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Network Working Group                                         C. GravesRequest for Comments: 1646                                     T. ButtsCategory: Informational                                        M. Angel                                                   Open Connect Systems                                                              July 1994TN3270 Extensions for LUname and Printer SelectionStatus 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.Abstract   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   TN3270E@list.nih.gov . 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.1. INTRODUCTION   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   communicate the out-of-band information flows.  This session is   called the SSCP-LU session, and the session with the application is   called the LU-LU session (in VTAM an applications is just another   Logical Unit).Graves, Butts & Angel                                           [Page 2]

RFC 1646                   TN3270 Extensions                   July 1994   One such out-of-band flow is the LUSTAT message which tells the   application that the status of the terminal has changed, and is how a   printer or screen tells the application that it is ready, or is not   ready to receive data.   There are also flows which must be able to flow in the LU-LU session   to help control the use of the terminal by applications.  The block   of information sent in a session is called an RU (Request Unit) and   it tells what type of data this block contains, how long it is and if   more data (RUs) is coming along.  This is a gross over simplification   of what RUs are and do, but it should help understand their use in   the TN3270 documents.  Some of the VTAM/SNA terms used to describe   what an RU is requesting are:  Chains/chaining which tell a session   partner that another RU is being sent or not being sent in this   transmission.  Brackets which are used to indicate that a unit of   work is complete, such as when a printout of a file is complete.   The determination of what part of the VTAM/SNA protocols such as   brackets and chaining are to be used are managed by VTAM tables   called LOGMODE tables.  These tables are selected when an LU-LU   session is started and set up such things as bracket, and/or chaining   protocols; and the type of terminal data contained in the RUs, such   as printer data without screen formatting data (LU type 1), 3270   screen formatted data (LU type 2) and 3270 screen formatted data for   a printer (LU type 3).  The LOGMODE tables also contain the size of   the RU to be sent and received.  These tables also communicate the   screen size of 3270 terminals such as 24X80 (Model 2), 27X132 (Model   5), etc.  Each LU has a LOGMODE table entry hard assigned to it as   part of the VTAM configuration (often called a GEN).  The selection   of these table entries can't be controlled by the terminal LU or PU.   They can only be selected by the user at connection/logon time or by   the application when the connection is established.  The actual   LOGMODE entries to be used during a session are sent at session logon   time, in a special type of RU called a BIND.  Once the bind has been   sent then the rules for the use of the session have been set, can't   be changed, and must be followed.   The purpose of the TN3287 protocol is to provide a general IBM 3270   host printer communications facility.  Its primary goal is to allow a   method of connecting printer devices and printer-oriented processes   to each other.  This protocol will allow a TN3270 Client to process   3287 print data streams.   This memo supplements and extends the STD 8,RFC 854, TELNET Protocol   Specification.  This memo also presents an example of the correct   implementation.Graves, Butts & Angel                                           [Page 3]

RFC 1646                   TN3270 Extensions                   July 19942. GENERAL CONSIDERATIONS   A TELNET connection is a Transmission Control Protocol (TCP)   connection used to transmit data with interspersed TELNET control   information.   The companion document, STD 8,RFC 854 -- "TELNET Protocol   Specification" should be consulted for further information about the   TELNET command, codes and code sequences referenced in this   specification.3. CLIENT-SERVER NEGOTIATION   The TN3270 Client and Server require a specific negotiation protocol.   After the negotiation is complete, all transmission between the   Client and Server is in TELNET Binary format with a TELNET "End-Of-   Record(EOR)" sequence at the end of each data stream.   Support for the TN3287 data stream requires that both sides:      A.  Are able to exchange binary data.      B. Can establish the agreement between client and server on the         terminal type that will be used.      C. Agree to use the TELNET IAC EOR as a delimiter for inbound         and outbound TN3287 data streams   This implementation requires the options: TERMINAL-TYPE and BINARY be   successfully negotiated between the Client and Server before   processing of any print data streams.   This implementation supports host applications that can mix LU 1 and   LU 3 type data in the data stream.3.1  TN3287 SERVER   The maximum Request Unit (RU) size is server specific, but should not   exceed 4 kilobytes.   The LU type is determined by the bind from the mainframe application.   The server, when bound, must remember LU 1 or LU 3 type.   The server will automatically unbind the session upon receipt of a   TELNET CLOSE command.  The printer will be reported to VTAM as   powered down until a new TELNET connection is established.Graves, Butts & Angel                                           [Page 4]

RFC 1646                   TN3270 Extensions                   July 19943.2  TN3287 CLIENT   The TN3287 Client is a TN3270 client created specifically to print   mainframe 3270 print data.  The client emulates the IBM device type   that it identifies itself to the TN3270 server as, in this case, an   IBM 3287 model 1 type printer.  The design of this printer protocol   is aligned with the way printing occurs in the IBM host and how 3270   printers function.  These printer extensions DO NOT support a 3270   printer client that cannot accept both types LU 1 and LU 3 printer   streams.  No IBM printer operates in this fashion, and as a result,   no TN3270 server could function properly with mainframe applications   if it didn't allow for a mixing of LU 1 and LU 3 data streams.  The   common way in which this can occur is printer sharing between   multiple IBM host applications, such as CICS and JES.  Since there is   no restriction, the JES can be configured to output LU 1 data   streams, and the CICS can be  configured for LU 3 data streams.   Therefore, the server will identify what LU type the current   application connected to the server is using.  If that type is LU 1,   ALL message records sent to the Client will be preceded by one byte   of binary zeros (0x00).  If the first byte is not zeros, then that   byte will be a valid LU type 3 Write-Command-Code(WCC), which can   NEVER be zeros.  Thus, the client can tell the LU type of data as   each record is received.   This protocol does allow for the client to shutdown if the client   does not wish to support both LU types.  This is accomplished by   detecting an invalid data type from the received record, and   notifying the user that the mainframe application has sent LU type x   print data and should be configured for LU type y printing.4.  COMMAND STRUCTURE      1. All TELNET commands consist of at least a two-byte sequence:         the "Interpret-as-Command(IAC)" escape character followed by         the code for the command.   NOTE:  Since the TELNET IAC character (255 decimal) is used as a   delimiter (together with EOR) in the inbound and outbound data   streams, a data byte within the data stream itself that has the same   value as the IAC command is sent as two bytes (255, 255) and one byte   is discarded.4.1  TELNET COMMANDS   Command meaning - WILL and DO commands are used to obtain and grant   permission for the subsequent subnegotiation.  Both sides must   exchange WILL TERM-TYPE and DO TERM-TYPE before subnegotiation.Graves, Butts & Angel                                           [Page 5]

RFC 1646                   TN3270 Extensions                   July 1994   The actual exchange of information is done within the option   subcommand.   <IAC DO TERMINAL-TYPE>  Sender requests that the other party begin   terminal-type sub-negotiation.   <IAC WILL TERMINAL-TYPE>  Sender is willing to send terminal-type   information in a subsequent sub-negotiation.   <IAC SB TERMINAL-TYPE SEND IAC SE>  Sender requests the receiver to   transmit his terminal-type.   <IAC SB TERM TYPE IS IBM-3287-1 IAC SE>   Sender is stating the name   of his terminal-type.  The code for <IS> is 0.  Optionally, a   specific Logical Unit (LU) can be requested by using the TERMINAL-   TYPE string below.   If no LUname is specified, the first available   3287 LU is selected.      IAC SB TERM-TYPE IS IBM-3287-1 @ LUNAME IAC SE   <IAC DO BINARY>  Sender requests that sender of the data starts   transmitting or confirms that the sender of data is expected to   transmit characters that are to be interpreted as 8 bits of binary   data by the receiver.   <IAC WILL BINARY>   Sender requests permission to begin transmitting,   or confirms it will now begin transmitting binary data.   An <EOR> is sent at the end of each SNA Request Unit (RU) end of   chain, in either direction.   The first byte following the <EOR> is a   Write-Command-Code(WCC) for LU 3 data streams.   An <AO> is sent at the end of the SNA RU and end of bracket.  This   signifies the end of the print output or file by the IBM host   application and possibly a change of LU type.4.2   COMMAND VALUES                     TELNET COMMAND                     CODE                     IAC  Interpret as Command           255                     DO                                  253                     WILL                                251                     SB  SuBnegotiation option           250                     SE  Subnegotiation End              240                     TERMINAL-TYPE                        24                     SEND                                  1                     IS                                    0Graves, Butts & Angel                                           [Page 6]

RFC 1646                   TN3270 Extensions                   July 1994                     EOR  End-Of-Record                   25                     BINARY                                0                     AO  Abort Output                    245                     IP  Interrupt Process               244                     AYT  Are You There                  246                     BREAK                               243   NOTE:  The above codes and code sequences have the indicated meaning   only when immediately preceded by an "Interpret as Command (IAC)".5.  TN3270 Printer Status Message   The status message can be sent at any time.  It must be sent every   time the TN3270 Server sends an End-of-Record(EOR) indicator to the   TN3270 Client, or when a printing error occurs at the Client.  The   Printer Status Message is only sent by the TN3270 Client. Once the   End-Of-Record IAC is processed, the TN3270 Client sends the status   message to the server when it is ready to receive more print data.      MESSAGE DESCRIPTION:      SOH  %  R  S1  S2  IAC  EOR                               SOH = 0X01                               % = 0X6C                               R = 0XD9                               S1 = Status/Sense Byte 0                               S2 = Status/Sense Byte 1                               IAC = Telnet IAC Character                               EOR = Telnet EOR Character5.1   Status/Sense Byte description5.1.1.  S/S Byte 0:        High Order                                          Low Order        _____________________________________________________________        |                                                           |        |   0      1      2      3      4      5      6      7      |        |___________________________________________________________|          Bit Number:       Bit Definition:                0           Always Zero                1           Always ZeroGraves, Butts & Angel                                           [Page 7]

RFC 1646                   TN3270 Extensions                   July 1994                2           Always Zero                3           Always Zero                4           Always Zero                5           Unit Specify - is set due to an error                            condition.  The reason for the error                            condition will be indicated in S/S Byte 1.                            See Note 1*.                6           Device End - when this bit sent in response                            to a data message it indicates the client                            has successfully processed the data message                            from the server and notifies the server to                            send a new data message to the client when                            available.   See Note 2*.                7           Always Zero   Note 1*:   A negative response to the Server's data message would be   S/S Byte 0 Bit 5 "Unit Specify condition".  The possible Unit Specify   conditions are listed below.  (SeeSection 3.2 for bit settings for   the Unit Specify conditions listed below.)                Unit Specify Condition:    SNA Sense Code sent to host:                Command Rejected                     0X10030000                Intervention Required                0X08020000                Data Check                           0X10010000                Operation Check                      0X10050000                Component Disconnected (LU)          0X08020000   Note 2*:   Device End -  A positive response to the Server's data   message would be the "Device End" bit (S/S Byte 0 Bit 6) to indicate   a ready to receive data from the host condition.  This will also be   sent after clearing a previous Unit Specify condition of   "Intervention Required".Graves, Butts & Angel                                           [Page 8]

RFC 1646                   TN3270 Extensions                   July 19945.1.2.  S/S Byte 1:         High Order                                           Low Order       ______________________________________________________________       |                                                            |       |    0      1      2      3      4      5      6      7      |       |____________________________________________________________|          Bit Number:       Bit Definition:               0            Always Zero               1            Always Zero               2            Command Rejected (CR) -- This bit                            indicates an invalid 3270 command                            generated.               3            Intervention Required - Printer Not Ready.                            See Note 3*.               4            Component Disconnected - Printer is powered                            off or printer cable not connected.  See                            Note 4*.               5            Data Check - Invalid print data               6            Always Zero               7            Operation Check - An illegal buffer address                            or incomplete order sequence   Note 3*:  The Intervention Required is cleared by sending an S/S   message with the "Device End" bit (Bit 6 of S/S byte  0).  The LUSTAT   sent to the host is 0X00010000.  The IBM host interprets this as a   "printer now ready" condition.   Note 4*:  The Component disconnected is cleared by sending an S/S   message with the "Device End" bit  (Bit 6 of S/S byte 0).  The LUSTAT   sent to the host is 0X082B0000.  The IBM host interprets this as a   "printer now ready -- presentation space integrity may be lost"   condition.Graves, Butts & Angel                                           [Page 9]

RFC 1646                   TN3270 Extensions                   July 19946.  The following is an example of the Client-Server negotiation    process.      Server:   IAC DO TERMINAL-TYPE      Client:        IAC WILL TERMINAL-TYPE      Server:   IAC SB TERMINAL-TYPE SEND IAC SE      Client:        IAC SB TERMINAL-TYPE IS IBM-3287-1 IAC SE      Note: To request a specific LU the TERMINAL-TYPE string would be:      IAC SB TERMINAL-TYPE IS IBM-3287-1 @ LUNAME IAC SE      (The client has specified its terminal type is an IBM-3287-1)      Server:   IAC DO END-OF-RECORD      Client:        IAC WILL END-OF-RECORD      Server:   IAC WILL END-OF-RECORD      Client:        IAC DO END-OF-RECORD      (The Server and Client have both agreed to transmit End-Of-Record      (EOR)).      Server:   IAC DO TRANSMIT-BINARY      Client:        IAC WILL TRANSMIT-BINARY      Server:   IAC WILL TRANSMIT-BINARY      Client:        IAC DO TRANSMIT-BINARY      (The Server and Client have both agreed to use binary      transmission)      Server:   0x00 (3270 PRINT DATA)      Client:        (S/S with DEV END) IAC EOR      Server:   0x00 (3270 PRINT DATA) IAC EOR      NOTE:  LU 1 type data is prefaced with a 0x00 character. LU 3      type data is not prefaced with a special character.  This      character will precede print data in each chain, and should be      discarded before the print data is processed.   An <IAC EOR> must      be received before changing to LU 1 or LU 3 type data.      Client:        (S/S with IR) IAC EOR (This indicates a paper jam                    at printer.)      Client:        (S/S with DE) IAC EOR (This indicates the clearing                    of above condition.)      Server:  0x00 (3270 PRINT DATA) (This indicates start of LU 1               data)      Server:   (3270 PRINT DATA)Graves, Butts & Angel                                          [Page 10]

RFC 1646                   TN3270 Extensions                   July 1994      Server:   (3270 PRINT DATA)      Server:   (3270 PRINT DATA) IAC EOR      Client:        (S/S with DE) IAC EOR      Server:   0x00 (LAST 3270 PRINT DATA) IAC EOR      Client:        (S/S with DE) IAC EOR      Server:   IAC AO      (The Abort Output <AO> signifies the end-of-bracket -- end of      print job)7.  SECURITY CONSIDERATIONS   This document does not specify a security methodology to insure that   the client requesting a printer LU name is authorized to access that   LU.  Currently, this is left up to individual server implementations.   The design of the protocols described in this document allow for the   future incorporation of the RFCs regarding encryptions and   authentication protocols and services.  However, before this may   occur, certain extensions may be required to the protocols defined in   this document or to the encryptions and authentication services and   protocols.8. ERROR CONDITIONS   After a client and server have successfully completed negotiation, a   number of potential error conditions may be detected by the server   which require notifying the client and aborting the connection.   When an error condition is detected by the server, the client must be   negotiated back into NVT mode by the server sending a "WONT/DONT   BINARY" TELNET sequence and the client responding with the   appropriate "DONT/WONT BINARY" TELNET sequence.   The server should immediately send the appropriate error message to   the client as an ASCII string and then close the connection. The   error message should be prefixed by a numeric identifier to precisely   notify the client of the specific error condition. The error message   sent to the client should be routed to the proper console or log for   corrective action.   Below is a list of error conditions identified by numeric value,   error text, meaning of the error and recovery procedure.      Message: "01 No LU's of the type configured"         Meaning: The configuration definition on the server                  does not include the LU type requested.Graves, Butts & Angel                                          [Page 11]

RFC 1646                   TN3270 Extensions                   July 1994         Recovery: Notify your Systems Administrator as this                   is a permanent error condition.      Message: "02 Requested LU unavailable"         Meaning: The requested LU is not available at                  this time.         Recovery: This may be a temporary error and may                   be retried periodically.  If the condition                   persists contact your Systems Administrator.      Message: "03 Requested LU type is inconsistent with configuration"         Meaning: The LU requested does not match the terminal                  type in the server configuration.         Recovery: Notify your Systems Administrator as this                   is a permanent error condition.      Message: "04 Requested LU is not configured"         Meaning: The LU is not defined in server configuration.         Recovery: Notify your Systems Administrator as this                   is a permanent error condition.   When a client receives a message not defined in the above list, the   message should be displayed to a console or log and the connection to   the server should be closed.  No other recovery should be attempted   as this is most likely a fatal error condition.  (Notify your Systems   Administrator.)9. REFERENCES   [1] Postel, J., and J. Reynolds, "TELNET Protocol Specification", STD       8,RFC 854, USC/Information Services Institute, May 1983.   [2] VanBokkeln, J., "TELNET Terminal-Type Option"RFC 1091, FTP       Software Inc., February 1989.   [3] Postel, J., and J. Reynolds, "TELNET Binary Transmission", STD       27,RFC 856, USC/Information Services Institute, May 1983.Graves, Butts & Angel                                          [Page 12]

RFC 1646                   TN3270 Extensions                   July 1994Authors' Addresses       Cleve Graves       2711 LBJ Freeway       Dallas, Texas  75234       Phone: (214) 484-5200       EMail: cvg@oc.com       Thomas Butts       2711 LBJ Freeway       Dallas, Texas  75234       Phone: (214) 484-5200       EMail: tom@oc.com       Michelle Angel       2711 LBJ Freeway       Dallas, Texas  75234       Phone: (214) 484-5200       EMail: angel@oc.comGraves, Butts & Angel                                          [Page 13]