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v Using 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.
v If 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.
v Compression 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.
v If 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:
v Performance considerations for Intersystem Communications Function
v Performance 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:
v Eliminate unused record formats.
v Use separate record formats instead of multipurpose record formats with option indicators.
v Code to use the same record format for repeated operations.
v Set the maximum program devices equal to 1.
v Use a nonshared file.
v Use a separate indicator area.
v The use of the ICF keywords force data and confirm should be minimized.
v Use the Request to Send keyword only when necessary.
v Use the Invite Only keyword when soliciting input from multiple devices, otherwise use the Read
keyword instead.
v If 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
v ICF Programming
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