Outbound session pacing

When the application program is acting as the primary logical unit, you can specify AUTH=NVPACE to nullify pacing from that application program. VTAM® does not wait for a pacing response before sending data to the NCP on behalf of this session. VPACE, the default, is normally used to prevent overloading buffers in the communication controller with outbound messages from VTAM. However, you can specify NVPACE when either of the following situations occur:

The application program sends only single-element request units (RUs) to any one logical unit and, after sending each RU, waits for a response before sending the next RU.
The application program sends chains of RUs containing a limited number of elements and does either of the following:
- After sending one chain, the application waits for a response before it starts sending the next chain.
- The application sends the change direction indicator in the last element actions of the chain.

Local flow control is a part of network flow control and can affect application program design. For primary or secondary application programs, macros that cause data to be sent on a session (SEND, SESSIONC, OPNDST, or CLSDST) are not posted complete when a virtual route (VR) is blocked because of congestion. The application program is posted when the VR is again opened. The data to be sent is left in application program buffers.

An application program that issues a synchronous SEND request does not receive control until the request is processed, even if the route is not blocked. For an asynchronous request, the program receives control as soon as the request is accepted by VTAM. However, further processing of the SEND RPLs for this session is suspended as long as the VR is blocked.