CPI-C Reference

Conversation Types

Just as two CRMs communicate using a logical connection, two programs exchange data using a conversation. For example, the conversation between Program A and Program C is shown in Figure 1 as a single bold line between the two programs. The line indicating the conversation is shown on top of the logical connection because a conversation allows programs to communicate "over" the logical connection between the CRMs.

CPI Communications supports two types of conversations:

• Mapped conversations allow programs to exchange arbitrary data records in data formats agreed upon by the application programmers. CPI Communications supports both the traditional pass through method, where the application program encodes and decodes the data, and external routines that encode and decode user data.

• Basic conversations allow programs to exchange data in a standardized format. This format is a stream of data containing 2-byte logical length fields (referred to as LLs) that specify the amount of data to follow before the next length field. The typical data pattern is "LL, data, LL, data". Each grouping of "LL, data" is referred to as a logical record.

  Notes:

  1. Because of the detailed manipulation of data and resulting complexity of error conditions, the use of basic conversations is intended for programs with specialized requirements. A more complete discussion of basic and mapped conversations is provided in the Usage Notes section of Send_Data (CMSEND).

  2. Because OSI TP CRMs do not exchange the conversation characteristic that determines whether a conversation will be mapped or basic, the remote application must also issue a Set_Conversation_Type call when basic conversations are being used, to override the default value of CM_MAPPED_CONVERSATION for the conversation_type conversation characteristic.

For further information on basic and mapped conversations, refer to SNA LU 6.2 Reference: Peer Protocols (SC31-6808) and SNA Transaction Programmer's Reference Manual for LU Type 6.2 (GC30-3084).