FAR: Face-Aware Routing for Mobicast in Large-Scale Sensor Networks

QINGFENG HUANGPalo Alto Research Center (PARC) Inc.andSANGEETA BHATTACHARYA, CHENYANG LU, and GRUIA-CATALIN ROMANWashington University in St. Louis

ACM Transactions on Sensor Networks (TOSN), November 2005ACM Transactions on Sensor Networks (TOSN), November 2005

Chien-Ku Lai

Outline

IntroductionMobicast OverviewFace-Aware Routing for MobicastTopology DiscoverySimulation ResultsConclusion

Introduction

Wireless Sensor NetworksMobicast

Introduction- Wireless Sensor Networks

Wireless sensor networks : are large-scale distributed embedded systems com

posed of small devices sensors wireless communication interfaces microprocessors maybe some actuators

will soon be feasible to deploy dense collections of sensors to perform distributed micro-sensing of physical environments

Introduction- Wireless Sensor Networks (cont.)

Many sensor network applications have fundamental spatiotemporal constraints

an intruder tracking application example an information scouting example

Introduction- Mobicast

Mobicast represents a new information dissemination

paradigm with spatiotemporal semanticsallow applications to specify their spatiotem

poral constraints by requesting a mobile delivery zone

in turn enables the application to build a continuously changing group configuration

Introduction- Mobicast (cont.)

ChallengeHole

Introduction

This article presents :a new Face-Aware Routing protocol (FAR) f

or mobicasta related spatial neighborhood discovery alg

orithm

Mobicast Overview

Limitation of Approaches Based on GeocastAdvantages of Just-in-Time Delivery

About Mobicast

The mobicast service supports a type of application information delivery request right-place and right-time just-in-time

Limitation of Approaches Based on Geocast

Duplicate area

Advantages of Just-in-Time Delivery

Face-Aware Routing for Mobicast

The Planar Spatial NeighborhoodFace-Aware Routing

About face routing

The idea of face routing is inspired by previous geometric routing algorithmsCompass routingFACE-2GPSRGOAFR+

Faces

The Planar Spatial Neighborhood

A

Face

D Spatial neighborE

C

BP

F

The Planar Spatial Neighborhood

G

Face

Spatial neighbor

C

BP

F

L

N

HI

J

K

M

The Planar Spatial Neighborhood

M

Face

D Spatial neighborE

CF

L

N

G O

HI

J

K

Face-Aware Routing

The face-aware algorithm consists of two methods for forwarding packets:greedy forwarding timed forwarding

About FAR

Packet Format

Greedy Forwarding

Timed Forwarding

Protocol Termination

Packet Format

Packet header

1 2 3 4 5 6 7 8

Sender location

Packet sending time-stamp

Initial delivery zone coordinates

Delivery zone velocity

Message lifetime

Message type

Sender packet sequence number

The last forwarder location

• identify each packet on the network

Greedy Forwarding

Greedy forwarding applies to all nodes that are currently (or previously) covered by the mobica

st delivery zone or have at least one spatial neighbor that is currentl

y (or previously) covered by the mobicast delivery zone

In such cases, a node forwards a new packet in an “as-soon-as possible” fashion

Timed Forwarding

Timed forwarding applies to a node that has no spatial neighbor in the current delive

ry zonebut either itself will soon be in the delivery zone or has at least one spatial neighbor that will be in

the delivery zone

Example

G

L

M

E

FI

HP

C

BA

J

D

NK

P G

L

M

EN

F

AA

JC

B

D

K

Greedy forwarding mode

Timed forwarding mode

Timed Forwarding (cont.)

the expected 1-hop network latency

the hop distance

The forwarding decision of X is as follows:(1) If Ta ≤ 0 forward the packet as soon as possible(2) If Ta > 0 delay the forwarding for time length Ta

Protocol Termination

A packet is not simply ignored if it has expired

An expired packet is dropped only in the timed forwarding mode

If a node is in greedy forwarding mode it will forward the packet even if the packet h

as expired

FAR assumption

The perpendicular span to be no smaller than the maximum communication range

Topology Discovery

Face IdentificationFace Traversal TerminationCost MinimizationThe Outer Face

Topology Discovery

Face Identification

How to make each discovery message traverse the correct face ?using a ring-buffer on each node for storing

the incident planar edges

A

B C

DA’s ring-buffer:

A-B

A-C

A-D

Face Traversal Termination

How to determine when a message has traversed the whole face ?A node determines if an incoming discovery

message dm has completed a full traversal of a face by the following criterion :

the outgoing edge for dm is contained in its ordered traversal list

“when the message comes back to a node already traversed” does not work

Face Traversal Termination

Example

G

Cost Minimization

How to coordinate between nodes such that only one discovery message flows around each face ?On each face, ideally one traversing discove

ry message will suffice

Cost Minimization (cont.)

Two strategies for reducing the number of discovery messagesRandom starting timeStarting location-based tiebreaking rule

east is preferred, if there is still a tie, north is preferred

The Outer Face

A practical way to identify an “outer” face is from its sizea discovery message has a max hop count

Simulation Results

Spatial ReliabilityTemporal Characteristics

Simulation environment

600 sensors1000 × 400 m2 areadispersed randomly under the uniform di

stribution120 × 100 m2 rectangular delivery zoneNS2 network simulatorIEEE 802.11 MAC protocol

Spatial Reliability

Average and Standard Deviation of Delivery Ratio of FAR, Greedy and Geocast

Temporal Characteristics- Slacktime

Temporal Characteristics- Slacktime (cont.)

Temporal Characteristics- Slacktime (cont.)

Conclusion

FARSpatial neighborhood discovery protocol

Conclusion- FAR

FARa new face aware mobicast routing protocol

which, in theory, reliably delivers messages spatially

has good mobicast temporal characteristics relies on the notion of spatial neighborhoods features a novel timed face aware forwardin

g method

Conclusion- Spatial neighborhood discovery protocol

This paper addressed key issues a spatial neighborhood discovery protocol must consider face identificationdiscovery terminationduplicate elimination

Question?

Thank you.Thank you.