A Javascript Implementation of the Binary DIS Protocol Don McGregor, Don Brutzman, Curt Blais, MOVES Institute

Javascript & Web Networking Javascript? That’s just a toy language, right? Not any more. Simulation applications can be written in Javascript, and there are significant advantages to doing so New Javascript networking standards (Websockets, WebRTC) allow low latency, high (ish) performance directly into the web page 2

Web Networking 3 Web Server Content: Javascript, 3D, images, graphing, Maps, mash-ups Websocket (Javascript TCP socket) WebRTC (Javascript UDP) Web Page: Internet Explorer Web Page: Firefox Mobile

Web Networking Websockets allow low latency TCP sockets between web page pages and servers in Javascript—no polling, not wrapped in HTTP WebRTC can allow low latency UDP Javascript messages directly between web pages Performance is not bad--~5K messages per second to desktop clients for websockets It’s all unicast—no broadcast or multicast, with all that implies 4

Why Do It? Compelling economic & system management advantages for web-based simulation –Distribute all applications from a central web server, where it can be easily upgraded –Cross-platform, including mobile –Moves at web speed—can mash up with maps, graphics, WebGL, Twitter, IM, … –Scale out on cloud, low barrier to entry. Cloud-side compute resources are effectively infinite –How many desktop apps do you use today, vs how many web based applications? That’s because the economics are that compelling 5

What Message Format? 66 These are the pipes; What format should we send state information such as position and orientation?

Message Format: JSON One option is to send messages in JSON format This is the approach taken by WebLVC But this requires you to specify the format of the JSON Lots of standards meetings 7

Message Format: DIS Classical Javascript wasn’t very good at handling binary More modern Javascript can use “ArrayBuffers” to manipulate binary data Support is good (~80% of current browsers in the wild, will only get better as old browsers are upgraded). See So why not use this to implement classic IEEE ? 8

DIS in Javascript Strong standards support, lots of gateway support for HLA, TENA, AIS, other protocols to DIS It’s already standardized DIS can be verbose and carries redundant information compared to HLA RPR-FOM, which is what WebLVC is based on Protocol issues such as heartbeat 9

Using Javascript DIS 10 // Receive and decode a message NetworkSingleton.prototype.onMessage = function(evt) { // convert from binary to javascript object var pduFactory = new dis.PduFactory(); var pdu = pduFactory.createPdu(evt.data); switch(pdu.pduType) { case 1: ….. // Convert to local (or lat/lon/alt) coordinates var localCoordinates = rangeCoordinates.ECEFtoENU(espdu.entityLocation.x, espdu.entityLocation.y, espdu.entityLocation.z); // Encode DIS var dataBuffer = new ArrayBuffer(1500); var os = new dis.OutputStream(dataBuffer); espdu.encodeToBinaryDIS(os); var trimmedData = dataBuffer.slice(0, os.currentPosition); websocketConnection.send(trimmedData);

Performance Compared to JSON Binary DIS vs JSON-encoded DIS, longer bars better Yellow JSON DIS, red binary DIS 11

Performance Notes See benchmark your own browser, or create new benchmarkshttp://jsperf.com/javascript-dis-native-vs-json/2 Both JSON and binary formats can be workable; depending on Javascript engine they can even be about the same Browsers and Javascript engines matter a lot! JSON can be as fast as binary on some browsers and Javascript engines (IE 11, for example) JSON can be faster on IE 11 than binary on Firefox I suspect in the long term results will converge towards the current Safari benchmarks as Javascript engines improve OK performance on mobile—and it works on mobile! OK for a few thousand messages per second into the web page (depending on lots of stuff) which puts about a 10% load on desktop CPU In general, the simulation implementation is more likely to be an issue than the networking overhead, particularly with 3D. 12

Binary Javascript DIS Vs WebLVC 13 WebLVC JSON update messages have less state information and can be parsed somewhat faster, but it’s in the same ballpark WebLVC can also avoid DIS heartbeats

Google Maps Example Application on server side listens for traditional native UDP DIS on the local ethernet network. In this case, AIS (real time commercial ship locations) is being translated into DIS by JBUS Web page receives forwarded DIS messages via websockets, decodes, does coordinate conversion to lat/lon, displays icon on map. Also sends DIS updates based on web browser geolocation Uses Google Maps Javascript API to implement a real-time mapping application. Works on modern browsers and mobile, including IOS and Android 14

Google Maps + DIS in Browser 15

Availability Free, BSD non-viral license open-dis-code/ –Includes server side code (to convert native UDP to websocket transport) and client code in languages/javascript directory NodeJS is a scalable server-side Javascript framework popular in Silicon Valley (used at linkedin, twitter, ebay, etc.) –NodeJS DIS javascript module available at 16

Future Work Open Street Map vs Google Maps to avoid proprietary vendor dependencies, requirement to have a Google Maps server inside classified areas Server side architecture for scalability: how much to put on client vs server? How to limit traffic to the client? Inherent unicast problems as the number of clients increase? Node.js transport gateways on the server side? Integration with voice, video in web browsers and DIS intercom PDUs Integrate with 17