+.NC "Network Service Interface"
+.sh 1 "Connectionless Network Service"
+.pp
+This section describes the interface to the ISO connectionless network service.
+There are really two interfaces to the CLNS: the internal interface
+and the IPC interface.
+The internal interface is based on
+procedure calls. It is used only within the kernel. The IPC interface
+allows a user process to access the CLNS directly. This is used only
+for testing and debugging purposes.
+.sh 2 "Primitives"
+.pp
+The CLNS is, by definition, connectionless. Therefore, there are no
+primitives associated with connection establishment or connection release.
+There is one primitive associated with data transfer: N-UNITDATA.
+The parameters to a N-UNITDATA request are: source NSAP address,
+destination NSAP address, quality of service, and user data.
+The parameters of a N-UNITDATA indication are identical to those of the
+request.
+In this implementation, the quality of service parameter is not supported.
+.sh 2 "Internal Interface"
+.pp
+Within the kernel, an N-UNITDATA request is effected by the procedure
+\fIclnp_output()\fR:
+.(b
+\fC
+.TS
+tab(+);
+l s s.
+clnp_output(m0, isop, datalen, flags)
+.T&
+l l l.
+ +struct mbuf+*m0;+/* data */
+ +struct isopcb+*isop;+/* ISO protocol control block */
+ +int+datalen;+
+ +int+flags;+/* flags */
+.TE
+\fR
+.)b
+This procedure will construct a DT NPDU, route it, and transmit it on
+the appropriate subnetwork. \fIM0\fR is an mbuf chain containing the
+user data portion of the N-UNITDATA request. \fIIsopcb\fR is the iso protocol
+control block previously allocated. \fIClnp_output\fR will use the following
+fields: \fIisop_laddr\fR, isop_faddr, isop_route, isop_options,
+isop_optindex, \fI and \fRisop_clnpcache\fR.
+\fIDatalen\fR specifies the number of bytes of user data.
+The \fIflags\fR parameter will be discussed in a subsequent chapter.
+.pp
+A N-UNITDATA indication occurs when a DT NPDU arrives. The indication is
+generated by calling the appropriate upper layer protocol input routine.
+In the case of TP, the procedure \fItpclnp_input()\fR is called:
+.(b
+\fC
+.TS
+tab(+);
+l s s.
+tpclnp_input(m, src, dst, len)
+.T&
+l l l.
+ +struct mbuf+*m;+/* DT NPDU */
+ +struct iso_addr+*src;+/* source of packet */
+ +struct iso_addr+*dst;+/* destination of packet */
+ +int+len;+/* length of clnp header */
+.TE
+\fR
+.)b
+\fIM\fR contains the entire DT NPDU packet. \fILen\fR indicates the size
+of the CLNP header. In other words, the user data of the DT NPDU begins
+\fIlen\fR bytes into \fIm\fR. \fISrc\fR and \fIdst\fR indicate the
+source and destination NSAP addresses of the packet.
+.sh 3 "CLNP/Subnetwork Interface"
+.pp
+The design of the interface between the subnetwork and the CLNP is
+determined by the design of the Unix network interface drivers. CLNP
+follows the conventional mechanisms for exchanging packets with a network
+interface. See the section on Network Interface Drivers in Chapter Five
+for more information on these conventions.
+.sh 2 "IPC (\*(lqRaw\*(rq) Interface"
+.pp
+The IPC interface to the CLNS allows direct (called \*(lqraw\*(rq)
+access to CLNP.
+This interface is intended for testing and debugging only.
+Its use results in the
+transmission of CLNP datagrams with nonstandard identification fields.
+These raw packets may be rejected by a system not employing the same
+convention. See the section on network implementation for more information
+about the conventions.
+.pp
+In order to gain access to the raw interface
+a \fIsocket\fR, with address family AF_ISO and type SOCK_RAW must be created.
+With this socket in hand,
+the system calls \fIsendto()\fR and \fIrecvfrom()\fR can be used to
+transmit and receive raw CLNP datagrams.
+.sh 3 "Sending raw datagrams"
+.pp
+The format of the \fIsendto()\fR system call is:
+.(b
+\fC
+.TS
+tab(+);
+l s s.
+cc = sendto(s, msg, len, flags, to, tolen)
+.T&
+l l l.
+int+cc,s;
+char+*msg;
+int+len,flags;
+struct sockaddr+*to;
+int+to;
+.TE
+\fR
+.)b
+\f\fIS\fR is the socket previously created. \fIMsg\fR is a pointer to
+the data for the NPDU. CLNP will prepend a header to this data before
+transmission. \fILen\fR specifies the number of bytes of data. The
+\fIflags\fR parameter is unused and should be zero. \fITo\fR specifies the
+NSAP address to be used as the destination address. The size (in bytes)
+of \fIto\fR is given in \fItolen\fR. CLNP will automatically insert
+the source address based upon the route taken by the packet. The number of
+user data bytes transmitted is returned as \fIcc\fR. See \fIsendto(2)\fR
+for more information on this system call.
+.sh 3 "Receiving raw datagrams"
+.pp
+The format of the \fIrecvfrom()\fR system call is:
+.(b
+\fC
+.TS
+tab(+);
+l s s.
+cc = recvfrom(s, buf, len, flags, from, fromlen)
+.T&
+l l l.
+int+cc,s;
+char+*buf;
+int+len,flags;
+struct sockaddr+*from;
+int+*fromlen;
+.TE
+\fR
+.)b
+When used with a CLNP raw socket \fIs\fR, \fIrecvfrom()\fR will read a
+NPDU from the CLNS. If no packet is available, the call will block.
+\fIBuf\fR specifies a buffer of \fIlen\fR bytes into which the NPDU will
+be read. The entire packet, including the header, will be read into the
+buffer. The \fIflags\fR parameter is unused, and should be zero. If
+\fIfrom\fR is non-zero, the source address of the NPDU is filled in.
+\fIFromlen\fR is a value-result parameter, initialized to the size of
+the buffer associated with \fIfrom\fR, and modified on return to
+indicate the actual size of the address stored there. The total number
+of bytes received (header and data) is returned as \fIcc\fR.
+See \fIrecvfrom(2)\fR for more information about this system call.
+.sh 1 "Connection Oriented Network Service"
+.pp
+The ARGO Connection Oriented Network Service (CONS) is not a complete
+implementation of the
+OSI network service.
+It is that subset of the OSI network service that is used
+by ARGO Transport and by ARGO CLNP.
+.\" FIGURE
+.so ../wisc/figs/NS_primitives.nr
+.pp
+.CF
+shows which CONS service elements are provided.
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