only a few seconds may perform best. Setting this value too low may result in extra error handling
impacting system capacity.
y
No 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.).
y
LAN 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.
y
Communications 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).
y
When 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.
y
The 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
y
When 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
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