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I4BTEL(4)		 BSD Kernel Interfaces Manual		     I4BTEL(4)

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 tele-
     phony 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	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 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>.

BSD				 July 28, 2002				   BSD

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | STANDARDS | AUTHORS

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