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Wireless Services

Key questions

  1. What service do we want to create?
  2. For whom do we create the service?
  3. What kind of devices do they have?
  4. What are the devices communication capabilities?
  5. Do we need a client program for user device?
  6. What is our communication model?
  7. What is required from user & how can we help on it?
  8. What can we optimise in the service?

Communication models

  • Five communication models
    1. Request-reply
    2. Push
    3. Publish-subscribe
    4. P2P
    5. Ad-hoc

Request-reply

  • Client requests data & server provides the data requested
  • Most common model
  • Latency heavily affected

Push

  • Server sends data to client without requests
  • Can be intrusive
  • Who may push data to mobile devices?
    • Push validation, whitelists
    • OMA Push Proxy Gateway (OMA PPG)
  • Is the communication capability always on at user's device?
    • E.g. is Bluetooth communication capability turned on by default?

Publish-subscribe

  • Client subscribes itself to server
    • Whenever subscribed data in server changes it is pushed to the client
  • Advantages over request-reply
    • Reduced bandwidth requirements
      • Server App only sends data changes for a specific point to clients registered to exception on that point
    • Reduces latency problems
      • Client App no longer constantly asking for new data
      • Data not delayed by polling cycles

Publish-subscribe ...

  • How to handle subscriptions
    • Server side
      • Lost connection → unsubscribe?
      • Timers
    • Client side
      • Automated re-subcriptions
      • When to give up?
  • Retransmissions?
  • Limitations to amount of subscribees?
  • Allow anonymity to subscribers?
  • Presence based services

P2P

  • Communication Apps (devices) are equal
    • Either can initiate the connection
    • Data transmission can go in both ways
    • End-to-end security
    • How to handle differences in device capabilities
      • Division of calculation
  • ComLab - Peerhood project
    • P2P neighborhood
    • Provides information about devices & their Apps that are within communication range
    • Supports multiple communication technologies
    • Provides capability to switch between commmunication technologies seamlessly

Ad-hoc

  • Spontaneous temporary connections
  • All communicating devices can be mobile
    • App can not rely on connections remaining functional
  • Routing is problematic
  • Load balancing
    • Movement of nodes may cause extra burden to others

Client

  • Is there a need to create one?
    • Can the service be used with an existing application
      • E.g. microbrowser .. instant messaging client (imo)
  • UI
    • What kind of interaction has to be supported
    • How many hardware platforms have to be supported
  • Data storage
    • Do you need to store data at the device?
    • Can data be stored & how much space is available?

User aspects

  • Whats required from the user?
    • Creation of connection
      • Is the wireless connection creation simple enough?
    • Interaction with the service?
  • Transparent service
    • The service access & running does not require any user action
      • E.g. information walls
    • Where to draw the line on automation

User apsects ...

  • How can we help the user to use the service
    • personalisation
      • What is too much automation?
    • Configuration
      • Can the user know when the selections are done?
    • Context-Awareness
      • Location
      • Time
      • Role

Optimisation

  • What to optimise?
    • Minimise data transfer?
    • Minimise packet amount/payload?
    • Minimise client processor use?
    • Security Vs. usability
  • Selections depend on requirements of the service & the user

Wireless posibilities

  • Mobility
  • Presence & availability
    • Mobile device is most of the time with user
  • Location
    • Utilise user's location to customise the service
  • Context-Aware application

Next

  • Architectures
Last modified: 2013/07/01 14:41