JES2 invokes Exit 57 before receiving a job while performing receiving an NJE job across a TCP/IP line. Before invoking Exit 57 JES2:

• Allocates a dummy $JCT and $JQE. JES2 initializes these data areas with minimal information.
• Receives the NJE data area and invokes Exit 57 to perform installation-specific processing.
• After returning from Exit 57, JES2 determines if exit 57 indicated whether the NJE data area should be received. If exit 57 indicated the NJE data area should not be received, JES2 places the NJE job in hold on the transmitting node. Otherwise, JES2 continues to process the NJE job. You cannot use this exit to update IBM-defined JCT or JQE fields in the dummy JCT and dummy JQE, respectively. You can, however, update user-defined fields (such as JCTUSERx) or any $JCTX extensions you have created. JES2 propagates changes to 'user' fields to the $JCT and $JQE.