On Jul 28, 2008, at 5:55 PM, Noah Kantrowitz wrote:
TCP has many semantics that can be undesirable for some games, in particular "guaranteed delivery" regardless of effective time oftransmission. In many real-time applications (FPS games come to mind),state data becomes out of date very quickly, thus if the transmission cannot be completed in a particular time window, it is better not to receive the data at all. In these games the state updates can become roughly like a stream.In any game network protocol I have ever seen, this is simply not true. For example, position is generally not sent as an absolute, but as difference. Aside from periodic resyncs, the moment-to-moment updates generally all doneed to be received.
Quake 3 famously issues updates solely via udp as a delta between the last known state of the receiver and the sender bi-directionally. This has been widely copied in games of that genre in the following years and was considered at the time to be a huge advance over the mixture of reliable and unreliable transmission modes used before.
UDP has a lower overhead than TCP, making it advantageous for sending streaming data where intermittent loss is preferable to indeterminate data lag.The overheard will be lower than implementing a similar system yourself in UDP. Also dynamic window sizing means that the overhead is generally toosmall to speak of.
The lower overhead is more of a bonus, not the main benefit. The main benefit is direct control over the delivery and retransmission semantics. At the expense, of course, of having to implement these things yourself.
I'm not trying to argue that UDP is better, but it certainly has its advantages for specific applications.
-Casey