Adjust LAN lines for optimum communications performance

Several parameters that you can change in the line description (LIND) and the controller description (CTLD) play an important role in system performance.

The following information can help you to understand the line considerations for local area networks.

• MAXFRAME on the line description (LIND) and the controller description (CTLD): Maximizing the frame size in a LAN environment supplies the best performance for large transfers. A large frame size does not negatively affect performance for small transfers. Configure both the iSeries™ system and the other link station for large frames. Otherwise, of the two maximum frame size values, the smaller is used when you transfer data. Bridges might also limit the maximum frame size. You should change the default value from 1994 to a larger size.
• LANMAXOUT on the CTLD (for advanced program-to-program communications (APPC) environments): This parameter governs how often the sending system waits for an acknowledgment. The LANACKFRQ parameter value on one system should never have a greater value than the LANMAXOUT parameter value on the other system. The parameter values of the sending system should match the values on the receiving system.
• Setting appropriate values for the LANMAXOUT parameter along with the LAN acknowledgment frequency (LANACKFRQ) parameter for both the sending stations and receiving stations is essential for optimal performance. Other values might decrease throughput by 50% or even more if conditions trigger time-outs.
• LANWDWSTP for advanced program-to-program communications (APPC) on the controller description (CTLD): If there are network congestion or overruns to certain target system adapters, then increasing the value from the default of *NONE to 2 or more might improve performance.

In general, setting the LANMAXOUT parameter value to *CALC or 2 offers the best performance for interactive environments and adequate performance for larger transfer environments.

• For large transfer environments, changing the LANMAXOUT value might significantly increase performance. As starting points, use the following guidelines:
  • When you are communicating with a recent model personal computer, increase the LANMAXOUT parameter, but keep the LANACKFRQ parameter set to *CALC. For older models of personal computers, use *CALC for both values to limit buffer overruns.
  • If LANACKFRQ and LANMAXOUT parameter values are changed without noticeable performance improvements, change the values back to *CALC.

For more information on iSeries server communications, see the Communications Configuration book.