197 lines
6.8 KiB
Plaintext
197 lines
6.8 KiB
Plaintext
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.TH CONS 4P "9 December 1988"
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.ds ]W Wisconsin ARGO 1.0
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.UC 4
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.SH NAME
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CONS \- Connection Oriented Network Service
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.SH SYNOPSIS
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For use as a network service (CONS):
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.nf
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.sp
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\fB#include <sys/socket.h>\fR
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\fB#include <sys/mbuf.h>\fR
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\fB#include <netargo/iso.h>\fR
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\fB#include <netargo/cons.h>\fR
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\fB#include <netargo/iso_errno.h>\fR
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.sp
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\fBint cons_output(isop, m, len, isdatagram)\fR
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.sp
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or for use as a subnetwork service (COSNS):
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.sp
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\fB#include <sys/socket.h>\fR
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\fB#include <sys/mbuf.h>\fR
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\fB#include <netargo/iso.h>\fR
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\fB#include <net/if.h>\fR
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\fB#include <netargo/cons.h>\fR
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\fB#include <netargo/iso_errno.h>\fR
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.sp
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\fBint cosns_output(ifp, m, dst)
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.fi
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.SH DESCRIPTION
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.PP
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The Connection Oriented Network Service (CONS) implemented for the AOS R2
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at the University of Wisconsin - Madison
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supports transport protocols, acting as a network service,
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and it also supports other network protocols, acting as a subnetwork
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service or link-layer service.
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Several software modules are combined to provide these services.
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.TP 10
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X.25
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The CCITT X.25 packet layer and link layer protocols run on
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a coprocessor (the EICON Network Adapter), which serves as a DTE.
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.TP 10
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Ecn driver
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A device driver manages the interaction between
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the coprocessor and the PC/RT.
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.TP 10
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CONS "glue"
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A software module implements portions of the OSI CONS (ISO 8878),
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which describes a way to use the X.25 protocols to support the
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OSI connection-oriented network service.
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.PP
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The OSI CONS contains several "service elements"
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that ARGO does not use or support.
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Expedited data,
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quality of service maintenance,
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call collision resolution,
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permanent virtual circuits,
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user data on connect and release,
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user-level acknowledgement
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("receipt confirmation" in CCITT/ISO argot), and reset/resynchronize
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are not supported.
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Several of the service primitives for connection establishment
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and release are not supported, and
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numerous parameters to other primitives specified in the OSI CONS
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are not supported.
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The CONS glue does provide all the support necessary to run
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ISO transport classes 0 and 4 over X.25, and ISO CLNP (also called
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ISO IP) over X.25.
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The subnetwork dependent convergence functions implemented in the glue
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permit interoperability with
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OSINET and EAN at this writing.
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Interoperability with other networks will be established in the future.
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.PP
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The coprocessor that implements the X.25 link and packet layers
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is the Eicon Technologies Access/X.25 Stand-Alone Network Adaper
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(see \fIecn(4)\fR).
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.PP
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The glue module provides two interfaces to higher layers:
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a "subnetwork service" (COSNS) used by network layer protocols, which
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has a typical BSD kernel device driver interface
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and
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a "network service" (CONS) used by transport protocols, which has
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a procedure call interface similar to that of IP and CLNP.
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.PP
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The network service is reliable and sequenced but does not
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provide a graceful close service; it provides only an abort service.
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.PP
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The subnetwork service is neither reliable nor sequenced.
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The subnetwork service implemented by the glue hides the
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connection-oriented aspects of the protocols; nevertheless,
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we call it the "connection-oriented subnetwork service" (COSNS)
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here, for lack of a better name.
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.SS "LIBRARIES
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No libraries are needed to use the CONS, however,
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the numerous error values returned by X.25 cannot be accommodated
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by the standard \fIperror()\fR in the C library.
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The ISO library
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.nf
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.sp
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.in +5
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\fC/usr/argo/lib/libisodir.a\fR
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.in -5
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.sp
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.fi
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provides an expanded perror() to handle the additional error return codes.
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.SS "ERROR VALUES
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.PP
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The error codes returned by the CONS are taken from
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the diagnostic code of the X.25 level 3 packets, as
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descibed in figure 14-B of ISO 8208 (the ISO standard which
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is equivalent to CCITT X.25).
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The actual error value returned in
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\fIerrno\fR
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is the X.25 diagnostic code in the lower 10 bits
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logically "or"ed with the hexadecimal value 0x8400 (bits
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10 and 15 set, counting from zero at the the least significant bit).
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The error values can be found in
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the file
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.nf
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.in +5
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.sp
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\fC<netargo/iso_errno.h>\fR
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.sp
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.in -5
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.fi
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.SS "PROTOCOL IDENTIFICATION
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.PP
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The purpose of this section is to describe how incoming packets
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are forwarded from the glue to the various higher
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layers (ISO transport, CLNP), how
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routes are chosen from the higher layers to the glue, and
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how NSAP-addresses are related to all this.
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.SS Outgoing path:
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The ARGO transport entity routes packets either to
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the CONS glue, to the CLNP module, or to the DARPA Internet IP
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module, based on the value of the network service parameter
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given to the transport layer by the user.
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The \fInetserv\fR property of records in the ARGO
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directory service database
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can be used to determine the network service to be used by the
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transport layer. See also \fIisodir(5)\fR and \fIisodir(3)\fR.
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.PP
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The connectionless network layer entity routes packets to the
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COSNS based on the routing table entries in the connectionless network layer.
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This means that any type of NSAP-address supported by the kernel
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may be used with a CLNP packet
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that is routed over X.25.
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.PP
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When the glue creates an X.25 Call Request packet, it
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places an X.121 address (DTE address)
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in both the Calling and Called DTE address fields.
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The X.121 addresses are extracted from the \fISNPA cache\fR,
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a table that maps NSAP-addresses to SNPA-addresses, and
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is maintained by the ES-IS protocol module of the OSI network layer.
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In addition to placing a DTE address in the X.25 packet,
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the "glue" may
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uses the 1984 Called Address Extension facility to convey the
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NSAP-addresses.
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Whether or not this is done depends on the compile-time option -DX25_1984.
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.SS Incoming path:
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The X.25 Call Request User Data field and the
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1984 X.25 Address Extension Facility are used
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to determing the incoming path through the network layer.
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The NSAP addresses passed up along with the packet are taken from the
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Address Extension facility, if present.
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If the facility is absent, the glue creates two type-37 NSAP-addresses,
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filling in the X.121 address from the called and
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calling DTE-addresses on the Call Request packet, if present.
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The glue then requests of the ES-IS module to add an entry to the
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SNPA cache to associate the calling DTE address with its
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derived NSAP-address.
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These cache entries have a holding of 5 minutes, and get
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refreshed as long as there is activity on the virtual circuit
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resulting from the call request.
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.PP
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If a Call Request packet contains a protocol identifier
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as described in ISO PTDR 9577, this protocol identifier is used
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to route the packet to the higher layers.
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If there is no protocol identifier, the higher layer is assumed to be ISO
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transport.
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.SH "BUGS
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.PP
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If an incoming X.25 Call Request contains no DTE-addresses and
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no NSAP-addresses (in the Address Extension facility)
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the kernel panics.
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.SH "SEE ALSO
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.PP
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isodir(3),
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ecn(4),
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clnp(4),
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tp(4),
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isodir(5),
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isoroute(8),
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ifconfig(8),
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netstat(1),
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xstat(8),
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"ARGO 1.0 Kernel Programmer's Manual"
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