_intro.txt

一个通讯程序源码

.*s 1 "Introduction"

ECU (Extended Call Utility) is a personal and research
communications program originally written for
users of SCO UNIX V.3.2/386 and XENIX V on 80286 and 80386 systems.
Support for other systems has been added and further porting
is possible with "minor" effort to other systems based on or
similar to UNIX System V.
This preliminary document describes ECU functionality and implementation
from a technical point of view and provides at least rudimentary
documentation for its features and commands.

ECU provides the classic terminal communications facility of passing
keyboard data to a serial line and incoming data to the computer video
display.  In addition, a dialing directory, a function key mapping
feature, and session logging are available.

A very flexible procedure (script) language is also incorporated to
automate many communications tasks.  In addition to
augmenting interactive tasks, by using shell scripts and ECU
procedures, ECU can perform batch-style communications sessions
in an entirely "unattended" fashion.
Because of limitations of my nroff program, the procedure language
is described in a separate document.

ECU presents to the host a flexible "ANSI" terminal type, accepting
any valid video control sequences from MS-DOS or SCO documentation
as of late 1990.  It also fares well, though imperfectly, with
Sun and VT-100 in-band video control sequences.
Standards are great: everybody should have one, especially if
they call it "ANSI."
For more information,
refer to the section below titled "ANSI Filter."

The program supports almost any local terminal (console) which
can be described in a termcap database entry.
For more information, refer to "Supported Terminals."

ECU supports numerous file transfer protocols: as of this writing,
XMODEM, XMODEM/CRC, XMODEM-1K, YMODEM/CRC Batch, ZMODEM/CRC-16,
ZMODEM/CRC-32, Kermit and SEAlink are supported.
For more information, refer to the sections describing the
individual interactive and procedure file transfer commands.

This document is better than that supplied with
ECU 2.0, but is still rough in many places.
It attempts to get across to the inquiring mind how ECU
works.  In places, an understanding of the UNIX programming model, UNIX,
XENIX and UUCP constructs and asynchronous communications techniques
is assumed.  In other places, the document goes into tedious detail
about the simplest of concepts.  A great deal of attention has been
placed in accurate and robust coding of the program.  Perhaps, time
permitting, one day I can say the same for this document.