Advanced Program-to-Program Communication

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Advanced Program-to-Program Communication (APPC) is a data communications support that allows programs on an IBM i server to communicate with programs on other systems that have compatible communications support.

APPC on the IBM i system provides an application programming interface to the Systems Network Architecture (SNA) logical unit (LU) type 6.2 and node type 2.1 architectures.

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 TCP/IP.

The IBM i APPC support handles the protocol needed for communicating between an application program that runs on your IBM i 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 IBM i system provides the following program interfaces:
  • The 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.
  • The Common Programming Interface (CPI) Communications call interface. Using CPI Communication calls carries the LU 6.2 verbs.
  • The CICS® file interface. In CICS/400 support, the LU 6.2 verbs are carried out by using EXEC CICS commands.
  • The sockets application programming 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 IBM i 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 on APPN, High-Performance Routing (HPR) is an enhancement to APPN that enables improved availability and persistence during network outages.