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Author: Archie Cobbs <archie@whistle.com>
$FreeBSD: head/share/man/man4/ng_async.4 52419 1999-10-21 09:06:11Z julian $
$Whistle: ng_async.8,v 1.6 1999/01/25 23:46:25 archie Exp $
.Dd January 19, 1999 .Dt NG_ASYNC 8 .Os FreeBSD 3 .Sh NAME .Nm ng_async .Nd asynchronous framing netgraph node type .Sh SYNOPSIS .Fd #include <netgraph/ng_async.h> .Sh DESCRIPTION The .Nm async node type performs conversion between synchronous frames and asynchronous frames, as defined for the PPP protocol in RFC 1662. Asynchronous framing uses flag bytes and octet-stuffing to simulate a frame oriented connection over an octet-oriented asynchronous line.
p The node trasmits and receives asynchronous data on the .Dv async hook. Incoming data mbuf boundaries are ignored, while outgoing data is sent as a complete frame at a time.
p There are two synchronous hooks, .Dv sync and .Dv sync2 . For both hooks, received packets are encoded as asynchronous frames and sent out on .Dv async . Hook .Dv sync2 differs from .Dv sync only in that any configured address and control field compression and/or control character escaping is disabled when the frame is encoded. This is useful for transmitting PPP LCP packets, which are always sent this way.
p This node supports ``flag sharing'' for packets transmitted on .Dv async . This is an optimization where the trailing flag byte of one frame is shared with the opening flag byte of the next. Flag sharing between frames is disabled after one second of transmit idle time. .Sh HOOKS This node type supports the following hooks:
p l -tag -width foobar t Dv async Asynchronous connection. Typically this hook would be connected to a .Xr ng_tty 8 node, which handles transmission of serial data over a tty device. t Dv sync Synchronous connection. This hook sends and receives synchronous frames. For PPP, these frames contain no address, control, or checksum fields; each frame begins with the PPP protocol number. Typically this hook would be connected to the .Dv downstream hook of a .Xr ng_ppp 8 type node. .El .Sh CONTROL MESSAGES This node type supports the generic control messages, plus the following: l -tag -width foo t Dv NGM_ASYNC_CMD_GET_STATS This command returns a .Dv "struct ng_async_stat" containing node statistics for packet, octet, and error counts. t Dv NGM_ASYNC_CMD_CLR_STATS Clears the node statistics. t Dv NGM_ASYNC_CMD_SET_CONFIG Sets the node configuration, which is described by a .Dv "struct ng_async_cfg" : d -literal -offset 4n struct ng_async_cfg { u_char enabled; /* Turn encoding on/off */ u_char acfcomp; /* Address/control field comp. */ u_int16_t amru; /* Max receive async frame len */ u_int16_t smru; /* Max receive sync frame len */ u_int32_t accm; /* ACCM encoding */ }; .Ed
p The .Dv enabled field enables or disables all encoding/decoding functions (default disabled). When disabled, the node operates in simple ``pass through'' mode. Setting .Dv acfcomp enables address and control field compression on transmission (for packets received on the .Dv sync hook only; default off). .Dv amru and .Dv smru are the asynchronous and synchronous MRU (maximum receive unit) values, respectively. These both default to 1600; note that the async MRU applies to the incoming frame length after asynchronous decoding. Finally, .Dv accm is the asynchronous character control map, which controls the escaping of characters 0x00 thorough 0x1f (default 0xffffffff). t Dv NGM_ASYNC_CMD_GET_CONFIG This command returns the current configuration structure. .El .Sh SHUTDOWN This node shuts down upon receipt of a .Dv NGM_SHUTDOWN control message, or when all hooks have been disconnected. .Sh SEE ALSO .Xr netgraph 4 , .Xr ng_ppp 8 , .Xr ng_tty 8 , .Xr ngctl 8 . .Rs .%A W. Simpson .%T "PPP in HDLC-link Framing" .%O RFC 1662 .Re .Sh AUTHOR Archie Cobbs <archie@whistle.com>