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Keywords: real-time transport protocol, dsr, distributed speeech recognition, xfe, extended front-end, xafe, extended advanced front-end
Network Working Group Q. Xie
Request for Comments: 4060 D. Pearce
Category: Standards Track Motorola
May 2005
RTP Payload Formats for European Telecommunications
Standards Institute (ETSI) European Standard
ES 202 050, ES 202 211, and ES 202 212
Distributed Speech Recognition Encoding
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 Internet Society (2005).
Abstract
This document specifies RTP payload formats for encapsulating
European Telecommunications Standards Institute (ETSI) European
Standard ES 202 050 DSR Advanced Front-end (AFE), ES 202 211 DSR
Extended Front-end (XFE), and ES 202 212 DSR Extended Advanced
Front-end (XAFE) signal processing feature streams for distributed
speech recognition (DSR) systems.
Xie & Pearce Standards Track [Page 1]
RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
Table of Contents
1. Introduction ....................................................2
1.1. Conventions and Acronyms ...................................3
2. ETSI DSR Front-end Codecs .......................................4
2.1. ES 202 050 Advanced DSR Front-end Codec ....................4
2.2. ES 202 211 Extended DSR Front-end Codec ....................4
2.3. ES 202 212 Extended Advanced DSR Front-end Codec ...........5
3. DSR RTP Payload Formats .........................................6
3.1. Common Considerations of the Three DSR RTP Payload
Formats ....................................................6
3.1.1. Number of FPs in Each RTP Packet ....................6
3.1.2. Support for Discontinuous Transmission ..............6
3.1.3. RTP Header Usage ....................................6
3.2. Payload Format for ES 202 050 DSR ..........................7
3.2.1. Frame Pair Formats ..................................7
3.3. Payload Format for ES 202 211 DSR ..........................9
3.3.1. Frame Pair Formats ..................................9
3.4. Payload Format for ES 202 212 DSR .........................11
3.4.1. Frame Pair Formats .................................12
4. IANA Considerations ............................................14
4.1. Mapping MIME Parameters into SDP ..........................15
4.2. Usage in Offer/Answer .....................................16
4.3. Congestion Control ........................................16
5. Security Considerations ........................................16
6. Acknowledgments ................................................16
7. References .....................................................16
7.1. Normative References ......................................16
7.2. Informative References ....................................17
1. Introduction
Distributed speech recognition (DSR) technology is intended for a
remote device acting as a thin client (a.k.a. the front-end) to
communicate with a speech recognition server (a.k.a. a speech
engine), over a network connection to obtain speech recognition
services. More details on DSR over Internet can be found in RFC 3557
[10].
To achieve interoperability with different client devices and speech
engines, the first ETSI standard DSR front-end ES 201 108 was
published in early 2000 [11]. An RTP packetization for ES 201 108
frames is defined in RFC 3557 [10] by IETF.
In ES 202 050 [1], ETSI issues another standard for an Advanced DSR
front-end that provides substantially improved recognition
performance when background noise is present. The codecs in ES 202
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RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
050 use a slightly different frame format from that of ES 201 108 and
thus the two do not inter-operate with each other.
The RTP packetization for ES 202 050 front-end defined in this
document uses the same RTP packet format layout as that defined in
RFC 3557 [10]. The differences are in the DSR codec frame bit
definition and the payload type MIME registration.
The two further standards, ES 202 211 and ES 202 212, provide
extensions to each of the DSR front-end standards. The extensions
allow the speech waveform to be reconstructed for human audition and
can also be used to improve recognition performance for tonal
languages. This is done by sending additional pitch and voicing
information for each frame along with the recognition features.
The RTP packet format for these extended standards is also defined in
this document.
It is worthwhile to note that the performance of most speech
recognizers are extremely sensitive to consecutive frame losses and
DSR speech recognizers are no exception. If a DSR over RTP session
is expected to endure high packet loss ratio between the front-end
and the speech engine, one should consider limiting the maximum
number of DSR frames allowed in a packet, or employing other loss
management techniques, such as FEC or interleaving, to minimize the
chance of losing consecutive frames.
1.1. Conventions and Acronyms
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
they appear in this document, are to be interpreted as described in
RFC 2119 [4].
The following acronyms are used in this document:
DSR - Distributed Speech Recognition
ETSI - the European Telecommunications Standards Institute
FP - Frame Pair
DTX - Discontinuous Transmission
VAD - Voice Activity Detection
Xie & Pearce Standards Track [Page 3]
RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
2. ETSI DSR Front-end Codecs
Some relevant characteristics of ES 202 050 Advanced, ES 202 211
Extended, and ES 202 212 Extended Advanced DSR front-end codecs are
summarized below.
2.1. ES 202 050 Advanced DSR Front-end Codec
The front-end calculation is a frame-based scheme that produces an
output vector every 10 ms. In the front-end feature extraction,
noise reduction by two stages of Wiener filtering is performed first.
Then, waveform processing is applied to the de-noised signal and
mel-cepstral features are calculated. At the end, blind equalization
is applied to the cepstral features. The front-end algorithm
produces at its output a mel-cepstral representation in the same
format as ES 210 108, i.e., 12 cepstral coefficients [C1 - C12], C0
and log Energy. Voice activity detection (VAD) for the
classification of each frame as speech or non-speech is also
implemented in Feature Extraction. The VAD information is included
in the payload format for each frame pair to be sent to the remote
recognition engine as part of the payload. This information may
optionally be used by the receiving recognition engine to drop
non-speech frames. The front-end supports three raw sampling rates:
8 kHz, 11 kHz, and 16 kHz (Note that unlike some other speech codecs,
the feature frame size of DSR presented to RTP packetization is not
dependent on the number of speech samples used in each 10 ms sample
frame. This will become more evident in the following sections).
After calculation of the mel-cepstral representation, the
representation is first quantized via split-vector quantization to
reduce the data rate of the encoded stream. Then, the quantized
vectors from two consecutive frames are put into a FP, as described
in more detail in Section 3.2.
2.2. ES 202 211 Extended DSR Front-end Codec
Some relevant characteristics of ES 202 211 Extended DSR front-end
codec are summarized below.
ES 202 211 is an extension of the mel-cepstrum DSR Front-end standard
ES 201 108 [11]. The mel-cepstrum front-end provides the features
for speech recognition but these are not available for human
listening. The purpose of the extension is allow the reconstruction
of the speech waveform from these features so that they can be
replayed. The front-end feature extraction part of the processing is
exactly the same as for ES 201 108. To allow speech reconstruction
additional fundamental frequency (perceived as pitch) and voicing
class (e.g., non-speech, voiced, unvoiced and mixed) information is
Xie & Pearce Standards Track [Page 4]
RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
needed. This extra information is provided by the extended front-end
processing algorithms at the device side. It is compressed and
transmitted along with the front-end features to the server. This
extra information may also be useful for improved speech recognition
performance with tonal languages such as Mandarin, Cantonese and
Thai.
Full information about the client side signal processing algorithms
used in the standard are described in the specification ES 202 211
[2].
The additional fundamental frequency and voicing class information is
compressed for each frame pair. The pitch for the first frame of the
FP is quantized to 7 bits and the second frame is differentially
quantized to 7 bits. The voicing class is indicated with one bit for
each frame. The total for the extension information for a frame pair
therefore consists of 14 bits plus an additional 2 bits of CRC error
protection computed over these extension bits only.
The total information for the frame pair is made up of 92 bits for
the two compressed front-end feature frames (including 4 bits for
their CRC) plus 16 bits for the extension (including 2 bits for their
CRC) and 4 bits of null padding to give a total of 14 octets per
frame pair. As for ES 201 208 the extended frame pair also
corresponds to 20ms of speech. The extended front-end supports three
raw sampling rates: 8 kHz, 11 kHz, and 16 kHz.
The quantized vectors from two consecutive frames are put into an FP,
as described in more detail in Section 3.3 below.
The parameters received at the remote server from the RTP extended
DSR payload specified here can be used to synthesize an intelligible
speech waveform for replay. The algorithms to do this are described
in the specification ES 202 211 [2].
2.3. ES 202 212 Extended Advanced DSR Front-end Codec
ES 202 212 is the extension for the DSR Advanced Front-end ES 202 050
[1]. It provides the same capabilities as the extended mel-cepstrum
front-end described in Section 2.2 but for the DSR Advanced
Front-end.
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RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
3. DSR RTP Payload Formats
3.1. Common Considerations of the Three DSR RTP Payload Formats
The three DSR RTP payload formats defined in this document share the
following consideration or behaviours.
3.1.1. Number of FPs in Each RTP Packet
Any number of FPs MAY be aggregate together in an RTP payload and
they MUST be consecutive in time. However, one SHOULD always keep
the RTP payload size smaller than the MTU in order to avoid IP
fragmentation and SHOULD follow the recommendations given in Section
3.1 in RFC 3557 [10] when determining the proper number of FPs in an
RTP payload.
3.1.2. Support for Discontinuous Transmission
Same considerations described in Section 3.2 of RFC 3557 [10] apply
to all the three DSR RTP payloads defined in this document.
3.1.3. RTP Header Usage
The format of the RTP header is specified in RFC 3550 [8]. The three
payload formats defined here use the fields of the header in a manner
consistent with that specification.
The RTP timestamp corresponds to the sampling instant of the first
sample encoded for the first FP in the packet. The timestamp clock
frequency is the same as the sampling frequency, so the timestamp
unit is in samples.
As defined by all three front-end codecs, the duration of one FP is
20 ms, corresponding to 160, 220, or 320 encoded samples with a
sampling rate of 8, 11, or 16 kHz being used at the front-end,
respectively. Thus, the timestamp is increased by 160, 220, or 320
for each consecutive FP, respectively.
The DSR payload for all three front-end codecs is always an integral
number of octets. If additional padding is required for some other
purpose, then the P bit in the RTP header may be set and padding
appended as specified in RFC 3550 [8].
The RTP header marker bit (M) MUST be set following the general rules
for audio codecs, as defined in Section 4.1 in RFC 3551 [9].
Xie & Pearce Standards Track [Page 6]
RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
This document does not specify the assignment of an RTP payload type
for these three new packet formats. It is expected that the RTP
profile under which any of these payload formats is being used will
assign a payload type for this encoding or will specify that the
payload type is to be bound dynamically.
3.2. Payload Format for ES 202 050 DSR
An ES 202 050 DSR RTP payload datagram uses exactly the same layout
as defined in Section 3 of RFC 3557 [10], i.e., a standard RTP header
followed by a DSR payload containing a series of DSR FPs.
The size of each ES 202 050 FP remains 96 bits or 12 octets, as
defined in the following sections. This ensures that a DSR RTP
payload will always end on an octet boundary.
3.2.1. Frame Pair Formats
3.2.1.1. Format of Speech and Non-speech FPs
The following mel-cepstral frame MUST be used, as defined in [1]:
Pairs of the quantized 10ms mel-cepstral frames MUST be grouped
together and protected with a 4-bit CRC forming a 92-bit long FP. At
the end, each FP MUST be padded with 4 zeros to the MSB 4 bits of the
last octet in order to make the FP aligned to the octet boundary.
The following diagram shows a complete ES 202 050 FP:
Frame #1 in FP:
===============
(MSB) (LSB)
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+-----+-----+-----+-----+
: idx(2,3) | idx(0,1) | Octet 1
+-----+-----+-----+-----+-----+-----+-----+-----+
: idx(4,5) | idx(2,3) (cont) : Octet 2
+-----+-----+-----+-----+-----+-----+-----+-----+
| idx(6,7) |idx(4,5)(cont) Octet 3
+-----+-----+-----+-----+-----+-----+-----+-----+
idx(10,11)| VAD | idx(8,9) | Octet 4
+-----+-----+-----+-----+-----+-----+-----+-----+
: idx(12,13) | idx(10,11) (cont) : Octet 5
+-----+-----+-----+-----+-----+-----+-----+-----+
| idx(12,13) (cont) : Octet 6/1
+-----+-----+-----+-----+
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RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
Frame #2 in FP:
===============
(MSB) (LSB)
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+
: idx(0,1) | Octet 6/2
+-----+-----+-----+-----+-----+-----+-----+-----+
| idx(2,3) |idx(0,1)(cont) Octet 7
+-----+-----+-----+-----+-----+-----+-----+-----+
: idx(6,7) | idx(4,5) | Octet 8
+-----+-----+-----+-----+-----+-----+-----+-----+
: idx(8,9) | idx(6,7) (cont) : Octet 9
+-----+-----+-----+-----+-----+-----+-----+-----+
| idx(10,11) | VAD |idx(8,9)(cont) Octet 10
+-----+-----+-----+-----+-----+-----+-----+-----+
| idx(12,13) | Octet 11
+-----+-----+-----+-----+-----+-----+-----+-----+
CRC for Frame #1 and Frame #2 and padding in FP:
================================================
(MSB) (LSB)
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+-----+-----+-----+-----+
| 0 | 0 | 0 | 0 | CRC | Octet 12
+-----+-----+-----+-----+-----+-----+-----+-----+
The 4-bit CRC in the FP MUST be calculated using the formula
(including the bit-order rules) defined in 7.2 in [1].
Therefore, each FP represents 20ms of original speech. Note that
each FP MUST be padded with 4 zeros to the MSB 4 bits of the last
octet in order to make the FP aligned to the octet boundary, as shown
above. This makes the total size of an FP 96 bits, or 12 octets.
Note that this padding is separate from padding indicated by the P
bit in the RTP header.
The definition of the indices and 'VAD' flag are described in [1] and
their value is only set and examined by the codecs in the front-end
client and the recognizer.
3.2.1.2. Format of Null FP
Null FPs are sent to mark the end of a transmission segment. Details
on transmission segment and the use of Null FPs can be found in RFC
3557 [10].
Xie & Pearce Standards Track [Page 8]
RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
A Null FP for the ES 202 050 front-end codec is defined by setting
the content of the first and second frame in the FP to null (i.e.,
filling the first 88 bits of the FP with zeros). The 4-bit CRC MUST
be calculated the same way as described in Section 7.2.4 of [1], and
4 zeros MUST be padded to the end of the Null FP in order to make it
aligned to the octet boundary.
3.3. Payload Format for ES 202 211 DSR
An ES 202 211 DSR RTP payload datagram is very similar to that
defined in Section 3 of RFC 3557 [10], i.e., a standard RTP header
followed by a DSR payload containing a series of DSR FPs.
The size of each ES 202 211 FP is 112 bits or 14 octets, as defined
in the following sections. This ensures that a DSR RTP payload will
always end on an octet boundary.
3.3.1. Frame Pair Formats
3.3.1.1. Format of Speech and Non-speech FPs
The following mel-cepstral frame MUST be used, as defined in Section
6.2.4 in [2]:
Immediately following two frames (Frame #1 and Frame #2) worth of
codebook indices (or 88 bits), there is a 4-bit CRC calculated on
these 88 bits. The pitch indices of the first frame (Pidx1: 7 bits)
and the second frame (Pidx2: 5 bits) of the frame pair then follow.
The class indices of the two frames in the frame pair worth 1 bit
each (Cidx1 and Cidx2) next follow. Finally, a 2-bit CRC calculated
on the pitch and class bits (total: 14 bits) of the frame pair is
included (PC-CRC). The total number of bits in a frame pair packet
is therefore 44 + 44 + 4 + 7 + 5 + 1 + 1 + 2 = 108. At the end, each
FP MUST be padded with 4 zeros to the MSB 4 bits of the last octet in
order to make the FP aligned to the octet boundary.
Xie & Pearce Standards Track [Page 9]
RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
The following diagram shows a complete ES 202 211 FP:
Frame #1 in FP:
===============
(MSB) (LSB)
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+-----+-----+-----+-----+
: idx(2,3) | idx(0,1) | Octet 1
+-----+-----+-----+-----+-----+-----+-----+-----+
: idx(4,5) | idx(2,3) (cont) : Octet 2
+-----+-----+-----+-----+-----+-----+-----+-----+
| idx(6,7) |idx(4,5)(cont) Octet 3
+-----+-----+-----+-----+-----+-----+-----+-----+
idx(10,11) | idx(8,9) | Octet 4
+-----+-----+-----+-----+-----+-----+-----+-----+
: idx(12,13) | idx(10,11) (cont) : Octet 5
+-----+-----+-----+-----+-----+-----+-----+-----+
| idx(12,13) (cont) : Octet 6/1
+-----+-----+-----+-----+
Frame #2 in FP:
===============
(MSB) (LSB)
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+
: idx(0,1) | Octet 6/2
+-----+-----+-----+-----+-----+-----+-----+-----+
| idx(2,3) |idx(0,1)(cont) Octet 7
+-----+-----+-----+-----+-----+-----+-----+-----+
: idx(6,7) | idx(4,5) | Octet 8
+-----+-----+-----+-----+-----+-----+-----+-----+
: idx(8,9) | idx(6,7) (cont) : Octet 9
+-----+-----+-----+-----+-----+-----+-----+-----+
| idx(10,11) |idx(8,9)(cont) Octet 10
+-----+-----+-----+-----+-----+-----+-----+-----+
| idx(12,13) | Octet 11
+-----+-----+-----+-----+-----+-----+-----+-----+
CRC for Frame #1 and Frame #2 in FP:
====================================
(MSB) (LSB)
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+
| CRC | Octet 12/1
+-----+-----+-----+-----+
Xie & Pearce Standards Track [Page 10]
RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
Extension information and padding in FP:
========================================
(MSB) (LSB)
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+
: Pidx1 | Octet 12/2
+-----+-----+-----+-----+-----+-----+-----+-----+
| Pidx2 | Pidx1 (cont) : Octet 13
+-----+-----+-----+-----+-----+-----+-----+-----+
| 0 | 0 | 0 | 0 | PC-CRC |Cidx2|Cidx1| Octet 14
+-----+-----+-----+-----+-----+-----+-----+-----+
The 4-bit CRC and the 2-bit PC-CRC in the FP MUST be calculated using
the formula (including the bit-order rules) defined in 6.2.4 in [2].
Therefore, each FP represents 20ms of original speech. Note, as
shown above, each FP MUST be padded with 4 zeros to the MSB 4 bits of
the last octet in order to make the FP aligned to the octet boundary.
This makes the total size of an FP 112 bits, or 14 octets. Note,
this padding is separate from padding indicated by the P bit in the
RTP header.
3.3.1.2. Format of Null FP
A Null FP for the ES 202 211 front-end codec is defined by setting
all the 112 bits of the FP with zeros. Null FPs are sent to mark the
end of a transmission segment. Details on transmission segment and
the use of Null FPs can be found in RFC 3557 [10].
3.4. Payload Format for ES 202 212 DSR
Similar to other ETSI DSR front-end encoding schemes, the encoded DSR
feature stream of ES 202 212 is transmitted in a sequence of FPs,
where each FP represents two consecutive original voice frames.
An ES 202 212 DSR RTP payload datagram is very similar to that
defined in Section 3 of RFC 3557 [10], i.e., a standard RTP header
followed by a DSR payload containing a series of DSR FPs.
The size of each ES 202 212 FP is 112 bits or 14 octets, as defined
in the following sections. This ensures that an ES 202 212 DSR RTP
payload will always end on an octet boundary.
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RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
3.4.1. Frame Pair Formats
3.4.1.1. Format of Speech and Non-speech FPs
The following mel-cepstral frame MUST be used, as defined in Section
7.2.4 of [3]:
Immediately following two frames (Frame #1 and Frame #2) worth of
codebook indices (or 88 bits), there is a 4-bit CRC calculated on
these 88 bits. The pitch indices of the first frame (Pidx1: 7 bits)
and the second frame (Pidx2: 5 bits) of the frame pair then follow.
The class indices of the two frames in the frame pair worth 1 bit
each next follow (Cidx1 and Cidx2). Finally, a 2-bit CRC (PC-CRC)
calculated on the pitch and class bits (total: 14 bits) of the frame
pair is included. The total number of bits in frame pair packet is
therefore 44 + 44 + 4 + 7 + 5 + 1 + 1 + 2 = 108. At the end, each FP
MUST be padded with 4 zeros to the MSB 4 bits of the last octet in
order to make the FP aligned to the octet boundary. The padding
brings the total size of a FP to 112 bits, or 14 octets. Note that
this padding is separate from padding indicated by the P bit in the
RTP header.
The following diagram shows a complete ES 202 212 FP:
Frame #1 in FP:
===============
(MSB) (LSB)
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+-----+-----+-----+-----+
: idx(2,3) | idx(0,1) | Octet 1
+-----+-----+-----+-----+-----+-----+-----+-----+
: idx(4,5) | idx(2,3) (cont) : Octet 2
+-----+-----+-----+-----+-----+-----+-----+-----+
| idx(6,7) |idx(4,5)(cont) Octet 3
+-----+-----+-----+-----+-----+-----+-----+-----+
idx(10,11)| VAD | idx(8,9) | Octet 4
+-----+-----+-----+-----+-----+-----+-----+-----+
: idx(12,13) | idx(10,11) (cont) : Octet 5
+-----+-----+-----+-----+-----+-----+-----+-----+
| idx(12,13) (cont) : Octet 6/1
+-----+-----+-----+-----+
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RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
Frame #2 in FP:
===============
(MSB) (LSB)
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+
: idx(0,1) | Octet 6/2
+-----+-----+-----+-----+-----+-----+-----+-----+
| idx(2,3) |idx(0,1)(cont) Octet 7
+-----+-----+-----+-----+-----+-----+-----+-----+
: idx(6,7) | idx(4,5) | Octet 8
+-----+-----+-----+-----+-----+-----+-----+-----+
: idx(8,9) | idx(6,7) (cont) : Octet 9
+-----+-----+-----+-----+-----+-----+-----+-----+
| idx(10,11) | VAD |idx(8,9)(cont) Octet 10
+-----+-----+-----+-----+-----+-----+-----+-----+
| idx(12,13) | Octet 11
+-----+-----+-----+-----+-----+-----+-----+-----+
CRC for Frame #1 and Frame #2 in FP:
====================================
(MSB) (LSB)
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+
| CRC | Octet 12/1
+-----+-----+-----+-----+
Extension information and padding in FP:
========================================
(MSB) (LSB)
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+
: Pidx1 | Octet 12/2
+-----+-----+-----+-----+-----+-----+-----+-----+
| Pidx2 | Pidx1 (cont) : Octet 13
+-----+-----+-----+-----+-----+-----+-----+-----+
| 0 | 0 | 0 | 0 | PC-CRC |Cidx2|Cidx1| Octet 14
+-----+-----+-----+-----+-----+-----+-----+-----+
The codebook indices, VAD flag, pitch index, and class index are
specified in Section 6 of [3]. The 4-bit CRC and the 2-bit PC-CRC in
the FP MUST be calculated using the formula (including the bit-order
rules) defined in 7.2.4 in [3].
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RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
3.4.1.2. Format of Null FP
A Null FP for the ES 202 212 front-end codec is defined by setting
all 112 bits of the FP with zeros. Null FPs are sent to mark the end
of a transmission segment. Details on transmission segments and the
use of Null FPs can be found in RFC 3557 [10].
4. IANA Considerations
For each of the three ETSI DSR front-end codecs covered in this
document, a new MIME subtype registration has been registered by the
IANA for the corresponding payload type, as described below.
Media Type name: audio
Media subtype names:
dsr-es202050 (for ES 202 050 front-end)
dsr-es202211 (for ES 202 211 front-end)
dsr-es202212 (for ES 202 212 front-end)
Required parameters: none
Optional parameters:
rate: Indicates the sample rate of the speech. Valid values include:
8000, 11000, and 16000. If this parameter is not present, 8000
sample rate is assumed.
maxptime: see RFC 3267 [7]. If this parameter is not present,
maxptime is assumed to be 80ms.
Note, since the performance of most speech recognizers are
extremely sensitive to consecutive FP losses, if the user of the
payload format expects a high packet loss ratio for the session,
it MAY consider to explicitly choose a maxptime value for the
session that is shorter than the default value.
ptime: see RFC 2327 [5].
Encoding considerations: These types are defined for transfer via RTP
[8] as described in Section 3 of RFC 4060.
Security considerations: See Section 5 of RFC 4060.
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RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
Person & email address to contact for further information:
Qiaobing.Xie@motorola.com
Intended usage: COMMON. It is expected that many VoIP applications
(as well as mobile applications) will use this type.
Author: Qiaobing.Xie@motorola.com
Change controller: IETF Audio/Video transport working group
4.1. Mapping MIME Parameters into SDP
The information carried in the MIME media type specification has a
specific mapping to fields in the Session Description Protocol (SDP)
[5], which is commonly used to describe RTP sessions. When SDP is
used to specify sessions employing ES 202 050, ES 202 211, or ES 202
212 DSR codec, the mapping is as follows:
o The MIME type ("audio") goes in SDP "m=" as the media name.
o The MIME subtype ("dsr-es202050", "dsr-es202211", or
"dsr-es202212") goes in SDP "a=rtpmap" as the encoding name.
o The optional parameter "rate" also goes in "a=rtpmap" as clock
rate. If no rate is given, then the default value (i.e., 8000) is
used in SDP.
o The optional parameters "ptime" and "maxptime" go in the SDP
"a=ptime" and "a=maxptime" attributes, respectively.
Example of usage of ES 202 050 DSR:
m=audio 49120 RTP/AVP 101
a=rtpmap:101 dsr-es202050/8000
a=maxptime:40
Example of usage of ES 202 211 DSR:
m=audio 49120 RTP/AVP 101
a=rtpmap:101 dsr-es202211/8000
a=maxptime:40
Example of usage of ES 202 212 DSR:
m=audio 49120 RTP/AVP 101
a=rtpmap:101 dsr-es202212/8000
a=maxptime:40
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RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
4.2. Usage in Offer/Answer
All SDP parameters in this payload format are declarative, and all
reasonable values are expected to be supported. Thus, the standard
usage of Offer/Answer as described in RFC 3264 [6] should be
followed.
4.3. Congestion Control
Congestion control for RTP MUST be used in accordance with RFC 3550
[8], and in any applicable RTP profile, e.g., RFC 3551 [9].
5. Security Considerations
Implementations using the payload defined in this specification are
subject to the security considerations discussed in the RTP
specification RFC 3550 [8] and any RTP profile, e.g., RFC 3551 [9].
This payload does not specify any different security services.
6. Acknowledgments
The design presented here is based on that of RFC 3557 [10]. The
authors wish to thank Magnus Westerlund and others for their reviews
and comments.
7. References
7.1. Normative References
[1] European Telecommunications Standards Institute (ETSI) Standard
ES 202 050, "Speech Processing, Transmission and Quality
Aspects (STQ); Distributed Speech Recognition; Advanced Front-
end Feature Extraction Algorithm; Compression Algorithms",
http://pda.etsi.org/pda/.
[2] European Telecommunications Standards Institute (ETSI) Standard
ES 202 211, "Speech Processing, Transmission and Quality
Aspects (STQ); Distributed Speech Recognition; Extended front-
end feature extraction algorithm; Compression algorithms; Back-
end speech reconstruction algorithm", http://pda.etsi.org/pda/.
[3] European Telecommunications Standards Institute (ETSI) Standard
ES 202 212, "Speech Processing, Transmission and Quality
aspects (STQ); Distributed speech recognition; Extended
advanced front-end feature extraction algorithm; Compression
algorithms; Back-end speech reconstruction algorithm",
http://pda.etsi.org/pda/.
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RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[5] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998.
[6] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
the Session Description Protocol (SDP)", RFC 3264, June 2002.
[7] Sjoberg, J., Westerlund, M., Lakaniemi, A., and Q. Xie,
"Real-Time Transport Protocol (RTP) Payload Format and File
Storage Format for the Adaptive Multi-Rate (AMR) and Adaptive
Multi-Rate Wideband (AMR-WB) Audio Codecs", RFC 3267,
June 2002.
[8] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications", STD 64,
RFC 3550, July 2003.
[9] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
Conferences with Minimal Control", STD 65, RFC 3551, July 2003.
[10] Xie, Q., "RTP Payload Format for European Telecommunications
Standards Institute (ETSI) European Standard ES 201 108
Distributed Speech Recognition Encoding", RFC 3557, July 2003.
7.2. Informative References
[11] European Telecommunications Standards Institute (ETSI) Standard
ES 201 108, "Speech Processing, Transmission and Quality
Aspects (STQ); Distributed Speech Recognition; Front-end
Feature Extraction Algorithm; Compression Algorithms",
http://pda.etsi.org/pda/.
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RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
Authors' Addresses
Qiaobing Xie
Motorola, Inc.
1501 W. Shure Drive, 2-F9
Arlington Heights, IL 60004
US
Phone: +1-847-632-3028
EMail: qxie1@email.mot.com
David Pearce
Motorola Labs
UK Research Laboratory
Jays Close
Viables Industrial Estate
Basingstoke, HANTS RG22 4PD
UK
Phone: +44 (0)1256 484 436
EMail: bdp003@motorola.com
Xie & Pearce Standards Track [Page 18]
RFC 4060 RTP Payloads for ETSI DSR Codecs May 2005
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Xie & Pearce Standards Track [Page 19]