RFC 1576 (rfc1576) - Page 3 of 12

TN3270 Current Practices

RFC 1576                TN3270 Current Practices            January 1994


   In an SNA environment, a client session is identified by a Logical
   Unit (LU) name.  In a non-SNA environment, there is not a LU name
   associated with a client session.  The closest thing to a LU name in
   the TN3270 environment is the client's IP address.  Although some
   telnet servers are connected to the host using SNA, TN3270 clients
   using these servers have no defined way to determine the LU name
   associated with the session.

   Telnet servers that exist in non-SNA environments do not have to be
   concerned about providing TN3270 clients with support for the SNA
   functions described in this document.

   TN3270 does not support typical SNA responses and is classified as a
   non-SNA protocol.  A TN3270 emulator is not aware or concerned about
   how the telnet server is connected to a 3270 host application.

   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.

   Some typical "SNA" functions such as the SYSREQ and ATTN keys have
   been mapped to existing telnet commands and are supported by some
   telnet server implementations.

   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].  This negotiation and the resulting data flow will be
   described below.

   RFC 1041 [1] attempted to standardize the method of negotiating 3270
   terminal support by defining the 3270 Regime Telnet Option.
   Historically, very few developers and vendors ever implemented RFC
   1041.

   All references in this document to the 3270 datastream, SNA versus
   non-SNA operation, 3270 datastream commands, orders, structured
   fields and the like rely on [6].

   References to SNA Request and Response Units rely on [7].  References
   to SNA and SSCP rely on [12].










TN3270 Enhancements Working Group