Intel 7xx Servers, 170 Servers, AS/400 RISC Server manual APPC, ICF, CPI-C, and Anynet

only a few seconds may perform best. Setting this value too low may result in extra error handling impacting system capacity.

yNo single station can or is expected to use the full bandwidth of the LAN media. It offers up to the media's rated speed of aggregate capacity for the attached stations to share. The disk access time is usually the limiting resource. The data rate is governed primarily by the application efficiency attributes (for example, amount of disk accesses, amount of CPU processing of data, application blocking factors, etc.).

yLAN can achieve a significantly higher data rate than most supported WAN protocols. This is due to the desirable combination of having a high media speed along with optimized protocol software.

yCommunications applications consume CPU resource (to process data, to support disk I/O, etc.) and communications line resource (to send and receive data). The amount of line resource that is consumed is proportional to the total number of bytes sent or received on the line. Some additional CPU resource is consumed to process the communications software to support the individual sends (puts or writes) and receives (gets or reads).

yWhen several sessions use a line concurrently, the aggregate data rate may be higher. This is due to the inherent inefficiency of a single session in using the link. In other words, when a single job is executing disk operations or doing non-overlapped CPU processing, the communications link is idle. If several sessions transfer concurrently, then the jobs may be more interleaved and make better use of the communications link.

yThe CPU usage for high speed connections is similar to "slower speed" lines running the same type of work. As the speed of a line increases from a traditional low speed to a high speed, performance characteristics may change.

y Interactive transactions may be slightly faster y Large transfers may be significantly faster

y A single job may be too serialized to utilize the entire bandwidth y High throughput is more sensitive to frame size

y High throughput is more sensitive to application efficiency

y System utilization from other work has more impact on throughput

yWhen developing scalable communication applications, consider taking advantage of the Asynchronous and Overlapped I/O Sockets interface. This interface provides methods for threaded client server model applications to perform highly concurrent and have memory efficient I/O. Additional implementation information is available in the Sockets Programming guide.

5.7 APPC, ICF, CPI-C, and Anynet

•Ensure that APPC is configured optimally for best performance: LANMAXOUT on the CTLD (for

APPC environments): This parameter governs how often the sending system waits for an acknowledgment. Never allow LANACKFRQ on one system to have a greater value than LANMAXOUT on the other system. The parameter values of the sending system should match the values on the receiving system. In general, a value of *CALC (i.e., LANMAXOUT=2) offers the best performance for interactive environments, and adequate performance for large transfer environments. For large transfer environments, changing LANMAXOUT to 6 may provide a significant performance increase. LANWNWSTP for APPC on the controller description (CTLD): If

IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
© Copyright IBM Corp. 2008	Chapter 5 - Communications Performance	74