For performance reasons, IBM recommends that each transaction program scheduled as multi-trans be assigned to a unique class of APPC/MVS transaction initiators. Those classes are defined in the ASCHPMxx parmlib member and assigned to transaction programs in the TP profile. Each class consists of a range (maximum and minimum number) of transaction initiators that are available for running transaction programs of that class. See z/OS MVS Planning: APPC/MVS Management for more details about defining classes of transaction initiators.