Hi everyone,

I want to build a small client-server network for a spaceship game using TCP [to simplify things].

I'm kind of new on game network programming so i searched a bit on the web and it seems to me that

the easiest implementation is quake 3-like network algorithm.

note:a easy-to-program solution is preferable to one with high performance (within limits of course)

I was thinking to let the server manage the REAL state of the game and send information of it to the clients.

Meanwhile,clients only send "controller input data" for example

"client X has pressed button01" that mean he want to move forward etc.

"client X has pressed button02" that mean he want to fire primary weapon and so on.

Thinking about this,since it's my first experience in this kind of programming i've some question that come to mind:

-It should be safe since all the physics is managed on the server side.

-Sending input data without prediction on the client side and waiting for the server response for the new state

could deliver a strong lag on player having high ping: if player X has 150ms of ping,when he press the move button

he will actually start moving 300ms later [client-srv //position computation// srv- client]

-What's the best way to synchronize packets? I was thinking about sending a timestamp withing each packet

but,what will this time is referred to? I can't use local machine time since it could be different and...

will be a time synchronization (to a webserver for example) be reliable with some millisecond precision?

Can you guys please give me some opinions on those points?

Will the "send input to server" system hit so hard on performance?

Thanks in advance.

As you've pointed out the problem with sending the inputs to the server is they take time for the server to process and return the result.

What you can do is send the key press to the server and then stimulate the key press immediately on the client. Then the server predicts the movement and possible future position of where it expects the player to be and sends the info back to the client which can use this data along with its current position data to work out its location.

I know you said for simplicity to keep it TCP but if packets are supposed to be sent often then id recommend using a UDP socket instead as TCP sends a message to the server which processes it then sends a confirmation message its been received. UDP just sends the message without waiting around for that confirmation back making it much quicker

Hope that helps with your problem

Thanks to both for the reply!

@bb_buster

So i start moving without waiting the server and eventually fix the position depending on the server response?

I had in mind to use UDP but i don't want to get a lot of problem due to data loss since,for what i know,they're pretty tricky to find.

Anyway it should be possible to switch to UDP by implementing an ack solution.

@Ashaman73

1. Sure,using packets is the idea.

2. The problem is that,those ships don't move slowly,i hope that it could be solved by using an high priority on the position check.

As you said,i'll test it out without prediction first.

3. Oh god...that's so simple as smart!I didn't thought about masking the lag in that way,thanks!

Oh another thing,what is a normal update time of the network?

I suppose to have to transfer data from the client to the server only when the user do something but what about

the other way?

Every how many update cycles should i transfer the data from server-->client to update other players position etc?

(having for example 60 update call per second)

Thanks again.

Thanks for the detailed answer,i'll do some testing between 15-20 Hz

And thanks for pointing out the lag issue.

I don't know how much it effects the network state but it's good you pointed it out.

In the end that computational lag should be masked since every client will have the same 70ms offsett (plus the connection lag).

Thanks.