Maximum length request/response unit size (MAXLENRU) parameter

The maximum length of a systems network architecture (SNA) request/response unit (RU) can be specified with the MAXLENRU parameter in a mode description for APPC, APPN, and HPR.

If you select a value of *CALC for the MAXLENRU parameter, the system selects an efficient size that is compatible with the frame size that you choose. (The frame size is on the line description command.) Many newer input/output processors support IOP assist. Changing the RU size to a value other than *CALC may negate this performance feature.

In most situations, the use of the *CALC value for the MAXLENRU parameter gives you the optimal RU size. If *CALC is not used, consider the following situations when deciding on the appropriate value:

• Choose an RU size that is slightly less than the maximum frame size or a multiple of the maximum frame size. This setting ensures that the largest possible frame size transmits all the time.
• For frame relay, use RU sizes that; when combined with your packet size and protocol, minimize communications costs.
• For token-ring, Ethernet, and wireless network users, use a large RU size that is slightly less than a multiple of the frame size.
• For X.25, optimal values are from 241 through 32768. Pacing values must be coordinated when considering performance with the MAXLENRU parameter.
• For synchronous data link control (SDLC), do not change the *CALC value on the MAXLENRU parameter.

For more information about iSeries™ configuration, see Communications Configuration.