General format of output function management headers (SLU P)

IMS appends a header to the first or only-in-chain transmission of all messages sent, except the IMS null message and VTAM® commands and indicators.

This header describes the type of message that follows and, if appropriate, indicates the output component that is to receive the message. The header can also contain optional MFS information. SLU P uses header type X'42'.

The length of the output function management header varies from 5 to 42 bytes. The format is:
Byte 0
Message header length including length byte (binary)
Byte 1
Header type (X'42')
Byte 2
Message descriptor 1 (flag byte is binary)
Byte 3
Message descriptor 2 (flag byte is binary)
Byte 4
Output component identification (binary)
Bytes 5-41
MFS data (length byte: binary; names: EBCDIC)