174 lines
6.0 KiB
Groff
174 lines
6.0 KiB
Groff
.\" Copyright (c) 1996-1999 Whistle Communications, Inc.
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.\" All rights reserved.
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.\"
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.\" Subject to the following obligations and disclaimer of warranty, use and
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.\" redistribution of this software, in source or object code forms, with or
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.\" without modifications are expressly permitted by Whistle Communications;
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.\" provided, however, that:
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.\" 1. Any and all reproductions of the source or object code must include the
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.\" copyright notice above and the following disclaimer of warranties; and
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.\" 2. No rights are granted, in any manner or form, to use Whistle
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.\" Communications, Inc. trademarks, including the mark "WHISTLE
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.\" COMMUNICATIONS" on advertising, endorsements, or otherwise except as
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.\" such appears in the above copyright notice or in the software.
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.\"
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.\" THIS SOFTWARE IS BEING PROVIDED BY WHISTLE COMMUNICATIONS "AS IS", AND
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.\" TO THE MAXIMUM EXTENT PERMITTED BY LAW, WHISTLE COMMUNICATIONS MAKES NO
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.\" REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING THIS SOFTWARE,
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.\" INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT.
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.\" WHISTLE COMMUNICATIONS DOES NOT WARRANT, GUARANTEE, OR MAKE ANY
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.\" REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS OF THE USE OF THIS
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.\" SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, RELIABILITY OR OTHERWISE.
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.\" IN NO EVENT SHALL WHISTLE COMMUNICATIONS BE LIABLE FOR ANY DAMAGES
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.\" RESULTING FROM OR ARISING OUT OF ANY USE OF THIS SOFTWARE, INCLUDING
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.\" WITHOUT LIMITATION, ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
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.\" PUNITIVE, OR CONSEQUENTIAL DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR
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.\" SERVICES, LOSS OF USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF WHISTLE COMMUNICATIONS IS ADVISED OF THE POSSIBILITY
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.\" OF SUCH DAMAGE.
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.\"
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.\" Author: Archie Cobbs <archie@FreeBSD.org>
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.\"
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.\" $FreeBSD$
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.\" $Whistle: ng_async.8,v 1.6 1999/01/25 23:46:25 archie Exp $
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.\"
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.Dd November 13, 2012
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.Dt NG_ASYNC 4
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.Os
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.Sh NAME
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.Nm ng_async
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.Nd asynchronous framing netgraph node type
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.Sh SYNOPSIS
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.In sys/types.h
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.In netgraph/ng_async.h
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.Sh DESCRIPTION
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The
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.Nm async
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node type performs conversion between synchronous frames and
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asynchronous frames, as defined for the PPP protocol in RFC 1662.
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Asynchronous framing uses flag bytes and octet-stuffing
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to simulate a frame oriented connection over an octet-oriented
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asynchronous serial line.
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.Pp
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The node transmits and receives asynchronous data on the
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.Dv async
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hook.
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Mbuf boundaries of incoming data are ignored.
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Once a complete packet has been received, it is decoded and
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stripped of all framing bytes, and transmitted out the
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.Dv sync
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hook as a single frame.
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.Pp
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Synchronous frames are transmitted and received on the
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.Dv sync
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hook.
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Packets received on this hook are encoded as asynchronous frames
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and sent out on
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.Dv async .
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Received packets should start with the address and control fields,
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or the PPP protocol field if address and control field compression
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is employed, and contain no checksum field.
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If the first four bytes are
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.Dv "0xff 0x03 0xc0 0x21"
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(an LCP protocol frame) then complete control character escaping
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is enabled for that frame (in PPP, LCP packets are always sent with
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no address and control field compression and all control characters
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escaped).
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.Pp
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This node supports
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.Dq flag sharing
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for packets transmitted on
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.Dv async .
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This is an optimization where the trailing flag byte
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of one frame is shared with the opening flag byte of the next.
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Flag sharing between frames is disabled after one second of transmit
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idle time.
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.Sh HOOKS
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This node type supports the following hooks:
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.Bl -tag -width ".Va async"
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.It Va async
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Asynchronous connection.
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Typically this hook would be connected to a
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.Xr ng_tty 4
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node, which handles transmission of serial data over a tty device.
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.It Va sync
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Synchronous connection.
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This hook sends and receives synchronous frames.
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For PPP, these frames should contain address, control, and protocol fields,
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but no checksum field.
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Typically this hook would be connected to an individual link hook of a
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.Xr ng_ppp 4
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type node.
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.El
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.Sh CONTROL MESSAGES
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This node type supports the generic control messages, plus the following:
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.Bl -tag -width foo
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.It Dv NGM_ASYNC_CMD_SET_CONFIG Pq Ic setconfig
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Sets the node configuration, which is described by a
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.Dv "struct ng_async_cfg" :
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.Bd -literal -offset 4n
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struct ng_async_cfg {
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u_char enabled; /* Turn encoding on/off */
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uint16_t amru; /* Max receive async frame length */
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uint16_t smru; /* Max receive sync frame length */
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uint32_t accm; /* ACCM encoding */
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};
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.Ed
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The
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.Dv enabled
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field enables or disables all encoding/decoding functions (default disabled).
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When disabled, the node operates in simple
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.Dq pass through
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mode.
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The
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.Dv amru
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and
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.Dv smru
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fields are the asynchronous and synchronous MRU (maximum receive unit) values,
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respectively.
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These both default to 1600; note that the async MRU
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applies to the incoming frame length after asynchronous decoding.
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The
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.Dv accm
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field is the asynchronous character control map, which controls the escaping
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of characters 0x00 thorough 0x1f (default 0xffffffff).
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.It Dv NGM_ASYNC_CMD_GET_CONFIG Pq Ic getconfig
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This command returns the current configuration structure.
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.It Dv NGM_ASYNC_CMD_GET_STATS Pq Ic getstats
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This command returns a
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.Dv "struct ng_async_stat"
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containing node statistics for packet, octet, and error counts.
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.It Dv NGM_ASYNC_CMD_CLR_STATS Pq Ic clrstats
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Clears the node statistics.
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.Pp
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.El
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.Sh SHUTDOWN
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This node shuts down upon receipt of a
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.Dv NGM_SHUTDOWN
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control message, or when all hooks have been disconnected.
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.Sh SEE ALSO
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.Xr netgraph 4 ,
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.Xr ng_ppp 4 ,
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.Xr ng_tty 4 ,
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.Xr ngctl 8
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.Rs
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.%A W. Simpson
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.%T "PPP in HDLC-link Framing"
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.%O RFC 1662
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.Re
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.Rs
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.%A W. Simpson
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.%T "The Point-to-Point Protocol (PPP)"
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.%O RFC 1661
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.Re
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.Sh HISTORY
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The
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.Nm
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node type was implemented in
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.Fx 4.0 .
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.Sh AUTHORS
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.An Archie Cobbs Aq archie@FreeBSD.org
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