These are being presented only in the context of the advantages of deploying IB and RoCE. We do not discuss cables and connectors.
HCAs provide the point at which an IB end node (for example, a server) connects to an IB net- work. These are the equivalent of the Ethernet (NIC) card but they do much more. HCAs provide address translation mechanism under the control of the operating system which allows an application to access the HCA directly. The same address translation mechanism is the means by which an HCA accesses memory on behalf of a user level application. The application refers to virtual addresses while the HCA has the ability to translate these addresses into physical addresses in order to affect the actual message transfer.
InfiniBand range extension is accomplished by encapsulating the InfiniBand traffic onto the WAN link and extending sufficient buffer credits to ensure full bandwidth across the WAN.
The InfiniBand subnet manager assigns Local Identifiers (LIDs) to each port connected to the InfiniBand fabric and develops a routing table based on the assigned LIDs. The IB Subnet Manager is a concept of Software Defined Networking (SDN) which eliminates the interconnect complexity and enables the creation of very large scale compute and storage infrastructures.
IB switches are conceptually similar to standard networking switches but are designed to meet IB performance requirements. They implement flow control of the IB Link Layer to prevent packet dropping, and to support congestion avoidance and adaptive routing capabilities, and advanced Quality of Service. Many switches include a Subnet Manager. At least one Subnet Manager is required to configure an IB fabric.