- 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。
之前用iperf测试过56Gb网卡的tcp传输性能曲线如下：在单线程时的测试值与上图的tcp测试曲线基本一致。
刀片3上的网卡标称兼容性好，可适应56Gb IB， 40Gb Eth（40/56Gb的含义是这个意思吗？）。
测试结果为能达到50Gb/s IB.
单线程下只能达到 12Gb/s Eth, 8线程时能达到30Gb/s Eth(在包长很大时).
包长为2KB， 8线程能达到27Gb/s Eth。
刀片2上的网卡标称为40Gb Eth.
单线程下只能达到12Gb/s, 8线程时能达到36Gb/s.（下图为40Gb Eth 网卡测试结果，测试的msg_size=10KB）
包长为2KB， 8线程能达到35Gb/s。
