IBM AS/400 manual Advanced program-to-program communications, Dependent LU requester support

Advanced program-to-program communications

Advanced program-to-program communications (APPC) is data communications support that allows programs on an AS/400 system to communicate with programs on other systems having compatible communications support, such as: System/38 and System/36. APPC on the AS/400 system provides an application programming interface to the Systems Network Architecture (SNA) LU type 6.2 and node type 2.1 architectures that makes it possible to communicate with System/390.

The APPC support handles all of the SNA protocol requirements when your system is communicating with a remote system that uses the LU type 6.2 and node type 2.1 architectures. You can connect your system to any other system that supports the APPC program interface. APPC application programs can also communicate over lines using the Internet Protocol (IP) of Transmission Control Protocol/Internet Protocol (TCP/IP).

The AS/400 APPC support handles the protocol needed for communicating between an application program that runs on your AS/400 system, and an application that runs on a remote system. The protocol consists of a set of verbs that are common to the local and remote systems in a network. However, the way in which each system provides a program interface to the verbs may differ.

The AS/400 system provides the following program interfaces:

vThe intersystem communications function (ICF) file interface. In ICF, the LU 6.2 verbs are carried out by using data description specifications (DDS) keywords and system-supplied formats.

vThe Common Programming Interface (CPI) Communications call interface. Using CPI Communication calls carries the LU 6.2 verbs.

vThe CICS file interface. In CICS/400 support, the LU 6.2 verbs are carried out by using EXEC CICS commands.

vThe sockets application program interface (API). For the sockets API, the LU 6.2 verbs are carried out by using the socket functions.

The APPC support also handles networking functions, and allows peer systems in a network to start and end sessions without a controlling host system.

The AS/400 Advanced Peer-to-Peer Networking (APPN) support is an enhancement to the node type 2.1 architecture. APPN provides additional networking functions such as searching distributed directories, dynamically selecting routes, routing of intermediate sessions, creating and starting remote locations, and routing data by using transmission priorities.

Built upon APPN, high-performance routing (HPR) is an enhancemnet to APPN that enables improved availability and persistence during network outages.

Dependent LU requester support

Dependent LU Requester Support (DLUR) allows dependent secondary logical units (LU 0, 1, 2, and 3) an entry point into the APPN network. DLUR support gives the appearance of having an adjacent connection to VTAM, but allows traversing the APPN network through intermediate nodes.

DLUR supports the following controllers, displays, and printers:

vHost devices, including 3270 emulation (*EML), remote job entry (*RJE), and program-to-program communications (*PGM)

vSNA Passthrough upstream devices

vDHCF display devices

vNRF display and printer devices

vSNUF devices (DSNX)

The normal SSCP-PU and SSCP-LU flows for dependent LUs are encapsulated in a control point server (CP-SVR) pipe. This pipe consists of two LU 6.2 sessions:

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