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Supporting User Mobility in Ubiquitous Computing Environment

(Aug. 2001 - May. 2002)

Mobile Computing has been an active research area over the years. It has gained more intensive consideration since the recent proliferation of network-enabled portable devices and inexpensive wireless communication. All these advancing technologies are enabling "ubiquitous personal computing environment". In such an environment, a user can access his/her personalized services at anytime, anywhere, through any possible mobile/fixed terminals in a secure way. A wealth of research work has been conducted to approach this goal. Most of them focused on the host mobility problem. With host mobility, a user can access the same service while traveling. However, he/she is required to always carry the mobile host. We argue that this is only a special case of user mobility. In the ubiquitous computing environment, user mobility} not only includes host mobility, but also includes the case where a user is free to switch from one host to another. In a broader sense, a user is free to migrate his/her service environment. This means that the user, instead of host, is the real end receiver of any service.

One fundamental problem is how to dynamically migrate the user's session as the user moves, so that the service always follows him/her. We refer to this problem as user-level handoff. This is in contrast to the traditional host-level handoff scenario, where a mobile host switches from one network to another. The unique challenges of this problem are as follows: 

  • How to seamlessly migrate the user's video session, i.e., how to capture, store and forward the execution state of the video session, so that the service continuation is preserved?
  • How to migrate a session to a new system environment totally different from the previous one (host platform, network connection, or even the user application itself)? More challengingly, how to correctly reflect the user's QoS preferences under such condition?
  • Upon addressing all the above problems, how to optimize the system performance, i.e., accelerate session creation and deployment, minimize handoff delay, etc.?

These problems demand mobility support from both system (OS, network) level and application level. However, supporting user mobility at application layer is not a viable solution. Making each application to be mobility-aware will greatly complicate its development. Moreover, legacy applications are not considered. On the other hand, system-level solutions are insufficient since they are not aware of application semantics. This is quite essential to address the problem of user-level handoff across heterogeneous platforms. We believe that the middleware solution is the best to address these problems due to its following advantages.

  • The middleware system offers enough flexibility to be easily deployed on various computing platforms, even on the handheld device. It can also easily cooperate with existing system solutions. 
  • By keeping the general mobility functionalities (user location management, personal information management, state transfer management, etc.) that are application-neutral in the middleware layer, applications are not needed to be mobility-aware. Another advantage is that the middleware framework is ready to accommodate a rich yet expanding set of applications. 
  • Without loss of generality, the middleware layer still allows its overlying applications to inject any application-specific policies. 

We designed and implemented a middleware framework to support user mobility in the Active Space of Gaia Project. Its major mobility functions include user-level handoff management and service instantiation across heterogeneous computing platforms. Furthermore, we make several enhancements to improve system performance, such as accelerating user-level handoff, therefore saving state information storage/transportation overhead. We tested our framework using two multimedia applications (Mobile Video Player and Mobile Audio Player). 

Active Space

    

Screenshots of Mobile Video Player

(Session Migration from desktop PC to iPaq)

 

 

Publication:
  • Yi Cui, Klara Nahrsetedt, and Dongyan Xu, Seamless User-level Handoff in Ubiquitous Multimedia Service Delivery, Multimedia Tools and Applications Journal (ACM/Kluwer), Special Issue on Mobile Multimedia and Communications and m-Commerce, February, 2004. [pdf].