Controlling outbound coattailing

By controlling the channel delay timer for VTAM® and the attention interrupt delay timer, you can affect outbound coattailing in your system.

VTAM saves PIUs for transfer over a channel until one of the following events occurs:

Data flowing at transmission priority two (TP2) is available.
A virtual route pacing response must be transmitted.
An attention interrupt from an NCP or an SNA cluster controller (for example, the 3174) occurs.
The PIU queue for VTAM reaches its limit.
For each VTAM channel delay interval, VTAM calculates the queue depth (QDPTH tuning statistic) by multiplying the number of PIUs transferred during the channel delay interval by a percentage (currently 75 percent).
The channel delay timer or the backup three-second timer expires.