00001 /* 00002 * SpanDSP - a series of DSP components for telephony 00003 * 00004 * t38_core.h - An implementation of T.38, less the packet exchange part 00005 * 00006 * Written by Steve Underwood <steveu@coppice.org> 00007 * 00008 * Copyright (C) 2005 Steve Underwood 00009 * 00010 * All rights reserved. 00011 * 00012 * This program is free software; you can redistribute it and/or modify 00013 * it under the terms of the GNU Lesser General Public License version 2.1, 00014 * as published by the Free Software Foundation. 00015 * 00016 * This program is distributed in the hope that it will be useful, 00017 * but WITHOUT ANY WARRANTY; without even the implied warranty of 00018 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 00019 * GNU Lesser General Public License for more details. 00020 * 00021 * You should have received a copy of the GNU Lesser General Public 00022 * License along with this program; if not, write to the Free Software 00023 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. 00024 * 00025 * $Id: t38_core.h,v 1.38 2009/04/12 14:18:02 steveu Exp $ 00026 */ 00027 00028 /*! \file */ 00029 00030 #if !defined(_SPANDSP_T38_CORE_H_) 00031 #define _SPANDSP_T38_CORE_H_ 00032 00033 /*! \page t38_core_page T.38 real time FAX over IP message handling 00034 There are two ITU recommendations which address sending FAXes over IP networks. T.37 specifies a 00035 method of encapsulating FAX images in e-mails, and transporting them to the recipient (an e-mail 00036 box, or another FAX machine) in a store-and-forward manner. T.38 defines a protocol for 00037 transmitting a FAX across an IP network in real time. The core T.38 modules implements the basic 00038 message handling for the T.38, real time, FAX over IP (FoIP) protocol. 00039 00040 The T.38 protocol can operate between: 00041 - Internet-aware FAX terminals, which connect directly to an IP network. The T.38 terminal module 00042 extends this module to provide a complete T.38 terminal. 00043 - FAX gateways, which allow traditional PSTN FAX terminals to communicate through the Internet. 00044 The T.38 gateway module extends this module to provide a T.38 gateway. 00045 - A combination of terminals and gateways. 00046 00047 T.38 is the only standardised protocol which exists for real-time FoIP. Reliably transporting a 00048 FAX between PSTN FAX terminals, through an IP network, requires use of the T.38 protocol at FAX 00049 gateways. VoIP connections are not robust for modem use, including FAX modem use. Most use low 00050 bit rate codecs, which cannot convey the modem signals accurately. Even when high bit rate 00051 codecs are used, VoIP connections suffer dropouts and timing adjustments, which modems cannot 00052 tolerate. In a LAN environment the dropout rate may be very low, but the timing adjustments which 00053 occur in VoIP connections still make modem operation unreliable. T.38 FAX gateways deal with the 00054 delays, timing jitter, and packet loss experienced in packet networks, and isolate the PSTN FAX 00055 terminals from these as far as possible. In addition, by sending FAXes as image data, rather than 00056 digitised audio, they reduce the required bandwidth of the IP network. 00057 00058 \section t38_core_page_sec_1 What does it do? 00059 00060 \section t38_core_page_sec_2 How does it work? 00061 00062 Timing differences and jitter between two T.38 entities can be a serious problem, if one of those 00063 entities is a PSTN gateway. 00064 00065 Flow control for non-ECM image data takes advantage of several features of the T.30 specification. 00066 First, an unspecified number of 0xFF octets may be sent at the start of transmission. This means we 00067 can add endless extra 0xFF bytes at this point, without breaking the T.30 spec. In practice, we 00068 cannot add too many, or we will affect the timing tolerance of the T.30 protocol by delaying the 00069 response at the end of each image. Secondly, just before an end of line (EOL) marker we can pad 00070 with zero bits. Again, the number is limited only by need to avoid upsetting the timing of the 00071 step following the non-ECM data. 00072 */ 00073 00074 /*! T.38 indicator types */ 00075 enum t30_indicator_types_e 00076 { 00077 T38_IND_NO_SIGNAL = 0, 00078 T38_IND_CNG, 00079 T38_IND_CED, 00080 T38_IND_V21_PREAMBLE, 00081 T38_IND_V27TER_2400_TRAINING, 00082 T38_IND_V27TER_4800_TRAINING, 00083 T38_IND_V29_7200_TRAINING, 00084 T38_IND_V29_9600_TRAINING, 00085 T38_IND_V17_7200_SHORT_TRAINING, 00086 T38_IND_V17_7200_LONG_TRAINING, 00087 T38_IND_V17_9600_SHORT_TRAINING, 00088 T38_IND_V17_9600_LONG_TRAINING, 00089 T38_IND_V17_12000_SHORT_TRAINING, 00090 T38_IND_V17_12000_LONG_TRAINING, 00091 T38_IND_V17_14400_SHORT_TRAINING, 00092 T38_IND_V17_14400_LONG_TRAINING, 00093 T38_IND_V8_ANSAM, 00094 T38_IND_V8_SIGNAL, 00095 T38_IND_V34_CNTL_CHANNEL_1200, 00096 T38_IND_V34_PRI_CHANNEL, 00097 T38_IND_V34_CC_RETRAIN, 00098 T38_IND_V33_12000_TRAINING, 00099 T38_IND_V33_14400_TRAINING 00100 }; 00101 00102 /*! T.38 data types */ 00103 enum t38_data_types_e 00104 { 00105 T38_DATA_NONE = -1, 00106 T38_DATA_V21 = 0, 00107 T38_DATA_V27TER_2400, 00108 T38_DATA_V27TER_4800, 00109 T38_DATA_V29_7200, 00110 T38_DATA_V29_9600, 00111 T38_DATA_V17_7200, 00112 T38_DATA_V17_9600, 00113 T38_DATA_V17_12000, 00114 T38_DATA_V17_14400, 00115 T38_DATA_V8, 00116 T38_DATA_V34_PRI_RATE, 00117 T38_DATA_V34_CC_1200, 00118 T38_DATA_V34_PRI_CH, 00119 T38_DATA_V33_12000, 00120 T38_DATA_V33_14400 00121 }; 00122 00123 /*! T.38 data field types */ 00124 enum t38_field_types_e 00125 { 00126 T38_FIELD_HDLC_DATA = 0, 00127 T38_FIELD_HDLC_SIG_END, 00128 T38_FIELD_HDLC_FCS_OK, 00129 T38_FIELD_HDLC_FCS_BAD, 00130 T38_FIELD_HDLC_FCS_OK_SIG_END, 00131 T38_FIELD_HDLC_FCS_BAD_SIG_END, 00132 T38_FIELD_T4_NON_ECM_DATA, 00133 T38_FIELD_T4_NON_ECM_SIG_END, 00134 T38_FIELD_CM_MESSAGE, 00135 T38_FIELD_JM_MESSAGE, 00136 T38_FIELD_CI_MESSAGE, 00137 T38_FIELD_V34RATE 00138 }; 00139 00140 /*! T.38 field classes */ 00141 enum t38_field_classes_e 00142 { 00143 T38_FIELD_CLASS_NONE = 0, 00144 T38_FIELD_CLASS_HDLC, 00145 T38_FIELD_CLASS_NON_ECM 00146 }; 00147 00148 /*! T.38 message types */ 00149 enum t38_message_types_e 00150 { 00151 T38_TYPE_OF_MSG_T30_INDICATOR = 0, 00152 T38_TYPE_OF_MSG_T30_DATA 00153 }; 00154 00155 /*! T.38 transport types */ 00156 enum t38_transport_types_e 00157 { 00158 T38_TRANSPORT_UDPTL = 0, 00159 T38_TRANSPORT_RTP, 00160 T38_TRANSPORT_TCP 00161 }; 00162 00163 /*! T.38 TCF management types */ 00164 enum t38_data_rate_management_types_e 00165 { 00166 T38_DATA_RATE_MANAGEMENT_LOCAL_TCF = 1, 00167 T38_DATA_RATE_MANAGEMENT_TRANSFERRED_TCF = 2 00168 }; 00169 00170 #define T38_RX_BUF_LEN 2048 00171 #define T38_TX_BUF_LEN 16384 00172 00173 /*! T.38 data field */ 00174 typedef struct 00175 { 00176 /*! Field type */ 00177 int field_type; 00178 /*! Field contents */ 00179 const uint8_t *field; 00180 /*! Field length */ 00181 int field_len; 00182 } t38_data_field_t; 00183 00184 /*! 00185 Core T.38 state, common to all modes of T.38. 00186 */ 00187 typedef struct t38_core_state_s t38_core_state_t; 00188 00189 typedef int (t38_tx_packet_handler_t)(t38_core_state_t *s, void *user_data, const uint8_t *buf, int len, int count); 00190 00191 typedef int (t38_rx_indicator_handler_t)(t38_core_state_t *s, void *user_data, int indicator); 00192 typedef int (t38_rx_data_handler_t)(t38_core_state_t *s, void *user_data, int data_type, int field_type, const uint8_t *buf, int len); 00193 typedef int (t38_rx_missing_handler_t)(t38_core_state_t *s, void *user_data, int rx_seq_no, int expected_seq_no); 00194 00195 #if defined(__cplusplus) 00196 extern "C" 00197 { 00198 #endif 00199 00200 /*! \brief Convert the code for an indicator to a short text name. 00201 \param indicator The type of indicator. 00202 \return A pointer to a short text name for the indicator. */ 00203 SPAN_DECLARE(const char *) t38_indicator_to_str(int indicator); 00204 00205 /*! \brief Convert the code for a type of data to a short text name. 00206 \param data_type The data type. 00207 \return A pointer to a short text name for the data type. */ 00208 SPAN_DECLARE(const char *) t38_data_type_to_str(int data_type); 00209 00210 /*! \brief Convert the code for a type of data field to a short text name. 00211 \param field_type The field type. 00212 \return A pointer to a short text name for the field type. */ 00213 SPAN_DECLARE(const char *) t38_field_type_to_str(int field_type); 00214 00215 /*! \brief Convert the code for a CM profile code to text description. 00216 \param profile The profile code from a CM message. 00217 \return A pointer to a short text description of the profile. */ 00218 SPAN_DECLARE(const char *) t38_cm_profile_to_str(int profile); 00219 00220 /*! \brief Convert a JM message code to text description. 00221 \param data The data field of the message. 00222 \param len The length of the data field. 00223 \return A pointer to a short text description of the profile. */ 00224 SPAN_DECLARE(const char *) t38_jm_to_str(const uint8_t *data, int len); 00225 00226 /*! \brief Convert a V34rate message to an actual bit rate. 00227 \param data The data field of the message. 00228 \param len The length of the data field. 00229 \return The bit rate, or -1 for a bad message. */ 00230 SPAN_DECLARE(int) t38_v34rate_to_bps(const uint8_t *data, int len); 00231 00232 /*! \brief Send an indicator packet 00233 \param s The T.38 context. 00234 \param indicator The indicator to send. 00235 \param count The number of copies of the packet to send. 00236 \return The delay to allow after this indicator is sent. */ 00237 SPAN_DECLARE(int) t38_core_send_indicator(t38_core_state_t *s, int indicator, int count); 00238 00239 /*! \brief Find the delay to allow for HDLC flags after sending an indicator 00240 \param s The T.38 context. 00241 \param indicator The indicator to send. 00242 \return The delay to allow for initial HDLC flags after this indicator is sent. */ 00243 SPAN_DECLARE(int) t38_core_send_flags_delay(t38_core_state_t *s, int indicator); 00244 00245 /*! \brief Send a data packet 00246 \param s The T.38 context. 00247 \param data_type The packet's data type. 00248 \param field_type The packet's field type. 00249 \param field The message data content for the packet. 00250 \param field_len The length of the message data, in bytes. 00251 \param count The number of copies of the packet to send. 00252 \return ??? */ 00253 SPAN_DECLARE(int) t38_core_send_data(t38_core_state_t *s, int data_type, int field_type, const uint8_t field[], int field_len, int count); 00254 00255 /*! \brief Send a data packet 00256 \param s The T.38 context. 00257 \param data_type The packet's data type. 00258 \param field The list of fields. 00259 \param fields The number of fields in the list. 00260 \param count The number of copies of the packet to send. 00261 \return ??? */ 00262 SPAN_DECLARE(int) t38_core_send_data_multi_field(t38_core_state_t *s, int data_type, const t38_data_field_t field[], int fields, int count); 00263 00264 /*! \brief Process a received T.38 IFP packet. 00265 \param s The T.38 context. 00266 \param buf The packet contents. 00267 \param len The length of the packet contents. 00268 \param seq_no The packet sequence number. 00269 \return 0 for OK, else -1. */ 00270 SPAN_DECLARE(int) t38_core_rx_ifp_packet(t38_core_state_t *s, const uint8_t *buf, int len, uint16_t seq_no); 00271 00272 /*! Set the method to be used for data rate management, as per the T.38 spec. 00273 \param s The T.38 context. 00274 \param method 1 for pass TCF across the T.38 link, 2 for handle TCF locally. 00275 */ 00276 SPAN_DECLARE(void) t38_set_data_rate_management_method(t38_core_state_t *s, int method); 00277 00278 /*! Set the data transport protocol. 00279 \param s The T.38 context. 00280 \param data_transport_protocol UDPTL, RTP or TPKT. 00281 */ 00282 SPAN_DECLARE(void) t38_set_data_transport_protocol(t38_core_state_t *s, int data_transport_protocol); 00283 00284 /*! Set the non-ECM fill bit removal mode. 00285 \param s The T.38 context. 00286 \param fill_bit_removal TRUE to remove fill bits across the T.38 link, else FALSE. 00287 */ 00288 SPAN_DECLARE(void) t38_set_fill_bit_removal(t38_core_state_t *s, int fill_bit_removal); 00289 00290 /*! Set the MMR transcoding mode. 00291 \param s The T.38 context. 00292 \param mmr_transcoding TRUE to transcode to MMR across the T.38 link, else FALSE. 00293 */ 00294 SPAN_DECLARE(void) t38_set_mmr_transcoding(t38_core_state_t *s, int mmr_transcoding); 00295 00296 /*! Set the JBIG transcoding mode. 00297 \param s The T.38 context. 00298 \param jbig_transcoding TRUE to transcode to JBIG across the T.38 link, else FALSE. 00299 */ 00300 SPAN_DECLARE(void) t38_set_jbig_transcoding(t38_core_state_t *s, int jbig_transcoding); 00301 00302 SPAN_DECLARE(void) t38_set_max_buffer_size(t38_core_state_t *s, int max_buffer_size); 00303 00304 SPAN_DECLARE(void) t38_set_max_datagram_size(t38_core_state_t *s, int max_datagram_size); 00305 00306 SPAN_DECLARE(int) t38_get_fastest_image_data_rate(t38_core_state_t *s); 00307 00308 /*! Set the T.38 version to be emulated. 00309 \param s The T.38 context. 00310 \param t38_version Version number, as in the T.38 spec. 00311 */ 00312 SPAN_DECLARE(void) t38_set_t38_version(t38_core_state_t *s, int t38_version); 00313 00314 /*! Set the sequence number handling option. 00315 \param s The T.38 context. 00316 \param check TRUE to check sequence numbers, and handle gaps reasonably. FALSE 00317 for no sequence number processing (e.g. for TPKT over TCP transport). 00318 */ 00319 SPAN_DECLARE(void) t38_set_sequence_number_handling(t38_core_state_t *s, int check); 00320 00321 /*! Set the TEP handling option. 00322 \param s The T.38 context. 00323 \param allow_for_tep TRUE to allow for TEP playout, else FALSE. 00324 */ 00325 SPAN_DECLARE(void) t38_set_tep_handling(t38_core_state_t *s, int allow_for_tep); 00326 00327 /*! Get a pointer to the logging context associated with a T.38 context. 00328 \brief Get a pointer to the logging context associated with a T.38 context. 00329 \param s The T.38 context. 00330 \return A pointer to the logging context, or NULL. 00331 */ 00332 SPAN_DECLARE(logging_state_t *) t38_core_get_logging_state(t38_core_state_t *s); 00333 00334 /*! Initialise a T.38 core context. 00335 \brief Initialise a T.38 core context. 00336 \param s The T.38 context. 00337 \param rx_indicator_handler Receive indicator handling routine. 00338 \param rx_data_handler Receive data packet handling routine. 00339 \param rx_rx_missing_handler Missing receive packet handling routine. 00340 \param rx_packet_user_data An opaque pointer passed to the rx packet handling routines. 00341 \param tx_packet_handler Packet transmit handling routine. 00342 \param tx_packet_user_data An opaque pointer passed to the tx_packet_handler. 00343 \return A pointer to the T.38 context, or NULL if there was a problem. */ 00344 SPAN_DECLARE(t38_core_state_t *) t38_core_init(t38_core_state_t *s, 00345 t38_rx_indicator_handler_t *rx_indicator_handler, 00346 t38_rx_data_handler_t *rx_data_handler, 00347 t38_rx_missing_handler_t *rx_missing_handler, 00348 void *rx_user_data, 00349 t38_tx_packet_handler_t *tx_packet_handler, 00350 void *tx_packet_user_data); 00351 00352 /*! Release a signaling tone transmitter context. 00353 \brief Release a signaling tone transmitter context. 00354 \param s The T.38 context. 00355 \return 0 for OK */ 00356 SPAN_DECLARE(int) t38_core_release(t38_core_state_t *s); 00357 00358 /*! Free a signaling tone transmitter context. 00359 \brief Free a signaling tone transmitter context. 00360 \param s The T.38 context. 00361 \return 0 for OK */ 00362 SPAN_DECLARE(int) t38_core_free(t38_core_state_t *s); 00363 00364 #if defined(__cplusplus) 00365 } 00366 #endif 00367 00368 #endif 00369 /*- End of file ------------------------------------------------------------*/