Channel Adapters

Sometimes the specification uses the term xCA when it is referring to something that is applicable to either a TCA or HCA.

CAs Are the Real Players (Switches and Routers Are Just Traffic Cops)

The real players are the CAs. When a CA must send information to or read information from another CA, the request to do so is output through one of the CA's ports in the form of a request packet. Each CA port has a unique address assigned to it during configuration. The request packet contains the address of the destination port on the destination CA.

Once the request packet is transmitted into the fabric by a CA, it is guided through the subnet by switches. If the destination CA port is in a different subnet, the packet must also transit one or more routers to get to it.

Endnode = CA

An endnode is defined as a device other than a switch, router, or a repeater: in other words, it's a CA. The endnode acts either as the initiator or the ultimate recipient of a packet. The specification's exact definition of an endnode is:

“An endnode is any node that contains a Channel Adapter and thus it has multiple queue pairs and is permitted to establish connections, end to end context, and generate messages. Also referred to as Host Channel Adapter or Target Channel Adapter, two specific types of endnodes.”