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 ------------------------------------------------------------*/