Network on-line operators
RFC 121

Document Type RFC - Unknown (April 1971; No errata)
Last updated 2013-03-02
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Network Working Group                                     M. Krilanovich
Request for Comments: 121                    Computer Research Lab, UCSB
NIC: 5833                                                  21 April 1971

                       NETWORK ON-LINE OPERATORS


   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.

Krilanovich                                                     [Page 1]
RFC 121                Network On-Line Operators              April 1971

   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:

Krilanovich                                                     [Page 2]
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