tjs@UF.MSC.UMN.EDU ("Tim Salo") (07/17/89)
Effective X.3/Telnet Gateway for Unix Desired
---------------------------------------------
Overview
--------
This note describes the need for a gateway which would enable
asynchronous devices attached to X.25 networks to communicate
effectively with Unix hosts using Telnet. The gateway should
translate between X.3/X.25 and Telnet/TCP/IP protocols.
Furthermore, the gateway should use one-character X.25 packets
when required and one-line X.25 packets with local echoing when
possible. This note assumes that Line Mode Telnet is available.
I am looking for people with experience with or opinions about
such a gateway. Additionally, I would like to know whether
anyone has or plans to develop, or has interest in working on, an
RFC for or prototype implementation of such a gateway. I will
summarize the responses.
X.3/Telnet Gateway Requirement
------------------------------
The configuration of the desired X.3/Telnet Gateway is shown
below. The X.3 PAD, X.25 Packet-Switched Data Network and
Telnet Host are existing products. The X.3/Telnet Gateway is the
product which is desired.
........
______ . . ______________ _______
| | . . | | | Telnet|
TTY ___| X.3 |___. X.25 .___| X.3/Telnet | | (Unix)|
^ | PAD | ^ . PSDN . ^ | Gateway | | Host |
^ |______| ^ . . ^ |______________| |_______|
^ ^ ........ ^ | |
async X.25 X.25 | |
| |
Telnet/TCP/IP (ethernet) | |
=============================================
X.3/Telnet Gateway Configuration
The X.3/Telnet Gateway should map between telnet connections and
X.3 connections, including X.3 SET PAD PARAMETERS and telnet
option negotiations. The X.3/Telnet Gateway must work well with
Unix hosts.
1. Efficient use should be made of the X.25 network; local
echoing at the X.3 PAD and large packets should be used when
possible.
2. Effective support for Unix software which relies upon one-
character-at-a-time communications and echoing by the Unix
user program should be provided. Programs such as "vi",
"less", and "more" should operate, from the perspective of
the terminal user, the same as if the terminal were directly
attached to the Unix host.
3. The gateway should automatically switch the X.3 PAD between
line-at-a-time and character-at-a-time communications. It
is assumed that Line Mode Telnet is available on the Unix
host to signal the gateway, through the telnet protocol,
when the user software moves into and out of character-at-
a-time communications. The gateway, upon receipt of an
indication that the user software in entering character-at-
a-time communications, should issue SET PAD PARAMETER
packets to the remote X.3 PAD to prepare it for one-
character X.25 packets. Upon receipt of an indication of
line-at-a-time communications, the gateway should issue SET
PAD PARAMETERS to prepare the remote PAD forward at the end
of a line and to echo locally.
Proposed X.3/Telnet Gateway Architecture
----------------------------------------
The X.3/Telnet Gateway should be a combined X.3 PAD and telnet
client. The telnet client and Unix host must implement the Line
Mode Telnet option to provide signalling of the movement of the
Unix user software in and out of character-at-a-time mode.
X.3/Telnet Gateway Unix Host
___________________ _______________
| | | G | | | | | | | U |
_____ | | | a | T | T | | T | T | K | s |
| | | X | X | t | e | C | | C | e | e | e |
TTY ___| X.3 |_____| . | . | e | l | P | | P | l | r | r |
^ | PAD | ^ | 2 | 3 | w | n | / | | / | n | n | |
^ |_____| ^ | 5 | | a | e | I | | I | e | e | S |
^ | ^ | | | y | t | P | | P | t | l | W |
async | X.25 |___|___|___|___|___| |___|___|___|___|
|______________| ^ | |_______| |
X.3/X.28 ^ | TCP/IP |
^ |_______________|
^ Telnet (line mode)
^
X.3/Telnet Gateway
Functionality
------------------
Feel free to send comments to:
Tim Salo
Minnesota Supercomputer Center
tjs@msc.umn.edu
(612) 626-0347