gtps2m0c | ACF/SNA Data Communications Reference |
Figure 1 illustrates TPF's inbound message flow for ALC and SNA terminals. See the TPF Data Communications Services Reference additional information on message routing and message flow.
Figure 1. TPF Inbound Message Flow
The TPF inbound message flow consists of three components:
The primary function of this component is to move the message from an I/O buffer into a core block and then obtain an Entry Control Block (ECB). The core block containing the message is attached to the ECB and the message is passed to either:
Other ancillary Protocol Handling functions include:
TPF passes a data message to the Communications Source (COMMSRCE) program that handles its specific line discipline or terminal type. The data message can be input to an application, a logon/logoff request, or an unsolicited message request. In general, COMMSRCE converts the terminal's network address into an address used internally by TPF. The internal address format is a RID for SNA sources or an LEID for non-SNA sources (terminals). If the destination of the message from an SNA source is a non-SNA application, the RID format is then converted to an LEID format. The message is then edited to remove imbedded control characters and examined to determine whether it is a data, logon/logoff, or request for unsolicited messages. The edited message is passed to one of three system services for subsequent processing:
The ROUTER ensures that the message can be delivered to the application. The program checks to verify that the:
If the message cannot be delivered, then a message is returned to the originator stating why the message is undeliverable. The text of the messages returned by the system is:
If the message can be delivered, the application is entered with the message attached to level 0 of the ECB and a Routing Control Parameter List (RCPL) in EBW000 of the ECB.
The application is responsible for decoding the transaction code and starting the appropriate programs. If the message was from a 3270 terminal and the application requires ALC type input, the 3270 Simulator package may be called to reformat the message text. When processing is complete the application issues a ROUTC macro to send a reply to the terminal.