什么时候使用UDP代替TCP? [英] When is it appropriate to use UDP instead of TCP?

问题描述

由于TCP保证了数据包的传递，因此可以被认为是可靠的"，而UDP不保证任何内容，因此数据包可能会丢失.在应用程序中而不是通过TCP流使用UDP传输数据的优势是什么?在哪种情况下，UDP是更好的选择，为什么?

Since TCP guarantees packet delivery and thus can be considered "reliable", whereas UDP doesn't guarantee anything and packets can be lost. What would be the advantage of transmitting data using UDP in an application rather than over a TCP stream? In what kind of situations would UDP be the better choice, and why?

我假设UDP更快，因为它没有创建和维护流的开销，但是如果某些数据永远不会到达目的地，那不是无关紧要的吗?

I'm assuming that UDP is faster since it doesn't have the overhead of creating and maintaining a stream, but wouldn't that be irrelevant if some data never reaches its destination?

推荐答案

这是我最喜欢的问题之一. UDP被误解了.

This is one of my favorite questions. UDP is so misunderstood.

在您真的希望快速获得对另一台服务器的简单答复的情况下，UDP最有效.通常，您希望答案在一个响应数据包中，并且您准备实现自己的协议以提高可靠性或重新发送. DNS是此用例的完美描述.连接设置的成本太高了(但是，DNS 确实也支持TCP模式.

In situations where you really want to get a simple answer to another server quickly, UDP works best. In general, you want the answer to be in one response packet, and you are prepared to implement your own protocol for reliability or to resend. DNS is the perfect description of this use case. The costs of connection setups are way too high (yet, DNS does support a TCP mode as well).

另一种情况是，当您传递的数据可能会丢失，因为传入的新数据将替换先前的数据/状态.想到天气数据，视频流，股票报价服务(不用于实际交易)或游戏数据.

Another case is when you are delivering data that can be lost because newer data coming in will replace that previous data/state. Weather data, video streaming, a stock quotation service (not used for actual trading), or gaming data comes to mind.

另一种情况是，当您管理大量状态时，由于操作系统无法处理那么多会话，因此您希望避免使用TCP.今天，这种情况很少见.实际上，现在可以使用用户级TCP堆栈，以便应用程序编写器可以对该TCP状态所需的资源进行更精细的控制.在2003年之前，UDP确实是该镇唯一的游戏.

Another case is when you are managing a tremendous amount of state and you want to avoid using TCP because the OS cannot handle that many sessions. This is a rare case today. In fact, there are now user-land TCP stacks that can be used so that the application writer may have finer grained control over the resources needed for that TCP state. Prior to 2003, UDP was really the only game in town.

另一种情况是多播流量. UDP可以多播到多个主机，而TCP根本不能这样做.

One other case is for multicast traffic. UDP can be multicasted to multiple hosts whereas TCP cannot do this at all.

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