gtps2m0q | ACF/SNA Data Communications Reference |
Both host and remote applications can include an FMH when transmitting a message. An FMH contains information about the text of the message. For example, an FMH might be used to indicate the results of some host processing. The FMH contains 2 fields: the header length (HL) field and the control information (CI) field. The HL field is 1 byte long. The CI field is 1 - 255 bytes long. Content and usage for the CI field is determined by the user when designing the host and remote application programs. When included, the FMH is the first part of the message text. The presence of an FMH is indicated in the RCPL. When the FMH length field (HL) is set to zero, the output message is not sent. This procedure is sometimes used to comply with TPFs requirement that all input messages receive a reply. Only the first segment in a multiple segment input message can include an FMH; the remaining segments must not include one. Messages that include an FMH are often referred to as data and control messages.