t38_core.h

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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 1.39 2009/07/14 13:54:22 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 /*! T.38 Packet categories used for setting the redundancy level and packet repeat
00171     counts on a packet by packet basis. */
00172 enum t38_packet_categories_e
00173 {
00174     /*! \brief Indicator packet */
00175     T38_PACKET_CATEGORY_INDICATOR = 0,
00176     /*! \brief Control data packet */
00177     T38_PACKET_CATEGORY_CONTROL_DATA = 1,
00178     /*! \brief Terminating control data packet */
00179     T38_PACKET_CATEGORY_CONTROL_DATA_END = 2,
00180     /*! \brief Image data packet */
00181     T38_PACKET_CATEGORY_IMAGE_DATA = 3,
00182     /*! \brief Terminating image data packet */
00183     T38_PACKET_CATEGORY_IMAGE_DATA_END = 4
00184 };
00185 
00186 #define T38_RX_BUF_LEN  2048
00187 #define T38_TX_BUF_LEN  16384
00188 
00189 /*! T.38 data field */
00190 typedef struct
00191 {
00192     /*! Field type */
00193     int field_type;
00194     /*! Field contents */
00195     const uint8_t *field;
00196     /*! Field length */
00197     int field_len;
00198 } t38_data_field_t;
00199 
00200 /*!
00201     Core T.38 state, common to all modes of T.38.
00202 */
00203 typedef struct t38_core_state_s t38_core_state_t;
00204 
00205 typedef int (t38_tx_packet_handler_t)(t38_core_state_t *s, void *user_data, const uint8_t *buf, int len, int count);
00206 
00207 typedef int (t38_rx_indicator_handler_t)(t38_core_state_t *s, void *user_data, int indicator);
00208 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);
00209 typedef int (t38_rx_missing_handler_t)(t38_core_state_t *s, void *user_data, int rx_seq_no, int expected_seq_no);
00210 
00211 #if defined(__cplusplus)
00212 extern "C"
00213 {
00214 #endif
00215 
00216 /*! \brief Convert the code for an indicator to a short text name.
00217     \param indicator The type of indicator.
00218     \return A pointer to a short text name for the indicator. */
00219 SPAN_DECLARE(const char *) t38_indicator_to_str(int indicator);
00220 
00221 /*! \brief Convert the code for a type of data to a short text name.
00222     \param data_type The data type.
00223     \return A pointer to a short text name for the data type. */
00224 SPAN_DECLARE(const char *) t38_data_type_to_str(int data_type);
00225 
00226 /*! \brief Convert the code for a type of data field to a short text name.
00227     \param field_type The field type.
00228     \return A pointer to a short text name for the field type. */
00229 SPAN_DECLARE(const char *) t38_field_type_to_str(int field_type);
00230 
00231 /*! \brief Convert the code for a CM profile code to text description.
00232     \param profile The profile code from a CM message.
00233     \return A pointer to a short text description of the profile. */
00234 SPAN_DECLARE(const char *) t38_cm_profile_to_str(int profile);
00235 
00236 /*! \brief Convert a JM message code to text description.
00237     \param data The data field of the message.
00238     \param len The length of the data field.
00239     \return A pointer to a short text description of the profile. */
00240 SPAN_DECLARE(const char *) t38_jm_to_str(const uint8_t *data, int len);
00241 
00242 /*! \brief Convert a V34rate message to an actual bit rate.
00243     \param data The data field of the message.
00244     \param len The length of the data field.
00245     \return The bit rate, or -1 for a bad message. */
00246 SPAN_DECLARE(int) t38_v34rate_to_bps(const uint8_t *data, int len);
00247 
00248 /*! \brief Send an indicator packet
00249     \param s The T.38 context.
00250     \param indicator The indicator to send.
00251     \return The delay to allow after this indicator is sent. */
00252 SPAN_DECLARE(int) t38_core_send_indicator(t38_core_state_t *s, int indicator);
00253 
00254 /*! \brief Find the delay to allow for HDLC flags after sending an indicator
00255     \param s The T.38 context.
00256     \param indicator The indicator to send.
00257     \return The delay to allow for initial HDLC flags after this indicator is sent. */
00258 SPAN_DECLARE(int) t38_core_send_flags_delay(t38_core_state_t *s, int indicator);
00259 
00260 /*! \brief Send a data packet
00261     \param s The T.38 context.
00262     \param data_type The packet's data type.
00263     \param field_type The packet's field type.
00264     \param field The message data content for the packet.
00265     \param field_len The length of the message data, in bytes.
00266     \param category The category of the packet being sent. This should be one of the values defined for t38_packet_categories_e.
00267     \return ??? */
00268 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 category);
00269 
00270 /*! \brief Send a data packet
00271     \param s The T.38 context.
00272     \param data_type The packet's data type.
00273     \param field The list of fields.
00274     \param fields The number of fields in the list.
00275     \param category The category of the packet being sent. This should be one of the values defined for t38_packet_categories_e.
00276     \return ??? */
00277 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 category);
00278 
00279 /*! \brief Process a received T.38 IFP packet.
00280     \param s The T.38 context.
00281     \param buf The packet contents.
00282     \param len The length of the packet contents.
00283     \param seq_no The packet sequence number.
00284     \return 0 for OK, else -1. */
00285 SPAN_DECLARE(int) t38_core_rx_ifp_packet(t38_core_state_t *s, const uint8_t *buf, int len, uint16_t seq_no);
00286 
00287 /*! Set the method to be used for data rate management, as per the T.38 spec.
00288     \param s The T.38 context.
00289     \param method 1 for pass TCF across the T.38 link, 2 for handle TCF locally.
00290 */
00291 SPAN_DECLARE(void) t38_set_data_rate_management_method(t38_core_state_t *s, int method);
00292 
00293 /*! Set the data transport protocol.
00294     \param s The T.38 context.
00295     \param data_transport_protocol UDPTL, RTP or TPKT.
00296 */
00297 SPAN_DECLARE(void) t38_set_data_transport_protocol(t38_core_state_t *s, int data_transport_protocol);
00298 
00299 /*! Set the non-ECM fill bit removal mode.
00300     \param s The T.38 context.
00301     \param fill_bit_removal TRUE to remove fill bits across the T.38 link, else FALSE.
00302 */
00303 SPAN_DECLARE(void) t38_set_fill_bit_removal(t38_core_state_t *s, int fill_bit_removal);
00304 
00305 /*! Set the MMR transcoding mode.
00306     \param s The T.38 context.
00307     \param mmr_transcoding TRUE to transcode to MMR across the T.38 link, else FALSE.
00308 */
00309 SPAN_DECLARE(void) t38_set_mmr_transcoding(t38_core_state_t *s, int mmr_transcoding);
00310 
00311 /*! Set the JBIG transcoding mode.
00312     \param s The T.38 context.
00313     \param jbig_transcoding TRUE to transcode to JBIG across the T.38 link, else FALSE.
00314 */
00315 SPAN_DECLARE(void) t38_set_jbig_transcoding(t38_core_state_t *s, int jbig_transcoding);
00316 
00317 /*! Set the maximum buffer size for received data at the far end.
00318     \param s The T.38 context.
00319     \param max_buffer_size The maximum buffer size.
00320 */
00321 SPAN_DECLARE(void) t38_set_max_buffer_size(t38_core_state_t *s, int max_buffer_size);
00322 
00323 /*! Set the maximum size of an IFP packet that is acceptable by the far end.
00324     \param s The T.38 context.
00325     \param max_datagram_size The maximum IFP packet length, in bytes.
00326 */
00327 SPAN_DECLARE(void) t38_set_max_datagram_size(t38_core_state_t *s, int max_datagram_size);
00328 
00329 /*! \brief Send a data packet
00330     \param s The T.38 context.
00331     \param category The category of the packet being sent. This should be one of the values defined for t38_packet_categories_e.
00332     \param setting The repeat count for the category. This should be at least one for all categories other an indicator packets.
00333                    Zero is valid for indicator packets, as it suppresses the sending of indicator packets, as an application using
00334                    TCP for the transport would require. As the setting is passed through to the transmission channel, additional
00335                    information may be encoded in it, such as the redundancy depth for the particular packet category. */
00336 SPAN_DECLARE(void) t38_set_redundancy_control(t38_core_state_t *s, int category, int setting);
00337 
00338 SPAN_DECLARE(void) t38_set_fastest_image_data_rate(t38_core_state_t *s, int max_rate);
00339 
00340 SPAN_DECLARE(int) t38_get_fastest_image_data_rate(t38_core_state_t *s);
00341 
00342 /*! Set the T.38 version to be emulated.
00343     \param s The T.38 context.
00344     \param t38_version Version number, as in the T.38 spec.
00345 */
00346 SPAN_DECLARE(void) t38_set_t38_version(t38_core_state_t *s, int t38_version);
00347 
00348 /*! Set the sequence number handling option.
00349     \param s The T.38 context.
00350     \param check TRUE to check sequence numbers, and handle gaps reasonably. FALSE
00351            for no sequence number processing (e.g. for TPKT over TCP transport).
00352 */
00353 SPAN_DECLARE(void) t38_set_sequence_number_handling(t38_core_state_t *s, int check);
00354 
00355 /*! Set the TEP handling option.
00356     \param s The T.38 context.
00357     \param allow_for_tep TRUE to allow for TEP playout, else FALSE.
00358 */
00359 SPAN_DECLARE(void) t38_set_tep_handling(t38_core_state_t *s, int allow_for_tep);
00360 
00361 /*! Get a pointer to the logging context associated with a T.38 context.
00362     \brief Get a pointer to the logging context associated with a T.38 context.
00363     \param s The T.38 context.
00364     \return A pointer to the logging context, or NULL.
00365 */
00366 SPAN_DECLARE(logging_state_t *) t38_core_get_logging_state(t38_core_state_t *s);
00367 
00368 /*! Initialise a T.38 core context.
00369     \brief Initialise a T.38 core context.
00370     \param s The T.38 context.
00371     \param rx_indicator_handler Receive indicator handling routine.
00372     \param rx_data_handler Receive data packet handling routine.
00373     \param rx_rx_missing_handler Missing receive packet handling routine.
00374     \param rx_packet_user_data An opaque pointer passed to the rx packet handling routines.
00375     \param tx_packet_handler Packet transmit handling routine.
00376     \param tx_packet_user_data An opaque pointer passed to the tx_packet_handler.
00377     \return A pointer to the T.38 context, or NULL if there was a problem. */
00378 SPAN_DECLARE(t38_core_state_t *) t38_core_init(t38_core_state_t *s,
00379                                                t38_rx_indicator_handler_t *rx_indicator_handler,
00380                                                t38_rx_data_handler_t *rx_data_handler,
00381                                                t38_rx_missing_handler_t *rx_missing_handler,
00382                                                void *rx_user_data,
00383                                                t38_tx_packet_handler_t *tx_packet_handler,
00384                                                void *tx_packet_user_data);
00385 
00386 /*! Release a signaling tone transmitter context.
00387     \brief Release a signaling tone transmitter context.
00388     \param s The T.38 context.
00389     \return 0 for OK */
00390 SPAN_DECLARE(int) t38_core_release(t38_core_state_t *s);
00391 
00392 /*! Free a signaling tone transmitter context.
00393     \brief Free a signaling tone transmitter context.
00394     \param s The T.38 context.
00395     \return 0 for OK */
00396 SPAN_DECLARE(int) t38_core_free(t38_core_state_t *s);
00397 
00398 #if defined(__cplusplus)
00399 }
00400 #endif
00401 
00402 #endif
00403 /*- End of file ------------------------------------------------------------*/

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