Different treatment of command sequences

Some of the differences between APPC mapped and MRO conversations are shown in the command sequence in Table 52.

Table 52. How the same command sequence operates differently in APPC mapped and MRO conversations
Commands APPC mapped MRO
EXEC CICS SEND
  CONVID(REM1)               
  FROM(data1)
  LENGTH(251)
sending is deferred data1 is sent
EXEC CICS
  SYNCPOINT
syncpoint request added to data1, and both are sent syncpoint request is sent with null data
EXEC CICS SEND
  CONVID(REM1)
  FROM(data2)
  LENGTH(251)
  INVITE
sending of data2, with INVITE, is deferred data2 with INVITE is sent
EXEC CICS WAIT
  CONVID(REM1)
data2, with INVITE, is sent (nothing to send)
EXEC CICS RECEIVE
  CONVID(REM1)
        .
        .
(INVITE received)
EXEC CICS SEND
  CONVID(REM1)
  FROM(data3)
  LENGTH(251)
  LAST
sending of data3, with LAST indicator, is deferred data3 is sent, but without LAST indicator
EXEC CICS
  SYNCPOINT
syncpoint request and LAST indicator added to data3 and sent syncpoint request and LAST indicator are sent with null data

The WAIT option can, of course, be added to the SEND command to cause immediate transmission on APPC links; for example:

  SEND CONVID(REM1)
       FROM(data2)
       LENGTH(251)
       INVITE
       WAIT
  RECEIVE SESSION(REM1)

There are no significant differences between the MRO and APPC mapped implementations of this command sequence. However, with MRO, a SEND command with the WAIT option causes CICS® to suspend the transaction until the partner system has received the data.

Unlike APPC, MRO allows only one outstanding SEND to be transmitted. This means that when a transaction issue two successive SEND commands (without the WAIT option) to transmit data, the second piece of data does not flow until the partner system has received the first.

A further implementation difference arises between APPC mapped and MRO for command sequences that contain an implicit change of direction. For MRO, a RECEIVE command must not be issued unless the conversation is in receive state (state 5).

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