SNA indicators and records
SNA indicators and records can be generated either explicitly as a result of a CICS® command, or automatically when CICS detects that they are needed.
The most common SNA indicators and records:
- Begin_bracket and conditional_end_bracket
- The begin_bracket (BB) and condition_end_bracket (CEB) indicators in the request header (RH) denote respectively the beginning and end of a conversation between two transactions. Because the BB is generated automatically at the start of a conversation, you need only consider the CEB. The CEB is generated by a SEND with the LAST option, an ISSUE ABEND, a FREE command, or task termination before the conversation is ended.
- Function management headers
- Function management headers (FMHs) are records
sent on a conversation which contain SNA control data. Several types
of FMH are defined under SNA; but only two (FMH5 and FMH7) are relevant
to APPC DTP.
The FMH5, also known as the attach FMH, is sent with BB and contains the information required to initiate the back-end transaction.
The FMH7 is issued by the ISSUE ERROR, ISSUE ABEND, and SYNCPOINT ROLLBACK commands. In addition, if the back-end system rejects the FMH5, an FMH7 is sent to the front-end transaction. The FMH7 contains a 4-byte code, called the sense code, which describes the error. This code is set in EIBERRCD (or CDBERRCD for basic conversations). The FMH7 may be followed by log data. This log data is included in message DFHZN2701 on the sending system and DFHZC3433 on the receiving system.
- Change direction
- The change direction (CD) indicator, found in the RH, switches
the issuing transaction from send state (state 2) to receive
state (state 5). CD is generated explicitly by either of
the following:
- A SEND command with the INVITE option
- A CONVERSE command.
- PS header (type 10)
- PS headers (type 10) are records sent on a conversation which contain syncpoint requests. These headers contain a 2-byte syncpoint request code (for example, prepare, request commit, committed, and forget). In addition, the initial record sent contains a 2-byte modifier specifying the conversation state after a successful syncpoint exchange.