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modem_connect_tones.h
Go to the documentation of this file.
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/*
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* SpanDSP - a series of DSP components for telephony
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*
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* modem_connect_tones.c - Generation and detection of tones
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* associated with modems calling and
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* answering calls.
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*
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* Written by Steve Underwood <steveu@coppice.org>
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*
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* Copyright (C) 2006 Steve Underwood
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*
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* All rights reserved.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License version 2.1,
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* as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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/*! \file */
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#if !defined(_SPANDSP_MODEM_CONNECT_TONES_H_)
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#define _SPANDSP_MODEM_CONNECT_TONES_H_
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/*! \page modem_connect_tones_page Modem connect tone detection
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\section modem_connect_tones_page_sec_1 What does it do?
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Some telephony terminal equipment, such as modems, require a channel which is as
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clear as possible. They use their own echo cancellation. If the network is also
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performing echo cancellation the two cancellors can end up squabbling about the
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nature of the channel, with bad results. A special tone is defined which should
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cause the network to disable any echo cancellation processes. This is the echo
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canceller disable tone.
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The tone detector's design assumes the channel is free of any DC component.
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\section modem_connect_tones_page_sec_2 How does it work?
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A sharp notch filter is implemented as a single bi-quad section. The presence of
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the 2100Hz disable tone is detected by comparing the notched filtered energy
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with the unfiltered energy. If the notch filtered energy is much lower than the
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unfiltered energy, then a large proportion of the energy must be at the notch
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frequency. This type of detector may seem less intuitive than using a narrow
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bandpass filter to isolate the energy at the notch freqency. However, a sharp
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bandpass implemented as an IIR filter rings badly. The reciprocal notch filter
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is very well behaved for our purpose.
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*/
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enum
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{
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/*! \brief This is reported when a tone stops. */
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MODEM_CONNECT_TONES_NONE
= 0,
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/*! \brief CNG tone is a pure 1100Hz tone, in 0.5s bursts, with 3s silences in between. The
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bursts repeat for as long as is required. */
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MODEM_CONNECT_TONES_FAX_CNG
= 1,
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/*! \brief ANS tone is a pure continuous 2100Hz+-15Hz tone for 3.3s+-0.7s. */
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MODEM_CONNECT_TONES_ANS
= 2,
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/*! \brief ANS with phase reversals tone is a 2100Hz+-15Hz tone for 3.3s+-0.7s, with a 180 degree
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phase jump every 450ms+-25ms. */
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MODEM_CONNECT_TONES_ANS_PR
= 3,
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/*! \brief The ANSam tone is a version of ANS with 20% of 15Hz+-0.1Hz AM modulation, as per V.8 */
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MODEM_CONNECT_TONES_ANSAM
= 4,
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/*! \brief The ANSam with phase reversals tone is a version of ANS_PR with 20% of 15Hz+-0.1Hz AM
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modulation, as per V.8 */
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MODEM_CONNECT_TONES_ANSAM_PR
= 5,
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/*! \brief FAX preamble in a string of V.21 HDLC flag octets. */
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MODEM_CONNECT_TONES_FAX_PREAMBLE
= 6,
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/*! \brief CED tone is the same as ANS tone. FAX preamble in a string of V.21 HDLC flag octets.
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This is only valid as a tone type to receive. It is never reported as a detected tone
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type. The report will either be for FAX preamble or CED/ANS tone. */
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MODEM_CONNECT_TONES_FAX_CED_OR_PREAMBLE
= 7
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};
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/*! \brief FAX CED tone is the same as ANS tone. */
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#define MODEM_CONNECT_TONES_FAX_CED MODEM_CONNECT_TONES_ANS
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/*!
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Modem connect tones generator descriptor. This defines the state
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of a single working instance of the tone generator.
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*/
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typedef
struct
modem_connect_tones_tx_state_s
modem_connect_tones_tx_state_t
;
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/*!
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Modem connect tones receiver descriptor. This defines the state
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of a single working instance of the tone detector.
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*/
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typedef
struct
modem_connect_tones_rx_state_s
modem_connect_tones_rx_state_t
;
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#if defined(__cplusplus)
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extern
"C"
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{
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#endif
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/*! \brief Initialise an instance of the modem connect tones generator.
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\param s The context.
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*/
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SPAN_DECLARE(
modem_connect_tones_tx_state_t
*)
modem_connect_tones_tx_init
(
modem_connect_tones_tx_state_t
*s,
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int
tone_type
);
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/*! \brief Release an instance of the modem connect tones generator.
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\param s The context.
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\return 0 for OK, else -1.
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*/
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SPAN_DECLARE(
int
)
modem_connect_tones_tx_release
(
modem_connect_tones_tx_state_t
*s);
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/*! \brief Free an instance of the modem connect tones generator.
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\param s The context.
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\return 0 for OK, else -1.
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*/
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SPAN_DECLARE(
int
)
modem_connect_tones_tx_free
(
modem_connect_tones_tx_state_t
*s);
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/*! \brief Generate a block of modem connect tones samples.
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\param s The context.
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\param amp An array of signal samples.
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\param len The number of samples to generate.
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\return The number of samples generated.
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*/
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SPAN_DECLARE_NONSTD
(
int
) modem_connect_tones_tx(
modem_connect_tones_tx_state_t
*s,
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int16_t amp[],
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int
len);
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/*! \brief Process a block of samples through an instance of the modem connect
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tones detector.
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\param s The context.
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\param amp An array of signal samples.
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\param len The number of samples in the array.
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\return The number of unprocessed samples.
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*/
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SPAN_DECLARE_NONSTD
(
int
) modem_connect_tones_rx(
modem_connect_tones_rx_state_t
*s,
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const int16_t amp[],
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int
len);
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/*! \brief Test if a modem_connect tone has been detected.
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\param s The context.
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\return TRUE if tone is detected, else FALSE.
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*/
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SPAN_DECLARE(
int
)
modem_connect_tones_rx_get
(
modem_connect_tones_rx_state_t
*s);
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/*! \brief Initialise an instance of the modem connect tones detector.
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\param s The context.
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\param tone_type The type of connect tone being tested for.
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\param tone_callback An optional callback routine, used to report tones
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\param user_data An opaque pointer passed to the callback routine,
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\return A pointer to the context.
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*/
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SPAN_DECLARE(
modem_connect_tones_rx_state_t
*)
modem_connect_tones_rx_init
(
modem_connect_tones_rx_state_t
*s,
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int
tone_type,
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tone_report_func_t
tone_callback
,
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void
*user_data);
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/*! \brief Release an instance of the modem connect tones detector.
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\param s The context.
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\return 0 for OK, else -1. */
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SPAN_DECLARE(
int
)
modem_connect_tones_rx_release
(
modem_connect_tones_rx_state_t
*s);
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/*! \brief Free an instance of the modem connect tones detector.
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\param s The context.
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\return 0 for OK, else -1. */
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SPAN_DECLARE(
int
)
modem_connect_tones_rx_free
(
modem_connect_tones_rx_state_t
*s);
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SPAN_DECLARE(const
char
*) modem_connect_tone_to_str(
int
tone);
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#if defined(__cplusplus)
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}
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#endif
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#endif
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/*- End of file ------------------------------------------------------------*/
src
spandsp
modem_connect_tones.h
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