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+Network Working Group                                         J. T. Korb
+Request for Comments: 877                              Purdue University
+                                                          September 1983
+
+
+
+          A Standard for the Transmission of IP Datagrams
+                               Over
+                       Public Data Networks
+
+
+
+
+This RFC specifies a standard adopted by CSNET, the VAN gateway, and
+other organizations for the transmission of IP datagrams over the
+X.25-based public data networks. 
+
+An X.25 virtual circuit is opened on demand when a datagram arrives at
+the network interface for transmission. A virtual circuit is closed
+after some period of inactivity (the length of the period depends on
+the cost associated with an open virtual circuit). A virtual circuit
+may also be closed if the interface runs out of virtual circuits. An
+algorithm for managing virtual circuits during peak demand is given
+in [1].
+
+STANDARDS
+
+1.1 The first octet in the Call User Data Field (the first data octet
+    in the Call Request packet) is used for protocol demultiplexing.
+    The value hex CC (binary 11001100, decimal 204) is used to mean
+    INTERNET PROTOCOL. 
+
+1.2 IP datagrams are sent as X.25 "complete packet sequences". That is,
+    datagrams begin on packet boundaries and the M bit ("more data") is
+    used for datagrams that are larger than one packet. There are no
+    additional headers or other data in the packets.
+
+1.3 Unless a larger packet size is negotiated, the maximum size of an
+    IP datagram transmitted over X.25 is 576 octets. If two sites
+    negotiate a large X.25 packet size (for example, 1024 octets), an
+    IP datagram of that size is allowed. 
+
+1.4 Either site may close a virtual circuit. If the virtual circuit is
+    closed or reset while a datagram is being transmitted, the datagram
+    is lost.
+
+GENERAL REMARKS
+
+2.1 Protocols above IP, such as TCP, do not affect this standard. In
+    particular, no attempt is made to open X.25 virtual circuits
+    corresponding to TCP connections.
+
+
+
+
+Korb                                                            [Page 1]
+
+RFC 877                                                   September 1983
+Transmission of IP Datagrams Over Public Data Networks
+
+
+2.2 Features of X.25 not discussed in this document are not used.
+    For example, interrupt packets and the D bit (indicating
+    end-to-end significance) are not used.
+
+2.3 Negotiable features (facilities) of X.25 are allowed. For
+    example, sites are free to negotiate larger packet and window
+    sizes.
+
+2.4 Some sites, such as CSNET sites, may attempt to open multiple
+    virtual circuits to a single site. Sites should attempt to
+    handle such incoming calls gracefully: transmit on the
+    additional circuits if possible and accept incoming datagrams
+    from them, but do not accept the CALL REQUEST, only to
+    immediately close the connection or ignore datagrams
+    transmitted on such circuits.
+
+
+REFERENCE
+
+[1] Comer, D.E. and Korb, J.T., "CSNET Protocol Software: The
+    IP-to-X.25 Interface", SIGCOMM Symposium on Communications
+    Architectures and Protocols, March 1983.
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+Korb                                                            [Page 2]
+