spandsp  0.0.6
t38_core.h
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1 /*
2  * SpanDSP - a series of DSP components for telephony
3  *
4  * t38_core.h - An implementation of T.38, less the packet exchange part
5  *
6  * Written by Steve Underwood <steveu@coppice.org>
7  *
8  * Copyright (C) 2005 Steve Underwood
9  *
10  * All rights reserved.
11  *
12  * This program is free software; you can redistribute it and/or modify
13  * it under the terms of the GNU Lesser General Public License version 2.1,
14  * as published by the Free Software Foundation.
15  *
16  * This program is distributed in the hope that it will be useful,
17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19  * GNU Lesser General Public License for more details.
20  *
21  * You should have received a copy of the GNU Lesser General Public
22  * License along with this program; if not, write to the Free Software
23  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
24  */
25 
26 /*! \file */
27 
28 #if !defined(_SPANDSP_T38_CORE_H_)
29 #define _SPANDSP_T38_CORE_H_
30 
31 /*! \page t38_core_page T.38 real time FAX over IP message handling
32 There are two ITU recommendations which address sending FAXes over IP networks. T.37 specifies a
33 method of encapsulating FAX images in e-mails, and transporting them to the recipient (an e-mail
34 box, or another FAX machine) in a store-and-forward manner. T.38 defines a protocol for
35 transmitting a FAX across an IP network in real time. The core T.38 modules implements the basic
36 message handling for the T.38, real time, FAX over IP (FoIP) protocol.
37 
38 The T.38 protocol can operate between:
39  - Internet-aware FAX terminals, which connect directly to an IP network. The T.38 terminal module
40  extends this module to provide a complete T.38 terminal.
41  - FAX gateways, which allow traditional PSTN FAX terminals to communicate through the Internet.
42  The T.38 gateway module extends this module to provide a T.38 gateway.
43  - A combination of terminals and gateways.
44 
45 T.38 is the only standardised protocol which exists for real-time FoIP. Reliably transporting a
46 FAX between PSTN FAX terminals, through an IP network, requires use of the T.38 protocol at FAX
47 gateways. VoIP connections are not robust for modem use, including FAX modem use. Most use low
48 bit rate codecs, which cannot convey the modem signals accurately. Even when high bit rate
49 codecs are used, VoIP connections suffer dropouts and timing adjustments, which modems cannot
50 tolerate. In a LAN environment the dropout rate may be very low, but the timing adjustments which
51 occur in VoIP connections still make modem operation unreliable. T.38 FAX gateways deal with the
52 delays, timing jitter, and packet loss experienced in packet networks, and isolate the PSTN FAX
53 terminals from these as far as possible. In addition, by sending FAXes as image data, rather than
54 digitised audio, they reduce the required bandwidth of the IP network.
55 
56 \section t38_core_page_sec_1 What does it do?
57 
58 \section t38_core_page_sec_2 How does it work?
59 
60 Timing differences and jitter between two T.38 entities can be a serious problem, if one of those
61 entities is a PSTN gateway.
62 
63 Flow control for non-ECM image data takes advantage of several features of the T.30 specification.
64 First, an unspecified number of 0xFF octets may be sent at the start of transmission. This means we
65 can add endless extra 0xFF bytes at this point, without breaking the T.30 spec. In practice, we
66 cannot add too many, or we will affect the timing tolerance of the T.30 protocol by delaying the
67 response at the end of each image. Secondly, just before an end of line (EOL) marker we can pad
68 with zero bits. Again, the number is limited only by need to avoid upsetting the timing of the
69 step following the non-ECM data.
70 */
71 
72 /*! T.38 indicator types */
74 {
75  T38_IND_NO_SIGNAL = 0,
76  T38_IND_CNG,
77  T38_IND_CED,
78  T38_IND_V21_PREAMBLE,
79  T38_IND_V27TER_2400_TRAINING,
80  T38_IND_V27TER_4800_TRAINING,
81  T38_IND_V29_7200_TRAINING,
82  T38_IND_V29_9600_TRAINING,
83  T38_IND_V17_7200_SHORT_TRAINING,
84  T38_IND_V17_7200_LONG_TRAINING,
85  T38_IND_V17_9600_SHORT_TRAINING,
86  T38_IND_V17_9600_LONG_TRAINING,
87  T38_IND_V17_12000_SHORT_TRAINING,
88  T38_IND_V17_12000_LONG_TRAINING,
89  T38_IND_V17_14400_SHORT_TRAINING,
90  T38_IND_V17_14400_LONG_TRAINING,
91  T38_IND_V8_ANSAM,
92  T38_IND_V8_SIGNAL,
93  T38_IND_V34_CNTL_CHANNEL_1200,
94  T38_IND_V34_PRI_CHANNEL,
95  T38_IND_V34_CC_RETRAIN,
96  T38_IND_V33_12000_TRAINING,
97  T38_IND_V33_14400_TRAINING
98 };
99 
100 /*! T.38 data types */
102 {
103  T38_DATA_NONE = -1,
104  T38_DATA_V21 = 0,
105  T38_DATA_V27TER_2400,
106  T38_DATA_V27TER_4800,
107  T38_DATA_V29_7200,
108  T38_DATA_V29_9600,
109  T38_DATA_V17_7200,
110  T38_DATA_V17_9600,
111  T38_DATA_V17_12000,
112  T38_DATA_V17_14400,
113  T38_DATA_V8,
114  T38_DATA_V34_PRI_RATE,
115  T38_DATA_V34_CC_1200,
116  T38_DATA_V34_PRI_CH,
117  T38_DATA_V33_12000,
118  T38_DATA_V33_14400
119 };
120 
121 /*! T.38 data field types */
123 {
124  T38_FIELD_HDLC_DATA = 0,
125  T38_FIELD_HDLC_SIG_END,
126  T38_FIELD_HDLC_FCS_OK,
127  T38_FIELD_HDLC_FCS_BAD,
128  T38_FIELD_HDLC_FCS_OK_SIG_END,
129  T38_FIELD_HDLC_FCS_BAD_SIG_END,
130  T38_FIELD_T4_NON_ECM_DATA,
131  T38_FIELD_T4_NON_ECM_SIG_END,
132  T38_FIELD_CM_MESSAGE,
133  T38_FIELD_JM_MESSAGE,
134  T38_FIELD_CI_MESSAGE,
135  T38_FIELD_V34RATE
136 };
137 
138 /*! T.38 field classes */
140 {
141  T38_FIELD_CLASS_NONE = 0,
142  T38_FIELD_CLASS_HDLC,
143  T38_FIELD_CLASS_NON_ECM
144 };
145 
146 /*! T.38 message types */
148 {
149  T38_TYPE_OF_MSG_T30_INDICATOR = 0,
150  T38_TYPE_OF_MSG_T30_DATA
151 };
152 
153 /*! T.38 transport types */
155 {
156  T38_TRANSPORT_UDPTL = 0,
157  T38_TRANSPORT_RTP,
158  T38_TRANSPORT_TCP
159 };
160 
161 /*! T.38 TCF management types */
163 {
164  T38_DATA_RATE_MANAGEMENT_LOCAL_TCF = 1,
165  T38_DATA_RATE_MANAGEMENT_TRANSFERRED_TCF = 2
166 };
167 
168 /*! T.38 Packet categories used for setting the redundancy level and packet repeat
169  counts on a packet by packet basis. */
171 {
172  /*! \brief Indicator packet */
174  /*! \brief Control data packet */
176  /*! \brief Terminating control data packet */
178  /*! \brief Image data packet */
180  /*! \brief Terminating image data packet */
182 };
183 
184 #define T38_RX_BUF_LEN 2048
185 #define T38_TX_BUF_LEN 16384
186 
187 /*! T.38 data field */
188 typedef struct
189 {
190  /*! Field type */
192  /*! Field contents */
193  const uint8_t *field;
194  /*! Field length */
197 
198 /*!
199  Core T.38 state, common to all modes of T.38.
200 */
202 
203 typedef int (t38_tx_packet_handler_t)(t38_core_state_t *s, void *user_data, const uint8_t *buf, int len, int count);
204 
205 typedef int (t38_rx_indicator_handler_t)(t38_core_state_t *s, void *user_data, int indicator);
206 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);
207 typedef int (t38_rx_missing_handler_t)(t38_core_state_t *s, void *user_data, int rx_seq_no, int expected_seq_no);
208 
209 #if defined(__cplusplus)
210 extern "C"
211 {
212 #endif
213 
214 /*! \brief Convert the code for an indicator to a short text name.
215  \param indicator The type of indicator.
216  \return A pointer to a short text name for the indicator. */
217 SPAN_DECLARE(const char *) t38_indicator_to_str(int indicator);
218 
219 /*! \brief Convert the code for a type of data to a short text name.
220  \param data_type The data type.
221  \return A pointer to a short text name for the data type. */
222 SPAN_DECLARE(const char *) t38_data_type_to_str(int data_type);
223 
224 /*! \brief Convert the code for a type of data field to a short text name.
225  \param field_type The field type.
226  \return A pointer to a short text name for the field type. */
227 SPAN_DECLARE(const char *) t38_field_type_to_str(int field_type);
228 
229 /*! \brief Convert the code for a CM profile code to text description.
230  \param profile The profile code from a CM message.
231  \return A pointer to a short text description of the profile. */
232 SPAN_DECLARE(const char *) t38_cm_profile_to_str(int profile);
233 
234 /*! \brief Convert a JM message code to text description.
235  \param data The data field of the message.
236  \param len The length of the data field.
237  \return A pointer to a short text description of the profile. */
238 SPAN_DECLARE(const char *) t38_jm_to_str(const uint8_t *data, int len);
239 
240 /*! \brief Convert a V34rate message to an actual bit rate.
241  \param data The data field of the message.
242  \param len The length of the data field.
243  \return The bit rate, or -1 for a bad message. */
244 SPAN_DECLARE(int) t38_v34rate_to_bps(const uint8_t *data, int len);
245 
246 /*! \brief Send an indicator packet
247  \param s The T.38 context.
248  \param indicator The indicator to send.
249  \return The delay to allow after this indicator is sent. */
250 SPAN_DECLARE(int) t38_core_send_indicator(t38_core_state_t *s, int indicator);
251 
252 /*! \brief Find the delay to allow for HDLC flags after sending an indicator
253  \param s The T.38 context.
254  \param indicator The indicator to check.
255  \return The delay to allow for initial HDLC flags after this indicator is sent. */
256 SPAN_DECLARE(int) t38_core_send_flags_delay(t38_core_state_t *s, int indicator);
257 
258 /*! \brief Find the delay to allow for modem training after sending an indicator
259  \param s The T.38 context.
260  \param indicator The indicator to check.
261  \return The delay to allow for modem training after this indicator is sent. */
262 SPAN_DECLARE(int) t38_core_send_training_delay(t38_core_state_t *s, int indicator);
263 
264 /*! \brief Send a data packet
265  \param s The T.38 context.
266  \param data_type The packet's data type.
267  \param field_type The packet's field type.
268  \param field The message data content for the packet.
269  \param field_len The length of the message data, in bytes.
270  \param category The category of the packet being sent. This should be one of the values defined for t38_packet_categories_e.
271  \return ??? */
272 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);
273 
274 /*! \brief Send a data packet
275  \param s The T.38 context.
276  \param data_type The packet's data type.
277  \param field The list of fields.
278  \param fields The number of fields in the list.
279  \param category The category of the packet being sent. This should be one of the values defined for t38_packet_categories_e.
280  \return ??? */
281 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);
282 
283 /*! \brief Process a received T.38 IFP packet.
284  \param s The T.38 context.
285  \param buf The packet contents.
286  \param len The length of the packet contents.
287  \param seq_no The packet sequence number.
288  \return 0 for OK, else -1. */
289 SPAN_DECLARE(int) t38_core_rx_ifp_packet(t38_core_state_t *s, const uint8_t *buf, int len, uint16_t seq_no);
290 
291 /*! Set the method to be used for data rate management, as per the T.38 spec.
292  \param s The T.38 context.
293  \param method 1 for pass TCF across the T.38 link, 2 for handle TCF locally.
294 */
295 SPAN_DECLARE(void) t38_set_data_rate_management_method(t38_core_state_t *s, int method);
296 
297 /*! Set the data transport protocol.
298  \param s The T.38 context.
299  \param data_transport_protocol UDPTL, RTP or TPKT.
300 */
302 
303 /*! Set the non-ECM fill bit removal mode.
304  \param s The T.38 context.
305  \param fill_bit_removal TRUE to remove fill bits across the T.38 link, else FALSE.
306 */
308 
309 /*! Set the MMR transcoding mode.
310  \param s The T.38 context.
311  \param mmr_transcoding TRUE to transcode to MMR across the T.38 link, else FALSE.
312 */
313 SPAN_DECLARE(void) t38_set_mmr_transcoding(t38_core_state_t *s, int mmr_transcoding);
314 
315 /*! Set the JBIG transcoding mode.
316  \param s The T.38 context.
317  \param jbig_transcoding TRUE to transcode to JBIG across the T.38 link, else FALSE.
318 */
320 
321 /*! Set the maximum buffer size for received data at the far end.
322  \param s The T.38 context.
323  \param max_buffer_size The maximum buffer size.
324 */
325 SPAN_DECLARE(void) t38_set_max_buffer_size(t38_core_state_t *s, int max_buffer_size);
326 
327 /*! Set the maximum size of an IFP packet that is acceptable by the far end.
328  \param s The T.38 context.
329  \param max_datagram_size The maximum IFP packet length, in bytes.
330 */
332 
333 /*! \brief Send a data packet
334  \param s The T.38 context.
335  \param category The category of the packet being sent. This should be one of the values defined for t38_packet_categories_e.
336  \param setting The repeat count for the category. This should be at least one for all categories other an indicator packets.
337  Zero is valid for indicator packets, as it suppresses the sending of indicator packets, as an application using
338  TCP for the transport would require. As the setting is passed through to the transmission channel, additional
339  information may be encoded in it, such as the redundancy depth for the particular packet category. */
340 SPAN_DECLARE(void) t38_set_redundancy_control(t38_core_state_t *s, int category, int setting);
341 
342 SPAN_DECLARE(void) t38_set_fastest_image_data_rate(t38_core_state_t *s, int max_rate);
343 
344 SPAN_DECLARE(int) t38_get_fastest_image_data_rate(t38_core_state_t *s);
345 
346 /*! Set the T.38 version to be emulated.
347  \param s The T.38 context.
348  \param t38_version Version number, as in the T.38 spec.
349 */
350 SPAN_DECLARE(void) t38_set_t38_version(t38_core_state_t *s, int t38_version);
351 
352 /*! Set the sequence number handling option.
353  \param s The T.38 context.
354  \param check TRUE to check sequence numbers, and handle gaps reasonably. FALSE
355  for no sequence number processing (e.g. for TPKT over TCP transport).
356 */
357 SPAN_DECLARE(void) t38_set_sequence_number_handling(t38_core_state_t *s, int check);
358 
359 /*! Set the TEP handling option.
360  \param s The T.38 context.
361  \param allow_for_tep TRUE to allow for TEP playout, else FALSE.
362 */
363 SPAN_DECLARE(void) t38_set_tep_handling(t38_core_state_t *s, int allow_for_tep);
364 
365 /*! Get a pointer to the logging context associated with a T.38 context.
366  \brief Get a pointer to the logging context associated with a T.38 context.
367  \param s The T.38 context.
368  \return A pointer to the logging context, or NULL.
369 */
371 
372 /*! Restart a T.38 core context.
373  \brief Restart a T.38 core context.
374  \param s The T.38 context.
375  \return 0 for OK, else -1. */
376 SPAN_DECLARE(int) t38_core_restart(t38_core_state_t *s);
377 
378 /*! Initialise a T.38 core context.
379  \brief Initialise a T.38 core context.
380  \param s The T.38 context.
381  \param rx_indicator_handler Receive indicator handling routine.
382  \param rx_data_handler Receive data packet handling routine.
383  \param rx_rx_missing_handler Missing receive packet handling routine.
384  \param rx_packet_user_data An opaque pointer passed to the rx packet handling routines.
385  \param tx_packet_handler Packet transmit handling routine.
386  \param tx_packet_user_data An opaque pointer passed to the tx_packet_handler.
387  \return A pointer to the T.38 context, or NULL if there was a problem. */
389  t38_rx_indicator_handler_t *rx_indicator_handler,
390  t38_rx_data_handler_t *rx_data_handler,
391  t38_rx_missing_handler_t *rx_missing_handler,
392  void *rx_user_data,
393  t38_tx_packet_handler_t *tx_packet_handler,
394  void *tx_packet_user_data);
395 
396 /*! Release a signaling tone transmitter context.
397  \brief Release a signaling tone transmitter context.
398  \param s The T.38 context.
399  \return 0 for OK */
400 SPAN_DECLARE(int) t38_core_release(t38_core_state_t *s);
401 
402 /*! Free a signaling tone transmitter context.
403  \brief Free a signaling tone transmitter context.
404  \param s The T.38 context.
405  \return 0 for OK */
406 SPAN_DECLARE(int) t38_core_free(t38_core_state_t *s);
407 
408 #if defined(__cplusplus)
409 }
410 #endif
411 
412 #endif
413 /*- End of file ------------------------------------------------------------*/