DELAY operand

When defining a channel, consider the effects of the DELAY operand on the LINE definition statement. This operand specifies the maximum amount of time that VTAM® queues an outbound PIU with transmission priority 0 or 1 before transmitting it over the channel. When the PIU is eventually sent, it and the queued PIUs following it are sent as a block.

When you specify DELAY=0, VTAM sends each PIU over the channel as it arrives on the queue. When a nonzero value for DELAY is specified, the blocking of low-priority PIUs can save host processor instructions. However, a high channel delay time can cause increased response time because some of the PIUs are delayed before being sent.

Occasional bursts affect throughput only for the next second or two. However, a continuing series of bursts can severely affect capacity if there is little nonchannel-to-channel activity. A few sessions of interactive traffic are more likely to accentuate this condition than a large number, when traffic on the channel is likely to be more randomly distributed.

You might want to increase the DELAY operand value over that of the default to:

Decrease host processor overhead when response time is less important.
Take advantage of a smoothing effect on the queuing that can occur with larger values, an effect that can be useful for application programs with sessions conducted in bursts.

You can specify different DELAY values for different channel-attached devices. The following are general guidelines for picking an appropriate DELAY value for a particular channel-attached device.

If you want to experiment with DELAY values greater than the default, you can activate in succession a series of major nodes with increasing values beyond the default.