Formally Analyzing Two-user Centralized and Replicated Architectures

We have developed a formal performance model for centralized and replicated architectures involving two users, giving equations for response, feedthrough, and task completion times. The model explains previous empirical results by showing that (a) low network latency favors the centralized architecture and (b) asymmetric processing powers favor the centralized architecture. In addition, it makes several new predictions, showing that under certain practical conditions, (a) centralizing the application on the slower machine may be the optimal solution, (b) centralizing the application on the faster machine is sometimes better than replicating, and (c) as the duration of the collaboration increases, the difference in performances of centralized and replicated architectures gets magnified. We have verified these predictions through new experiments for which we created synthesized logs based on parameters gathered from actual collaboration logs. Our results increase the understanding of centralized and replicated architectures and can be used by (a) users of adaptive systems to decide when to perform architecture changes, (b) users who have a choice of systems with different architectures to choose the system most suited for a particular collaboration mode (defined by the values of the collaboration parameters), and (c) users locked into a specific architecture to decide how to change the hardware and other collaboration parameters to improve performance.