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comparison spandsp-0.0.3/spandsp-0.0.3/src/spandsp/t38_core.h @ 5:f762bf195c4b

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import spandsp-0.0.3
author Peter Meerwald <pmeerw@cosy.sbg.ac.at>
date Fri, 25 Jun 2010 16:00:21 +0200
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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 General Public License version 2, as
14 * 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 General Public License for more details.
20 *
21 * You should have received a copy of the GNU General Public License
22 * along with this program; if not, write to the Free Software
23 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
24 *
25 * $Id: t38_core.h,v 1.11 2006/12/07 13:22:26 steveu Exp $
26 */
27
28 /*! \file */
29
30 #if !defined(_T38_CORE_H_)
31 #define _T38_CORE_H_
32
33 /*! \page t38_core_page T.38 real time FAX over IP message handling
34 There are two ITU recommendations which address sending FAXes over IP networks. T.37 specifies a
35 method of encapsulating FAX images in e-mails, and transporting them to the recipient (an e-mail
36 box, or another FAX machine) in a store-and-forward manner. T.38 defines a protocol for
37 transmitting a FAX across an IP network in real time. The core T.38 modules implements the basic
38 message handling for the T.38, real time, FAX over IP (FoIP) protocol.
39
40 The T.38 protocol can operate between:
41 - Internet-aware FAX terminals, which connect directly to an IP network. The T.38 terminal module
42 extends this module to provide a complete T.38 terminal.
43 - FAX gateways, which allow traditional PSTN FAX terminals to communicate through the Internet.
44 The T.38 gateway module extends this module to provide a T.38 gateway.
45 - A combination of terminals and gateways.
46
47 T.38 is the only standardised protocol which exists for real-time FoIP. Reliably transporting a
48 FAX between PSTN FAX terminals, through an IP network, requires use of the T.38 protocol at FAX
49 gateways. VoIP connections are not robust for modem use, including FAX modem use. Most use low
50 bit rate codecs, which cannot convey the modem signals accurately. Even when high bit rate
51 codecs are used, VoIP connections suffer dropouts and timing adjustments, which modems cannot
52 tolerate. In a LAN environment the dropout rate may be very low, but the timing adjustments which
53 occur in VoIP connections still make modem operation unreliable. T.38 FAX gateways deal with the
54 delays, timing jitter, and packet loss experienced in packet networks, and isolate the PSTN FAX
55 terminals from these as far as possible. In addition, by sending FAXes as image data, rather than
56 digitised audio, they reduce the required bandwidth of the IP network.
57
58 \section t38_core_page_sec_1 What does it do?
59
60 \section t38_core_page_sec_2 How does it work?
61
62 Timing differences and jitter between two T.38 entities can be a serious problem, if one of those
63 entities is a PSTN gateway.
64
65 Flow control for non-ECM image data takes advantage of several features of the T.30 specification.
66 First, an unspecified number of 0xFF octets may be sent at the start of transmission. This means we
67 can add endless extra 0xFF bytes at this point, without breaking the T.30 spec. In practice, we
68 cannot add too many, or we will affect the timing tolerance of the T.30 protocol by delaying the
69 response at the end of each image. Secondly, just before an end of line (EOL) marker we can pad
70 with zero bits. Again, the number is limited only by need to avoid upsetting the timing of the
71 step following the non-ECM data.
72 */
73
74 enum t30_indicator_types_e
75 {
76 T38_IND_NO_SIGNAL = 0,
77 T38_IND_CNG,
78 T38_IND_CED,
79 T38_IND_V21_PREAMBLE,
80 T38_IND_V27TER_2400_TRAINING,
81 T38_IND_V27TER_4800_TRAINING,
82 T38_IND_V29_7200_TRAINING,
83 T38_IND_V29_9600_TRAINING,
84 T38_IND_V17_7200_SHORT_TRAINING,
85 T38_IND_V17_7200_LONG_TRAINING,
86 T38_IND_V17_9600_SHORT_TRAINING,
87 T38_IND_V17_9600_LONG_TRAINING,
88 T38_IND_V17_12000_SHORT_TRAINING,
89 T38_IND_V17_12000_LONG_TRAINING,
90 T38_IND_V17_14400_SHORT_TRAINING,
91 T38_IND_V17_14400_LONG_TRAINING,
92 T38_IND_V8_ANSAM,
93 T38_IND_V8_SIGNAL,
94 T38_IND_V34_CNTL_CHANNEL_1200,
95 T38_IND_V34_PRI_CHANNEL,
96 T38_IND_V34_CC_RETRAIN,
97 T38_IND_V33_12000_TRAINING,
98 T38_IND_V33_14400_TRAINING
99 };
100
101 enum t38_data_types_e
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 enum t38_field_types_e
122 {
123 T38_FIELD_HDLC_DATA = 0,
124 T38_FIELD_HDLC_SIG_END,
125 T38_FIELD_HDLC_FCS_OK,
126 T38_FIELD_HDLC_FCS_BAD,
127 T38_FIELD_HDLC_FCS_OK_SIG_END,
128 T38_FIELD_HDLC_FCS_BAD_SIG_END,
129 T38_FIELD_T4_NON_ECM_DATA,
130 T38_FIELD_T4_NON_ECM_SIG_END,
131 T38_FIELD_CM_MESSAGE,
132 T38_FIELD_JM_MESSAGE,
133 T38_FIELD_CI_MESSAGE,
134 T38_FIELD_V34RATE
135 };
136
137 enum t38_field_classes_e
138 {
139 T38_FIELD_CLASS_NONE = 0,
140 T38_FIELD_CLASS_HDLC,
141 T38_FIELD_CLASS_NON_ECM,
142 };
143
144 enum t38_message_types_e
145 {
146 T38_TYPE_OF_MSG_T30_INDICATOR = 0,
147 T38_TYPE_OF_MSG_T30_DATA
148 };
149
150 enum t38_transport_types_e
151 {
152 T38_TRANSPORT_UDPTL = 0,
153 T38_TRANSPORT_RTP,
154 T38_TRANSPORT_TCP
155 };
156
157 #define T38_RX_BUF_LEN 2048
158 #define T38_TX_BUF_LEN 16384
159
160 typedef struct
161 {
162 int numocts;
163 const uint8_t *data;
164 } asn1_dyn_oct_str_t;
165
166 typedef struct
167 {
168 uint8_t field_data_present;
169 unsigned int field_type;
170 asn1_dyn_oct_str_t field_data;
171 } data_field_element_t;
172
173 typedef struct t38_core_state_s t38_core_state_t;
174
175 typedef int (t38_tx_packet_handler_t)(t38_core_state_t *s, void *user_data, const uint8_t *buf, int len, int count);
176
177 typedef int (t38_rx_indicator_handler_t)(t38_core_state_t *s, void *user_data, int indicator);
178 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);
179 typedef int (t38_rx_missing_handler_t)(t38_core_state_t *s, void *user_data, int rx_seq_no, int expected_seq_no);
180
181 #include <sys/time.h>
182
183 /*
184 Core T.38 state, common to all modes of T.38.
185 */
186 struct t38_core_state_s
187 {
188 t38_tx_packet_handler_t *tx_packet_handler;
189 void *tx_packet_user_data;
190
191 t38_rx_indicator_handler_t *rx_indicator_handler;
192 t38_rx_data_handler_t *rx_data_handler;
193 t38_rx_missing_handler_t *rx_missing_handler;
194 void *rx_user_data;
195
196 /*! NOTE - Bandwidth reduction shall only be done on suitable Phase C data, i.e., MH, MR
197 and - in the case of transcoding to JBIG - MMR. MMR and JBIG require reliable data
198 transport such as that provided by TCP. When transcoding is selected, it shall be
199 applied to every suitable page in a call. */
200
201 /*! Method 1: Local generation of TCF (required for use with TCP).
202 Method 2: Transfer of TCF is required for use with UDP (UDPTL or RTP).
203 Method 2 is not recommended for use with TCP. */
204 int data_rate_management_method;
205
206 /*! The emitting gateway may indicate a preference for either UDP/UDPTL, or
207 UDP/RTP, or TCP for transport of T.38 IFP Packets. The receiving device
208 selects the transport protocol. */
209 int data_transport_protocol;
210
211 /*! Indicates the capability to remove and insert fill bits in Phase C, non-ECM
212 data to reduce bandwidth in the packet network. Optional. See Note. */
213 int fill_bit_removal;
214
215 /*! Indicates the ability to convert to/from MMR from/to the line format to
216 improve the compression of the data, and reduce the bandwidth, in the
217 packet network. Optional. See Note. */
218 int mmr_transcoding;
219
220 /*! Indicates the ability to convert to/from JBIG to reduce bandwidth. Optional.
221 See Note. */
222 int jbig_transcoding;
223
224 /*! For UDP (UDPTL or RTP) modes, this option indicates the maximum
225 number of octets that can be stored on the remote device before an overflow
226 condition occurs. It is the responsibility of the transmitting application to
227 limit the transfer rate to prevent an overflow. The negotiated data rate
228 should be used to determine the rate at which data is being removed from
229 the buffer. */
230 int max_buffer_size;
231
232 /*! This option indicates the maximum size of a UDPTL packet or the
233 maximum size of the payload within an RTP packet that can be accepted by
234 the remote device. */
235 int max_datagram_size;
236
237 /*! This is the version number of ITU-T Rec. T.38. New versions shall be
238 compatible with previous versions. */
239 int t38_version;
240
241 /*! The fastest data rate supported by the T.38 channel. */
242 int fastest_image_data_rate;
243
244 /*! Internet aware FAX (IAF) mode. */
245 int iaf;
246
247 int tx_seq_no;
248 int rx_expected_seq_no;
249
250 int current_rx_indicator;
251 int current_tx_indicator;
252
253 int missing_packets;
254
255 logging_state_t logging;
256 };
257
258 #ifdef __cplusplus
259 extern "C" {
260 #endif
261
262 /*! \brief Convert the code for an indicator to a short text name.
263 \param indicator The type of indicator.
264 \return A pointer to a short text name for the indicator. */
265 const char *t38_indicator(int indicator);
266
267 /*! \brief Convert the code for a type of data to a short text name.
268 \param data_type The data type.
269 \return A pointer to a short text name for the data type. */
270 const char *t38_data_type(int data_type);
271
272 /*! \brief Convert the code for a type of data field to a short text name.
273 \param field_type The field type.
274 \return A pointer to a short text name for the field type. */
275 const char *t38_field_type(int field_type);
276
277 int t38_core_send_indicator(t38_core_state_t *s, int indicator, int count);
278
279 int t38_core_send_data(t38_core_state_t *s, int data_type, int field_type, const uint8_t *msg, int msglen);
280
281 /*! \brief Process a received T.38 IFP packet.
282 \param s The T.38 context.
283 \param seq_no The packet sequence number.
284 \param buf The packet contents.
285 \param len The length of the packet contents.
286 \return 0 for OK, else -1. */
287 int t38_core_rx_ifp_packet(t38_core_state_t *s, int seq_no, const uint8_t *buf, int len);
288
289 /*! Set the method to be used for data rate management, as per the T.38 spec.
290 \param s The T.38 context.
291 \param method 1 for pass TCF across the T.38 link, 2 for handle TCF locally.
292 */
293 void t38_set_data_rate_management_method(t38_core_state_t *s, int method);
294
295 /*! Set the data transport protocol.
296 \param s The T.38 context.
297 \param data_transport_protocol UDPTL, RTP or TPKT.
298 */
299 void t38_set_data_transport_protocol(t38_core_state_t *s, int data_transport_protocol);
300
301 /*! Set the non-ECM fill bit removal mode.
302 \param s The T.38 context.
303 \param fill_bit_removal TRUE to remove fill bits across the T.38 link, else FALSE.
304 */
305 void t38_set_fill_bit_removal(t38_core_state_t *s, int fill_bit_removal);
306
307 /*! Set the MMR transcoding mode.
308 \param s The T.38 context.
309 \param mmr_transcoding TRUE to transcode to MMR across the T.38 link, else FALSE.
310 */
311 void t38_set_mmr_transcoding(t38_core_state_t *s, int mmr_transcoding);
312
313 /*! Set the JBIG transcoding mode.
314 \param s The T.38 context.
315 \param jbig_transcoding TRUE to transcode to JBIG across the T.38 link, else FALSE.
316 */
317 void t38_set_jbig_transcoding(t38_core_state_t *s, int jbig_transcoding);
318
319 void t38_set_max_buffer_size(t38_core_state_t *s, int max_buffer_size);
320
321 void t38_set_max_datagram_size(t38_core_state_t *s, int max_datagram_size);
322
323 int t38_get_fastest_image_data_rate(t38_core_state_t *s);
324
325 /*! Set the T.38 version to be emulated.
326 \param s The T.38 context.
327 \param t38_version Version number, as in the T.38 spec.
328 */
329 void t38_set_t38_version(t38_core_state_t *s, int t38_version);
330
331 t38_core_state_t *t38_core_init(t38_core_state_t *s,
332 t38_rx_indicator_handler_t *rx_indicator_handler,
333 t38_rx_data_handler_t *rx_data_handler,
334 t38_rx_missing_handler_t *rx_missing_handler,
335 void *rx_user_data);
336 #ifdef __cplusplus
337 }
338 #endif
339
340 #endif
341 /*- End of file ------------------------------------------------------------*/

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