18.3.3 SDI Simulation Evolution

Three separate versions of the SDI simulations  were constructed: Sim87, Sim88, and Sim89. Each was more elaborate and used more capable hardware than its predecessor. Sim87, for example, executed on a single 32-node Mark III; Sim89, in contrast, was implemented to run on the 128-node Mark IIIJfp. Configuration was flexible; Figure 18.10 shows a typical example using two hypercubes and a network of Ethernet-connected workstations. The internal structure of the simulation showed similar evolution. Sim87 was not much more elaborate than indicated in Figure 18.9 but it evolved to the much more capable version shown in Figure 18.11 for Sim89 [Meier:90a], [Yeung:90a].

  
Figure 18.10: Typical Sim89 Hardware Configuration

Features of Sim89 included more elaborate individual modules, outlined below.

• The intermediate abstraction of ``platform'' was introduced and platforms became hosts to instances of multiple modules as shown. The importance of the platform beyond that of definitional convenience was that a platform in general becomes associated with a satellite whose location and trajectory with respect to the emerging scenario determine its view and computational progress. A typical platform might host a sensor, a tracker, and a battle planner of some type and consist of as many subcubes. Multiple platforms of each type were permitted and multiple platform types could be created; communication links between the platforms completed the constellation and determined the flow of information.

    
  Figure 18.11: An Evolved SDI Simulation, Sim89
  

• An important platform class was the simulated Ground Command Center, included in the Simulation to model the effects that the human command element could have on the progress and outcome of the scenarios being simulated. The Command Center included the elements of:
  1. Graphics interpretations of the progress of the simulation (Figure 18.12 (Color Plate)).
  2. A fully concurrent database that received, processed, and made pertinent data available to other command center elements.
  3. A Look Ahead Planner which in itself was a medium-fidelity simulation, capable of projecting the current state of the simulation forward rapidly and analyzing the prospective results of various command options.

Figure 18.12: A complex strategic defense situation graphically summarized.

The Command Center was an important conceptual step. It re-positioned the role of the workstations from one of passive display of the activities occurring internally to the hypercube, to the role of the key user interface into a network computing environment assisted by large-scale parallel machines. It, in effect, helped us merge our own mental picture of the paradigm of network computing with that of parallel processing and into the more unifying view of cooperative, high-performance computing.