UC 协议含义及测试结果比较

RC (Reliable Connection) : a connection is established between endnotes, and messages are reliabled sent between them.
UD (Unreliable Datagram): a single packet message can be sent to an endnote without first establishing a connection; transmission is not guranteed.
UC (Unreliable Connection): a connection is established between endnodes, and messages are sent, but transmission is not guarranteed. This is optional.
RD (Reliable Datagram): a single packet can be reliably sent to any endnote without a one-to-one connection. This is optional.

In the above, "reliably send" means that data is, barring catastrophic failure(除非灾难性问题), guaranteed to arrive in order, checked for correctness, with its receipt acknowledged.

The RC, UC and RD classes also support remote DMA(RDMA): moving data directly into or out of the memory of an endnote.

来源：

http://buyya.com/superstorage/chap42.pdf

下面用qperf测试了rc, rc_rdma_read, rc_rdma_write, tcp这几种可靠传输协议在message size从1Byte~8KByte的带宽变化情况。