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+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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+
+
+                                                                [Page 1]
+
+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.
+
+
+
+
+                                                                [Page 2]
+
+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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+                                                                [Page 3]
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