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MOBILE & UBIQUITOUS COMPUTING

Lâm Vĩnh Tuyên Nguyễn Công Thương

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Outline

Introduction Association Interoperation Sensing and context-awareness Security and privacy Adaptation Summary

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Introduction

Mobile computing: (1980) Paradigm in which users could carry their

personal computers and retain some connectivity to other machines

Laptops, PDAs, mobile phones, … Infrared, WiFi, Bluetooth, GPRS, … Size, battery capacity >< processing

power, screen and resource restrictions

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Introduction (cont) Ubiquitous computing: (Mark Weiser

1988) To be found everywhere

Wearable computing: Devices attached to clothes, worn like

watches, jewellery, … Context-aware computing:

E.g: device will automatically switch itself to “vibrate” instead of “ring” when it is in the cinema

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Introduction (cont) Volatile systems: changes are common

rather than exceptional Relevant forms of volatility:

Failures of devices and communication links

Changes in the characteristics of communication such as bandwidth

The creation and destruction of associations between software components resident on the devices

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Introduction (cont)

Smart space (SS): physical space with embedded services (servers, printers, sensors, …)

Types of movement occur in SS: Physical mobility Logical mobility Add or withdraw static devices Devices may fail and disappear from a

space

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Introduction (cont)

Device model: Limited energy Resource constraints Sensors and actuators Motes Camera phones

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Introduction (cont)

Volatile connectivity: Technology: Bluetooth, WiFi, GPRS, … Disconnection Variable bandwidth and latency:

Too big => increase error rates Too small => increase congestion and

waste energy

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Introduction (cont)

Spontaneous interoperation: interactions during association

Lowered trust and privacy: Trust in volatile systems is problematic

because of spontaneous interoperation Privacy: user may distrust systems

because of their sensing capabilities

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Association

Logical relationship formed when at least one of a given pair of components communicates with the other over some well-defined period of time

Network bootstrapping: solutions rely on servers accessible within SS (e.g: DHCP)

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Association (cont)

The association problem and the boundary principle: How to associate approximately =>

address 2 main aspects: scale and scope Smart space need to have system

boundaries Solution to the association problem is

using “Discovery services”

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Association (cont) Discovery services (DS): is a directory

service The directory data required by a

particular client There may be no infrastructure in the SS

to host a directory server Services registered in the directory may

spontaneously disappear The protocols need to be sensitive to the

energy and bandwidth they consume

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Association (cont)

Methods for service de/registration

Explanation

Lease:=register(address,attributes)

Register the service at the given address with the given attributes; a lease is returned

Refresh(lease) Refresh the lease returned at registration

Deregister(lease) Remove the service record registered under the given lease

Method invoked to look up a service

serviceSet:=query(attributeSpecification)

Return a set of registered services whose attributes match the given specification

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Association (cont) Issues in the design of a DS:

Low-effort, appropriate association: without any human effort

Service description and query language: match services to client’s request for services

Smart-space-specific discovery: access an instance (scope) of DS which is appropriate to physical circumstances

Directory implementation: network bandwidth, timeliness of DS and energy consumption

Service volatility: handle client and service disappearance

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Association (cont) Physical association: the following

techniques have been developed Human input to scope discovery: Sensing and physical constrained channels to

scope discover: Direct association: without using a DS

Address-sensing: use a device to sense the network address of the target device directly

Physical stimulus: use it to cause the target device to send its address

Temporal or physical correlation: use temporary or physically correlated stimuli to associate devices

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Interoperation Models for interoperation including various

forms of inter-process communication, method invocation and procedure invocation

Problem: software interface incompatibility Approach:

Allow interfaces to be heterogeneous Constrain interfaces to be identical in syntax

across as wide a class of components as possible

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Interoperation (cont) Data-oriented programming for volatile

systems: Models for interoperation between indirectly

associated components: Event systems Tuple spaces

Designs for interoperation between directly associated components: JetSend: for interactions between appliances

such as cameras, printers, scanners and TVs Speakeasy

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Interoperation (cont)

Event System

Event Service

Publisher Subscriber

event

(structured data)

event

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Sensing & context-awareness

Sensors: some examples Location, velocity and orientation:

satellite navigation units, accelerometers, magnetometer

Ambient conditions: thermometers, sensors measure light intensity, sound intensity

Presence: sensors measure physical load

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Sensing & context-awareness (cont)

4 challenges in designing context-aware systems: Integration of idiosyncratic sensors Abstracting from sensor data Sensor outputs may need to be

combined Context is dynamic

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Sensing & context-awareness (cont)

Architectures support context-aware applications: Sensing in the infrastructure: set of

sensors is relatively stable Wireless sensor networks:

Set of sensors forms a volatile system Consist of a number of small, low-cost

devices or nodes each with facilities for sensing, computing and wireless communication

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Sensing & context-awareness (cont)

Location-sensing: the most attentionType Mechanism Limitations Accuracy Type of location

dataPrivacy

GPS Multilateration from satellite radio sources

Outdoors only (satellite visibility)

1-10m Absolute geographic coordinates (latitude, longitude, altitude)

Yes

Active Bat Infrared sensing

Sunlight or fluorescent light

Room size

Proximity to known entity

Tag identity disclosed

Easy Living

Vision, triangulation

Camera installations

Variable Relative (room) coordinates

No

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Sensing & context-awareness (cont)

Architecture for location-sensing: The location stack: it divides location-

sensing systems for individual SS into layers The sensor layer: contains drivers for extracting

raw data from a variety of location sensors The measurements layer: turns raw data into

common measurement types including distance, angle and velocity

The fusion layer: combines the measurements from different sensors to infer the location of an object

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Security and Privacy

User and admin require security for their data and resources (confidentiality, integrity, availability) – Trust is lowered in volatile systems.

Privacy – ability to control the accessibility of information.

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Hardware related issues

Portable devices are more easily stolen and tampered. A security design should not rely on the integrity of any subset of devices.

Devices in volatile systems don’t have sufficient computing resources for assymetric (public-key) cryptography symmetric cryptography sharing key.

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Hardware related issues

Energy – security protocol must be design to minimize communication overheads and new type of denial of service attack.

Disconnected operation – avoid security protocols that rely on continuous online access to a server.

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New type of resource sharing

The admin of a smart space expose a service accessible to visitors over wireless network.

Two employees of the same company exchange a document between their mobile phone at a conference.

A nurse take a wireless heart-rate monitor from a box, attaches it to patient.

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New type of resource sharing Secure spontaneous device association

– secure transient association problem. Goal is to create a secure channel

between two devices by securely exchanging a session key.

Assumptions: any device or user Not share a secret with the other. Not posess the other’s public key. Don’t have access to a trusted third party.

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Potential threats

Attacker can eavesdrop, replay and synthesize messages.

Attacker may attempt to launch a man-in-the-middle attack.

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Solutions Users can exchange their own key,

but short string can be learned by exhaustive search.

Using side channel with certain physical properties: one of devices generates a fresh session key and sends it to the other over a receive-constrained channel: physical contact, infrared, audio, laser, barcode and camera.

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Solutions (cont.) Use a constrained channel to physically

authenticate one device’s public key, then use it to exchange a session key devices are powerful enough.

Exchange a session key insecurely and then validate it - use a physical constrained channel to verify that the key is possesed solely by the required physical source.

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Association methods The methods are vary in the degree of

security but are suitable for spontaneous association: None requires online access. None requires users to authenticate

themselves.

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Location-based authentication

Users require privacy don’t want to provide personal information.

Admins require security require access control.

Base on location of the services’ clients.

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Privacy protection

Even though users withhold their identity, there may be some type of potentially identifying information.

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Solutions

Provide name and addresses in service accesses.

Using MAC-level address – visible to other devices such as access point.

Using RFID tags. link to the user’s personal

information. using “soft” address.

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Solutions (cont.)

Using privacy proxy: each device has a secure, private channel to the proxy.

Problems: Central point of vulnerability. Proxies don’t hide which services the

users access.

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Solutions (cont.)

Mixing: Construct an overlay network of proxies

that encrypt, aggregate, re-order, and forward messages. Each proxy trusts and shares keys only with its neighbors.

Obscure users’ locations by exploiting the presence of many users in each location.

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Adaptation

Devices in volatile systems are much more heterogeneous than PCs in processing power, I/O capabilities and energy capacity.

The presence of runtime change itself: runtime conditions such as the available bandwidth and energy are prone to chage dramatically.

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Context-aware adaptation of content

Multimedia application. Send the same content bandwidth

limitations and device heterogeneity. Content is a function of context:

media producer should take account not only of the consuming device’s capability, but also such factors as the preferences of the device’s user, and the nature of his or her task.

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Solutions

HTTP protocol: A client specifies preferences for the

MIME types of the content it cac accept in its request header.

The server try to match those preferences in the content it returns.

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Solutions (cont.) Type-specific compression: proxies perform

compression: Compression should be lossy but specific to the

media type semantic information can be used to decide which media features it is important to retain.

Transcoding should be performed on the fly because statically pre-prepared content forms will not provide sufficient flexibility to cope with dynamic data.

Transcoding should be performed in proxy servers so that both clients and services are transparently separated from transcoding concerns.

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Problems Volatile systems require adaption between

any pair of dynamically associated devices. Adaption is not restricted to clients of

particular services. There are potentially many more providers

whose content needs to be adapted. The providers may also be too resource-

poor to perform certain types of adaption themselves.

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Adapting to changingsystem resources

OS support for adaptation to volatile resources: Satyanarayanan: Application request and obtain resource

reservation. Notify the user of changed levels of

resource availability they can act according to application.

OS notify the application of changing resource conditions and the application adapt according to its particular needs.

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Solutions

OS support for adaptation to volatile resources: Odyssey architecture: Applications manage data types (video,

images) When resource conditions change, they

adjust the fidelity – the type-specific quality

Viceroy divides the device’s total resources between each of several applications running on it.

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Solutions (cont.)

Odyssey architecture Each application runs with a window of

tolerance to changes in resource conditions.

When the viceroy has to change resource levels to a value outside the window of tolerance, it makes an upcall into the application, which then reacting accordingly.

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Solutions (cont.)

Taking advantage of smart space resources: Cyber foraging: A processing-limited device discovers a

compute server in a smart space and overloads some of its processing load to it.

Energy-aware adaptation: save the portable device’s batteries by allocating work to the mains-powerd compute server.

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Solutions (cont.) Challenging requirements:

The application needs to be decomposed.

The compute server should run a part of the application that involves relatively little communication with portable device.

The overall energy consumption for the portable device must be satisfactory.

Communication is energy-intensive energy cost of communication is high.

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Solutions (cont.) Goyal and Carter: decompose the

application in to separate communicating programs. Example the speech recognition The application runs entirely on the mobile

device. The mobile device runs only the user

interface, which ships the digital audio to a program running on the compute server

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Summary

Volatile systems: The set of users, hardware and software

components are unpredictable changed. Connection bandwidth can vary widely. Components are heterogeneous. Energy is limited.

Association. Interoperation.

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Summary

Sensing and context awareness. Security and privacy. Adaptation.

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Question

Thank you very much