CO2509 Mobile Computing

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CO2509 Mobile Computing

• Software Systems for Mobile Computing
• An introduction to key problems, concepts and
  solutions of mobile software.
• What is the difference between mobile computing
  and distributed computing?
• Chris Casey (ccasey_at_uclan.ac.uk , cm226)

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Key Features

• Summary of content
• Mobile Software using Java
• Distributed software technology
• Mobile phone software
• Wireless systems
• WAN, MAN, LAN PAN
• Assessment
• Examination 50 Coursework 50

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Lecture Goals

• You have learnt this material if you can
• Give examples of mobile systems and explain the
  advantages of mobility
• Outline solutions to key problems
• Suggest advantages disadvantages
• Recognise some key terms

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What is Mobile Computing?

• Access to information processing whenever and
  wherever you want
• Does it need to be wireless?
• An example of distributed computing
• Distributed computing includes fixed networks

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Why Mobile Computing?

• Possible Goals
• Communication
• Distributing processing workload
• Share data
• Convenience
• Location independence
• Travel-related service

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What are the goals?

• A mobile game
• Mobile device Web access to Google
• Mobile device Web access to your bank
• Laptop access to Astronomy simulation
• Web Email

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Key Mobile Problems

• Communication Problems
• Transferring the data between components
• Security Problems
• Preventing eavesdropping and impersonation
• Data Problems
• Formatting and ensuring consistency of data
• Distribution Problems
• Deciding the location of data and processing
• User Interface Issues
• Languages and programming issues

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Communication Problems

• Bandwidth
• An inherent problem dependant on the physical
  link the communications protocols.
• Possible Solutions
• Data compression

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Communication Problems

• Error Control
• Broken connections
• Transferring data across a lossy link.
• Bits changed
• Blocks lost
• Possible Solutions
• Higher level protocols
• Check for errors resend
• Ignore e.g. voice transmission

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Communication Problems

• Data exchange
• Sender receivers interpretation of data
• Different devices different output capabilities
• Possible Solutions
• self-defining data, (XML, Schema)
• e.g. SOAP use XML for requests to a service
• transforming data for display- (XML, XSL)

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Locating Destinations

• Finding where someone or some service is
• Finding a route through a network
• Possible solutions
• Directory Services
• e.g. DNS Domain Name Service
• Routing tables

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Security Problems

• Interception (Snooping)
• Possible solutions
• Encryption, steganography
• Authentication (To whom are you talking?)
• Possible solutions
• Signatures / Certificates (which rely on
  encryption)
• Authorisation
• Access rights to data and services

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Security Problems

• Attacks
• Virus, Trojan Horse,
• Defect Attacks (e.g. Buffer Overflow),
• Denial of Service
• Possible solutions
• Training Procedures
• Limit permissions for untrusted software
• Firewalls virus checkers

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Data Problems

• Concurrency
• Multiple programs (threads) operating
  simultaneously
• (Think joint bank accounts)
• Classic problems
• Mutual Exclusion
• Ensure one program doesnt access data
  temporarily inconsistent because of another
  program
• (e.g. transferring money between accounts)
• Synchronisation
• Ensuring a program doesnt access information
  until its ready
• (e.g. withdrawing money before the salary is paid)

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Data Problems

• Consistency
• Multiple copies of data can get out of step
• Especially when components can be disconnected
• Reliability
• Risks of hardware/software failure data loss
• State / Stateless Protocols
• Basic HTTP protocol is stateless
• The server has no memory of earlier requests
• The use of cookies introduces state
• The server accesses data it stored on a client

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Distribution Problems

• Architecture where everything is
• Client/server
• Peer-to-peer
• Multi-tier architecture

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Client/server
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Peer-to-peer
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Multi-tier architecture

• A 3-tier architecture

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3-tier Architecture Benefits

• Separate the concerns
• Can support may different user interfaces
• The essence of the application is the server
• This communicates with the database using a
  standard language (SQL) which is independent of
  the particular database
• Database specialises in storing data, can easily
  upgrade.

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User Interface Problems

• Potentially slow and variable response time
• Limited Device Capability
• Screen size resolution
• Processing power
• Input devices special keyboard, pointing devices
• Bandwidth (y do u spel lyk ths)
• Connection failure
• Potential Solutions
• Cut-down user interface widgets
• Cut-down HTML (WML or XHTML-MP)
• Client-side server-side processing balance

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Languages

• Java, C have common features
• Safety-conscious
• Control program capability
• Avoid common errors memory leaks
• Interpreter checks code
• Strongly object-based
• Component-based user interface development

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Why Java?

• Portable
• Compiled to bytecode assembly language for an
  imaginary machine, which is implemented in
  software
• the Virtual Machine is supported on many systems
• J2ME cut-down version for mobile devices
• Mature
• Time for problems to be removed
• Feature Rich
• Large collection of libraries (APIs)
• Freely Available

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Program Structure

• Communication-based
• Set-up a communication link
• Read and write data
• Remote Procedure Call
• Make method calls across machines
• the run-time system hides the communication

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Interoperability

• Accessing services from different systems,
  machines, operating systems, vendors
• Standards Middleware
• CORBA
• Web Services

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Summary

• Mobile computing benefits
• Communication, distribution, convenience
• Mobile computing is complex
• Errors can occur during communication
• Communication implies concurrency
• Concurrent programming is difficult
• User interface is an especial problem