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Appendix D. Personal Computer File Transfer through the
3708
Overview
The purpose of this appendix is to assist customers who wish to develop their own
programs to transfer files through the 3708. Its intention is not to describe a
particular implementation of personal computer (PC) file transfer, but rather to
discuss the major features and functions of the 3708 that must be taken into account
when transferring files.
IBM has developed its own software product, IBM PC/HOST File Transfer and
Terminal Emulator Program (FTTERM), that uses an IBM PC to transfer files
through the 3708.
Personal Computer file transfer with a 3708 refers to the ability of a personal
computer (PC) to transfer data between its diskette and either an IBM SNA or
ASCII host (which may be another PC).
To control the exchange of data, PC file transfer requires two compatible programs:
one in the host and the other in the PC. These programs communicate between
themselves and provide the set of rules and conventions necessary to transfer files in
the customer's particular environment.
When the 3708 is present, it resides between the two communication programs and
monitors the data stream between them. Depending upon its configuration and
mode of operation, the 3708 performs certain functions; for example, when it
recognizes certain characters (such as line turnaround or control characters) or
detects error conditions (such as parity or framing errors) in the data stream.
These functions of the 3708 must be taken into account by the customer's file
transfer programs and in some cases may be used by the customer to enhance the
performance of their file transfers.
The following sections examine these functions for each of the 3708's three modes of
operation - protocol enveloping, protocol conversion, and ASCII pass-through.
Protocol Enveloping
In protocol enveloping mode, communication between a downstream device and an
upstream SNA host occurs in a line-by-line manner. Generally, this is controlled
through the use of line turnaround (LTA) characters. Up to five different LTA
characters may be defined by the 3708's control terminal operator for each port on
the 3708 capable of operating in protocol enveloping mode.
Protocol Enveloping Data Flow
When data is received by the 3708 from a downstream PC, the incoming data
characters are stored in a receive queue. For more information on data flow in
protocol enveloping mode, see "Data Flow Description" on page 5-11. For a
description of 3708 queues and buffers, see Appendix E, "Key Data Forma:ts and
Control Blocks."
Appendix D. Personal Computer File Transfer through the 3708
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