.\" $NetBSD: isdntel.4,v 1.7.18.1 2019/09/02 16:39:20 martin Exp $
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.\" Copyright (c) 1997, 1999 Hellmuth Michaelis. All rights reserved.
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.\"	$Id: isdntel.4,v 1.7.18.1 2019/09/02 16:39:20 martin Exp $
.\"
.\" $FreeBSD$
.\"
.\"	last edit-date: [Mon Dec 13 23:13:39 1999]
.\"
.Dd April 21, 1999
.Dt ISDNTEL 4
.Os
.Sh NAME
.Nm isdntel
.Nd ISDN B-channel telephony interface driver
.Sh SYNOPSIS
.Cd "pseudo-device isdntel" Ar count
.Sh DESCRIPTION
The
.Nm
driver provides an interface to the B-channel for telephony applications
and is currently used by the
.Xr isdnd 8
for answering machine support. The driver is part of the isdn4bsd package.
.Pp
The lower six bits of the driver's minor number are used to specify a
unit number, whereas the upper two bits specify a functionality.
.Pp
Functionality zero is the usual telephony data stream i/o driver.
.Pp
Functionality one is used to enable commands to dial out and hang up and
receive responses about the state of the dial out progress and status.
This commands may change in the future, for details see the file
.Pa /usr/include/netisdn/i4b_tel_ioctl.h
and the
.Xr isdntel 8
utility.
.Pp
The telephony data stream comes out of the line in a bit-reversed format,
so the
.Nm
driver does the bit-reversion process in any case.
.Pp
Additionally, the user can specify to do A-law to mu-law, mu-law to A-law
or no conversion at all in the
.Nm
driver by using the
.Xr isdntelctl 8
utility.
.Pp
The driver is able to process several ioctl's:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It Ar I4B_TEL_GETAUDIOFMT
get currently used audio format conversion.
.It Ar I4B_TEL_SETAUDIOFMT
set currently used audio format conversion.
.It Ar I4B_TEL_EMPTYINPUTQUEUE
clear the input queue.
.El
.Pp
For the I4B_TEL_GETAUDIOFMT and I4B_TEL_SETAUDIOFMT, the following
parameters are available:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It Ar CVT_NONE
do no A-law/mu-law audio format conversion. The conversion path looks like
this:
.Pp
USER <--> bitreversing <--> ISDN-line
.Pp
.It Ar CVT_ALAW2ULAW
set audio format conversion to do an audio conversion from A-law
(on the ISDN line) to mu-law (in the userland).
The
.Xr read 2
conversion path looks like this:
.Pp
USER <-- mu-law/A-law <-- bitreversing <-- ISDN-line
.Pp
and the
.Xr write 2
conversion path looks like this:
.Pp
USER --> mu-law/A-law --> bitreversing --> ISDN-line
.Pp
.It Ar CVT_ULAW2ALAW
set audio format conversion to do an audio conversion from mu-law
(on the ISDN line) to A-law (in the userland).
The
.Xr read 2
conversion path looks like this:
.Pp
USER <-- A-law/mu-law <-- bitreversing <-- ISDN-line
.Pp
and the
.Xr write 2
conversion path looks like this:
.Pp
USER --> A-law/mu-law --> bitreversing --> ISDN-line
.El
.Sh SEE ALSO
.Xr isdnd.rc 5 ,
.Xr isdnd 8 ,
.Xr isdntel 8 ,
.Xr isdntelctl 8
.Sh STANDARDS
A-law and mu-law are specified in ITU Recommendation G.711.
.Sh AUTHORS
The
.Nm
device driver and this man page were written by
.An Hellmuth Michaelis Aq Mt hm@kts.org .