SDISC Assembler Call - NetEx

Figure 3. NETEX and the ISO ModelSession Layer ServicesAs the highest layer within NETEX (referring to the ISO model above), the NETEX session layer softwareprovides the general interface to the user’s application/utility program. The NETEX session layer servicesinclude: program-to-program connection using the best available network path, reading data, writing data,disconnection, and statistics gathering. The user requests these services using a standard NETEX RequestBlock (NRB) (containing parameters), and the NETEX requests described in “NETEX Session Services”.The session layer software implements user requests by requesting services from the underlying transportlayer.Transport Layer ServicesThe transport layer provides the actual data movement services for NETEX. This is an internal layer usedonly by the session service code, not the end user. It transmits and receives user data, along with internalprotocol information, to provide fast, efficient communications over the network. The transport layer accomplishesits function by performing services for the session layer software above it and by requesting servicesof the network layer below it.The transport software manages the network path chosen by the session software. The session user does notneed to be concerned with the actual hardware and software used to transmit data, nor with NETEX-to-NETEX message delivery. The transport layer sets up hardware and software tables, provides buffering, andestablishes linkages to manage the flow of information. Also, the protocol used by the transport layer softwareprovides true full-duplex communications between subsystems, permitting asynchronous reads andwrites. Because the transport layer provides a full-duplex operation, data can flow continuously, as long as itPage 6 Introduction MAN-REF-H307IP-04