MAXBUFU formulas

The number of buffers required for a message (RU) is determined by the following formula:

(29 + RU size) ÷ bufsize

Note: This formula applies to FID4 (subarea connections).

The number 29 is obtained by adding the size of the transmission header (26) to the size of the request/response header (3).

For channel-attached cluster controllers, the number of buffers required for a message is determined by the following formula:

(13 + RU size) ÷ (bufsize - 16)

The number 13 is the sum of the channel link header (4) plus the transmission header (6) plus the request/response header (3).

The bufsize is the buffer pool value you use to start VTAM®. If you are unsure about this value, look at your start options for the IOBUF buffer size specification.

The MAXBFRU value you use must be greater (for NCPs and PU2.0 channel attached devices) than or equal to the number of buffers required for the largest message (RU) your system receives. For T2.1 channel-attached devices, the value should be greater, but does not have to be. This minimizes the number of attention interrupts needed to process large messages. Use the preceding formula to calculate the lower limit for MAXBFRU, given the size of the largest message.