https://www.ibm.com/docs/en/ims/15.6.0?topic=isiccm-format-user-portion-irm-hwssmpl0-hwssmpl1-user-written-message-exit-routines
IMS 15.6 - Communications and connections - Format of user portion of IRM for HWSSMPL0, HWSSMPL1,...
Following the 4-byte length field and the 28-byte fixed portion of the IMS request message (IRM) header in IMS Connect client input messages, user-written...