In order to accomplish dependable onboard evolution, we develop a methodology which is called "guarded software upgrading" (GSU). The core of the methodology is a low-cost error containment and recovery protocol that escorts an upgraded software component through onboard validation, and guarded operation, safeguarding mission functions. The message-driven confidence-driven (MDCD) nature of the protocol eliminates the need for costly process coordination or atomic action, yet guarantees that the system will reach a consistent global state upon the completion of the rollback or roll-forward actions carried out by individual processes during error recovery. To validate the ability of the MDCD protocol to enhance system reliability when a software component undergoes onboard upgrading in a realistic, non-ideal environment, we conduct a stochastic activity network model based analysis. The results confirm the effectiveness of the protocol as originally surmised. Moreover, the model-based analyse's provides useful insight about the system behavior resulting from the use of the protocol under various conditions in its execution environment, facilitating effective use of the protocol.
['Ann T. Tai', 'Kam S. Tso', 'Leon Alkalai', 'Savio N. Chau', 'William H. Sanders']
On the effectiveness of a message-driven confidence-driven protocol for guarded software upgrading