Content Cruising System :Peer-to-Peer Distribution System

for Location-based Contents

Takaaki Ishida (ishi@sfc.wide.ad.jp)Keijiro Ehara(popo@sfc.wide.ad.jp)

Masayoshi Imaike(isle@sfc.wide.ad.jp)

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

Research Motivation

It is required to realize free and robust location based services that do not necessarily depend on specific infrastructures.

We designed new location-based contents sharing system by using of wireless P2P ad-hoc communication instead of current central management model.

→Content Cruising System

Background2: 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 ApproachLocation-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.

Content Cruising System

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.

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.

Content Cruising System

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

( To

Dis

play

or 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 Sensing Equipm

ents( G

PS, Clock, etc )

Monitoring

Send Contents

Con

tent

sC

ontentsControllingStorage 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 kｄ-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

143longitude

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

　Lin

k-lo

cal m

ultic

ast

PDA bGPS Presentation

PresentationAlgorithm

Transmission

Algorithm

Selection

Algorithm

Tran

smis

sion

Alg

orith

mS

elec

tion

Alg

orith

m

PresentationAlgorithm

Timer A

lgorithmTi

mer

Alg

orith

m

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.

Demonstration 2• Objectives:

– To introduce the overview of CCS which is completed by autonomous cooperation of many nodes through working with a simulator that represent people’s move.

• Operation:– Simulator Generates numerous “Virtual nodes” as an

emulator which has same function of CCS servant application.

– “Real nodes(=PDA)” are sending their location information which is gotten by GPS to a simulator, and they work as if one of the virtual nodes on the simulator.

– Each real node’s status which is calculated on a simulator is send back to real node, and it is shown on the display of each PDA.

Architecture of Demonstration2

Walking Model on Simulatoror

Cursor Key of Remote Host

Context Manager

Receive Send

Storage

TransmissionAlgorithm

SelectionAlgorithm

GPS

Presentation

ContextManager

PDA a

PresentationAlgorithm

Context Manager

Receive Send

Storage

TransmissionAlgorithm

SelectionAlgorithm

Context Manager

Receive Send

Storage

TransmissionAlgorithm

SelectionAlgorithm

Context Manager

Receive Send

Storage

TransmissionAlgorithm

SelectionAlgorithm

PresentationAlgorithm

Calculated by Simulator

PDA b

GPS

Presentation

GPS

Presentation

PresentationAlgorithm

PDA c

PresentationAlgorithm

Emulator of PDA a Emulator of PDA b Emulator of PDA c Emulator of Virtual Node

Connected by WLAN （ IPv6 or IPv4 Network ）

Simulator

ContextManager

ContextManager

Map モードの動作イメージMap mode （ PDA a）

前提：• コンテンツのヘッダは、下記のデータが含まれている。

1. ContentID （位置情報＋発信時刻＋ IP アドレスを MD5,SHA-1 でハッシュ化したもの）

2. Destination （コンテンツの目的地）3. Duration （コンテンツの生存時間）4. IP アドレス（発信したノードの Source アドレス）5. 発信者の位置情報

画面説明：• 地図中の円は、 PDA のラジオレンジであり、

この円が自分の現在地を中心（赤丸）に地図上をスクロールする。

• 届いたコンテンツの Destination は × 印で地図上に plot される。受信時は点滅（または赤色）する。

• 地図上に plot された Destination は Duration（生存時間）が過ぎると消滅する。

• コンテンツを送信したノードは” 5” を元に、一定時間緑の■で地図上に plot される。

• 自分が送信するときは、赤丸が点滅する。• 受け取ったコンテンツのうち、 Destination が半径 5m 以内

に入ったものは、 Message Board にコンテンツが表示される。（複数ある場合は最も近いもののみを表示）

• “Write a Message” をクリックすると「メッセージ書き込みモード」に。” Debugging Mode” をクリックすると「デバッグモード」へと切り替わる。

Message Board

You find a Message !“ROAD CONSTRUCTION, NEXT 4 MILES”

Message Writing Mode Debugging Mode

Go to

メッセージ書き込みモードの動作イメージMassage Writing mode （ PDA a）

画面説明：• “Target Your Content’s Destination” ：

• 地図上で、カーソルキーを用いてコンテンツの目的地を定める。• “Writing Message” ：

• メッセージを作成• “Drop Your Content” ：

• コンテンツを発信する。

Writing Message

“Famous rest rant is around here !”

Target Your Content’s Destination

Drop your Content

Message Writing Mode Debugging Mode

Go to

デバッグモードの動作イメージDebugging mode （ PDA a）

目的：• CCS のアプリケーション動作を、コンテンツ送受信の流れで説明する。画面説明：• 自分が受け取ったコンテンツと送信したコンテンツをそれぞれ時系列で上から順に表示する。（メッセージは上に新しいメッセージが積み上げられていく）。• 表示するものは、

• メッセージの内容（赤字）• Source Address （ from 以下）• Destination Address （ = リンクローカル・ブロードキャストアドレス送信時のみ。 To 以下）• 受信日時（ at 以下）を今のところ検討中。

You received “Famous rest rant is around here !”from fe80::205:4eff:fe40:555bat Sat, 15 May 2004 16:08:09 +0900 (JST)------------------------------

You received “ROAD CONSTRUCTION, NEXT 4 MILES” from fe80::205:4eff:fe40:777bat Sat, 15 May 2004 16:07:55 +0900 (JST)------------------------------

You send “Watch your step !” to fe80::205:4eff:fe::0at Sat, 15 May 2004 16:07:50 +0900 (JST)------------------------------

Now you are receiving these Contents

Drop your Content

Message Writing Mode Debugging Mode

Go to

Issue of Using CCS under Sparse Movements of Nodes

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

CA

B

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 AGPS

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

Content’s destination point

Background1: Location based serviceGeographically dependent contents:Traffic information, Campaigns advertisements of local stores, Evacuation

instructions for a local disaster, etc.

The value of this kind of contents depends on Time and Place

These Contents’ Value becomes:1. higher around destination area2. lower as time go on.for both senders and receivers

The service distributing contents to users at appropriate time and place is generally called location based service.

Content’s value in Real Space

•Geographical destination of each content is set previously.•The node which receives the content calculates its distance from the destination.•As a node move closer to destination, the node tends to send the content.Informational flood suppressed to fixed targeted area.And the node that newly enters into the area will receive the content

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.