<pre>Network Working Group                                     M. Krilanovich
Request for Comments: 121                    Computer Research Lab, UCSB
NIC: 5833                                                  21 April 1971


                       <span class="h1">NETWORK ON-LINE OPERATORS</span>

PREFACE

   The operators described in this document have been implemented within
   UCSB's On-Line System and make the Network (via the NCP) accessible
   to On-Line System users.

   A set of operators is provided to facilitate the use of the Network
   by On-Line System users.  The operators are defined on LVL I on
   system 'NET', and serve an an interface between the users and the
   Network Control Program (NCP), which supervises all Network
   operations at this site.

   A concept fundamental to On-Line System Network operations is that of
   a completion code variable.  Associated with each socket that is not
   in the closed state is a unique variable, called a completion code
   variable.  This variable serves two purpose: it identifies the local
   socket referenced, and upon completion of the operation it contains a
   completion code to indicate the outcome of the operation to the user.
   It may be used at any time for any purpose other than Network
   operations.  Its value at the beginning of a Network operation is
   immaterial rather it is the variable itself that is important.  In
   all Network operations, whenever a completion code variable is called
   for, the only acceptable type variable is a LO storage location,
   either case 1 or case 2.

   In those operations requiring a socket to be specified by its socket
   identifier, the following format is used: the site number of UCSB is
   always used for local sockets, and so this item is never specified.
   The site number of a foreign socket, if specified, must be a positive
   integer or a LO storage location, and must be less then 256 in value.
   If not specified, the site number of a foreign socket will default to
   the site number of UCSB.  A socket number is specified as an integer,
   either unsigned, in which case it is assumed to be positive, or with
   an explicit minus sign, or a LO storage location, of any value.
   Negative socket numbers are represented internally in two's
   complement form and therefore for the purpose of the gender of a
   socket, a socket number is even or odd according to whether its
   absolute value is even or odd, respectively.






<span class="grey">Krilanovich                                                     [Page 1]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-2" ></span>
<span class="grey"><a href="./rfc121">RFC 121</a>                Network On-Line Operators              April 1971</span>


   In all operations involving the On-Line System Network operators,
   there are certain conventions concerning the format of the data sent
   and received.  The data is grouped in 'messages' consisting of three
   fields, op code, length, an text, in that order.  The op code is one
   byte in length and is a code which indicates how the text field is to
   be interpreted.  The length field is two bytes long, and gives the
   length, in bits, of the text field, which contains the actual data.
   (The op code and length fields together are termed a header.)

   The following op codes are presently defined:

     op code                        meaning

       0          This op code is a NOP.  No text field exists, and the
                  contents of the length field are unpredictable. (This
                  op code is used mainly as a delimiter.)

       1          The text field contains EBCDIC characters, one
                  character per byte.  The On-Line System operators
                  consider the characters as intended for display as
                  soon as the text field has been received.

       2          The text contains codes for keypushes, one byte per
                  key.  The On-Line operators consider the keys as
                  intended for execution as soon as the text field has
                  been received.

       3          The same as for an op code of 2, except that the On-
                  Line operators consider that the execution of the keys
                  will be delayed until all data for that receive
                  operation has been received.

   The standard format of data sent or received by the On-Line System
   operators is a string of messages, with the last message indicated by
   a header with a NOP op code, called a trailer.  These conventions are
   the default situation; any of them may be overridden by appropriate
   programming.  Following is a description of each operator, its
   function and key sequence.

   (1) OPEN

      By invoking this operator, the user requests that the specified
      local socket be removed from the closed state and thus be prepared
      to participate in data transfer.  There are three distinct
      operations that can be performed by this operator and these are
      described below:





<span class="grey">Krilanovich                                                     [Page 2]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-3" ></span>
<span class="grey"><a href="./rfc121">RFC 121</a>                Network On-Line Operators              April 1971</span>


      (A) CONNECT

         By invoking this operator, the user requests that the specified
         local socket be logically connected to the specified foreign
         socket, and that transfer of data be enabled between the two
         sockets.  Processing at the terminal is suspended until the
         foreign sockets either accepts or rejects the connection
         attempt.  This operation is valid only when the local socket is
         in the closed state.

         The key sequence is as follows:

            UP Q1 Q2,Q3[,Q4] RETURN

         where

            Q1 is the completion code variable to be associated with the
               local socket.
            Q2 is the socket number of the local socket.
            Q3 is the socket number of the foreign socket.
            Q4 is the site number of the foreign socket.

      The following completion codes are possible for this operation:

            0, The operation was successful and the connection has been
               established
            4, The specified completion code variable is already
               assigned to a socket; the operation was suppressed
            8, The specified local socket is not in the closed state;
               the operation was suppressed
            12, All communication paths to the specified foreign site
               are in use; the operator was suppressed
            16, Local resources are insufficient to support another
               connection; the operation was suppressed
            20, The connection attempt was rejected by the foreign
               process
            28, The specified foreign site is invalid; the operation was
               suppressed
            36, Either hardware at the foreign site is inoperative or
               the NCP's counter-part at the foreign site does not exist
               or has failed
            40, Local and foreign sockets are both either send or
               receive sockets; the operation was suppressed
            44, By operator command, all Network operations were
               terminated; the socket will be closed
            60, An NCP control transmission error occurred; the
               operation as suppressed




<span class="grey">Krilanovich                                                     [Page 3]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4" ></span>
<span class="grey"><a href="./rfc121">RFC 121</a>                Network On-Line Operators              April 1971</span>


      (B) LISTEN

         This operation is a request for notification of any connection
         attempt directed toward the specified local socket.  Processing
         at the terminal is suspended until such a call is received.
         This operation is valid only when the designated local socket
         is in the closed state.

         The key sequence is as follows:

            UP Q1 Q2 RETURN

         where

            Q1 is the completion code variable to be associated with the
               local socket.
            Q2 is the socket number of the local socket.

            The following completion codes are possible for this
               operation:

            0, The operation was successful and a call has been received
            4, The specified completion code variable is already
                      assigned to a socket; the operation was suppressed
            8, The specified local socket is not in the closed state;
                      the operation was suppressed
            12, Local resource are insufficient to support another
                      connection; the operation was suppressed
            44, By operator command, all Network operations were
                      terminated; the socket will be closed

      (C) ACCEPT

         This operation accepts connection with the foreign socket whose
         call caused successful completion of a previous LISTEN
         operation by the specified local socket.  After completion of
         this operation, data may be transferred to or from the local
         socket, depending on its gender.  This operation is valid only
         when the last operation referencing the local socket as a
         LISTEN operation.  Processing at the terminal is suspended
         until the operation is completed.

      The key sequence is as follows:

            UP Q RETURN






<span class="grey">Krilanovich                                                     [Page 4]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-5" ></span>
<span class="grey"><a href="./rfc121">RFC 121</a>                Network On-Line Operators              April 1971</span>


      where

            Q is the completion code variable associated with the local
               socket by a previous LISTEN operation.

               The following completion codes are possible for this
               operation:

                  0, The operation as successful, and the connection is
                      established
                  4, The specified local socket is in the closed state
                      (the NCP may have received an abort notification
                      from the foreign process); the operation was
                      suppressed
                  8, The previous operation specifying the designated
                      local socket was not a LISTEN; the operation was
                      suppressed
                  12, All communication paths to the specified foreign
                      site are in use; the socket has been returned to
                      the closed state


   (2) CLOSE

      This operation is a request that the specified local socket be
      returned to the closed state.  If the last operation involving
      this socket was a LISTEN, this operation refuses the foreign
      process connection attempt.  If the last operation was a CONNECT,
      the attempt is aborted.  If a connection is established, any data
      in transit form the local socket is allowed to reach the foreign
      socket and to be either received or flushed before the local
      socket is closed.

      Processing at the terminal is suspended until the socket has been
      returned to the closed state.

      The key sequence is as follows:

            DWN Q












<span class="grey">Krilanovich                                                     [Page 5]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-6" ></span>
<span class="grey"><a href="./rfc121">RFC 121</a>                Network On-Line Operators              April 1971</span>


      where

            Q  is the completion code variable associated with the local
               socket.

            The following completion codes are possible for this
            operation:

                  0, The operation was successful, and the socket has
                      been returned to the closed state
                  8, The specified completion code variable is not
                      currently assigned to a socket; the operation was
                      suppressed
                  12, The specified local socket is in the process of
                      being closed the operation was suppressed, but the
                      local socket will be closed
                  36, Either hardware at the foreign site is
                      inoperative, or the NCP's counterpart at the
                      foreign site does not exist or has failed
                  44, By operator command, all Network operations were
                      terminated; the socket will be closed
                  60, An NCP control transmission error occurred; the
                      operation was aborted
                  64, A transmission error occurred the operation was
                      aborted, but the socket will be closed

   (3) SEND

      This operation caused data to be sent to the foreign socket.
      Processing at the terminal is suspended until the data has been
      received by the foreign socket, or until it has been queued
      locally by the NCP.

      The possible key sequence are as follows:

            STORE  Q1 Q2 text Q2
            STORE +Q1 Q2 text Q2
            STORE -Q1 Q2 text Q2
            STORE .Q1[X]Q3 RETURN

      where

            Q1 is the completion code variable associated with the local
               socket.
            Q2 is any key except RESET.
            'Text' is a string of any length of any keys except Q2 and
               RESET.
            Q3 is an unsigned integer.  If it is preceded by 'X', the



<span class="grey">Krilanovich                                                     [Page 6]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-7" ></span>
<span class="grey"><a href="./rfc121">RFC 121</a>                Network On-Line Operators              April 1971</span>


               integer is assumed to be in hexadecimal.
               [X]Q3 should have a value less then 256.

      If Q1 is the first key after STORE, the keys comprising 'text' are
      not executed but rather are sent as a one byte code per key, in
      one or more standard messages.  They are preceded by a header with
      the op code which indicates keys to be executed as soon as they
      are received, and followed by a trailer.  If a '+' precedes Q1,
      the headers and the text will be sent, but no trailer.  If a  '-'
      precedes Q1, only the text will be sent.  If a '.' precedes Q1,
      [X]Q3 will be sent as a one byte number, with no header or
      trailer.

      The following completion codes are possible for this operation:

            0, The operation was successful, and the data has been sent
            4, The specified local socket is not a send socket; the
               operation was suppressed
            8, The specified completion code variable is not assigned to
               a socket; the operation was suppressed
            12, A previous send operation is in progress ;the operation
               was suppressed
            16, The connection is not fully open; the operation was
               suppressed
            20, The foreign socket terminated the connection before
               completion of the send operation; not all the data was
               transmitted
            36, Either hardware at the foreign site is inoperative, or
               the NCP's counterpart at the foreign site does not exist
               or has failed
            44, By operator command, all Network operations were
               terminated the socket will be closed
            52, One or more interrupts were received from the foreign
               socket; the operation was suppressed
            60, An NCP control transmission error occurred; the
               operation was aborted and the socket will be closed
            64, A transmission error occurred; the operation was aborted
               and the socket will be closed

   (4) RECEIVE

      This operation causes data to be received from the foreign socket.
      Processing at the terminal is suspended until the data sent by the
      foreign socket has been received by the local socket and
      processed.

      The possible key sequences are as follows:




<span class="grey">Krilanovich                                                     [Page 7]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-8" ></span>
<span class="grey"><a href="./rfc121">RFC 121</a>                Network On-Line Operators              April 1971</span>


            LOAD  Q1
            LOAD +Q1
            LOAD -Q1 Q2, Q3 RETURN
            LOAD .Q1 Q4 RETURN

      where

            Q1 is the completion code variable associated with the local
               socket.
            Q2 is a positive integer, or a LO storage location, less
               then 256.
            Q3 is a positive integer, or a LO storage location, less
               than 65536
            Q4 is a positive integer less than 5.

      If Q1 is the first key after LOAD, one or more standard messages
      will be received and executed.  The data may or may not be
      executed, as soon as it is received, depending on the op code.
      Processing of manual keypushes is suspended until a trailer is
      received.  If Q1 is preceded by a '+', the operation is as above,
      except that only one message, with no trailer, is received, and
      the operation is only performed if there is data queued for the
      local socket, ready to be received. ('LOAD +' is intended mainly
      for use with the Network On-Line Interface.)  If Q1 is preceded by
      a '-', a string of text whose length, in bits, is Q3, is received
      and processed according to the op code Q2.  If a '.' precedes Q1,
      Q4 bytes of data are read and placed, right justified, in the LO
      accumulator.

      The following completion codes are possible for this operation:

            0, The operation was successful and the data has been
               received
            4, The specified local socket is not a receive socket; the
               operation was suppressed
            8, The specified completion code variable is not assigned to
               a socket; the operation was suppressed
            12, A previous receive operation is in progres; the
               operation was suppressed
            16, The connection is not fully open; the operation was
               suppressed
            20, The foreign socket terminated the connection before
               completion of the receive operation; data is
               unpredictable
            36, Either hardware at the foreign site is inoperative, or
               the NCP's counterpart at the foreign site does not exist
               or has failed
            44, By operator command, all Network operations were



<span class="grey">Krilanovich                                                     [Page 8]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-9" ></span>
<span class="grey"><a href="./rfc121">RFC 121</a>                Network On-Line Operators              April 1971</span>


               terminated; the socket will be closed
            52, One or more interrupts were received from the foreign
               socket; the operation was suppressed
            60, An NCP control transmission error occurred; the
               operation was suppressed and the socket will be closed
            200, There was no data queued for the local socket; the
               operation was suppressed (applicable only to 'LOAD +')

   (5) CHECK

      This operation causes the status of the specified local socket to
      be displayed.  There is no completion code variable associated
      with this operation, since it is always successful and the socket
      is identified by its socket number.  This operation is valid at
      any time, and with one exception, noted below, is always completed
      immediately.

      The possible key sequences are as follows:

            DISPLAY (Q RETURN...)...
            DISPLAY (Q?)...
            DISPLAY RETURN...

      where

            Q is the socket number of the local socket whose status is
            to be displayed.

      Successive RETURN'S will display the status of local sockets with
      successively higher socket numbers, and once DISPLAY has been
      pushed, it need not be pushed for subsequent occurrences of Q.

      If Q is followed by a '?', processing at the terminal will be
      suspended until the socket is not in the closed state, at which
      time the status will be displayed.  If the socket is not closed at
      the time the '?' is pushed, response is as if the '?' were a
      RETURN.

      If DISPLAY is followed immediately by a RETURN, the status of all
      non-closed sockets owned by the terminal is displayed, each
      preceded by its associated completion code variable.  If this
      information is more than will fit on one tube, successive RETURN'S
      will display the remainder of the information.








<span class="grey">Krilanovich                                                     [Page 9]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-10" ></span>
<span class="grey"><a href="./rfc121">RFC 121</a>                Network On-Line Operators              April 1971</span>


      The status has the following format:

            'lclno' 'mnem' 'fgnsite' 'fgnno' 'deficit'

      where

            'lclno' is the socket number of the local socket.
            'mnem' is a mnemonic of up to eight characters for the
               status.
            'fgnsite' is the site number of the foreign socket, or
               blank.
            'fgnno' is the socket number of the foreign socket, or
               blank.
            'deficit' is the send/receive deficit in the form
               'bytes.bits', or blank.

      Following are the possible mnemonics, together with their
      interpretations:

         'MNEM'                               MEANING
         ______                               _______

         OPEN           A connection is fully established.
                        No SEND/RECEIVE operation is in progress.
                        'fgnsite' and 'fgnno' are the site number and
                        the socket number of the connected socket.
                        'deficit' is the number of bits queued locally
                        at the socket by the NCP and available to
                        satisfy a future RECEIVE operation, or awaiting
                        output as the result of a previous SEND
                        operation.

         LISTEN         A LISTEN has been issued.

         CONNECT        A CONNECT has been issued. 'fngsite' and 'fgnno'
                        are the site and socket numbers of the foreign
                        socket.

         DECISION       A LISTEN has been completed. 'fgnsite' and
                        'fgnno' are the site and socket numbers of the
                        calling socket.

         CALL(S)        One or more calls have been received for the
                        local socket.  No LISTEN or CONNECT has been
                        issued.

         I/O            A connection is fully established.  A
                        SEND/RECEIVE operation is in progress. 'fgnsite'



<span class="grey">Krilanovich                                                    [Page 10]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-11" ></span>
<span class="grey"><a href="./rfc121">RFC 121</a>                Network On-Line Operators              April 1971</span>


                        and 'fgnno' are the site and socket numbers of
                        the connected socket. 'deficit' is the number of
                        bits yet to be sent or received.

         CLOSED         The socket is in the closed state.

         &lt;--DRAIN       The foreign socket is attempting to close the
                        connection.  The NCP has data yet to be read by
                        the local socket. 'fgnsite' and 'fgnno' are the
                        site and socket numbers of the connected socket.
                        'deficit' is the number of bits yet to be
                        received.

         DRAINED        The foreign socket is attempting to close the
                        connection.  The NCP is awaiting arrival at the
                        foreign site of data currently in transit.
                        'fgnsite' and 'fgnno' are the site and socket
                        numbers of the connected socket.

         CLOSING        The local socket has issued a CLOSE.  The NCP is
                        in the process of returning  the local socket to
                        the closed state. 'fgnsite' and 'fgnno' are the
                        site and socket numbers of the connected socket.

         DRAIN--&gt;       The local socket has issued a CLOSE.  The NCP is
                        completing the last SEND operation before
                        returning the local socket to the closed state.
                        'fgnsite' and 'fgnno' are the site and socket
                        numbers of the connected socket. 'deficit' is
                        the number of bits the NCP has yet to transmit.

   (6) IDENTIFY

      This operation is used to identify a local socket by its
      completion code variable.  The operation is valid at any time, and
      is always completed immediately.  Since it is always successful,
      there are no completion codes for the operation, and the contents
      of the completion code variable are not changed.

      The key sequence is:

            ID Q...

      where

            Q is the completion code variable associated with the local
               socket.




<span class="grey">Krilanovich                                                    [Page 11]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-12" ></span>
<span class="grey"><a href="./rfc121">RFC 121</a>                Network On-Line Operators              April 1971</span>


      The response is a display of Q, followed by 'IS UNDEFINED' if the
      socket is in the closed state, or the socket number associated
      with it if it is not closed.  After ID has been pushed once, it
      need not be pushed again for subsequent occurrences of Q.

   (7) PURGE

      This operator is used to dissociate all completion code variables
      from sockets, and to issue a CLOSE to all sockets currently in use
      at the terminal.  The operation is valid at any time, and is
      always completed immediately.  Since it is always successful.
      there are no completion codes for the operation, and the contents
      of the completion code variables are not changed.

      The key sequence is:

            DEL RETURN

   (8) SIGNAL

      This operation is used to convey a signal to the foreign process.
      The significance of the signal is completely user-dependent.  The
      effect is that the next time the foreign socket attempts to
      initiate a RECEIVE or SEND operation, the operation will be
      suppressed, and a completion code supplied indicating that a
      signal had been received.  Processing at the terminal is suspended
      until the signal has been sent to the foreign NCP.  This operation
      is valid only when the socket is fully open.

      The key sequence is:

            REFL Q

      where

            Q is the completion code variable associated with the local
               socket.

      The following completion codes are possible for this operation:

            0, The operation was successful, and the signal has been
               sent
            4, The specified completion code variable is not assigned to
               a socket; the operation was suppressed
            8, The connection is not fully open;the operation was
               suppressed





<span class="grey">Krilanovich                                                    [Page 12]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-13" ></span>
<span class="grey"><a href="./rfc121">RFC 121</a>                Network On-Line Operators              April 1971</span>


      (9) CONVERSATIONAL CONTROLLER

      This operator is intended primarily for use with the Network On-
      Line Interface, and is used to carry on a 'conversation' with the
      foreign process.  Any data queued locally for the specified local
      receive socket is received and displayed as characters.  Any keys
      pushed will be sent from the specified local send socket.  The
      user has the option of specifying whether or not upper keyboard
      buttons are to be sent.  In any case, the buttons ERASE, REPEAT,
      ENTER, PRED, and RESET, will not be sent, and pushing any of
      these, except RESET, will cause suspension of data reception until
      a button other than these four is pushed.  Pushing RESET always
      terminates the operation.

      The key sequence is as follows:

            ARG [,] [-]Q1[-]Q2

      where

            Q1 is the completion code variable associated with the local
               send socket.
            Q2 is the completion code variable associated with the local
               receive socket.

      If ARG is followed by ',', both upper and lower keyboard buttons
      will be sent, and the operation will be terminated only by pushing
      RESET.  If no ',' follows ARG, only lower keyboard buttons will be
      sent, and the operation is terminated by pushing RESET or any
      upper keyboard button.  If a '-' precedes Q1, no headers will be
      sent, and if a '-' precedes Q2, no headers will be received.  In
      any case, if headers are to be received, the operation is
      terminated when a trailer is received, and a corresponding trailer
      is sent if headers are to be sent.

      The completion codes for the send socket are the same as for the
      SEND operation, and the completion codes for the receive socket
      are the same as for the RECEIVE operation.  If a non-zero
      completion code is found, a message is displayed, either 'OUTPUT
      ERROR' or 'INPUT ERROR', depending on whether the send socket for
      the receive socket encountered the non-zero completion code, and
      the operation is terminated.


          [ This RFC was put into machine readable form for entry ]
          [ into the online RFC archives by Gruss Gottfried 01/98 ]





Krilanovich                                                    [Page 13]
</pre>