IUCV is a CMS facility for transferring data between virtual machines. SU uses the IUCV SEND/RECV protocol. The source machine sends HLI commands to the sink machine. The sink machine executes each command and sends the output back to the source machine. If, while executing an HLI command, the sink machine receives another command, it puts the second command on a message queue which it processes in the order received.
The following figure illustrates this process. A source machine sends an HLI command to IUCV (1). The command is transmitted to the sink machine, which puts the command on its message queue to await processing (2). The sink machine accepts the command from the message queue (3), executes the command, and sends the output to IUCV (4). IUCV transmits the output back to the source machine (5):
The time it takes IUCV to transfer data back and forth (HLI commands and test literals to the sink machine, field values back to the source machine) depends on the size of your record work area. The larger the work area, the longer it takes IUCV to transfer your data. It is a good idea to use the SHO command to limit your record work area to the fields you need so that the work area is as small as possible.
The HLI NEX command has a multiple record option that packs several records into a single blocked record that IUCV transfers to a single record area. IUCV can transfer this single blocked record faster than it can transfer the individual records separately.
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