1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
|
<pre>Network Working Group Q. Xie
Request for Comments: 4788 Motorola
Updates: <a href="./rfc3558">3558</a> R. Kapoor
Category: Standards Track Qualcomm
January 2007
<span class="h1">Enhancements to RTP Payload Formats for EVRC Family Codecs</span>
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document updates the Enhanced Variable Rate Codec (EVRC) RTP
payload formats defined in <a href="./rfc3558">RFC 3558</a> with several enhancements and
extensions. In particular, it defines support for the header-free
and interleaved/bundled packet formats for the EVRC-B codec, a new
compact bundled format for the EVRC and EVRC-B codecs, as well as
discontinuous transmission (DTX) support for EVRC and EVRC-B-encoded
speech transported via RTP. Voice over IP (VoIP) applications
operating over low bandwidth dial-up and wireless networks require
such enhancements for efficient use of the bandwidth.
<span class="grey">Xie & Kapoor Standards Track [Page 1]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-2" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
Table of Contents
<a href="#section-1">1</a>. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-3">3</a>
<a href="#section-1.1">1.1</a>. Support of EVRC-B Codec . . . . . . . . . . . . . . . . . <a href="#page-3">3</a>
<a href="#section-1.2">1.2</a>. Compact (Header-free) Bundled Format . . . . . . . . . . . <a href="#page-3">3</a>
<a href="#section-1.3">1.3</a>. Discontinuous Transmission (DTX) . . . . . . . . . . . . . <a href="#page-4">4</a>
<a href="#section-2">2</a>. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-5">5</a>
<a href="#section-3">3</a>. EVRC-B Codec . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-5">5</a>
<a href="#section-4">4</a>. Compact Bundled Format . . . . . . . . . . . . . . . . . . . . <a href="#page-5">5</a>
<a href="#section-4.1">4.1</a>. Single-Rate Operation . . . . . . . . . . . . . . . . . . <a href="#page-5">5</a>
<a href="#section-5">5</a>. Storage Format for EVRC-B Codec . . . . . . . . . . . . . . . <a href="#page-6">6</a>
<a href="#section-6">6</a>. Media Type Definitions . . . . . . . . . . . . . . . . . . . . <a href="#page-6">6</a>
<a href="#section-6.1">6.1</a>. Registration of Media Type EVRC1 . . . . . . . . . . . . . <a href="#page-6">6</a>
<a href="#section-6.2">6.2</a>. Registration of Media Type EVRCB . . . . . . . . . . . . . <a href="#page-9">9</a>
<a href="#section-6.3">6.3</a>. Registration of Media Type EVRCB0 . . . . . . . . . . . . <a href="#page-11">11</a>
<a href="#section-6.4">6.4</a>. Registration of Media Type EVRCB1 . . . . . . . . . . . . <a href="#page-12">12</a>
<a href="#section-6.5">6.5</a>. Updated Registration of Media Type EVRC . . . . . . . . . <a href="#page-13">13</a>
<a href="#section-6.6">6.6</a>. Updated Registration of Media Type EVRC0 . . . . . . . . . <a href="#page-15">15</a>
<a href="#section-6.7">6.7</a>. Mapping MIME Parameters into SDP . . . . . . . . . . . . . <a href="#page-17">17</a>
<a href="#section-6.8">6.8</a>. Usage in Offer/Answer . . . . . . . . . . . . . . . . . . <a href="#page-18">18</a>
<a href="#section-7">7</a>. Backward Compatibility with <a href="./rfc3558">RFC 3558</a> . . . . . . . . . . . . . <a href="#page-19">19</a>
<a href="#section-8">8</a>. IANA Considerations . . . . . . . . . . . . . . . . . . . . . <a href="#page-19">19</a>
<a href="#section-9">9</a>. Security Considerations . . . . . . . . . . . . . . . . . . . <a href="#page-19">19</a>
<a href="#section-10">10</a>. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-19">19</a>
<a href="#section-11">11</a>. References . . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-20">20</a>
<a href="#section-11.1">11.1</a>. Normative References . . . . . . . . . . . . . . . . . . . <a href="#page-20">20</a>
<a href="#section-11.2">11.2</a>. Informative References . . . . . . . . . . . . . . . . . . <a href="#page-20">20</a>
<span class="grey">Xie & Kapoor Standards Track [Page 2]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-3" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>
This document defines support for the header-free and interleaved/
bundled packet formats for the EVRC-B codec, a new compact bundled
format for the EVRC and EVRC-B codecs, as well as discontinuous
transmission (DTX) support for EVRC and EVRC-B-encoded speech
transported via RTP. Voice over IP (VoIP) applications operating
over low bandwidth dial-up and wireless networks require such EVRC
RTP payload capabilities for efficient use of the bandwidth.
<span class="h3"><a class="selflink" id="section-1.1" href="#section-1.1">1.1</a>. Support of EVRC-B Codec</span>
EVRC-B [<a href="#ref-3" title=""Enhanced Variable Rate Codec, Speech Service Option 3 and 68 for Wideband Spread Spectrum Digital Systems"">3</a>] is an extension to EVRC [<a href="#ref-2" title=""Enhanced Variable Rate Codec, Speech Service Option 3 for Wideband Spread Spectrum Digital Systems"">2</a>] developed in the Third
Generation Partnership Project 2 (3GPP2). EVRC-B [<a href="#ref-3" title=""Enhanced Variable Rate Codec, Speech Service Option 3 and 68 for Wideband Spread Spectrum Digital Systems"">3</a>] compresses each
20 milliseconds of 8000Hz, 16-bit sampled speech input into output
frames of one of the four different sizes: Rate 1 (171 bits), Rate
1/2 (80 bits), Rate 1/4 (40 bits), or Rate 1/8 (16 bits). In
addition, there are two zero-bit codec frame types: null frames and
erasure frames, similar to EVRC [<a href="#ref-2" title=""Enhanced Variable Rate Codec, Speech Service Option 3 for Wideband Spread Spectrum Digital Systems"">2</a>]. One significant enhancement in
EVRC-B is the use of 1/4-rate frames that were not used in EVRC.
This provides lower average data rates (ADRs) compared to EVRC, for a
given voice quality.
Since speech frames encoded by EVRC-B are different from those
encoded by EVRC, EVRC-B and EVRC codecs do not interoperate with each
other. At the initiation of an RTP session, the RTP sender and
receiver need to indicate (e.g., using MIME subtypes that are
separate from those of EVRC) that EVRC-B is to be used for the
ensuing session.
<span class="h3"><a class="selflink" id="section-1.2" href="#section-1.2">1.2</a>. Compact (Header-free) Bundled Format</span>
The current interleaved/bundled packet format defined in <a href="./rfc3558">RFC 3558</a>
allows bundling of multiple speech frames of different rates in a
single RTP packet, sending mode change requests, and interleaving.
To support these functions, a Table of Contents (ToC) is used in each
RTP packet, in addition to the standard RTP header. The size of the
ToC varies depending on the number of EVRC frames carried in the
packet [<a href="#ref-4" title=""RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV)"">4</a>].
The current header-free packet format defined in <a href="./rfc3558">RFC 3558</a> is more
compact and optimized for use over wireless links. It eliminates the
need for a ToC by requiring that each RTP packet contain only one
speech frame (of any allowable rate), i.e., bundling is not allowed.
Moreover, interleaving and mode change requests are not supported in
the header-free format [<a href="#ref-4" title=""RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV)"">4</a>].
<span class="grey">Xie & Kapoor Standards Track [Page 3]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
The compact bundled format described in this document presents the
user an alternative to the header-free format defined in <a href="./rfc3558">RFC 3558</a>.
This format allows bundling of multiple EVRC or EVRC-B frames without
the addition of extra headers, as would be in the case of the
interleaved/bundled format. However, in order to use this compact
bundled format, only one EVRC/EVRC-B rate (full rate or 1/2 rate) can
be used in the session. Similar to the header-free format defined in
<a href="./rfc3558">RFC 3558</a>, interleaving and mode change requests are not supported in
the compact bundled format.
<span class="h3"><a class="selflink" id="section-1.3" href="#section-1.3">1.3</a>. Discontinuous Transmission (DTX)</span>
Information carried in frames of EVRC and EVRC-B codecs varies little
during periods of silence. The transmission of these frames across
the radio interface in a wireless system is expensive, in terms of
capacity; therefore, suppression of these frames is desirable. Such
an operation is called DTX, also known as silence suppression.
In general, when DTX/silence suppression is applied, the first few
frames of silence may be transmitted at the beginning of the period
of silence to establish background noise. Then, a portion of the
stream of subsequent silence frames is not transmitted, and is
discarded at the sender. At the receiver, background or comfort
noise may be generated by using the previously received silence
frames.
The full detail of DTX/silence suppression operation can be found in
DTX [<a href="#ref-8" title=""Discontinuous Transmission (DTX) of Speech in cdma2000 Systems"">8</a>] as well as in <a href="./rfc3551">RFC 3551</a> [<a href="#ref-9" title=""RTP Profile for Audio and Video Conferences with Minimal Control"">9</a>], and in <a href="./rfc3558">RFC 3558</a> [<a href="#ref-4" title=""RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV)"">4</a>]. This
document only defines the additional optional MIME parameters
(silencesupp, dtxmax, dtxmin, and hangover) for setting up a DTX/
silence suppression session, where "silencesupp" is for indicating
the capability and willingness of using DTX/silence suppression;
"dtxmax" and "dtxmin", for indicating the desired range of DTX update
interval; and "hangover", for indicating the desired number of
silence frames at the beginning of each silence period to establish
background noise at the receiver (see <a href="#section-6.1">Section 6.1</a> for detailed
definition).
The EVRC and EVRC-B codecs, in variable-rate operation mode, send
1/8-rate frames during periods of silence, while in single-rate
operation mode (see <a href="#section-4">Section 4</a>), silence is encoded and sent in frames
of the same rate as that of speech frames. The DTX parameters
defined in this document apply to 1/8-rate frames in the variable-
rate mode and to silence frames in the single-rate operation mode.
For simplicity, in the rest of this document the term "silence frame"
refers either to an 1/8-rate frame in variable-rate operation or a
frame that contains only silence in the signal-rate operation.
<span class="grey">Xie & Kapoor Standards Track [Page 4]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-5" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. Conventions</span>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in <a href="./rfc2119">RFC 2119</a> [<a href="#ref-1" title=""Key words for use in RFCs to Indicate Requirement Levels"">1</a>].
<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. EVRC-B Codec</span>
Three RTP packet formats are supported for the EVRC-B codec: the
interleaved/bundled packet format, the header-free packet format, and
the compact bundled packet format. For the interleaved/bundled and
header-free packet formats, the operational details and capabilities,
such as ToC, interleaving, and bundling, of EVRC-B, are exactly the
same as those of EVRC, as defined in <a href="./rfc3558">RFC 3558</a> [<a href="#ref-4" title=""RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV)"">4</a>], except that the
mode change request field in the ToC MUST be interpreted according to
the definition of the RATE_REDUC parameter in EVRC-B [<a href="#ref-3" title=""Enhanced Variable Rate Codec, Speech Service Option 3 and 68 for Wideband Spread Spectrum Digital Systems"">3</a>]. The
compact bundled packet format for EVRC-B is defined in <a href="#section-4">Section 4</a> of
this document.
<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. Compact Bundled Format</span>
A packet in the compact bundled format consists of an RTP header,
followed by a sequence of one or more consecutive EVRC/EVRC-B codec
data frames of the same rate, as shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RTP Header [<a href="#ref-4" title=""RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV)"">4</a>] |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| |
| One or more EVRC/EVRC-B data frames of same rate |
| .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The codec data frames MUST be generated from the output of the codec
following the procedure described in <a href="./rfc3558#section-5.2">Section 5.2 in RFC 3558</a> [<a href="#ref-4" title=""RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV)"">4</a>], and
all MUST be of the same rate and size.
<span class="h3"><a class="selflink" id="section-4.1" href="#section-4.1">4.1</a>. Single-Rate Operation</span>
As mentioned earlier, in order to use the compact bundled format, all
the EVRC/EVRC-B data frames in the session MUST be of the same rate.
This packet format may carry only full or half-rate frames.
<span class="grey">Xie & Kapoor Standards Track [Page 5]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-6" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
For a session that uses the compact bundled format, the rate for the
session can be determined during the session setup signaling, for
example, via Session Description Protocol (SDP) exchanges. See
<a href="#section-6">Section 6</a> below for more details.
<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>. Storage Format for EVRC-B Codec</span>
The storage format is used for storing EVRC-B-encoded speech frames,
e.g., as a file or e-mail attachment.
The file begins with a magic number to identify the vocoder that is
used. The magic number for EVRC-B corresponds to the ASCII character
string:
"#!EVRC-B\n"
(or 0x2321 0x4556 0x5243 0x2d42 0x0a in hexadecimal).
Note that the "\n" is an important part of both this magic number and
the "#!EVRC\n" magic number defined in <a href="./rfc3558#section-11">Section 11 of RFC 3558</a>, and
the "\n" MUST be included in any comparison of either magic number,
since, otherwise, a prefix of the EVRC-B magic number could be
mistaken for the EVRC magic number.
The codec data frames are stored in consecutive order, with a single
ToC entry field, extended to one octet, prefixing each codec data
frame. The ToC field, as defined in Section 5.1 of [<a href="#ref-4" title=""RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV)"">4</a>], is extended
to one octet by setting the four most significant bits of the octet
to zero. For example, a ToC value of 4 (a full-rate frame) is stored
as 0x04.
Speech frames lost in transmission and non-received frames MUST be
stored as erasure frames to maintain synchronization with the
original media.
<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>. Media Type Definitions</span>
<span class="h3"><a class="selflink" id="section-6.1" href="#section-6.1">6.1</a>. Registration of Media Type EVRC1</span>
Type name: audio
Subtype names: EVRC1
Required parameters: none
<span class="grey">Xie & Kapoor Standards Track [Page 6]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-7" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
Optional parameters:
ptime: See <a href="./rfc4566">RFC 4566</a> [<a href="#ref-7" title=""SDP: Session Description Protocol"">7</a>].
maxptime: The maximum amount of media that can be encapsulated in
each packet, expressed as time in milliseconds. The time MUST
be calculated as the sum of the time the media present in the
packet represents. The time SHOULD be a multiple of the
duration of a single codec data frame (20 msec). If not
signaled, the default maxptime value MUST be 200 milliseconds.
fixedrate: Indicates the EVRC rate of the session while in
single-rate operation. Valid values include: 0.5 and 1, where
a value of 0.5 indicates the 1/2 rate, while a value of 1
indicates the full rate. If this parameter is not present, 1/2
rate is assumed.
silencesupp: Permissible values are 0 and 1. A value of 1
indicates that the sender of this parameter: a) is capable of
receiving silence-suppressed speech using DTX, AND b) is
capable of and will send out silence-suppressed speech using
DTX, unless the other end indicates that it does not want to
receive silence-suppressed speech using DTX.
A value of 0 indicates that the sender of this parameter: a)
does NOT want to receive silence-suppressed speech using DTX,
AND b) will NOT send out silence-suppressed speech using DTX.
If this parameter is not present, the default value 1 MUST be
assumed. If the RTP receiver indicates through the use of SIP
signaling or other means that it is incapable of or unwilling
to use silence suppression using DTX, silence suppression using
DTX as specified in this document MUST NOT be used for the
session.
dtxmax: Permissible values are from 0 to 255. Indicates the
maximum DTX update interval in number of frames. During DTX,
the RTP sender occasionally updates the RTP receiver about the
change in background noise characteristics, etc., by sending a
new silence frame to the RTP receiver. The RTP receiver may
use 'dtxmax' to indicate to the RTP sender the maximum interval
(in number of frames) between any two DTX updates it expects to
receive from the RTP sender.
If this parameter is not present in a session that uses DTX,
the default value 32, as specified in [<a href="#ref-8" title=""Discontinuous Transmission (DTX) of Speech in cdma2000 Systems"">8</a>], MUST be assumed.
This parameter MUST be ignored if silence suppression using DTX
is not used for the session.
<span class="grey">Xie & Kapoor Standards Track [Page 7]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-8" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
Note also that if the RTP receiver elects to detect DTX using
dtxmax, the dtxmax parameter will affect the amount of delay
the RTP receiver sees before detecting DTX in the stream.
dtxmin: Permissible values are from 0 to 255. Indicates the
minimum DTX update interval in number of frames. The RTP
receiver may use 'dtxmin' to indicate to the RTP sender the
minimal interval (in number of frames) between any two DTX
updates it expects to receive from the RTP sender.
If this parameter is not present, the default value 12, as
specified in [<a href="#ref-8" title=""Discontinuous Transmission (DTX) of Speech in cdma2000 Systems"">8</a>] MUST be assumed. This parameter MUST be
ignored if silence suppression using DTX is not used for the
session.
hangover: Permissible values are from 0 to 255. Indicates the
number of consecutive silence frames transmitted at the end of
an active speech interval but before the DTX interval begins.
When setting up an RTP session that uses DTX, an RTP receiver
can use this parameter to signal the number of silence frames
it expects to receive before the beginning of DTX. While
hangover=0 is allowed, it is RECOMMENDED that hangover be set
to 1 or greater since the presence of silence frames at the end
of an active speech can help the RTP receiver to identify the
beginning of the DTX period.
If this parameter is not present for a session that uses DTX,
the default value 1, as specified in [<a href="#ref-8" title=""Discontinuous Transmission (DTX) of Speech in cdma2000 Systems"">8</a>] MUST be assumed. This
parameter MUST be ignored if silence suppression using DTX is
not used for the session.
Encoding considerations:
This media type is framed binary data (see <a href="./rfc4288#section-4.8">RFC 4288, Section 4.8</a>)
and is defined for transfer of EVRC-encoded data via RTP, using
the compact bundled format as described in <a href="./rfc4788">RFC 4788</a>.
Security considerations: See <a href="./rfc4788#section-9">Section 9 of RFC 4788</a>.
Interoperability considerations: none
Published specification:
The EVRC vocoder is specified in 3GPP2 C.S0014 [<a href="#ref-2" title=""Enhanced Variable Rate Codec, Speech Service Option 3 for Wideband Spread Spectrum Digital Systems"">2</a>]. Transfer
method with compact bundled RTP format is specified in <a href="./rfc4788">RFC 4788</a>.
Applications that use this media type:
It is expected that many VoIP applications (as well as mobile
applications) will use this type.
<span class="grey">Xie & Kapoor Standards Track [Page 8]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-9" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
Additional information: none
Person & email address to contact for further information:
Qiaobing Xie <Qiaobing.Xie@motorola.com>
Intended usage: COMMON
Restrictions on usage:
This media type depends on RTP framing; hence, it is only defined
for transfer via RTP (<a href="./rfc3550">RFC 3550</a> [<a href="#ref-5" title=""RTP: A Transport Protocol for Real-Time Applications"">5</a>]). Transfer within other
framing protocols is not defined at this time.
Author:
Qiaobing Xie
Change controller:
IETF Audio/Video Transport working group delegated from the IESG.
<span class="h3"><a class="selflink" id="section-6.2" href="#section-6.2">6.2</a>. Registration of Media Type EVRCB</span>
Type name: audio
Subtype names: EVRCB
Required parameters: none
Optional parameters:
ptime: see <a href="./rfc4566">RFC 4566</a> [<a href="#ref-7" title=""SDP: Session Description Protocol"">7</a>].
maxptime: The maximum amount of media that can be encapsulated in
each packet, expressed as time in milliseconds. The time MUST
be calculated as the sum of the time the media present in the
packet represents. The time SHOULD be a multiple of the
duration of a single codec data frame (20 msec). If not
signaled, the default maxptime value MUST be 200 milliseconds.
maxinterleave: Maximum number for interleaving length (field LLL
in the Interleaving Octet). The interleaving lengths used in
the entire session MUST NOT exceed this maximum value. If not
signaled, the maxinterleave length MUST be 5.
silencesupp: see <a href="#section-6.1">Section 6.1</a> for definition. If this parameter
is not present, the default value 1 MUST be assumed.
<span class="grey">Xie & Kapoor Standards Track [Page 9]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-10" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
dtxmax: see <a href="#section-6.1">Section 6.1</a>
dtxmin: see <a href="#section-6.1">Section 6.1</a>
hangover: see <a href="#section-6.1">Section 6.1</a>
Encoding considerations:
This media type is framed binary data (see <a href="./rfc4288#section-4.8">RFC 4288, Section 4.8</a>)
and is defined for transfer of EVRC-B-encoded data via RTP using
the Interleaved/Bundled packet format specified in <a href="./rfc3558">RFC 3558</a> [<a href="#ref-4" title=""RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV)"">4</a>].
Security considerations: See <a href="./rfc4788#section-9">Section 9 of RFC 4788</a>.
Interoperability considerations: none
Published specification:
The EVRC-B vocoder is specified in 3GPP2 C.S0014-B [<a href="#ref-3" title=""Enhanced Variable Rate Codec, Speech Service Option 3 and 68 for Wideband Spread Spectrum Digital Systems"">3</a>]. Transfer
method with Interleaved/Bundled packet format via RTP is specified
in <a href="./rfc3558">RFC 3558</a>.
Applications that use this media type:
It is expected that many VoIP applications (as well as mobile
applications) will use this type.
Additional information:
The following information applies for storage format only.
Magic number: #!EVRC-B\n (see <a href="./rfc4788#section-5">Section 5 of RFC 4788</a>)
File extensions: evb, EVB
Macintosh file type code: None
Object identifier or OID: None
Person & email address to contact for further information:
Qiaobing Xie <Qiaobing.Xie@motorola.com>
Intended usage: COMMON
Restrictions on usage:
This media type may be used with RTP framing (<a href="./rfc3550">RFC 3550</a> [<a href="#ref-5" title=""RTP: A Transport Protocol for Real-Time Applications"">5</a>]) and as
a storage format. When used with RTP, the procedures in <a href="#section-3">Section 3</a>
MUST be followed. In all other contexts, the storage format
defined in <a href="#section-5">Section 5</a> MUST be used.
Author:
Qiaobing Xie
<span class="grey">Xie & Kapoor Standards Track [Page 10]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-11" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
Change controller:
IETF Audio/Video Transport working group delegated from the IESG.
<span class="h3"><a class="selflink" id="section-6.3" href="#section-6.3">6.3</a>. Registration of Media Type EVRCB0</span>
Type name: audio
Subtype names: EVRCB0
Required parameters: none
Optional parameters:
silencesupp: see <a href="#section-6.1">Section 6.1</a> for definition. If this parameter
is not present, the default value 1 MUST be assumed.
dtxmax: see <a href="#section-6.1">Section 6.1</a>
dtxmin: see <a href="#section-6.1">Section 6.1</a>
hangover: see <a href="#section-6.1">Section 6.1</a>
Encoding considerations:
This media type is framed binary data (see <a href="./rfc4288#section-4.8">RFC 4288, Section 4.8</a>)
and is defined for transfer of EVRC-B-encoded data via RTP using
the Header-Free packet format specified in <a href="./rfc3558">RFC 3558</a> [<a href="#ref-4" title=""RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV)"">4</a>].
Security considerations: See <a href="./rfc4788#section-9">Section 9 of RFC 4788</a>.
Interoperability considerations: none
Published specification:
The EVRC-B vocoder is specified in 3GPP2 C.S0014-B [<a href="#ref-3" title=""Enhanced Variable Rate Codec, Speech Service Option 3 and 68 for Wideband Spread Spectrum Digital Systems"">3</a>]. Transfer
method with Header-Free packet format via RTP is specified in <a href="./rfc3558">RFC</a>
<a href="./rfc3558">3558</a> and <a href="./rfc4788">RFC 4788</a>.
Applications that use this media type:
It is expected that many VoIP applications (as well as mobile
applications) will use this type.
Additional information: none
Person & email address to contact for further information:
Qiaobing Xie <Qiaobing.Xie@motorola.com>
<span class="grey">Xie & Kapoor Standards Track [Page 11]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-12" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
Intended usage: COMMON
Restrictions on usage:
This media type depends on RTP framing; hence, it is only defined
for transfer via RTP (<a href="./rfc3550">RFC 3550</a> [<a href="#ref-5" title=""RTP: A Transport Protocol for Real-Time Applications"">5</a>]). Transfer within other
framing protocols is not defined at this time.
Author:
Qiaobing Xie
Change controller:
IETF Audio/Video Transport working group delegated from the IESG.
<span class="h3"><a class="selflink" id="section-6.4" href="#section-6.4">6.4</a>. Registration of Media Type EVRCB1</span>
Type name: audio
Subtype names: EVRCB1
Required parameters: none
Optional parameters:
ptime: see <a href="./rfc4566">RFC 4566</a> [<a href="#ref-7" title=""SDP: Session Description Protocol"">7</a>].
maxptime: The maximum amount of media that can be encapsulated in
each packet, expressed as time in milliseconds. The time MUST
be calculated as the sum of the time the media present in the
packet represents. The time SHOULD be a multiple of the
duration of a single codec data frame (20 msec). If not
signaled, the default maxptime value MUST be 200 milliseconds.
fixedrate: Indicates the EVRC-B rate of the session while in
single-rate operation. Valid values include: 0.5 and 1, where
a value of 0.5 indicates the 1/2 rate while a value of 1
indicates the full rate. If this parameter is not present, 1/2
rate is assumed.
silencesupp: see <a href="#section-6.1">Section 6.1</a> for definition. If this parameter
is not present, the default value 1 MUST be assumed.
dtxmax: see <a href="#section-6.1">Section 6.1</a>
dtxmin: see <a href="#section-6.1">Section 6.1</a>
<span class="grey">Xie & Kapoor Standards Track [Page 12]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-13" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
hangover: see <a href="#section-6.1">Section 6.1</a>
Encoding considerations:
This media type is framed binary data (see <a href="./rfc4288#section-4.8">RFC 4288, Section 4.8</a>)
and is defined for transfer of EVRC-B-encoded data via RTP using
the compact bundled format as described in <a href="./rfc4788">RFC 4788</a>.
Security considerations: See <a href="./rfc4788#section-9">Section 9 of RFC 4788</a>.
Interoperability considerations: none.
Published specification:
The EVRC-B vocoder is specified in 3GPP2 C.S0014-B [<a href="#ref-3" title=""Enhanced Variable Rate Codec, Speech Service Option 3 and 68 for Wideband Spread Spectrum Digital Systems"">3</a>]. Transfer
method with compact bundled RTP format is specified in <a href="./rfc4788">RFC 4788</a>.
Applications that use this media type:
It is expected that many VoIP applications (as well as mobile
applications) will use this type.
Additional information: none
Person & email address to contact for further information:
Qiaobing Xie <Qiaobing.Xie@motorola.com>
Intended usage: COMMON
Restrictions on usage:
This media type depends on RTP framing; hence, it is only defined
for transfer via RTP (<a href="./rfc3550">RFC 3550</a> [<a href="#ref-5" title=""RTP: A Transport Protocol for Real-Time Applications"">5</a>]). Transfer within other
framing protocols is not defined at this time.
Author:
Qiaobing Xie
Change controller:
IETF Audio/Video Transport working group delegated from the IESG.
<span class="h3"><a class="selflink" id="section-6.5" href="#section-6.5">6.5</a>. Updated Registration of Media Type EVRC</span>
(The definition is from <a href="./rfc3558">RFC 3558</a>, added with the optional DTX
parameters, and updated with the new template specified in [<a href="#ref-10" title=""Media Type Registration of RTP Payload Formats"">10</a>].)
Type name: audio
Subtype names: EVRC
<span class="grey">Xie & Kapoor Standards Track [Page 13]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-14" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
Required parameters: none
Optional parameters:
ptime: Defined as usual for RTP audio (see <a href="./rfc4566">RFC 4566</a>).
maxptime: The maximum amount of media that can be encapsulated in
each packet, expressed as time in milliseconds. The time SHALL
be calculated as the sum of the time the media present in the
packet represents. The time SHOULD be a multiple of the
duration of a single codec data frame (20 msec). If not
signaled, the default maxptime value SHALL be 200 milliseconds.
maxinterleave: Maximum number for interleaving length (field LLL
in the Interleaving Octet). The interleaving lengths used in
the entire session MUST NOT exceed this maximum value. If not
signaled, the maxinterleave length SHALL be 5.
silencesupp: see <a href="#section-6.1">Section 6.1</a> for definition. If this parameter
is not present, the default value 1 MUST be assumed.
dtxmax: see <a href="#section-6.1">Section 6.1</a>
dtxmin: see <a href="#section-6.1">Section 6.1</a>
hangover: see <a href="#section-6.1">Section 6.1</a>
Encoding considerations:
This media type is framed binary data (see <a href="./rfc4288#section-4.8">RFC 4288, Section 4.8</a>),
and is defined for transfer of EVRC-encoded data via RTP using the
Interleaved/Bundled packet format specified in Sections <a href="#section-4.1">4.1</a>, <a href="#section-6">6</a>,
and 7 of <a href="./rfc3558">RFC 3558</a>. It is also defined for other transfer methods
using the storage format specified in <a href="./rfc3558#section-11">Section 11 of RFC 3558</a>.
Security considerations: See <a href="#section-14">Section 14</a>, "Security Considerations",
of <a href="./rfc3558">RFC 3558</a>.
Interoperability considerations:
The DTX parameters are receiver options. Existing <a href="./rfc3558">RFC 3558</a>
implementations will not send any of the DTX parameters in their
SDP and will ignore any DTX parameters they receive. The adaptive
DTX behavior of DTX-capable EVRC codecs (as detailed in [<a href="#ref-8" title=""Discontinuous Transmission (DTX) of Speech in cdma2000 Systems"">8</a>],
Section 4.3.5) ensures interoperability with non-DTX EVRC codecs.
Published specification:
The EVRC vocoder is specified in 3GPP2 C.S0014 [<a href="#ref-2" title=""Enhanced Variable Rate Codec, Speech Service Option 3 for Wideband Spread Spectrum Digital Systems"">2</a>]. Transfer
methods are specified in <a href="./rfc3558">RFC 3558</a>.
<span class="grey">Xie & Kapoor Standards Track [Page 14]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-15" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
Applications that use this media type:
It is expected that many VoIP applications (as well as mobile
applications) will use this type.
Additional information:
The following information applies for storage format only.
Magic number: #!EVRC\n (see <a href="./rfc3558#section-11">Section 11 of RFC 3558</a>)
File extensions: evc, EVC
Macintosh file type code: none
Object identifier or OID: none
Person & email address to contact for further information:
Qiaobing Xie <Qiaobing.Xie@motorola.com>
Intended usage: COMMON
Restrictions on usage:
This media type may be used with RTP framing (<a href="./rfc3550">RFC 3550</a> [<a href="#ref-5" title=""RTP: A Transport Protocol for Real-Time Applications"">5</a>]) and as
a storage format. When used with RTP, the procedures in <a href="./rfc3558#section-4.1">RFC 3558,
Section 4.1</a>, MUST be followed. In all other contexts, the storage
format defined in <a href="./rfc3558#section-11">RFC 3558, Section 11</a>, MUST be used.
Author:
Adam Li/Qiaobing Xie
Change controller:
IETF Audio/Video Transport working group delegated from the IESG.
<span class="h3"><a class="selflink" id="section-6.6" href="#section-6.6">6.6</a>. Updated Registration of Media Type EVRC0</span>
(The definition is from <a href="./rfc3558">RFC 3558</a>, added with the optional DTX
parameters, and updated with the new template specified in [<a href="#ref-10" title=""Media Type Registration of RTP Payload Formats"">10</a>].)
Type name: audio
Subtype names: EVRC0
Required parameters: none
Optional parameters:
silencesupp: see <a href="#section-6.1">Section 6.1</a> for definition. If this parameter
is not present, the default value 1 MUST be assumed.
<span class="grey">Xie & Kapoor Standards Track [Page 15]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-16" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
dtxmax: see <a href="#section-6.1">Section 6.1</a>
dtxmin: see <a href="#section-6.1">Section 6.1</a>
hangover: see <a href="#section-6.1">Section 6.1</a>
Encoding considerations:
This media type is framed binary data (see <a href="./rfc4288#section-4.8">RFC 4288, Section 4.8</a>)
and is only defined for transfer of EVRC-encoded data via RTP
using the Header-Free packet format specified in <a href="./rfc3558#section-4.2">Section 4.2 of
RFC 3558</a>.
Security considerations: See <a href="#section-14">Section 14</a>, "Security Considerations",
of <a href="./rfc3558">RFC 3558</a>.
Interoperability considerations:
The DTX parameters are receiver options. Existing <a href="./rfc3558">RFC 3558</a>
implementations will not send any of the DTX parameters in their
SDP and will ignore any DTX parameters they receive. The adaptive
DTX behavior of DTX-capable EVRC codecs (as detailed in [<a href="#ref-8" title=""Discontinuous Transmission (DTX) of Speech in cdma2000 Systems"">8</a>],
Section 4.3.5) ensures interoperability with non-DTX EVRC codecs.
Published specification:
The EVRC vocoder is specified in 3GPP2 C.S0014 [<a href="#ref-2" title=""Enhanced Variable Rate Codec, Speech Service Option 3 for Wideband Spread Spectrum Digital Systems"">2</a>]. Transfer
methods are specified in <a href="./rfc3558">RFC 3558</a>.
Applications that use this media type:
It is expected that many VoIP applications (as well as mobile
applications) will use this type.
Additional information: none
Person & email address to contact for further information:
Qiaobing Xie <Qiaobing.Xie@motorola.com>
Intended usage: COMMON
Restrictions on usage:
This media type depends on RTP framing; hence, it is only defined
for transfer via RTP (<a href="./rfc3550">RFC 3550</a> [<a href="#ref-5" title=""RTP: A Transport Protocol for Real-Time Applications"">5</a>]). Transfer within other
framing protocols is not defined at this time.
Author:
Adam Li/Qiaobing Xie
<span class="grey">Xie & Kapoor Standards Track [Page 16]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-17" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
Change controller:
IETF Audio/Video Transport working group delegated from the IESG.
<span class="h3"><a class="selflink" id="section-6.7" href="#section-6.7">6.7</a>. Mapping MIME Parameters into SDP</span>
The information carried in the MIME media type specification has a
specific mapping to fields in the Session Description Protocol (SDP)
[<a href="#ref-7" title=""SDP: Session Description Protocol"">7</a>], which is commonly used to describe RTP sessions. When SDP is
used to specify sessions employing the compact bundled format for
EVRC/EVRC-B-encoded speech, the mapping is as follows:
o The MIME type ("audio") goes in SDP "m=" as the media name.
o The MIME subtype ("EVRC", "EVRC0", "EVRC1", "EVRCB", EVRCB0", or
"EVRCB1") goes in SDP "a=rtpmap" as the encoding name.
o The optional parameters "ptime" and "maxptime" (for subtypes EVRC,
EVRC1, EVRCB, and EVRCB1) go in the SDP "a=ptime" and "a=maxptime"
attributes, respectively.
o The optional parameter "maxinterleave" (for subtypes EVRC and
EVRCB) goes in the SDP "a=fmtp" attribute by copying it directly
from the MIME media type string as "maxinterleave=value".
o The optional parameter "fixedrate" (for subtypes EVRC1 and EVRCB1)
goes in the "a=fmtp" attribute by copying it directly from the
MIME media type string as "fixedrate=value".
o The optional parameters "silencesupp", "dtxmax", "dtxmin", and
"hangover" go in the "a=fmtp" attribute by copying it directly
from the MIME media type string as "silencesupp=value",
"dtxmax=value", "dtxmin=value", and "hangover=value",
respectively.
Example of usage of EVRC1:
m=audio 49120 RTP/AVP 97
a=rtpmap:97 EVRC1/8000
a=fmtp:97 fixedrate=0.5
a=maxptime:120
Example of usage of EVRCB:
m=audio 49120 RTP/AVP 97
a=rtpmap:97 EVRCB/8000
a=maxptime:120
<span class="grey">Xie & Kapoor Standards Track [Page 17]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-18" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
Example of usage of EVRCB0:
m=audio 49120 RTP/AVP 97
a=rtpmap:97 EVRCB0/8000
Example of usage of EVRCB1:
m=audio 49120 RTP/AVP 97
a=rtpmap:97 EVRCB1/8000
a=fmtp:97 fixedrate=0.5
a=maxptime:100
Example of usage of EVRC with DTX with silencesupp=1:
m=audio 49120 RTP/AVP 97
a=rtpmap:97 EVRC/8000
a=fmtp:97 silencesupp=1 dtxmax=32 dtxmin=12 hangover=1
Example of usage of EVRC with DTX with silencesupp=0:
m=audio 49120 RTP/AVP 97
a=rtpmap:97 EVRC/8000
a=fmtp:97 silencesupp=0
<span class="h3"><a class="selflink" id="section-6.8" href="#section-6.8">6.8</a>. Usage in Offer/Answer</span>
All SDP parameters in this payload format are declarative, and all
reasonable values are expected to be supported. In particular, when
DTX is supported, the RTP sender implementation SHOULD support
hangover, dtxmin, and dtxmax values from 0 to 255. Thus, the
standard usage of Offer/Answer, as described in <a href="./rfc3264">RFC 3264</a> [<a href="#ref-6" title=""An Offer/Answer Model with the Session Description Protocol (SDP)"">6</a>], SHOULD
be followed.
In addition, the following rules MUST be followed while negotiating
DTX parameters:
1. If any DTX parameter is not present in either offer and/or
answer, the default value of the DTX parameter MUST be assumed.
2. If silencesupp is present and set to 0 in either offer or answer,
the values of all received DTX parameters other than silencesupp
SHOULD be ignored.
3. In an offer or answer, the value of dtxmax SHOULD always be
larger than or equal to the value of dtxmin, regardless of
whether the values are indicated explicitly or implicitly by
default. Moreover, if the indicated value of dtxmin is larger
<span class="grey">Xie & Kapoor Standards Track [Page 18]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-19" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
than that of dtxmax, an RTP sender MUST ignore the indicated
values and MUST fall back on using the default dtxmin and dtxmax
values.
<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>. Backward Compatibility with <a href="./rfc3558">RFC 3558</a></span>
This document adds new optional DTX parameters to the original EVRC
payload subtypes "EVRC" and "EVRC0" defined in <a href="./rfc3558">RFC 3558</a>. Since the
new DTX parameters are receiver options, we expect that the existing
<a href="./rfc3558">RFC 3558</a> implementations will not send any of the DTX parameters in
their SDP and will ignore any DTX parameters they receive. The
adaptive DTX behavior of DTX-capable EVRC codecs (as detailed in [<a href="#ref-8" title=""Discontinuous Transmission (DTX) of Speech in cdma2000 Systems"">8</a>],
Section 4.3.5) ensures the backward interoperability between the DTX-
capable EVRC codec and non-DTX EVRC codecs.
<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>. IANA Considerations</span>
Four (4) new MIME subtype registrations - "EVRC1", "EVRCB", "EVRCB0",
and "EVRCB1" - are defined in this document (see <a href="#section-6.1">Section 6.1</a> -
<a href="#section-6.4">Section 6.4</a>) for EVRC-B and compact bundled payload format support.
For all the EVRC and EVRC-B RTP payload formats defined in <a href="./rfc3558">RFC 3558</a>
[<a href="#ref-4" title=""RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV)"">4</a>] and <a href="./rfc4788">RFC 4788</a>, four additional optional parameters -
"silencesupp", "dtxmax", "dtxmin", and "hangover" - are defined and
used in DTX.
The MIME subtype registrations "EVRC" and "EVRC0", originally defined
in <a href="./rfc3558">RFC 3558</a> [<a href="#ref-4" title=""RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV)"">4</a>], are updated with the optional DTX parameters (see
Sections <a href="#section-6.5">6.5</a> and <a href="#section-6.6">6.6</a>).
<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>. Security Considerations</span>
Implementations using the payload defined in this specification are
subject to the security considerations discussed in <a href="./rfc3558">RFC 3558</a> [<a href="#ref-4" title=""RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV)"">4</a>], <a href="./rfc3550">RFC</a>
<a href="./rfc3550">3550</a> [<a href="#ref-5" title=""RTP: A Transport Protocol for Real-Time Applications"">5</a>], and any appropriate profile (for example, <a href="./rfc3551">RFC 3551</a> [<a href="#ref-9" title=""RTP Profile for Audio and Video Conferences with Minimal Control"">9</a>]).
This payload does not specify any different security services.
<span class="h2"><a class="selflink" id="section-10" href="#section-10">10</a>. Acknowledgements</span>
The following people have made significant contributions to this
document (in alphabetical order): Parag Agashe, Jim Ashley,
Harikishan Desineni, Serafin Diaz, Harinath Garudadri, Gouri
Johanssen, Ananth Kandhadai, Waqar Mohsin, Ashok Roy, Gino Scribano,
and Gajinder Singh Vij.
Special thanks to Colin Perkins, Magnus Westerlund, and Adam Li for
their careful review and comments that significantly improved the
quality of this document.
<span class="grey">Xie & Kapoor Standards Track [Page 19]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-20" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
<span class="h2"><a class="selflink" id="section-11" href="#section-11">11</a>. References</span>
<span class="h3"><a class="selflink" id="section-11.1" href="#section-11.1">11.1</a>. Normative References</span>
[<a id="ref-1">1</a>] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.
[<a id="ref-2">2</a>] "Enhanced Variable Rate Codec, Speech Service Option 3 for
Wideband Spread Spectrum Digital Systems", 3GPP2 C.S0014,
January 1997.
[<a id="ref-3">3</a>] "Enhanced Variable Rate Codec, Speech Service Option 3 and 68
for Wideband Spread Spectrum Digital Systems", 3GPP2 C.S0014-B
v1.0, May 2006.
[<a id="ref-4">4</a>] Li, A., "RTP Payload Format for Enhanced Variable Rate Codecs
(EVRC) and Selectable Mode Vocoders (SMV)", <a href="./rfc3558">RFC 3558</a>,
July 2003.
[<a id="ref-5">5</a>] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications",
<a href="./rfc3550">RFC 3550</a>, July 2003.
[<a id="ref-6">6</a>] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
the Session Description Protocol (SDP)", <a href="./rfc3264">RFC 3264</a>, June 2002.
[<a id="ref-7">7</a>] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", <a href="./rfc4566">RFC 4566</a>, July 2006.
[<a id="ref-8">8</a>] "Discontinuous Transmission (DTX) of Speech in cdma2000
Systems", 3GPP2 C.S0076-0, Version 1.0, December 2005.
<span class="h3"><a class="selflink" id="section-11.2" href="#section-11.2">11.2</a>. Informative References</span>
[<a id="ref-9">9</a>] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
Conferences with Minimal Control", <a href="./rfc3551">RFC 3551</a>, July 2003.
[<a id="ref-10">10</a>] Casner, S., <a style="text-decoration: none" href='https://www.google.com/search?sitesearch=datatracker.ietf.org%2Fdoc%2Fhtml%2F&q=inurl:draft-+%22Media+Type+Registration+of+RTP+Payload+Formats%22'>"Media Type Registration of RTP Payload Formats"</a>,
Work in Progress, March 2006.
<span class="grey">Xie & Kapoor Standards Track [Page 20]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-21" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
Authors' Addresses
Qiaobing Xie
Motorola, Inc.
1501 W. Shure Drive, 2-F9
Arlington Heights, IL 60004
US
Phone: +1-847-632-3028
EMail: Qiaobing.Xie@Motorola.com
Rohit Kapoor
Qualcomm Inc.
US
Phone: +1-858-845-1161
EMail: rkapoor@qualcomm.com
<span class="grey">Xie & Kapoor Standards Track [Page 21]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-22" ></span>
<span class="grey"><a href="./rfc4788">RFC 4788</a> EVRC RTP Format Enhancements January 2007</span>
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a>, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST,
AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY
IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and <a href="https://www.rfc-editor.org/bcp/bcp79">BCP 79</a>.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
<a href="http://www.ietf.org/ipr">http://www.ietf.org/ipr</a>.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Xie & Kapoor Standards Track [Page 22]
</pre>
|
