zeromq 各种端口在达到高水位（HWM）时的行为

不管怎么弄，用zmq做视频传输，720p分辨率时，延迟超级大，达到了5s以上
看来用zeromq做视频低延迟通讯，是很困难的了。。。

链接：http://zeromq.org/area:faq#toc7

原文
How does the HWM (high water mark) work with any socket type?

On PUB and ROUTER sockets, when the SNDHWM is reached on outgoing pipes, messages are dropped. DEALER and PUSH sockets will block when their outgoing pipes are full. On incoming pipes, SUB sockets will drop received messages when they reach their RCVHWM. PULL and DEALER sockets will refuse new messages and force messages to wait upstream due to TCP backpressure.

翻译
HWM（高水位标记）与各种插座类型一起使用时会发生什么事？

在 PUB 和 ROUTER 类型套接字上，当在传出管道上达到 SNDHWM 时，将会丢弃消息。而DEALER 和 PUSH 类型套接字将会堵塞。在传入管道上，到达 RCVHWM 时，SUB 类型套接字将会丢弃消息，而 PULL 和 DEALER 套接字将拒绝新消息并强制消息在上游等待。