RFC 4060
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
RFC 4060: 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 💖
Okay bestie, first the basics 🎀 This one comes from the Network Working Group. Q. Xie and D. Pearce, both at Motorola, wrote it in May 2005. It's on the Standards Track, so it's an actual Internet standard, not just an opinion 👑 Its title block doesn't have any Obsoletes or Updates lines, so it doesn't replace or change any other RFC 💅
Status of This Memo ✨
This document is an Internet standards track protocol for the Internet community, and it asks for discussion and suggestions for improvements. For the standardization state and status of this protocol, check the current edition of the "Internet Official Protocol Standards" (STD 1). Distribution of this memo is unlimited 🌸
Copyright Notice 🦋
Copyright (C) The Internet Society (2005).
Abstract 🧚
This doc is all about RTP payload formats for wrapping up the 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. These are for distributed speech recognition (DSR) systems, and they're giving main character energy 🔥
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 ....................................171. Introduction 🎀
Distributed speech recognition (DSR) is for a remote device acting as a thin client (a.k.a. the front-end) that talks to a speech recognition server (a.k.a. a speech engine) over a network connection to get speech recognition services. You can find more details on DSR over the Internet in RFC 3557 [10] 💅
To get interoperability between different client devices and speech engines, the first ETSI standard DSR front-end, ES 201 108, was published in early 2000 [11]. The IETF defined an RTP packetization for ES 201 108 frames in RFC 3557 [10] ✨
ES 202 050 [1] is another ETSI standard, this time for an Advanced DSR front-end that gives much better recognition performance when there's background noise. The codecs in ES 202 050 use a slightly different frame format from ES 201 108, so the two don't inter-operate with each other 🙈
The RTP packetization for the ES 202 050 front-end defined in this document uses the same RTP packet format layout as RFC 3557 [10]. The differences are in the DSR codec frame bit definition and the payload type MIME registration 🦋
ES 202 211 and ES 202 212 are two more standards, and they add extensions to each of the DSR front-end standards. The extensions let the speech waveform be reconstructed for human listening, and they can also improve recognition performance for tonal languages. They do this by sending extra 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 🫶
Okay, real talk, the performance of most speech recognizers is extremely sensitive to consecutive frame losses, and DSR speech recognizers are no exception 💀 If a DSR over RTP session is expected to endure a 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. Another option is 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 Detection2. ETSI DSR Front-end Codecs 🧚
Here are some relevant characteristics of the ES 202 050 Advanced, ES 202 211 Extended, and ES 202 212 Extended Advanced DSR front-end codecs 🍓
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 front-end feature extraction, noise reduction by two stages of Wiener filtering happens 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 a mel-cepstral representation at its output, in the same format as ES 210 108. That means 12 cepstral coefficients [C1 - C12], C0, and log Energy ✨ Voice activity detection (VAD), which classifies 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, and it's sent to the remote recognition engine as part of the payload. The receiving recognition engine may optionally use this information 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 the mel-cepstral representation is calculated, it's 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 FP, as described in more detail in Section 3.2 🫶
2.2. ES 202 211 Extended DSR Front-end Codec 🌈
Here are some relevant characteristics of the ES 202 211 Extended DSR front-end codec 🎀
ES 202 211 is an extension of the mel-cepstrum DSR Front-end standard ES 201 108 [11]. The mel-cepstrum front-end provides features for speech recognition, but those features aren't available for human listening. The purpose of the extension is to allow the reconstruction of the speech waveform from these features, so 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, extra fundamental frequency (perceived as pitch) and voicing class information (e.g., non-speech, voiced, unvoiced, and mixed) are needed. This extra information is provided by the extended front-end processing algorithms on the device side. It's compressed and sent 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 is 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. So the total extension information for a frame pair is 14 bits, plus an extra 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), plus 4 bits of null padding. That gives 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 gives you the same capabilities as the extended mel-cepstrum 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 considerations and 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. One SHOULD also 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 🌈
The same considerations described in Section 3.2 of RFC 3557 [10] apply to all three DSR RTP payloads defined in this document ✨
3.1.3. RTP Header Usage ✨
okay so the RTP header format is specced in RFC 3550 [8] 🎀, and all three payload formats use its fields in a way that is totally consistent with that spec. no notes 💅
The RTP timestamp points at the sampling instant of the first sample encoded for the first FP in the packet 🕰️. The timestamp clock frequency matches the sampling frequency, so the timestamp unit is in samples 🦋.
All three front-end codecs make one FP last 20 ms 🌈. That's 160, 220, or 320 encoded samples at a sampling rate of 8, 11, or 16 kHz (used at the front-end, respectively) 💖. So the timestamp goes up by 160, 220, or 320 for each consecutive FP, respectively. the math is giving clean 🙈
The DSR payload for all three front-end codecs is always a whole number of octets 🫶. If extra padding is needed for some other reason, 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]. 🔥
This document does not assign 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 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]. In other words, it's a standard RTP header followed by a DSR payload full of DSR FPs 🧚.
Each ES 202 050 FP stays at 96 bits, or 12 octets, as defined in the sections below. This makes sure a DSR RTP payload always ends on an octet boundary. so clean 🍓
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, which makes a 92-bit long FP. At the end, each FP MUST be padded with 4 zeros in the MSB 4 bits of the last octet, so the FP lines up on 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
+-----+-----+-----+-----+
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]. 🧮
So each FP represents 20ms of original speech 🎧. Note that each FP MUST be padded with 4 zeros in the MSB 4 bits of the last octet so it lines up on the octet boundary, as shown above. That makes the total size of an FP 96 bits, or 12 octets. Also, this padding is separate from the padding indicated by the P bit in the RTP header, so don't mix them up 🙈.
The definitions of the indices and the 'VAD' flag are described in [1]. Their values are 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 segments and the use of Null FPs can be found in RFC 3557 [10] 📚.
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 so it's 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 the one defined in Section 3 of RFC 3557 [10]. So again, it's a standard RTP header followed by a DSR payload with a series of DSR FPs 🦋.
Each ES 202 211 FP is 112 bits, or 14 octets, as defined in the sections below. This makes sure a DSR RTP payload always ends 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]:
Right after the two frames' worth of codebook indices (Frame #1 and Frame #2, which is 88 bits total), there's a 4-bit CRC calculated on those 88 bits 🔐. Then come the pitch indices: Pidx1 (7 bits) from the first frame and Pidx2 (5 bits) from the second frame of the frame pair. Next up are the class indices, where each of the two frames gets 1 bit (Cidx1 and Cidx2). Last but not least, there's a 2-bit CRC calculated on the pitch and class bits (14 bits total) of the frame pair, called 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 in the MSB 4 bits of the last octet so the FP lines up on the octet boundary 💖.
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
+-----+-----+-----+-----+
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]. 🧠
So each FP represents 20ms of original speech 🎶. Just like before, each FP MUST be padded with 4 zeros in the MSB 4 bits of the last octet so it lines up on the octet boundary, as shown above. That makes the total size of an FP 112 bits, or 14 octets. And yes, this padding is separate from the 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 112 bits of the FP to 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] 📮.
3.4. Payload Format for ES 202 212 DSR 🌈
Just like the other ETSI DSR front-end encoding schemes, the encoded DSR feature stream of ES 202 212 gets sent 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 the one defined in Section 3 of RFC 3557 [10]. Again, that's a standard RTP header followed by a DSR payload containing a series of DSR FPs ✨.
Each ES 202 212 FP is 112 bits, or 14 octets, as defined in the sections below. This makes sure an ES 202 212 DSR RTP payload always ends on an octet boundary 👑.
3.4.1. Frame Pair Formats 💅
3.4.1.1. Format of Speech and Non-speech FPs ✨
okay bestie, this is where the frame pair (FP) actually gets built 🧚 The following mel-cepstral frame MUST be used, as defined in Section 7.2.4 of [3]:
So the layout goes like this: two frames' worth of codebook indices come first (88 bits total), followed immediately by a 4-bit CRC calculated on those 88 bits. Then you get the pitch indices, Pidx1 (7 bits) for frame one and Pidx2 (5 bits) for frame two. The class indices come next, 1 bit each for the two frames (Cidx1 and Cidx2). Finally there's a 2-bit PC-CRC, calculated over the pitch and class bits (14 bits total) 💅
Let's do the math real quick: 44 + 44 + 4 + 7 + 5 + 1 + 1 + 2 = 108, so the frame pair packet has 108 bits total. Then each FP MUST be padded with 4 zeros to the MSB 4 bits of the last octet, so the FP lines up on the octet boundary 🦋 That padding brings the FP up to 112 bits, or 14 octets. Also, this padding is totally separate from the padding the P bit in the RTP header tells you about, so don't mix them up 🙈
Here's the full ES 202 212 FP, broken down piece by piece:
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
+-----+-----+-----+-----+
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 all 112 bits of the FP to zeros. Null FPs are sent to mark the end of a transmission segment. You can find the details on transmission segments and how Null FPs are used in RFC 3557 [10] ✨
4. IANA Considerations 🌸
okay so IANA registered a new MIME subtype for each of the three ETSI DSR front-end codecs covered in this document, one for each corresponding payload type. Here's the registration template:
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.
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 group4.1. Mapping MIME Parameters into SDP 🎀
The MIME media type info has a specific mapping onto fields in the Session Description Protocol (SDP) [5], which is what people usually use to describe RTP sessions. When SDP is used to specify sessions that employ the ES 202 050, ES 202 211, or ES 202 212 DSR codec, the mapping works like this:
- The MIME type ("audio") goes in SDP "m=" as the media name.
- The MIME subtype ("dsr-es202050", "dsr-es202211", or "dsr-es202212") goes in SDP "a=rtpmap" as the encoding name.
- 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.
- 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:40Example of usage of ES 202 211 DSR:
m=audio 49120 RTP/AVP 101
a=rtpmap:101 dsr-es202211/8000
a=maxptime:40Example of usage of ES 202 212 DSR:
m=audio 49120 RTP/AVP 101
a=rtpmap:101 dsr-es202212/8000
a=maxptime:404.2. 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 💀
Okay, this one is serious, so listen up 🙈 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. Thank you so much to them 💖
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/.
[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/.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.comFull Copyright Statement 💖
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📦 where this page comes from
- ietf: rfc4060 2005-05
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms