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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
58 Mbuf boundaries of incoming data are ignored.
59 Once a complete packet has been received, it is decoded and
60 stripped of all framing bytes, and transmitted out the
62 hook as a single frame.
64 Synchronous frames are transmitted and received on the
67 Packets received on this hook are encoded as asynchronous frames
70 Received packets should start with the address and control fields,
71 or the PPP protocol field if address and control field compression
72 is employed, and contain no checksum field.
73 If the first four bytes are
74 .Dv "0xff 0x03 0xc0 0x21"
75 (an LCP protocol frame) then complete control character escaping
76 is enabled for that frame (in PPP, LCP packets are always sent with
77 no address and control field compression and all control characters
82 for packets transmitted on
84 This is an optimization where the trailing flag byte
85 of one frame is shared with the opening flag byte of the next.
86 Flag sharing between frames is disabled after one second of transmit
89 This node type supports the following hooks:
91 .Bl -tag -width foobar
93 Asynchronous connection.
94 Typically this hook would be connected to a
96 node, which handles transmission of serial data over a tty device.
98 Synchronous connection.
99 This hook sends and receives synchronous frames.
100 For PPP, these frames should contain address, control, and protocol fields,
101 but no checksum field.
102 Typically this hook would be connected to an individual link hook of a
107 This node type supports the generic control messages, plus the following:
109 .It Dv NGM_ASYNC_CMD_GET_STATS
110 This command returns a
111 .Dv "struct ng_async_stat"
112 containing node statistics for packet, octet, and error counts.
113 .It Dv NGM_ASYNC_CMD_CLR_STATS
114 Clears the node statistics.
115 .It Dv NGM_ASYNC_CMD_SET_CONFIG
116 Sets the node configuration, which is described by a
117 .Dv "struct ng_async_cfg" :
118 .Bd -literal -offset 4n
119 struct ng_async_cfg {
120 u_char enabled; /* Turn encoding on/off */
121 u_int16_t amru; /* Max receive async frame len */
122 u_int16_t smru; /* Max receive sync frame len */
123 u_int32_t accm; /* ACCM encoding */
129 field enables or disables all encoding/decoding functions (default disabled).
130 When disabled, the node operates in simple
137 fields are the asynchronous and synchronous MRU (maximum receive unit) values,
139 These both default to 1600; note that the async MRU
140 applies to the incoming frame length after asynchronous decoding.
143 field is the asynchronous character control map, which controls the escaping
144 of characters 0x00 thorough 0x1f (default 0xffffffff).
145 .It Dv NGM_ASYNC_CMD_GET_CONFIG
146 This command returns the current configuration structure.
149 This node shuts down upon receipt of a
151 control message, or when all hooks have been disconnected.
159 .%T "PPP in HDLC-link Framing"
164 .%T "The Point-to-Point Protocol (PPP)"
170 node type was implemented in
173 .An Archie Cobbs Aq archie@FreeBSD.org