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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(1) 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


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

STANDARDS

     A-Law and u-Law are specified in ITU Recommendation G.711.

SEE ALSO

     g711conv(1), isdnphone(1), isdnd.rc(5), isdnd(8), isdntelctl(8)

AUTHORS

     The i4btel device driver and this manpage were written by Hellmuth
     Michaelis <hm@FreeBSD.org>.

FreeBSD 5.4			 July 28, 2002			   FreeBSD 5.4

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