Copy

ScriptCommands

Optimizing Difference Delivery

PreviousProgram

Image

CurrentProgram

Image

download

copy

CopyDownloadDownload

Copy

ScriptCommands

download

CMD_DECODE_SCRIPT

(2) And then, it starts building the program image only after the host program sends decode message.

Results – Using Rsync with decode The performance of using Rsync algorithm with

decode command is similar to just using Rsync. But, the performance for changing a constant has

improved (speed up of 9.0).

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

Case 1 Case 2 Case 3 Case 4 Case5

Sp

eed

up

Fixed Block ComparisonRsyncRsync + decode

Related Work

Wireless Sensor Network Programming(1) XNP: network programming for TinyOS(2) MOAP: multihop network programming by UCLA(3) Deluge: multihop network programming by UC Berkeley(4) Reijers et al: algorithms for updating binary image. Updating

code at instruction level.(5) Kapur et al: Incremental network programming based on (4).(6) Mate and Trickle: Network programming of virtual machine

code. Outside Wireless Sensor Network

Rsync and LBFS: mechanisms for distributing the new version of file over a low bandwidth network.

Conclusion

We extended TinyOS network programming implementation (XNP) for incremental update.

The host program generates the program difference using Rsync algorithm and sends the difference to the sensor node.

The sensor node stores the program difference in its external flash memory and rebuilds the new program image using the difference and the previous image.

We have got 2 – 2.5 of speed up for small changes in the source code.

Future Work

Combine Incremental Program Update with multihop delivery. Deluge or MOAP

Study on nesC compiler support to further increase the level of sharing.