How does a VTAM application program receive a request on the expedited-flow?

Expedited-flow requests tell the receiver to do something that has higher priority than receiving normal-flow requests (for example, to stop sending normal-flow requests or to prepare to shut down communication with the other end of the session). Because of this, VTAM sends an expedited-flow request immediately, before sending any normal-flow traffic that might be waiting to be sent. Normal-flow traffic is handled separately from the expedited-flow traffic.

A VTAM application program specifies RTYPE=DFASY and/or a DFASY exit routine on the RECEIVE macro instruction to receive requests on the expedited-flow.

The DFASY exit routine provides a way for VTAM to notify an application program that an expedited-flow data-flow-control request has arrived. The requests that can be received by an application program in a DFASY exit are:

• Quiesce at End of Chain (QEC)

• Release Quiesce (RELQ)

• Request Shutdown (RSHUTD)

• Shutdown Complete (SHUTC)

• Shutdown (SHUTD)

• Signal (SIG)

• Stop Bracket Initiation (SBI)