xref: /freebsd/share/man/man4/ng_async.4 (revision 41466b50c1d5bfd1cf6adaae547a579a75d7c04e)
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33.\" Author: Archie Cobbs <archie@FreeBSD.org>
34.\"
35.\" $FreeBSD$
36.\" $Whistle: ng_async.8,v 1.6 1999/01/25 23:46:25 archie Exp $
37.\"
38.Dd January 19, 1999
39.Dt NG_ASYNC 4
40.Os
41.Sh NAME
42.Nm ng_async
43.Nd asynchronous framing netgraph node type
44.Sh SYNOPSIS
45.In netgraph/ng_async.h
46.Sh DESCRIPTION
47The
48.Nm async
49node type performs conversion between synchronous frames and
50asynchronous frames, as defined for the PPP protocol in RFC 1662.
51Asynchronous framing uses flag bytes and octet-stuffing
52to simulate a frame oriented connection over an octet-oriented
53asynchronous serial line.
54.Pp
55The node transmits and receives asynchronous data on the
56.Dv async
57hook.  Mbuf boundaries of incoming data are ignored.
58Once a complete packet has been received, it is decoded and
59stripped of all framing bytes, and transmitted out the
60.Dv sync
61hook as a single frame.
62.Pp
63Synchronous frames are transmitted and received on the
64.Dv sync
65hook.
66Packets received on this hook are encoded as asynchronous frames
67and sent out on
68.Dv async .
69Received packets should start with the address and control fields,
70or the PPP protocol field if address and control field compression
71is employed, and contain no checksum field.  If the first four bytes are
72.Dv "0xff 0x03 0xc0 0x21"
73(an LCP protocol frame) then complete control character escaping
74is enabled for that frame (in PPP, LCP packets are always sent with
75no address and control field compression and all control characters
76escaped).
77.Pp
78This node supports
79.Dq flag sharing
80for packets transmitted on
81.Dv async .
82This is an optimization where the trailing flag byte
83of one frame is shared with the opening flag byte of the next.
84Flag sharing between frames is disabled after one second of transmit
85idle time.
86.Sh HOOKS
87This node type supports the following hooks:
88.Pp
89.Bl -tag -width foobar
90.It Dv async
91Asynchronous connection.
92Typically this hook would be connected to a
93.Xr ng_tty 4
94node, which handles transmission of serial data over a tty device.
95.It Dv sync
96Synchronous connection.  This hook sends and receives synchronous frames.
97For PPP, these frames should contain address, control, and protocol fields,
98but no checksum field.
99Typically this hook would be connected to an individual link hook of a
100.Xr ng_ppp 4
101type node.
102.El
103.Sh CONTROL MESSAGES
104This node type supports the generic control messages, plus the following:
105.Bl -tag -width foo
106.It Dv NGM_ASYNC_CMD_GET_STATS
107This command returns a
108.Dv "struct ng_async_stat"
109containing node statistics for packet, octet, and error counts.
110.It Dv NGM_ASYNC_CMD_CLR_STATS
111Clears the node statistics.
112.It Dv NGM_ASYNC_CMD_SET_CONFIG
113Sets the node configuration, which is described by a
114.Dv "struct ng_async_cfg" :
115.Bd -literal -offset 4n
116struct ng_async_cfg {
117  u_char    enabled;  /* Turn encoding on/off */
118  u_int16_t amru;     /* Max receive async frame len */
119  u_int16_t smru;     /* Max receive sync frame len */
120  u_int32_t accm;     /* ACCM encoding */
121};
122.Ed
123.Pp
124The
125.Dv enabled
126field enables or disables all encoding/decoding functions (default disabled).
127When disabled, the node operates in simple
128.Dq pass through
129mode.
130The
131.Dv amru
132and
133.Dv smru
134fields are the asynchronous and synchronous MRU (maximum receive unit) values,
135respectively.  These both default to 1600; note that the async MRU
136applies to the incoming frame length after asynchronous decoding.
137The
138.Dv accm
139field is the asynchronous character control map, which controls the escaping
140of characters 0x00 thorough 0x1f (default 0xffffffff).
141.It Dv NGM_ASYNC_CMD_GET_CONFIG
142This command returns the current configuration structure.
143.El
144.Sh SHUTDOWN
145This node shuts down upon receipt of a
146.Dv NGM_SHUTDOWN
147control message, or when all hooks have been disconnected.
148.Sh SEE ALSO
149.Xr netgraph 4 ,
150.Xr ng_ppp 4 ,
151.Xr ng_tty 4 ,
152.Xr ngctl 8
153.Rs
154.%A W. Simpson
155.%T "PPP in HDLC-link Framing"
156.%O RFC 1662
157.Re
158.Rs
159.%A W. Simpson
160.%T "The Point-to-Point Protocol (PPP)"
161.%O RFC 1661
162.Re
163.Sh HISTORY
164The
165.Nm
166node type was implemented in
167.Fx 4.0 .
168.Sh AUTHORS
169.An Archie Cobbs Aq archie@FreeBSD.org
170