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DIS-XML: Moving DIS to Open Data Exchange Standards
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SEE PROFILEDIS-XML: Moving DIS to Open Data Exchange Standards
Don McGregor
Don Brutzman
Curtis Blais
Adrian Armold
Naval Postgraduate School MOVES Institute
700 Dyer Road RM267
Monterey, CA 93943
mcgredo@nps.edu, brutzman@nps.edu, clblais@nps.edu, adarmold@nps.edu
Mark Falash
Eytan Pollak
L-3 Communications Link Simulation & Training (Link)
12351 Research Parkway
Orlando, FL 32826
mdfalash@link.com, epollak@link.com
Keywords:
DIS, XML, marshalling, unmarshalling, data binding
ABSTRACT: The Distributed Interactive Simulation (DIS) IEEE-1278.1 standard is used in many military simulations.
The binary data format for DIS does not lend itself to use in emerging web services standards or data analysis andstorage tools because the data format is not recognized by most general purpose data manipulation tools. We examine
an alternate XML-based representation of DIS information. An XML representation unlocks legacy data by placing it ina standard data format, and thereby integrates with the many XML data transformation, storage, and analysis tools. An
XML-based approach also allows easy generation of programming language Application Program Interfaces (APIs).
The information contained in DIS PDUs can shift between any of several representations, including the binary IEEE1278.1 standard, XML, or programming language objects. The XML representation can be used in web services
applications or passed over instant messaging channels. Initial tests demonstrate satisfactory performance.

1. Overview and Motivation
Distributed Interactive Simulation (DIS) [1] is acommunications protocol standard used in many military
simulations, including large-scale High Level
Architecture (HLA) federations through network bridges
commonly called DIS gateways. The protocol defines,
among other things, a set of Protocol Data Units (PDUs).
The PDUs are specified in a binary format to promote
efficiency. A single host may process thousands of PDUs
per second, and binary formats are a more efficient format
from which to extract information. The greater efficiency
comes at a cost. Because the data is in a binary format it
cannot be easily processed by tools that are unaware of
the DIS standard. For example, it might be useful tosearch an archive of all PDUs exchanged in an exercise inorder to find entities that passed through a particular areaor that meet some other criteria. If the archived PDUs arein the binary DIS format this task is more difficult than itneeds to be; the tools that search the PDU archive need tounderstand the IEEE standard format. It would be more
useful to reuse powerful, industry standard tools toprocess the information, but these tools typically do notunderstand the binary DIS format.

Many DIS implementations read DIS PDUs from the
network and transform them into programming language
objects [2] [3]. Within the context of the simulation
programming logic the PDUs are more easily handled as
objects, typically with accessor methods to retrieve
individual PDU fields. Users may modify the field values
and then write the PDU back to the network in IEEE1278.1 format. The process of changing between object
and binary PDU format and back again is called
marshalling and unmarshalling, or sometimes serializationand deserialization. The information contained in the two
representations of the PDU is essentially identical, anddiffer only in format. This presents one possible avenue
for tool-based processing of DIS information: theprogramming language objects. But this approach isultimately unsatisfactory, for the same reason that thebinary DIS format is problematic: the tools need tounderstand the programming Application Program
Interface (API), and in general this is unlikely to be thecase for third-party tools. What is needed is a format thatcan both represent the information in a PDU and be usedby other tools, all without giving up the performance andbackwards compatibility advantages of the IEEE-1278.1

binary format or the programming convenience of an
object-based API. The Extensible Markup Language(XML) [4] is a natural choice to meet these requirements.

•

2. Background•Today’s modern Command and Control (C2) andModeling and Simulation (M&S) systems seek to exploit
web-based standards and technologies to achieve the levelof information and software access as is available in theInternet and World Wide Web. The Department of
Defense is rapidly transitioning to a Global Information
Grid (GIG) that will enable diverse systems acrossmultiple communities of interest to readily exchange dataand services to improve decision-making [5]. In 2002, theDefense Modeling and Simulation Office sponsored an
initiative called the Extensible Modeling and Simulation
Framework (XMSF) involving academia and industry(specifically, the Naval Postgraduate School, George
Mason University, and Science Applications International
Corporation, joined later by Old Dominion University’s
Virginia Modeling, Analysis, and Simulation Center) topromote application of web-based standards to military
M&S. XMSF is “a composable set of standards, profiles
and recommended practices for web-based modeling andsimulation” [6]. Over the past 3.5 years, numerous
research projects have been started to demonstrateapplication of XMSF principles, including:•
Extensible Battle Management Language (XBML):
XML representation of Battle Management Language
constructs for passing orders and commands to live,
constructive, and robotic forces [7].
•XMSF Overlay Multicast (XOM): Demonstrates theability to perform many-to-many multicast over anopen network by employing middleware relay agentsthat cooperate to form an overlay “meta-network”
that replicates the traditional multicast tree andachieves network use efficiency equal to Internet
Protocol multicast [8].
•Web-Enabled Run-Time Interface (WE-RTI):
Demonstrates ability to create an HLA federate thatis able to communicate with a Run-Time
Infrastructure (RTI) using Web Services [9].
•Scenario Authoring and Visualization for Advanced
Graphical Environments (SAVAGE): Demonstrationof tools, techniques, and capabilities related to the
Extensible 3D Graphics (X3D) international standard
for web-based 3D [10]•Visual Simulation Toolkit (Viskit): Graphical User
Interface for designing discrete event simulations
using an underlying XML representation of thesimulation event graph with auto-generation of Java
code for execution [11].
•SAVAGE Modeling and Analysis Language(SMAL): XML language for describing objects andenvironment to initialize discrete event simulations.

•

•

•

•

World-Class Modeling (WCM) Project: Event-based
interactions via Web Services between the Naval
Simulation System (NSS) and the Combined Arms
Analysis Tool for the 21st Century (COMBATXXI).
[12]
XML-based Tactical Chat (XTC): Exploiting
community open source XML-based chatmechanisms for human-to-human, human-tomachine, machine-to-human, and machine-tomachine interactions, including use as a transportmechanism for standards such as DIS PDUs [13].
XMSF Profiles: Definition of formal technicalspecifications for application of interoperable webbased technologies to enable composable andreusable M&S [14, 15].
Mediation Services: Web services for C2/M&S
information exchange using the Command andControl Information Exchange Data Model(C2IEDM) [16].
Mobility Common Operational Picture (M-COP):
Specification of a common data model for
representation and exchange of C2 and M&S
information and processes relating to ground vehicle
mobility data needed for maneuver planning [17].
XML Schema-based Binary Compression (XSBC):
Leveraging the structural information in XML
Schema to provide efficient compression anddecompression of XML data streams [18, 19].

It is evident from these examples that researchers arecovering a broad spectrum of topics within XMSF, frompolicy and standardization issues, to modeling andnetworking frameworks, to simulation design andimplementation, to cross-simulation (or C2 system)
interactions, to efficient messaging and transport. The
DIS-XML work described in this paper is anothercomplementary effort under the XMSF umbrella. It
extends the scope of application of the DIS standard toworld-wide proportions through web-enabling theprotocol. Details about the approach and capabilities arepresented in the following sections.

3. DIS to XML
A fragment from the IEEE-1278.1 specification thatspecifies the binary layout of DIS is shown in Table 1.
The actual PDU has binary data at the offsets defined in
the specification. Figure 1 shows what an XML
representation of the data defined by the PDU fragment
above might look like.

Field size
(bits)

96

Entity State PDU fields

PDU Header

Protocol Version – 8-bit
enumeration
Exercise ID – 8-bit
unsigned integer
PDU Type – 8-bit
enumeration
Protocol Family – 8-bit
enumeration
Timestamp – 32-bit
unsigned integer
Length – 16-bit unsigned
integer
Padding – 16 bits unused

Table 1. Binary Format DIS Specification Fragment<PduHeader protocolVersion=”6”
exerciseId=”0”
pduType=”1”
protocolFamily=”1”
timestamp=”0”
length=”144”/>
Figure 1. XML Equivalent of the Binary DIS Content
Once the data is represented in XML format, the fullrange of XML tools can be brought to bear on DIS data:archiving, transformation, database, web services, and soon. However, the XML format is obviously less efficientfor hosts in high-traffic environments to process. What isneeded is a way to shift the information contained in a
PDU to the most convenient format for any particular
context, so binary data can be used in high traffic
environments, and XML for archiving and data exchangewith systems outside of the traditional DIS problem
space. Combined with the need for a programming
language representation of the PDUs, there are at least
three convenient ways to represent the data: IEEE-1278.1
binary, XML, and programming language objects. The
representations of the data and transformations between
the representations are shown in Figure 2.

Figure 2. Translating DIS Data across Three Formats
The DIS data can of course be saved in still moreformats—for example, a relational database. But there aremany open source and commercial tools that allow users

to map XML to other formats. XML is in effect auniversal, platform-neutral format that allows the data to
be easily transformed into any other format one may wish,
usually with freely available tools.

4. Implementation
Our implementation of the ideas outlined above uses as its
starting point an XML schema. Schemas are XML
documents that describe the structure of an XML
document. The World Wide Web Consortium specifies
the format of schema documents [20]. We have written an
XML schema that describes the major aspects of DIS
PDUs. An example fragment from the schema is shown in
Figure 3.
<xsd:complexType name="HeaderType"><xsd:attribute name="protocolVersion"
type="xsd:byte"
default="6"/><xsd:attribute name="exerciseID"
type="xsd:unsignedByte"
default="0"/>…
<xsd:attribute name="length"
type="xsd:unsignedShort"/></xsd:complexType>
Figure 3. XML Schema Fragment for DIS PDUHeader Format
Some portions of the PDU header are omitted for brevity.
As can be seen, the schema is in XML format, but
describes the structure of another XML document, in thiscase one that contains a representation of DIS PDUs. The
name and type of PDU header attributes are specified,along with any useful default values. A valid XML
fragment as described by this schema fragment was
shown in Figure 1. Writing the schema is a matter ofreading the IEEE-1278.1 specification and writing acorresponding schema document that contains the same
information.
Once the schema is written there are a number of toolsthat can automatically translate the XML schema into
programming language objects. This is a major savings inprogrammer labor. We used Sun Microsystem’s Java
Architecture for XML Binding (JAXB) [21]. JAXB takes
the DIS XML schema as input and produces Java
interfaces and classes that correspond to objects describedin the schema. The generated classes have the ability tomarshal and unmarshal themselves from XML
documents, and have getter and setter methods for theattributes and values specified in the schema. An example
code fragment from a generated Java language interface
file is shown in Figure 4.

public interface HeaderType {byte getProtocolFamily();
void setProtocolFamily(bytevalue);…
}

Figure 4. Java Language Interface File
Generated from the DIS XML Schema
As mentioned, the generated Java classes can marshal andunmarshal themselves from XML documents. The
example XML document in Figure 5 expresses a DIS
PDU that can be directly read and written from the Javaclasses.
Note that not all values defined in IEEE-1278.1 are shownin the XML document. This is the result of the use ofdefault values in the schema. If the value of the field does
not differ from the default value, then it is not printed in
the XML document. Its value is implicit, and retrieving
the attribute or value from the API or XML tool will yield
the default value.
The schema for DIS (which was written manually) and
JAXB together gave us the ability to read and write XML
to Java objects. The ability to marshal and unmarshal toIEEE-1278.1 is another matter. Obviously JAXB has noknowledge of DIS. The programmer must write code tomarshal and unmarshal to binary format DIS. We havewritten code to do this for the major DIS PDUs. Similarcode can be written or generated to marshal the PDUs toother formats or emerging standards, such as the Efficient
XML Interchange (EXI) [22].

<DIS><EntityStatePdu capabilities="0" entityAppearance="0" forceID="0"numberOfArticulationParameters="0"><PduHeader length=”144” pduType="1" protocolFamily="1" timestamp="0"/><EntityID application=”1” entity=”2” site=”0”/><Entity/><AlternativeEntity/><EntityLinearVelocity/><EntityLocation x="62.0"/><EntityOrientation/><DeadReckoningParameters
otherParameters="000000000000000000000000000000"><EntityLinearAcceleration/><EntityAngularVelocity/></DeadReckoningParameters><EntityMarking characterSet="0" characters="0000000000000000000000"/></EntityStatePdu></DIS>

Figure 5. Entity State PDU in XML Format
binary DIS PDUs. The control panel and the Xj3D scene
being driven by the controls are shown in Figure 6.

5. Example Uses
The NPS team and our industry partners have
implemented several examples using DIS-XML.
X3D Scene Binding using Xj3D: X3D [23], from theWeb3d Consortium (http://www.web3d.org), is an open
standard for 3D content. Xj3D [24] is an implementationof an X3D browser. It includes an IEEE-1278.1
networking component, which can read selected DIS
PDUs and use the PDU data to move objects in the 3D
scene. As a simple test we devised a minimal 3D scenethat could be driven by a Java application that generates

Figure 6. X3D scene in Xj3D With IEEE1278.1 PDU Generator

DIS-XML across XMPP Chat. Extensible Messaging
and Presence Protocol (XMPP) is an Internet Engineering
Task Force (IETF) standard for instant messaging [25].
XMPP uses an open XML standard as a basis forconferences and instant messaging. The standard can beused for much more than just instant messaging; it is ineffect an XML-enabled communications backbone thatcan be used to pass XML between automated endpoints.
With the open source Wildfire XMPP server [26] andSmack API [27] we used XMPP as a multicast DIS bridge
between networks that were not multicast-enabled. A
process on one of the multicast islands reads IEEE-1278.1
binary PDUs, converts them into the XML representation,and sends them to an XMPP multi-user chat room

(MUC). On the other network, a process reads XML fromthe XMPP MUC, unmarshals it to the Java object
representation, and then marshals it out on the local
network as IEEE-1278.1 binary format PDUs. For
debugging purposes a user may optionally observe a text
representation of the PDUs by simply joining the MUC
with a standard XMPP client.
Figure 7 shows the earlier DIS-XML PDU example
embedded in an XMPP message. Multiple DIS PDUs canbe embedded in a single chat message, providing
additional efficiency in bandwidth and processing.

<message id=”qoU4g-67”
to=”adarmold@surfaris.cs.nps.navy.mil/Exodus
type=”groupchat”
from=”disxml@conference.surfaris.cs.nps.navy.mil/snerd0”><body>A DISXML message from the sender. </body><properties mlns=http://www.jivesoftware.com/xmlns/xmpp/properties”><property><name>disXML</name><value type=”string”><?xml version=”1.0” encoding=”UTF-8” standalone=”yes”?><DIS><EntityStatePdu capabilities="0" entityAppearance="0" forceID="0"numberOfArticulationParameters="0"><PduHeader length=”144” pduType="1" protocolFamily="1"timestamp="0"/><EntityID application=”1” entity=”2” site=”0”/><Entity/><AlternativeEntity/><EntityLinearVelocity/><EntityLocation x="62.0"/><EntityOrientation/><DeadReckoningParameters
otherParameters="000000000000000000000000000000"><EntityLinearAcceleration/><EntityAngularVelocity/></DeadReckoningParameters><EntityMarking characterSet="0" characters="0000000000000000000000"/></EntityStatePdu></DIS></value></property></properties></message>

Figure 7. Entity State PDU in XML Format Embedded in XMPP Message
Performance is adequate for small quantities of PDUs
when run on commodity laptop hardware. Approximately
100 PDUs per second can be sent across a local XMPP
server. Further server performance optimizations arelikely.

L-3 Communications Link Simulation & Training(Link): Internal Research and Development (IRAD)
efforts have been pursuing commercial web-based andgame-based technologies since 2004, including DIS-XML
and Xj3D implementations. Link has produced numerous

prototypes of a Next Generation Trainer (NGT) to
demonstrate the feasibility of applying these technologies
to the simulation-based training domain. During the 2004
Interservice/Industry Training, Simulation, and Education
Conference, Link demonstrated a scenario comprised of
an F16 flight simulator along with Aviation Combined
Arms Tactical Trainer (AVCATT) Semi-AutomatedForces (SAF) and Xj3D communicating via DIS-XML.
This scenario was enhanced in early 2005 to a multi-site
demonstration, which included four F16 simulatorsconnected through a wide area network (L-3 Corporate
Network). Two of the F16 simulators are located in
Arlington, Texas with 2 more F16 simulators, AVCATT
SAF, and Xj3D in Orlando, Florida. Exercise Control,
Monitoring and Fault Insertion capabilities are located in
Orlando, but controlled via the IOS in Binghamton, New
York. Figure 8 illustrates where DIS-XML and Xj3D
were applied in this configuration. Publishing andsubscribing to data objects through the NGT Event
Handlers provides the capability to communicate between
simulation elements. Events are distributed using the
XML Communications Bus and the Java DIS-XML
gateway to native DIS applications by converting DISXML documents to DIS PDUs and vice versa. A total of
approximately 30 entities were involved in the simulation,and real-time, man-in-the-loop performance was good,with no user-perceived latency in the display. Application
elements interface to the Event Handlers using Java
objects, which are based in part on the Java-DIS-XML
implementation. The Event Handler converts the objects
to DIS-XML documents and publishes them tosubscribers. The XML communications bus was initially
implemented using JBoss Java Messaging Service (JMS).
There are ongoing efforts to evaluate alternative
messaging and data communications mechanisms such as
TCP multicast, SOAP, and HTTP variants.

Figure 8. Link Four F16 Ownship Demonstration
Configuration

Other Uses: The NPS Autonomous Unmanned Vehicle
Workbench (AUVW) project [28] allows mission
planning and analysis for unmanned submersibles and air
vehicles. The AUV Workbench uses realistic physics
models of undersea and air vehicles to generate DIS
packets, which are used to visualize scenes in the Xj3D
browser or embedded Xj3D application panel. The Xj3D
browser has integrated DIS-XML as an alternative
protocol stack for driving entities in the scenegraph.
Entities in Xj3D can be configured to listen on XMPP
multi-user chat rooms for DIS messages in XML format.
Likewise, the AUV Workbench has been configured toallow sending DIS messages in XML format across the
XMPP backbone.
MATLAB [29] is a scientific analysis tool that is widelyused to analyze and chart data. The DIS-XML Javalibraries can be called from within MATLAB. This allows
MATLAB to read DIS network traffic or archived DIS
PDUs from disk in either binary or XML format andmake use of MATLAB’s analysis facilities.

6. Future Work
XML’s main benefit is that it is ubiquitous and often used
as a standard for interchange between formats. Whileuseful, this is really only interoperability on the level ofsyntax. Much more could be done if there was agreement
at the level of data semantics. This requires agreement on
the meaning of the XML elements and attributes. We
have written an XML schema that describes the DIS
PDUs. Another, equally valid schema written by anotherauthor may use different element or attribute names. The
same semantic information is denoted by two different
names, and exchanging XML data between applications
using the two schemas will require manual
disambiguation or other mapping operations. Just as
existing applications can exploit commonality due to thestandardization of IEEE-1278.1 binary PDUs, futureapplications can benefit from a single, agreed-uponstandard for XML representations of DIS. The NPS DISXML schema and codebase has been submitted to the
SISO DIS Working Gropu for further study and potential
standardization.
XML, while a standard for interchange of data, imposes a
significant load on hosts when it is processed. One ideathat is being investigated by several companies andorganizations is a binary format for XML. This would be
more compact than text format XML and be much fasterto parse, while remaining completely interchangeablewith the original text XML. Standardization efforts areunderway; the W3C has set up an Efficient XML
Interchange (EXI) Working Group [22]. In the meantime,several companies are working on their own

implementations, such as Sun Microsystem’s Fast Infoset[30] and the MOVES Institute’s Extensible Schema
Based Compression (XSBC) [18]. A standardized binary
XML format, would, when passed over the network, besomewhat larger than a hand-coded binary protocol, but
probably easier and nearly as fast to parse. If DIS data ispassed between applications in EXI format we anticipate
that this will significantly increase the observed
performance while retaining the benefits of XML. To
further inform ongoing efforts, follow-on work will createa table of all DIS PDUs with size in bytes for DIS native
binary format, DIS-XML text format, DIS-XML
compressed under XSBC, and DIS-XML under the Fast
Infoset.

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[20] World-Wide Web Consortium (W3C): XML
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Acknowledgements
Thanks to Alan Hudson and Justin Couch of Yumetech
for supporting implementation of DIS communications in
the X3D specification and the Xj3D reference
implementation of the X3D standard. Thanks to numerous
NPS students who developed XML encodings of the DIS
PDU formats. Thanks to the DIS Working Group for
review and comment on early drafts of the paper. Thanks
to the XBC Working Group for advancing requirements
for binary XML encodings.

Author Biographies

DON MCGREGOR is a Research Associate in the Naval
Postgraduate School’s Modeling, Virtual Environments,
and Simulation (MOVES) Institute. His research interests
include binary XML, simulation, and high performancecluster computing. Mr. McGregor has an MS in Industrial
Engineering from Oregon State University.
DON BRUTZMAN is a computer scientist and Associate
Professor working in the Modeling, Virtual
Environments, and Simulation (MOVES) Institute andInformation Sciences Department at the Naval
Postgraduate School. He chairs the Undersea Warfare
Academic Committee and USW curriculum. His researchinterests include underwater robotics, real-time 3Dcomputer graphics, artificial intelligence and highperformance networking. He is a member of the Instituteof Electrical and Electronic Engineers (IEEE), theAssociation for Computing Machinery (ACM) Special
Interest Group on Graphics (SIGGRAPH) and theAmerican Association for Artificial Intelligence (AAAI).
He serves on the board on the newly formed World Wide
Consortium for the Global Information Grid (W2COG).
He is a board member of the non-profit Camp SEA Lab
Monterey Bay, which is building a youth-oriented yearround residential science camp. He is a founding memberof the non-profit Web3D Consortium Board of Directors.
He organized and led the SIGGRAPH Online 2001 team,designing and developing a huge audio/video/Web/XML
information archive. Currently he leads the Extensible
3D (X3D) Working Group for the ISO X3D/VRML
Specification, and directs development of numerous
research projects as part of the Extensible Modeling and
Simulation Framework (XMSF). Dr. Brutzman received aPh.D. in Computer Science from the Naval Postgraduate
School.
ADRIAN ARMOLD is a graduate student at the Naval
Postgraduate School’s majoring in Modeling, Virtual
Environments, and Simulation (MOVES). His researchinterests include open source implementations andstandards supporting chat mechanisms for tacticaloperations.
CURTIS BLAIS is a Research Associate in the Naval
Postgraduate School’s Modeling, Virtual Environments,
and Simulation (MOVES) Institute. His research interests
include multi-agent systems and operational ontologies
for semantic interoperability. Mr. Blais has a MS in
Mathematics from the University of Notre Dame. He iscurrently a Ph.D. candidate in MOVES researching an
ontological framework for obtaining valued information
at the right time in semantically rich network-centricarchitectures.

MARK FALASH is a Senior Principal Investigator for
L-3 Communications Link Simulation & Training (Link)
Internal Research and Development in Orlando, Florida.
His current responsibilities involve investigation oftechnologies and products applicable to the next
generation of Link training systems. He is the technicallead for projects applying web based, Information (IT)and Game Technologies to training systems, developmentof training preparedness and readiness tools targetinghomeland security opportunities, and core architecture
and infrastructure for a product line of virtual training
simulators and reconfigurable simulators. He has
published several papers on common architecture
approaches for virtual training systems, IT and web based
infrastructure and use of Operational Analysis in a
training system for Homeland Security. He received an
M.S. in Computer Science from California State
University, Chico.

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EYTAN POLLAK is currently director of Strategic
Technologies at L-3 Communications Link Simulation &Training in Orlando, Florida. Recent projects include thedevelopment of operational analysis techniques, common
simulation architectures, reconfigurable simulators, andsynthetic environment technologies. Dr. Pollak has
provided technical leadership and guidance for distributed
training systems applied to aviation and ground platforms
and external research programs. He has published papers
and awarded patents on operational training analysis,
common architectures for training systems, embedded
simulation, and reconfigurable simulators. Dr. Pollak
serves as adjunct professor of Electrical Engineering at
the University of Central Florida. He received his Ph.D.
from Purdue University.