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Next: Verification Query Rollback Versus Up: Network Management of Predictive Previous: Calibration Mode of Operation

Model and Simulation

An initial test of this concept has been performed in a simulation  of a predictive management system implemented with Maisie [18]. Maisie  is the simulation environment used here. Its suitability for this has been demonstrated in the RDRN  network management and control design and development and in [19] to develop a mobile wireless network parallel simulation  environment. The parallel simulation  environment shows a speedup over the currently used commercial sequential simulation packages. The environment and a set of modules which have been developed for mobile network simulation are described in [19]. Maisie uses a language which has been influenced by a classic work describing the characteristics of a parallel programming  language structure [20]. The programming features developed in [20] are used in many parallel programming languages  besides Maisie . Since every Maisie entity has a built-in input queue, each LP is comprised of three additional Maisie entities:

There is also a gvt entity for the calculation of GVT . All three of the above entities work together to implement Virtual Time as described in [7]. The first entity above, representing the PP, contains a delay mechanism in order to implement the sliding lookahead window . The gvt process should notify all processes to cease forward simulation when GVT reaches the end of the window. In this version of the predictive management system, each LP simply compares its LVT to the current time and holds processing until current time is back within the lookahead sliding window.

Determination of Global Virtual Time (GVT) should be done as defined by [21]. This algorithm allows GVT to be determined in a message-passing environment as opposed to the easier case of a shared memory environment. It also allows normal processing to continue during the GVT determination phase. However, in this implementation each output message is sent to the gvt entity as well as to its proper destination. In addition, the gvt entity checks all LPs for their current LVT and chooses the minimum message send time and LVT as the current GVT. The gvt entity is allowed to execute in parallel with the other entities in this simulation, it does not stop the other entities while performing its computation and thus may not always be perfectly accurate. This is because messages may be in transit when the poll takes place, and because the LPs are changing while the GVT computation is taking place. However, the results were close enough for the purpose of these experiments.




next up previous
Next: Verification Query Rollback Versus Up: Network Management of Predictive Previous: Calibration Mode of Operation

Steve Bush
Thu Feb 27 15:34:42 CST 1997