content cruising system under dense region of mobile nodes takaaki ishida*, masayoshi imaike** *...

Content Cruising System under Dense Region of Mobile Nodes

Takaaki Ishida*, Masayoshi Imaike*** Research Institute for Digital Media and Content, Keio University

** FEAC International Corp.*[email protected], **[email protected]

Introduction

About Location-based ServiceThe service distributing contents to users depending on their

positional information is called location based service.

“You can find a McDonald's around

here!”

“ROAD CONSTRUCTION, NEXT 4 MILES”

Source of image: KDDI Corporation JAPAN

Topics of our Research

• Research Motivation:– To realize free and robust location based services that do not

necessarily depend on specific infrastructures.

• Keywords:– Accidental encountering the valuable information through

Wireless P2P ad-hoc communication– Adopting simple “Store & Forward” transmission model instead

of complicated routing protocol– Generation of new communication model by utilizing of “Physical

Movement “of mobile nodes

• We are developing “Content Cruising System“ which is decentralized in form that mobile nodes distributed in various places sharing the functions to store and to distribute the contents.

Content Cruising System

OverviewSender:1) adds the metadata which describes“Destination point”, “Duration”, and “Content ID” to the content.2) then send it to one-hop neighbors which

happen to meet.

Content

metadata

Receivers & Mediatorsprompt the content to be transferred to the destination point, .and to be remained around the destination area during the duration by cooperation of scattered mobile nodes.


GPSPresentation

Context

Manager

Receive

Send

Storage

IPv6　

Link-local all node multicast

PDA a

Con

text

Man

ager

Rec

eive

Sen

d

Sto

rage

IPv6　

Link

-loca

l all

node

mul

ticas

t

PDA b

GPS Presentation

Presentation Algorithm

Transm

issionA

lgorithm

Selection

AlgorithmT

rans

mis

sion

Alg

orith

m

Sel

ectio

nA

lgor

ithm

Tim

er Algorithm

Tim

er A

lgor

ithm

Frequency C

ontrolA

lgorithmF

requ

ency

Con

trol

Alg

orith

m

Presentation Algorithm

Operation of CCS Servent

2

1

e=a

y = ae -kd

(0.0)

Configuration of Transmission Algorithm

Centripetal Force Interval Time of Sending

y - １ k ｄ-1

R R(0.0)

aa

a

2a

“d” is the distance from the destination point, “a” is a coefficient, .”k” is the parameter which define the dependence with distance.

Two autonomous control mechanisms under Dense Region of Mobile Nodes

Concerns about Scalability

• Two unforeseen phenomena which cause a malfunction under dense region of mobile nodes– Increase in the number of mobile nodes– Increase in the number of of contents

• To avoid these problems, CCS has autonomous control mechanisms which are constructed by cooperation of several modules and algorithms.

transmission interval = 3sec

Mobile nodes connected to same link

data

data

data

data data

data

data

data data


data data data

data data data datadata


Increase in the number of nodes

Destination point

Total amount of network traffics on same link

Function of Timer resetDestination of the content

Only the node which is nearest to the destination point in same link sends the content


Mobile nodes connected to same link



Autonomous Control Mechanism to the Increase of mobile nodes

Only the node which is nearest to the destination point sends the content

data

data

data

data

data

data

data

data

data

data data

data

data

data

data data data

reset reset reset reset reset resetdata

reset

data

datareset reset reset reset reset reset

reset

↑transmitting ratio of each content←distance from the destination 　

node 1

distance from the destination →

node 2

Traffics consumed by node1 Traffics consumed by node2

Total amount of network traffics on

same link are:

Increase in the number of contents

Function of Frequency Control Algorithm

n

i

iTtraffictotal1

　

)/(1

max

n

i

i TTC

Tmax

The following information is added to the header of each content exchanged by CCS: -data size (byte)-default transmission frequency (sec)-congestion control coefficient (decimal)

T = data size / default transmission frequency

Net

wor

k tr

affic

on

sam

e lin

k

Increasing of number of content Each node calculates “C”. according to header info and reconfigures the transmission frequency of each content multiplying it by this value of “C”.

Verification Experiments

1m

experimental environmentEnvironment setting• 5 sets of PDAs which CCS servant

application was installed were placed in effective radius of wireless LAN.

• One node was located at the center point of all, and the other four nodes had the implicit latitude and longitude set up as if they were placed in a line every other meter from the center node.

• Whenever the node was one meter away from the destination point of content, Transmitting Frequency is set up so that it might shift by a unit of one second.

Allocation points of PDAs

（ Virtual latitude and longitude ）

Destination point of content

Within same radio range

Distance from the destination

0m 1m 2m 3m 4m

Transmission interval

3sec 4sec 5sec 6sec 7sec

Verification experiment of Timer Algorithm

• A dummy content (data size: 1Kbyte, destination: same position with the center node, default transmission frequency at the destination: once per 5 sec) was sent to the five nodes, and the number of transmissions in each nodes were counted for duration of 6 minutes.

• The experiment was conducted in two cases whether the timer algorithm is applied or not.

59 59

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00

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Tra

nsm

ittio

n C

ount

1 2 3 4 5

Node ID (Distance from the destination)

Without Timer Algorithm With Timer Algorithm

Experimental Result of Timer Algorithm

Verification experiment of Frequency Control Algorithm

• The congestion control coefficient was set up as the restriction of bandwidth to be 2.5Kbyte/sec.

• Dummy contents (data size: 1Kbyte, destination: same position of the center node, default transmission frequency at the destination: once per 2 sec) were sent to the five nodes.

• The experiments were conducted five times with numbers of content being changed (the restriction of bandwidth was multiplied by the experiment number each time), and total traffic which flows on the link was measured in 5 minutes per experiment.

• These experiments were conducted in two cases (with or without Frequency Control Algorithm) in same condition, and both average traffics were compared.

Experimental Result of Frequency Control Algorithm

0

2000

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12000

default double triple quadruple quintuple

Multiplication Factor of Network Load

Aver

age

of O

bser

ved

Netw

ork

Traffi

c (

byte

/sec

)

Restriction of Bandwidth With Frequency Control AlgorithmWithout Frequency Control Algorithm

Summary

• To make the CSS work properly under the severe environment dense with mobile nodes, it is a critical issue to find a solution to handle the increasing nodes and contents. The "Timer algorithm" and "Frequency control algorithm" are developed as autonomous control mechanisms in order to avoid malfunction in such a situation.

• Both of these mechanisms worked well through the experiments by using of several PDAs. Hereafter, we will continue to verify practical effectiveness of these mechanisms assuming more realistic situation by using of a simulator.

Thank you for listening

Current Operation of Location-based Service

GPS

Data Base

area A

It requires:•Costly equipments (numerous base stations, Content storage/distribution servers, etc.)•Central management.•Continuous network connectivity .

The problem of single point of failure arisesWe cannot use it:•in some developing region without such an infrastructure•in a disastrous situation where the infrastructure is damaged

Internet

Get it’s Location informationareaA

Base station

Send Location information as a query

Retrieve content of it’s area from DB

1m

タイマーアルゴリズムの検証• 実験内容

– 10 台の愛・ MATE を無線 LAN の有効　半径内に設置

– 中心ノードの緯度経度を固定– 中心ノードから実測 1m 置きに並んでいるよ

うに、他の 9 台の端末の緯度経度を固定※右図参照

– 送信頻度を以下のように定め、中心ノードから約 5KB のデータを発信してタイマーアルゴリズムが機能しているかを調べた。

• T ＝ α ＋ X^β×φ※ 今回の実験では、パラメータを以下のように定

め、送信頻度 T は 1 秒以下を切捨てとした。α ＝ 3sec, 　 X ＝ 1m, 　 β ＝ 2, 　 Φ ＝ 0.2

– 上記の計算式により、各設置端末の送信インターバルは理論上下記の数値となる。

• 比較検証– 同じ条件で、タイマーアルゴリズムを入れた

場合と入れない場合の送信回数を比較した。

端末の設置位置（仮想の緯度経度）コンテンツの目的地

1hopの距離

中心ノードからの距離

1m 2m 3m 4m 5m 6m 7m 8m 9m 10m

送信インターバル

3sec 3sec 3sec 3sec 4sec 4sec 4sec 5sec 6sec 7sec

隠れ端末を想定した場合

2秒ごと

3秒ごと

3秒ごと

6秒ごと

6秒ごと

3秒ごと

2秒ごと

3秒ごと

6秒ごと

6秒ごと

3秒ごと

3秒ごと

2秒ごと

4秒ごと

4秒ごと

4秒ごと

4秒ごと

3秒ごと

2秒ごと

2秒ごと

11

2

2

3

4 5

1

1

1 2 3 54

54

3

1 2 3 4 53 322 4 4共有リンク上での送出間隔

6

×2

2 31 54

About each Algorithm

• Transmission Algorithm ：– Objectives:

To change the frequency of transmission depending on the relation between their location and content’s destination.

• Selection Algorithm ：– Objectives:

To avoid the depuration of content which it received.– Operation:

It compares the Content ID of the new content with those of the old ones in order to detect the duplication.If duplication is detected, this module discards the old content .

• Timer Algorithm:– Objectives:

To set the timer to next transmission on each content depending on Transmission Algorithm.– Operation:

• Set the timer to next transmission on each content• Reset a timer of the content when it received same content from others. • Stop resetting a timer randomly.

• Presentation Algorithm ：– Objectives:

To pick up the content whose destination is close to user’s location from Storage Module. – Operation:

Display the content whose destination is within the range of 5 meters.

ノード数に対するスケーラビリティーの検証

3秒ごと

data

data

data

data

data

data

data

data

data

data data

data

data

data

3秒ごと

2秒ごと

data data data


reset

data


reset

タイマーリセットを入れた場合

同一リンク上のノードが配信するコンテンツ

ノード数増加に対するスケーラビリティー

Destination of the content

Mobile Ad-hoc CommunicationIn the mobile wireless Communication:

Mobile nodes have their radio device’s range.(ex. Bluetooth → 10m, IEEE802.11b →100m, etc.)

In their radio range, they can:1. detect the nodes which are close geographically2. broadcast contents to their One-hop neighbors which they happen to meet.3. The nodes which receive the content forward it to other nodes.

Wireless P2PAd-hoc communication

Merits and Demerits

Using the catenation of ad-hoc communication as a location based services generates both merits and demerits.

Merits:• Contents are transferred to further areas by physical

movements of numerous mobile nodes.• Costly equipments and network infrastructure are not

needed.

Demerits:• Contents are spread disorderly in wide area through

multi-hop communication.

Our Approach

Location-based service will be realized If information flooding can be suppressed to fixed geographical areas.

To attain the goal which mentioned above:

1. Each content shall have it’s “Geographical destination” and “Duration” previously.

2. Content sender adds these information to each content as meta-data.

3. Mobile nodes which receive the content change frequency of transmitting the content depending on their location information which is obtained by GPS.

→Contents are gathered around destination area autonomously by cooperation of mobile nodes.

Objectives

• Location based transmission: Contents are transferred and sustained in a specified area autonomously.

• Location-awareness: Contents are found by users in a relevant location automatically.

• Location based selection: Unnecessary contents are eliminated based on the user's location.

想定する情報伝播モデル• 情報の憑依と地縛

– 発信されたコンテンツは「どこに配布したいか」「どのくらいの時間停留させたいか」といった発信者の配布ポリシーを持ち、近隣のノードに無作為に伝達される。

– コンテンツはノードの物理的な移動に従い各地へと運搬され、実空間上を移動する。また、運搬の過程において、発信されたコンテンツは自身の配布ポリシーにそぐわないノードから自然に離脱する。→ 情報の憑依

– 目的とされる地域に近づいたコンテンツはその地に留まり、地域に新しく入ってきた移動ノードに次々と複製と憑依を繰り返すことによって、その地域に停留していく。→情報の地縛

• このようにコンテンツの配布ポリシーを元に多数のモバイルノードが自律・分散的に協調作業を行なってコンテンツを運搬していくことで、あたかもコンテンツ自体に意思があるかのように送信や消滅等自らの次の行動を決定していくという情報伝達のイメージを想定し、システムの設計を行った。

設計コンセプト

• 自律・分散・協調モデル– 統治者が存在しない。あるのは共通のルールのみ。

• シンプルなネットワーク設計– 相互のネゴシエーションやルーティングを前提としない、一方向のブロードキャスト型モデル。

• Context Aware & Action– ノード同士が互いの状況を感知せず、共通のルールに基づいて自律的にアクションを起こすことによって全体の分散・協調システムとして機能する。

• Sensitive Network– 移動先がどのようなネットワークかをネットワーク自体が感知して、自律的に制御する。

→このような条件で、もし情報の流れをコントロールすることが出来れば実空間上における Robustな情報配信システムが実現できる。

共通条件である「位置」と「時間」を基準ルールとして設定。まずはロケーションベースサービスへの適用を想定した実装を行なっ

ている。

設計コンセプト

OverviewSender:1) adds the metadata which describes“Destination point”, “Duration”, and “Content ID” to the content.2) then send it to one-hop neighbors which

happen to meet.

Content

Metadata（ COMPASS ）

Receivers & Mediatorsprompt the content to be transferred to the destination point, .and to be remained around the destination area during the duration by cooperation of scattered mobile nodes.


• 通信部分– IPv6リンクローカルオールノードマルチキャスト

• モジュール群– Context Manager

• センサーから環境情報（ context）を取得。• Contextと COMPASSを照合し、コンテンツのスケジュールを管理する。

– Sendモジュール• One Hop Neighborsにコンテンツを同報する

– Receiveモジュール• One Hop Neighborsからコンテンツを受信する

– Storageモジュール• 受信したコンテンツをコンテンツ IDと紐付けて蓄積する

• アルゴリズム– Selection Algorithm

• 受信したコンテンツの重複チェック（コンテンツ IDによる識別）• FIFOオーダーにより、最新情報の生存率を上げる。

– Transmission Algorithm• 送信頻度を計算

– Timer Algorithm• 送信スケジュールの管理• タイマーリセット機能

– Frequency Control Algorithm• 帯域状況を監視して送信頻度を調整

Architecture of CCS Servent

万博での IT実証実験

全ての交通機関を媒介にした新しいコミュニケーションモデルの実現にむ

けて

アドホックネットワーク向けルーティング制御プロトコルの分類

フラット型

Reactive（ On-Demand）型

ハイブリッド型

Proactive（ Table-Driven）型

階層型位置情報補助型

OLSR　　 FSR

TBRPF　　 DSDV

LANMAR IARP

GSR CGSR

　

DSR　　　 TORA

AODV 　　 ABR　IERP　　　 DLAR

ZRP BRP

CBRP

CGSR　 LANMAR

ZRP HSR

LAR 　　　 GPSR

DREAM 　 GeoCast

　

太字：　 RFC 化されたプロトコル

複数経路型

ルーティング制御プロトコルの型の分類　

型内　容階層型ネットワークの規模が大きくなった場合に、制御パケットの増

加等により、フラット型のルーティングでは機能しなくなることが考えられる。そこでクラスタリング等によってネットワークに階層を持たせて制御を行う。

位置情報補助型各ノードが GPS（ Global Positioning System）等の位置情報が検出可能な機器を有している場合に、その位置情報を利用して経路の形成を効率よく行う。

複数経路型複数の経路を選択可能にすることで、経路探索回数の削減や、パケットの到達率の向上を図る。

フラット型ルーティングテーブルを作成するタイミングに応じて、 Reactive（ On-Demand）型プロトコルとProactive（ Table-Driven）型プロトコル、これらのハイブリッド型プロトコル、および他のプロトコルに大きく分類される。

Reactive型（ On-Demand）

Proactive型（ Table-Driven）

Hybrid型

・ DSR (Dynamic Source Routing)・ AODV (Ad hoc On-demand Distance Vector algorithm)・ IERP (IntErzone Routing Protocol)・ DLAR (Dynamic Load-Aware Routing)

・ OLSR (Optimized Link State Routing protocol)・ TBRPF (Topology Broadcast based on Reverse Path Forwarding routing protocol)・ FSR (Fisheye State Routing protocol)・ LANMAR (LANd MARk routing protocol)・ IARP (IntrAzone Routing Protocol)・ DSDV (Destination Sequenced Distance Vector routing)・ GSR (Global State Routing)・ CGSR (Clustered Gateway Switch Routing)・ ZRP (Zone Routing Protocol)・ BRP (Bordercast Resolution Protocol)・ CBRP (Cluster-based Routing Protocol)

MANET WGで検討中の主なフラット型の　　　ルーティング制御プロトコル

Reactive型と Proactive型の比較

利点欠点ReactiveProtocol（ DSR、 AODV）

・非通信時に制御メッセージ（経路情報）が流れない

・通信を行う際に遅延が生じる

ProactiveProtocol（ OLSR、 TBRPF）

・通信を行う際に遅延が発生しない（経路は既に確定している）

・非通信時に制御メッセージ（経路情報）が通信される（定期的な情報交換によりネットワークトポロジ情報を更新）

・インターネットのルーティングプロトコル（ RIP, OSPF ）は Proactive 型・ MAC レイヤなのでルーティングとはいえないが、 CSMA/CA は Reactive 型・ Proactive 型では、トポロジーの変更頻度に応じて更新間隔を調整する必要がある　　　－更新間隔が長すぎると経路情報が古くなり、短すぎるとトラフィックのオーバヘッドが　　　　大きくなる－いかにトポロジー更新情報を効率よく（少ないオーバヘッドで）伝達するかが重要・ Proactive 型では、トポロジーから Dijkstra アルゴリズムにより最短経路を決定　

LBS としての評価（ IMSA2003 の sim の結果）

Without Transmitting Algorithm

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1 26 51 76 101 126151176201226251 276301326351376 401426451476501 526551576601626 651676701726751 776

distance from the destination point

rece

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tio

population min population max

Rate of Flow is Maximum

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Rate of Flow is Minimum

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Graph1

Graph2

Graph3

Origin (0, 0) is the destination point.X-axis shows the distance from the destination point (graphs show in the range of 800m from the destination point). Y-axis shows the rate of content-reception. The numbers used for the rate of content-reception is calculated by taking the average from 3 different destination points.

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()

送信

回数

タイマーなしタイマーあり

1: B is separated from A 2: A communicates with C directly.

1.Solved by nodes’ movement • When the glued node’s

problem occurs:• The situations the

glued node will be able to receive the content are shown below.

Star-mark : content’s destination point

Node A: First content’s holder

When NodeA approaches NodeB and sends the content to NodeB,

Node C will be “Glued Node”.

A

B

C

AB

C

AB

CA

B

C

3: B approaches destination point closer than A

B

3秒ごと

同一セグメント上の同報

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data

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data data

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3秒ごと

2秒ごと

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reset

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reset

同期を取る場合（ランダムにリセットを設定）

Random発生

Random発生

コンテンツ数に対するスケーラビリティーの実証

↑ 各コンテンツの送信頻度

双方のノードが消費する帯域は

→ コンテンツ目的地からの距離　← コンテンツ目的地からの距離　

ノード 1 ノード 2

ノード 1 が送信するコンテンツの総和ノード 2 が送信するコンテンツの総和

11

ノード３

ノード 1

ノード２

3秒ごと

3秒ごと

2秒ごと

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3秒ごと

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3

32

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1

1

31 2 4 5 86 7

876

54 7

1 2 3 4 53 322 44 55共有リンク上での送出間隔

6

11

3秒ごと → 6秒ごと









2

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1

1 2 3 54

54

3


6

×2


2秒ごと

3秒ごと

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11

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×2

2 31 54

reset


reset

reset

2秒ごと

3秒ごと

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3秒ごと

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3秒ごと

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3秒ごと

random

reset

×2

×2

×2 ×2

reset

Content Cruising System :Peer-to-Peer Distribution System

for Location-based Contents

Takaaki Ishida ([email protected])Keijiro Ehara([email protected])

Masayoshi Imaike([email protected])

Graduate School of Media and Governance of Keio University

JAPAN

Background1:Location-based ServiceThe service distributing contents to users depending on their

positional information is called location based service.

“You can find a McDonald's around

here!”

“ROAD CONSTRUCTION, NEXT 4 MILES”

Source of image: KDDI Corporation JAPAN

Current Operation of Location-based Service

GPS

Data Base

area A

It requires:•Costly equipments (numerous base stations, Content storage/distribution servers, etc.)•Central management.•Continuous network connectivity .

The problem of single point of failure arisesWe cannot use it:•in some developing region without such an infrastructure•in a disastrous situation where the infrastructure is damaged

Internet

Get it’s Location informationareaA

Base station

Send Location information as a query

Retrieve content of it’s area from DB

Framework of Servant Application

CCS is operated by cooperation of simple servant

applications which have same function installed on

each mobile nodes.

Servant application consists of 4 modules:• Sender Module• Receiver Module• Storage Module• Context /Status Manager

Oth

er P

rogr

ams

( T

o D

ispl

ay o

r P

lay

Con

tent

s )

Inside of Mobile Node

Other Mobile Nodes (One-hop neighbors)

Receiver Sender

Storage

Context/Status Manager

Servant Application

Receive Contents

Context S

ensing Equipm

ents( G

PS

, Clock, etc )

Monitoring

Send Contents

Con

ten

tsC

onten

tsControllingStorage module compares the Content ID of the new content with those of the old ones in order to detect the duplication.

If duplication is detected, this module discards the old content .

Contents

Sender module broadcasts the content according to the Transmission Algorithm

2

1

e=a

y = ae -kd

(0.0)

Configuration of Transmission Algorithm

Centripetal Force Interval Time of Sending

y - １ k ｄ-1

R R(0.0)

aa

a

2a

“d” is the distance from the destination point, “a” is a coefficient, .”k” is the parameter which define the dependence with distance.

Demonstration

139 140 141 14213813735

3637

38

Real Space Communication

（ Demo1 ： ad-hoc Communication using radio-device ＆ IPv6）

802.11b

143

longitude

latitude

Virtual Simulation

（ Demo2 ： Generating virtual nodes, and realization of assuming environment in virtual space） Mapping situation

Red balls are real, Blue balls are virtual nodes.

Both of real and virtual nodes distribute messages according to their location（ transmitting algorithm of the centripetal force）

Around this area , you’ll find green message

A screen image of the CCS demonstration

Screen of real node Screen of projector

Summary

• The purpose of our research is to realize the contents distribution system which is decentralized in form that mobile nodes distributed in various places sharing the functions to store and to distribute the contents.

• We proposed the Content Cruising System to realize the form of a decentralized content-transmission system in real space.

• This system brings about the mechanism in which contents are transmitted autonomously, by adopting a simple algorithm in ad-hoc communication.

• Estimated effectiveness of the transmission algorithm which is applied in CCS is verified by the simulation with assumed movement patterns of people in real space.

Thank you.

Demonstration 1

• Objectives:– To confirm our designed system is work well

through the implementation of servant programs on

• Outline ：– Users get their location information by GPS.– Users send content depending on

transmission algorithm to their one-hop neighbors by IPv6 link-local multicast.

Architecture of Demonstration1

GPSPresentation

Context

Manager

Receive

Send

Storage

IPv6　

Link-local multicast

PDA a

Con

text

Man

ager

Rec

eive

Sen

d

Sto

rage

IPv6　

Link

-loca

l mul

ticas

t

PDA b

GPS Presentation

PresentationAlgorithm

Transm

issionA

lgorithm

Selection

Algorithm

Tra

nsm

issi

onA

lgor

ithm

Sel

ectio

nA

lgor

ithm

PresentationAlgorithm

Tim

er Algorithm

Tim

er A

lgor

ithm

Transmission Schedule

• “Context Manager” has a timer to schedule the time for each content to be sent.

• When receiving the same content from other nodes, “Storage module” discards the older one, and “Context Manager” will set it’s timer of the new content.

→ We call this workings “Timer-Reset”

• In CCS, transmitting frequency becomes higher as a node approaches the destination (cf. transmission algorithm).

• Hence, only the closest node to destination among its one-hop neighbors always sends the content to other nodes by this mechanism.

Working of “Timer-Reset”

Each node resets its timer of this content to send

Destination of the content

×

Hidden terminal problem will be generated

We call the node like this

“Glued Node”

Approach to solve “Glued node’s problem”

There thought to be 2 ways to avoid this problem.

• Passive avoidance– Waiting the nodes’ movements

• Active avoidance– Adoption of random timer-reset

1: B is separated from A 2: A communicates with C directly.

1.Solved by nodes’ movement • When the glued node’s

problem occurs:• The situations the

glued node will be able to receive the content are shown below.

Star-mark : content’s destination point

Node A: First content’s holder

When NodeA approaches NodeB and sends the content to NodeB,

Node C will be “Glued Node”.

A

B

C

AB

C

AB

CA

B

C

3: B approaches destination point closer than A

B

2.Solved by adoption of “Random Timer-Resets”

• By adding a redundancy to normal “Timer-Reset”, to make content be sent to Glued nodes.

• In precise, we cause ‘no-reset event’ to “Timer-Reset” by a certain probability,and when the “no-reset event” occurs, the nodes which received same content :– does not reset their timer.– Send the content to their one-hop neighbors

immediately.

• We call this working “Random Timer-Resets”.

Working of “Random Timer-Resets”Destination of the content

“no-reset event” occurs

Glued Node

The node send content to one-hop neighbors Irrespective of the remaining time

Types of Location-based ServiceType1:Cell Broadcast of many radio station

station A

GPS

Data Base

area A

station C station B

However, they must require:Wide area wireless-network, Costly equipments, and Central management.Moreover, the problem of single point of failure arises

Internet

Type2:Retreive location-based contents by using of GPS

Location information

What is Content Cruising System?

But, before that, I will talk about our motivation of this research.

Research Motivation目的：災害時などに備え、インターネットへの接続やWe use Wireless P2P ad-hoc communication as free and robust

location based services instead of current central management model.

Merit:• Contents are transferred to further target areas by physical

movements of numerous mobile nodes.• Costly equipments and network infrastructure are not needed.

Problem:→Free and robust location based services are realized by co-operation

of scattered mobile nodes.

Analogy of Voice Communication

Problems

Through the catenation of ad-hoc communication,

contents are spread to wide area by physical movements of mobile nodes without specific infrastructure or equipments.

→This propagation model is similar to the rumors flooding model.

Contents are spread disorderly in wide area through multi-hop communication.

content cruising system under dense region of mobile nodes takaaki ishida*, masayoshi imaike** *...

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