APPC mapped or basic?

APPC conversations can be either mapped or basic. For CICS®-to-CICS applications, you can use mapped conversations. Basic, or unmapped, conversations are useful to communicate with systems that do not support mapped conversations. These systems include some APPC devices.

The two protocols are similar. The main difference is the way that user data is formatted for transmission. In mapped conversations, the application sends the data that you want the partner to receive. In basic conversations, the application must include additional control bytes to convert the data to an SNA-defined format called a generalized data stream (GDS). Also, in EXEC CICS commands for basic conversations, you must include the keyword GDS.

Table 1 summarizes the differences between mapped and basic conversations that apply to the CICS API.

CPI Communications has different rules (see EXEC CICS or CPI Communications?.

Table 1. APPC conversations – mapped or basic?
Mapped	Basic
The conversation partners exchange data that is relevant only to the application.	Both partners must package the user data before sending, and unpackage it on receipt.
All conversations for a transaction share the same EXEC Interface Block for status reporting.	Each conversation has its own area for state information.
The transaction can handle exception conditions or let them default.	The transaction must test for exception conditions in a data area set aside for the purpose.
A RECEIVE command issued in send state causes conversation turnaround.	A RECEIVE command is illegal in send state.
Transactions can be written in any of the supported languages.	Transactions can be written in assembler language or C only.
You can cause a conversation to time out if the partner does not respond. To do this, you specify the RTIMOUT option of the PROFILE definition.	You cannot cause a conversation to time out if the partner does not respond.