MOBILE & UBIQUITOUS COMPUTING

 
 

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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) 

Remove the service record registered under the given lease 

Deregister(lease) 

Refresh the lease returned at registration 

Refresh(lease) 

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

Lease:=register(address,attributes) 

Explanation 

Methods for service de/registration 

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

serviceSet:=query(attributeSpecification) 

Method invoked to look up a service

 
 

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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 attention

 

No 

Relative (room) coordinates 

Variable 

Camera installations 

Vision, triangulation 

Easy Living 

Tag identity disclosed 

Proximity to known entity 

Room size 

Sunlight or fluorescent light 

Infrared sensing 

Active Bat 

Yes 

Absolute geographic coordinates (latitude, longitude, altitude) 

1-10m 

Outdoors only (satellite visibility) 

Multilateration from satellite radio sources 

GPS 

Privacy 

Type of location data 

Accuracy 

Limitations 

Mechanism 

Type

 
 

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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 changing 
system 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