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The most obvious components of SIMNET are the simulators themselves, but several other software applications are also required, each involving substantial software development efforts with tens or hundreds of thousands of lines of code:
Management, Command and Control (MCC) system. Loads the selected terrain database (described in the “Terrain Databases” section), and initializes all simulators at appropriate locations on the terrain. Simulates artillery, air support, supply, and repair functions. Can function as a Tactical Operations Center (TOC) or Army Logistics Operations Center (ALOC). Each MCC typically supports one battalion’s worth of assets. Typically uses one computer and multiple monitors, organized according the different functions being provided in the exercise. Multiple MCC systems can be used to permit multiple exercises to take place simultaneously on the same network.
Network Operations and Management (NOM) system. Allows simulators to be initiated en masse or individually. Provides an overview of the status of all nodes on the network and all simulators at a site. Alerts operators to network errors and other anomalous events, and provides the ability to send test packets to diagnose and debug problems. Typically uses one computer with one or more monitors.
Data Collection and Analysis System. Provides After-Action Review (AAR) and data analysis functions. Includes the following components:
Plan View Display (PVD). Provides a variable-resolution map display of the battlefield, intervisibility computations (i.e., which entities can see which others), plus detailed information on the status and location of all simulated vehicles. Typically uses one computer with one or more large display screens.
Data Logger (DL). Records all data packet traffic on the network and can play packets back onto the network, so that a simulator, an AAR vehicle, or the PVD, shows exactly what was happening at any point in time and space. Packets can be played back in real time, faster, or slower. The DLs in use circa 1990 could record approximately 900 vehicle-hours on one 500 MB disk. Typically uses one computer with one or more large disk drive, and (optionally) one or more recorders for voice traffic.
Voice Logger (VL). A 16-channel recorder for recording analog voice communications among vehicles on up to 16 radio frequencies. Synchronizes with the Data Logger, so radio communications can be compared with the recorded events. The VLs in use circa 1990 could play back any two selected channels at a time, and could record approximately 8 hours of voice communications on a standard tape cassette. Later, digital voice logging was added.
Semi-Automated Forces (SAF). A system of manned workstations representing the decision-making command post in the SAF organization, which allows a few controllers to project substantial enemy forces onto the battlefield and/or to provide friendly flanking and supporting units. Vehicle movements in subordinate units are controlled by the SAF software. Subordinate units receive orders and semi-autonomously plan their actions and maneuvers, reporting information back to their commanding units as they would in a real operation. Subordinate units behave sufficiently realistically that the SAF commander does not need to constantly micro-manage them to produce credible military operational behaviors. SAF includes one or more computers and one or more color map displays showing the current state of the battlefield as reported by the SAF units. SAF software was extended to support fixed- and rotary-wing aircraft, artillery units, and logistics trains for fuel and ammunition.
Stealth/After-Action Review (AAR) vehicle. Includes a simple set of controls for navigating around the battlefield. Each vehicle includes out-the-window and map displays that allow the operator an “omniscient” perspective, superior to that of any real-world vehicle. There were three versions in use circa 1990:
- The Stealth-1 included a high-capacity image generator with a single large-screen display, a Data Logger, a Plan View Display, and an analog radio receiver.
- The Stealth-3 contained a standard image generator (which was sometimes borrowed from an existing on-site simulator) and three low-resolution monitors, a Data Logger, a Plan View Display, and an analog radio receiver.
- The Stealth-8 was similar to the Stealth-3, but with 8 low-resolution monitors, which could be arranged in any desired pattern. Other components are the same as the other versions.
These vehicles were employed in various ways, both during and after an exercise. For example, a Stealth vehicle (initially called a “flying carpet”) sends no data packets and hence cannot be seen by any other vehicle. It can be flown freely, driven over the ground, or tethered to another vehicle, either occupying the same location or following it at a fixed distance. There is also a “water-skiing” mode that allows the Stealth vehicle to swing around the vehicle to which it is tethered to observe it and its surroundings from different perspectives.
When replaying a pre-recorded exercise, the Stealth vehicle can travel in time as well as space; i.e., it can jump backward or forward to an earlier or later time in the exercise. This is particularly useful in providing after-action reviews to the troops to discuss what occurred at significant points.
Generic Vehicle (GV). By modifying the controls and vehicle dynamics, and by broadcasting appropriate vehicle appearance packets, a Generic Vehicle can be used to represent any existing or hypothetical vehicle. Examples include a First Sergeant’s vehicle (e.g., a HMMWV), a logistics vehicle (e.g., a HEMTT, an Air Liaison Officer’s or Forward Air Controller’s vehicle, a maintenance vehicle (e.g., an M88 recovery vehicle), an M113 (Armored Personnel Carrier) or M577 (Command Post Carrier), or almost anything else within imagination. No doubt additional applications have now been added.
Long-Haul Network (LHN) interface. Aggregates packets from each Local Area Network (LAN) and transmits them to a remote site. Includes a gateway computer with links to wire or fiber-optic cables. Circa 1990, two 56-kbps telephone lines were used for each site being connected. Dial-up lines were sufficient to accommodate 100 simulated vehicles per site.
Long-Haul Voice (LHV) communications. Requires an additional 56-kpbs line. Circa 1990, control signals were sent via the phone lines to indicate when transmissions began and ended, because the analog radio voice activation protocol then in use would not work over analog circuits. Subsequently converted to digital voice communications for better voice fidelity and to interoperate with the Electronic Model of the Battlefield (EMB) component.
Electronic Model of the Battlefield (EMB). Models the interaction of radio transmissions with the terrain and other electronic communications. Voice transmissions are digitized at the transmitter and compressed to reduce network bandwidth requirements. Header information for each transmission includes the transmitter location, frequency, emitted power, and antenna orientation. The EMB computes the received signal strength for each source and receiver based on the path length between them, including diffraction effects across major obstacles such as hills or mountains. A receiver model determines which of the competing signals are captured (FM radios, for example, lock in on the strongest signal received). The “winning” signal is then decoded and mixed with the appropriate level of noise. This signal could be a jamming signal (intentionally or unintentionally). The results of these computations (using the Longley–Rice model) are communicated to the various radio receivers, which then convert digital signals to analog form to be fed into the headsets of the crews. Transmission data may also be used by other simulators for determining source location, either for navigational purposes or for anti-radiation weapons (such as signal-seeking missiles).
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