t38_core.h

Go to the documentation of this file.
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 1.31 2008/11/30 13:44:35 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 #define T38_RX_BUF_LEN  2048
00164 #define T38_TX_BUF_LEN  16384
00165 
00166 /*! T.38 data field */
00167 typedef struct
00168 {
00169     int field_type;
00170     const uint8_t *field;
00171     int field_len;
00172 } t38_data_field_t;
00173 
00174 /*!
00175     Core T.38 state, common to all modes of T.38.
00176 */
00177 typedef struct t38_core_state_s t38_core_state_t;
00178 
00179 typedef int (t38_tx_packet_handler_t)(t38_core_state_t *s, void *user_data, const uint8_t *buf, int len, int count);
00180 
00181 typedef int (t38_rx_indicator_handler_t)(t38_core_state_t *s, void *user_data, int indicator);
00182 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);
00183 typedef int (t38_rx_missing_handler_t)(t38_core_state_t *s, void *user_data, int rx_seq_no, int expected_seq_no);
00184 
00185 #if defined(__cplusplus)
00186 extern "C"
00187 {
00188 #endif
00189 
00190 /*! \brief Convert the code for an indicator to a short text name.
00191     \param indicator The type of indicator.
00192     \return A pointer to a short text name for the indicator. */
00193 const char *t38_indicator_to_str(int indicator);
00194 
00195 /*! \brief Convert the code for a type of data to a short text name.
00196     \param data_type The data type.
00197     \return A pointer to a short text name for the data type. */
00198 const char *t38_data_type_to_str(int data_type);
00199 
00200 /*! \brief Convert the code for a type of data field to a short text name.
00201     \param field_type The field type.
00202     \return A pointer to a short text name for the field type. */
00203 const char *t38_field_type_to_str(int field_type);
00204 
00205 /*! \brief Convert the code for a CM profile code to text description.
00206     \param profile The profile code from a CM message.
00207     \return A pointer to a short text description of the profile. */
00208 const char *t38_cm_profile_to_str(int profile);
00209 
00210 /*! \brief Convert a JM message code to text description.
00211     \param data The data field of the message.
00212     \param len The length of the data field.
00213     \return A pointer to a short text description of the profile. */
00214 const char *t38_jm_to_str(const uint8_t *data, int len);
00215 
00216 /*! \brief Convert a V34rate message to an actual bit rate.
00217     \param data The data field of the message.
00218     \param len The length of the data field.
00219     \return The bit rate, or -1 for a bad message. */
00220 int t38_v34rate_to_bps(const uint8_t *data, int len);
00221 
00222 /*! \brief Send an indicator packet
00223     \param s The T.38 context.
00224     \param indicator The indicator to send.
00225     \param count The number of copies of the packet to send.
00226     \return ??? */
00227 int t38_core_send_indicator(t38_core_state_t *s, int indicator, int count);
00228 
00229 /*! \brief Send a data packet
00230     \param s The T.38 context.
00231     \param data_type The packet's data type.
00232     \param field_type The packet's field type.
00233     \param field The message data content for the packet.
00234     \param field_len The length of the message data, in bytes.
00235     \param count The number of copies of the packet to send.
00236     \return ??? */
00237 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);
00238 
00239 /*! \brief Send a data packet
00240     \param s The T.38 context.
00241     \param data_type The packet's data type.
00242     \param field The list of fields.
00243     \param fields The number of fields in the list.
00244     \param count The number of copies of the packet to send.
00245     \return ??? */
00246 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);
00247 
00248 /*! \brief Process a received T.38 IFP packet.
00249     \param s The T.38 context.
00250     \param buf The packet contents.
00251     \param len The length of the packet contents.
00252     \param seq_no The packet sequence number.
00253     \return 0 for OK, else -1. */
00254 int t38_core_rx_ifp_packet(t38_core_state_t *s, const uint8_t *buf, int len, uint16_t seq_no);
00255 
00256 /*! Set the method to be used for data rate management, as per the T.38 spec.
00257     \param s The T.38 context.
00258     \param method 1 for pass TCF across the T.38 link, 2 for handle TCF locally.
00259 */
00260 void t38_set_data_rate_management_method(t38_core_state_t *s, int method);
00261 
00262 /*! Set the data transport protocol.
00263     \param s The T.38 context.
00264     \param data_transport_protocol UDPTL, RTP or TPKT.
00265 */
00266 void t38_set_data_transport_protocol(t38_core_state_t *s, int data_transport_protocol);
00267 
00268 /*! Set the non-ECM fill bit removal mode.
00269     \param s The T.38 context.
00270     \param fill_bit_removal TRUE to remove fill bits across the T.38 link, else FALSE.
00271 */
00272 void t38_set_fill_bit_removal(t38_core_state_t *s, int fill_bit_removal);
00273 
00274 /*! Set the MMR transcoding mode.
00275     \param s The T.38 context.
00276     \param mmr_transcoding TRUE to transcode to MMR across the T.38 link, else FALSE.
00277 */
00278 void t38_set_mmr_transcoding(t38_core_state_t *s, int mmr_transcoding);
00279 
00280 /*! Set the JBIG transcoding mode.
00281     \param s The T.38 context.
00282     \param jbig_transcoding TRUE to transcode to JBIG across the T.38 link, else FALSE.
00283 */
00284 void t38_set_jbig_transcoding(t38_core_state_t *s, int jbig_transcoding);
00285 
00286 void t38_set_max_buffer_size(t38_core_state_t *s, int max_buffer_size);
00287 
00288 void t38_set_max_datagram_size(t38_core_state_t *s, int max_datagram_size);
00289 
00290 int t38_get_fastest_image_data_rate(t38_core_state_t *s);
00291 
00292 /*! Set the T.38 version to be emulated.
00293     \param s The T.38 context.
00294     \param t38_version Version number, as in the T.38 spec.
00295 */
00296 void t38_set_t38_version(t38_core_state_t *s, int t38_version);
00297 
00298 /*! Set the sequence number handling option.
00299     \param s The T.38 context.
00300     \param check TRUE to check sequence numbers, and handle gaps reasonably. FALSE
00301            for no sequence number processing (e.g. for TPKT over TCP transport).
00302 */
00303 void t38_set_sequence_number_handling(t38_core_state_t *s, int check);
00304 
00305 /*! Get a pointer to the logging context associated with a T.38 context.
00306     \brief Get a pointer to the logging context associated with a T.38 context.
00307     \param s The T.38 context.
00308     \return A pointer to the logging context, or NULL.
00309 */
00310 logging_state_t *t38_core_get_logging_state(t38_core_state_t *s);
00311 
00312 t38_core_state_t *t38_core_init(t38_core_state_t *s,
00313                                 t38_rx_indicator_handler_t *rx_indicator_handler,
00314                                 t38_rx_data_handler_t *rx_data_handler,
00315                                 t38_rx_missing_handler_t *rx_missing_handler,
00316                                 void *rx_user_data,
00317                                 t38_tx_packet_handler_t tx_packet_handler,
00318                                 void *tx_packet_user_data);
00319 
00320 #if defined(__cplusplus)
00321 }
00322 #endif
00323 
00324 #endif
00325 /*- End of file ------------------------------------------------------------*/

Generated on Thu Feb 12 14:16:07 2009 for spandsp by  doxygen 1.5.5