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In the Iterative model, the Listener and Server portions of the application coexist in the same CICS or IMS TP, so the TP holds the socket until all application processing has been completed. The Iterative model uses this sequence:
Create a socket
Bind it to a local address
Listen (make TCP/IP aware that the socket is available)
Select (wait for a connection request)
Accept the connection request
Read or write the data
Close
The advantages of the Iterative model are:
Simplicity
Reduced network overhead and delay because a TRM exchange sequence is not required
Less CPU intensive
Higher single-threaded transaction throughput
The disadvantages of the Iterative model are:
Severely limits concurrent access to TPs that run for a long time
Server application contains all of the SEAPI calls (Create to Close)
Each TP has its own Listener, which means duplicate code
Select with timeout causes a CICS region to sleep