IBM AS/400 manual Performance considerations for intersystem communications function

vUsing larger sends for a given large transfer (record sizes) provides a higher application data rate and decreases CPU time. With the larger record size, the CPU has less processing to do because there are fewer application reads and writes to transfer the same amount of data.

vIf a value of *CALC is selected for maximum Systems Network Architecture (SNA) request/response unit (RU), the system selects an efficient size compatible with the frame size. The frame size is on the line description that you choose. Changing the RU size to a value other than *CALC may negate the performance feature.

vCompression with APPC should be used with caution and only for slower speed wide area network (WAN) environments. Many suggest that compression should be used with speeds 19.2 kbps and slower.

vIf you are doing tasks that include repetitive, small puts; better performance is achieved if you use ICF or CPI Communications.

See the following topics for a more complete discussion of APPC applications:

vPerformance considerations for Intersystem Communications Function

vPerformance considerations for Common Programming Interface communications

For information about AS/400 communications, see the Communications Configuration book.

For more information about CICS/400, see the CICS/400 Administration and Operations Guide .

Performance considerations for intersystem communications function

You can use intersystem communications function (ICF) to write application programs that you want to communicate with advanced program-to-program communications (APPC). ICF also provides program-to-device communications between the AS/400 system and hardware devices. You must determine which system is to send data first before you write the program. ICF data management handles the communication functions and the data for your program. In particular, ICF should be used to do tasks that include repetitive, small inputs.

To optimize ICF performance, consider the following:

vEliminate unused record formats.

vUse separate record formats instead of multipurpose record formats with option indicators.

vCode to use the same record format for repeated operations.

vSet the maximum program devices equal to 1.

vUse a nonshared file.

vUse a separate indicator area.

vThe use of the ICF keywords force data and confirm should be minimized.

vUse the Request to Send keyword only when necessary.

vUse the Invite Only keyword when soliciting input from multiple devices, otherwise use the Read keyword instead.

vIf using the Invite keyword to solicit from multiple program devices, follow it with a Read-from-invited operation, not a Read operation.

To create device descriptions to get your system set up for ICF, do the following:

1.Type the appropriate Create Device Description commands on the AS/400 command line and press F4.

2.Use the online help information to choose the parameter values.

3.Press Enter. The device description is created.

For more information about ICF, see

v“Application program interface (API) performance considerations” on page 17

vICF Programming

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