5 ms·

> The article describes TCP as evil, but then they go on to reimplement TCP over UDP in a way more inefficient manner, not realizing their problems with TCP wer

by exDM69 13y ago

> The article describes TCP as evil, but then they go on to reimplement TCP over UDP in a way more inefficient manner, not realizing their problems with TCP were problems with the internet. Almost every real-time game out there "re-implements" parts of TCP over UDP because the mechanisms that TCP use are unsuitable for real time communication. If a packet goes lost over a 150 ms latency (something modern game engines manage gracefully), the server will receive a resent packet that contains information from 450 ms ago. Additionally a packet going lost with TCP will inhibit the delivery of successfully received packets that were sent after the one gone missing. Re-sending an old packet (like TCP does) is worse than not receiving the packet at all in multi player gaming. You do need (semi-) reliable delivery, connection management and flow control over UDP but implemented differently than TCP. When a packet goes lost, you send the up-to-date information instead, not what was relevant 300 ms ago. TCP is a wonderful protocol but absolutely useless for multi player gaming. Everyone who has been writing netcode for real-time games (there are exceptions like RTS, MMORPG, etc) knows that.

louiz 13y ago
I think “real-time” does not mean what you think it means. I’ve read a lot of things like “TCP is not suitable for real-time online games”, in this thread, where the author of this sentence excludes RTS, MMORPG, etc. As if these were not real-time games. According to http://en.wikipedia.org/wiki/Real-time_game#Real-time http://en.wikipedia.org/wiki/Real-time_game#Real-time (and also the fact the RTS means real-time strategy), any game that is not turn based is a real-time game. It’s not just you, but I had to choose one of the posts in this thread for my response. Saying “TCP is a wonderful protocol but absolutely useless for multi player gaming” is just plain wrong. A lot of online, real-time games are using TCP. Saying that TCP is useless for multi player gaming is really misleading and I’m tired of reading this. There are a lot of valid reason to choose TCP over UDP (for example the fact that your game doesn’t require any round-trip to be shorter than, say, 500ms, because that’s how the engine works). Of course, TCP would not really be suitable for an FPS like quake, but that’s only one case of real-time game, there are a lot of different kind of games, for which TCP is the best choice.
- exDM69 13y ago
  > I think “real-time” does not mean what you think it means. There are various definitions of "real-time" and we should not make this an argument about semantics. I meant real-time in the sense of "a soft real time software system" or the "Quake" sense of the word. http://en.wikipedia.org/wiki/Real-time_computing#Criteria_for_real-time_computing http://en.wikipedia.org/wiki/Real-time_computing#Criteria_fo... In other words, "real-time" in the sense that missing deadlines will mean that the quality of service is degraded. Deadlines here mean delivering the packets in time for the next simulation timestep. Yes, TCP can be successfully used in games classified as "real time" as opposed to turn based, such as RTS games or MMORPGs. But when analyzing it them from a software standpoint, they might be just very fast turn based games. Here's another interesting piece about networking multiplayer games, this time in an RTS game (Age of Empires): http://www.gamasutra.com/view/feature/3094/1500_archers_on_a_288_network_.php http://www.gamasutra.com/view/feature/3094/1500_archers_on_a... The solution they used was essentially a 15 frames per second lock step loop. It looks like real time to the player but from a software standpoint it really isn't. You and I agree on everything except the definition of "real-time". There are applications where TCP works well and applications where UDP is better. I'm sorry if my words were a bit overgeneralized and it annoys you.
  - mcguire 13y ago
    Could you provide an example of a real-time game?
    - exDM69 13y ago
      For some definition of real-time, a racing simulator is real-time because it will produce incorrect results (with catastrophic consequences) if there is too much latency. An RTS like Age of Empires is not because it will only lag annoyingly but still produce correct results.
    - hnisnotreddit 13y ago
      Here's two: Kaillera: https://en.wikipedia.org/wiki/Kaillera https://en.wikipedia.org/wiki/Kaillera GGPO: https://en.wikipedia.org/wiki/GGPO https://en.wikipedia.org/wiki/GGPO

by exDM69 13y ago

louiz 13y ago

I think “real-time” does not mean what you think it means. I’ve read a lot of things like “TCP is not suitable for real-time online games”, in this thread, where the author of this sentence excludes RTS, MMORPG, etc. As if these were not real-time games. According to http://en.wikipedia.org/wiki/Real-time_game#Real-time http://en.wikipedia.org/wiki/Real-time_game#Real-time (and also the fact the RTS means real-time strategy), any game that is not turn based is a real-time game. It’s not just you, but I had to choose one of the posts in this thread for my response. Saying “TCP is a wonderful protocol but absolutely useless for multi player gaming” is just plain wrong. A lot of online, real-time games are using TCP. Saying that TCP is useless for multi player gaming is really misleading and I’m tired of reading this. There are a lot of valid reason to choose TCP over UDP (for example the fact that your game doesn’t require any round-trip to be shorter than, say, 500ms, because that’s how the engine works). Of course, TCP would not really be suitable for an FPS like quake, but that’s only one case of real-time game, there are a lot of different kind of games, for which TCP is the best choice.

exDM69 13y ago
> I think “real-time” does not mean what you think it means. There are various definitions of "real-time" and we should not make this an argument about semantics. I meant real-time in the sense of "a soft real time software system" or the "Quake" sense of the word. http://en.wikipedia.org/wiki/Real-time_computing#Criteria_for_real-time_computing http://en.wikipedia.org/wiki/Real-time_computing#Criteria_fo... In other words, "real-time" in the sense that missing deadlines will mean that the quality of service is degraded. Deadlines here mean delivering the packets in time for the next simulation timestep. Yes, TCP can be successfully used in games classified as "real time" as opposed to turn based, such as RTS games or MMORPGs. But when analyzing it them from a software standpoint, they might be just very fast turn based games. Here's another interesting piece about networking multiplayer games, this time in an RTS game (Age of Empires): http://www.gamasutra.com/view/feature/3094/1500_archers_on_a_288_network_.php http://www.gamasutra.com/view/feature/3094/1500_archers_on_a... The solution they used was essentially a 15 frames per second lock step loop. It looks like real time to the player but from a software standpoint it really isn't. You and I agree on everything except the definition of "real-time". There are applications where TCP works well and applications where UDP is better. I'm sorry if my words were a bit overgeneralized and it annoys you.
- mcguire 13y ago
  Could you provide an example of a real-time game?
  - exDM69 13y ago
    For some definition of real-time, a racing simulator is real-time because it will produce incorrect results (with catastrophic consequences) if there is too much latency. An RTS like Age of Empires is not because it will only lag annoyingly but still produce correct results.
  - hnisnotreddit 13y ago
    Here's two: Kaillera: https://en.wikipedia.org/wiki/Kaillera https://en.wikipedia.org/wiki/Kaillera GGPO: https://en.wikipedia.org/wiki/GGPO https://en.wikipedia.org/wiki/GGPO