I work on a product that supports both UDP (IP) and TCP/IP communication between client and server. It started out with IPX over 15 years ago with IP support added 13 years ago. We added TCP/IP support 3 or 4 years ago. Wild guess coming up: The UDP to TCP code ratio is probably about 80/20. The product is a database server, so reliability is critical. We have to handle all of the issues imposed by UDP (packet loss, packet doubling, packet order, etc.) already mentioned in other answers. There are rarely any problems, but they do sometimes occur and so must be handled. The benefit to supporting UDP is that we are able to customize it a bit to our own usage and tweak a bit more performance out of it.

Every network is going to be different, but the UDP communication protocol is generally a little bit faster for us. The skeptical reader will rightly question whether we implemented everything correctly. Plus, what can you expect from a guy with a 2 digit rep? Nonetheless, I just now ran a test out of curiosity. The test read 1 million records (select * from sometable). I set the number of records to return with each individual client request to be 1, 10, and then 100 (three test runs with each protocol). The server was only two hops away over a 100Mbit LAN. The numbers seemed to agree with what others have found in the past (UDP is about 5% faster in most situations). The total times in milliseconds were as follows for this particular test:

1记录 IP: 390760 ms TCP: 416,903毫秒 10个记录 IP: 91,707 ms TCP: 95,662毫秒 100条记录 IP: 29,664 ms TCP: 30,968毫秒

IP和TCP传输的数据总量大致相同。我们在UDP通信方面有额外的开销，因为我们拥有一些与TCP/IP“免费”相同的东西(校验和，序列号等)。例如，Wireshark显示对下一组记录的请求在UDP中是80字节，在TCP中是84字节。

请参阅Steven的Unix网络编程的22.4节，“何时使用UDP而不是TCP”。

另外，请参阅关于UDP总是比TCP更快的误解的其他SO回答。

史蒂文的话可以总结如下:

使用UDP广播和组播，因为这是你唯一的选择(任何新的应用程序使用组播) 你可以在简单的请求/回复应用中使用UDP，但你需要构建自己的ack、超时和重传 不要使用UDP进行批量数据传输。

我们知道UDP是一种无连接协议，的确如此

适用于需要简单请求-响应通信的流程。 适用于有内部流动、误差控制的工艺 适用于广泛铸造和多播

具体的例子:

用于SNMP 用于RIP等路由更新协议

UDP can be used when an app cares more about "real-time" data instead of exact data replication. For example, VOIP can use UDP and the app will worry about re-ordering packets, but in the end VOIP doesn't need every single packet, but more importantly needs a continuous flow of many of them. Maybe you here a "glitch" in the voice quality, but the main purpose is that you get the message and not that it is recreated perfectly on the other side. UDP is also used in situations where the expense of creating a connection and syncing with TCP outweighs the payload. DNS queries are a perfect example. One packet out, one packet back, per query. If using TCP this would be much more intensive. If you dont' get the DNS response back, you just retry.

这并不总是明确的。然而，如果您需要保证数据包以正确的顺序无丢失地传递，那么TCP可能是您想要的。

另一方面，UDP适用于传输信息的短数据包，其中信息的顺序不太重要，或者数据可以放入单个数据包中 包。

当您希望向许多用户广播相同的信息时，这种方法也很合适。

其他时候，当您正在发送序列数据时，它是合适的，但如果有些数据丢失了 错过你不太关心的(例如VOIP应用程序)。

有些协议更复杂，因为需要的是TCP的一些(但不是全部)功能，但比UDP提供的功能更多。这就是应用层必须做到的 实现附加功能。在这些情况下，UDP也是合适的(例如，互联网广播，顺序很重要，但不是每个数据包都需要通过)。

它在哪里/可以被使用的例子 1)时间服务器向局域网上的一堆机器广播正确的时间。 2) VOIP协议 3) DNS查找 4)请求局域网服务，例如:where are you? 5)网络电台 还有许多其他的……

在unix上，您可以输入grep udp /etc/services以获得实现的udp协议列表 今天……有几百个。

UDP是完美的VoIP地址，其中数据包必须发送不考虑其可靠性… 视频聊天是UDP的一个例子(你可以在任何视频聊天期间通过wireshark网络捕获来检查它)。 而且TCP不能与DNS和SNMP协议一起使用。 UDP没有任何开销，而TCP有很多开销