ISTD 2003

Interactive Systems Technical Design

Lecture #2

Wireless ad hoc networking formobile peer-to-peer communications

ISTD 2003

Wireless Ad Hoc Networking

• Webster: ad hoc ~ • “formed or used for specific or immediate

problems or needs“• ”fashioned from whatever is immediately

available”

• No fixed/static network infrastructure

• Nodes provide network functionality

ISTD 2003

Variability of the Mobile Environment

Connectivity• connected• semi-connected (asymmetric)• weakly connected• disconnected

Mobile device capability• form factor• GUI• multimedia• real-time multimedia

Mobility• stationary• nomadic (pedestrian speed)• mobile (vehicular speed)• roaming (mobile across networks)

Source: Helal

ISTD 2003

Case Studies

Hocman – Fast Motor Bikers and Ad Hoc Networking

Mobility Studio, Interactive Institute, Sweden

Hummingbird – Inter-Personal Awareness Device

Play Studio, Interactive Institute, Sweden

ISTD 2003

The Hocman Prototype

Fast Motor Bikers and Ad Hoc Networking

Mattias EsbjörnssonOskar Juhlin

Mattias Östergren

INTERACTIVE INSTITUTE

Best Paper Award1st Int. Conf. Mobile and Ubiquitous Multimedia (MUM

2002)Oulu, Finland, Dec 2002

http://www.mum2002.oulu.fi

ISTD 2003

BikeTalk Project

• Ethnographic fieldworkDesign requirements

• The Hocman prototype• Architectural design• Implementation

• Evaluation• Performance evaluation• User evaluation

ISTD 2003

Ethnographic Fieldwork

• User-centered and contextual design• Identification of motor biker’s activities

• Leisure• Social• Visual• Interaction occurs

• Opportunistic encounters• Because it is organized

• Co-movement• Place-centered movement

Design requirements

ISTD 2003

Motor Bikers’ Activities Illustrated

ISTD 2003

Design Requirements

• Added value: augment rather than rationalize

• Social interaction: sustain encounters

• Identification: better means to get to know others

• Heterogeneous user groups: biker culture is

diverse

• Invitation for joint rides: selecting participants from

previous encounters

• Simultaneous activities: user attention varies

ISTD 2003

Architectural Design Principles

• Handheld mobile device

• Mobile context of use

• Wireless ad hoc networking

• No network infrastructure available!

• Peer-to-peer communications

• Data sharing between peers

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Network Design

• Wireless ad hoc networking

• No network infrastructure available!

IEEE 802.11b IBSS• ”IP over single-hop ad hoc networking”• Requires no infrastructure

ISTD 2003

IEEE 802.11 Topologies

IBSSIndependent Basic Service Set Infrastructure Basic Service Set

Extended Service Set

Distribution System

ISTD 2003

Wireless ad hoc networking with IEEE 802.11b IBSS

IBSSIndependent Basic Service Set

Each biker is a 802.11b node

ISTD 2003

Peer-to-peer communications

• Motivation: data sharing between peers

• Requires

• Rapid mutual peer discovery

• Data transfer between peers

• Support for two modes of user attention

• Cruise: automatic download and logging while

driving

• Browse: manual HTML browsing

ISTD 2003

Rapid Mutual Peer Discovery

• Each node keeps a list of known peers• When timer for entry expires, remove it from list• Each node broadcasts a hello message at regular

interval• When node A receives hello message from node B

• If present(B): reset B’s timer• Else: append B and send reply(A,B) message

• When C receives a reply(A,B) message• If not present(A) and (present(B) or B=C): append A

ISTD 2003

Rapid Mutual Peer Discovery Illustrated

AB

C

1. A sends hello(A)

1. A, B, C | A

2. B sends reply(A, B)

2. A, B, C | A, B

3. C sends reply(A, C)

3. A, B, C | A, B, C

ISTD 2003

Data Transfer Between Peers

”Limited” HTTP 1.0Data• HTML pages• Embedded resources, e.g images

Retrieval method #1: Get1. check local cache2. HTTP GET w/ Keep-Alive

Retrieval method #2: Reload• HTTP GET w/ If-Modified-Since and Keep-Alive

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Hocman architectureOperation sequence in cruise mode

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Hocman UI (Browse Mode)

Browser

• local pages

• remote pages

Peers

• current peers

• reachable peers

Log

• event log

• encounters

empty logcruise modereload

ISTD 2003

Implementation

• Mobile devices• Compaq iPAQ 3660 + Orinoco WLAN card• Sympol PPT 2700 + built-in Spectrum24 WLAN• WLAN: IEEE 802.11b IBSS

• Mobile platform• Pocket PC

• Programming environment• C/C++

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Hocman in Use

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Performance Evaluation

vC

Peer Index page size # embeddedResource size

[bytes] resources [bytes]

A 1 310 2 (image, audio) 67 914

B 921 1 (image) 8 597

C 1 241 1 (image) 7 138

A B

C

Data sharing

C

Data sharing

ISTD 2003

Performance Evaluation (cont.)

• Peer C drives by at three different speeds v(50 km/h, 70 km/h and 90 km/h)• Five repetitions for each speed

• Log and cache is cleared for each repetition

• Data sharing• Peer C downloads data from peers A and CB• Peers A and B download data from peer C

• Performance criteria: number of failed downloads

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Performance Evaluation (cont.)

Number of failures of the 5 repetitions

Peer Download from Data Peer C’s speed50 70 90

page . . .A image . . 3audio . . 4

CB page . . .image 2 . 2

ISTD 2003

Performance Evaluation (cont.)

Number of failures of the 5 repetitions

Peer Download from Data Peer C’s speed50 70 90

A C page . . .image . .

1

B C page . . .image . .

.

ISTD 2003

Performance Evaluation (cont.)

Cumulative percentage of failures of all downloads

Peer C’s speedData 50 70 90page . . .

image 10 . 30audio . . 80

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User Evaluation

• Specific route

• Hocman in cruise mode

• Two groups of three bikers

• Monitoring of actions after the ride

• Interviews

• Results not yet available …

ISTD 2003

Conclusion : Hocman Meets Requirements

• Added value: awareness of encounters, information sharing

• Social interaction: logs encounters, images, audio clips

• Identification: icons, downloaded pages

• Heterogeneous user groups: HTML is flexible

• Invitation for joint rides: phone numbers, URL’s, e-mail

address

• Simultaneous activities: automatic background

downloads, HTML browser

ISTD 2003

More Information

• http://www.tii.se/mobility/Biketalk/index.htm

• Publicly available• Source code• Binaries for ARM and MIPS

ISTD 2003

Hummingbird

Inter-Personal Awareness Device

Lars-Erik HolmquistJennica Falk

Joakim Wigström

INTERACTIVE INSTITUTE

Journal of Personal Technologies, 1999

http://www.playresearch.com/

ISTD 2003

IPAD (Inter-Personal Awareness Device)

• Contact facilitator, not mediator• Helps to initiate a contact, but not necessarily

maintain it

• Identified properties• Inter: IPAD utilizes relationship between itself and

other IPAD’s• Personal: IPAD is personal, carried all times

• Awareness: IPAD conveys awareness of others

•Device: IPAD is a self-sufficient device, not reliant on any infrastructure (e.g. network) except that provided by other IPAD’s

ISTD 2003

Simple Principles of Functionality

• A Hummingbird does not do anything on its own

• If two or more Hummingbirds belonging to the users in the same group are ”close” (<100 m) they will produce a sound – they ”hum”

• Additionally, Hummingbird’s display provides the identity of the other users in the vicinity

ISTD 2003

Building Blocks

• Microcontroller• LCD screen (2 x 8 characters)• Miniature speaker• Radio transceiver (433,92 MHz)• Rechargeable batteries (10-15 h per

charge)• Two switches (hum on/off, power on/off)

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Continous Operation of A Hummingbird

• Transmitting of own identification code• Listening for the codes of other

Hummingbirds possibly in the vicinity• Displaying of the codes of Hummingbirds

found in the vicinity

ISTD 2003

User Experience and Evaluation #1

Familiar setting: home, office, school, …

Key findings from a small evaluation in office setting• Hummingbird placed in the background of user’s attention• Awareness information provided by Hummingbird was

useful but not ”crucial”• Possibly increased the informal interaction between users

In familiar setting Hummingbird was mostly in the background of the user’s attention

ISTD 2003

User Experience and Evaluation #2

Unfamiliar setting: rock festival, conference, …

Key findings from small evaluations in Roskilde rock festival and SIGGRAPH conference

• Hummingbird promoted feeling of ”connection”• Frustration when user could not make visual connection in

addition to Hummingbird’s connection• Users wanted more precise information on distance and

location• Sensation of not being alone in a crowd• Natural complement to other daily activities

ISTD 2003

Future IPAD’s ?

ISTD 2003

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