In short, TCP will work hard to deliver 100% of the packets. So when a packet is lost, TCP asks to re-send the packet. This is fine to display a webpage or send a file, but it can't be tolerated in games where time continuity matters. I think it's the same issue in VOIP and video conferencing too.
UDP vs TCP
131–140 of 198 posts
Re: UDP vs TCP
#132The entire article makes me shudder in disbelief. It's aimed at people who don't know the difference between UDP and TCP (and possibly wet string). Yet he recommends they implement their own reliably protocol over UDP, and they avoid TCP because it's better to implement your own QoS? Why not add obtaining PhD in quantum mechanics just to round it out? It wouldn't alter the odds of pulling it off overly.
It's framed in the context of building networking for action games that are sensitive to networking. Fourth paragraph:
The choice you make depends entirely on what sort of game you want to network.
So from this point on, and for the rest of this article series, I’m going to assume you want to network an action game.
You know games like Halo, Battlefield 1942, Quake, Unreal, CounterStrke, Team Fortress and so on.Re: UDP vs TCP
#133Earlier quoted context omitted.
It's a bit dogmatic to state "never use TCP". In the context of games, one example that comes to mind is turn-based multiplayer games (Hearthstone, for example). In this case, I would at least consider TCP over UDP as the overall amount of packets transmitted within a session is relatively low and packet loss is more consequential than latency. As far as negative interactions between TCP and UDP on the same interface…
It's a bit dogmatic to state "never use TCP". I was wondering about this too. Yesterday in the "WebRTC: the future of web games" post we had Matheus28, the creator of Agar.io, saying that his games are built on WebSockets, a TCP-based protocol. Agar.io is real-time and massively multiplayer, and seems to run smoothly enough. So is it completely critical to use UDP? I am curious as someone who has recently gotten into…
I'd argue that Agar would run smoother on UDP. The decision was not really a decision here. WebSockets provide TCP only. One can use WebRTC data channels now but there are still issues woth compatibility.
And it's all tradeoffs. For example, Ultima Online used TCP and worked relatively fine on decent networks. In case of a packet drop, you'd observe a complete pause on the world but most animations / movement had a 100ms or more buffer area. If you wanted to move some direction, your character would start moving, if there was no ack after a single step (100ms if running) then it would stop. The world was being streamed as diffs from previous state so it depended on tcp's reliability.
Anarchy online used udp for game and tcp for chat. While the OP argues against this, I think it is a good seperation. I remember playing it on a congested network and the game state fucked up really bad. Tunneling over a tcp stream to a vps server close to game servers made it playable for my case. Maybe they should have gone with tcp. Or their networking code did not compensate for UDP's issues better.
On the other hand, anything more action packed like a fps would probably be better off with UDP as the author suggests.
Re: UDP vs TCP
#134What are some alternative protocols? It's been a while since my networking class, but if I remember correctly with UDP you have some serious issues where you can end up clobbering your network, filling up buffers in the middle and dropping tons of packets. The lack of congestion control is a huge no-no. For instance in the example he gives, sure you can tolerate dropped packets for player-position data, but how do yo…
DCCP and SCTP are the two main alternative transport protocols on top of IP
- UDP: unordered unreliable datagrams
- DCCP: unordered unreliable datagrams with congestion control
- SCTP: optionally-ordered reliable datagrams with congestion control
- TCP: ordered reliable stream with congestion control
Re: UDP vs TCP
#135I think tcp have an unfair reputation. Our networks are better now then 30 years ago ... Worst case latency for tcp is like 3 seconds, compared to the packet never arriving. The trick is to hide the lag with animations. I think google, facebook, and world of warcraft use tcp for their real time apps !?
Sad to see you being downvoted when you're absolutely right. Yes, UDP is better for a twitch game, at the expense of a lot more work. No, unless you're building a AAA mouse-and-keyboard shooter, you probably don't need more than a TCP connection sending data packets back and forth using a somewhat well-thought-out protocol.
I think the biggest mistake is only testing the app on localhost. While real world users can experience up to 150ms latency and fluctuations. It doesn't matter if you use TCP or UDP you still need a strategy for handling different levels of latency. For testing I use netem to add delay ...
The second biggest mistake is trusting the client. People never cheat in online games, right !? smile Network latency is often less then it takes to render, so naive solutions with simple broadcast servers work well until you need to deal with rouge clients using teleport hacks etc.
There are no set rules when making real time distributed and scalable applications like MMO Games. In my experience it's best to start with a naive demo/prototype to see where the bottlenecks are. I would suggest starting with TCP and then only switching to UDP, or more likely making your own protocol (TCP ontop of UDP smile), when you know the requirements.
Re: UDP vs TCP
#136Earlier quoted context omitted.
I'm not sure I follow your argument. Say I want to communicate from player A the position of player A to player B. The position is really only relevant for a 200 ms time frame or so (the game might support teleports, jumping, dashing, etc). In a TCP setting, even if a packet is old (>200ms), I have no choice but to send it regardless, and all new packets must queue behind it. The whole point behind using UDP for game…
You're right in that UDP will let you send the most updated data without requiring everything to be sent. My main issue was that UDP does not give you lower latency. TCP algorithms are extremely aggressive to the point I doubt you could get more recent packets on the wire with UDP. The problem is, the OS throws everything into the same buffer, and unless you're clairvoyant you won't be able to skip sending old packet…
Waiting for retransmission of a lost segment in front of you in the queue is massive latency.
Re: UDP vs TCP
#137The main difference between TCP and UDP, as this programmer discovered, relates to quality of realtime service. Times to use UDP over TCP * When you need the lowest latency * When LATE data is worse than GAPS (loss of) in data. * When you want to implement your own form of error correction to handle late/missing/mangled data. TCP is best when * You need all of the data to arrive, period. * You want to automatically m…
People talk like most games use UDP, but they don't.
Pretty much the only genre that does is First Person Shooters.
MMOs (like world or warcraft) MOBAs (like Dota) RTSs (like Starcraft) Action RPGs (like Diablo)
All of these are action games and use TCP.
In most genres people would rather have the simulation pause when there is packet loss, and then run fast to catch up rather than have unreliable data about player locations.
Due to the large number of geographical locations you can have your servers in these days, it's common for most of your players to have pings <30ms. With that kind of latency and a few tweaks, it's possible for a single packet lost to be recovered very quickly with TCP.
Re: UDP vs TCP
#138The main difference between TCP and UDP, as this programmer discovered, relates to quality of realtime service. Times to use UDP over TCP * When you need the lowest latency * When LATE data is worse than GAPS (loss of) in data. * When you want to implement your own form of error correction to handle late/missing/mangled data. TCP is best when * You need all of the data to arrive, period. * You want to automatically m…
People talk like most games use UDP, but they don't. Pretty much the only genre that does is First Person Shooters. MMOs (like world or warcraft) MOBAs (like Dota) RTSs (like Starcraft) Action RPGs (like Diablo) All of these are action games and use TCP. In most genres people would rather have the simulation pause when there is packet loss, and then run fast to catch up rather than have unreliable data about player l…
>> In most genres people would rather have the simulation pause when there is packet loss, and then run fast to catch up rather than have unreliable data about player locations.
I thought that modern games use interpolation to compensate for this, because network lags are always present in WAN.
Re: UDP vs TCP
#139Earlier quoted context omitted.
People talk like most games use UDP, but they don't. Pretty much the only genre that does is First Person Shooters. MMOs (like world or warcraft) MOBAs (like Dota) RTSs (like Starcraft) Action RPGs (like Diablo) All of these are action games and use TCP. In most genres people would rather have the simulation pause when there is packet loss, and then run fast to catch up rather than have unreliable data about player l…
>> In most genres people would rather have the simulation pause when there is packet loss, and then run fast to catch up rather than have unreliable data about player locations. I thought that modern games use interpolation to compensate for this, because network lags are always present in WAN.
You can't use interpolation to compensate for late packets. Interpolation is generating data between two data points that you have.
You are talking about extrapolation which is the prediction of future data from previous data points.
Once again, First Person Shooter games will tend to do extrapolation, but few games of other genres do that kind of thing.
Re: UDP vs TCP
#140That's a pretty obnoxious 'donate' button. They can't make it even larger?
The guy is providing valuable information for free, he can make his donate button as large as he wants.
Yeah, sure. He can put the Donate button all over the screen if he wants but then no-one would donate. I also think it's obnoxious.