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APPC Subsystem on MPE XL Node Manager's Guide: HP 3000 MPE/iX Computer Systems > Chapter 1 Introduction
The APPC Subsystem |
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The APPC subsystem is a component of several of Hewlett-Packard's LU 6.2 products; multiple LU 6.2 products on the same node use one APPC subsystem. The APPC subsystem implements the base set of basic conversation verbs and certain option sets. These verbs are implemented as intrinsics that are accessed by the transaction programs associated with Hewlett-Packard's LU 6.2 products. The APPC subsystem implements the Data Flow Control and Presentation Services layers of the SNA architecture. SNA/SDLC Link/XL must be installed on the same processor with the APPC subsystem. SNA/SDLC Link/XL provides the Path Control and Transmission Control layers of SNA. Figure 1-2 “The APPC Subsystem in the SNA Architecture” shows the APPC subsystem and the SNA link product as they relate to the SNA architecture. SNA/SDLC Link/XL is made up of a Programmable Serial Interface (PSI) card and a software module called SNA Transport. In order to connect the HP 3000 directly to multiple remote systems, or to connect multiple communication lines from the HP 3000 to a remote system, you need to install multiple copies of SNA/SDLC Link/XL. The APPC subsystem, together with SNA/SDLC Link/XL, allows the HP 3000 to function as either a Node Type 2.0 or a Node Type 2.1. As a Node Type 2.0, the HP 3000 can communicate with a Node Type 5 (like an IBM mainframe). As a Node Type 2.1, the HP 3000 can communicate peer-to-peer with another Node Type 2.1 (like an IBM AS/400). As a Node Type 2.1, the HP 3000 can participate in Advanced Peer-to-Peer Networking (APPN). APPN is an extension to SNA that allows Type 2.1 (peer) nodes to communicate without the intervention of the SSCP on a host node. In an APPN network, certain nodes are configured as Network Nodes, which perform intermediate session routing between nodes. The HP 3000 functions as a Low Entry Networking (LEN) node in an APPN network. It cannot perform intermediate session routing, but if it is connected to a Network Node, it can take advantage of the Network Node's intermediate routing capabilities to communicate with non-adjacent nodes (nodes not directly connected to the HP 3000).
The APPC subsystem supports 256 active APPC sessions. The combined total of active sessions, for all LU 6.2 products running on the APPC subsystem, may not exceed 256. Each TP conversation requires one session. Though conversations can be initiated locally or remotely, all APPC sessions are controlled locally by the node manager. The node manager can activate or deactivate sessions interactively with control operator commands or programmatically with control operator intrinsics. The node manager can also control the number of active sessions automatically through configuration. APPC session parameters must be defined in APPC subsystem configuration. For more information on APPC subsystem configuration, see Chapter 4 “APPC Subsystem Configuration” in this manual. The LUs on an HP 3000 node can be configured as dependent LUs or independent LUs.
Figure 1-3 “HP 3000 in an Example SNA Network” shows an HP 3000 directly connected to two IBM AS/400s and to an IBM host. A separate copy of SNA/SDLC Link/XL is required for each HP-to-IBM connection. The dotted lines in Figure 1-3 “HP 3000 in an Example SNA Network” represent APPC sessions. Independent LU INDLUA on the HP 3000 is conducting a session with independent LU AS400LU1 on IBM AS/400 #1. INDLUA cannot communicate with either of the remote independent LUs AS400LU2 or AS400LU3, because they are connected to the HP 3000 through a different local SNA node (a different copy of SNA/SDLC Link/XL). Independent LU INDLUB on the HP 3000 is conducting three parallel sessions with independent LU AS400LU2 on IBM AS/400 #2. INDLUB is also conducting a session with AS400LU3 on IBM AS/400 #3. INDLUB can conduct sessions with LUs on two different nodes, because both nodes are connected to the HP 3000 through the same copy of SNA/SDLC Link/XL. AS/400 #2 is directly connected to the HP 3000. It is configured as a Network Node, so it can route sessions from the HP 3000 to AS/400 #3, which is not directly connected to the HP 3000. Dependent LU DEPLUA on the HP 3000 is conducting one session with dependent LU HOSTLU on the IBM host. Because it is a dependent LU, it can conduct only one session at a time. Every APPC session with a remote dependent LU requires one local dependent LU on the HP 3000.
Through the APPC subsystem, the node manager can control the network activities for LU 6.2 products. The APPC subsystem interface provides interactive control operator commands that allow the node manager to perform the following functions:
The APPC subsystem also provides programmatic control operator intrinsics that allow transaction programs to perform the following functions:
Chapter 2 “Interactive Control Operator Commands” describes the control operator commands, and Chapter 3 “Control Operator Intrinsics” describes the control operator intrinsics. The APPC subsystem generates error and warning messages and provides an internal tracing facility. Internal tracing records APPC subsystem internal activity. It can be activated or deactivated as needed. There is also a logging facility that you can configure to record major APPC subsystem events such as startup and shutdown. Logging configuration is described in the SNA Link/XL Node Manager's Guide. |
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