FM header format reference

Each header's length is defined by a 1-byte length field. The value in this field includes the length field itself. A concatenation flag indicates whether an additional header follows.

Within the header formats, variable- and fixed-length parameters are positional by command code. A 1-byte length field precedes each variable-length positional parameter. The value contained in this length field can be X'00' through X'08' and does not include the length field itself. If the length field contains X'00', the variable parameter is omitted and the next positional variable-length parameter length field occurs followed by its variable-length parameter field.

Trailing positional parameter length fields of X'00's at the end of the header can be eliminated for input to IMS and are not sent on output from IMS. IMS also does not send trailing blanks for any of these names.

When receiving a header, IMS ignores any coded parameters beyond the last parameter to which it is sensitive (that is, that IMS supports). The other LU 6.1 subsystem should do the same when receiving headers that IMS sends.