Chapter 11. PSN Usage

The Previous Chapter

The previous chapter started by introducing the concept of services, how a CA is located, and the discovery of what services that CA provides. Having located a service provider, a communications channel must be established between the local application program and the service provider. This chapter provided a basic description of the process used in establishing a communications channel between a RC, UC, RD, or UD QP type in the local CA and a QP of the same type in the CA that will provide the desired service.

This Chapter

This chapter provides a detailed discussion of how PSNs in request packets are generated by the requester QP's SQ Logic (or, in RD, the requester EEC's Send Logic) and how they are verified by the responder QP's RQ Logic (or, in RD, the responder EEC's Receive Logic). It describes how the Start PSN is assigned to one QP's SQ Logic (or, in RD, one EEC's Send Logic) and the expected PSN (ePSN) is assigned to the other QP's RQ Logic (or, in RD, the other EEC's Receive Logic). It describes how, when using RD, RC, and UC the PSN in each response packet is verified by the requester QP's SQ Logic (or, in RD, the requester EEC's Send Logic). The concepts of valid and invalid PSNs, as well as duplicate requests and responses, are introduced. This chapter concludes the introductory portion of the book (i.e., Part 1).

The Next Chapter

The next chapter provides a detailed description of the verbs used to create a QP, modify its operational characteritics, obtain its current operational characteristics, and destroy it. It provides a detailed description of the creation of a QP and the steps required to program it. The QP state machine is described in detail.