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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
 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

Graves, Butts & Angel [Page 3] RFC 1646 TN3270 Extensions July 1994


 A TELNET connection is a Transmission Control Protocol (TCP)
 connection used to transmit data with interspersed TELNET control
 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


 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 1994

3.2 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.


    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.


 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
 <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 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.


                   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                                    0

Graves, 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.
                             SOH = 0X01
                             % = 0X6C
                             R = 0XD9
                             S1 = Status/Sense Byte 0
                             S2 = Status/Sense Byte 1
                             IAC = Telnet IAC Character
                             EOR = Telnet EOR Character

5.1 Status/Sense Byte description

5.1.1. 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 Zero

Graves, 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.  (See Section 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 1994

5.1.2. 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
             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"

Graves, Butts & Angel [Page 9] RFC 1646 TN3270 Extensions July 1994

6. The following is an example of the Client-Server negotiation

    Client:        IAC WILL TERMINAL-TYPE
    Client:        IAC SB TERMINAL-TYPE IS IBM-3287-1 IAC SE
    Note: To request a specific LU the TERMINAL-TYPE string would be:
    (The client has specified its terminal type is an IBM-3287-1)
    Server:   IAC DO END-OF-RECORD
    Client:        IAC WILL END-OF-RECORD
    Client:        IAC DO END-OF-RECORD
    (The Server and Client have both agreed to transmit End-Of-Record
    Client:        IAC DO TRANSMIT-BINARY
    (The Server and Client have both agreed to use binary
    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
    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)


 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


 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


 [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 1994

Authors' Addresses

     Cleve Graves
     2711 LBJ Freeway
     Dallas, Texas  75234
     Phone: (214) 484-5200
     Thomas Butts
     2711 LBJ Freeway
     Dallas, Texas  75234
     Phone: (214) 484-5200
     Michelle Angel
     2711 LBJ Freeway
     Dallas, Texas  75234
     Phone: (214) 484-5200

Graves, Butts & Angel [Page 13]

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