    Network Working Group                                         S. Crocker
    Request for Comments: 123                                           UCLA
    NIC #5837                                                    20 April 71
    Categories: D.1
    Obsoletes: RFCs 66, 80
    Updates: RFCs 98, 101

                            A Proferred Official ICP

    By Initial Connection Protocol (ICP), I mean a third level protocol
    which is initiated by a user process at one site in order to contact a
    server process at another site.  Typically, the user process will be a
    Telnet and the server process will be a logger, but there may be other
    cases.

    In this RFC, I wish to describe a family of ICPs suitable for
    establishing one pair of connections (one in each direction) between any
    user process and any server process, and to propose further a particular
    subset of this family as the standard ICP for connecting user processes
    to loggers on systems which accept teletype-like devices.

    Notation

    We have no standard notation for describing system calls which initiate
    and close connections or cause data to be sent, so I will use the
    following ad hoc notation.

    Init (local = l, foreign = f, size = s)

       causes the local Host to attempt to establish a connection between
       socket l at the local Host and socket f, with a byte size of s for
       the connection.

       l is a 32 bit local socket number,
       f is a 40 bit foreign socket number, the high-order eight bits
       of which specify the foreign Host, and
       s is an eight bit non-zero byte size.
       The sum of l and f must be odd.

    Listen (local = l, size = s)

       causes the local Host to wait for a request for connection to local
       socket l with byte size s.  The process will be woken when a
       connection is established.  The parameters l and s are the same as
       for Init.

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    Send (socket = l, data = d)

       The data named by d is sent over the connection attached to local
       socket l. l must be a send socket attached to a connection.  d is the
       name of a data area.

    Receive (socket = l, data = d)

       The receive side counterpart to send.

    Close (socket = l)

       Any connection currently attached to a local socket l is closed.

    A Family of ICPs

    Briefly, a server process at a site attaches a well-advertised send
    socket L and listens.  A user process initiates connection to L from its
    receive socket U.  The byte size for this connection is 32.  The server
    process then transmits a 32-bit even number S and closes the connection.
    The 32-bit number S and its successor, S+1, are the socket number the
    server will use.  The final steps are for sockets S and S+1 at the
    server site to be connected to sockets U+1 and U respectively at the
    user site.

    Using the notation, the server executes the following sequence:

       Listen (socket = L, size = 32)
       [Wait until a user connects]
       Send (socket = L, data = S)
       Close (socket = L)
       Init (local = S, foreign = U+1, size = Bu)
       Init (local = S+1, foreign = U, size = Bs)

    The user executes the following:

       Init (local = U, foreign = L, size = 32)
       Receive (socket = U, data = S)
       Close (socket = U)
       Init (local = U+1, foreign = S, size = Bu)
       Init (local = U, foreign = S+1, size = Bs)

    Note that L is a send socket (odd), while S and U are receive sockets
    (even).  Where L, S or U are used as values of local, they are 32-bit
    numbers; where they are values of foreign, they are 40-bit numbers.  The
    parameters Bs and Bu are the byte sizes to be sent by the server and
    user, respectively.

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    Examination of the above sequences reveals that an ICP is characterized
    by the three numbers L, Bs and Bu, and must meet the restrictions that

       (a) L is a send socket,
       (b) Bs and Bu are legal byte sizes, and
       (c) for each L there is only on pair of associated byte sizes.

    This last restriction prevents two distinct services from being
    available through the same socket and distinguished only by the byte
    sizes.

    Telnet ICP

    For connecting teletype-like users, i.e. interactive and ASCII, to Hosts
    serving such users, I propose an ICP of the form described above and
    characterized by L = 1, Bs = Bu = 8. [There has been some confusion
    about socket numbers.  Here I specifically mean L = X00000001]

    Formalities

    I propose that the Telnet ICP be made official.  Comments should be
    published before the May NWG meeting, the subject will be discussed
    there, and we will decide there to accept or reject this protocol.

           [ This RFC was put into machine readable form for entry ]
              [ into the online RFC archives by Jeff Sorte 5/97 ]

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