src/h224/q922.cxx

   1 /*
   2  * q922.h
   3  *
   4  * Q.922 PDU implementation for the OpenH323 Project.
   5  *
   6  * Copyright (c) 2006 Network for Educational Technology, ETH Zurich.
   7  * Written by Hannes Friederich.
   8  *
   9  * The contents of this file are subject to the Mozilla Public License
  10  * Version 1.0 (the "License"); you may not use this file except in
  11  * compliance with the License. You may obtain a copy of the License at
  12  * http://www.mozilla.org/MPL/
  13  *
  14  * Software distributed under the License is distributed on an "AS IS"
  15  * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
  16  * the License for the specific language governing rights and limitations
  17  * under the License.
  18  *
  19  * Contributor(s): ______________________________________.
  20  *
  21  * $Log$
  22  * Revision 1.6  2007/04/02 05:51:33  rjongbloed
  23  * Tidied some trace logs to assure all have a category (bit before a tab character) set.
  24  *
  25  * Revision 1.5  2007/03/12 23:19:01  csoutheren
  26  * Add ability to remove H.224
  27  *
  28  * Revision 1.4  2006/05/03 17:45:51  hfriederich
  29  * reverting incorrect byte orderings in fcs from previous patch
  30  *
  31  * Revision 1.3  2006/05/01 10:29:50  csoutheren
  32  * Added pragams for gcc < 4
  33  *
  34  * Revision 1.2  2006/04/24 12:53:50  rjongbloed
  35  * Port of H.224 Far End Camera Control to DevStudio/Windows
  36  *
  37  * Revision 1.1  2006/04/20 16:48:17  hfriederich
  38  * Initial version of H.224/H.281 implementation.
  39  *
  40  */
  41
  42 #include <ptlib.h>
  43
  44 #ifdef __GNUC__
  45 #pragma implementation "q922.h"
  46 #endif
  47
  48 #include <opal/buildopts.h>
  49
  50 #if OPAL_H224
  51
  52 #include <h224/h323h224.h>
  53
  54 #include <h224/q922.h>
  55
  56 #define Q922_FCS_SIZE 2
  57
  58 #define Q922_OK 0x00
  59 #define Q922_FLAG 0x7e
  60 #define Q922_ERROR 0x7f
  61
  62 /*
  63  * FCS lookup table.
  64  * Code based on implementation in RFC1549
  65  */
  66 static WORD fcstable[256] = {
  67         0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
  68         0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
  69         0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
  70         0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
  71         0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
  72         0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
  73         0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
  74         0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
  75         0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
  76         0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
  77         0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
  78         0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
  79         0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
  80         0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
  81         0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
  82         0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
  83         0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
  84         0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
  85         0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
  86         0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
  87         0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
  88         0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
  89         0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
  90         0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
  91         0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
  92         0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
  93         0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
  94         0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
  95         0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
  96         0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
  97         0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
  98         0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
  99 };
 100
 101 Q922_Frame::Q922_Frame(PINDEX size)
 102 : PBYTEArray(Q922_HEADER_SIZE + size)
 103 {
 104   informationFieldSize = size;
 105 }
 106
 107
 108 Q922_Frame::~Q922_Frame()
 109 {
 110 }
 111
 112
 113 void Q922_Frame::SetInformationFieldSize(PINDEX size)
 114 {
 115   informationFieldSize = size;
 116   SetMinSize(Q922_HEADER_SIZE+informationFieldSize);
 117 }
 118
 119
 120 BOOL Q922_Frame::Decode(const BYTE *data, PINDEX size)
 121 {
 122   // a valid frame must contain at least 2xFLAG, 3 octets Q922 header,
 123   // 2 octets FCS and at least 1 octet information
 124   if(size < 2+3+2+1)
 125     return FALSE;
 126
 127   PINDEX octetIndex = 0;
 128   BYTE bitIndex = 7;
 129   BYTE onesCounter = 0;
 130
 131   if(!FindFlagEnd(data, size, octetIndex, bitIndex))
 132     return FALSE;
 133
 134   BYTE firstOctet;
 135   BYTE secondOctet;
 136
 137   // read the two first octets
 138   if(octetIndex >= size || DecodeByte(data, &firstOctet, octetIndex, bitIndex, onesCounter) != Q922_OK)
 139     return FALSE;
 140
 141   if(octetIndex >= size || DecodeByte(data, &secondOctet, octetIndex, bitIndex, onesCounter) != Q922_OK)
 142     return FALSE;
 143
 144   PINDEX arrayIndex = 0;
 145   while(octetIndex < size) {
 146
 147     BYTE decodedByte;
 148     BYTE result = DecodeByte(data, &decodedByte, octetIndex, bitIndex, onesCounter);
 149
 150     if(result == Q922_ERROR)
 151       return FALSE;
 152
 153     if(result == Q922_FLAG) {
 154
 155       // Found end flag
 156       // FCS is contained in firstOctet and secondOctet.
 157       WORD fcs = (secondOctet << 8) | firstOctet;
 158
 159       // Calculate FCS from data to check
 160       WORD calculatedFCS = CalculateFCS((const BYTE *)theArray, arrayIndex);
 161
 162       if (fcs != calculatedFCS) {
 163         PTRACE(2, "Q.922\tFrame has incorrect checksum");
 164         return FALSE;
 165       }
 166
 167       if(arrayIndex > Q922_HEADER_SIZE) {
 168         SetInformationFieldSize(arrayIndex - Q922_HEADER_SIZE);
 169         return TRUE;
 170       }
 171
 172       return FALSE;
 173     }
 174
 175     theArray[arrayIndex] = firstOctet;
 176     arrayIndex++;
 177
 178     firstOctet = secondOctet;
 179     secondOctet = decodedByte;
 180
 181     // Q922-frames must not exceed an information field size of 260 octets
 182     if(arrayIndex >= 260+Q922_HEADER_SIZE)
 183       return FALSE;
 184   }
 185
 186   return FALSE;
 187 }
 188
 189 PINDEX Q922_Frame::GetEncodedSize() const
 190 {
 191   if(informationFieldSize == 0) {
 192         return 0; // cannot encode
 193   }
 194
 195   // dataSize is High Order Address, Low Order Address, Control, Information and
 196   // Frame Check Sequence (FCS, 2 Bytes)
 197   PINDEX dataSize = Q922_HEADER_SIZE + informationFieldSize + Q922_FCS_SIZE;
 198
 199   // Due to possible need for bit insertion, the size may grow.
 200   // For simplicity, we assume twice the data size, which will certainly be enough.
 201   // So, encoded size is 3*FLAG + 2*dataSize + 3*FLAG;
 202   return 3+2*dataSize+3;
 203 }
 204
 205 BOOL Q922_Frame::Encode(BYTE *buffer, PINDEX & size) const
 206 {
 207   BYTE bitIndex = 7;
 208   return Encode(buffer, size, bitIndex);
 209 }
 210
 211 BOOL Q922_Frame::Encode(BYTE *buffer, PINDEX & size, BYTE & theBitIndex) const
 212 {
 213   if(informationFieldSize == 0) {
 214     return FALSE;
 215   }
 216
 217   PINDEX octetIndex = 0;
 218   BYTE bitIndex = theBitIndex;
 219   BYTE onesCounter = 0;
 220
 221   // storing three FLAG sequencs.
 222   // since the FLAG sequences may be not byte-aligned, the first FLAG sequence is encoded
 223   // into a dummy buffer and extracted from there
 224   buffer[0] = 0;
 225   BYTE dummy[3];
 226   EncodeOctetNoEscape(Q922_FLAG, dummy, octetIndex, bitIndex);
 227   EncodeOctetNoEscape(Q922_FLAG, dummy, octetIndex, bitIndex);
 228   buffer[0] = dummy[1];
 229   buffer[1] = dummy[1];
 230   octetIndex = 1;
 231   EncodeOctetNoEscape(Q922_FLAG, buffer, octetIndex, bitIndex);
 232   EncodeOctetNoEscape(Q922_FLAG, buffer, octetIndex, bitIndex);
 233
 234   // calculating the FCS
 235   PINDEX dataSize = GetInformationFieldSize() + Q922_HEADER_SIZE;
 236   WORD fcs = CalculateFCS((const BYTE *)theArray, dataSize);
 237
 238   // Encoding the data byte-by-byte
 239   PINDEX i;
 240   PINDEX count = Q922_HEADER_SIZE + informationFieldSize;
 241   for(i = 0; i < count; i++) {
 242     EncodeOctet(theArray[i], buffer, octetIndex, bitIndex, onesCounter);
 243   }
 244
 245   // Encoding the FCS
 246   EncodeOctet((BYTE)fcs, buffer, octetIndex, bitIndex, onesCounter);
 247   EncodeOctet((BYTE)(fcs >> 8), buffer, octetIndex, bitIndex, onesCounter);
 248
 249   // Appending three FLAG sequences to the buffer
 250   // the buffer is not necessary byte aligned!
 251   EncodeOctetNoEscape(Q922_FLAG, buffer, octetIndex, bitIndex);
 252   EncodeOctetNoEscape(Q922_FLAG, buffer, octetIndex, bitIndex);
 253   EncodeOctetNoEscape(Q922_FLAG, buffer, octetIndex, bitIndex);
 254
 255   // determining correct number of octets
 256   if(bitIndex == 7) {
 257         octetIndex--;
 258   }
 259
 260   size = octetIndex;
 261   theBitIndex = bitIndex;
 262
 263   return TRUE;
 264
 265 }
 266
 267 BOOL Q922_Frame::FindFlagEnd(const BYTE *buffer,
 268                                                          PINDEX bufferSize,
 269                                                          PINDEX & octetIndex, BYTE & bitIndex)
 270 {
 271   BYTE positionsCorrect = 0;
 272
 273   while(octetIndex < bufferSize) {
 274
 275     BYTE bit = DecodeBit(buffer, octetIndex, bitIndex);
 276
 277     switch(positionsCorrect) {
 278       case 0:
 279                 if(bit == 0) {
 280                   positionsCorrect = 1;
 281                 }
 282                 break;
 283       case 1:
 284       case 2:
 285       case 3:
 286       case 4:
 287       case 5:
 288       case 6:
 289         if(bit == 1) {
 290           positionsCorrect++;
 291                 } else {
 292           positionsCorrect = 1;
 293         }
 294         break;
 295       case 7:
 296         if(bit == 0) {
 297           positionsCorrect = 0xff;
 298         } else {
 299           // got 0x7f, ABORT sequence
 300           return FALSE;
 301         }
 302         break;
 303       default:
 304         return FALSE;
 305     }
 306
 307     if(positionsCorrect == 0xff) {
 308       break;
 309     }
 310   }
 311
 312   if(positionsCorrect != 0xff) {
 313     return FALSE;
 314   }
 315
 316   // First FLAG sequence found, bit index determined.
 317   // now check for additinal FLAG sequences
 318   BYTE octet = Q922_FLAG;
 319
 320   while(octet == Q922_FLAG && octetIndex < bufferSize) {
 321
 322     PINDEX startOctetIndex = octetIndex;
 323     BYTE startBitIndex = bitIndex;
 324
 325     BYTE positionsCorrect = 0;
 326
 327     unsigned i;
 328     for(i = 0; i < 8; i++) {
 329
 330       BYTE bit = DecodeBit(buffer, octetIndex, bitIndex);
 331
 332       switch(positionsCorrect) {
 333             case 0:
 334           if(bit == 1) {
 335             positionsCorrect = 0xf0;
 336           } else {
 337             positionsCorrect++;
 338                   }
 339           break;
 340         case 1:
 341         case 2:
 342         case 3:
 343         case 4:
 344         case 5:
 345         case 6:
 346           if(bit == 0) {
 347                     positionsCorrect = 0xf0;
 348           } else {
 349             positionsCorrect++;
 350           }
 351           break;
 352                 case 7:
 353                   if(bit == 1) {
 354                         // 0x7f read
 355                     return FALSE;
 356                   }
 357                   break;
 358         default:
 359           return FALSE;
 360       }
 361
 362       if(positionsCorrect == 0xf0) {
 363         octetIndex = startOctetIndex;
 364         bitIndex = startBitIndex;
 365         return TRUE;
 366       }
 367     }
 368   }
 369
 370   return FALSE;
 371 }
 372
 373 BYTE Q922_Frame::DecodeByte(const BYTE *buffer,
 374                                                         BYTE *destination,
 375                                                         PINDEX & octetIndex,
 376                                                         BYTE & bitIndex,
 377                                                         BYTE & onesCounter)
 378 {
 379   // decoded byte is copied to destination.
 380   // returns Q922_OK if decoding succesful,
 381   // returns Q922_FLAG if ending FLAG detected,
 382   // returns Q922_ERROR if there was an error
 383
 384   BYTE decodedByte = 0x00;
 385
 386   PINDEX i;
 387   for(i = 0; i < 8; i++) {
 388
 389         BYTE bit = DecodeBit(buffer, octetIndex, bitIndex);
 390
 391         if(bit) {
 392       onesCounter++;
 393
 394       if(onesCounter == 6) {
 395
 396         // Either FLAG or ERROR
 397         bit = DecodeBit(buffer, octetIndex, bitIndex);
 398
 399                 if(i == 6 && !bit)  { // FLAG is byte aligned AND has only 6 consecutive ones
 400           return Q922_FLAG;
 401         } else {
 402           return Q922_ERROR;
 403         }
 404       }
 405
 406     } else {
 407           if(onesCounter == 5) {
 408             // discard bit, read again
 409                 bit = DecodeBit(buffer, octetIndex, bitIndex);
 410           }
 411
 412       onesCounter = 0;
 413     }
 414
 415     decodedByte |= (bit << i);
 416   }
 417
 418   *destination = decodedByte;
 419   return Q922_OK;
 420 }
 421
 422 BYTE Q922_Frame::DecodeBit(const BYTE *buffer,
 423                                                    PINDEX & octetIndex,
 424                                                    BYTE & bitIndex)
 425 {
 426   BYTE bit = (buffer[octetIndex] >> bitIndex) & 0x01;
 427
 428   if(bitIndex == 0) {
 429     octetIndex++;
 430     bitIndex = 8;
 431   }
 432   bitIndex--;
 433
 434   return bit;
 435 }
 436
 437 void Q922_Frame::EncodeOctet(BYTE octet, BYTE *buffer,
 438                                                          PINDEX & octetIndex,
 439                                                          BYTE & bitIndex,
 440                                                          BYTE & onesCounter) const
 441 {
 442   // data is sent out with LSB first, so we need
 443   // to reverse the bit direction.
 444   // In addition, it is required to insert a zero
 445   // bit after 5 consecutive ones to avoid FLAG emulation
 446
 447   PINDEX i;
 448   for(i = 0; i < 8; i++) {
 449     // reading one bit from the octet and write it to the buffer
 450     BYTE bit = (BYTE)((octet >> i) & 0x01);
 451
 452     EncodeBit(bit, buffer, octetIndex, bitIndex);
 453
 454     if(bit) {
 455       onesCounter++;
 456
 457       if(onesCounter == 5) {
 458         // insert a zero bit
 459         EncodeBit(0, buffer, octetIndex, bitIndex);
 460         onesCounter = 0;
 461       }
 462     } else {
 463       onesCounter = 0;
 464     }
 465   }
 466 }
 467
 468 void Q922_Frame::EncodeOctetNoEscape(BYTE octet,
 469                                                                          BYTE *buffer,
 470                                                                          PINDEX & octetIndex,
 471                                                                          BYTE & bitIndex) const
 472 {
 473   // data is sent out with LSB first, so we need
 474   // to reverse the bit direction.
 475
 476   PINDEX i;
 477   for(i = 0; i < 8; i++) {
 478     // reating one bit from the octet and write it to the buffer
 479     BYTE bit = (BYTE)((octet >> i) & 0x01);
 480
 481     EncodeBit(bit, buffer, octetIndex, bitIndex);
 482   }
 483 }
 484
 485 void Q922_Frame::EncodeBit(BYTE bit,
 486                                                    BYTE *buffer,
 487                                                    PINDEX & octetIndex,
 488                                                    BYTE & bitIndex) const
 489 {
 490   if(bitIndex == 7) {
 491     buffer[octetIndex] = 0;
 492   }
 493
 494   buffer[octetIndex] |= ((bit & 0x01) << bitIndex);
 495
 496   // adjusting bit/byte index
 497   if(bitIndex == 0) {
 498     octetIndex++;
 499     bitIndex = 8;
 500   }
 501
 502   bitIndex--;
 503 }
 504
 505 WORD Q922_Frame::CalculateFCS(const BYTE *data, PINDEX length) const
 506 {
 507   // initial value of FCS is all ones.
 508   WORD fcs = 0xffff;
 509
 510   while(length--) {
 511     fcs = (fcs >> 8) ^ fcstable[(fcs ^ *data++) & 0xff];
 512   }
 513
 514   // take one's complement
 515   fcs = ~fcs;
 516
 517   return fcs;
 518 }
 519
 520 #endif // OPAL_H224