Software Reference Manual - NetEx

BFX Send File Control (SND)
This module receives control from the TIC, TRC, or JSC main modules when a file is to be transferred. The
parameters to be used for the transfer are specified in the TROL that was built by the PRM module or internally
generated as is the case when called by the default JMODULE (SUB). Its flow of control is as follows:
1. The sending block module is called for the first time. On a first time call, the block module will call the
record module to open the file for input and determine the maximum record size. This initialization logic
is illustrated in Figure 25 on page 85.
2. On return from the block module, RCV adjusts the BLOCK= value upwards if necessary. Based on the
calling main program (which is specified in the TROL) it calls CON (BFX session offer or BFX session
connect) with the TROL as the passed parameter. These modules will allow the connection to complete
and complete the buffer size, least common multiple, minimum byte count, and file mode negotiations as
detailed in the BFX General Design Specification.
3. Upon completion of connection negotiation, SND allocates the requested number of buffers and begins
the transfer process. It uses a multiple buffering technique to overlap NETEX processing of the incoming
record with the file writes performed by the block module. Figure 26 on page 86 below shows the normal
flow of data transfer.
4. Whenever the block module is called to provide a block to be sent to NETEX, the block module may return
with a message. The message will be sent to the RCV control module in the other application, and
its contents will be placed on the SYSPRINT log files of both applications. If the message indicates a
normal or abnormal end of transfer, SND will send the message and wait for a disconnect indication from
the other BFX to indicate acknowledgement of the ending indication.
5. If an abnormal end indication is received from the receiving remote BFX, SND will call the block and
record modules with an error indication. In that case, the block and record modules are to close the file
and return without any additional data. Upon return from the block module, SND will free the buffers allocated
in step 2 and will return to the module that called SND.
6. If the called block module returns an informational message, it will be forwarded to the opposite RCV
module for logging. In addition, the message will be recorded locally on the SYSPRINT file. If an error
or end of transfer message is returned from the record module, SND will forward the message and wait
for a disconnect indication from the other side to acknowledge end of transfer.
Page 84 Appendix B: BFX Internal Summary MAN-REF-H211-05