z/OS Communications Server: IP IMS Sockets Guide
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Explicit-mode client call sequence

z/OS Communications Server: IP IMS Sockets Guide
SC27-3653-00

The call sequence to be used by an explicit-mode client program is:

Call
Explanation of Function
INITAPI
Open the interface. (Required only for client programs that use MVS™ TCP/IP socket calls).
SOCKET
Obtain a socket descriptor.
CONNECT
Request connection to the IMS™ Listener port.
WRITE
Send a transaction-request message (TRM).
READ
Test for successful transaction initiation. 1
WRITE/READ
Explicit-mode transactions can issue any number of READ or WRITE socket call sequences.
READ
Ensure that the server ended normally and that the database changes are committed.
CLOSE
Terminate the connection and release socket resources.
1 If the Listener is unable to initiate the transaction, it sends a request-status message (RSM) to the client indicating the reason for failure. Therefore, the client must be prepared to receive that message. It is suggested that a convention be established that the server initiate the conversation by sending an opening message. By following this convention, the client will receive either positive or negative notification of transaction status before initiating application data exchange.

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