APPC Subsystem on MPE/XL Node Manager's Guide (30294-90007)

18 Chapter1

Introduction

APPC Overview

IBM’s Logical Unit 6.2 (LU 6.2) architecture speciﬁes a common set of

functions and protocols that application programs running on separate

processors can use to communicate with each other. LU 6.2 allows for

standardized program-to-program communication, which IBM calls

Advanced Program-to-Program Communication, or APPC.

The functions and protocols that LU 6.2 architecture speciﬁes are called

verbs. Application programs used for communicating in an LU 6.2

environment are called transaction programs, or TPs. When two TPs

communicate with each other, they are said to communicate with each

other over a conversation.

LU 6.2 Verbs

The functions and protocols for communication are speciﬁed in the form

of programmatic conversation verbs. These conversation verbs allow

programs to perform such functions as initiating a conversation with

another program, sending and receiving data, requesting conﬁrmation

from the partner program, requesting and granting permission to send

data, and terminating a conversation.

LU 6.2 architecture speciﬁes two types of conversation verbs that TPs

can use to communicate: basic conversation verbs and mapped

conversation verbs.

• Basic conversation verbs. Basic conversation verbs are used to

write TPs that provide a service or system for other TPs. They are

also used to write TPs that require certain privileged functions that

only basic conversation verbs allow. The LU 6.2 data stream (called

the general data stream) requires a unique data format. A

programmer using basic conversation verbs must provide data

formatting and certain error recovery functions in the TP itself.

• Mapped conversation verbs. Mapped conversation verbs are used

to simplify the programmatic interface. A programmer using

mapped conversation verbs is freed from providing formatting

functions for the data in the general data stream. However, data

formatting must be provided in an underlying TP or system.

Both groups of conversation verbs (basic and mapped) are further

divided into base sets and option sets. The base set of a group of

verbs must be implemented in all products that use that set, while

product developers may or may not choose to implement additional

option sets. The APPC subsystem implements the base set of basic

conversation verbs and certain option sets. The LU 6.2 API product

implements the base set of mapped conversation verbs and certain

option sets.