{"id":2091,"date":"2017-12-01T14:40:04","date_gmt":"2017-12-01T05:40:04","guid":{"rendered":"http:\/\/www.codedojo.com\/?p=2091"},"modified":"2020-02-27T10:01:00","modified_gmt":"2020-02-27T01:01:00","slug":"stress-testing-unitys-llapi-what-are-the-limits","status":"publish","type":"post","link":"https:\/\/www.codedojo.com\/?p=2091","title":{"rendered":"Stress testing Unity’s LLAPI, what are the limits?"},"content":{"rendered":"
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NetTest – a tool for stress testing the LLAPI, full Unity project download at the bottom!<\/p><\/div>\n

Update 2\/27\/2020:\u00a0 Don’t use LLAPI, Unity is going to stop working on it at the end of 2020 so you’ll be screwed I guess.\u00a0 <\/em><\/h1>\n

Luckily their replacement netcode isn’t ready yet so now you don’t know what to do except maybe try third party libraries or use simple TCP sockets.\u00a0 Thanks, Unity<\/em><\/h1>\n

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Seth, what the hell do you know about netcode, anyway?!<\/h1>\n

Woah, with the attitude already.\u00a0 Look, I’m all about multiplayer.\u00a0 Have<\/a> been<\/a> for a long time<\/a>.\u00a0 I’ve gone from being excited to get two people walking on the same ANSI map in LORD2<\/a>\u00a0in the early 90s to hitting the 70,000 concurrent user mark during busy times in Growtopia<\/a>.<\/p>\n

In addition to writing my own junk<\/a>, I regularly play with Unity and Unreal and am constantly trying to see how they can fit my developing style – mostly\u00a0I need them because it’s becoming a losing battle to try to maintain your own 3D engine if you also want to actually design and release games too.<\/p>\n

What’s LLAPI, anyway?<\/h1>\n

LLAPI stands for Low Level Application Programming Interface.\u00a0 It’s what Unity’s HLAPI (High level) API is built on.\u00a0 I guess both of those can be called part of UNet. (Unity networking)<\/p>\n

Why not just use the HLAPI like a normal person?<\/h1>\n

That might be ok for some projects, especially round-based networked games without too many players.<\/p>\n

When you are targeting MMO level network performance where a server may have to track stats of millions of players and simulate a world for weeks instead of minutes, the first rule is:<\/p>\n

Stay as low level as you reasonably can.\u00a0<\/strong><\/h3>\n

I don’t want someone else’s net code to even think about touching my gameobjects, I just want it to deliver reliable\/unreliable packets that I write\/read straight bytes to.\u00a0 That’s it.\u00a0 I want to handle things like prediction, dead reckoning, and variable serialization, myself!<\/p>\n

What’s the deal with UDP, TCP, and WebSockets?<\/h1>\n

Both UDP<\/strong> and TCP<\/strong> are internet protocols built on top of IP.<\/p>\n

TCP<\/strong>\u00a0is a bidirectional socket based connection that insures your data is correct and sent in the right order.<\/p>\n

It’s like calling Jeff, he picks up the phone and you can both talk until one of you puts the phone down.\u00a0 Oh, and after you say something, you make sure Jeff understood you correctly each time, so that eats up a bit of time.<\/p>\n

UDP\u00a0<\/strong>is is a stateless connection where single packets get sent.\u00a0 You write your message on a rock and throw it at Jeff’s window.\u00a0 While it gets there fast, it’s possible you’ll miss and Jeff will never see it. If dozens of people are throwing rocks, he needs to examine each one carefully to figure out which pile to put it with so the text is attributed to the right thrower.\u00a0 He might read the second rock you threw before the first one.<\/p>\n

WebSockets<\/strong>\u00a0are basically TCP<\/strong> with a special handshake that’s done over HTTP first.\u00a0 To continue this already questionable analogy, it’s as if you had to call Jeff’s mom for permission, and then she gave you his cell number to call.<\/p>\n

In theory WebSocket performance could be similar to TCP but in practice they are much slower and unreliable, I don’t really know why but hey, that’s what we get.\u00a0 I suspect this will improve later.<\/p>\n

For games, UDP is nice because you can send some of your packets fast with no verification that they were received, and others (more important packets, like dying) with verification which sort of makes those packets work like TCP.<\/p>\n

That said, most games probably would be ok with a straight TCP\u00a0 steam as well and having a connected state can make things easier, like easily applying SSL to everything and not worrying about unordered packets.<\/p>\n

Why use WebSockets instead of UDP or TCP? Just use UDP or TCP for everything, moran<\/h1>\n

BECAUSE I CAN’T!\u00a0 Browsers won’t allow the Unity plugin to run anymore, they just allow straight javascript\/WebGL these days.\u00a0 It hurts.\u00a0 I mean, I wrote a cool\u00a0multiplayer space taxi test<\/a> for Unity using TCP sockets and now nobody can even play it.<\/p>\n

What does LLAPI use?<\/h1>\n

It can read from both sockets (UDP) and WebSockets at the same time and route them so your game can let them play together.\u00a0 But how fast is it, and does it work?<\/p>\n

This brings us to the second rule of netcode:<\/p>\n

Use stress tests without game code to notice glaring problems early and more clearly<\/h3>\n

Which finally brings us to the point of this post.\u00a0 NetTest<\/strong> is a little utility I wrote that can:<\/p>\n