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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
46 .In netgraph/ng_async.h
50 node type performs conversion between synchronous frames and
51 asynchronous frames, as defined for the PPP protocol in RFC 1662.
52 Asynchronous framing uses flag bytes and octet-stuffing
53 to simulate a frame oriented connection over an octet-oriented
54 asynchronous serial line.
56 The node transmits and receives asynchronous data on the
59 Mbuf boundaries of incoming data are ignored.
60 Once a complete packet has been received, it is decoded and
61 stripped of all framing bytes, and transmitted out the
63 hook as a single frame.
65 Synchronous frames are transmitted and received on the
68 Packets received on this hook are encoded as asynchronous frames
71 Received packets should start with the address and control fields,
72 or the PPP protocol field if address and control field compression
73 is employed, and contain no checksum field.
74 If the first four bytes are
75 .Dv "0xff 0x03 0xc0 0x21"
76 (an LCP protocol frame) then complete control character escaping
77 is enabled for that frame (in PPP, LCP packets are always sent with
78 no address and control field compression and all control characters
83 for packets transmitted on
85 This is an optimization where the trailing flag byte
86 of one frame is shared with the opening flag byte of the next.
87 Flag sharing between frames is disabled after one second of transmit
90 This node type supports the following hooks:
91 .Bl -tag -width ".Va async"
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_SET_CONFIG Pq Ic setconfig
110 Sets the node configuration, which is described by a
111 .Dv "struct ng_async_cfg" :
112 .Bd -literal -offset 4n
113 struct ng_async_cfg {
114 u_char enabled; /* Turn encoding on/off */
115 uint16_t amru; /* Max receive async frame length */
116 uint16_t smru; /* Max receive sync frame length */
117 uint32_t accm; /* ACCM encoding */
122 field enables or disables all encoding/decoding functions (default disabled).
123 When disabled, the node operates in simple
130 fields are the asynchronous and synchronous MRU (maximum receive unit) values,
132 These both default to 1600; note that the async MRU
133 applies to the incoming frame length after asynchronous decoding.
136 field is the asynchronous character control map, which controls the escaping
137 of characters 0x00 thorough 0x1f (default 0xffffffff).
138 .It Dv NGM_ASYNC_CMD_GET_CONFIG Pq Ic getconfig
139 This command returns the current configuration structure.
140 .It Dv NGM_ASYNC_CMD_GET_STATS Pq Ic getstats
141 This command returns a
142 .Dv "struct ng_async_stat"
143 containing node statistics for packet, octet, and error counts.
144 .It Dv NGM_ASYNC_CMD_CLR_STATS Pq Ic clrstats
145 Clears the node statistics.
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