Mobility Support (1)

In addition to the general-purpose SOMA basic services, we have developed a specific layer for the mobility support that includes the User Virtual Environment (UVE), the Mobile Virtual Terminal (MVT), and the Virtual Resource Manager (VRM). Mobility-enabled applications can be implemented on top of this layered service architecture, as shown in the Figure.

Figure. The SOMA-based mobility middleware

(click here for a larger view of the picture)

The UVE service permits users to connect to different points of attachment to the network, possibly via different and heterogeneous terminals, while maintaining personal configurations and services as indicated in their user profiles. Any user specifies her profile information at the first registration, and has the possibility to modify it at any time. The profile includes not only simple attributes, such as preferred icon arrangement on the display, but also complex data, such as personal X.509 certificates, resources requested to the hosting environment to perform ordinary tasks (e.g., a printer of a specified quality) and user constraints to direct QoS adaptation depending on the currently used terminal type (e.g., if one user is connected via her mobile phone, she can suggest the mobility middleware to deliver her incoming mail after discarding large-sized attachments). In addition, a nomadic user may have to suspend operations temporarily and to resume them at a different location. In this case, the SOMA-based mobility middleware provides automatic/manual functionality to save the state of the user session (persistency service), and to move and restore it to the new point of attachment. In the new location, the user finds her previously configured services, possibly adapted and scaled depending on the resources locally available, and can also receive the results of pending operations. MA-based applications return execution results to requesting users independently of their current point of attachment. If the destination user is disconnected when agents are ready to yield back results, the UVE should interact with the mobility middleware to temporarily freeze agents on stable storage, and to restart them only at user reconnection.

The MVT service supports the migration of any mobile device between different physical locations in the network, by permitting the mobile terminal to continue local execution, while preserving the state of the interactions with network resources and services. The SOMA-based MVT service provides a solution framework to fully support out-of-band computations, persistency of interaction state and dynamic rebinding of resources/services. Traceability after migration is obtained via fixed proxy entities, discovery or directory services. A unique proxy is maintained at a fixed location for any mobile device in the system; the registration of mobile terminals to local discovery services is preferred when connection/disconnection notification should address the limited scope of the hosting locality; the registration to a directory service makes mobile devices visible to all authorized entities in the global system. In addition, the MVT is able to reestablish dynamically mobile terminal bindings to network resources/services. The MVT can requalify references to bind to equivalent resources/services in the new hosting locality, maintain references to remote resources if requalification is either impossible or undesired, and support the creation of new bindings to previously unknown resources/services. The MVT exploits the MA persistency service to save terminal active bindings on stable storage media. After disconnection, the agent execution environment on the mobile device can continue to operate, possibly performing all MA-based out-of-band operations.

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