RFC 1647 (rfc1647) - Page 2 of 34

TN3270 Enhancements

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
   negotiation as a standard.  RFC 1041 attempted to standardize the
   method of negotiating 3270 terminal support by defining the 3270
   Regime Telnet Option.  Very few developers and vendors ever
   implemented RFC 1041.

   This document will refer to the existing practice of negotiating
   these three Telnet Options before exchanging the 3270 data stream as
   "traditional tn3270".

   NOTE: Except where otherwise stated, this document does not
   distinguish between Telnet servers that represent SNA devices and
   those that represent non-SNA 3270 devices.



Kelly