4 ms·

TCP for twitch game? Ugh. Cool that you're getting a ton of throughput but you don't use UDP for throughput, you use it so that the one dropped packet doesn't

TCP for twitch game? Ugh. Cool that you're getting a ton of throughput but you don't use UDP for throughput, you use it so that the one dropped packet doesn't back up all of your time-sensitive data. You want to drop packets that are out of order since you're using dead-reckoning to keep the game state psuedo-in-sync. Seriously, there's a reason everyone uses UDP(or IPX!) since the days of doom.

corysama 11y ago
The whole article is about doing a test to see if they can get away with using TCP instead of UDP. They end up pretty pleased with the results. Though, they don't spend nearly as much time talking about latency as they do about throughput. > For our high throughput needs, prevailing wisdom would suggest you need to write your server in C++, use UDP rather than TCP and run on a very high spec bare metal box running linux. We are already running the client in javascript; so if we ran over TCP (websockets), wrote the server code in managed C#, ran on Windows on a VM in the cloud – is this just madness?
benaadams 11y ago
Its a constraint of the browser technology stack; not only do we have to use websockets for real-time (TCP/IP) but we also have to go over SSL/TLS as intermediary hardware/software (routers, proxies etc) still routinely break websocket connections otherwise. (Disclaimer: Author of article)
- vvanders 11y ago
  I really hope your game designers know how to mask latency. If you're going over TCP/IP then expect to need to resolve a game model that can sustain at least ~750ms of latency. I totally understand the browser constraint part but you're going to hit some serious issues once you start having real-world clients that have >3% packet drop. It gets even worse when you start adding different discrete layers on a single TCP connection(chat, larger game state not related to twitch parts, etc). Each one of those channels has the chance to drop a single packet and then your whole world comes to a stop until you can roundtrip that single packet that's unrelated to the realtime info you care about. FWIW most stacks end up implemented channels over UDP with unreliable+unordered, reliable+unordered and reliable+ordered for the different latency needs of the specific channel. I've done a fair bit of this stuff in a production environment and have to echo my original comment. TCP is great for lockstep but if you're doing dead-reckoning it will fall apart on anything other than a LAN. Edit: I also don't mean this as a dig, just that I've seen many teams go through this and it's usually at a point where it's too late to make any changes.
  - benaadams 11y ago
    Not saying its easy and we have discovered the reason most MMOs have long wind up animations for actions... The other layers (chat, non-space game state) are handled by discrete microservices on other connections to other hosts - to keep the space flight data slim and connection dedicated in use. Can always give it a try, our next public playtest is on Saturday 6 Feb 8pm GMT/UK | 12pm Pacific | 3pm Eastern US at http://www.ageofascent.com/ http://www.ageofascent.com/ Just don't try it on a phone; give us a chance with the latency ;-)
    - vvanders 11y ago
      I wish you the best of luck but I really think you've got a poor technology fit for what you're trying to do. Games like SubSpace/Continuum were doing 300+ player twitch based on UDP based connections over 56k dialup back in '97. Any sort of packet loss(and subsequent TCP exp backoff) is going to weak havok on your latency.
      - terry526 11y ago
        Listening to this podcast atm; interesting stuff. http://hanselminutes.com/509/inside-age-of-ascent-with-ben-adams http://hanselminutes.com/509/inside-age-of-ascent-with-ben-a...
      - Scaevolus 11y ago
        "Windows/DirectX/UDP is too well-supported and mainstream, let's build a twitch MMO using Javascript/WebGL/WebSockets!" I wonder what the intersection of "people that want to play MMOs" and "people that don't want to install anything" is. There are good game streaming technologies (e.g. Guild Wars) that minimize the patch time, so it feels like a bit of a straw-man.
      - twodave 11y ago
        Holy cow, talk about a flashback. I played the crap out of that game for about a decade.
        11y ago
- jsprogrammer 11y ago
  WebRTC can give you UDP semantics.
- devit 11y ago
  You can probably work around this issue by using hundreds of parallel TCP connections in a round robin fashion. Assuming you are sending a packet per frame, this setup means that you are only sending a packet every few seconds per TCP connection, which means retransmissions should have already happened by the time you send another packet.

corysama 11y ago

The whole article is about doing a test to see if they can get away with using TCP instead of UDP. They end up pretty pleased with the results. Though, they don't spend nearly as much time talking about latency as they do about throughput. > For our high throughput needs, prevailing wisdom would suggest you need to write your server in C++, use UDP rather than TCP and run on a very high spec bare metal box running linux. We are already running the client in javascript; so if we ran over TCP (websockets), wrote the server code in managed C#, ran on Windows on a VM in the cloud – is this just madness?

benaadams 11y ago

Its a constraint of the browser technology stack; not only do we have to use websockets for real-time (TCP/IP) but we also have to go over SSL/TLS as intermediary hardware/software (routers, proxies etc) still routinely break websocket connections otherwise. (Disclaimer: Author of article)

vvanders 11y ago
I really hope your game designers know how to mask latency. If you're going over TCP/IP then expect to need to resolve a game model that can sustain at least ~750ms of latency. I totally understand the browser constraint part but you're going to hit some serious issues once you start having real-world clients that have >3% packet drop. It gets even worse when you start adding different discrete layers on a single TCP connection(chat, larger game state not related to twitch parts, etc). Each one of those channels has the chance to drop a single packet and then your whole world comes to a stop until you can roundtrip that single packet that's unrelated to the realtime info you care about. FWIW most stacks end up implemented channels over UDP with unreliable+unordered, reliable+unordered and reliable+ordered for the different latency needs of the specific channel. I've done a fair bit of this stuff in a production environment and have to echo my original comment. TCP is great for lockstep but if you're doing dead-reckoning it will fall apart on anything other than a LAN. Edit: I also don't mean this as a dig, just that I've seen many teams go through this and it's usually at a point where it's too late to make any changes.
- benaadams 11y ago
  Not saying its easy and we have discovered the reason most MMOs have long wind up animations for actions... The other layers (chat, non-space game state) are handled by discrete microservices on other connections to other hosts - to keep the space flight data slim and connection dedicated in use. Can always give it a try, our next public playtest is on Saturday 6 Feb 8pm GMT/UK | 12pm Pacific | 3pm Eastern US at http://www.ageofascent.com/ http://www.ageofascent.com/ Just don't try it on a phone; give us a chance with the latency ;-)
  - vvanders 11y ago
    I wish you the best of luck but I really think you've got a poor technology fit for what you're trying to do. Games like SubSpace/Continuum were doing 300+ player twitch based on UDP based connections over 56k dialup back in '97. Any sort of packet loss(and subsequent TCP exp backoff) is going to weak havok on your latency.
    - terry526 11y ago
      Listening to this podcast atm; interesting stuff. http://hanselminutes.com/509/inside-age-of-ascent-with-ben-adams http://hanselminutes.com/509/inside-age-of-ascent-with-ben-a...
    - Scaevolus 11y ago
      "Windows/DirectX/UDP is too well-supported and mainstream, let's build a twitch MMO using Javascript/WebGL/WebSockets!" I wonder what the intersection of "people that want to play MMOs" and "people that don't want to install anything" is. There are good game streaming technologies (e.g. Guild Wars) that minimize the patch time, so it feels like a bit of a straw-man.
    - twodave 11y ago
      Holy cow, talk about a flashback. I played the crap out of that game for about a decade.
      - 11y ago
jsprogrammer 11y ago
WebRTC can give you UDP semantics.
devit 11y ago
You can probably work around this issue by using hundreds of parallel TCP connections in a round robin fashion. Assuming you are sending a packet per frame, this setup means that you are only sending a packet every few seconds per TCP connection, which means retransmissions should have already happened by the time you send another packet.