RFC1123                  REMOTE LOGIN -- TELNET             October 1989


              formatting rules have been applied to the data stream, and
              a "raw" mode, in which the application has direct access
              to every character as it was entered.  A Server Telnet
              must be implemented in such a way that these modes have
              the same effect for remote as for local terminals.  For
              example, suppose a CR LF or CR NUL is received by the
              Server Telnet on an ASCII host.  In raw mode, a CR
              character is passed to the application; in formatted mode,
              the local system's end-of-line convention is used.

      3.3.2  Data Entry Terminals

         DISCUSSION:
              In addition to the line-oriented and character-oriented
              ASCII terminals for which Telnet was designed, there are
              several families of video display terminals that are
              sometimes known as "data entry terminals" or DETs.  The
              IBM 3270 family is a well-known example.

              Two Internet protocols have been designed to support
              generic DETs: SUPDUP [TELNET:16, TELNET:17], and the DET
              option [TELNET:18, TELNET:19].  The DET option drives a
              data entry terminal over a Telnet connection using (sub-)
              negotiation.  SUPDUP is a completely separate terminal
              protocol, which can be entered from Telnet by negotiation.
              Although both SUPDUP and the DET option have been used
              successfully in particular environments, neither has
              gained general acceptance or wide implementation.

              A different approach to DET interaction has been developed
              for supporting the IBM 3270 family through Telnet,
              although the same approach would be applicable to any DET.
              The idea is to enter a "native DET" mode, in which the
              native DET input/output stream is sent as binary data.
              The Telnet EOR command is used to delimit logical records
              (e.g., "screens") within this binary stream.

         IMPLEMENTATION:
              The rules for entering and leaving native DET mode are as
              follows:

              o    The Server uses the Terminal-Type option [TELNET:10]
                   to learn that the client is a DET.

              o    It is conventional, but not required, that both ends
                   negotiate the EOR option [TELNET:9].

              o    Both ends negotiate the Binary option [TELNET:3] to




 



RFC1123                  REMOTE LOGIN -- TELNET             October 1989


                   enter native DET mode.

              o    When either end negotiates out of binary mode, the
                   other end does too, and the mode then reverts to
                   normal NVT.


      3.3.3  Option Requirements

         Every Telnet implementation MUST support the Binary option
         [TELNET:3] and the Suppress Go Ahead option [TELNET:5], and
         SHOULD support the Echo [TELNET:4], Status [TELNET:6], End-of-
         Record [TELNET:9], and Extended Options List [TELNET:8]
         options.

         A User or Server Telnet SHOULD support the Window Size Option
         [TELNET:12] if the local operating system provides the
         corresponding capability.

         DISCUSSION:
              Note that the End-of-Record option only signifies that a
              Telnet can receive a Telnet EOR without crashing;
              therefore, every Telnet ought to be willing to accept
              negotiation of the End-of-Record option.  See also the
              discussion in Section 3.2.3.

      3.3.4  Option Initiation

         When the Telnet protocol is used in a client/server situation,
         the server SHOULD initiate negotiation of the terminal
         interaction mode it expects.

         DISCUSSION:
              The Telnet protocol was defined to be perfectly
              symmetrical, but its application is generally asymmetric.
              Remote login has been known to fail because NEITHER side
              initiated negotiation of the required non-default terminal