Send-only protocol

Client application programs use the send-only protocol to submit commit then send (CM0) input messages to IMS in rapid succession without requiring the client application to wait for a response. The send-only protocol is designed for fast, high volume input.

Clients configured to support synchronous callout requests also use the send-only protocol to return responses from an external data or service provider to an IMS application program that issued the synchronous callout request and that is waiting for the response in an IMS dependent region.

The output generated by IMS in response to send only input is stored on an asynchronous hold queue associated with tpipe used by the client application and can be retrieved later by issuing a RESUME TPIPE call.

If send-only input messages must be processed by IMS in the order in which they are sent by the client, the send-only protocol offers two options that can help ensure that IMS receives the messages in the order in which IMS Connect receives them from the client application:
  • Send-only protocol with the acknowledgment option
  • Send-only protocol with the serial delivery option

When the send-only protocol is used to return responses from a data or service provider external to the IMS installation, the send-only message does not contain a transaction code, but rather the data requested by the IMS application or, in the event there was a problem processing the callout request, error codes.

The following figure shows an example of the CM0 send-only protocol flow when the commit confirmed flag is on. The CM0 flow, also known as the IMS standard flow, enqueues IMS output before sending it to the client. However, in this case for non-response transactions, the client does not expect any output from IMS.

Figure 1. Send-only protocol flow
begin figure description. Diagram flow chart of send-only protocol as described in surrounding text. end figure description.
The preceding sample flow assumes the following:
  • CM0 is specified in the state-data section of the message prefix.
  • The transaction bit and the commit confirmed bit is specified in the control-data section of the message prefix.