---
name: "i4btel"
section: "4"
platform: "linux"
package: "freebsd-manpages"
version: "6.0-5"
release: "Debian 4.0 (Etch)"
platforms: ["linux"]
url: "https://new.carta.tech/i4btel"
---

# i4btel(4)

isdn4bsd ISDN B-channel telephony interface driver

## NAME

**i4btel** – isdn4bsd ISDN B-channel telephony interface driver

## SYNOPSIS

**device** **"i4btel"** \[count\]

## DESCRIPTION

The **i4btel** driver provides an interface to the ISDN 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\_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 parameters 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)](/read/2.md) conversion path looks like this:

  USER \<-- u-law/A-law \<-- bitreversing \<-- ISDN-line

  and the [write(2)](/write/2.md) 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)](/read/2.md) conversion path looks like this:

  USER \<-- A-law/u-law \<-- bitreversing \<-- ISDN-line

  and the [write(2)](/write/2.md) conversion path looks like this:

  USER --\> A-law/u-law --\> bitreversing --\> ISDN-line

## SEE ALSO

g711conv(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⟩.