Proxy-based Adaptation for Mobile Computing ECET 581 Spring 07

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Proxy-based Adaptationfor Mobile ComputingECET
581 Spring 07

• Authors Markus Endler
• Hana Rubinsztejn
• Ricardo C. A. da Rocha
• Vagner Sacramento
• ISSN 0193-9741

By Douglas A. Schultz 1/29/07 For Professor Lin
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Introduction

• Proxies have 3 main problem solving uses
• Throughput and latency issues. (wired to
  wireless)
• Host mobility.
• Limited resources of MH (mobile hosts).
• This report reviews
• General proxy based approaches.
• Implementation techniques.
• Successful well know examples.

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Introduction

• Proxy is an intermediary placed in the path
  between a server and its clients.
• Proxies act as
• Protocol translators.
• Caches and content adapters.
• Usually reside at the border between wired and
  wireless networks.
• A Wireless Access Point (AP) is a common example.

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Introduction

• Proxies perform complex tasks for mobile
  networks
• Handover, Session or consistency measurement
• Personalization, authentication, check pointing
• Service/resource discovery.

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Introduction

• Advantages of proxies
• Proxy handles the wireless-dependent translation
  and trans-coding, for the server.
• Processing for protocol and content is
  distributed to other nodes, saving serving
  processing.
• Proxy placement at the wireless interface gives
  faster response to wireless conditions, link
  quality, and disconnection detection.
• Transformations for any communications layer can
  be implemented.

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Introduction

• Proxy based middleware solves problems in
• Web access, multimedia streaming, and database
  access.
• Proxy terminology
• Gateway, intermediary, or agent.
• an entity that intercepts communication or
  performs some service on behalf of some mobile
  client.

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Classifying Proxy-Based Approaches

• Different characteristics of the bridge between
  wired and wireless networks as in
• Throughput, latency, reliability and probability
  of disconnection.
• Mobile Host characteristics like
• Display size, user input/output mechanism,
  processing power, memory size, and Power
  limitations.
• Application type requirements
• Response time, network latency, disconnection
  transparency, and cache coherence.

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Classifying Proxy-Based Approaches

• Two main classifications of proxies
• General architecture characteristics.
• Tasks or functionalities assigned.
• Architecture-based Classification
• Level, Placement, Single-/Multi-protocol, and
  Communication and Extensibility.

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Architecture-based Classification

• Level
• Communication-level
• Handles issues of communications protocols and
  abstractions.
• Goal is to provide device mobility and make
  wireless link transparent to the higher software
  layers.
• Typical adaptations include
• Wired to wireless protocol translation,
  buffering, and handover management.

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Architecture-based Classification

• Middleware-level
• Non-application or Non-protocol specific tasks.
• As in content adaptation, management of cached
  data, service or resource discovery, security,
  and authentication.
• Application-level
• Application specific tasks.
• As in caching for Web based applications (fast
  response time) vs. database where consistency is
  more important.

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Architecture-based Classification

• Placement
• Server-side
• Only at stationary network node.
• Client-side
• Only at mobile node.
• Interceptor model
• Proxy pair, one mobile client one stationary
  server.
• Migratory proxy or agent
• Moves between mobile and stationary nodes.

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Architecture-based Classification

• Placement continued.
• Server-side proxies work with any device.
• Client-side proxies require more resources
  usually thick-clients.
• Architecture
• Centralized
• All functionality is bundled into the Proxy.
• De-centralized
• Several proxies perform separate functions.

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Architecture-based Classification

• Single and multi-protocol
• Single protocol commonly used for TCP or HTTP.
• Multi-protocol like UDP, SMTP, SMS, and WSP and
  dynamically switches between protocols.
• Communication
• Synchronous mode
• Proxy does an adaptation task in response to an
  explicit client request.
• Asynchronous mode
• The proxy does long-term work based on user
  preferences, then sends asynchronous
  notifications to the client.
• This is common for the role of user agents in
  searching, collecting and aggregating
  information for the user.
• WAP is one example that supports both.

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Architecture-based Classification

• Communication continued
• Communication among proxies is also supported.
• For session management, check pointing, and
  multicasting.
• Direct mode
• Proxy knows which other proxy to interact with.
• Indirect mode
• Server or another proxy acts as a router for
  message exchange.

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Architecture-based Classification

• Extensibility/Programmability
• Extensibility, the possibility to adapt and
  customize its functions, is an important
  architecture characteristic.
• A generic framework is provided to tailor to the
  application.
• Another group of proxy infra-structures further
  support the dynamic loading of filters or new
  modules.

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Common Proxy Tasks

• Protocol Translation and Optimization
• Proxies deal with communication specific issues
  like
• Flow control, error detection, recovery, and
  medium multiplexing.
• Connection oriented protocols like TCP need
  proxies for handling disconnections, burst packet
  losses or varying round trip delay times.

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Common Proxy Tasks

• Content Adaptation
• Aims at transforming the payload for optimized
  transmission and presentation at the mobile
  device
• Distillation and Refinement
• General term for several forms of data
  compression.
• Summarization
• Lossy compression where specific parts of the
  original data are selected for presentation,
  aiming at the least possible loss of information.
• Intelligent Filtering
• Mechanism to transform, drop or delay data
  delivery by applying filters on a data path,
  according to network or target device conditions.

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Common Proxy Tasks

• Trans-coding
• General process of transforming the format and
  representation of content.
• Caching and Consistency Management
• Main goals of caching
• Are to reduce traffic to and from the source
  server.
• Restrict the user-perceived latency, conserve
  wireless bandwidth and the mobile devices
  battery power.
• Handle client disconnections.

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Common Proxy Tasks

• Session Management
• Maintaining an applications or services session
  state in spite of disconnections and mobility of
  the user.
• Handover Management
• Occurs when a user previously connected to some
  network reconnects to the same or to a new
  network.

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Common Proxy Tasks

• Discovery and Auto-configuration
• Accessing a service through a proxy, eliminates
  the choice from the client.
• Jini, a distributed system, uses proxy-based
  approaches for service discovery.
• Dynamic service reconfiguration, like WebPADS.
• Security and Privacy
• Public-key security model.
• One protocol for secure device-to-proxy
  communication.
• Another protocol for secure proxy-to-proxy
  communication.

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Common Proxy Tasks

• Check-pointing and Recovery
• Recovery is typically based on check-pointing.
• Check-pointing is snapshots of distributed data.
• Other tasks
• Personalization
• Content Creation
• Name Resolution

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Proxy Frameworks

• Adapter Development
• Module responsible for implementing a
  trans-coding function of a message or its
  content.
• Adapter Selection
• Programmable interfaces or via rule-based
  configuration.
• Context Monitoring
• The collection of the network state.
• Adapter Loading and Execution
• Configurable or dynamic proxies.

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Conclusion

• Challenges and Future
• Scalability of server-side proxies as the number
  of clients increase.
• Combine the end-to-end and proxy approaches.
• Open Pluggable Edge Services
• Develop infra-structures that collectively
  perform adaptations for a huge variety of devices
  and protocols.
• Dynamic proxy configuration
• The proxys functionality is shaped according to
  dynamic demand by the clients, server load, or
  the current mobile network conditions.