Header analysis program (XHAP)
- XIMA with assembled message switching messages.
- XMRJ with corrected reject messages.
- Reservations Programs through the use of the SENDT macro with messages destined for Host Airline Message Switching terminals.
This program checks the address section of each message by verifying each destination mnemonic up to the end-of-address. Each HA destination in the address section is checked using the mnemonic City Code Index Table (XC1CC) and the Function Code Index Table (XF1FF). Special distribution codes (otherwise known as group codes) are also used as a shorthand method of addressing a particular set of terminals. These are found using the Special Distribution List (XD0LS). Messages with errors in the address section are sent to the Message Reject Program (03-XMRJ) which in turn either transmits them back to the originator for correction or sends them to the Construct Reject Program for transmission to a reject operator.
When all addressees have been found, the message is placed in the appropriate output queues (using the XU2TQ which points to the XT0CB). The Terminal Routing Table (XR1TR) indicates which line or terminal queue should be used while the priority code determines into which of the three priorities the message will be placed.
Just prior to placing the message on the output queue, the receiving terminal is checked to determine if alternate routine is required. This can cause the message to be placed on the alternate terminal's output queue. Messages for a high-speed terminal are intercepted in its output queue.
Answerback messages are sent to half-duplex terminals. This requires the use of the Line Index (XLCI) and Terminal Index (XK1CT) in order to find the originator address. The Input Log Directory (XI0DS) is used to maintain the input message sequence number, data-time received and message file address (for input retrieval purposes) when the input logging option is used in the system. Messages from the reservation programs are not logged on the XILD.
When the first HA destination contains an “XC” function, the message is treated as a service message (e.g. Retrieval Request) and control is transferred to the Service Message Dispatcher Program (XSMD).
When it finds the output queues empty, XHAP enters either the Output Message Assembly and Transmission Program for low-speed message transmission or the Long Message Transmitter Program for high speed message transmission upon adding a message entry into the output queue.