June 2008 WEI short course - L9 trickle 1 Wireless Embedded InterNet working Foundations of Ubiquitous Sensor Networks - Trickle - Polite Reliable Responsive

June 2008 WEI short course - L9 trickle 1

Wireless Embedded InterNetworking

Foundations of Ubiquitous Sensor Networks

- Trickle -Polite Reliable Responsive Dissemination and

Consistency

David E. CullerUniversity of California, Berkeley


Network wide communication- Flood

0

112

2

2

22


The Problem

Ni, S.Y., Tseng, Y.C., Chen, Y.S., Sheu, J.P.: The broadcast storm problem in a mobile ad hoc network. MobiCom'99

• Everybody responds!

http://www.cs.berkeley.edu/~culler/cs294-f03/papers/bcast-storm.pdf


Flood Dynamics• Experimental Setup

– 13x13 grid of nodes– separation 2ft– flat open surface– Identical length antennas,

pointing vertically upwards.– Fresh batteries on all nodes– Identical orientation of all

nodes– The region was clean of

external noise sources.• Range of signal strength

settings• Log many runs

Ganesan, Krishnamachari, Woo, Culler, Estrin and Wicker, Complex Behavior at Scale: An Experimental Study of Low-Power Wireless Sensor Networks , UCLA Computer

Science Technical Report UCLA/CSD-TR 02-0013

http://lecs.cs.ucla.edu/~deepak/PAPERS/empirical.pdf


Recast the problem

• The goal is NOT to flood

• The goal is to bring the network to a new consistent state

– all nodes have the same piece of information

– All nodes receive the same command

– All nodes form a spanning tree

» DHCP delegation

» Multihop Router Advertisements

• Respond rapidly to a change

• Quiesce to very low communication rate

• Never stomp on each other

• High scalability– Extent AND density


A first step• Grow the tree slowly

• Avoid Contention at every transmission

• Avoid Redundant Transmissions

• Adapt to huge range of density

• Make sure it eventually gets to everyone– Even if they are not listening

– Or arrive late

• With very simple mechanism


Trickle – better than flood

• Want the communication rate per unit area to be constant, regardless of the density of nodes

– Lots of nodes, transmit infrequently

– Few node, transmit more frequently

• Nodes listen before transmitting

• Estimate density based on how many nodes you hear from

– Arrival during timer wait extends timer

• If new value is disseminated by others, no need for you to transmit it.

• Increase delay over time so ambient rate approaches zero.

• Shorten delay when new epoch appears.


Epidemic NW protocols

• Goal: scalable, robust communication algorithms that adapt to changing conditions with little state or protocol

• Basic operation: – From time to time (based on local state and what you’ve heard) transmit a packet of

information to whomever hears the message

– From time to time, hear a packet which causes an update to local state

– Continuous process to ensure full reliability

• Adapt to density, coverage, interference, loss, schedule, …


Trickle – till consisten

0

112

2

2

22


Solution: Trickle

• “Every once in a while, broadcast what data you have, unless you’ve heard some other nodes broadcast the same thing recently.”

• Behavior (simulation and deployment):– Maintenance: a few sends per hour

– Propagation: less than a minute

– Scalability: thousand-fold density changes

• Instead of flooding a network, establish a trickle of packets, just enough to stay up to date.

• As long as each node communicates with others, inconsistencies will be found

• Either reception or transmission is sufficient


Algorithm

• Define a desired detection latency, • Choose a redundancy constant k

– k = (receptions + transmissions)

– In an interval of length

• Trickle keeps the rate as close to k/ as possible

• Choose timer t random in (• If inconsistent broadcast is heard before t, reset tomin.

• If c < k consistent broadcasts are heard by t, broadcast

• Otherwise suppress and double up tomax.

• When there is nothing new to say, stay quiet


Example: K=1


Work is logarithmic with loss rate


Short-Listen effect – why /2

• With unsynchronized intervals and no min, some nodes get small t and broadcast even though they are hearing enough to suppress


Impact of listen-only period


Numerous Applications

• Eliminates the “voodoo constants” in advertisement, route update, and the like.

• Extends to dissemination of large object


Robust OTA Programming

• Every byte must (eventually) be correctly received by all nodes!

• Reliable Pipelined Epidemic Distribution of series of pages

– Constrained storage hierarchy» Packet (32 bytes) << RAM (4K) << program (128K) < external

flash (512K)– Lossy links, Critical Contention– Density-aware– Robust to asymmetric links– Dynamic adjustment of advertisements– Minimize set of concurrent data broadcasts– Spatial multiplexing

• Page Advertise, Request/Fix, Xfer– Density-aware suppression and snoop on each

• Packet CRC + Page CRC• 159 Byte memory footprint

flash

…

Maintain

Request

Transmit


OTA Programming•Learn about the environment after deployment

– sensing range, network characteristics, etc.


OTA Programming

•Learn about the environment after deployment– sensing range, network characteristics, etc.


OTA Programming

• Learn about the environment after deployment– sensing data, network characteristics, etc.

• Embedded nature of sensor networks

• Network scales reaching thousands of nodes

• A necessity in debugging and testing cycle


What is Deluge?

•A reliable data dissemination protocol for program images over a multihop network.

•Combined with a bootloader (TOSBoot) Network Programming

0101010101010101011010101101010101010101

Program


Data Representation

•Program divided into pages, each consisting of N packets.

101110

110010

010000

101111

000011

Program

Packets

1234 N

•Reduced RAM requirements

•Allows for spatial multiplexing


How Does Deluge Work?(Glossing over many details)

•Nodes periodically advertise– Suppress similar advertisements

Version 2 here.

I only have version 1.




•Neighboring nodes request data– Suppress similar requests

Send me page 1!

Send me page 1!



•Requested data is broadcast

Packet 12of page 1!



•Dropped packets are NACKed

Repeat packet 4 of page 1!

Repeat packet 32 of page 1!



•Dropped packets are sent again

Packet 4 of page 1!



•Advertise for propagation to next hop

Version 2 here.



Spatial Multiplexing

•Propagate in “waves”

•Exploit limited radio range for concurrent broadcasts.

•Reduced completion time

•o(d + Sobj) vs. o(d * Sobj)

Page 0Page 1


Epidemic Propagation

•Epidemic propagation from one source


Epidemic Propagation

•Epidemic propagation from one source or many


Deluge Features

•Epidemic propagation from one source or many– Continuous propagation effort by all nodes

– Turn on/off radios at will

– Reach nodes with intermittent connectivity

Will find a path if it exists

•Aggressive message suppression– Scales with density

– Ultra low quiescent traffic


Deluge Features

• Management– Multiple program images– Image metadata– User confirmation on expensive operations

»Minimize operator error

• Robustness– Redundant CRCs– Golden Image with write protect– Load Golden Image

»Watchdog trigger»Golden gesture

• TOSBoot– TOSBoot as isolated code– Verify CRCs– Verify system voltage

0101010101010101011010101101010101010101

0101010101010101011010101101010101010101

0101010101010101011010101101010101010101

ProgA ProgB ProgC

Program NameCompile TimeUserIDHostnamePlatform

CRASH!

CR

CC

RC

CR

CC

RC

CR

CC

RC

CR

CC

RC

CR

CC

RC

CR

CC

RC01010

10101010101011010101101010101010101


Deluge - Lessons Learned

•Advantages– Ease of reprogramming 100’s-1000’s of nodes

– Does not erase node IDs

– Golden Image is immensely useful

– Quickly switch between images

– More reliable than uisp or msp430-bsl

– Deluge over 802.15.4 more efficient that 802.11!

•Disadvantages– Ease of reprogramming 100’s-1000’s of nodes


Take-aways

• Many embedded network applications will be built as “application overlays” on UDP

• Use trickle as a “polite gossip” adaptive congestion control.

• Additional optimizations through scheduling

Documents

June 2008 WEI short course - L9 trickle 1 Wireless Embedded InterNet working Foundations of Ubiquitous Sensor Networks - Trickle - Polite Reliable Responsive