TN3270 Extensions for LUname and Printer Selection
RFC 1646

Document Type RFC - Informational (July 1994; No errata)
Authors Michelle Angel  , Thomas Butts  , Cleve Graves 
Last updated 2013-03-02
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Network Working Group                                         C. Graves
Request for Comments: 1646                                     T. Butts
Category: Informational                                        M. Angel
                                                   Open Connect Systems
                                                              July 1994

           TN3270 Extensions for LUname and Printer Selection

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.


   This document describes protocol extensions to TN3270.  There are two
   extensions outlined in this document.  The first defines a way by
   which a TN3270 client can request a specific device (LUname) from a
   TN3270 server.  The second extension specifies how a TN3270 printer
   device can be requested by a TN3270 client and the manner in which
   the 3270 printer status information can be sent to the TN3270 server.
   Discussions and suggestions for improvements to these enhancements
   should be sent to the TN3270E Working Group mailing list . These extensions will be called TN3287 in this
   document.  This information is being provided to members of the
   Internet community that want to support the 3287 data stream within
   the TELNET protocol.


   The need to communicate with IBM mainframe systems has a number of
   unique requirements associated with it.  This document addresses
   those needs in a TCP/IP communications network.

   IBM terminals are generically referred to as 3270's which includes a
   broad range of terminals and devices,not all of which actually begin
   with the numbers 327x.

   The 3270 family of terminals and the IBM mainframe applications
   systems are VERY closely coupled and it is the nature of the way the
   3270s and the applications interact which require that this document
   be available to provide a consistent way for the TCP/IP environment
   to interact effectively with the 3270 applications of the IBM
   mainframe world.

Graves, Butts & Angel                                           [Page 1]
RFC 1646                   TN3270 Extensions                   July 1994

   IBM mainframe applications systems have existed for almost two
   decades now and are used to serve tens of thousands of users daily.
   For this reason it is usually the need of a mainframe environment to
   add TCP/IP network support WITHOUT writing new applications to run
   with the TCP network.  The TN3270 series of documents addresses how
   this can be done and maintain compatibility with those mainframe
   application systems.

   One of the unique characteristics of the 3270 terminals is their
   ability to communicate status information in an out-of-band data
   flow.  These status's are in turn used by the applications systems to
   support error recovery, and conflict resolutions, examples of these
   are printer out of paper, and terminal powered up.  The terminals are
   also half duplex and block mode in their operations, which results in
   the need to communicate when blocks are being sent, when they end,
   and when they cannot be sent.  This document describes these
   characteristics in IBM VTAM/SNA terms.  Some VM mainframe application
   systems do not use VTAM, so for those systems these terms don't
   apply.  For any systems which use VTAM these terms apply and are
   dealt with in some way by the TCP/IP to VTAM interface.

   VTAM/SNA is a hierarchical network and some of that hierarchy needs
   to be addressed by the TCP network attaching to it if the
   applications systems are to continue to provide the same applications
   support that they have provided to the 3270 terminals.

   The 3270 terminal environment consists of a terminal controller with
   terminals attached to that controller.  In VTAM/SNA this controller
   is called a PU (Physical Unit) and the terminals called LUs (Logical
   Units).  The PU is used to communicate management information to the
   VTAM/SNA system, and the LU is used by the application to communicate
   with the terminal.  VTAM/SNA identifies each LU and PU in a network
   by a unique name.  These names are referred to as LUnames and
   PUnames, and is how the network is managed and the applications
   identify what terminals are being communicated with in the network.
   The actual connection between a terminal and the applications is
   referred to as a session, and it is this session which has both in-
   band and out-of-band information flows sent between the applications
   and the terminals.

   VTAM/SNA 3270 terminals actually have two sessions when communicating
   with the applications.  One session is directly connected with the
   application and the other session is connected directly to VTAM.  It
   is the session with VTAM, also called the SSCP, that is used to
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