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33 .\" Author: Archie Cobbs <archie@FreeBSD.org>
36 .\" $Whistle: ng_async.8,v 1.6 1999/01/25 23:46:25 archie Exp $
43 .Nd asynchronous framing netgraph node type
45 .In netgraph/ng_async.h
49 node type performs conversion between synchronous frames and
50 asynchronous frames, as defined for the PPP protocol in RFC 1662.
51 Asynchronous framing uses flag bytes and octet-stuffing
52 to simulate a frame oriented connection over an octet-oriented
53 asynchronous serial line.
55 The node transmits and receives asynchronous data on the
57 hook. Mbuf boundaries of incoming data are ignored.
58 Once a complete packet has been received, it is decoded and
59 stripped of all framing bytes, and transmitted out the
61 hook as a single frame.
63 Synchronous frames are transmitted and received on the
66 Packets received on this hook are encoded as asynchronous frames
69 Received packets should start with the address and control fields,
70 or the PPP protocol field if address and control field compression
71 is 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
74 is enabled for that frame (in PPP, LCP packets are always sent with
75 no address and control field compression and all control characters
80 for packets transmitted on
82 This is an optimization where the trailing flag byte
83 of one frame is shared with the opening flag byte of the next.
84 Flag sharing between frames is disabled after one second of transmit
87 This node type supports the following hooks:
89 .Bl -tag -width foobar
91 Asynchronous connection.
92 Typically this hook would be connected to a
94 node, which handles transmission of serial data over a tty device.
96 Synchronous connection. This hook sends and receives synchronous frames.
97 For PPP, these frames should contain address, control, and protocol fields,
98 but no checksum field.
99 Typically this hook would be connected to an individual link hook of a
104 This node type supports the generic control messages, plus the following:
106 .It Dv NGM_ASYNC_CMD_GET_STATS
107 This command returns a
108 .Dv "struct ng_async_stat"
109 containing node statistics for packet, octet, and error counts.
110 .It Dv NGM_ASYNC_CMD_CLR_STATS
111 Clears the node statistics.
112 .It Dv NGM_ASYNC_CMD_SET_CONFIG
113 Sets the node configuration, which is described by a
114 .Dv "struct ng_async_cfg" :
115 .Bd -literal -offset 4n
116 struct 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 */
126 field enables or disables all encoding/decoding functions (default disabled).
127 When disabled, the node operates in simple
134 fields are the asynchronous and synchronous MRU (maximum receive unit) values,
135 respectively. These both default to 1600; note that the async MRU
136 applies to the incoming frame length after asynchronous decoding.
139 field is the asynchronous character control map, which controls the escaping
140 of characters 0x00 thorough 0x1f (default 0xffffffff).
141 .It Dv NGM_ASYNC_CMD_GET_CONFIG
142 This command returns the current configuration structure.
145 This node shuts down upon receipt of a
147 control message, or when all hooks have been disconnected.
155 .%T "PPP in HDLC-link Framing"
160 .%T "The Point-to-Point Protocol (PPP)"
166 node type was implemented in
169 .An Archie Cobbs Aq archie@FreeBSD.org