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 General Public License version 2, as
00014  * 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 General Public License for more details.
00020  *
00021  * You should have received a copy of the GNU General Public License
00022  * 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 1.20 2007/06/08 13:49:38 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 enum t30_indicator_types_e
00075 {
00076     T38_IND_NO_SIGNAL = 0,
00077     T38_IND_CNG,
00078     T38_IND_CED,
00079     T38_IND_V21_PREAMBLE,
00080     T38_IND_V27TER_2400_TRAINING,
00081     T38_IND_V27TER_4800_TRAINING,
00082     T38_IND_V29_7200_TRAINING,
00083     T38_IND_V29_9600_TRAINING,
00084     T38_IND_V17_7200_SHORT_TRAINING,
00085     T38_IND_V17_7200_LONG_TRAINING,
00086     T38_IND_V17_9600_SHORT_TRAINING,
00087     T38_IND_V17_9600_LONG_TRAINING,
00088     T38_IND_V17_12000_SHORT_TRAINING,
00089     T38_IND_V17_12000_LONG_TRAINING,
00090     T38_IND_V17_14400_SHORT_TRAINING,
00091     T38_IND_V17_14400_LONG_TRAINING,
00092     T38_IND_V8_ANSAM,
00093     T38_IND_V8_SIGNAL,
00094     T38_IND_V34_CNTL_CHANNEL_1200,
00095     T38_IND_V34_PRI_CHANNEL,
00096     T38_IND_V34_CC_RETRAIN,
00097     T38_IND_V33_12000_TRAINING,
00098     T38_IND_V33_14400_TRAINING
00099 };
00100 
00101 enum t38_data_types_e
00102 {
00103     T38_DATA_NONE = -1,
00104     T38_DATA_V21 = 0,
00105     T38_DATA_V27TER_2400,
00106     T38_DATA_V27TER_4800,
00107     T38_DATA_V29_7200,
00108     T38_DATA_V29_9600,
00109     T38_DATA_V17_7200,
00110     T38_DATA_V17_9600,
00111     T38_DATA_V17_12000,
00112     T38_DATA_V17_14400,
00113     T38_DATA_V8,
00114     T38_DATA_V34_PRI_RATE,
00115     T38_DATA_V34_CC_1200,
00116     T38_DATA_V34_PRI_CH,
00117     T38_DATA_V33_12000,
00118     T38_DATA_V33_14400
00119 };
00120 
00121 enum t38_field_types_e
00122 {
00123     T38_FIELD_HDLC_DATA = 0,
00124     T38_FIELD_HDLC_SIG_END,
00125     T38_FIELD_HDLC_FCS_OK,
00126     T38_FIELD_HDLC_FCS_BAD,
00127     T38_FIELD_HDLC_FCS_OK_SIG_END,
00128     T38_FIELD_HDLC_FCS_BAD_SIG_END,
00129     T38_FIELD_T4_NON_ECM_DATA,
00130     T38_FIELD_T4_NON_ECM_SIG_END,
00131     T38_FIELD_CM_MESSAGE,
00132     T38_FIELD_JM_MESSAGE,
00133     T38_FIELD_CI_MESSAGE,
00134     T38_FIELD_V34RATE
00135 };
00136 
00137 enum t38_field_classes_e
00138 {
00139     T38_FIELD_CLASS_NONE = 0,
00140     T38_FIELD_CLASS_HDLC,
00141     T38_FIELD_CLASS_NON_ECM,
00142 };
00143 
00144 enum t38_message_types_e
00145 {
00146     T38_TYPE_OF_MSG_T30_INDICATOR = 0,
00147     T38_TYPE_OF_MSG_T30_DATA
00148 };
00149 
00150 enum t38_transport_types_e
00151 {
00152     T38_TRANSPORT_UDPTL = 0,
00153     T38_TRANSPORT_RTP,
00154     T38_TRANSPORT_TCP
00155 };
00156 
00157 #define T38_RX_BUF_LEN  2048
00158 #define T38_TX_BUF_LEN  16384
00159 
00160 typedef struct
00161 {
00162     int field_type;
00163     const uint8_t *field;
00164     int field_len;
00165 } t38_data_field_t;
00166 
00167 typedef struct t38_core_state_s t38_core_state_t;
00168 
00169 typedef int (t38_tx_packet_handler_t)(t38_core_state_t *s, void *user_data, const uint8_t *buf, int len, int count);
00170 
00171 typedef int (t38_rx_indicator_handler_t)(t38_core_state_t *s, void *user_data, int indicator);
00172 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);
00173 typedef int (t38_rx_missing_handler_t)(t38_core_state_t *s, void *user_data, int rx_seq_no, int expected_seq_no);
00174 
00175 #include <sys/time.h>
00176 
00177 /*
00178     Core T.38 state, common to all modes of T.38.
00179 */
00180 struct t38_core_state_s
00181 {
00182     /*! Handler routine to transmit IFP packets generated by the T.38 protocol engine */
00183     t38_tx_packet_handler_t *tx_packet_handler;
00184     /*! An opaque pointer passed to tx_packet_handler */
00185     void *tx_packet_user_data;
00186 
00187     /*! Handler routine to process received indicator packets */
00188     t38_rx_indicator_handler_t *rx_indicator_handler;
00189     /*! Handler routine to process received data packets */
00190     t38_rx_data_handler_t *rx_data_handler;
00191     /*! Handler routine to process the missing packet condition */
00192     t38_rx_missing_handler_t *rx_missing_handler;
00193     /*! An opaque pointer passed to any of the above receive handling routines */
00194     void *rx_user_data;
00195 
00196     /*! NOTE - Bandwidth reduction shall only be done on suitable Phase C data, i.e., MH, MR
00197         and - in the case of transcoding to JBIG - MMR. MMR and JBIG require reliable data
00198         transport such as that provided by TCP. When transcoding is selected, it shall be
00199         applied to every suitable page in a call. */
00200 
00201     /*! Method 1: Local generation of TCF (required for use with TCP).
00202         Method 2: Transfer of TCF is required for use with UDP (UDPTL or RTP).
00203         Method 2 is not recommended for use with TCP. */
00204     int data_rate_management_method;
00205     
00206     /*! The emitting gateway may indicate a preference for either UDP/UDPTL, or
00207         UDP/RTP, or TCP for transport of T.38 IFP Packets. The receiving device
00208         selects the transport protocol. */
00209     int data_transport_protocol;
00210 
00211     /*! Indicates the capability to remove and insert fill bits in Phase C, non-ECM
00212         data to reduce bandwidth in the packet network. Optional. See Note. */
00213     int fill_bit_removal;
00214 
00215     /*! Indicates the ability to convert to/from MMR from/to the line format to
00216         improve the compression of the data, and reduce the bandwidth, in the
00217         packet network. Optional. See Note. */
00218     int mmr_transcoding;
00219 
00220     /*! Indicates the ability to convert to/from JBIG to reduce bandwidth. Optional.
00221         See Note. */
00222     int jbig_transcoding;
00223 
00224     /*! For UDP (UDPTL or RTP) modes, this option indicates the maximum
00225         number of octets that can be stored on the remote device before an overflow
00226         condition occurs. It is the responsibility of the transmitting application to
00227         limit the transfer rate to prevent an overflow. The negotiated data rate
00228         should be used to determine the rate at which data is being removed from
00229         the buffer. */
00230     int max_buffer_size;
00231 
00232     /*! This option indicates the maximum size of a UDPTL packet or the
00233         maximum size of the payload within an RTP packet that can be accepted by
00234         the remote device. */
00235     int max_datagram_size;
00236 
00237     /*! This is the version number of ITU-T Rec. T.38. New versions shall be
00238         compatible with previous versions. */
00239     int t38_version;
00240     
00241     /*! The fastest data rate supported by the T.38 channel. */
00242     int fastest_image_data_rate;
00243     
00244     /*! TRUE if IFP packet sequence numbers are relevant. For some transports, like TPKT
00245         over TCP they are not relevent. */
00246     int check_sequence_numbers;
00247 
00248     /*! The sequence number for the next packet to be transmitted */
00249     int tx_seq_no;
00250     /*! The sequence number expected in the next received packet */
00251     int rx_expected_seq_no;
00252 
00253     /*! The current receive indicator - i.e. the last indicator received */
00254     int current_rx_indicator;
00255     /*! The current receive data type - i.e. the last data type received */
00256     int current_rx_data_type;
00257     /*! The current receive field type - i.e. the last field_type received */
00258     int current_rx_field_type;
00259     /*! The current transmit indicator - i.e. the last indicator transmitted */
00260     int current_tx_indicator;
00261 
00262     /*! A count of missing receive packets. This count might not be accurate if the
00263         received packet numbers jump wildly. */
00264     int missing_packets;
00265 
00266     logging_state_t logging;
00267 };
00268 
00269 #if defined(__cplusplus)
00270 extern "C"
00271 {
00272 #endif
00273 
00274 /*! \brief Convert the code for an indicator to a short text name.
00275     \param indicator The type of indicator.
00276     \return A pointer to a short text name for the indicator. */
00277 const char *t38_indicator(int indicator);
00278 
00279 /*! \brief Convert the code for a type of data to a short text name.
00280     \param data_type The data type.
00281     \return A pointer to a short text name for the data type. */
00282 const char *t38_data_type(int data_type);
00283 
00284 /*! \brief Convert the code for a type of data field to a short text name.
00285     \param field_type The field type.
00286     \return A pointer to a short text name for the field type. */
00287 const char *t38_field_type(int field_type);
00288 
00289 /*! \brief Send an indicator packet
00290     \param s The T.38 context.
00291     \param indicator The indicator to send.
00292     \param count The number of copies of the packet to send.
00293     \return ??? */
00294 int t38_core_send_indicator(t38_core_state_t *s, int indicator, int count);
00295 
00296 /*! \brief Send a data packet
00297     \param s The T.38 context.
00298     \param data_type The packet's data type.
00299     \param field_type The packet's field type.
00300     \param field The message data content for the packet.
00301     \param field_len The length of the message data, in bytes.
00302     \param count The number of copies of the packet to send.
00303     \return ??? */
00304 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);
00305 
00306 /*! \brief Send a data packet
00307     \param s The T.38 context.
00308     \param data_type The packet's data type.
00309     \param field The list of fields.
00310     \param fields The number of fields in the list.
00311     \param count The number of copies of the packet to send.
00312     \return ??? */
00313 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);
00314 
00315 /*! \brief Process a received T.38 IFP packet.
00316     \param s The T.38 context.
00317     \param buf The packet contents.
00318     \param len The length of the packet contents.
00319     \param seq_no The packet sequence number.
00320     \return 0 for OK, else -1. */
00321 int t38_core_rx_ifp_packet(t38_core_state_t *s, const uint8_t *buf, int len, uint16_t seq_no);
00322 
00323 /*! Set the method to be used for data rate management, as per the T.38 spec.
00324     \param s The T.38 context.
00325     \param method 1 for pass TCF across the T.38 link, 2 for handle TCF locally.
00326 */
00327 void t38_set_data_rate_management_method(t38_core_state_t *s, int method);
00328 
00329 /*! Set the data transport protocol.
00330     \param s The T.38 context.
00331     \param data_transport_protocol UDPTL, RTP or TPKT.
00332 */
00333 void t38_set_data_transport_protocol(t38_core_state_t *s, int data_transport_protocol);
00334 
00335 /*! Set the non-ECM fill bit removal mode.
00336     \param s The T.38 context.
00337     \param fill_bit_removal TRUE to remove fill bits across the T.38 link, else FALSE.
00338 */
00339 void t38_set_fill_bit_removal(t38_core_state_t *s, int fill_bit_removal);
00340 
00341 /*! Set the MMR transcoding mode.
00342     \param s The T.38 context.
00343     \param mmr_transcoding TRUE to transcode to MMR across the T.38 link, else FALSE.
00344 */
00345 void t38_set_mmr_transcoding(t38_core_state_t *s, int mmr_transcoding);
00346 
00347 /*! Set the JBIG transcoding mode.
00348     \param s The T.38 context.
00349     \param jbig_transcoding TRUE to transcode to JBIG across the T.38 link, else FALSE.
00350 */
00351 void t38_set_jbig_transcoding(t38_core_state_t *s, int jbig_transcoding);
00352 
00353 void t38_set_max_buffer_size(t38_core_state_t *s, int max_buffer_size);
00354 
00355 void t38_set_max_datagram_size(t38_core_state_t *s, int max_datagram_size);
00356 
00357 int t38_get_fastest_image_data_rate(t38_core_state_t *s);
00358 
00359 /*! Set the T.38 version to be emulated.
00360     \param s The T.38 context.
00361     \param t38_version Version number, as in the T.38 spec.
00362 */
00363 void t38_set_t38_version(t38_core_state_t *s, int t38_version);
00364 
00365 /* Set the sequence number handling option.
00366     \param s The T.38 context.
00367     \param check TRUE to check sequence numbers, and handle gaps reasonably. FALSE
00368            for no sequence number processing (e.g. for TPKT over TCP transport).
00369 */
00370 void t38_set_sequence_number_handling(t38_core_state_t *s, int check);
00371 
00372 t38_core_state_t *t38_core_init(t38_core_state_t *s,
00373                                 t38_rx_indicator_handler_t *rx_indicator_handler,
00374                                 t38_rx_data_handler_t *rx_data_handler,
00375                                 t38_rx_missing_handler_t *rx_missing_handler,
00376                                 void *rx_user_data,
00377                                 t38_tx_packet_handler_t tx_packet_handler,
00378                                 void *tx_packet_user_data);
00379 
00380 #if defined(__cplusplus)
00381 }
00382 #endif
00383 
00384 #endif
00385 /*- End of file ------------------------------------------------------------*/

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