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Intro and Problem Statement Don McGregor Research Associate MOVES Institute firstname.lastname@example.org
MV-3500 DoD Modeling & Simulation Network Protocols
Admin This class is intended to introduce you to the simulation network protocols used in DoD M&S applications This will require a little background on networking first, then we can look at two of the major protocols, DIS and HLA.
Admin Grading Two midterms (50%) Final project (25%) Programming assignments (25%) Contact: Watkins 281 (stop by any time) Phone (don’t) x-7605 Email:mcgredo at nps edu; put MV3500 in the subject Web page: https://www.movesinstitute.org/~mcgredo/MV3500
Textbook Networked Graphics, Steed & Oliveira Read chapters 1 & 2 Chapter 2 will probably be over your head a bit; just roll with it.
Other Sources “I want to know everything about networking” Stevens: Unix Network Programming and TCP/IP Illustrated (V 1, 2, 3) Zyda: Networked Virtual Environments Gaffer on Games: http://gafferongames.com/http://gafferongames.com/ Game Developer’s Conference Some commercial techniques are encumbered with intellectual property restrictions Neyland: Virtual Combat: A Guide to DIS SISO: DIS Plain and Simple Alexander, Massively Multiplayer Game Development
Live, Virtual, Constructive The military wants to do a variety of simulations, including but not limited to Live: Real people, real systems Virtual: Real people, simulated systems Constructive: simulated people, simulated systems
Live An E-5 is driving a Stryker at NTC. The Stryker is generating Blue Force Tracker data. This is a real person driving a real vehicle. Perhaps he sees other live vehicles on his BFT. To increase the training experience, we might want to display simulated enemy forces as well. The training exercise is now no longer completely live—the BFT may be displaying computer-generated forces as well, a constructive element
Virtual An F-18 pilot is in a 6-axis dome simulator. This is a simulated weapon controlled by a real person. We can inject the Stryker BFT data into the F-18 simulator so that the pilot sees Strykers on the ground on the simulated NTC terrain The training now has live and virtual components
Constructive Suppose we don’t have all the live simulation red force necessary to achieve the training objectives. We can create computer-generated, AI-controlled tanks and inject them into the training environment The E-5 on the Stryker may see these on his situational display The F-18 pilot can see the computer-generated forces in his dome terrain The training is live, virtual, and constructive
How Do We Get There? Notice that these all involve sending data between computers, sometimes computers that are a long ways apart geographically What data do we want to send? What semantics do we need? What about practical issues, like latency and reliability? What if the computers are running different operating systems on different CPU architectures? What if the Stryker is using BFT and the dome simulator something else? Can you come up with some examples of the state data that we need to exchange?
Data (X,Y,Z), orientation, what entity type, terrain, velocity, unique entity identifiers, ….
Semantics Semantics are “meaning” associated with the values we send. Can you just transmit a few bytes of data to another host and call it good? Three floating point numbers (X,Y,Z) isn’t enough— also implied is a coordinate system with which those values are associated. These are the semantics associated with the three floating point numbers Are they referring to lat/lon/altitude? MGRS? What units? Where is the origin? How do we determine a position message is referring to a particular M1A2 tank? Semantics is extremely tricky to do in the general case. It is basically all the assumptions you make about data values
Practical Issues The speed of light limits network traffic speed, and the reality is often much worse. Human reaction time is around 250ms, and long haul network latency can often approach or exceed this. This can make “twitch” applications tricky; air to air combat, first person shooter, etc What if we send a message and it doesn’t arrive?
What Do We Want to Do? “Get relevant data to other computers in a format that can be understood, fast enough to be useful” This problem statement also happens to coincide with a lot of other commercial applications. The DoD uses the standards adopted by industry for “basic plumbing”, and adds its own “protocols” for its applications
Commercial Applications First Person Shooter Games: Modern Warfare, Call of Duty et al Massively Multiplayer Online Games (MMOG). Large scale, with thousands or tens of thousands of participants. World of Tanks Online worlds--live simulations and role playing in a virtual world; less emphasis on physics, more on human interaction. Second Life, Open Simulator To an extent there has been a convergence between the capabilities of military & commercial, but commercial is heavily focused on games What’s the difference between training and games, anyway? More of an issue of the goals than the technology
Protocols What do network protocols do? Basically, they are an agreed-upon way for applications to talk to each other If you have a Boeing flight simulator and a General Dynamics tank simulator and a Hughes helicopter trainer, it would be helpful if all of them could cooperate in the same networked virtual environment
“NVE?” Huh? What’s a “Networked Virtual Environment?” An illusion of a virtual environment that is shared between participating users. This is typically done across a network. In the tanks & helos example, we have a virtual battlefield, users controlling vehicles, and each user can view the virtual world from their own point of view.
Protocols So how do simulations talk to each other? Generally this happens across the network (“distributed”) as multiple computers cooperate on the problem. The substrate used by all modern simulations is TCP/IP sockets. This is a protocol, but DoD simulation protocols are built on top of TCP/IP Simulation protocols started with ad-hoc protocols, made up for each task Moved on to Distributed Interactive Simulation (DIS) and High Level Architecture (HLA) Web-based protocols are emerging
Simplified Diagram “Basic Plumbing”: TCP/IP “Semantics”: Simulation Protocol (DIS, HLA, etc) The Application: OneSAF, VBS2, etc Host 1 “Basic Plumbing”: TCP/IP “Semantics”: Simulation Protocol (DIS, HLA, etc) The Application: OneSAF, VBS2, etc The Network:State information messages sent Host 2
Protocols What if Strykers are generating BFT data with (X, Y, Z) in lat/lon/altitude, and the dismounted infantry simulator is using a simulation protocol coordinate system that using MGRS? The contents of the protocols are slightly different, in different order, floats vs. doubles, different semantics, etc. The lowest level, TCP/IP, simply ships bytes around with no knowledge of the contents In our simplified diagram, the protocols are in the second row of boxes The simulation application (VBS2, OneSAF, etc) make use of the protocols What happens if an application sends a DIS protocol message to an HLA application? What happens if VBS2 sends a DIS message to another DIS application?
Installed Base vs Emerging From the 90’s until very recently the classic thing to do was run desktop simulation applications written in compiled C++ or Java applications. This has meant a lot of conventional programming and network programming I think the world is moving towards web-based and cloud-based applications, which require some different technology The economics are compelling. See the lack of desktop applications when compared to web applications. 10 years ago you installed a desktop mail application; now you use a web-based mail application Good integration with mobile devices
Installed Base Technology Compiled App Compiled Apps Communicating Over Network
Brave New World The transition makes teaching the class a bit difficult. Most of the installed base of simulations use the compiled applications on workstations model. Much of the future is oriented towards the web. The technologies used are very different, and requires some context switching. We’ll try to give you some of both, but remember to keep clear which is which
Background During this class, we’ll look at each of these elements: – TCP/IP sockets – Ad-hoc protocols – DIS – HLA – Web Technology