04 - RDMA


  • remote direct memory access networking technology to enable high-performance, low-latency network operations

It is not TCP+socket.

The goal was to connect and integrate CPUs via network as efficiently as possible

RDMA is used within datacenters and supercomputers.

ChatGPT uses RDMA.

Sending and receiving is made by using two specific functions that specified where to receive and to whom send data.


  • Infiniband: is the most famous and the most standard
  • iWarp
  • SoftROCE: works with any NIC and is an implementation of iWARP
  • SoftiWARP is a full software implementation of iWARP

Infiniband has 3 transport modes:

  • reliable connected (RC)
    • One Queue Pair (QP) per connection, reliability using ACK
  • unreliable connected (UC)
    • One QP per connection, not reliable
  • unreliable datagram (UD)
    • One QP can be used for multiple connections