TN3270 Enhancements
RFC 1647

Document Type RFC - Proposed Standard (July 1994; No errata)
Obsoleted by RFC 2355
Last updated 2013-03-02
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Network Working Group                                          B. Kelly
Request for Comments: 1647                            Auburn University
Category: Standards Track                                     July 1994

                          TN3270 Enhancements

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This document describes a protocol that more fully supports 3270
   devices than do the existing tn3270 practices.  Specifically, it
   defines a method of emulating both the terminal and printer members
   of the 3270 family of devices via Telnet; it provides for the ability
   of a Telnet client to request that it be assigned a specific device-
   name (also referred to as "LU name" or "network name"); finally, it
   adds support for a variety of functions such as the ATTN key, the
   SYSREQ key, and SNA response handling.

   This protocol would be negotiated and implemented under a new Telnet
   Option and would be unrelated to the Telnet 3270 Regime Option as
   defined in RFC 1041 [1].

TABLE OF CONTENTS

   1.  Introduction ...............................................  2
   2.  TN3270E OVERVIEW ...........................................  3
   3.  COMMAND NAMES AND CODES ....................................  4
   4.  COMMAND MEANINGS ...........................................  5
   5.  DEFAULT SPECIFICATION ......................................  6
   6.  MOTIVATION .................................................  7
   7.  TN3270E SUB-NEGOTIATION RULES ..............................  7
      7.1  DEVICE-TYPE Negotiation ................................  7
          7.1.1 Device Pools ......................................  8
          7.1.2 CONNECT Command ...................................  9
          7.1.3 ASSOCIATE Command ................................. 10
          7.1.4 Device Selection Rules ............................ 10
          7.1.5 Accepting a Request ............................... 11
          7.1.6 REJECT Command .................................... 12
      7.2  FUNCTIONS Negotiation .................................. 13
          7.2.1 Commands .......................................... 13

Kelly                                                           [Page 1]
RFC 1647                  TN3270 Enhancements                  July 1994

          7.2.2 List of TN3270E Functions ......................... 14
   8.  TN3270E DATA MESSAGES ...................................... 15
      8.1  The TN3270E Message Header ............................. 16
          8.1.1 DATA-TYPE Field ................................... 16
          8.1.2 REQUEST-FLAG Field ................................ 17
          8.1.3 RESPONSE-FLAG Field ............................... 17
          8.1.4 SEQ-NUMBER Field .................................. 18
   9.  BASIC TN3270E .............................................. 18
      9.1  3270 Mode and NVT Mode ................................. 19
   10. DETAILS OF PROCESSING TN3270E FUNCTIONS .................... 20
      10.1 The SCS-CTL-CODES Function ............................. 20
      10.2 The DATA-STREAM-CTL Function ........................... 20
      10.3 The BIND-IMAGE Function ................................ 21
      10.4 The RESPONSES Function ................................. 22
         10.4.1 Response Messages ................................. 23
      10.5 The SYSREQ Function .................................... 26
         10.5.1 Background ........................................ 26
         10.5.2 TN3270E Implementation of SYSREQ .................. 27
   11. THE 3270 ATTN KEY .......................................... 28
   12. 3270 STRUCTURED FIELDS ..................................... 29
   13. IMPLEMENTATION GUIDELINES .................................. 29
      13.1 3270 Data Stream Notes ................................. 29
      13.2 Negotiation of the TN3270E Telnet Option ............... 30
      13.3 A "Keep-alive" Mechanism ............................... 30
      13.4 Examples ............................................... 31
   14. SECURITY CONSIDERATIONS .................................... 33
   15. REFERENCES ................................................. 33
   16. AUTHOR'S NOTE .............................................. 34
   17. AUTHOR'S ADDRESS ........................................... 34

1.  Introduction

   Currently, support for 3270 terminal emulation over Telnet is
   accomplished by the de facto standard of negotiating three separate
   Telnet Options - Terminal-Type [2], Binary Transmission [3], and End
   of Record [4].  Note that there is no RFC that specifies this
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