Live , virtual , and constructive Live , Virtual , and Constructive ( LVC ) Simulation is a broadly used taxonomy for classifying Models and Simulation ( M & S ) . However , categorizing a simulation as a live , virtual , or constructive environment is problematic since there is no clear division between these categories . The degree of human participation in a simulation is infinitely variable , as is the degree of equipment realism . The categorization of simulations also lacks a category for simulated people working real equipment . Categories . The LVC categories are defined as follows : Other associated terms are as follows : LVC - IA bridges M & S technology to the people who need and use the information gained through simulation . To accomplish this a LVC - IA provides the following : History . Prior to 1990 , the field of M & S was marked by fragmentation and limited coordination between activities across key communities . In recognition of these deficiencies , Congress directed the Department of Defense ( DoD ) to “ . . . establish an Office of the Secretary of Defense ( OSD ) level joint program office for simulation to coordinate simulation policy , to establish interoperability standards and protocols , to promote simulation within the military departments , and to establish guidelines and objectives for coordination [ sic ] of simulation , wargaming , and training . ” ( ref Senate Authorization Committee Report , FY91 , DoD Appropriations Bill , SR101 - 521 , pp . 154 – 155 , October 11 , 1990 ) Consistent with this direction , the Defense Modeling and Simulation Office ( DMSO ) was created , and shortly afterwards many DoD Components designated organizations and / or points of contact to facilitate coordination of M & S activities within and across their communities . For over a decade , the ultimate goal of the DoD in M & S is to create a LVC - IA to assemble models and simulations quickly , which create an operationally valid LVC environment to train , develop doctrine and tactics , formulate operational plans and assess warfighting situations . A common use of these LVC environments will promote closer interaction between operations and acquisition communities . These M & S environments will be constructed from composeable components interoperating through an integrated architecture . A robust M & S capability enables the DOD to meet operational and support objectives effectively across the diverse activities of the military services , combatant commands and agencies . The number of available architectures have increased over time . M & S trends indicate that once a community of use develops around an architecture , that architecture is likely to be used regardless of new architectural developments . M & S trends also indicate that few , if any , architectures will be retired as new ones come online . When a new architecture is created to replace one or more of the existing set , the likely outcome is one more architecture will be added to the available set . As the number of mixed - architecture events increase over time , the inter - architecture communication problem increases as well . M & S has made significant progress in enabling users to link critical resources through distributed architectures . In the mid 1980s , SIMNET became the first successful implementation of a large - scale , real - time , man - in - the - loop simulator networking for team training and mission rehearsal in military operations . The earliest successes that came through the SIMNET program was the demonstration that geographically dispersed simulation systems could support distributed training by interacting with each other across network connections . The Aggregate Level Simulation Protocol ( ALSP ) extended the benefits of distributed simulation to the force - level training community so that different aggregate - level simulations could cooperate to provide theater - level experiences for battle - staff training . The ALSP has supported an evolving “ confederation of models ” since 1992 , consisting of a collection of infrastructure software and protocols for both inter - model communication through a common interface and time advance using a conservative Chandy - Misra based algorithm . At about the same time , the SIMNET protocol evolved and matured into the Distributed Interactive Simulation ( DIS ) Standard . DIS allowed an increased number of simulation types to interact in distributed events , but was primarily focused on the platform - level training community . DIS provided an open network protocol standard for linking real - time platform - level wargaming simulations . In the mid 1990s , the Defense Modeling and Simulation Office ( DMSO ) sponsored the High Level Architecture ( HLA ) initiative . Designed to support and supplant both DIS and ALSP , investigation efforts were started to prototype an infrastructure capable of supporting these two disparate applications . The intent was to combine the best features of DIS and ALSP into a single architecture that could also support uses in the analysis and acquisition communities while continuing to support training applications . The DoD test community started development of alternate architectures based on their perception that HLA yielded unacceptable performance and included reliability limitations . The real - time test range community started development of the Test and Training Enabling Architecture ( TENA ) to provide low - latency , high - performance service in the hard - real - time application of integrating live assets in the test - range setting . TENA , through its common infrastructure , including the TENA Middleware and other complementary architecture components , such as the TENA Repository , Logical Range Archive , and other TENA utilities and tools , provides the architecture and software implementation and capabilities necessary to quickly and economically enable interoperability among range systems , facilities , and simulations . Similarly , the U . S . Army started the development of the Common Training Instrumentation Architecture ( CTIA ) to link a large number of live assets requiring a relatively narrowly bounded set of data for purposes of providing After Action Reviews ( AARs ) on Army training ranges in the support of large - scale exercises . Other efforts that make the LVC architecture space more complex include universal interoperability software packages such as OSAMS or CONDOR developed and distributed by commercial vendors . As of 2010 all of the DoD architectures remain in service with the exception of SIMNET . Of the remaining architectures : CTIA , DIS , HLA , ALSP and TENA , some are in early and growing use ( e . g . , CTIA , TENA ) while others have seen a user - base reduction ( e . g . , ALSP ) . Each of the architectures is providing an acceptable level of capability within the areas where they have been adopted . However , DIS , HLA , TENA , and CTIA - based federations are not inherently interoperable with each other . when simulations rely on different architectures , additional steps must be taken to ensure effective communication between all applications . These additional steps , typically involving interposing gateways or bridges between the various architectures , may introduce increased risk , complexity , cost , level of effort , and preparation time . Additional problems extend beyond the implementation of individual simulation events . As a single example , the ability to reuse supporting models , personnel ( expertise ) , and applications across the different protocols is limited . The limited inherent interoperability between the different protocols introduces a significant and unnecessary barrier to the integration of live , virtual , and constructive simulations . Challenges . The current status of LVC interoperability is fragile and subject to several reoccurring problems that must be resolved ( often anew ) whenever live , virtual or constructive simulation systems are to be components in a mixed - architecture simulation event . Some of the attendant problems stem from simulation system capability limitations and other system - to - system incompatibilities . Other types of problems arise from the general failure to provide a framework which achieves a more complete semantic - level interoperability between disparate systems . Interoperability , Integration and Composeablity have been identified as the most technical challenging aspects of a LVC - IA since at least 1996 . The " Study on the Effectiveness of Modeling and Simulation in the Weapon System Acquisition Process " identified cultural and managerial challenges as well . By definition a LVC - IA is a socialtechnical system , a technical system that interacts directly with people . The following table identifies the 1996 challenges associated with the technical , cultural and managerial aspects . In addition , the challenges or gaps found in a 2009 study are also included . The table shows there is little difference between the challenges of 1996 and the challenges of 2009 . Approaches to a Solution . A virtual or constructive model usually focuses on the fidelity or accuracy of the element being represented . A live simulation , by definition represents the highest fidelity , since it is reality . But a simulation quickly becomes more difficult when it is created from various live , virtual and constructive elements , or sets of simulations with various network protocols , where each simulation consists of a set of live , virtual and constructive elements . The LVC simulations are socialtechical systems due to the interaction between people and technology in the simulation . The users represent stakeholders from across the acquisition , analysis , testing , training , planning and experimentation communities . M & S occurs across the entire Joint Capabilities Integration Development System ( JCID ) lifecycle . See the " M & S in the JCID Process " figure . A LVC - IA is also considered an Ultra Large Scale ( ULS ) system due to the use by a wide variety of stakeholders with conflicting needs and the continuously evolving construction from heterogeneous parts . By definition , people are not just users but elements of a LVC simulation . During the development of various LVC - IA environments , attempts to understand the foundational elements of integration , composability and interoperability emerged . As of 2010 , our understanding of these three elements are still evolving , just as software development continues to evolve . Consider software architecture ; as a concept it was first identified in the research work of Edsger Dijkstra in 1968 and David Parnas in the early 1970s . The area of software architecture was only recently adopted in 2007 by ISO as ISO / IEC 42010 : 2007 . Integration is routinely described using the methods of architectural and software patterns . The functional elements of integration can be understood due to universality of integration patterns , e . g . Mediation ( intra - communication ) and Federation ( inter - communication ) ; process , data synchronization and concurrency pattern s . A LVC - IA is dependent on the Interoperability and Composability attributes , not just the technical aspects , but the social or cultural aspects as well . There are sociotechnical challenges , as well as ULS system challenges associated with these features . An example of a cultural aspect is the problem of composition validity . In an ULS the ability to control all interfaces to ensure a valid composition is extremely difficult . The VV & A paradigms are challenged to identify a level of acceptable validity . Interoperability . The study of interoperability concerns methodologies to interoperate different systems distributed over a network system . Andreas Tolk introduced the Levels of Conceptual Interoperability Model ( LCIM ) which identified seven levels of interoperability among participating systems as a method to describe technical interoperability and the complexity of interoperations . Zeigler ' s Architecture for M & S extends on the three basic levels of interoperability ; pragmatic , semantic , and syntactic . The pragmatic level focuses on the receiver ’ s interpretation of messages in the context of application relative to the sender ’ s intent . The semantic level concerns definitions and attributes of terms and how they are combined to provide shared meaning to messages . The syntactic level focuses on a structure of messages and adherence to the rules governing that structure . The linguistic interoperability concept supports simultaneous testing environment at multiple levels . The LCIM associate the lower layers with the problems of simulation interoperation while the upper layers relate to the problems of reuse and composition of models . They conclude “ simulation systems are based on models and their assumptions and constraints . If two simulation systems are combined , these assumptions and constraints must be aligned accordingly to ensure meaningful results ” . This suggests that levels of interoperability that have been identified in the area of M & S can serve as guidelines to discussion of information exchange in general . The Zeigler Architecture provides an architecture description language or conceptual model in which to discuss M & S . The LCIM provides a conceptual model as a means to discuss integration , interoperability and composability . The three linguistic elements relates the LCIM to the Ziegler conceptual model . Architectural and structural complexity an area of research in systems theory to measure the cohesion and coupling and is based on the metrics commonly used in software development projects . Zeigler , Kim , and Praehofer presents a theory of modeling and simulation which provides a conceptual framework and an associated computational approach to methodological problems in M & S . The framework provides a set of entities and relations among the entities that , in effect , present a ontology of the M & S domain . Composability . Petty and Weisel formulated the current working definition : " Composability is the capability to select and assemble simulation components in various combinations into simulation systems to satisfy specific user requirements . " Both a technical and user interaction is required indicative of a sociotechnical system is involved . The ability for a user to access data or access models is an important factor when considering composability metrics . If the user does not have visibility into a repository of models , the aggregation of models becomes problematic . In " Improving the Composability of Department of Defense Models and Simulation " , the factors associated with the ability to provide composability are as follows : LVC requires Integratablity , Interoperability , and Composability . Page et al . suggest defining Integratability contending with the physical / technical realms of connections between systems , which include hardware and firmware , protocols , networks , etc . , Interoperability contending with the software and implementation details of interoperations ; this includes exchange of data elements via interfaces , the use of middleware , mapping to common information exchange models , etc . , and Composability contending with the alignment of issues on the modeling level . As captured , among others , by Tolk , successful interoperation of solutions of LVC components requires " integratability of infrastructures , interoperability of systems , and composability of models " . LVC Architectures must holistically address all three aspects in well aligned systemic approaches . Economic Drivers . To produce the greatest impact from its investments , the DoD needs to manage its M & S programs utilizing an enterprise - type approach . This includes both identifying gaps in M & S capabilities that are common across the enterprise and providing seed moneys to fund projects that have widely - applicable payoffs , and conducting M & S investment across the Department in ways that are systematic and transparent . In particular , “ Management processes for models , simulations , and data that … Facilitate the cost effective and efficient development of M & S systems and capabilities … . ” such as are cited in the vision statement require comprehensive Departmental M & S best - practice investment strategies and processes . M & S investment management requires metrics , both for quantifying the extent of potential investments and for identifying and understanding the full range of benefits resulting from these investments . There is at this time no consistent guidance for such practice . The development & use costs associated with LVC can be summarized as follows : In contrast , the fidelity of M & S is highest in Live , lower in Virtual , and lowest in Constructive . As such , DoD policy is a mixed use of LVC through the Military Acquisition life cycle , also known as the LVC Continuum . In the LVC Continuum figure to the right , the JCIDS process is related to the relative use of LVC through the Military Acquisition life cycle .