Audio Video Transport WG Q. Xie
Internet-Draft D. Pearce
Expires: December 16, 2004 Motorola
June 17, 2004
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
draft-ietf-avt-rtp-dsr-codecs-03.txt
Status of this Memo
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance with
RFC 3668.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on December 16, 2004.
Abstract
This document specifies RTP payload formats for encapsulating ETSI
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 Expires December 16, 2004 [Page 1]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
Table of Contents
1. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1 ETSI ES 202 050 Advanced DSR Front-end Codec . . . . . . . 4
2.2 ETSI ES 202 211 Extended DSR Front-end Codec . . . . . . . 4
2.3 ETSI 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 ES 202 212 DSR . . . . . . . . . . . . . . 11
3.4.1 Frame Pair Formats . . . . . . . . . . . . . . . . . . 11
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
4.1 Mapping MIME Parameters into SDP . . . . . . . . . . . . . 15
4.2 Usage in Offer/Answer . . . . . . . . . . . . . . . . . . 16
5. Security Considerations . . . . . . . . . . . . . . . . . . . 16
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.1 Normative References . . . . . . . . . . . . . . . . . . . . 16
7.2 Informative References . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . . 19
Xie & Pearce Expires December 16, 2004 [Page 2]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
1. Conventions
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 [5].
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
2. Introduction
Distributed speech recognition (DSR) technology is intended for a
remote device acting as a thin client, also known as the front-end,
to communicate with a speech recognition server, also called a speech
engine, over a network connection to obtain speech recognition
services. More details on DSR over Internet can be found in RFC 3557
[11].
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 [12], and an RTP packetization for ES 201 108
frames is defined in RFC 3557 [11] 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
050 uses 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 [11]. 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, provided
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.
Xie & Pearce Expires December 16, 2004 [Page 3]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
The RTP packet format for these extended standards are 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
the 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.
2.1 ETSI ES 202 050 Advanced DSR Front-end Codec
Some relevant characteristics of ES 202 050 Advanced DSR front-end
codec are summarized below.
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 coeffients [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 (It is worthwhile to 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 an frame pair (FP),
as described in more detail in Section 3.2 below.
2.2 ETSI ES 202 211 Extended DSR Front-end Codec
Some relevant characteristics of ES 202 211 Extended DSR front-end
codec are summarized below.
Xie & Pearce Expires December 16, 2004 [Page 4]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
ES 202 211 is an extension of the mel-cepstrum DSR Front-end standard
ES 201 108 [12]. 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
needed. This is the extra information that is provided by the
extended front-end processing algorithms at the device side that 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 quantised to 7 bits and the second frame is differentially
quantized with 5 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 and 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 ETSI 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
Xie & Pearce Expires December 16, 2004 [Page 5]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
front-end described in section 2.2 but for the DSR Advanced
Front-end.
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 [11] 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 [11] 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 [9]. 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 the three front-end codecs, the duration of one FP
is 20 ms, corresponding to 160, 220, or 320 encoded samples with
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 these 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 in the header may be
set and padding appended as specified in RFC 3550 [9].
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 [10].
Xie & Pearce Expires December 16, 2004 [Page 6]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
The assignment of an RTP payload type for these three new packet
formats is outside the scope of this document, and will not be
specified here. 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 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 [11], 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 is still 96 bits or 12 octets (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]:
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
+-----+-----+-----+-----+
Xie & Pearce Expires December 16, 2004 [Page 7]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
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, 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 96 bits, or 12 octets. Note, 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 [11].
A Null FP for the ES 202 050 front-end codec is defined by setting
Xie & Pearce Expires December 16, 2004 [Page 8]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
the content of the first and second frame in the FP to null (i.e.,
filling the first 88 bits of the FP with 0's). The 4-bit CRC MUST be
calculated the same way as described in 7.2.4 in [1], and 4 zeros
MUST be padded to the end of the Null FP to made it octet aligned.
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 [11], 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 (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]:
As defined in Section 6.2.4 in [2], after two frames (Frame #1 and
Frame #2) worth of codebook indices, or 88 bits, a 4-bit CRC
calculated on these 88 bits immediately follows it. 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 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 following diagram shows a complete ES 202 211 FP:
Xie & Pearce Expires December 16, 2004 [Page 9]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
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 Expires December 16, 2004 [Page 10]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
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 0's. 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 [11].
3.4 Payload Format 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 frame
pairs (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 [11], 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 (defined in
the following sections). This ensures that an ES 202 212 DSR RTP
payload will always end on an octet boundary.
3.4.1 Frame Pair Formats
Xie & Pearce Expires December 16, 2004 [Page 11]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
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 in [3]:
As defined in Section 7.2.4 in [3], after two frames (Frame #1 and
Frame #2) worth of codebook indices, or 88 bits, a 4-bit CRC
calculated on these 88 bits immediately follows it. 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, 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
+-----+-----+-----+-----+
Xie & Pearce Expires December 16, 2004 [Page 12]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
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].
3.4.1.2 Format of Null FP
A Null FP for the ES 202 212 front-end codec is defined by setting
Xie & Pearce Expires December 16, 2004 [Page 13]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
all the 112 bits of the FP with 0's. 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 [11].
4. IANA Considerations
For each of the three ETSI DSR front-end codecs covered in this
document, a new MIME subtype registration is required 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 [8]. 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 [6].
Encoding considerations: These types are defined for transfer via RTP
[9] as described in Section 3 of RFC XXXX.
Security considerations: See Section 5 of RFC XXXX.
Person & email address to contact for further information:
Qiaobing.Xie@motorola.com
Xie & Pearce Expires December 16, 2004 [Page 14]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
Intended usage: COMMON. It is expected that many VoIP applications
(as well as mobile applications) will use this type.
Author/Change controller:
* Qiaobing.Xie@motorola.com
* 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)
[6], 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
Xie & Pearce Expires December 16, 2004 [Page 15]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
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 [7] should be
followed.
5. Security Considerations
Implementations using the payload defined in this specification are
subject to the security considerations discussed in the RTP
specification RFC 3550 [9] and any RTP profile, e.g. RFC 3551 [10].
This payload does not specify any different security services.
Congestion control for RTP MUST be used in accordance with RFC 3550
[9], and any applicable RTP profile, e.g. RFC 3551 [10].
6. Acknowledgments
The design presented here is based on that of RFC 3557 [11]. The
authors wish to thank for the review and comments from Magnus
Westerlund and others.
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; Front-end
Feature Extraction Algorithm; Compression Algorithms", (http://
pda.etsi.org/pda/) , October 2002.
[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/) , November 2003.
[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/) , November 2003.
[4] Bradner, S., "The Internet Standards Process -- Revision 3",
Xie & Pearce Expires December 16, 2004 [Page 16]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
BCP 9, RFC 2026, October 1996.
[5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[6] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998.
[7] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
the Session Description Protocol (SDP)", RFC 3264, June 2002.
[8] 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.
[9] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications", RFC
3550, July 2003.
[10] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
Conferences with Minimal Control", RFC 3551, July 2003.
[11] 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
[12] 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://
webapp.etsi.org/pda/) , April 2000.
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
Xie & Pearce Expires December 16, 2004 [Page 17]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
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 Expires December 16, 2004 [Page 18]
Internet-Draft RTP Payloads for ETSI DSR Codecs June 2004
Intellectual Property Statement
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 BCP 78 and BCP 79.
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
http://www.ietf.org/ipr.
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.
Disclaimer of Validity
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 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.
Full Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Xie & Pearce Expires December 16, 2004 [Page 19]
