spandsp  0.0.6
modem_connect_tones.h
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00001 /*
00002  * SpanDSP - a series of DSP components for telephony
00003  *
00004  * modem_connect_tones.c - Generation and detection of tones
00005  *                         associated with modems calling and
00006  *                         answering calls.
00007  *
00008  * Written by Steve Underwood <steveu@coppice.org>
00009  *
00010  * Copyright (C) 2006 Steve Underwood
00011  *
00012  * All rights reserved.
00013  *
00014  * This program is free software; you can redistribute it and/or modify
00015  * it under the terms of the GNU Lesser General Public License version 2.1,
00016  * as published by the Free Software Foundation.
00017  *
00018  * This program is distributed in the hope that it will be useful,
00019  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00020  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00021  * GNU Lesser General Public License for more details.
00022  *
00023  * You should have received a copy of the GNU Lesser General Public
00024  * License along with this program; if not, write to the Free Software
00025  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
00026  */
00027  
00028 /*! \file */
00029 
00030 #if !defined(_SPANDSP_MODEM_CONNECT_TONES_H_)
00031 #define _SPANDSP_MODEM_CONNECT_TONES_H_
00032 
00033 /*! \page modem_connect_tones_page Modem connect tone detection
00034 
00035 \section modem_connect_tones_page_sec_1 What does it do?
00036 Some telephony terminal equipment, such as modems, require a channel which is as
00037 clear as possible. They use their own echo cancellation. If the network is also
00038 performing echo cancellation the two cancellors can end up squabbling about the
00039 nature of the channel, with bad results. A special tone is defined which should
00040 cause the network to disable any echo cancellation processes. This is the echo
00041 canceller disable tone.
00042 
00043 The tone detector's design assumes the channel is free of any DC component.
00044 
00045 \section modem_connect_tones_page_sec_2 How does it work?
00046 A sharp notch filter is implemented as a single bi-quad section. The presence of
00047 the 2100Hz disable tone is detected by comparing the notched filtered energy
00048 with the unfiltered energy. If the notch filtered energy is much lower than the
00049 unfiltered energy, then a large proportion of the energy must be at the notch
00050 frequency. This type of detector may seem less intuitive than using a narrow
00051 bandpass filter to isolate the energy at the notch freqency. However, a sharp
00052 bandpass implemented as an IIR filter rings badly. The reciprocal notch filter
00053 is very well behaved for our purpose. 
00054 */
00055 
00056 enum
00057 {
00058     /*! \brief This is reported when a tone stops. */
00059     MODEM_CONNECT_TONES_NONE = 0,
00060     /*! \brief CNG tone is a pure 1100Hz tone, in 0.5s bursts, with 3s silences in between. The
00061                bursts repeat for as long as is required. */
00062     MODEM_CONNECT_TONES_FAX_CNG = 1,
00063     /*! \brief ANS tone is a pure continuous 2100Hz+-15Hz tone for 3.3s+-0.7s. */
00064     MODEM_CONNECT_TONES_ANS = 2,
00065     /*! \brief ANS with phase reversals tone is a 2100Hz+-15Hz tone for 3.3s+-0.7s, with a 180 degree
00066                phase jump every 450ms+-25ms. */
00067     MODEM_CONNECT_TONES_ANS_PR = 3,
00068     /*! \brief The ANSam tone is a version of ANS with 20% of 15Hz+-0.1Hz AM modulation, as per V.8 */
00069     MODEM_CONNECT_TONES_ANSAM = 4,
00070     /*! \brief The ANSam with phase reversals tone is a version of ANS_PR with 20% of 15Hz+-0.1Hz AM
00071                modulation, as per V.8 */
00072     MODEM_CONNECT_TONES_ANSAM_PR = 5,
00073     /*! \brief FAX preamble in a string of V.21 HDLC flag octets. */
00074     MODEM_CONNECT_TONES_FAX_PREAMBLE = 6,
00075     /*! \brief CED tone is the same as ANS tone. FAX preamble in a string of V.21 HDLC flag octets.
00076                This is only valid as a tone type to receive. It is never reported as a detected tone
00077                type. The report will either be for FAX preamble or CED/ANS tone. */
00078     MODEM_CONNECT_TONES_FAX_CED_OR_PREAMBLE = 7
00079 };
00080 
00081 /*! \brief FAX CED tone is the same as ANS tone. */
00082 #define MODEM_CONNECT_TONES_FAX_CED MODEM_CONNECT_TONES_ANS
00083 
00084 /*!
00085     Modem connect tones generator descriptor. This defines the state
00086     of a single working instance of the tone generator.
00087 */
00088 typedef struct modem_connect_tones_tx_state_s modem_connect_tones_tx_state_t;
00089 
00090 /*!
00091     Modem connect tones receiver descriptor. This defines the state
00092     of a single working instance of the tone detector.
00093 */
00094 typedef struct modem_connect_tones_rx_state_s modem_connect_tones_rx_state_t;
00095 
00096 #if defined(__cplusplus)
00097 extern "C"
00098 {
00099 #endif
00100 
00101 /*! \brief Initialise an instance of the modem connect tones generator.
00102     \param s The context.
00103 */
00104 SPAN_DECLARE(modem_connect_tones_tx_state_t *) modem_connect_tones_tx_init(modem_connect_tones_tx_state_t *s,
00105                                                                            int tone_type);
00106 
00107 /*! \brief Release an instance of the modem connect tones generator.
00108     \param s The context.
00109     \return 0 for OK, else -1.
00110 */
00111 SPAN_DECLARE(int) modem_connect_tones_tx_release(modem_connect_tones_tx_state_t *s);
00112 
00113 /*! \brief Free an instance of the modem connect tones generator.
00114     \param s The context.
00115     \return 0 for OK, else -1.
00116 */
00117 SPAN_DECLARE(int) modem_connect_tones_tx_free(modem_connect_tones_tx_state_t *s);
00118 
00119 /*! \brief Generate a block of modem connect tones samples.
00120     \param s The context.
00121     \param amp An array of signal samples.
00122     \param len The number of samples to generate.
00123     \return The number of samples generated.
00124 */
00125 SPAN_DECLARE_NONSTD(int) modem_connect_tones_tx(modem_connect_tones_tx_state_t *s,
00126                                                 int16_t amp[],
00127                                                 int len);
00128 
00129 /*! \brief Process a block of samples through an instance of the modem connect
00130            tones detector.
00131     \param s The context.
00132     \param amp An array of signal samples.
00133     \param len The number of samples in the array.
00134     \return The number of unprocessed samples.
00135 */
00136 SPAN_DECLARE_NONSTD(int) modem_connect_tones_rx(modem_connect_tones_rx_state_t *s,
00137                                                 const int16_t amp[],
00138                                                 int len);
00139                              
00140 /*! \brief Test if a modem_connect tone has been detected.
00141     \param s The context.
00142     \return TRUE if tone is detected, else FALSE.
00143 */
00144 SPAN_DECLARE(int) modem_connect_tones_rx_get(modem_connect_tones_rx_state_t *s);
00145 
00146 /*! \brief Initialise an instance of the modem connect tones detector.
00147     \param s The context.
00148     \param tone_type The type of connect tone being tested for.
00149     \param tone_callback An optional callback routine, used to report tones
00150     \param user_data An opaque pointer passed to the callback routine,
00151     \return A pointer to the context.
00152 */
00153 SPAN_DECLARE(modem_connect_tones_rx_state_t *) modem_connect_tones_rx_init(modem_connect_tones_rx_state_t *s,
00154                                                                            int tone_type,
00155                                                                            tone_report_func_t tone_callback,
00156                                                                            void *user_data);
00157 
00158 /*! \brief Release an instance of the modem connect tones detector.
00159     \param s The context.
00160     \return 0 for OK, else -1. */
00161 SPAN_DECLARE(int) modem_connect_tones_rx_release(modem_connect_tones_rx_state_t *s);
00162 
00163 /*! \brief Free an instance of the modem connect tones detector.
00164     \param s The context.
00165     \return 0 for OK, else -1. */
00166 SPAN_DECLARE(int) modem_connect_tones_rx_free(modem_connect_tones_rx_state_t *s);
00167 
00168 SPAN_DECLARE(const char *) modem_connect_tone_to_str(int tone);
00169 
00170 #if defined(__cplusplus)
00171 }
00172 #endif
00173 
00174 #endif
00175 /*- End of file ------------------------------------------------------------*/