I4BTEL(4) BSD Kernel Interfaces Manual I4BTEL(4)NAMEi4btel — isdn4bsd ISDN B-channel telephony interface driver
SYNOPSIS
pseudo-device "i4btel" [count]
DESCRIPTION
The i4btel driver provides an interface to the B-channel for telephony
applications and is currently used by the isdnd(8) for answering machine
support. The driver is part of the isdn4bsd package.
The lower six bits of the drivers's minor number is used to specify a
unit number, whereas the upper two bits specify a functionality.
Functionality zero is the usual telephony data stream i/o driver.
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
<i4b_machine/i4b_tel_ioctl.h> and the isdnphone(8) utility.
The telephony data stream comes out of the line in a bit-reversed format,
so the i4btel driver does the bit-reversion process in any case.
Additionally, the user can specify to do A-law to u-law, u-law to A-law
or no conversion at all in the i4btel driver by using the isdntelctl(8)
utility.
The driver is able to process several ioctl's:
I4B_TEL_GETAUDIOFMT
get currently used audio format conversion.
I4B_TEL_SETAUDIOFMT
set currently used audio format conversion.
I4B_TEL_EMPTYINPUTQUEUE
clear the input queue.
For the I4B_TEL_GETAUDIOFMT and I4B_TEL_SETAUDIOFMT, the following param‐
eters are available:
CVT_NONE
do no A-law/u-law audio format conversion. The conversion
path looks like this:
USER <--> bitreversing <--> ISDN-line
CVT_ALAW2ULAW
set set audio format conversion to do an audio conversion
from A-law (on the ISDN line) to u-law (in the userland).
The read(2) conversion path looks like this:
USER <-- u-law/A-law <-- bitreversing <-- ISDN-line
and the write(2) conversion path looks like this:
USER --> u-law/A-law --> bitreversing --> ISDN-line
CVT_ULAW2ALAW
set set audio format conversion to do an audio conversion
from u-law (on the ISDN line) to A-law (in the userland).
The read(2) conversion path looks like this:
USER <-- A-law/u-law <-- bitreversing <-- ISDN-line
and the write(2) conversion path looks like this:
USER --> A-law/u-law --> bitreversing --> ISDN-line
SEE ALSOg711conv(1), isdnd.rc(5), isdnd(8), isdnphone(8), isdntelctl(8)STANDARDS
A-Law and u-Law are specified in ITU Recommendation G.711.
AUTHORS
The i4btel device driver and this manpage were written by Hellmuth
Michaelis ⟨hm@FreeBSD.org⟩.
BSD April 21, 1999 BSD
