Initiating a process: ATTACH FM header

The ATTACH FM header is used to attach a process to receive session input. It carries the name of the process to be attached synchronously, as well as other parameters used by the attached process.

Because ATTACH is defined for synchronous execution, you must understand the relationships between the process to be attached, the IMS message types and execution modes, and the SCHEDULER process.

IMS sends the ATTACH FM header without a SCHEDULER FM header:

On the conversational, response mode, or IMS command output message replies resulting from an input ATTACH.
On asynchronous replies that result from a message received on the same session with ATTACH EB.
When the other half session is bound without SCHEDULER model support.
On system messages sent by IMS through SYSMSG.

An IMS message can consist of either single or multiple SNA chains as indicated within the ATTACH ATTIU parameter. The ATTACH FM header can be present only once for each input or output IMS message. For output MFS demand-paged messages, the ATTACH FM header is present only on the first output SNA chain. The first input paging request to the demand-paged output must contain an ATTACH (for DPN=QMODEL); subsequent input page requests for the same demand-paged output message can optionally contain an ATTACH (which must also indicate DPN=QMODEL).