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Cyber security analysis tools are necessary to evaluate the security, reliability, and resilience of networked information systems against cyber attack. It is common practice in modern cyber security analysis to separately utilize real systems computers, routers, switches, firewalls, computer emulations (e.g., virtual machines) and simulation models to analyze the interplay between cyber threats and safeguards. In contrast, Sandia National Laboratories has developed new methods to combine these evaluation platforms into a cyber Live, Virtual, and Constructive (LVC) testbed. The combination of real, emulated, and simulated components enables the analysis of security features and components of a networked information system.When performing cyber security analysis on a target system, it is critical to represent realistically the subject security components in high fidelity. In some experiments, the security component may be the actual hardware and software with all the surrounding components represented in simulation or with surrogate devices. Sandia National Laboratories has developed a cyber LVC testbed that combines modeling and simulation capabilities with virtual machines and real devices to represent, in varying fidelity, secure networked information system architectures and devices. Using this capability, secure networked information system architectures can be represented in our testbed on a single computing platform. This provides an "experiment-in-a-box" capability. The result is rapidly produced, large scale, relatively low-cost, multi-fidelity representations of networked information systems. These representations enable analysts to quickly investigate cyber threats and test protection approaches and configurations.

New challenges in high performance computing and communications are driving the need for fast, geographically distributed networks. Applications such as modeling physical phenomena, interactive visualization, large data set transfers, and distributed supercomputing require high performance networking ISt89]lRa92][Ca921. One measure of a communication network's performance is the time it takes to complete a task-such as transferring a data file or displaying a graphics image on a remote monitor. Throughput, defined as the ratio of the number of useful data bits transmitted per the time required to transmit those bits, is a useful gauge of how well a communication system meets this performance measure. This paper develops and describes an analytical model of throughput. The model is a tool network designers can use to predict network throughput. It also provides insight into those parts of the network that act as a performance bottleneck.

A half-bridge inverter circuit capable of providing a wide range of ac output voltages and frequencies is presented. The inverter uses asymmetrical thyristors (ASCR's), which have the advantages of highpower handling capability, small turn-on and turn-off times, and exhibit the same ruggedness associated with conventional thyristors in regards to surge current and gating requirements. By using ASCR's for the main and auxiliary devices, the inverter offers other advantages such as low snubber-power loss, low commutation loss, simple protection circuits, and the ability to operate at high frequencies with different types of loads. Output voltage control is obtained by feeding the inverter from a variable dc source. Two fixed-value auxiliary dc sources are used to obtain a constant-current interruption capability. The performance of the inverter is evaluated both analytically and experimentally.