-AVT Working Group L. Barbato
-Internet-Draft Xiph
-Expires: August 20, 2008 Feb 17, 2008
- RTP Payload Format for Vorbis Encoded Audio
- draft-ietf-avt-rtp-vorbis-09
-
-Status of This Memo
-
- By submitting this Internet-Draft, each author represents that any
- applicable patent or other IPR claims of which he or she is aware
- have been or will be disclosed, and any of which he or she becomes
- aware will be disclosed, in accordance with Section 6 of BCP 79.
- 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.
+Network Working Group L. Barbato
+Request for Comments: 5215 Xiph
+Category: Standards Track August 2008
- 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 August 20, 2008.
+ RTP Payload Format for Vorbis Encoded Audio
-Copyright Notice
+Status of This Memo
- Copyright (C) The IETF Trust (2008).
+ 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.
Abstract
This document describes an RTP payload format for transporting Vorbis
encoded audio. It details the RTP encapsulation mechanism for raw
- Vorbis data and details the delivery mechanisms for the decoder
- probability model, referred to as a codebook and other setup
+ Vorbis data and the delivery mechanisms for the decoder probability
+ model (referred to as a codebook), as well as other setup
information.
- Also included within this memo are media type registrations, and the
+ Also included within this memo are media type registrations and the
details necessary for the use of Vorbis with the Session Description
Protocol (SDP).
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-Editors Note
- All references to RFC XXXX are to be replaced by references to the
- RFC number of this memo, when published.
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Table of Contents
2.1. RTP Header . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Payload Header . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Payload Data . . . . . . . . . . . . . . . . . . . . . . . 6
- 2.4. Example RTP Packet . . . . . . . . . . . . . . . . . . . . 7
+ 2.4. Example RTP Packet . . . . . . . . . . . . . . . . . . . . 8
3. Configuration Headers . . . . . . . . . . . . . . . . . . . . 8
3.1. In-band Header Transmission . . . . . . . . . . . . . . . 9
- 3.1.1. Packed Configuration . . . . . . . . . . . . . . . . . 9
- 3.2. Out of Band Transmission . . . . . . . . . . . . . . . . . 11
- 3.2.1. Packed Headers . . . . . . . . . . . . . . . . . . . . 11
- 3.3. Loss of Configuration Headers . . . . . . . . . . . . . . 12
- 4. Comment Headers . . . . . . . . . . . . . . . . . . . . . . . 12
- 5. Frame Packetization . . . . . . . . . . . . . . . . . . . . . 13
- 5.1. Example Fragmented Vorbis Packet . . . . . . . . . . . . . 14
- 5.2. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 16
- 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
- 6.1. Packed Headers IANA Considerations . . . . . . . . . . . . 18
- 7. SDP related considerations . . . . . . . . . . . . . . . . . . 19
+ 3.1.1. Packed Configuration . . . . . . . . . . . . . . . . . 10
+ 3.2. Out of Band Transmission . . . . . . . . . . . . . . . . . 12
+ 3.2.1. Packed Headers . . . . . . . . . . . . . . . . . . . . 12
+ 3.3. Loss of Configuration Headers . . . . . . . . . . . . . . 13
+ 4. Comment Headers . . . . . . . . . . . . . . . . . . . . . . . 13
+ 5. Frame Packetization . . . . . . . . . . . . . . . . . . . . . 14
+ 5.1. Example Fragmented Vorbis Packet . . . . . . . . . . . . . 15
+ 5.2. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 17
+ 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
+ 6.1. Packed Headers IANA Considerations . . . . . . . . . . . . 19
+ 7. SDP Related Considerations . . . . . . . . . . . . . . . . . . 20
7.1. Mapping Media Type Parameters into SDP . . . . . . . . . . 20
- 7.1.1. SDP Example . . . . . . . . . . . . . . . . . . . . . 20
- 7.2. Usage with the SDP Offer/Answer Model . . . . . . . . . . 21
- 8. Congestion Control . . . . . . . . . . . . . . . . . . . . . . 21
- 9. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
- 9.1. Stream Radio . . . . . . . . . . . . . . . . . . . . . . . 21
- 10. Security Considerations . . . . . . . . . . . . . . . . . . . 22
- 11. Copying Conditions . . . . . . . . . . . . . . . . . . . . . . 22
- 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22
- 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
- 13.1. Normative References . . . . . . . . . . . . . . . . . . . 23
- 13.2. Informative References . . . . . . . . . . . . . . . . . . 23
+ 7.1.1. SDP Example . . . . . . . . . . . . . . . . . . . . . 21
+ 7.2. Usage with the SDP Offer/Answer Model . . . . . . . . . . 22
+ 8. Congestion Control . . . . . . . . . . . . . . . . . . . . . . 22
+ 9. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
+ 9.1. Stream Radio . . . . . . . . . . . . . . . . . . . . . . . 22
+ 10. Security Considerations . . . . . . . . . . . . . . . . . . . 23
+ 11. Copying Conditions . . . . . . . . . . . . . . . . . . . . . . 23
+ 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
+ 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
+ 13.1. Normative References . . . . . . . . . . . . . . . . . . . 24
+ 13.2. Informative References . . . . . . . . . . . . . . . . . . 25
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1. Introduction
Vorbis is a general purpose perceptual audio codec intended to allow
maximum encoder flexibility, thus allowing it to scale competitively
- over an exceptionally wide range of bitrates. At the high quality/
+ over an exceptionally wide range of bit rates. At the high quality/
bitrate end of the scale (CD or DAT rate stereo, 16/24 bits), it is
in the same league as MPEG-4 AAC. Vorbis is also intended for lower
and higher sample rates (from 8kHz telephony to 192kHz digital
discrete channels).
Vorbis encoded audio is generally encapsulated within an Ogg format
- bitstream [11], which provides framing and synchronization. For the
- purposes of RTP transport, this layer is unnecessary, and so raw
+ bitstream [RFC3533], which provides framing and synchronization. For
+ the purposes of RTP transport, this layer is unnecessary, and so raw
Vorbis packets are used in the payload.
1.1. Conformance and Document Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
- document are to be interpreted as described in BCP 14, [1] and
+ document are to be interpreted as described in BCP 14, [RFC2119] and
indicate requirement levels for compliant implementations.
Requirements apply to all implementations unless otherwise stated.
2. Payload Format
- For RTP based transport of Vorbis encoded audio the standard RTP
- header is followed by a 4 octets payload header, then the payload
+ For RTP-based transport of Vorbis-encoded audio, the standard RTP
+ header is followed by a 4-octet payload header, and then the payload
data. The payload headers are used to associate the Vorbis data with
- its associated decoding codebooks as well as indicating if the
+ its associated decoding codebooks as well as indicate if the
following packet contains fragmented Vorbis data and/or the number of
whole Vorbis data frames. The payload data contains the raw Vorbis
- bitstream information. There are 3 types of Vorbis data, an RTP
+ bitstream information. There are 3 types of Vorbis data; an RTP
payload MUST contain just one of them at a time.
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2.1. RTP Header
- The format of the RTP header is specified in [2] and shown in Figure
+ The format of the RTP header is specified in [RFC3550] and shown in
Figure 1. This payload format uses the fields of the header in a
manner consistent with that specification.
-
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: RTP Header
The RTP header begins with an octet of fields (V, P, X, and CC) to
- support specialized RTP uses (see [2] and [3] for details). For
- Vorbis RTP, the following values are used.
+ support specialized RTP uses (see [RFC3550] and [RFC3551] for
+ details). For Vorbis RTP, the following values are used.
Version (V): 2 bits
Padding (P): 1 bit
- Padding MAY be used with this payload format according to section 5.1
- of [2].
+ Padding MAY be used with this payload format according to Section 5.1
+ of [RFC3550].
Extension (X): 1 bit
- The Extension bit is used in accordance with [2].
+ The Extension bit is used in accordance with [RFC3550].
CSRC count (CC): 4 bits
- The CSRC count is used in accordance with [2].
+ The CSRC count is used in accordance with [RFC3550].
Marker (M): 1 bit
- Set to zero. Audio silence suppression not used. This conforms to
- section 4.1 of [10].
+ Set to zero. Audio silence suppression is not used. This conforms
+ to Section 4.1 of [VORBIS-SPEC-REF].
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Payload Type (PT): 7 bits
An RTP profile for a class of applications is expected to assign a
payload type for this format, or a dynamically allocated payload type
- SHOULD be chosen which designates the payload as Vorbis.
+ SHOULD be chosen that designates the payload as Vorbis.
Sequence number: 16 bits
The sequence number increments by one for each RTP data packet sent,
and may be used by the receiver to detect packet loss and to restore
- packet sequence. This field is detailed further in [2].
+ the packet sequence. This field is detailed further in [RFC3550].
Timestamp: 32 bits
A timestamp representing the sampling time of the first sample of the
first Vorbis packet in the RTP payload. The clock frequency MUST be
set to the sample rate of the encoded audio data and is conveyed out-
- of-band (e.g. as an SDP parameter).
+ of-band (e.g., as an SDP parameter).
SSRC/CSRC identifiers:
These two fields, 32 bits each with one SSRC field and a maximum of
- 16 CSRC fields, are as defined in [2].
+ 16 CSRC fields, are as defined in [RFC3550].
2.2. Payload Header
The 4 octets following the RTP Header section are the Payload Header.
- This header is split into a number of bitfields detailing the format
+ This header is split into a number of bit fields detailing the format
of the following payload data packets.
0 1 2 3
Ident: 24 bits
- This 24 bit field is used to associate the Vorbis data to a decoding
- Configuration. It is stored as network byte order integer.
+ This 24-bit field is used to associate the Vorbis data to a decoding
+ Configuration. It is stored as a network byte order integer.
Fragment type (F): 2 bits
- This field is set according to the following list
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+ This field is set according to the following list:
0 = Not Fragmented
+
1 = Start Fragment
+
2 = Continuation Fragment
+
3 = End Fragment
Vorbis Data Type (VDT): 2 bits
This field specifies the kind of Vorbis data stored in this RTP
packet. There are currently three different types of Vorbis
payloads. Each packet MUST contain only a single type of Vorbis
- packet (e.g. you must not aggregate configuration and comment packets
- in the same RTP payload)
+ packet (e.g., you must not aggregate configuration and comment
+ packets in the same RTP payload).
0 = Raw Vorbis payload
+
1 = Vorbis Packed Configuration payload
+
2 = Legacy Vorbis Comment payload
+
3 = Reserved
- The packets with a VDT of value 3 MUST be ignored
+ The packets with a VDT of value 3 MUST be ignored.
The last 4 bits represent the number of complete packets in this
payload. This provides for a maximum number of 15 Vorbis packets in
- the payload. If the payload contains fragmented data the number of
+ the payload. If the payload contains fragmented data, the number of
packets MUST be set to 0.
2.3. Payload Data
- Raw Vorbis packets are currently unbounded in length, application
+ Raw Vorbis packets are currently unbounded in length; application
profiles will likely define a practical limit. Typical Vorbis packet
sizes range from very small (2-3 bytes) to quite large (8-12
- kilobytes). The reference implementation [12] typically produces
- packets less than ~800 bytes, except for the setup header packets
- which are ~4-12 kilobytes. Within an RTP context, to avoid
+ kilobytes). The reference implementation [LIBVORBIS] typically
+ produces packets less than ~800 bytes, except for the setup header
+ packets, which are ~4-12 kilobytes. Within an RTP context, to avoid
fragmentation, the Vorbis data packet size SHOULD be kept
sufficiently small so that after adding the RTP and payload headers,
the complete RTP packet is smaller than the path MTU.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Each Vorbis payload packet starts with a two octet length header,
which is used to represent the size in bytes of the following data
- payload, followed by the raw Vorbis data padded to the nearest byte
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- boundary, as explained by the vorbis specification [10]. The length
- value is stored as network byte order integer.
+ payload, and is followed by the raw Vorbis data padded to the nearest
+ byte boundary, as explained by the Vorbis I Specification
+ [VORBIS-SPEC-REF]. The length value is stored as a network byte
+ order integer.
- For payloads which consist of multiple Vorbis packets the payload
+ For payloads that consist of multiple Vorbis packets, the payload
data consists of the packet length followed by the packet data for
each of the Vorbis packets in the payload.
block only and does not include the length field.
The payload packing of the Vorbis data packets MUST follow the
- guidelines set-out in [3] where the oldest Vorbis packet occurs
- immediately after the RTP packet header. Subsequent Vorbis packets,
- if any, MUST follow in temporal order.
+ guidelines set out in [RFC3551], where the oldest Vorbis packet
+ occurs immediately after the RTP packet header. Subsequent Vorbis
+ packets, if any, MUST follow in temporal order.
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+ Audio channel mapping is in accordance with the Vorbis I
+ Specification [VORBIS-SPEC-REF].
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- Channel mapping of the audio is in accordance with the Vorbis I
- Specification [10].
2.4. Example RTP Packet
.. vorbis data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 4: Example Raw Vorbis Packet
- The payload data section of the RTP packet begins with the 24 bit
- Ident field followed by the one octet bitfield header, which has the
+ The payload data section of the RTP packet begins with the 24-bit
+ Ident field followed by the one octet bit field header, which has the
number of Vorbis frames set to 2. Each of the Vorbis data frames is
prefixed by the two octets length field. The Packet Type and
Fragment Type are set to 0. The Configuration that will be used to
3. Configuration Headers
- Unlike other mainstream audio codecs Vorbis has no statically
+ Unlike other mainstream audio codecs, Vorbis has no statically
configured probability model. Instead, it packs all entropy decoding
configuration, Vector Quantization and Huffman models into a data
- block that must be transmitted to the decoder along with the
- compressed data. A decoder also requires information detailing the
- number of audio channels, bitrates and similar information to
- configure itself for a particular compressed data stream. These two
- blocks of information are often referred to collectively as the
- "codebooks" for a Vorbis stream, and are nominally included as
- special "header" packets at the start of the compressed data. In
- addition, the Vorbis I specification [10] requires the presence of a
- comment header packet which gives simple metadata about the stream,
- but this information is not required for decoding the frame sequence.
-
- Thus these two codebook header packets must be received by the
- decoder before any audio data can be interpreted. These requirements
- pose problems in RTP, which is often used over unreliable transports.
-
- Since this information must be transmitted reliably and, as the RTP
- stream may change certain configuration data mid-session, there are
- different methods for delivering this configuration data to a client,
- both in-band and out-of-band which is detailed below. In order to
- set up an initial state for the client application the configuration
- MUST be conveyed via the signalling channel used to setup the
- session. One example of such signalling is SDP [5] with the Offer/
- Answer Model [8]. Changes to the configuration MAY be communicated
- via a re-invite, conveying new SDP, or sent in-band in the RTP
- channel. Implementations MUST support in-band delivery of updated
- codebooks, and SHOULD support out-of-band codebook update using a new
- SDP file. The changes may be due to different codebooks as well as
- different bitrates of the RTP stream.
+ block that must be transmitted to the decoder with the compressed
+ data. A decoder also requires information detailing the number of
+ audio channels, bitrates, and similar information to configure itself
+ for a particular compressed data stream. These two blocks of
- For non chained streams, the recommended Configuration delivery
- method is inline the Packed Configuration (Section 3.1.1) in the SDP
- as explained in the IANA considerations (Section 7.1).
- The 24 bit Ident field is used to map which Configuration will be
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+ information are often referred to collectively as the "codebooks" for
+ a Vorbis stream, and are included as special "header" packets at the
+ start of the compressed data. In addition, the Vorbis I
+ specification [VORBIS-SPEC-REF] requires the presence of a comment
+ header packet that gives simple metadata about the stream, but this
+ information is not required for decoding the frame sequence.
+ Thus, these two codebook header packets must be received by the
+ decoder before any audio data can be interpreted. These requirements
+ pose problems in RTP, which is often used over unreliable transports.
+ Since this information must be transmitted reliably and, as the RTP
+ stream may change certain configuration data mid-session, there are
+ different methods for delivering this configuration data to a client,
+ both in-band and out-of-band, which are detailed below. In order to
+ set up an initial state for the client application, the configuration
+ MUST be conveyed via the signalling channel used to set up the
+ session. One example of such signalling is SDP [RFC4566] with the
+ Offer/Answer Model [RFC3264]. Changes to the configuration MAY be
+ communicated via a re-invite, conveying a new SDP, or sent in-band in
+ the RTP channel. Implementations MUST support an in-band delivery of
+ updated codebooks, and SHOULD support out-of-band codebook update
+ using a new SDP file. The changes may be due to different codebooks
+ as well as different bitrates of the RTP stream.
+
+ For non-chained streams, the recommended Configuration delivery
+ method is inside the Packed Configuration (Section 3.1.1) in the SDP
+ as explained the Mapping Media Type Parameters into SDP
+ (Section 7.1).
+
+ The 24-bit Ident field is used to map which Configuration will be
used to decode a packet. When the Ident field changes, it indicates
that a change in the stream has taken place. The client application
- MUST have in advance the correct configuration and if the client
+ MUST have in advance the correct configuration. If the client
detects a change in the Ident value and does not have this
- information it MUST NOT decode the raw Vorbis data associated until
+ information, it MUST NOT decode the raw associated Vorbis data until
it fetches the correct Configuration.
3.1. In-band Header Transmission
The Packed Configuration (Section 3.1.1) Payload is sent in-band with
the packet type bits set to match the Vorbis Data Type. Clients MUST
be capable of dealing with fragmentation and periodic re-transmission
- of [14] the configuration headers. The RTP timestamp value MUST
+ of [RFC4588] the configuration headers. The RTP timestamp value MUST
reflect the transmission time of the first data packet for which this
configuration applies.
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3.1.1. Packed Configuration
A Vorbis Packed Configuration is indicated with the Vorbis Data Type
field set to 1. Of the three headers defined in the Vorbis I
- specification [10], the Identification and the Setup MUST be packed
- as they are, while the comment header MAY be replaced with a dummy
- one.
+ specification [VORBIS-SPEC-REF], the Identification and the Setup
+ MUST be packed as they are, while the Comment header MAY be replaced
+ with a dummy one.
- The packed configuration follows a generic way to store Xiph codec
- configurations: The first field stores the number of the following
+ The packed configuration stores Xiph codec configurations in a
+ generic way: the first field stores the number of the following
packets minus one (count field), the next ones represent the size of
- the headers (length fields), the headers immediately follow the list
- of length fields. The size of the last header is implicit.
+ the headers (length fields), and the headers immediately follow the
+ list of length fields. The size of the last header is implicit.
The count and the length fields are encoded using the following
- logic: the data is in network byte order, every byte has the most
- significant bit used as flag and the following 7 used to store the
- value. The first N bit are to be taken, where N is number of bits
- needed to represent the value, taken modulo 7, and stored in the
- first byte. If there are more bits, the flag bit is set to 1 and the
- subsequent 7bit are stored in the following byte, if there are
- remaining bits set the flag to 1 and the same procedure is repeated.
- The ending byte has the flag bit set to 0. In order to decode it is
- enough to iterate over the bytes until the flag bit set to 0, for
- every byte the data is added to the accumulated value multiplied by
+ logic: the data is in network byte order; every byte has the most
+ significant bit used as a flag, and the following 7 bits are used to
+ store the value. The first 7 most significant bits are stored in the
+ first byte. If there are remaining bits, the flag bit is set to 1
+ and the subsequent 7 bits are stored in the following byte. If there
+ are remaining bits, set the flag to 1 and the same procedure is
+ repeated. The ending byte has the flag bit set to 0. To decode,
+ simply iterate over the bytes until the flag bit is set to 0. For
+ every byte, the data is added to the accumulated value multiplied by
128.
- The headers are packed in the same order they are present in ogg:
- Identification, Comment, Setup.
+ The headers are packed in the same order as they are present in Ogg
+ [VORBIS-SPEC-REF]: Identification, Comment, Setup.
The 2 byte length tag defines the length of the packed headers as the
- sum of the Configuration, Comment and Setup lengths.
+ sum of the Configuration, Comment, and Setup lengths.
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0 1 2 3
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Ident | 1 | 0 | 0|
+ | Ident | 0 | 1 | 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| length | n. of headers | length1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Ident field is set with the value that will be used by the Raw
Payload Packets to address this Configuration. The Fragment type is
- set to 0 since the packet bears the full Packed configuration, the
- number of packet is set to 1.
+ set to 0 because the packet bears the full Packed configuration. The
+ number of the packet is set to 1.
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+RFC 5215 Vorbis RTP Payload Format August 2008
3.2. Out of Band Transmission
The following packet definition MUST be used when Configuration is
- inlined in the SDP.
+ inside in the SDP.
3.2.1. Packed Headers
- As mentioned above the RECOMMENDED delivery vector for Vorbis
+ As mentioned above, the RECOMMENDED delivery vector for Vorbis
configuration data is via a retrieval method that can be performed
using a reliable transport protocol. As the RTP headers are not
- required for this method of delivery the structure of the
+ required for this method of delivery, the structure of the
configuration data is slightly different. The packed header starts
- with a 32 bit (network byte ordered) count field which details the
- number of packed headers that are contained in the bundle. Next is
- the Packed header payload for each chained Vorbis stream.
+ with a 32-bit (network-byte ordered) count field, which details the
+ number of packed headers that are contained in the bundle. The
+ following shows the Packed header payload for each chained Vorbis
+ stream.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of packed headers |
-
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0 1 2 3
Figure 7: Packed Headers Detail
- The key difference between the in-band format and this one, is that
- there is no need for the payload header octet. In this figure the
+ The key difference between the in-band format and this one is that
+ there is no need for the payload header octet. In this figure, the
comment has a size bigger than 127 bytes.
3.3. Loss of Configuration Headers
Unlike the loss of raw Vorbis payload data, loss of a configuration
- header lead to a situation where it will not be possible to
+ header leads to a situation where it will not be possible to
successfully decode the stream. Implementations MAY try to recover
- from error by requesting again the missing Configuration or, if the
- delivery method is in-band, by buffering the payloads waiting for the
- Configuration needed to decode them. The baseline reaction SHOULD be
- either reset or end the RTP session.
+ from an error by requesting again the missing Configuration or, if
+ the delivery method is in-band, by buffering the payloads waiting for
+ the Configuration needed to decode them. The baseline reaction
+ SHOULD either be reset or end the RTP session.
4. Comment Headers
- With the Vorbis Data Type flag set to 2, this indicates that the
- packet contain the comment metadata, such as artist name, track title
- and so on. These metadata messages are not intended to be fully
- descriptive but to offer basic track/song information. Clients MAY
- ignore it completely. The details on the format of the comments can
- be found in the Vorbis documentation [10].
+ Vorbis Data Type flag set to 2 indicates that the packet contains the
+ comment metadata, such as artist name, track title, and so on. These
+ metadata messages are not intended to be fully descriptive but rather
+ to offer basic track/song information. Clients MAY ignore it
+ completely. The details on the format of the comments can be found
+ in the Vorbis I Specification [VORBIS-SPEC-REF].
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0 1 2 3
Figure 8: Comment Packet
- The 2 bytes length field is necessary since this packet could be
+ The 2-byte length field is necessary since this packet could be
fragmented.
5. Frame Packetization
- Each RTP payload contains either one Vorbis packet fragment, or an
+ Each RTP payload contains either one Vorbis packet fragment or an
integer number of complete Vorbis packets (up to a maximum of 15
- packets, since the number of packets is defined by a 4 bit value).
+ packets, since the number of packets is defined by a 4-bit value).
Any Vorbis data packet that is less than path MTU SHOULD be bundled
in the RTP payload with as many Vorbis packets as will fit, up to a
maximum of 15, except when such bundling would exceed an
application's desired transmission latency. Path MTU is detailed in
- [6] and [7].
+ [RFC1191] and [RFC1981].
A fragmented packet has a zero in the last four bits of the payload
header. The first fragment will set the Fragment type to 1. Each
fragment after the first will set the Fragment type to 2 in the
payload header. The consecutive fragments MUST be sent without any
- other payloads being sent between the first and the last fragment.
+ other payload being sent between the first and the last fragment.
The RTP payload containing the last fragment of the Vorbis packet
will have the Fragment type set to 3. To maintain the correct
- sequence for fragmented packet reception the timestamp field of
+ sequence for fragmented packet reception, the timestamp field of
fragmented packets MUST be the same as the first packet sent, with
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the sequence number incremented as normal for the subsequent RTP
- payloads, this will affect the RTCP jitter measurement. The length
+ payloads; this will affect the RTCP jitter measurement. The length
field shows the fragment length.
5.1. Example Fragmented Vorbis Packet
- Here is an example fragmented Vorbis packet split over three RTP
+ Here is an example of a fragmented Vorbis packet split over three RTP
payloads. Each of them contains the standard RTP headers as well as
- the 4 octets Vorbis headers.
+ the 4-octet Vorbis headers.
Packet 1:
Figure 9: Example Fragmented Packet (Packet 1)
- In this payload the initial sequence number is 1000 and the timestamp
- is 12345. The Fragment type is set to 1, the number of packets field
- is set to 0, and as the payload is raw Vorbis data the VDT field is
- set to 0.
+ In this payload, the initial sequence number is 1000 and the
+ timestamp is 12345. The Fragment type is set to 1, the number of
+ packets field is set to 0, and as the payload is raw Vorbis data, the
+ VDT field is set to 0.
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Packet 2:
Figure 10: Example Fragmented Packet (Packet 2)
- The Fragment type field is set to 2 and the number of packets field
- is set to 0. For large Vorbis fragments there can be several of this
- type of payloads. The maximum packet size SHOULD be no greater than
- the path MTU, including all RTP and payload headers. The sequence
- number has been incremented by one but the timestamp field remains
- the same as the initial payload.
+ The Fragment type field is set to 2, and the number of packets field
+ is set to 0. For large Vorbis fragments, there can be several of
+ these types of payloads. The maximum packet size SHOULD be no
+ greater than the path MTU, including all RTP and payload headers.
+ The sequence number has been incremented by one, but the timestamp
+ field remains the same as the initial payload.
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Packet 3:
This is the last Vorbis fragment payload. The Fragment type is set
to 3 and the packet count remains set to 0. As in the previous
- payloads the timestamp remains set to the first payload timestamp in
+ payloads, the timestamp remains set to the first payload timestamp in
the sequence and the sequence number has been incremented.
5.2. Packet Loss
As there is no error correction within the Vorbis stream, packet loss
will result in a loss of signal. Packet loss is more of an issue for
fragmented Vorbis packets as the client will have to cope with the
- handling of the Fragment Type. In case of loss of fragments the
+ handling of the Fragment Type. In case of loss of fragments, the
client MUST discard all the remaining Vorbis fragments and decode the
incomplete packet. If we use the fragmented Vorbis packet example
- above and the first RTP payload is lost the client MUST detect that
+ above and the first RTP payload is lost, the client MUST detect that
the next RTP payload has the packet count field set to 0 and the
Fragment type 2 and MUST drop it. The next RTP payload, which is the
final fragmented packet, MUST be dropped in the same manner. If the
- missing RTP payload is the last, the received two fragments will be
+ missing RTP payload is the last, the two fragments received will be
kept and the incomplete Vorbis packet decoded.
Loss of any of the Configuration fragment will result in the loss of
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6. IANA Considerations
Required parameters:
rate: indicates the RTP timestamp clock rate as described in RTP
- Profile for Audio and Video Conferences with Minimal Control.
- [3]
+ Profile for Audio and Video Conferences with Minimal Control
+ [RFC3551].
channels: indicates the number of audio channels as described in
RTP Profile for Audio and Video Conferences with Minimal
- Control. [3]
+ Control [RFC3551].
- configuration: the base64 [9] representation of the Packed
+ configuration: the base64 [RFC4648] representation of the Packed
Headers (Section 3.2.1).
Encoding considerations:
Security considerations:
- See Section 10 of RFC XXXX.
+ See Section 10 of RFC 5215.
Interoperability considerations:
Published specification:
- RFC XXXX [RFC Editor: please replace by the RFC number of this
- memo, when published]
+ RFC 5215
Ogg Vorbis I specification: Codec setup and packet decode.
- Available from the Xiph website, http://xiph.org
+ Available from the Xiph website, http://xiph.org/
Applications which use this media type:
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+
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Person & email address to contact for further information:
- Luca Barbato: <lu_zero@gentoo.org> IETF Audio/Video Transport
- Working Group
+ Luca Barbato: <lu_zero@gentoo.org>
+ IETF Audio/Video Transport Working Group
Intended usage:
Restriction on usage:
- This media type depends on RTP framing, and hence is only defined
- for transfer via RTP [2]
+ This media type depends on RTP framing, hence is only defined for
+ transfer via RTP [RFC3550].
Author:
IETF AVT Working Group delegated from the IESG
-
6.1. Packed Headers IANA Considerations
The following IANA considerations refers to the split configuration
- Packed Headers (Section 3.2.1) used within RFC XXXX.
+ Packed Headers (Section 3.2.1) used within RFC 5215.
Type name: audio
This media type contains binary data.
+ Security considerations:
+ See Section 10 of RFC 5215.
-
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-
-
- Security considerations:
+RFC 5215 Vorbis RTP Payload Format August 2008
- See Section 10 of RFC XXXX.
Interoperability considerations:
Published specification:
- RFC XXXX [RFC Editor: please replace by the RFC number of this
- memo, when published]
+ RFC 5215
Applications which use this media type:
- Vorbis encoded audio, configuration data.
+ Vorbis encoded audio, configuration data
Additional information:
IETF AVT Working Group delegated from the IESG
-7. SDP related considerations
+7. SDP Related Considerations
The following paragraphs define the mapping of the parameters
described in the IANA considerations section and their usage in the
- Offer/Answer Model [8]. In order to be forward compatible the
+ Offer/Answer Model [RFC3264]. In order to be forward compatible, the
implementation MUST ignore unknown parameters.
+7.1. Mapping Media Type Parameters into SDP
+ The information carried in the Media Type specification has a
+ specific mapping to fields in the Session Description Protocol (SDP)
+ [RFC4566], which is commonly used to describe RTP sessions. When SDP
+ is used to specify sessions, the mapping are as follows:
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-
-
-7.1. Mapping Media Type Parameters into SDP
+RFC 5215 Vorbis RTP Payload Format August 2008
- The information carried in the 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 the mapping are as follows:
o The type name ("audio") goes in SDP "m=" as the media name.
o The subtype name ("vorbis") goes in SDP "a=rtpmap" as the encoding
name.
- o The parameter "rate" also goes in "a=rtpmap" as clock rate.
+ o The parameter "rate" also goes in "a=rtpmap" as the clock rate.
- o The parameter "channels" also goes in "a=rtpmap" as channel count.
+ o The parameter "channels" also goes in "a=rtpmap" as the channel
+ count.
o The mandated parameters "configuration" MUST be included in the
SDP "a=fmtp" attribute.
-
If the stream comprises chained Vorbis files and all of them are
known in advance, the Configuration Packet for each file SHOULD be
passed to the client using the configuration attribute.
The port value is specified by the server application bound to the
address specified in the c= line. The channel count value specified
in the rtpmap attribute SHOULD match the current Vorbis stream or
- considered the maximum number of channels to be expected. The
- timestamp clock rate MUST be a multiple of the sample rate, different
- payload number MUST be used if the clock rate changes. The
+ should be considered the maximum number of channels to be expected.
+ The timestamp clock rate MUST be a multiple of the sample rate; a
+ different payload number MUST be used if the clock rate changes. The
Configuration payload delivers the exact information, thus the SDP
- information SHOULD be considered as a hint. An example is found
- below.
+ information SHOULD be considered a hint. An example is found below.
7.1.1. SDP Example
The following example shows a basic SDP single stream. The first
- configuration packet is inlined in the SDP, other configurations
- could be fetched at any time from the URIs provided. The inline
- base64 [9] configuration string is folded in this example due to RFC
+ configuration packet is inside the SDP; other configurations could be
+ fetched at any time from the URIs provided. The following base64
+ [RFC4648] configuration string is folded in this example due to RFC
line length limitations.
+
c=IN IP4 192.0.2.1
+
m=audio RTP/AVP 98
+
a=rtpmap:98 vorbis/44100/2
+
a=fmtp:98 configuration=AAAAAZ2f4g9NAh4aAXZvcmJpcwA...;
Note that the payload format (encoding) names are commonly shown in
- upper case. Media Type subtypes are commonly shown in lower case.
+ uppercase. Media Type subtypes are commonly shown in lowercase.
+ These names are case-insensitive in both places. Similarly,
+ parameter names are case-insensitive both in Media Type types and in
+ the default mapping to the SDP a=fmtp attribute. The a=fmtp line is
+
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- These names are case-insensitive in both places. Similarly,
- parameter names are case-insensitive both in Media Type types and in
- the default mapping to the SDP a=fmtp attribute. The a=fmtp line is
- a single line even if it is shown as multiple lines in this document
+ a single line, even if it is shown as multiple lines in this document
for clarity.
7.2. Usage with the SDP Offer/Answer Model
- The are no negotiable parameters. All the of them are declarative.
+ There are no negotiable parameters. All of them are declarative.
8. Congestion Control
The general congestion control considerations for transporting RTP
- data apply to vorbis audio over RTP as well. See the RTP
- specification [2] and any applicable RTP profile (e.g., [3]). Audio
- data can be encoded using a range of different bit rates, so it is
- possible to adapt network bandwidth by adjusting the encoder bit rate
- in real time or by having multiple copies of content encoded at
- different bit rates.
+ data apply to Vorbis audio over RTP as well. See the RTP
+ specification [RFC3550] and any applicable RTP profile (e.g.,
+ [RFC3551]). Audio data can be encoded using a range of different bit
+ rates, so it is possible to adapt network bandwidth by adjusting the
+ encoder bit rate in real time or by having multiple copies of content
+ encoded at different bit rates.
9. Example
The following example shows a common usage pattern that MAY be
- applied in such situation, the main scope of this section is to
+ applied in such a situation. The main scope of this section is to
explain better usage of the transmission vectors.
9.1. Stream Radio
- This is one of the most common situation: one single server streaming
- content in multicast, the clients may start a session at random time.
- The content itself could be a mix of live stream, as the webjockey's
- voice, and stored streams as the music she plays.
+ This is one of the most common situations: there is one single server
+ streaming content in multicast, and the clients may start a session
+ at a random time. The content itself could be a mix of a live stream
+ (as the webjockey's voice) and stored streams (as the music she
+ plays).
- In this situation we don't know in advance how many codebooks we will
- use. The clients can join anytime and users expect to start
+ In this situation, we don't know in advance how many codebooks we
+ will use. The clients can join anytime and users expect to start
listening to the content in a short time.
- On join the client will receive the current Configuration necessary
- to decode the current stream inlined in the SDP so that the decoding
- will start immediately after.
+ Upon joining, the client will receive the current Configuration
+ necessary to decode the current stream inside the SDP so that the
+ decoding will start immediately after.
- When the streamed content changes the new Configuration is sent in-
- band before the actual stream and the Configuration that has to be
- sent inline in the SDP updated. Since the in-band method is
- unreliable, an out of band fallback is provided.
+ When the streamed content changes, the new Configuration is sent in-
+ band before the actual stream, and the Configuration that has to be
+ sent inside the SDP is updated. Since the in-band method is
+ unreliable, an out-of-band fallback is provided.
The client may choose to fetch the Configuration from the alternate
source as soon as it discovers a Configuration packet got lost in-
+ band, or use selective retransmission [RFC3611] if the server
+ supports this feature.
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+RFC 5215 Vorbis RTP Payload Format August 2008
- band or use selective retransmission [13], if the server supports the
- feature.
+ A server-side optimization would be to keep a hash list of the
+ Configurations per session, which avoids packing all of them and
+ sending the same Configuration with different Ident tags.
- A serverside optimization would be to keep an hash list of the
- Configurations per session to avoid packing all of them and send the
- same Configuration with different Ident tags
-
- A clientside optimization would be to keep a tag list of the
- Configurations per session and don't process configuration packets
- already known.
+ A client-side optimization would be to keep a tag list of the
+ Configurations per session and not process configuration packets that
+ are already known.
10. Security Considerations
RTP packets using this payload format are subject to the security
- considerations discussed in the RTP specification [2], the base64
- specification [9] and the URI Generic syntax specification [4].
- Among other considerations, this implies that the confidentiality of
- the media stream is archieved by using encryption. Because the data
- compression used with this payload format is applied end-to-end,
- encryption may be performed on the compressed data.
+ considerations discussed in the RTP specification [RFC3550], the
+ base64 specification [RFC4648], and the URI Generic syntax
+ specification [RFC3986]. Among other considerations, this implies
+ that the confidentiality of the media stream is achieved by using
+ encryption. Because the data compression used with this payload
+ format is applied end-to-end, encryption may be performed on the
+ compressed data.
11. Copying Conditions
The authors agree to grant third parties the irrevocable right to
- copy, use and distribute the work, with or without modification, in
+ copy, use, and distribute the work, with or without modification, in
any medium, without royalty, provided that, unless separate
permission is granted, redistributed modified works do not contain
misleading author, version, name of work, or endorsement information.
12. Acknowledgments
- This document is a continuation of draft-moffitt-vorbis-rtp-00.txt
- and draft-kerr-avt-vorbis-rtp-04.txt. The Media Type declaration is
- a continuation of draft-short-avt-rtp-vorbis-mime-00.txt.
+ This document is a continuation of the following documents:
+
+ Moffitt, J., "RTP Payload Format for Vorbis Encoded Audio", February
+ 2001.
+
+ Kerr, R., "RTP Payload Format for Vorbis Encoded Audio", December
+ 2004.
+
+ The Media Type declaration is a continuation of the following
+ document:
+
+ Short, B., "The audio/rtp-vorbis MIME Type", January 2008.
Thanks to the AVT, Vorbis Communities / Xiph.Org Foundation including
Steve Casner, Aaron Colwell, Ross Finlayson, Fluendo, Ramon Garcia,
Pascal Hennequin, Ralph Giles, Tor-Einar Jarnbjo, Colin Law, John
Lazzaro, Jack Moffitt, Christopher Montgomery, Colin Perkins, Barry
Short, Mike Smith, Phil Kerr, Michael Sparks, Magnus Westerlund,
- David Barrett, Silvia Pfeiffer, Stefan Ehmann, Alessandro Salvatori.
- Politecnico di Torino (LS)^3/IMG Group in particular Federico
- Ridolfo, Francesco Varano, Giampaolo Mancini, Dario Gallucci, Juan
- Carlos De Martin.
-
-13. References
+ David Barrett, Silvia Pfeiffer, Stefan Ehmann, Gianni Ceccarelli, and
+Barbato Standards Track [Page 23]
+\f
+RFC 5215 Vorbis RTP Payload Format August 2008
-Barbato Expires August 20, 2008 [Page 22]
-\f
-Internet-Draft Vorbis RTP Payload Format Feb 2008
+ Alessandro Salvatori. Thanks to the LScube Group, in particular
+ Federico Ridolfo, Francesco Varano, Giampaolo Mancini, Dario
+ Gallucci, and Juan Carlos De Martin.
+13. References
13.1. Normative References
- [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
- Levels", RFC 2119.
+ [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery",
+ RFC 1191, November 1990.
- [2] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
- "RTP: A Transport Protocol for real-time applications", STD 64,
- RFC 3550.
+ [RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU
+ Discovery for IP version 6", RFC 1981,
+ August 1996.
- [3] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
- Conferences with Minimal Control.", STD 65, RFC 3551.
+ [RFC2119] Bradner, S., "Key words for use in RFCs to
+ Indicate Requirement Levels", BCP 14, RFC 2119,
+ March 1997.
- [4] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
- Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986.
+ [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer
+ Model with Session Description Protocol (SDP)",
+ RFC 3264, June 2002.
- [5] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
- Description Protocol", RFC 4566, July 2006.
+ [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
+ Jacobson, "RTP: A Transport Protocol for Real-Time
+ Applications", STD 64, RFC 3550, July 2003.
- [6] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
- November 1990.
+ [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for
+ Audio and Video Conferences with Minimal Control",
+ STD 65, RFC 3551, July 2003.
- [7] McCann et al., J., "Path MTU Discovery for IP version 6",
- RFC 1981.
+ [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
+ "Uniform Resource Identifier (URI): Generic
+ Syntax", STD 66, RFC 3986, January 2005.
- [8] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
- Session Description Protocol (SDP)", RFC 3264.
+ [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP:
+ Session Description Protocol", RFC 4566,
+ July 2006.
- [9] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
- RFC 3548.
+ [RFC4648] Josefsson, S., "The Base16, Base32, and Base64
+ Data Encodings", RFC 4648, October 2006.
+
+ [VORBIS-SPEC-REF] "Ogg Vorbis I specification: Codec setup and
+ packet decode. Available from the Xiph website,
+ http://xiph.org/vorbis/doc/Vorbis_I_spec.html".
- [10] "Ogg Vorbis I specification: Codec setup and packet decode.
- Available from the Xiph website,
- http://xiph.org/vorbis/doc/Vorbis_I_spec.html".
-13.2. Informative References
- [11] Pfeiffer, S., "The Ogg Encapsulation Format Version 0",
- RFC 3533.
- [12] "libvorbis: Available from the dedicated website,
- http://vorbis.com".
- [13] Friedman, T., Caceres, R., and A. Clark, "RTP Control Protocol
- Extended Reports (RTCP XR)", RFC 3611, November 2003.
- [14] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. Hakenberg,
- "RTP Retransmission Payload Format", RFC 4588, July 2006.
+Barbato Standards Track [Page 24]
+\f
+RFC 5215 Vorbis RTP Payload Format August 2008
+13.2. Informative References
+ [LIBVORBIS] "libvorbis: Available from the dedicated website,
+ http://vorbis.com/".
-Barbato Expires August 20, 2008 [Page 23]
-\f
-Internet-Draft Vorbis RTP Payload Format Feb 2008
+ [RFC3533] Pfeiffer, S., "The Ogg Encapsulation Format
+ Version 0", RFC 3533, May 2003.
+ [RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP
+ Control Protocol Extended Reports (RTCP XR)",
+ RFC 3611, November 2003.
+
+ [RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
+ Hakenberg, "RTP Retransmission Payload Format",
+ RFC 4588, July 2006.
Author's Address
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
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\f
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+RFC 5215 Vorbis RTP Payload Format August 2008
Full Copyright Statement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
-Acknowledgement
- Funding for the RFC Editor function is provided by the IETF
- Administrative Support Activity (IASA).
-Barbato Expires August 20, 2008 [Page 25]
-\f
+
+
+Barbato Standards Track [Page 26]
+\f
-<?xml version="1.0"?>
+<?xml version="1.0" encoding="US-ASCII" ?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
-<?rfc toc="yes" ?>
-<?rfc compact="yes" ?>
-<?rfc rfcedstyle="yes" ?>
-<rfc ipr="full3978" docName="draft-ietf-avt-rtp-vorbis-09">
+<?rfc rfcedstyle="yes"?>
+<?rfc subcompact="no"?>
+<?rfc toc="yes"?>
+<?rfc symrefs="yes" ?>
+<?rfc sortrefs="yes" ?>
+
+<rfc number="5215" category="std">
<front>
<title abbrev="Vorbis RTP Payload Format">RTP Payload Format for Vorbis Encoded Audio</title>
</address>
</author>
-<date day="17" month="Feb" year="2008" />
+<date month="August" year="2008" />
<area>General</area>
<workgroup>AVT Working Group</workgroup>
<keyword>Vorbis</keyword>
<keyword>RTP</keyword>
+<keyword>example</keyword>
+
<abstract>
<t>
This document describes an RTP payload format for transporting Vorbis encoded
audio. It details the RTP encapsulation mechanism for raw Vorbis data and
-details the delivery mechanisms for the decoder probability model, referred to
-as a codebook and other setup information.
+the delivery mechanisms for the decoder probability model (referred to
+as a codebook), as well as other setup information.
</t>
<t>
-Also included within this memo are media type registrations, and the details
+Also included within this memo are media type registrations and the details
necessary for the use of Vorbis with the Session Description Protocol (SDP).
</t>
</abstract>
-<note title="Editors Note">
-<t>
-All references to RFC XXXX are to be replaced by references to the RFC number
-of this memo, when published.
-</t>
-</note>
-
</front>
<middle>
<t>
Vorbis is a general purpose perceptual audio codec intended to allow
maximum encoder flexibility, thus allowing it to scale competitively
-over an exceptionally wide range of bitrates. At the high
+over an exceptionally wide range of bit rates. At the high
quality/bitrate end of the scale (CD or DAT rate stereo, 16/24 bits), it
is in the same league as MPEG-4 AAC.
Vorbis is also intended for lower and higher sample rates (from
<t>
Vorbis encoded audio is generally encapsulated within an Ogg format bitstream
-<xref target="rfc3533"></xref>, which provides framing and synchronization.
+<xref target="RFC3533"></xref>, which provides framing and synchronization.
For the purposes of RTP transport, this layer is unnecessary, and so raw Vorbis
packets are used in the payload.
</t>
<section anchor="Terminology" title="Conformance and Document Conventions">
-<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, <xref target="rfc2119"/> and indicate requirement levels for compliant implementations. Requirements apply to all implementations unless otherwise stated.</t>
+<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, <xref target="RFC2119"/> and indicate requirement levels for compliant implementations. Requirements apply to all implementations unless otherwise stated.</t>
<t>An implementation is a software module that supports one of the media types defined in this document. Software modules may support multiple media types, but conformance is considered individually for each type.</t>
<t>Implementations that fail to satisfy one or more "MUST" requirements are considered non-compliant. Implementations that satisfy all "MUST" requirements, but fail to satisfy one or more "SHOULD" requirements, are said to be "conditionally compliant". All other implementations are "unconditionally compliant".</t>
<section anchor="Payload Format" title="Payload Format">
<t>
-For RTP based transport of Vorbis encoded audio the standard RTP header is
-followed by a 4 octets payload header, then the payload data. The payload
+For RTP-based transport of Vorbis-encoded audio, the standard RTP header is
+followed by a 4-octet payload header, and then the payload data. The payload
headers are used to associate the Vorbis data with its associated decoding
-codebooks as well as indicating if the following packet contains fragmented
+codebooks as well as indicate if the following packet contains fragmented
Vorbis data and/or the number of whole Vorbis data frames. The payload data
contains the raw Vorbis bitstream information. There are 3 types of Vorbis
-data, an RTP payload MUST contain just one of them at a time.
+data; an RTP payload MUST contain just one of them at a time.
</t>
<section anchor="RTP Header" title="RTP Header">
<t>
-The format of the RTP header is specified in <xref target="rfc3550"></xref>
-and shown in Figure <xref target="RTP Header Figure"/>. This payload format
+The format of the RTP header is specified in <xref target="RFC3550"></xref>
+and shown in <xref target="RTP Header Figure"/>. This payload format
uses the fields of the header in a manner consistent with that specification.
</t>
<t>
The RTP header begins with an octet of fields (V, P, X, and CC) to support
-specialized RTP uses (see <xref target="rfc3550"></xref> and
-<xref target="rfc3551"></xref> for details). For Vorbis RTP, the following
+specialized RTP uses (see <xref target="RFC3550"></xref> and
+<xref target="RFC3551"></xref> for details). For Vorbis RTP, the following
values are used.
</t>
<t>
Padding (P): 1 bit</t>
<t>
-Padding MAY be used with this payload format according to section 5.1 of
-<xref target="rfc3550"></xref>.
+Padding MAY be used with this payload format according to Section 5.1 of
+<xref target="RFC3550"></xref>.
</t>
<t>
Extension (X): 1 bit</t>
<t>
-The Extension bit is used in accordance with <xref target="rfc3550"></xref>.
+The Extension bit is used in accordance with <xref target="RFC3550"></xref>.
</t>
<t>
CSRC count (CC): 4 bits</t>
<t>
-The CSRC count is used in accordance with <xref target="rfc3550"></xref>.
+The CSRC count is used in accordance with <xref target="RFC3550"></xref>.
</t>
<t>
Marker (M): 1 bit</t>
<t>
-Set to zero. Audio silence suppression not used. This conforms to section 4.1
-of <xref target="vorbis-spec-ref"></xref>.
+Set to zero. Audio silence suppression is not used. This conforms to Section 4.1
+of <xref target="VORBIS-SPEC-REF"></xref>.
</t>
<t>
Payload Type (PT): 7 bits</t>
<t>
An RTP profile for a class of applications is expected to assign a payload type
-for this format, or a dynamically allocated payload type SHOULD be chosen which
+for this format, or a dynamically allocated payload type SHOULD be chosen that
designates the payload as Vorbis.
</t>
Sequence number: 16 bits</t>
<t>
The sequence number increments by one for each RTP data packet sent, and may be
-used by the receiver to detect packet loss and to restore packet sequence. This
-field is detailed further in <xref target="rfc3550"></xref>.
+used by the receiver to detect packet loss and to restore the packet sequence. This
+field is detailed further in <xref target="RFC3550"></xref>.
</t>
<t>
<t>
A timestamp representing the sampling time of the first sample of the first
Vorbis packet in the RTP payload. The clock frequency MUST be set to the sample
-rate of the encoded audio data and is conveyed out-of-band (e.g. as an SDP parameter).
+rate of the encoded audio data and is conveyed out-of-band (e.g., as an SDP parameter).
</t>
<t>
SSRC/CSRC identifiers: </t>
<t>
These two fields, 32 bits each with one SSRC field and a maximum of 16 CSRC
-fields, are as defined in <xref target="rfc3550">
+fields, are as defined in <xref target="RFC3550">
</xref>.
</t>
<t>
The 4 octets following the RTP Header section are the Payload Header. This
-header is split into a number of bitfields detailing the format of the
+header is split into a number of bit fields detailing the format of the
following payload data packets.
</t>
<t>
Ident: 24 bits</t>
<t>
-This 24 bit field is used to associate the Vorbis data to a decoding
-Configuration. It is stored as network byte order integer.
+This 24-bit field is used to associate the Vorbis data to a decoding
+Configuration. It is stored as a network byte order integer.
</t>
<t>
Fragment type (F): 2 bits</t>
<t>
-This field is set according to the following list
+This field is set according to the following list:
</t>
<vspace blankLines="1" />
<list style="empty">
Vorbis Data Type (VDT): 2 bits</t>
<t>
This field specifies the kind of Vorbis data stored in this RTP packet. There
-are currently three different types of Vorbis payloads. Each packet MUST contain only a single type of Vorbis packet (e.g. you must not aggregate configuration and comment packets in the same RTP payload)
+are currently three different types of Vorbis payloads. Each packet MUST contain only a single type of Vorbis packet (e.g., you must not aggregate configuration and comment packets in the same RTP payload).
</t>
<vspace blankLines="1" />
<t> 3 = Reserved</t>
</list>
-<t> The packets with a VDT of value 3 MUST be ignored </t>
+<t> The packets with a VDT of value 3 MUST be ignored.</t>
<t>
The last 4 bits represent the number of complete packets in this payload. This
provides for a maximum number of 15 Vorbis packets in the payload. If the
-payload contains fragmented data the number of packets MUST be set to 0.
+payload contains fragmented data, the number of packets MUST be set to 0.
</t>
</section>
<section anchor="Payload Data" title="Payload Data">
<t>
-Raw Vorbis packets are currently unbounded in length, application profiles will
+Raw Vorbis packets are currently unbounded in length; application profiles will
likely define a practical limit. Typical Vorbis packet sizes range from very
small (2-3 bytes) to quite large (8-12 kilobytes). The reference implementation
-<xref target="libvorbis"></xref> typically produces packets less than ~800
-bytes, except for the setup header packets which are ~4-12 kilobytes. Within an
+<xref target="LIBVORBIS"></xref> typically produces packets less than ~800
+bytes, except for the setup header packets, which are ~4-12 kilobytes. Within an
RTP context, to avoid fragmentation, the Vorbis data packet size SHOULD be kept
sufficiently small so that after adding the RTP and payload headers, the
complete RTP packet is smaller than the path MTU.
<t>
Each Vorbis payload packet starts with a two octet length header, which is used
-to represent the size in bytes of the following data payload, followed by the
-raw Vorbis data padded to the nearest byte boundary, as explained by the <xref target="vorbis-spec-ref">vorbis specification</xref>. The length value is stored
-as network byte order integer.
+to represent the size in bytes of the following data payload, and is followed by the
+raw Vorbis data padded to the nearest byte boundary, as explained by the <xref target="VORBIS-SPEC-REF">Vorbis I Specification</xref>. The length value is stored
+as a network byte order integer.
</t>
<t>
-For payloads which consist of multiple Vorbis packets the payload data consists
+For payloads that consist of multiple Vorbis packets, the payload data consists
of the packet length followed by the packet data for each of the Vorbis packets
in the payload.
</t>
<t>
The payload packing of the Vorbis data packets MUST follow the guidelines
-set-out in <xref target="rfc3551"></xref> where the oldest Vorbis packet occurs
+set out in <xref target="RFC3551"></xref>, where the oldest Vorbis packet occurs
immediately after the RTP packet header. Subsequent Vorbis packets, if any, MUST
follow in temporal order.
</t>
<t>
-Channel mapping of the audio is in accordance with the
-<xref target="vorbis-spec-ref">Vorbis I Specification</xref>.
+Audio channel mapping is in accordance with the
+<xref target="VORBIS-SPEC-REF">Vorbis I Specification</xref>.
</t>
</section>
</figure>
<t>
-The payload data section of the RTP packet begins with the 24 bit Ident field
-followed by the one octet bitfield header, which has the number of Vorbis
+The payload data section of the RTP packet begins with the 24-bit Ident field
+followed by the one octet bit field header, which has the number of Vorbis
frames set to 2. Each of the Vorbis data frames is prefixed by the two octets
length field. The Packet Type and Fragment Type are set to 0. The Configuration
that will be used to decode the packets is the one indexed by the ident value.
<section anchor="Configuration Headers" title="Configuration Headers">
<t>
-Unlike other mainstream audio codecs Vorbis has no statically
+Unlike other mainstream audio codecs, Vorbis has no statically
configured probability model. Instead, it packs all entropy decoding
configuration, Vector Quantization and Huffman models into a data block
-that must be transmitted to the decoder along with the compressed data.
+that must be transmitted to the decoder with the compressed data.
A decoder also requires information detailing the number of audio
-channels, bitrates and similar information to configure itself for a
+channels, bitrates, and similar information to configure itself for a
particular compressed data stream. These two blocks of information are
often referred to collectively as the "codebooks" for a Vorbis stream,
-and are nominally included as special "header" packets at the start
+and are included as special "header" packets at the start
of the compressed data. In addition,
-the <xref target="vorbis-spec-ref">Vorbis I specification</xref>
-requires the presence of a comment header packet which gives simple
+the <xref target="VORBIS-SPEC-REF">Vorbis I specification</xref>
+requires the presence of a comment header packet that gives simple
metadata about the stream, but this information is not required for
decoding the frame sequence.
</t>
<t>
-Thus these two codebook header packets must be received by the decoder before
+Thus, these two codebook header packets must be received by the decoder before
any audio data can be interpreted. These requirements pose problems in RTP,
which is often used over unreliable transports.
</t>
Since this information must be transmitted reliably and, as the RTP
stream may change certain configuration data mid-session, there are
different methods for delivering this configuration data to a
-client, both in-band and out-of-band which is detailed below.
-In order to set up an initial state for the client application the
-configuration MUST be conveyed via the signalling channel used to setup
+client, both in-band and out-of-band, which are detailed below.
+In order to set up an initial state for the client application, the
+configuration MUST be conveyed via the signalling channel used to set up
the session. One example of such signalling is
-<xref target="rfc4566">SDP</xref> with the
-<xref target="rfc3264">Offer/Answer Model</xref>.
+<xref target="RFC4566">SDP</xref> with the
+<xref target="RFC3264">Offer/Answer Model</xref>.
Changes to the configuration MAY be communicated via a re-invite,
-conveying new SDP, or sent in-band in the RTP channel.
-Implementations MUST support in-band delivery of updated codebooks,
+conveying a new SDP, or sent in-band in the RTP channel.
+Implementations MUST support an in-band delivery of updated codebooks,
and SHOULD support out-of-band codebook update using a new SDP file.
The changes may be due to different codebooks as well as
different bitrates of the RTP stream.
</t>
-<t>For non chained streams, the recommended Configuration delivery
-method is inline the <xref target="Packed Configuration">Packed Configuration</xref> in the SDP as explained in the <xref target="Mapping Media Type Parameters into SDP"> IANA considerations</xref>.
+<t>For non-chained streams, the recommended Configuration delivery
+method is inside the <xref target="Packed Configuration">Packed
+Configuration</xref> in the SDP as explained the <xref
+target="Mapping Media Type Parameters into SDP"> Mapping Media Type
+Parameters into SDP</xref>.
</t>
<t>
-The 24 bit Ident field is used to map which Configuration will be used to
+The 24-bit Ident field is used to map which Configuration will be used to
decode a packet. When the Ident field changes, it indicates that a change in
the stream has taken place. The client application MUST have in advance the
-correct configuration and if the client detects a change in the Ident value and
-does not have this information it MUST NOT decode the raw Vorbis data
-associated until it fetches the correct Configuration.
+correct configuration. If the client detects a change in the Ident value and
+does not have this information, it MUST NOT decode the raw associated Vorbis
+data until it fetches the correct Configuration.
</t>
<section anchor="In-band Header Transmission" title="In-band Header Transmission">
The <xref target="Packed Configuration">Packed Configuration</xref> Payload is
sent in-band with the packet type bits set to match the Vorbis Data Type.
Clients MUST be capable of dealing with fragmentation and periodic
-<xref target="rfc4588">re-transmission of</xref> the configuration headers.
+<xref target="RFC4588">re-transmission of</xref> the configuration headers.
The RTP timestamp value MUST reflect the transmission time of the first data packet for which this configuration applies.
</t>
<t>
A Vorbis Packed Configuration is indicated with the Vorbis Data Type field set
to 1. Of the three headers defined in the
-<xref target="vorbis-spec-ref">Vorbis I specification</xref>, the
-Identification and the Setup MUST be packed as they are, while the comment
+<xref target="VORBIS-SPEC-REF">Vorbis I specification</xref>, the
+Identification and the Setup MUST be packed as they are, while the Comment
header MAY be replaced with a dummy one.</t>
<t>
-The packed configuration follows a generic way to store Xiph codec
-configurations: The first field stores the number of the following packets
+The packed configuration stores Xiph codec
+configurations in a generic way: the first field stores the number of the following packets
minus one (count field), the next ones represent the size of the headers
-(length fields), the headers immediately follow the list of length fields.
+(length fields), and the headers immediately follow the list of length fields.
The size of the last header is implicit.</t>
<t>
The count and the length fields are encoded using the following logic: the data
-is in network byte order, every byte has the most significant bit used as flag
-and the following 7 used to store the value.
-The first N bit are to be taken, where N is number of bits needed to represent
-the value, taken modulo 7, and stored in the first byte.
-If there are more bits, the flag bit is set to 1 and the subsequent 7bit are
-stored in the following byte, if there are remaining bits set the flag to 1 and
-the same procedure is repeated.
-The ending byte has the flag bit set to 0. In order to decode it is enough to
-iterate over the bytes until the flag bit set to 0, for every byte the data is
-added to the accumulated value multiplied by 128.</t>
-<t>
-The headers are packed in the same order they are present in ogg:
+is in network byte order; every byte has the most significant bit used
+as a flag, and the following 7 bits are used to store the value.
+The first 7 most significant bits are stored in the first byte.
+If there are remaining bits, the flag bit is set to 1 and the subsequent
+7 bits are stored in the following byte.
+If there are remaining bits, set the flag to 1 and the same procedure is
+repeated.
+The ending byte has the flag bit set to 0. To decode, simply iterate
+over the bytes until the flag bit is set to 0. For every byte, the data
+is added to the accumulated value multiplied by 128.</t>
+<t>
+The headers are packed in the same order as they are present in Ogg <xref target="VORBIS-SPEC-REF" />:
Identification, Comment, Setup.</t>
<t>
The 2 byte length tag defines the length of the packed headers as the sum of
-the Configuration, Comment and Setup lengths.</t>
+the Configuration, Comment, and Setup lengths.</t>
<figure anchor="Packed Configuration Figure" title="Packed Configuration Figure">
<artwork><![CDATA[
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
- | Ident | 1 | 0 | 0|
+ | Ident | 0 | 1 | 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| length | n. of headers | length1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</figure>
<t>The Ident field is set with the value that will be used by the Raw Payload
-Packets to address this Configuration. The Fragment type is set to 0 since the
-packet bears the full Packed configuration, the number of packet is set to 1.</t>
+Packets to address this Configuration. The Fragment type is set to 0 because the
+packet bears the full Packed configuration. The number of the packet is set to 1.</t>
</section>
</section>
<section anchor="Out of Band Transmission" title="Out of Band Transmission">
<t>
-The following packet definition MUST be used when Configuration is inlined
+The following packet definition MUST be used when Configuration is inside
in the SDP.
</t>
<section anchor="Packed Headers" title="Packed Headers">
<t>
-As mentioned above the RECOMMENDED delivery vector for Vorbis configuration
+As mentioned above, the RECOMMENDED delivery vector for Vorbis configuration
data is via a retrieval method that can be performed using a reliable transport
-protocol. As the RTP headers are not required for this method of delivery the
+protocol. As the RTP headers are not required for this method of delivery, the
structure of the configuration data is slightly different. The packed header
-starts with a 32 bit (network byte ordered) count field which details the number of packed headers that are contained in the bundle. Next is the Packed header
+starts with a 32-bit (network-byte ordered) count field, which details
+the number of packed headers that are contained in the bundle. The
+following shows the Packed header
payload for each chained Vorbis stream.
</t>
]]></artwork>
</figure>
<t>
-The key difference between the in-band format and this one, is that there is no
-need for the payload header octet. In this figure the comment has a size bigger
+The key difference between the in-band format and this one is that there is no
+need for the payload header octet. In this figure, the comment has a size bigger
than 127 bytes.
</t>
</section>
<t>
Unlike the loss of raw Vorbis payload data, loss of a configuration header
-lead to a situation where it will not be possible to successfully decode the
-stream. Implementations MAY try to recover from error by requesting again the
+leads to a situation where it will not be possible to successfully decode the
+stream. Implementations MAY try to recover from an error by requesting again the
missing Configuration or, if the delivery method is in-band, by buffering the
payloads waiting for the Configuration needed to decode them.
-The baseline reaction SHOULD be either reset or end the RTP session.
+The baseline reaction SHOULD either be reset or end the RTP session.
</t>
</section>
<section anchor="Comment Headers" title="Comment Headers">
<t>
-With the Vorbis Data Type flag set to 2, this indicates that the packet contain
-the comment metadata, such as artist name, track title and so on. These
-metadata messages are not intended to be fully descriptive but to offer basic
+Vorbis Data Type flag set to 2 indicates that the packet contains
+the comment metadata, such as artist name, track title, and so on. These
+metadata messages are not intended to be fully descriptive but rather to offer basic
track/song information. Clients MAY ignore it completely. The details on the
-format of the comments can be found in the <xref target="vorbis-spec-ref">Vorbis documentation</xref>.
+format of the comments can be found in the <xref target="VORBIS-SPEC-REF">Vorbis I Specification</xref>.
</t>
<figure anchor="Comment Packet Figure" title="Comment Packet">
<artwork><![CDATA[
</figure>
<t>
-The 2 bytes length field is necessary since this packet could be fragmented.
+The 2-byte length field is necessary since this packet could be fragmented.
</t>
</section>
<section anchor="Frame Packetization" title="Frame Packetization">
<t>
-Each RTP payload contains either one Vorbis packet fragment, or an integer
+Each RTP payload contains either one Vorbis packet fragment or an integer
number of complete Vorbis packets (up to a maximum of 15 packets, since the
-number of packets is defined by a 4 bit value).
+number of packets is defined by a 4-bit value).
</t>
<t>
Any Vorbis data packet that is less than path MTU SHOULD be bundled in the RTP
payload with as many Vorbis packets as will fit, up to a maximum of 15, except
when such bundling would exceed an application's desired transmission latency.
-Path MTU is detailed in <xref target="rfc1191"></xref> and <xref target="rfc1981"></xref>.
+Path MTU is detailed in <xref target="RFC1191"></xref> and <xref target="RFC1981"></xref>.
</t>
<t>
A fragmented packet has a zero in the last four bits of the payload header.
The first fragment will set the Fragment type to 1. Each fragment after the
first will set the Fragment type to 2 in the payload header. The consecutive
-fragments MUST be sent without any other payloads being sent between the first
+fragments MUST be sent without any other payload being sent between the first
and the last fragment. The RTP payload containing the last fragment of the
Vorbis packet will have the Fragment type set to 3. To maintain the correct
-sequence for fragmented packet reception the timestamp field of fragmented
+sequence for fragmented packet reception, the timestamp field of fragmented
packets MUST be the same as the first packet sent, with the sequence number
-incremented as normal for the subsequent RTP payloads, this will affect the
+incremented as normal for the subsequent RTP payloads; this will affect the
RTCP jitter measurement. The length field shows the fragment length.
</t>
<section anchor="Example Fragmented Vorbis Packet" title="Example Fragmented Vorbis Packet">
<t>
-Here is an example fragmented Vorbis packet split over three RTP payloads.
-Each of them contains the standard RTP headers as well as the 4 octets Vorbis
+Here is an example of a fragmented Vorbis packet split over three RTP payloads.
+Each of them contains the standard RTP headers as well as the 4-octet Vorbis
headers.
</t>
</figure>
<t>
-In this payload the initial sequence number is 1000 and the timestamp is 12345. The Fragment type is set to 1, the number of packets field is set to 0, and as
-the payload is raw Vorbis data the VDT field is set to 0.
+In this payload, the initial sequence number is 1000 and the timestamp is 12345. The Fragment type is set to 1, the number of packets field is set to 0, and as
+the payload is raw Vorbis data, the VDT field is set to 0.
</t>
<figure anchor="Example Fragmented Packet (Packet 2)" title="Example Fragmented Packet (Packet 2)">
</figure>
<t>
-The Fragment type field is set to 2 and the number of packets field is set to 0.
-For large Vorbis fragments there can be several of this type of payloads.
+The Fragment type field is set to 2, and the number of packets field is set to 0.
+For large Vorbis fragments, there can be several of these types of payloads.
The maximum packet size SHOULD be no greater than the path MTU,
including all RTP and payload headers. The sequence number has been incremented
-by one but the timestamp field remains the same as the initial payload.
+by one, but the timestamp field remains the same as the initial payload.
</t>
<figure anchor="Example Fragmented Packet (Packet 3)" title="Example Fragmented Packet (Packet 3)">
<t>
This is the last Vorbis fragment payload. The Fragment type is set to 3 and the
-packet count remains set to 0. As in the previous payloads the timestamp remains
+packet count remains set to 0. As in the previous payloads, the timestamp remains
set to the first payload timestamp in the sequence and the sequence number has
been incremented.
</t>
As there is no error correction within the Vorbis stream, packet loss will
result in a loss of signal. Packet loss is more of an issue for fragmented
Vorbis packets as the client will have to cope with the handling of the
-Fragment Type. In case of loss of fragments the client MUST discard all the
+Fragment Type. In case of loss of fragments, the client MUST discard all the
remaining Vorbis fragments and decode the incomplete packet. If we use the
-fragmented Vorbis packet example above and the first RTP payload is lost the
+fragmented Vorbis packet example above and the first RTP payload is lost, the
client MUST detect that the next RTP payload has the packet count field set
to 0 and the Fragment type 2 and MUST drop it.
The next RTP payload, which is the final fragmented packet, MUST be dropped
in the same manner.
-If the missing RTP payload is the last, the received two fragments will be
+If the missing RTP payload is the last, the two fragments received will be
kept and the incomplete Vorbis packet decoded.
</t>
</section>
<section anchor="IANA Considerations" title="IANA Considerations">
-<vspace blankLines="1" />
<list style="hanging">
<t hangText="Type name:"> audio </t>
-<vspace blankLines="1" />
<t hangText="Subtype name:"> vorbis </t>
-<vspace blankLines="1" />
<t hangText="Required parameters:">
-<vspace blankLines="1" />
-
<list style="hanging">
-<t hangText="rate:"> indicates the RTP timestamp clock rate as described in <xref target="rfc3551">RTP Profile for Audio and Video Conferences with Minimal Control.</xref>
+<t hangText="rate:"> indicates the RTP timestamp clock rate as described in <xref target="RFC3551">RTP Profile for Audio and Video Conferences with Minimal Control</xref>.
</t>
-<vspace blankLines="1" />
-<t hangText="channels:"> indicates the number of audio channels as described in <xref target="rfc3551">RTP Profile for Audio and Video Conferences with Minimal Control.</xref>
+<t hangText="channels:"> indicates the number of audio channels as described in <xref target="RFC3551">RTP Profile for Audio and Video Conferences with Minimal Control</xref>.
</t>
-<vspace blankLines="1" />
-<t hangText="configuration:"> the <xref target="rfc3548">base64</xref> representation of the <xref target="Packed Headers">Packed Headers</xref>.
+<t hangText="configuration:"> the <xref target="RFC4648">base64</xref> representation of the <xref target="Packed Headers">Packed Headers</xref>.
</t>
</list>
</t>
-<vspace blankLines="1" />
-
<t hangText="Encoding considerations:">
<vspace blankLines="1" />
This media type is framed and contains binary data.
</t>
-<vspace blankLines="1" />
-
<t hangText="Security considerations:">
<vspace blankLines="1" />
-See Section 10 of RFC XXXX.</t>
+See Section 10 of RFC 5215.</t>
-<vspace blankLines="1" />
<t hangText="Interoperability considerations:">
<vspace blankLines="1" />
None</t>
-<vspace blankLines="1" />
<t hangText="Published specification:">
-
<vspace blankLines="1" />
-RFC XXXX [RFC Editor: please replace by the RFC number of this memo, when published]
+RFC 5215
<vspace blankLines="1" />
-Ogg Vorbis I specification: Codec setup and packet decode. Available from the Xiph website, http://xiph.org
+Ogg Vorbis I specification: Codec setup and packet decode. Available from the Xiph website, http://xiph.org/
</t>
-<vspace blankLines="1" />
<t hangText="Applications which use this media type:">
<vspace blankLines="1"/>
Audio streaming and conferencing tools </t>
-<vspace blankLines="1" />
-
<t hangText="Additional information:">
<vspace blankLines="1" />
None </t>
-<vspace blankLines="1" />
-
<t hangText="Person & email address to contact for further information:">
-
<vspace blankLines="1" />
-
Luca Barbato: <lu_zero@gentoo.org><br/>
+<vspace blankLines="0" />
IETF Audio/Video Transport Working Group
</t>
-<vspace blankLines="1" />
-
<t hangText="Intended usage:">
<vspace blankLines="1" />
COMMON</t>
-<vspace blankLines="1" />
-
<t hangText="Restriction on usage:">
<vspace blankLines="1" />
-This media type depends on RTP framing, and hence is only defined for transfer via <xref target="rfc3550">RTP</xref></t>
-
-<vspace blankLines="1" />
+This media type depends on RTP framing, hence is only defined for transfer via <xref target="RFC3550">RTP</xref>.</t>
<t hangText="Author:">
<vspace blankLines="1"/>Luca Barbato</t>
-<vspace blankLines="1" />
-
<t hangText="Change controller:">
<vspace blankLines="1"/>IETF AVT Working Group delegated from the IESG</t>
-
-<vspace blankLines="1" />
</list>
<section anchor="Packed Headers IANA Considerations" title="Packed Headers IANA Considerations">
<t>
-The following IANA considerations refers to the split configuration <xref target="Packed Headers">Packed Headers</xref> used within RFC XXXX.
+The following IANA considerations refers to the split configuration <xref target="Packed Headers">Packed Headers</xref> used within RFC 5215.
</t>
-<vspace blankLines="1" />
-
<list style="hanging">
<t hangText="Type name:"> audio </t>
-<vspace blankLines="1" />
-
<t hangText="Subtype name:"> vorbis-config </t>
-<vspace blankLines="1" />
-
<t hangText="Required parameters:">
<vspace blankLines="1" />
None
</t>
-<vspace blankLines="1" />
-
<t hangText="Optional parameters:">
<vspace blankLines="1" />
None
</t>
-<vspace blankLines="1" />
-
<t hangText="Encoding considerations:">
<vspace blankLines="1" />
This media type contains binary data.
</t>
-<vspace blankLines="1" />
-
<t hangText="Security considerations:">
<vspace blankLines="1" />
-See Section 10 of RFC XXXX.
+See Section 10 of RFC 5215.
</t>
-<vspace blankLines="1" />
-
<t hangText="Interoperability considerations:">
<vspace blankLines="1" />
None
</t>
-<vspace blankLines="1" />
-
<t hangText="Published specification:">
<vspace blankLines="1" />
-RFC XXXX [RFC Editor: please replace by the RFC number of this memo,
- when published]
+RFC 5215
</t>
-<vspace blankLines="1" />
-
<t hangText="Applications which use this media type:">
<vspace blankLines="1" />
-Vorbis encoded audio, configuration data.
+Vorbis encoded audio, configuration data
</t>
-<vspace blankLines="1" />
-
<t hangText="Additional information:">
<vspace blankLines="1" />
None
</t>
-<vspace blankLines="1" />
-
<t hangText="Person & email address to contact for further information:">
<vspace blankLines="1" />
Luca Barbato: <lu_zero@gentoo.org>
IETF Audio/Video Transport Working Group
</t>
-<vspace blankLines="1" />
-
<t hangText="Intended usage:">
COMMON
</t>
-<vspace blankLines="1" />
-
<t hangText="Restriction on usage:">
<vspace blankLines="1" />
This media type doesn't depend on the transport.
</t>
-<vspace blankLines="1" />
-
<t hangText="Author:">
<vspace blankLines="1" />
Luca Barbato</t>
-<vspace blankLines="1" />
-
<t hangText="Change controller:">
<vspace blankLines="1" />
IETF AVT Working Group delegated from the IESG</t>
</section>
-<section anchor="SDP related considerations" title="SDP related considerations">
+<section anchor="SDP related considerations" title="SDP Related Considerations">
<t>
-The following paragraphs define the mapping of the parameters described in the IANA considerations section and their usage in the <xref target="rfc3264">Offer/Answer Model</xref>. In order to be forward compatible the implementation MUST ignore unknown parameters.
+The following paragraphs define the mapping of the parameters described in the IANA considerations section and their usage in the <xref target="RFC3264">Offer/Answer Model</xref>. In order to be forward compatible, the implementation MUST ignore unknown parameters.
</t>
<section anchor="Mapping Media Type Parameters into SDP" title="Mapping Media Type Parameters into SDP">
<t>
The information carried in the Media Type specification has a
-specific mapping to fields in the <xref target="rfc4566">Session Description
+specific mapping to fields in the <xref target="RFC4566">Session Description
Protocol (SDP)</xref>, which is commonly used to describe RTP sessions.
-When SDP is used to specify sessions the mapping are as follows:
+When SDP is used to specify sessions, the mapping are as follows:
</t>
-<vspace blankLines="1" />
<list style="symbols">
<t>The type name ("audio") goes in SDP "m=" as the media name.</t>
-<vspace blankLines="1" />
<t>The subtype name ("vorbis") goes in SDP "a=rtpmap" as the encoding name.</t>
-<vspace blankLines="1" />
-<t>The parameter "rate" also goes in "a=rtpmap" as clock rate.</t>
-<vspace blankLines="1" />
+<t>The parameter "rate" also goes in "a=rtpmap" as the clock rate.</t>
-<t>The parameter "channels" also goes in "a=rtpmap" as channel count.</t>
-<vspace blankLines="1" />
+<t>The parameter "channels" also goes in "a=rtpmap" as the channel count.</t>
<t>The mandated parameters "configuration" MUST be included in the SDP
"a=fmtp" attribute.</t>
-<vspace blankLines="1" />
</list>
<t>
The port value is specified by the server application bound to the address
specified in the c= line. The channel count value specified in the rtpmap
-attribute SHOULD match the current Vorbis stream or considered the maximum
+attribute SHOULD match the current Vorbis stream or should be considered the maximum
number of channels to be expected. The timestamp clock rate MUST be a multiple
-of the sample rate, different payload number MUST be used if the clock rate
+of the sample rate; a different payload number MUST be used if the clock rate
changes. The Configuration payload delivers the exact information, thus the
-SDP information SHOULD be considered as a hint.
+SDP information SHOULD be considered a hint.
An example is found below.
</t>
<section anchor="SDP Example" title="SDP Example">
<t>The following example shows a basic SDP single stream. The first
-configuration packet is inlined in the SDP, other configurations could be
-fetched at any time from the URIs provided. The inline
-<xref target="rfc3548">base64</xref> configuration string is folded in this
+configuration packet is inside the SDP; other configurations could be
+fetched at any time from the URIs provided. The following
+<xref target="RFC4648">base64</xref> configuration string is folded in this
example due to RFC line length limitations.</t>
+
<list style="empty">
<t>c=IN IP4 192.0.2.1</t>
<t>m=audio RTP/AVP 98</t>
</section>
<t>
-Note that the payload format (encoding) names are commonly shown in upper case.
-Media Type subtypes are commonly shown in lower case. These names are
+Note that the payload format (encoding) names are commonly shown in uppercase.
+Media Type subtypes are commonly shown in lowercase. These names are
case-insensitive in both places. Similarly, parameter names are
case-insensitive both in Media Type types and in the default mapping to the SDP
-a=fmtp attribute. The a=fmtp line is a single line even if it is shown as multiple lines in this document for clarity.
+a=fmtp attribute. The a=fmtp line is a single line, even if it is shown as multiple lines in this document for clarity.
</t>
</section>
<section anchor="Usage with the SDP Offer/Answer Mode" title="Usage with the SDP Offer/Answer Model">
<t>
-The are no negotiable parameters. All the of them are declarative.
+There are no negotiable parameters. All of them are declarative.
</t>
</section>
<section anchor="Congestion Control" title="Congestion Control">
<t>
The general congestion control considerations for transporting RTP
-data apply to vorbis audio over RTP as well. See the RTP specification
-<xref target="rfc3550" /> and any applicable RTP profile (e.g., <xref target="rfc3551" />).
+data apply to Vorbis audio over RTP as well. See the RTP specification
+<xref target="RFC3550" /> and any applicable RTP profile (e.g., <xref target="RFC3551" />).
Audio data can be encoded using a range of different bit rates, so
it is possible to adapt network bandwidth by adjusting the encoder
bit rate in real time or by having multiple copies of content encoded
<t>
The following example shows a common usage pattern that MAY be applied in
-such situation, the main scope of this section is to explain better usage
+such a situation. The main scope of this section is to explain better usage
of the transmission vectors.
</t>
<section anchor="Stream Radio" title="Stream Radio">
-<t>This is one of the most common situation: one single server streaming
-content in multicast, the clients may start a session at random time. The
-content itself could be a mix of live stream, as the webjockey's voice,
-and stored streams as the music she plays.</t>
+<t>This is one of the most common situations: there is one single server streaming
+content in multicast, and the clients may start a session at a random time. The
+content itself could be a mix of a live stream (as the webjockey's voice)
+and stored streams (as the music she plays).</t>
-<t>In this situation we don't know in advance how many codebooks we will use.
+<t>In this situation, we don't know in advance how many codebooks we will use.
The clients can join anytime and users expect to start listening to the content
in a short time.</t>
-<t>On join the client will receive the current Configuration necessary to
-decode the current stream inlined in the SDP so that the decoding will start
+<t>Upon joining, the client will receive the current Configuration necessary to
+decode the current stream inside the SDP so that the decoding will start
immediately after.</t>
-<t>When the streamed content changes the new Configuration is sent in-band
-before the actual stream and the Configuration that has to be sent inline in
-the SDP updated. Since the in-band method is unreliable, an out of band
+<t>When the streamed content changes, the new Configuration is sent in-band
+before the actual stream, and the Configuration that has to be sent inside
+the SDP is updated. Since the in-band method is unreliable, an out-of-band
fallback is provided.</t>
<t>The client may choose to fetch the Configuration from the alternate source
-as soon as it discovers a Configuration packet got lost in-band or use
-<xref target="RFC3611">selective retransmission</xref>, if the server supports
-the feature.</t>
+as soon as it discovers a Configuration packet got lost in-band, or use
+<xref target="RFC3611">selective retransmission</xref> if the server supports
+this feature.</t>
-<t>A serverside optimization would be to keep an hash list of the
-Configurations per session to avoid packing all of them and send the same
-Configuration with different Ident tags</t>
+<t>A server-side optimization would be to keep a hash list of the
+Configurations per session, which avoids packing all of them and sending the same
+Configuration with different Ident tags.</t>
-<t>A clientside optimization would be to keep a tag list of the Configurations
-per session and don't process configuration packets already known.</t>
+<t>A client-side optimization would be to keep a tag list of the Configurations
+per session and not process configuration packets that are already known.</t>
</section>
</section>
<t>
RTP packets using this payload format are subject to the security
considerations discussed in the
-<xref target="rfc3550">RTP specification</xref>, the
-<xref target="rfc3548">base64 specification</xref> and the
-<xref target="rfc3986">URI Generic syntax specification</xref>.
+<xref target="RFC3550">RTP specification</xref>, the
+<xref target="RFC4648">base64 specification</xref>, and the
+<xref target="RFC3986">URI Generic syntax specification</xref>.
Among other considerations, this implies that the confidentiality of the
-media stream is archieved by using encryption. Because the data compression used
+media stream is achieved by using encryption. Because the data compression used
with this payload format is applied end-to-end, encryption may be performed on
the compressed data.
</t>
</section>
<section title="Copying Conditions">
<t>The authors agree to grant third parties the irrevocable right to copy,
- use and distribute the work, with or without modification, in any medium,
+ use, and distribute the work, with or without modification, in any medium,
without royalty, provided that, unless separate permission is granted,
redistributed modified works do not contain misleading author, version,
name of work, or endorsement information.</t>
<section anchor="Acknowledgments" title="Acknowledgments">
<t>
-This document is a continuation of draft-moffitt-vorbis-rtp-00.txt and
-draft-kerr-avt-vorbis-rtp-04.txt. The Media Type declaration is a
-continuation of draft-short-avt-rtp-vorbis-mime-00.txt.
+This document is a continuation of the following documents:
+</t><t>
+Moffitt, J., "RTP Payload Format for Vorbis Encoded Audio", February 2001.
+</t><t>
+Kerr, R., "RTP Payload Format for Vorbis Encoded Audio", December 2004.
+</t><t>
+The Media Type declaration is a continuation of the following
+document:</t><t>
+Short, B., "The audio/rtp-vorbis MIME Type", January 2008.
</t>
<t>
Aaron Colwell, Ross Finlayson, Fluendo, Ramon Garcia, Pascal Hennequin, Ralph
Giles, Tor-Einar Jarnbjo, Colin Law, John Lazzaro, Jack Moffitt, Christopher
Montgomery, Colin Perkins, Barry Short, Mike Smith, Phil Kerr, Michael Sparks,
-Magnus Westerlund, David Barrett, Silvia Pfeiffer, Stefan Ehmann, Alessandro
-Salvatori. Politecnico di Torino (LS)³/IMG Group in particular Federico
-Ridolfo, Francesco Varano, Giampaolo Mancini, Dario Gallucci, Juan Carlos De Martin.
+Magnus Westerlund, David Barrett, Silvia Pfeiffer, Stefan Ehmann, Gianni Ceccarelli and Alessandro Salvatori. Thanks to the LScube Group, in particular Federico
+Ridolfo, Francesco Varano, Giampaolo Mancini, Dario Gallucci, and Juan Carlos De Martin.
</t>
</section>
<references title="Normative References">
-<reference anchor="rfc2119">
-<front>
-<title>Key words for use in RFCs to Indicate Requirement Levels </title>
-<author initials="S." surname="Bradner" fullname="Scott Bradner"></author>
-</front>
-<seriesInfo name="RFC" value="2119" />
-</reference>
-
-<reference anchor="rfc3550">
-<front>
-<title>RTP: A Transport Protocol for real-time applications</title>
-<author initials="H." surname="Schulzrinne" fullname=""></author>
-<author initials="S." surname="Casner" fullname=""></author>
-<author initials="R." surname="Frederick" fullname=""></author>
-<author initials="V." surname="Jacobson" fullname=""></author>
-</front>
-<seriesInfo name="STD" value="64"/>
-<seriesInfo name="RFC" value="3550" />
-</reference>
-
-<reference anchor="rfc3551">
-<front>
-<title>RTP Profile for Audio and Video Conferences with Minimal Control.</title>
-<author initials="H." surname="Schulzrinne" fullname=""></author>
-<author initials="S." surname="Casner" fullname=""></author>
-</front>
-<date month="July" year="2003" />
-<seriesInfo name="STD" value="65"/>
-<seriesInfo name="RFC" value="3551" />
-</reference>
-
-<reference anchor="rfc3986">
-<front>
-<title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
-<author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
-</author>
-<author initials="R." surname="Fielding" fullname="Roy T. Fielding">
-</author>
-<author initials="L." surname="Masinter" fullname="Larry Masinter">
-</author>
-</front>
-<date year="2005" month="January" />
-<seriesInfo name="STD" value="66"/>
-<seriesInfo name="RFC" value="3986" />
-</reference>
-
-<reference anchor="rfc4566">
-<front>
-<title>SDP: Session Description Protocol</title>
-<author initials="M." surname="Handley" fullname="M. Handley">
-<organization /></author>
-<author initials="V." surname="Jacobson" fullname="V. Jacobson">
-<organization /></author>
-<author initials="C." surname="Perkins" fullname="C. Perkins">
-<organization /></author>
-<date year="2006" month="July" />
-</front>
-<seriesInfo name="RFC" value="4566" />
-<format type="TXT" octets="108820" target="ftp://ftp.isi.edu/in-notes/rfc4566.txt" />
-</reference>
-
-<reference anchor="rfc1191">
-<front>
-<title>Path MTU discovery</title>
-<author initials="J." surname="Mogul" fullname="Jeffrey Mogul">
-<organization>Digital Equipment Corporation (DEC) , Western Research Laboratory</organization>
-<address>
-<email>mogul@decwrl.dec.com</email></address></author>
-<author initials="S." surname="Deering" fullname="Steve Deering">
-<organization>Xerox Palo Alto Research Center</organization>
-<address>
-<email>deering@xerox.com</email></address></author>
-<date year="1990" day="1" month="November" />
-</front>
-<seriesInfo name="RFC" value="1191" />
-<format type="TXT" octets="47936" target="ftp://ftp.isi.edu/in-notes/rfc1191.txt" />
-</reference>
-
-<reference anchor="rfc1981">
-<front>
-<title>Path MTU Discovery for IP version 6</title>
-<author initials="J." surname="McCann et al." fullname="J. McCann et al."></author>
-</front>
-<seriesInfo name="RFC" value="1981" />
-</reference>
-
-<reference anchor="rfc3264">
-<front>
-<title>An Offer/Answer Model with Session Description Protocol (SDP)</title>
-<author initials="J." surname="Rosenberg" fullname="Jonathan Rosenberg"></author>
-<author initials="H." surname="Schulzrinne" fullname="Henning Schulzrinne"></author>
-</front>
-<seriesInfo name="RFC" value="3264" />
-</reference>
-
-<reference anchor="rfc3548">
-<front>
-<title>The Base16, Base32, and Base64 Data Encodings</title>
-<author initials="S." surname="Josefsson" fullname="Simon Josefsson"></author>
-</front>
-<seriesInfo name="RFC" value="3548" />
-</reference>
-
-<reference anchor="vorbis-spec-ref">
+<?rfc include="reference.RFC.2119" ?>
+<?rfc include="reference.RFC.3550" ?>
+<?rfc include="reference.RFC.3551" ?>
+<?rfc include="reference.RFC.3986" ?>
+<?rfc include="reference.RFC.4566" ?>
+<?rfc include="reference.RFC.1191" ?>
+<?rfc include="reference.RFC.1981" ?>
+<?rfc include="reference.RFC.3264" ?>
+<?rfc include="reference.RFC.4648" ?>
+
+<reference anchor="VORBIS-SPEC-REF">
<front>
<title>Ogg Vorbis I specification: Codec setup and packet decode. Available from the Xiph website, http://xiph.org/vorbis/doc/Vorbis_I_spec.html</title>
</front>
<references title="Informative References">
-<reference anchor="rfc3533">
-<front>
-<title>The Ogg Encapsulation Format Version 0</title>
-<author initials="S." surname="Pfeiffer" fullname="Silvia Pfeiffer"></author>
-</front>
-<seriesInfo name="RFC" value="3533" />
-</reference>
+<?rfc include="reference.RFC.3533" ?>
-<reference anchor="libvorbis">
+<reference anchor="LIBVORBIS">
<front>
-<title>libvorbis: Available from the dedicated website, http://vorbis.com</title>
+<title>libvorbis: Available from the dedicated website, http://vorbis.com/</title>
</front>
</reference>
-<reference anchor="RFC3611">
-<front>
-<title>RTP Control Protocol Extended Reports (RTCP XR)</title>
-<author initials="T." surname="Friedman" fullname="T. Friedman" />
-<author initials="R." surname="Caceres" fullname="R. Caceres" />
-<author initials="A." surname="Clark" fullname="A. Clark" />
-<date year="2003" month="November"/>
-</front>
-<seriesInfo name="RFC" value="3611"/>
-</reference>
-<reference anchor="rfc4588">
-<front>
-<title>RTP Retransmission Payload Format</title>
-<author initials="J." surname="Rey" fullname="J. Rey">
-<organization /></author>
-<author initials="D." surname="Leon" fullname="D. Leon">
-<organization /></author>
-<author initials="A." surname="Miyazaki" fullname="A. Miyazaki">
-<organization /></author>
-<author initials="V." surname="Varsa" fullname="V. Varsa">
-<organization /></author>
-<author initials="R." surname="Hakenberg" fullname="R. Hakenberg">
-<organization /></author>
-<date year="2006" month="July" />
-</front>
-<seriesInfo name="RFC" value="4588" />
-<format type="TXT" octets="76630" target="ftp://ftp.isi.edu/in-notes/rfc4588.txt" />
-</reference>
+<?rfc include="reference.RFC.3611" ?>
+<?rfc include="reference.RFC.4588" ?>
+
</references>
</back>
</rfc>