next up previous
Next: Design Choice: Selecting Run-time Up: Adapting to Constraints: Choices Previous: Design Choice: Determining the

Design Choice: How transparent should the degradation be?

Having plotted the implementation space, the designer must next decide how the resource usage is to be monitored and controlled. For networked applications, this has generally been the congestion signal such as a packet loss, or for processor sensitive applications, by examining the process queue length [9]. In our abstractions, the control is through a generic adaptation controller, but this is generally integrated with some other component. The designer must next decide what the resource availabilities upon which to switch implementations, and whether this should include the user within the loop or not. Systems which exclude the user and use closed loop feedback need to worry about the stability of the control loop, and the effect that varying application utility will have upon the user. Systems which include the user must be certain that the user is educated about the need for their collusion in adapting the application. Systems in the latter case include battery monitors querying the user about whether to close down applications, or video conferencing system in which adaptation would reduce the quality to less than the minimum demanded [6].

Malcolm McIlhagga
Thursday June 11 16:17:19 BST 1998