NAME
isdntel —
ISDN B-channel telephony interface
driver
SYNOPSIS
pseudo-device isdntel
count
DESCRIPTION
Theisdntel 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 driver's minor number are 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 /usr/include/netisdn/i4b_tel_ioctl.h and the isdntel(8) utility.
The telephony data stream comes out of the line in a bit-reversed
format, so the isdntel driver does the bit-reversion
process in any case.
Additionally, the user can specify to do A-law to mu-law, mu-law
to A-law or no conversion at all in the isdntel
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 parameters are available:
- CVT_NONE
- do no A-law/mu-law audio format conversion. The conversion path looks like
this:
USER <--> bitreversing <--> ISDN-line
- 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
read(2) conversion path looks like this:
USER <-- mu-law/A-law <-- bitreversing <-- ISDN-line
and the write(2) conversion path looks like this:
USER --> mu-law/A-law --> bitreversing --> ISDN-line
- 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
read(2) conversion path looks like this:
USER <-- A-law/mu-law <-- bitreversing <-- ISDN-line
and the write(2) conversion path looks like this:
USER --> A-law/mu-law --> bitreversing --> ISDN-line
SEE ALSO
STANDARDS
A-law and mu-law are specified in ITU Recommendation G.711.
AUTHORS
The isdntel device driver and this man
page were written by Hellmuth Michaelis
<hm@kts.org>.