RFC338 - EBCDIC/ASCII Mapping for Network RJE

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　　Network Working Group R.T. Braden
Request for Comments: 338 UCLA/CCN
NIC: 9931 17 May 1972

EBCDIC/ASCII MAPPING FOR NETWORK RJE

A. INTRODUCTION

Under NETRJS [1], CCN's Network rje protocol [2], a virtual remote
batch terminal may be either EBCDIC or ASCII. CCN operates an IBM
360/91 which performs all of its normal processing in EBCDIC. When a
virtual ASCII terminal signs onto NETRJS, CCN translates the "card
reader" stream to EBCDIC and translates the "printer" stream back to
ASCII [3].

In recent months, a number of ASCII hosts (RAND PDP-10, Utah PDP-10,
Illinois PDP-11) have completed user processes for NETRJS. Several
users at these sites have noted deficiencies in the ASCII/EBCDIC
mapping rules originally implemented in NETRJS. Since their
objections were well founded, we have altered the existing mapping
and added a new one.

This RFChas three purposes:

(1) to make all users of NETRJS aware of the changed ASCII mapping

(2) to call this problem to the attention of the Network RJE
Protocol Committee

(3) to knowledge and support Joel Winett's pioneering work [4] in
this area.

THE EBCDIC CHIMERA

A year ago, Joel Winett Published RFC#183, containing the results of
his careful research into just what EBCDIC really means. He sounded
a clarion call for all EBCDIC sites to join in defining a Network
standards mapping. At this time, we at CCN were primarily absorbed
in the timely implementation of the NETRJS protocol to serve an
EBCDIC (!) user site, RAND, so we were not very supportive of his
efforts.

RFC#183 is a valuable document; we hope a copy falls into the hands
of Armonk. It is clear from RFC#183 that EBCDIC consists of a
standard ("basic") set of characters, combined with a number of
overlapping ad-hoc character happenings. Fortunately, if we exclude

special-purpose text composition programs, IBM 360 programs use only
the 89 "basic" EBCDIC graphics [5] shown in RFC#183 as well as in
Figure 1. An IBM 029 "EBCDIC" keypunch can create 63 graphics: the
89 basic EBCDIC graphics less the 26 lower case letters. In fact,
OS/360 requires an even smaller subset of EBCDIC, 60 characters
commonly called the "PL/1 character set". The PL/1 set consists of
the 89 basic graphics, less the 26 lower case letters as well as the
three graphics <cent sign>!" (cent sign, exclamation point, and
quotation).

C. CHARACTER MAPPING IN NETRJS

We consider now the requirements of a ASCII/EBCDIC mapping for NETRJS
or any rje protocol. These requirements are as follows:

Efficiency:

The translation should be character-to-character, so that the CPU
operation "translate" can be used and character scans obviated.
This is important because a significant volume of character data
may be moved during rje operations.

Usability:

(1) All of the 89 EBCDIC graphics should be mapped into
corresponding ASCII characters.

(2) The mapping should be as nearly transparent as possible, i.e.,
whenever the same graphic appears in both sets, it should map
onto itself.

(3) To minimize the adaptation required of an EBCDIC-oriented
programmer, the ASCII graphics should evoke the corresponding
EBCDIC graphic, when they are not identical.

Theses considerations led us to incorporate Winett's rules II (a) and
III (b) (see page 4 of the RFC#183) into NETRJS:

ASCII EBCDIC
----- ------
| |

~ <bent bar>

\ <cent sign>

This defines all 89 basic EBCDIC graphics in terms of ASCII.
However, there is still a question of how to map the 6 "maverick"
ASCII characters ( []{}^` ) which are not in EBCDIC and not in the
list above.

We could (and did) take the view that all CCN users are concerned
only with writing and executing normal 360 programs using EBCDIC and
that they would enter one of the maverick ASCII graphics only in
error. Our original choice, therefore, was to map the mavericks in
the input into EBCDIC question marks. We also assumed that, if a
user needs to access a larger subset of EBCDIC than the basic 89, he
should do so by doing his rje directly in EBCDIC.

We now realize that there were two deficiencies in the original
mapping rules.

1. The 360 program may be intended to manipulate ASCII text from
the Network. In that case, the Network user needs to have all
ASCII characters, including the mavericks, uniquely mapped
into EBCDIC in some (standard) manner.

2. The present mapping is convenient only if a user at an AT&T
Model 33/35 Teletype (or simulator thereof) needs a different
mapping for ease of use.

For the first case, we have changed the mapping of the 6 maverick
ASCII characters from "?", using instead Winett's rules III (c) and
III (d):

ASCII EBCDIC
----- ------
[ X'AD'
] X'BD'
{ X'8B'
} X'9B'
^ X'71'
` X'79'

For the user with a Model 33/35 Teletype, we have expanded the set of
virtual remote batch terminal types, adding "TTY" to "ASCII" and
"EBCDIC". A user establishes his virtual remote batch terminal as
type TTY by either doing his initial ICP to socket 15 (vs. 11 for
EBCDIC, 13 for ASCII), or by doing an ICP to Socket 1 and entering
the command "TTYRJS" (vs. "RJS" for EBCDIC, "ARJS" for ASCII). The
mapping used by NETRJS for a TTY remote is:

Model 33 Corresponding
Graphic ASCII EBCDIC
-------- ------------- ------
\ \ <bent bar>

<up arrow> ^ |

<left arrow> _ _

[ [ <cent sign>

] ] X'BD'

This is ugly, but it is probably the best we can do.

D. CONCLUSIONS

It is obvious that one pair of translation tables won't do the job;
NETRJS needs (at least) two mappings for each direction. How long
will it be before an important set of users appears with a different
terminal character set, requiring yet a different mapping? [6] An rje
server site needs to be prepared to provide a variety of translation
tables, and perhaps to allow a user to specify his own table(s); this
mini-subset of "Date Reconfiguration Service" might be necessary to
prevent translation-table-proliferation. The tendency in Network
discussions has been to put the burden upon the user sites to adapt
to different conventions. In the real world of users and servers,
the server will often have to do the adapting.

NOTES AND REFERENCES

[1] R.T. Braden, Interim NETRJS Specifications, RFC#189 (NIC
#7133), July 15, 1971.

[2] Please note that "RJS" is the proper name of a particular rje
package written at CCN the generic name for remote batch
service is "rje".

[3] Notice that the mapping question discussed in this RFCis
significant only for the virtual card reader and printer
connections in NETRJS. The punch connection is always
transparent, i.e., never translated. The remote operator
connections use the extended EBCDIC/ASCII mapping including
the maverick characters, but this is not important since
operator commands require only a limited character set.

[4] Joel Winett, "_The_ EBCDIC Codes and their Mapping to ASCII",
RFC#183 (NIC #7127), July 21, 1971.

[5] Winett lists only 88 basic EBCDIC graphics, excluding the
space which he regards as a control character. This is a
matter of taste, but we find it less confusing to include the
space as a graphic.

[6] CCN recently received a new Teletype-replacement terminal.
This machine has a bastardized graphic character set -- mostly
ASCII, with a sprinkling of both (!) EBCDIC and TTY.

+-------------------------------------+
| Full ASCII |
| a b ... z | ` ^ { } ~ |
| |
+-----+-------------------------------------+--------------+
|33/35| | AT&T TWX |
| | ` [ ] | (Mod 33/35 |
| | | tty) |
+------+-----+------+-----------------------+ | |
|Basic | | | | | |
|EBCDIC| | | <SP> | | |
| | | " | A B ... Z | | <left arrow> |
| | | ! | 0 1 ... 9 | | |
| | | | + - * / ( ) | | <up arrow> |
| | | | . , ' = | | |
| | | | $ & | | |
| | | | < > : ? % # @ | | |
| | | | | | |
| +-----+------+-----------------------+------+--------------+
| | | | |
| | | _ | |
| | | | |
| +------+-----------------------+------+
| | |
| | PL/1 <bent bar> | |
| | Set |
| +-----------------------+
| <cent sign> |
| Basic EBCDIC |
+-------------------------------------------+

Figure 1. Character Sets Commonly Abused

[This RFCis also available in .PS and .PDF format.]

[This RFCwas put into machine readable form for entry]
[into the online RFCarchives by Helene Morin, Viagenie, 12/99]

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