rfc2355.txt

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   A client representing a printer device uses this function to indicate
   its willingness to accept a data stream that includes SCS control
   codes.  For the purposes of NVT mode versus 3270 mode, SCS-DATA must
   be treated exactly like 3270-DATA (i.e., it can cause a switch from
   NVT mode to 3270 mode).

   When a printer device-type has been negotiated, either the SCS-CTL-
   CODES function or the DATA-STREAM-CTL function, or both, must be
   negotiated.  This enables the server to know when it should and
   should not accept a session with a host application on behalf of the
   client.  If only the SCS-CTL-CODES function is agreed to, then the
   server will not establish sessions with host applications that would
   send 3270 data stream control.  If both SCS-CTL-CODES and DATA-
   STREAM-CTL are agreed to, then the server will establish sessions
   both with host applications that would send SCS control codes and
   with those that would send 3270 orders.

   The server should send a TN3270E message with DATA-TYPE set to
   PRINT-EOJ at the end of each print job to indicate to the client that
   it may now take whatever action is appropriate for its environment
   (e.g., close a disk or spool file, etc.).  The server may have
   multiple criteria for determining when it should send a PRINT-EOJ,



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   such as receipt of SNA End Bracket from the host application, or
   expiration of a pre-defined timeout value.

10.2 The DATA-STREAM-CTL Function

   This function can only be supported on a 3270 printer session.

   Agreement to support this function requires that the party support
   the following TN3270E header values:

             Header field         Value
             ------------         -----
              DATA-TYPE          3270-DATA
              DATA-TYPE          PRINT-EOJ

   A client representing a printer device uses this function to indicate
   its willingness to accept a data stream that includes 3270 orders and
   attributes.

   When a printer device-type has been negotiated, either the SCS-CTL-
   CODES function or the DATA-STREAM-CTL function, or both, must be
   negotiated.  This enables the server to know when it should and
   should not accept a session with a host application on behalf of the
   client.  If only the DATA-STREAM-CTL function is agreed to, then the
   server will not establish sessions with host applications that would
   send SCS control codes in a data stream.  If both SCS-CTL-CODES and
   DATA-STREAM-CTL are agreed to, then the server will establish
   sessions both with host applications that would send SCS control
   codes and with those that would send 3270 orders.

   The server should send a TN3270E message with DATA-TYPE set to
   PRINT-EOJ at the end of each print job to indicate to the client that
   it may now take whatever action is appropriate for its environment
   (e.g., close a disk or spool file, etc.).  The server may have
   multiple criteria for determining when it should send a PRINT-EOJ,
   such as receipt of SNA End Bracket from the host application, or
   expiration of a pre-defined timeout value.














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10.3 The BIND-IMAGE Function

   This function can only be supported when the TN3270E server
   represents SNA terminals and printers.

   Agreement to support this function requires that the party support
   the following TN3270E header values:

             Header field         Value
             ------------         -----
              DATA-TYPE          BIND-IMAGE
              DATA-TYPE          UNBIND
              DATA-TYPE          SSCP-LU-DATA

   When BIND-IMAGE is in effect, the server must inform the client when
   an SNA session has been established with a host application, and when
   such a session has been terminated.  It uses DATA-TYPE values of
   BIND-IMAGE and UNBIND to convey this information.

   When establishing an SNA session on behalf of a client, the server
   will receive a Bind RU from the host application.  It will also
   receive a Start Data Traffic RU.  Once both of these have been
   responded to positively by the server, it must then inform the client
   of the presence of this session by sending it a data message with the
   DATA-TYPE flag set to BIND-IMAGE.  The data portion of this message
   must contain the bind image exactly as it was received in the Bind RU
   that the server accepted on behalf of the client.  The format and
   maximum length of this bind image are defined in [6].

   When an SNA session between the server and a host application is
   terminated, the server must send a data message to the client with
   the DATA-TYPE flag set to UNBIND.  If the server was notified of the
   session termination via an SNA Unbind RU, it should include the
   Unbind reason code in the data portion of the message it sends to the
   client.  If the server itself requested the SNA session termination
   (for example, as part of SYSREQ key processing), it should set the
   data portion of the UNBIND message to 0x01, indicating "normal end of
   session".

   Another aspect of the BIND-IMAGE function alters the allowable DATA-
   TYPE flag values slightly from the behavior described in the section
   entitled "Basic TN3270E".  When BIND-IMAGE is in effect, data
   messages with DATA-TYPE set to 3270-DATA or SCS-DATA are not allowed
   before the first BIND-IMAGE is received by the client; only SSCP-LU-
   DATA or NVT-DATA can be used to transmit user- oriented data.  The
   same applies to data messages exchanged after an UNBIND is sent and
   before another BIND-IMAGE is received by the client.  Once the client
   receives a BIND-IMAGE data message, the allowable DATA-TYPE values,



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   in addition to SSCP-LU-DATA, now include 3270-DATA and/or SCS-DATA,
   depending on whether a terminal or printer device-type was
   negotiated, and whether a printer client agreed to DATA-STREAM-CTL or
   SCS-CTL-CODES, or both.  (See the section entitled "The SYSREQ
   Function" for further discussion of the SSCP-LU session in an SNA
   environment.)

10.4 The RESPONSES Function

   This function can be supported for both terminal and printer sessions
   connected to both SNA and non-SNA servers.

   Agreement to support this function requires that the party support
   the following TN3270E header values:

             Header field         Value
             ------------         -----
              DATA-TYPE          RESPONSE
              DATA-TYPE          REQUEST
              RESPONSE-FLAG      -all values-
              REQUEST-FLAG       ERR-COND-CLEARED
              SEQ-NUMBER         binary values from 0-32767

   Whenever a data message is sent with a DATA-TYPE of either SCS-DATA
   or 3270-DATA, the sender must set the RESPONSE-FLAG field to either
   NO-RESPONSE, ERROR-RESPONSE, or ALWAYS-RESPONSE.  It is anticipated
   that the client side will normally set RESPONSE-FLAG to NO-RESPONSE.
   The server, if it represents an SNA device, should set RESPONSE-FLAG
   to reflect the response value set in the RH of the RU that generated
   this data message - Definite Response resulting in a RESPONSE-FLAG
   value of ALWAYS-RESPONSE, Exception Response resulting in ERROR-
   RESPONSE being set, and No Response causing a setting of NO-RESPONSE.
   A non-SNA server should set RESPONSE-FLAG to ERROR-RESPONSE.

   In addition, the sender must keep a count of the messages with a
   DATA-TYPE of 3270-DATA or SCS-DATA that it sends on a given TN3270E
   session.  This counter should start at zero for the first such
   message, and be incremented by one for each subsequent message.  Note
   that this counter is independent of any SNA sequence numbers, and
   should not be reset to zero as a result of Bind or Unbind.  If the
   counter reaches the maximum of 32767, it should be restarted at zero.
   The sender must place this value in the SEQ-NUMBER field of the
   TN3270E header before it sends the message.  Note that the SEQ-NUMBER
   field must be set regardless of the value of the RESPONSE-FLAG field.







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10.4.1 Response Messages

   Whenever a data message with a DATA-TYPE of either SCS-DATA or 3270-
   DATA is received, the receiver must attempt to process the data in
   the data portion of the message, then determine whether or not it
   should send a data message with a DATA-TYPE of RESPONSE.  If the data
   message it has just processed had a RESPONSE-FLAG value of NO-
   RESPONSE, or if it had a value of ERROR-RESPONSE and there were no
   errors encountered while processing the data, then no RESPONSE type
   message should be sent.  Otherwise, a data message should be sent in
   which the header DATA-TYPE field is set to RESPONSE, and in which the
   SEQ-NUMBER field is a copy of the SEQ-NUMBER field from the message
   to which this response corresponds.  The RESPONSE-FLAG field in this
   header must have a value of either POSITIVE-RESPONSE or NEGATIVE-
   RESPONSE.  A POSITIVE-RESPONSE should be sent if the previously
   processed message's header specified ALWAYS-RESPONSE and no errors
   were encountered in processing the data.  A NEGATIVE-RESPONSE should
   be sent when

    1) the previously processed message specified ERROR-RESPONSE
       or ALWAYS-RESPONSE and

    2) some kind of error occurred while processing the data.

   Normally only the client will be constructing and sending these
   RESPONSE messages.  A negative response sent by the client to the
   server is the equivalent of a Unit Check Status [7].  All references
   to device status and sense codes in this section rely on [7].

   The data portion of a RESPONSE message must consist of one byte of
   binary data.  The value of this byte gives a more detailed account of
   the results of having processed the previously received data message.
   The possible values for this byte are:

           For a RESPONSE-FLAG value of POSITIVE-RESPONSE -

             Value            Meaning
             -----            -------
             0x00      Successful completion (when sent by the client,
                       this is equivalent to "Device End").

           For a RESPONSE-FLAG value of NEGATIVE-RESPONSE -

             Value            Meaning
             -----            -------
             0x00      An invalid 3270 command was received
                       (equivalent to "Command Reject").




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             0x01      Printer is not ready (equivalent to
                       "Intervention Required").

             0x02      An illegal 3270 buffer address or order
                       sequence was received (equivalent to
                       "Operation Check").

             0x03      Printer is powered off or not connected
                       (equivalent to "Component Disconnected").

   When the server receives any of the above responses, it should pass
   along the appropriate information to the host application.  The
   appropriate information is determined by whether the server
   represents an SNA or a non-SNA device.

   An SNA server should pass along a POSITIVE-RESPONSE from the client
   as an SNA positive Response Unit to the host application.  It should
   translate a NEGATIVE-RESPONSE from the client into an SNA negative
   Response Unit in which the Sense Data Indicator bit is on and which
   contains one of the following sense codes:

          RESPONSE-FLAG        Equivalent        SNA Sense Code
          -------------        ----------        --------------
              0x00           Command Reject        0x10030000

              0x01        Intervention Required    0x08020000

              0x02           Operation Check       0x10050000

              0x03        Component Disconnected   0x08310000

   A non-SNA server should pass along a POSITIVE-RESPONSE from the
   client by setting the Device End Status bit on.  It should reflect a
   NEGATIVE-RESPONSE from the client by setting the Unit Check Status
   Bit on, and setting either the Command Reject, Intervention Required,
   or Operation Check Sense bit on when responding to the Sense command.

   In the case of Intervention Required or Component Disconnected being
   passed by the server to the host application, the host would normally
   refrain from sending any further data to the printer.  If and when
   the error condition at the client has been resolved, the client must
   send to the server a data message whose header DATA-TYPE field is set
   to REQUEST, and whose REQUEST-FLAG is set to ERR-COND-CLEARED.  Note
   that this message has no data portion.  Upon receipt of this message,
   the server should pass along the appropriate information to the host
   application so that it may resume sending printer output.  Again, the
   form of this information depen