RD Basic Operational Characteristics

For convenience sake, the basic characteristics of the RD service type, which were provided in “Reliable Datagram (RD) Service Type” on page 67, are replicated here:

• Connection needed. Before any messages may be transferred, a connection must be established between the EECs in the two CAs, and the EECs are each programmed with the identity of the remote EEC as well as the address of the port behind which the remote EEC resides. This is necessary so the two EECs can transmit packets to each other.

• Message size. Each message can be anywhere from zero to 2GB in size. Large messages are segmented into multi-packet transfers.

• Ack/Nak protocol. An Ack/Nak protocol permits the requester (i.e., the Send Logic of the EEC sending the message) to verify that all packets are delivered to the remote EEC.

• High traffic. Because the responder EEC must Ack or Nak each request packet received, this service class generates considerably more network traffic than the “unreliable” service types.

• Packet PSN checking. Each packet contains a PSN that the target EEC's Receive Logic uses to verify that all packets are received in order (and that each is only received and processed once) and that there are no missing packets.

• Two CRC fields in each packet are used to verify the integrity of the packet.

• Local EEC forwards request packets to EEC in remote CA. Upon receipt of each request packet from a local RD QP's SQ Logic, the local EEC's Send Logic inserts the packet's PSN and transmits the packet to the EEC in the remote CA.

• Remote EEC forwards request packets to remote QP. Upon receipt of each request packet, the EEC's Receive Logic in the remote CA validates the request packet's PSN and forwards the request packet to the targeted remote RD QP's RQ Logic for processing.

• Operations supported. Supports the following types of message transfer operations:

  - RDMA Read support is required.

  - RDMA Write support is required.

  - It is optional whether or not the CI supports Atomic operations. If it does, then it must support both the Atomic Fetch and Add and the Atomic Compare and Swap If Equal operations.

  - Send support is required.

  - Bind Memory Window support is required.