QP: Message Transfer Mechanism
The Previous Chapter
The previous chapter introduced the concept of device attributes, managers, management agents (MAs), and management datagrams (MADs).
This chapter introduces the concept of the Queue Pair (QP), the message transfer engine that lies at the heart of the IBA technology. Request and response packets, Packet Sequence Numbers (PSNs), and the Verb Layer (a quasi-API used to control an IBA HCA) are introduced. The four IBA QP types are introduced and the concept of the QP Context and its contents are defined. Finally, there is a rather detailed example of a message transfer from one CA to another.
The Next Chapter
The next chapter provides an introduction to the four IBA transport service types (RC, UC, RD, and UD QPs), as well as the two non-IBA transport service types (Raw IPv6 and Raw EtherType QPs) that permit packets associated with virtually any other network protocol to be tunneled through an IBA network encapsulated in "raw" IBA packets.
Figure 3-4 and Figure 3-5 should be viewed as two halves of one large illustration. This split illustration is referenced heavily in the following discussions. Note that many of the elements in the illustration are tagged with reference letters for ease of reference in the discussions that follow. Also keep in mind that, while there are several types of QPs, the split figure and the examples in this section describe message passing as it occurs on one type of QP (referred to as the Reliable Connected, or RC, type).