Mixing TCP and UDP

Question

I want to make a multiplayer game that runs on the Internet, not just low-latency, high throughput environments like LAN.

There are some networking aspects of my game where UDP clearly is better suited for, like transmitting information about the positions and velocities of various players. This data must be received as fast as possible, and resending dropped packets will not help because that data is irrelevant by the time it reaches the client. It is entirely OK for some packets to be dropped.

However, there are some other aspects of my game which strictly require in-order, guaranteed delivery. Automatic fragmentation (breaking apart and putting back together for large pieces of data) of packets would also be very useful. It seems like TCP does all of this. Data is not at all useful unless it is strictly in-order and there are no missing packets. Latency will inevitably suffer for this type of data in some cases, but that is unavoidable.

So, instead of implementing TCP-like features on top of UDP, (with data buffers, labeling packets with numbers to determine their order, packet acknowledgement systems), which, would be a ton of work to ensure it works correctly and efficiently, I'd like to just use TCP and UDP at the same time.

However, I have heard that TCP and UDP can fight each other for bandwidth if you use them together at the same time, and using TCP will increase the rate of UDP dropped packets. Is this really true? Are there any other issues that I will have to deal with when mixing these two protocols?

Answer 1

You could check for http://www.zeromq.org/, a good opensource intelligent transport layer library.