draft-ietf-avt-profile-new-02.txt   draft-ietf-avt-profile-new-03.txt 
Internet Engineering Task Force AVT WG Internet Engineering Task Force AVT WG
Internet Draft Schulzrinne Internet Draft Schulzrinne
ietf-avt-profile-new-02.txt Columbia U. ietf-avt-profile-new-03.txt Columbia U.
November 20, 1997 August 7, 1998
Expires: January 1, 1998 Expires: February 7, 1999
RTP Profile for Audio and Video Conferences with Minimal Control RTP Profile for Audio and Video Conferences with Minimal Control
STATUS OF THIS MEMO STATUS OF THIS MEMO
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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To learn the current status of any Internet-Draft, please check the To view the entire list of current Internet-Drafts, please check the
``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow ``1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern
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Distribution of this document is unlimited. Distribution of this document is unlimited.
ABSTRACT ABSTRACT
This memo describes a profile called ''RTP/AVP'' for the This memo describes a profile called "RTP/AVP" for the
use of the real-time transport protocol (RTP), version 2, use of the real-time transport protocol (RTP), version 2,
and the associated control protocol, RTCP, within audio and the associated control protocol, RTCP, within audio
and video multiparticipant conferences with minimal and video multiparticipant conferences with minimal
control. It provides interpretations of generic fields control. It provides interpretations of generic fields
within the RTP specification suitable for audio and video within the RTP specification suitable for audio and video
conferences. In particular, this document defines a set conferences. In particular, this document defines a set
of default mappings from payload type numbers to of default mappings from payload type numbers to
encodings. encodings.
The document also describes how audio and video data may The document also describes how audio and video data may
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within that slot and the remaining SDES items cyclically taking within that slot and the remaining SDES items cyclically taking
up the eighth slot, as defined in Section 6.2.2 of the RTP up the eighth slot, as defined in Section 6.2.2 of the RTP
specification. In other words, NAME is sent in RTCP packets 1, specification. In other words, NAME is sent in RTCP packets 1,
4, 7, 10, 13, 16, 19, while, say, EMAIL is used in RTCP packet 4, 7, 10, 13, 16, 19, while, say, EMAIL is used in RTCP packet
22. 22.
Security: The RTP default security services are also the default Security: The RTP default security services are also the default
under this profile. under this profile.
String-to-key mapping: A user-provided string ("pass phrase") is String-to-key mapping: A user-provided string ("pass phrase") is
hashed with the MD5 algorithm to a 16-octet digest. An !n!-bit hashed with the MD5 algorithm to a 16-octet digest. An n-bit key
key is extracted from the digest by taking the first !n! bits is extracted from the digest by taking the first n bits from the
from the digest. If several keys are needed with a total length digest. If several keys are needed with a total length of 128
of 128 bits or less (as for triple DES), they are extracted in bits or less (as for triple DES), they are extracted in order
order from that digest. The octet ordering is specified in RFC from that digest. The octet ordering is specified in RFC 1423,
1423, Section 2.2. (Note that some DES implementations require Section 2.2. (Note that some DES implementations require that
that the 56-bit key be expanded into 8 octets by inserting an the 56-bit key be expanded into 8 octets by inserting an odd
odd parity bit in the most significant bit of the octet to go parity bit in the most significant bit of the octet to go with
with each 7 bits of the key.) each 7 bits of the key.)
It is suggested that pass phrases are restricted to ASCII letters, It is suggested that pass phrases are restricted to ASCII letters,
digits, the hyphen, and white space to reduce the the chance of digits, the hyphen, and white space to reduce the the chance of
transcription errors when conveying keys by phone, fax, telex or transcription errors when conveying keys by phone, fax, telex or
email. email.
The pass phrase may be preceded by a specification of the encryption The pass phrase may be preceded by a specification of the encryption
algorithm. Any characters up to the first slash (ASCII 0x2f) are algorithm. Any characters up to the first slash (ASCII 0x2f) are
taken as the name of the encryption algorithm. The encryption format taken as the name of the encryption algorithm. The encryption format
specifiers should be drawn from RFC 1423 or any additional specifiers should be drawn from RFC 1423 or any additional
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timestamp clock rate; the names defined here are 3 or 4 timestamp clock rate; the names defined here are 3 or 4
characters long to allow a compact representation if needed; characters long to allow a compact representation if needed;
oindication of who has change control over the encoding (for oindication of who has change control over the encoding (for
example, ISO, ITU-T, other international standardization example, ISO, ITU-T, other international standardization
bodies, a consortium or a particular company or group of bodies, a consortium or a particular company or group of
companies); companies);
oany operating parameters or profiles; oany operating parameters or profiles;
oa reference to a further description, if available, for example o a reference to a further description, if available, for
(in order of preference) an RFC, a published paper, a patent example (in order of preference) an RFC, a published paper, a
filing, a technical report, documented source code or a patent filing, a technical report, documented source code or a
computer manual; computer manual;
ofor proprietary encodings, contact information (postal and ofor proprietary encodings, contact information (postal and
email address); email address);
othe payload type value for this profile, if necessary (see othe payload type value for this profile, if necessary (see
below). below).
Note that not all encodings to be used by RTP need to be assigned a Note that not all encodings to be used by RTP need to be assigned a
static payload type. Non-RTP means beyond the scope of this memo static payload type. There will be no additional static payload
(such as directory services or invitation protocols) may be used to types assigned beyond the ones described in this document. Non-RTP
establish a dynamic mapping between a payload type and an encoding means beyond the scope of this memo (such as directory services or
("dynamic payload types"). Applications should first use the range 96 invitation protocols) may be used to establish a dynamic mapping
to 127 for dynamic payload types. Only applications which need to between a payload type and an encoding ("dynamic payload types").
define more than 32 dynamic payload types may redefine codes below Applications should first use the range 96 to 127 for dynamic payload
96. Redefining payload types below 96 may cause incorrect operation types. Only applications which need to define more than 32 dynamic
if an attempt is made to join a session without obtaining session payload types may redefine codes below 96. Redefining payload types
description information that defines the dynamic payload types. below 96 may cause incorrect operation if an attempt is made to join
a session without obtaining session description information that
defines the dynamic payload types.
Note that dynamic payload types should not be used without a well- Dynamic payload types should not be used without a well-defined
defined mechanism to indicate the mapping. Systems that expect to mechanism to indicate the mapping. Systems that expect to
interoperate with others operating under this profile should not interoperate with others operating under this profile should not
assign proprietary encodings to particular, fixed payload types in assign proprietary encodings to particular, fixed payload types in
the range reserved for dynamic payload types. SDP (RFC XXXX ) defines the range reserved for dynamic payload types. The Session Description
such a mapping mechanism. Protocol (SDP), RFC 2327 [1], defines such a mapping mechanism.
The available payload type space is relatively small. Thus, new
static payload types are assigned only if the following conditions
are met:
oThe encoding is of interest to the Internet community at large.
oIt offers benefits compared to existing encodings and/or is
required for interoperation with existing, widely deployed
conferencing or multimedia systems.
oThe description is sufficient to build a decoder.
For implementor convenience, this profile contains descriptions of The available payload type space is relatively small. Thus, no new
static payload types will be assigned beyond the current list. For
implementor convenience, this profile contains descriptions of
encodings which do not currently have a static payload type assigned encodings which do not currently have a static payload type assigned
to them. to them. SDP uses the encoding names defined here.
The Session Description Protocol (SDP) (RFC XXXX) uses the encoding
names defined here.
4 Audio 4 Audio
4.1 Encoding-Independent Rules 4.1 Encoding-Independent Rules
For applications which send either no packets or comfort-noise For applications which send either no packets or comfort-noise
packets during silence, the first packet of a talkspurt, that is, the packets during silence, the first packet of a talkspurt, that is, the
first packet after a silence period, is distinguished by setting the first packet after a silence period, is distinguished by setting the
marker bit in the RTP data header to one. The marker bits in all marker bit in the RTP data header to one. The marker bits in all
other packets is zero. The beginning of a talkspurt may be used to other packets is zero. The beginning of a talkspurt may be used to
adjust the playout delay to reflect changing network delays. adjust the playout delay to reflect changing network delays.
Applications without silence suppression set the bit to zero. Applications without silence suppression set the bit to zero.
The RTP clock rate used for generating the RTP timestamp is The RTP clock rate used for generating the RTP timestamp is
independent of the number of channels and the encoding; it equals the independent of the number of channels and the encoding; it equals the
number of sampling periods per second. For !N!-channel encodings, number of sampling periods per second. For N-channel encodings, each
each sampling period (say, 1/8000 of a second) generates !N! samples. sampling period (say, 1/8000 of a second) generates N samples. (This
(This terminology is standard, but somewhat confusing, as the total terminology is standard, but somewhat confusing, as the total number
number of samples generated per second is then the sampling rate of samples generated per second is then the sampling rate times the
times the channel count.) channel count.)
If multiple audio channels are used, channels are numbered left-to- If multiple audio channels are used, channels are numbered left-to-
right, starting at one. In RTP audio packets, information from right, starting at one. In RTP audio packets, information from
lower-numbered channels precedes that from higher-numbered channels. lower-numbered channels precedes that from higher-numbered channels.
For more than two channels, the convention followed by the AIFF-C For more than two channels, the convention followed by the AIFF-C
audio interchange format should be followed [1], using the following audio interchange format should be followed [2], using the following
notation: notation:
l left l left
r right r right
c center c center
S surround S surround
F front F front
R rear R rear
channels description channel channels description channel
1 2 3 4 5 6 1 2 3 4 5 6
________________________________________________________________ ________________________________________________________________
2 stereo l r 2 stereo l r
3 l r c 3 l r c
4 quadrophonic Fl Fr Rl Rr 4 quadrophonic Fl Fr Rl Rr
4 l c r S 4 l c r S
5 Fl Fr Fc Sl Sr 5 Fl Fr Fc Sl Sr
6 l lc c r rc S 6 l lc c r rc S
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number of frames per packet. number of frames per packet.
RTP packets shall contain a whole number of frames, with frames RTP packets shall contain a whole number of frames, with frames
inserted according to age within a packet, so that the oldest frame inserted according to age within a packet, so that the oldest frame
(to be played first) occurs immediately after the RTP packet header. (to be played first) occurs immediately after the RTP packet header.
The RTP timestamp reflects the capturing time of the first sample in The RTP timestamp reflects the capturing time of the first sample in
the first frame, that is, the oldest information in the packet. the first frame, that is, the oldest information in the packet.
4.5 Audio Encodings 4.5 Audio Encodings
The characteristics of standard audio encodings are shown in Table 1;
those assigned static payload types are listed in Table 3. While most
audio codecs are only specified for a fixed sampling rate, some
sample-based algorithms (indicated by an entry of "var." in the
sampling rate column of Table 1) may be used with different sampling
rates, resulting in different coded bit rates. Non-RTP means MUST
indicate the appropriate sampling rate.
4.5.1 1016
Encoding 1016 is a frame based encoding using code-excited linear
prediction (CELP) and is specified in Federal Standard FED-STD 1016
[2,3,4,5].
4.5.2 CN
The CN (comfort noise) packet contains a single-octet message to the
receiver to play comfort noise at the absolute level specified. This
message would normally be sent once at the beginning of a silence
period (which also indicates the transition from speech to silence),
but rate of noise level updates is implementation specific. The
magnitude of the noise level is packed into the least significant
bits of the noise-level payload, as shown below.
name of sampling default name of sampling default
encoding sample/frame bits/sample rate ms/frame ms/packet encoding sample/frame bits/sample rate ms/frame ms/packet
____________________________________________________________________________ ____________________________________________________________________________
1016 frame N/A 8,000 30 30 1016 frame N/A 8,000 30 30
CN frame N/A var. CN frame N/A var.
DVI4 sample 4 var. 20 DVI4 sample 4 var. 20
G722 sample 8 16,000 20 G722 sample 8 16,000 20
G723 frame N/A 8,000 30 30 G723 frame N/A 8,000 30 30
G726-16 sample 2 8,000 20 G726-16 sample 2 8,000 20
G726-24 sample 3 8,000 20 G726-24 sample 3 8,000 20
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G727-40 sample 5 8,000 20 G727-40 sample 5 8,000 20
G728 frame N/A 8,000 2.5 20 G728 frame N/A 8,000 2.5 20
G729 frame N/A 8,000 10 20 G729 frame N/A 8,000 10 20
GSM frame N/A 8,000 20 20 GSM frame N/A 8,000 20 20
L8 sample 8 var. 20 L8 sample 8 var. 20
L16 sample 16 var. 20 L16 sample 16 var. 20
LPC frame N/A 8,000 20 20 LPC frame N/A 8,000 20 20
MPA frame N/A var. 20 MPA frame N/A var. 20
PCMA sample 8 var. 20 PCMA sample 8 var. 20
PCMU sample 8 var. 20 PCMU sample 8 var. 20
QCELP frame N/A 8,000 20
SX7300P frame N/A 8,000 15 30 SX7300P frame N/A 8,000 15 30
SX8300P frame N/A 8,000 15 30 SX8300P frame N/A 8,000 15 30
SX9600P frame N/A 8,000 15 30
VDVI sample var. var. 20 VDVI sample var. var. 20
Table 1: Properties of Audio Encodings (N/A: not applicable; var.: Table 1: Properties of Audio Encodings (N/A: not applicable; var.:
variable) variable)
The characteristics of standard audio encodings are shown in Table 1;
they are listed in order of their payload type in Table 4. Entries
with payload type "dyn" have a dynamic rather than static payload
type. While most audio codecs are only specified for a fixed sampling
rate, some sample-based algorithms (indicated by an entry of "var."
in the sampling rate column of Table 1) may be used with different
sampling rates, resulting in different coded bit rates. Non-RTP means
MUST indicate the appropriate sampling rate.
4.5.1 1016
Encoding 1016 is a frame based encoding using code-excited linear
prediction (CELP) and is specified in Federal Standard FED-STD 1016
[3,4,5,6].
4.5.2 CN
The CN (comfort noise) packet contains a single-octet message to the
receiver to play comfort noise at the absolute level specified. This
message would normally be sent once at the beginning of a silence
period (which also indicates the transition from speech to silence),
but rate of noise level updates is implementation specific. The
magnitude of the noise level is packed into the least significant
bits of the noise-level payload, as shown below.
The noise level is expressed in dBov, with values from 0 to 127 dBov. The noise level is expressed in dBov, with values from 0 to 127 dBov.
dBov is the level relative to the overload of the system. (Note: dBov is the level relative to the overload of the system. (Note:
Representation relative to the overload point of a system is Representation relative to the overload point of a system is
particularly useful for digital implementations, since one does not particularly useful for digital implementations, since one does not
need to know the relative calibration of the analog circuitry.) need to know the relative calibration of the analog circuitry.)
Example: In 16-bit linear PCM system (L16), a signal with 0 dBov Example: In 16-bit linear PCM system (L16), a signal with 0 dBov
represents a square wave with the maximum possible amplitude (+/- represents a square wave with the maximum possible amplitude (+/-
32767). -63 dBov corresponds to -58 dBm0 in a standard telephone 32767). -63 dBov corresponds to -58 dBm0 in a standard telephone
system. (dBm is the power level in decibels relative to 1 mW, with an system. (dBm is the power level in decibels relative to 1 mW, with an
impedance of 600 Ohms.) impedance of 600 Ohms.)
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sampling rates are needed, they should be defined through dynamic sampling rates are needed, they should be defined through dynamic
payload types. The RTP packet should not have the marker bit set. payload types. The RTP packet should not have the marker bit set.
The CN payload type is primarily for use with L16, DVI4, PCMA, PCMU The CN payload type is primarily for use with L16, DVI4, PCMA, PCMU
and other audio codecs that do not support comfort noise as part of and other audio codecs that do not support comfort noise as part of
the codec itself. G.723.1 and G.729 have their own comfort noise the codec itself. G.723.1 and G.729 have their own comfort noise
systems as part of Annexes A (G.723.1) and B (G.729), respectively. systems as part of Annexes A (G.723.1) and B (G.729), respectively.
4.5.3 DVI4 4.5.3 DVI4
DVI4 is specified, with pseudo-code, in [6] as the IMA ADPCM wave DVI4 is specified, with pseudo-code, in [7] as the IMA ADPCM wave
type. type.
However, the encoding defined here as DVI4 differs in three respects However, the encoding defined here as DVI4 differs in three respects
from this recommendation: from this recommendation:
oThe RTP DVI4 header contains the predicted value rather than oThe RTP DVI4 header contains the predicted value rather than
the first sample value contained the IMA ADPCM block header. the first sample value contained the IMA ADPCM block header.
oIMA ADPCM blocks contain an odd number of samples, since the oIMA ADPCM blocks contain an odd number of samples, since the
first sample of a block is contained just in the header first sample of a block is contained just in the header
(uncompressed), followed by an even number of compressed (uncompressed), followed by an even number of compressed
samples. DVI4 has an even number of compressed samples only, samples. DVI4 has an even number of compressed samples only,
using the 'predict' word from the header to decode the first using the 'predict' word from the header to decode the first
sample. sample.
oFor DVI4, the 4-bit samples are packed with the first sample in o For DVI4, the 4-bit samples are packed with the first sample
the four most significant bits and the second sample in the in the four most significant bits and the second sample in the
four least significant bits. In the IMA ADPCM codec, the four least significant bits. In the IMA ADPCM codec, the
samples are packed in little-endian order. samples are packed in little-endian order.
Each packet contains a single DVI block. This profile only defines Each packet contains a single DVI block. This profile only defines
the 4-bit-per-sample version, while IMA also specifies a 3-bit-per- the 4-bit-per-sample version, while IMA also specifies a 3-bit-per-
sample encoding. sample encoding.
The "header" word for each channel has the following structure: The "header" word for each channel has the following structure:
int16 predict; /* predicted value of first sample int16 predict; /* predicted value of first sample
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G729 is specified in ITU-T Recommendation G.729, "Coding of speech at G729 is specified in ITU-T Recommendation G.729, "Coding of speech at
8 kbit/s using conjugate structure-algebraic code excited linear 8 kbit/s using conjugate structure-algebraic code excited linear
prediction (CS-ACELP)". A complexity-reduced version of the G.729 prediction (CS-ACELP)". A complexity-reduced version of the G.729
algorithm is specified in Annex A to Rec. G.729. The speech coding algorithm is specified in Annex A to Rec. G.729. The speech coding
algorithms in the main body of G.729 and in G.729 Annex A are fully algorithms in the main body of G.729 and in G.729 Annex A are fully
interoperable with each other, so there is no need to further interoperable with each other, so there is no need to further
distinguish between them. The G.729 and G.729 Annex A codecs were distinguish between them. The G.729 and G.729 Annex A codecs were
optimized to represent speech with high quality, where G.729 Annex A optimized to represent speech with high quality, where G.729 Annex A
trades some speech quality for an approximate 50% complexity trades some speech quality for an approximate 50% complexity
reduction [7]. reduction [8].
A voice activity detector (VAD) and comfort noise generator (CNG) A voice activity detector (VAD) and comfort noise generator (CNG)
algorithm in Annex B of G.729 is recommended for digital simultaneous algorithm in Annex B of G.729 is recommended for digital simultaneous
voice and data applications and can be used in conjunction with G.729 voice and data applications and can be used in conjunction with G.729
or G.729 Annex A. A G.729 or G.729 Annex A frame contains 10 octets, or G.729 Annex A. A G.729 or G.729 Annex A frame contains 10 octets,
while the G.729 Annex B comfort noise frame occupies 2 octets: while the G.729 Annex B comfort noise frame occupies 2 octets:
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The encoding name "G729B" is assigned for the case when a particular The encoding name "G729B" is assigned for the case when a particular
RTP payload type is to contain G.729 Annex B comfort noise packets RTP payload type is to contain G.729 Annex B comfort noise packets
only. This may be necessary if the underlying RTP mechanism has no only. This may be necessary if the underlying RTP mechanism has no
means of distinguishing talkspurt from comfort-noise packets. means of distinguishing talkspurt from comfort-noise packets.
4.5.10 GSM 4.5.10 GSM
GSM (group speciale mobile) denotes the European GSM 06.10 GSM (group speciale mobile) denotes the European GSM 06.10
provisional standard for full-rate speech transcoding, prI-ETS 300 provisional standard for full-rate speech transcoding, prI-ETS 300
036, which is based on RPE/LTP (residual pulse excitation/long term 036, which is based on RPE/LTP (residual pulse excitation/long term
prediction) coding at a rate of 13 kb/s [8,9,10]. The text of the prediction) coding at a rate of 13 kb/s [9,10,11]. The text of the
standard can be obtained from standard can be obtained from
ETSI (European Telecommunications Standards Institute) ETSI (European Telecommunications Standards Institute)
ETSI Secretariat: B.P.152 ETSI Secretariat: B.P.152
F-06561 Valbonne Cedex F-06561 Valbonne Cedex
France France
Phone: +33 92 94 42 00 Phone: +33 92 94 42 00
Fax: +33 93 65 47 16 Fax: +33 93 65 47 16
Blocks of 160 audio samples are compressed into 33 octets, for an Blocks of 160 audio samples are compressed into 33 octets, for an
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packing than that specified here. packing than that specified here.
In the GSM encoding used by RTP, the bits are packed beginning from In the GSM encoding used by RTP, the bits are packed beginning from
the most significant bit. Every 160 sample GSM frame is coded into the most significant bit. Every 160 sample GSM frame is coded into
one 33 octet (264 bit) buffer. Every such buffer begins with a 4 bit one 33 octet (264 bit) buffer. Every such buffer begins with a 4 bit
signature (0xD), followed by the MSB encoding of the fields of the signature (0xD), followed by the MSB encoding of the fields of the
frame. The first octet thus contains 1101 in the 4 most significant frame. The first octet thus contains 1101 in the 4 most significant
bits (0-3) and the 4 most significant bits of F1 (0-3) in the 4 least bits (0-3) and the 4 most significant bits of F1 (0-3) in the 4 least
significant bits (4-7). The second octet contains the 2 least significant bits (4-7). The second octet contains the 2 least
significant bits of F1 in bits 0-1, and F2 in bits 2-7, and so on. significant bits of F1 in bits 0-1, and F2 in bits 2-7, and so on.
The order of the fields in the frame is as follows:
The order of the fields in the frame is described in Table 2.
4.5.10.2 GSM variable names and numbers 4.5.10.2 GSM variable names and numbers
So if F.i signifies the ith bit of the field F, and bit 0 is the most So if F.i signifies the ith bit of the field F, and bit 0 is the most
significant bit, and the bits of every octet are numbered from 0 to 7 significant bit, and the bits of every octet are numbered from 0 to 7
from most to least significant, then in the RTP encoding we have: from most to least significant, then in the RTP encoding we have the
bit pattern described in Table 3.
4.5.11 L8 4.5.11 L8
L8 denotes linear audio data, using 8-bits of precision with an L8 denotes linear audio data, using 8-bits of precision with an
offset of 128, that is, the most negative signal is encoded as zero. offset of 128, that is, the most negative signal is encoded as zero.
4.5.12 L16
L16 denotes uncompressed audio data, using 16-bit signed
representation with 65535 equally divided steps between minimum and
maximum signal level, ranging from -32768 to 32767. The value is
represented in two's complement notation and network byte order.
4.5.13 LPC
LPC designates an experimental linear predictive encoding contributed
by Ron Frederick, Xerox PARC, which is based on an implementation
written by Ron Zuckerman, Motorola, posted to the Usenet group
comp.dsp on June 26, 1992. The codec generates 14 octets for every
frame. The framesize is set to 20 ms, resulting in a bit rate of
5,600 b/s.
4.5.14 MPA
MPA denotes MPEG-I or MPEG-II audio encapsulated as elementary
streams. The encoding is defined in ISO standards ISO/IEC 11172-3
and 13818-3. The encapsulation is specified in RFC 2250 [12].
Sampling rate and channel count are contained in the payload. MPEG-I
audio supports sampling rates of 32, 44.1, and 48 kHz (ISO/IEC
11172-3, section 1.1; "Scope"). MPEG-II additionally supports
sampling rates of 16, 22.05 and 24 kHz.
4.5.15 PCMA and PCMU
PCMA and PCMU are specified in ITU-T Recommendation G.711. Audio data
is encoded as eight bits per sample, after logarithmic scaling. PCMU
denotes mu-law scaling, PCMA A-law scaling. A detailed description is
field field name bits field field name bits field field name bits field field name bits
__________________________________________________________ __________________________________________________________
1 LARc[0] 6 39 xmc[22] 3 1 LARc[0] 6 39 xmc[22] 3
2 LARc[1] 6 40 xmc[23] 3 2 LARc[1] 6 40 xmc[23] 3
3 LARc[2] 5 41 xmc[24] 3 3 LARc[2] 5 41 xmc[24] 3
4 LARc[3] 5 42 xmc[25] 3 4 LARc[3] 5 42 xmc[25] 3
5 LARc[4] 4 43 Nc[2] 7 5 LARc[4] 4 43 Nc[2] 7
6 LARc[5] 4 44 bc[2] 2 6 LARc[5] 4 44 bc[2] 2
7 LARc[6] 3 45 Mc[2] 2 7 LARc[6] 3 45 Mc[2] 2
8 LARc[7] 3 46 xmaxc[2] 6 8 LARc[7] 3 46 xmaxc[2] 6
skipping to change at page 18, line 48 skipping to change at page 18, line 47
32 xmc[15] 3 70 xmc[45] 3 32 xmc[15] 3 70 xmc[45] 3
33 xmc[16] 3 71 xmc[46] 3 33 xmc[16] 3 71 xmc[46] 3
34 xmc[17] 3 72 xmc[47] 3 34 xmc[17] 3 72 xmc[47] 3
35 xmc[18] 3 73 xmc[48] 3 35 xmc[18] 3 73 xmc[48] 3
36 xmc[19] 3 74 xmc[49] 3 36 xmc[19] 3 74 xmc[49] 3
37 xmc[20] 3 75 xmc[50] 3 37 xmc[20] 3 75 xmc[50] 3
38 xmc[21] 3 76 xmc[51] 3 38 xmc[21] 3 76 xmc[51] 3
Table 2: Ordering of GSM variables Table 2: Ordering of GSM variables
4.5.12 L16 given by Jayant and Noll [13]. Each G.711 octet shall be octet-
aligned in an RTP packet. The sign bit of each G.711 octet shall
L16 denotes uncompressed audio data, using 16-bit signed correspond to the most significant bit of the octet in the RTP packet
representation with 65535 equally divided steps between minimum and (i.e., assuming the G.711 samples are handled as octets on the host
Octet Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7 Octet Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7
_____________________________________________________________________________________________ _____________________________________________________________________________________________
0 1 1 0 1 LARc0.0 LARc0.1 LARc0.2 LARc0.3 0 1 1 0 1 LARc0.0 LARc0.1 LARc0.2 LARc0.3
1 LARc0.4 LARc0.5 LARc1.0 LARc1.1 LARc1.2 LARc1.3 LARc1.4 LARc1.5 1 LARc0.4 LARc0.5 LARc1.0 LARc1.1 LARc1.2 LARc1.3 LARc1.4 LARc1.5
2 LARc2.0 LARc2.1 LARc2.2 LARc2.3 LARc2.4 LARc3.0 LARc3.1 LARc3.2 2 LARc2.0 LARc2.1 LARc2.2 LARc2.3 LARc2.4 LARc3.0 LARc3.1 LARc3.2
3 LARc3.3 LARc3.4 LARc4.0 LARc4.1 LARc4.2 LARc4.3 LARc5.0 LARc5.1 3 LARc3.3 LARc3.4 LARc4.0 LARc4.1 LARc4.2 LARc4.3 LARc5.0 LARc5.1
4 LARc5.2 LARc5.3 LARc6.0 LARc6.1 LARc6.2 LARc7.0 LARc7.1 LARc7.2 4 LARc5.2 LARc5.3 LARc6.0 LARc6.1 LARc6.2 LARc7.0 LARc7.1 LARc7.2
5 Nc0.0 Nc0.1 Nc0.2 Nc0.3 Nc0.4 Nc0.5 Nc0.6 bc0.0 5 Nc0.0 Nc0.1 Nc0.2 Nc0.3 Nc0.4 Nc0.5 Nc0.6 bc0.0
6 bc0.1 Mc0.0 Mc0.1 xmaxc00 xmaxc01 xmaxc02 xmaxc03 xmaxc04 6 bc0.1 Mc0.0 Mc0.1 xmaxc00 xmaxc01 xmaxc02 xmaxc03 xmaxc04
7 xmaxc05 xmc0.0 xmc0.1 xmc0.2 xmc1.0 xmc1.1 xmc1.2 xmc2.0 7 xmaxc05 xmc0.0 xmc0.1 xmc0.2 xmc1.0 xmc1.1 xmc1.2 xmc2.0
8 xmc2.1 xmc2.2 xmc3.0 xmc3.1 xmc3.2 xmc4.0 xmc4.1 xmc4.2 8 xmc2.1 xmc2.2 xmc3.0 xmc3.1 xmc3.2 xmc4.0 xmc4.1 xmc4.2
9 xmc5.0 xmc5.1 xmc5.2 xmc6.0 xmc6.1 xmc6.2 xmc7.0 xmc7.1 9 xmc5.0 xmc5.1 xmc5.2 xmc6.0 xmc6.1 xmc6.2 xmc7.0 xmc7.1
10 xmc7.2 xmc8.0 xmc8.1 xmc8.2 xmc9.0 xmc9.1 xmc9.2 xmc10.0 10 xmc7.2 xmc8.0 xmc8.1 xmc8.2 xmc9.0 xmc9.1 xmc9.2 xmc10.0
11 xmc10.1 xmc10.2 xmc11.0 xmc11.1 xmc11.2 xmc12.0 xmc12.1 xcm12.2 11 xmc10.1 xmc10.2 xmc11.0 xmc11.1 xmc11.2 xmc12.0 xmc12.1 xcm12.2
12 Nc1.0 Nc1.1 Nc1.2 Nc1.3 Nc1.4 Nc1.5 Nc1.6 bc1.0 12 Nc1.0 Nc1.1 Nc1.2 Nc1.3 Nc1.4 Nc1.5 Nc1.6 bc1.0
13 bc1.1 Mc1.0 Mc1.1 xmaxc10 xmaxc11 xmaxc12 xmaxc13 xmaxc14 13 bc1.1 Mc1.0 Mc1.1 xmaxc10 xmaxc11 xmaxc12 xmaxc13 xmaxc14
skipping to change at page 19, line 41 skipping to change at page 19, line 40
24 xmc33.2 xmc34.0 xmc34.1 xmc34.2 xmc35.0 xmc35.1 xmc35.2 xmc36.0 24 xmc33.2 xmc34.0 xmc34.1 xmc34.2 xmc35.0 xmc35.1 xmc35.2 xmc36.0
25 Xmc36.1 xmc36.2 xmc37.0 xmc37.1 xmc37.2 xmc38.0 xmc38.1 xmc38.2 25 Xmc36.1 xmc36.2 xmc37.0 xmc37.1 xmc37.2 xmc38.0 xmc38.1 xmc38.2
26 Nc3.0 Nc3.1 Nc3.2 Nc3.3 Nc3.4 Nc3.5 Nc3.6 bc3.0 26 Nc3.0 Nc3.1 Nc3.2 Nc3.3 Nc3.4 Nc3.5 Nc3.6 bc3.0
27 bc3.1 Mc3.0 Mc3.1 xmaxc30 xmaxc31 xmaxc32 xmaxc33 xmaxc34 27 bc3.1 Mc3.0 Mc3.1 xmaxc30 xmaxc31 xmaxc32 xmaxc33 xmaxc34
28 xmaxc35 xmc39.0 xmc39.1 xmc39.2 xmc40.0 xmc40.1 xmc40.2 xmc41.0 28 xmaxc35 xmc39.0 xmc39.1 xmc39.2 xmc40.0 xmc40.1 xmc40.2 xmc41.0
29 xmc41.1 xmc41.2 xmc42.0 xmc42.1 xmc42.2 xmc43.0 xmc43.1 xmc43.2 29 xmc41.1 xmc41.2 xmc42.0 xmc42.1 xmc42.2 xmc43.0 xmc43.1 xmc43.2
30 xmc44.0 xmc44.1 xmc44.2 xmc45.0 xmc45.1 xmc45.2 xmc46.0 xmc46.1 30 xmc44.0 xmc44.1 xmc44.2 xmc45.0 xmc45.1 xmc45.2 xmc46.0 xmc46.1
31 xmc46.2 xmc47.0 xmc47.1 xmc47.2 xmc48.0 xmc48.1 xmc48.2 xmc49.0 31 xmc46.2 xmc47.0 xmc47.1 xmc47.2 xmc48.0 xmc48.1 xmc48.2 xmc49.0
32 xmc49.1 xmc49.2 xmc50.0 xmc50.1 xmc50.2 xmc51.0 xmc51.1 xmc51.2 32 xmc49.1 xmc49.2 xmc50.0 xmc50.1 xmc50.2 xmc51.0 xmc51.1 xmc51.2
maximum signal level, ranging from --32768 to 32767. The value is Table 3: GSM payload format
represented in two's complement notation and network byte order.
4.5.13 LPC
LPC designates an experimental linear predictive encoding contributed machine, the sign bit shall be the most signficant bit of the octet
by Ron Frederick, Xerox PARC, which is based on an implementation as defined by the host machine format). The 56 kb/s and 48 kb/s modes
written by Ron Zuckerman, Motorola, posted to the Usenet group of G.711 are not applicable to RTP, since G.711 shall always be
comp.dsp on June 26, 1992. The codec generates 14 octets for every transmitted as 8-bit samples.
frame. The framesize is set to 20 ms, resulting in a bit rate of
5,600 b/s.
4.5.14 MPA 4.5.16 QCELP
MPA denotes MPEG-I or MPEG-II audio encapsulated as elementary The packetization of the QCELP audio codec is described in [14].
streams. The encoding is defined in ISO standards ISO/IEC 11172-3
and 13818-3. The encapsulation is specified in RFC 2038 [11].
Sampling rate and channel count are contained in the payload. MPEG-I 4.5.17 RED
audio supports sampling rates of 32000, 44100, and 48000 Hz (ISO/IEC
11172-3, section 1.1; "Scope"). MPEG-II additionally supports ISO/IEC
11172-3 Audio. "TBD"). [Something missing here.]
4.5.15 PCMA and PCMU The redundant audio payload format "RED" is specified by RFC 2198
[15]. It defines a means by which multiple redundant copies of an
audio packet may be transmitted in a single RTP stream. Each packet
in such a stream contains, in addition to the audio data for that
packetization interval, a (more heavily compressed) copy of the data
from the previous packetization interval. This allows an
approximation of the data from lost packets to be recovered upon
decoding of the following packet, giving much improved sound quality
when compared with silence substitution for lost packets.
PCMA and PCMU are specified in ITU-T Recommendation G.711. Audio data 4.5.18 SX*
is encoded as eight bits per sample, after logarithmic scaling. PCMU
denotes mu-law scaling, PCMA A-law scaling. A detailed description is
given by Jayant and Noll [12]. Each G.711 octet shall be octet-
aligned in an RTP packet. The sign bit of each G.711 octet shall
correspond to the most significant bit of the octet in the RTP packet
(i.e., assuming the G.711 samples are handled as octets on the host
machine, the sign bit shall be the most signficant bit of the octet
as defined by the host machine format). The 56 kb/s and 48 kb/s modes
of G.711 are not applicable to RTP, since G.711 shall always be
transmitted as 8-bit samples.
4.5.16 RED The SX7300P, SX8300P and SX9600P codecs are part of the same
compatible family and distinguished by the first octet in each frame,
where "x" can be any value:
The redundant audio payload format "RED" is specified by RFC XXX. It 0 1 2 3 4 5 6 7
defines a means by which multiple redundant copies of an audio packet +-+-+-+-+-+-+-+-+
may be transmitted in a single RTP stream. Each packet in such a |0 0 x | SX7300P bitstream (14 byte frame)
stream contains, in addition to the audio data for that packetization |0 1 0 | SX8300P bitstream (16 byte frame)
interval, a (more heavily compressed) copy of the data from the |1 0 x | VAD bistream ( 2 byte frame)
previous packetization interval. This allows an approximation of the |1 1 x | SX9600P bitstream (18 byte frame)
data from lost packets to be recovered upon decoding of the following +-+-+-+-+-+-+-+-+
packet, giving much improved sound quality when compared with silence
substitution for lost packets.
4.5.17 SX7300P 4.5.18.1 SX7300P
The SX7300P is a low-complexity CELP-based audio codec operating at a The SX7300P is a low-complexity CELP-based audio codec operating at a
sampling rate of 8000 Hz. It encodes blocks of 120 audio samples (15 sampling rate of 8000 Hz. It encodes blocks of 120 audio samples (15
ms) into an encoded frame of 14 octets, yielding an encoded bit rate ms) into an encoded frame of 14 octets, yielding an encoded bit rate
of approximately 7467 b/s. of approximately 7467 b/s.
4.5.18 SX8300P 4.5.18.2 SX8300P
The SX8300P is a low-complexity CELP-based audio codec operating at a The SX8300P is a low-complexity CELP-based audio codec operating at a
sampling rate of 8000 Hz. It encodes blocks of 120 audio samples (15 sampling rate of 8000 Hz. It encodes blocks of 120 audio samples (15
ms) into an encoded frame of 16 octets, yielding an encoded bit rate ms) into an encoded frame of 16 octets, yielding an encoded bit rate
of approximately 8533 b/s. of approximately 8533 b/s.
4.5.18.3 SX9600P
The SX9600P is a low-complexity, toll-quality CELP-based audio codec
operating at a sampling rate of 8000 Hz. It encodes blocks of 120
audio samples (15 ms) into an encoded frame of 18 octets, yielding an
encoded bit rate of 9600 b/s.
4.5.19 VDVI 4.5.19 VDVI
VDVI is a variable-rate version of DVI4, yielding speech bit rates of VDVI is a variable-rate version of DVI4, yielding speech bit rates of
between 10 and 25 kb/s. It is specified for single-channel operation between 10 and 25 kb/s. It is specified for single-channel operation
only. Samples are packed into octets starting at the most-significant only. Samples are packed into octets starting at the most-significant
bit. bit.
It uses the following encoding: It uses the following encoding:
DVI4 codeword VDVI bit pattern DVI4 codeword VDVI bit pattern
skipping to change at page 21, line 43 skipping to change at page 21, line 42
15 11111111 15 11111111
5 Video 5 Video
The following video encodings are currently defined, with their The following video encodings are currently defined, with their
abbreviated names used for identification: abbreviated names used for identification:
5.1 CelB 5.1 CelB
The CELL-B encoding is a proprietary encoding proposed by Sun The CELL-B encoding is a proprietary encoding proposed by Sun
Microsystems. The byte stream format is described in RFC 2029 [13]. Microsystems. The byte stream format is described in RFC 2029 [16].
5.2 JPEG 5.2 JPEG
The encoding is specified in ISO Standards 10918-1 and 10918-2. The The encoding is specified in ISO Standards 10918-1 and 10918-2. The
RTP payload format is as specified in RFC 2035 [14]. RTP payload format is as specified in RFC 2035 [17].
5.3 H261 5.3 H261
The encoding is specified in ITU-T Recommendation H.261, "Video codec The encoding is specified in ITU-T Recommendation H.261, "Video codec
for audiovisual services at p x 64 kbit/s". The packetization and for audiovisual services at p x 64 kbit/s". The packetization and
RTP-specific properties are described in RFC 2032 [15]. RTP-specific properties are described in RFC 2032 [18].
5.4 H263 5.4 H263
The encoding is specified in ITU-T Recommendation H.263, "Video The encoding is specified in ITU-T Recommendation H.263, "Video
coding for low bit rate communication". The packetization and RTP- coding for low bit rate communication". The packetization and RTP-
specific properties are described in [16]. specific properties are described in [19].
5.5 MPV 5.5 MPV
MPV designates the use MPEG-I and MPEG-II video encoding elementary MPV designates the use MPEG-I and MPEG-II video encoding elementary
streams as specified in ISO Standards ISO/IEC 11172 and 13818-2, streams as specified in ISO Standards ISO/IEC 11172 and 13818-2,
respectively. The RTP payload format is as specified in RFC 2038 respectively. The RTP payload format is as specified in RFC 2250
[11], Section 3. [12], Section 3.
5.6 MP2T 5.6 MP2T
MP2T designates the use of MPEG-II transport streams, for either MP2T designates the use of MPEG-II transport streams, for either
audio or video. The encapsulation is described in RFC 2038 [11], audio or video. The encapsulation is described in RFC 2250 [12],
Section 2. See the description of the MPA audio encoding for contact Section 2.
information.
5.7 nv 5.7 MP1S
MP1S designates an MPEG-I systems stream, encapsulated according to
RFC 2250 [12].
5.8 MP2P
MP2P designates an MPEG-II program stream, encapsulated according to
RFC 2250 [12].
5.9 nv
The encoding is implemented in the program 'nv', version 4, developed The encoding is implemented in the program 'nv', version 4, developed
at Xerox PARC by Ron Frederick. Further information is available from at Xerox PARC by Ron Frederick. Further information is available from
the author: the author:
Ron Frederick Ron Frederick
Xerox Palo Alto Research Center Xerox Palo Alto Research Center
3333 Coyote Hill Road 3333 Coyote Hill Road
Palo Alto, CA 94304 Palo Alto, CA 94304
United States United States
electronic mail: frederic@parc.xerox.com electronic mail: frederic@parc.xerox.com
6 Payload Type Definitions 6 Payload Type Definitions
Table 4 defines this profile's static payload type values for the PT
Table 3 defines this profile's static payload type values for the PT
field of the RTP data header. A new RTP payload format specification field of the RTP data header. A new RTP payload format specification
may be registered with the IANA by name, and may also be assigned a may be registered with the IANA by name. In addition, payload type
static payload type value from the range marked in Section 3. values in the range 96-127 may be defined dynamically through a
conference control protocol, which is beyond the scope of this
In addition, payload type values in the range 96--127 may be defined document. For example, a session directory could specify that for a
dynamically through a conference control protocol, which is beyond given session, payload type 96 indicates PCMU encoding, 8,000 Hz
the scope of this document. For example, a session directory could sampling rate, 2 channels. The payload type range marked 'reserved'
specify that for a given session, payload type 96 indicates PCMU has been set aside so that RTCP and RTP packets can be reliably
encoding, 8,000 Hz sampling rate, 2 channels. The payload type range distinguished (see Section "Summary of Protocol Constants" of the RTP
marked 'reserved' has been set aside so that RTCP and RTP packets can protocol specification).
be reliably distinguished (see Section "Summary of Protocol
Constants" of the RTP protocol specification).
An RTP source emits a single RTP payload type at any given instant. An RTP source emits a single RTP payload type at any given instant.
The interleaving or multiplexing of several RTP media types within a The interleaving or multiplexing of several RTP media types within a
single RTP session is not allowed, but multiple RTP sessions may be single RTP session is not allowed, but multiple RTP sessions may be
used in parallel to send multiple media types. An RTP source may used in parallel to send multiple media types. An RTP source may
change payload types during a session. change payload types during a session.
The payload types currently defined in this profile are assigned to The payload types currently defined in this profile are assigned to
exactly one of three categories or media types : audio only, video exactly one of three categories or media types : audio only, video
only and those combining audio and video. A single RTP session only and those combining audio and video. A single RTP session
consists of payload types of one and only media type. consists of payload types of one and only media type.
Session participants agree through mechanisms beyond the scope of Session participants agree through mechanisms beyond the scope of
this specification on the set of payload types allowed in a given this specification on the set of payload types allowed in a given
session. This set may, for example, be defined by the capabilities session. This set may, for example, be defined by the capabilities
of the applications used, negotiated by a conference control protocol of the applications used, negotiated by a conference control protocol
or established by agreement between the human participants. The media or established by agreement between the human participants. The media
types in Table 3 are marked as "A" for audio, "V" for video and "AV" types in Table 4 are marked as "A" for audio, "V" for video and "AV"
for combined audio/video streams. for combined audio/video streams.
Audio applications operating under this profile should, at minimum, Audio applications operating under this profile should, at minimum,
be able to send and receive payload types 0 (PCMU) and 5 (DVI4). This be able to send and receive payload types 0 (PCMU) and 5 (DVI4). This
allows interoperability without format negotiation and successful allows interoperability without format negotiation and successful
negotation with a conference control protocol. negotation with a conference control protocol.
All current video encodings use a timestamp frequency of 90,000 Hz, All current video encodings use a timestamp frequency of 90,000 Hz,
the same as the MPEG presentation time stamp frequency. This the same as the MPEG presentation time stamp frequency. This
frequency yields exact integer timestamp increments for the typical frequency yields exact integer timestamp increments for the typical
skipping to change at page 23, line 49 skipping to change at page 24, line 6
and 50, 59.94 and 60 Hz field rates. While 90 kHz is the recommended and 50, 59.94 and 60 Hz field rates. While 90 kHz is the recommended
rate for future video encodings used within this profile, other rates rate for future video encodings used within this profile, other rates
are possible. However, it is not sufficient to use the video frame are possible. However, it is not sufficient to use the video frame
rate (typically between 15 and 30 Hz) because that does not provide rate (typically between 15 and 30 Hz) because that does not provide
adequate resolution for typical synchronization requirements when adequate resolution for typical synchronization requirements when
calculating the RTP timestamp corresponding to the NTP timestamp in calculating the RTP timestamp corresponding to the NTP timestamp in
an RTCP SR packet. The timestamp resolution must also be sufficient an RTCP SR packet. The timestamp resolution must also be sufficient
for the jitter estimate contained in the receiver reports. for the jitter estimate contained in the receiver reports.
The standard video encodings and their payload types are listed in The standard video encodings and their payload types are listed in
Table 3. Table 4.
PT encoding media type clock rate channels
name (Hz) (audio)
_______________________________________________________________
0 PCMU A 8000 1
1 1016 A 8000 1
2 G726-32 A 8000 1
3 GSM A 8000 1
4 G723 A 8000 1
5 DVI4 A 8000 1
6 DVI4 A 16000 1
7 LPC A 8000 1
8 PCMA A 8000 1
9 G722 A 16000 1
10 L16 A 44100 2
11 L16 A 44100 1
12 unassigned A
13 unassigned A
14 MPA A 90000 (see text)
15 G728 A 8000 1
16 DVI4 A 11025 1
17 DVI4 A 22050 1
18 G729 A 8000 1
19 CN A 8000 1
20 unassigned A
21 unassigned A
22 unassigned A
23 unassigned A
24 unassigned V
25 CelB V 90000
26 JPEG V 90000
27 unassigned V
28 nv V 90000
29 unassigned V
30 unassigned V
31 H261 V 90000
32 MPV V 90000
33 MP2T AV 90000
34 H263 V 90000
35--71 unassigned ?
72--76 reserved N/A N/A N/A
77 RED A N/A N/A
78--95 unassigned ?
96--127 dynamic ?
Table 3: Payload types (PT) for standard audio and video encodings
7 RTP over TCP and Similar Byte Stream Protocols 7 RTP over TCP and Similar Byte Stream Protocols
Under special circumstances, it may be necessary to carry RTP in Under special circumstances, it may be necessary to carry RTP in
protocols offering a byte stream abstraction, such as TCP, possibly protocols offering a byte stream abstraction, such as TCP, possibly
multiplexed with other data. If the application does not define its multiplexed with other data. If the application does not define its
own method of delineating RTP and RTCP packets, it SHOULD prefix each own method of delineating RTP and RTCP packets, it SHOULD prefix each
packet with a two-octet length field. packet with a two-octet length field.
(Note: RTSP [17] provides its own encapsulation and does not need an (Note: RTSP [20] provides its own encapsulation and does not need an
extra length indication.) extra length indication.)
8 Port Assignment 8 Port Assignment
As specified in the RTP protocol definition, RTP data is to be As specified in the RTP protocol definition, RTP data is to be
carried on an even UDP or TCP port number and the corresponding RTCP carried on an even UDP or TCP port number and the corresponding RTCP
packets are to be carried on the next higher (odd) port number. packets are to be carried on the next higher (odd) port number.
Applications operating under this profile may use any such UDP or TCP Applications operating under this profile may use any such UDP or TCP
port pair. For example, the port pair may be allocated randomly by a port pair. For example, the port pair may be allocated randomly by a
skipping to change at page 25, line 45 skipping to change at page 24, line 48
Applications need not have a default and may require that the port Applications need not have a default and may require that the port
pair be explicitly specified. The particular port numbers were chosen pair be explicitly specified. The particular port numbers were chosen
to lie in the range above 5000 to accomodate port number allocation to lie in the range above 5000 to accomodate port number allocation
practice within the Unix operating system, where port numbers below practice within the Unix operating system, where port numbers below
1024 can only be used by privileged processes and port numbers 1024 can only be used by privileged processes and port numbers
between 1024 and 5000 are automatically assigned by the operating between 1024 and 5000 are automatically assigned by the operating
system. system.
9 Bibliography 9 Bibliography
[1] Apple Computer, "Audio interchange file format AIFF-C," Aug. [1] M. Handley and V. Jacobson, "SDP: Session Description Protocol,"
Request for Comments (Proposed Standard) RFC 2327, Internet
Engineering Task Force, Apr. 1998.
[2] Apple Computer, "Audio interchange file format AIFF-C," Aug.
1991. (also ftp://ftp.sgi.com/sgi/aiff-c.9.26.91.ps.Z). 1991. (also ftp://ftp.sgi.com/sgi/aiff-c.9.26.91.ps.Z).
[2] Office of Technology and Standards, "Telecommunications: Analog [3] Office of Technology and Standards, "Telecommunications: Analog
to digital conversion of radio voice by 4,800 bit/second code excited to digital conversion of radio voice by 4,800 bit/second code excited
linear prediction (celp)," Federal Standard FS-1016, GSA, Room 6654; linear prediction (celp)," Federal Standard FS-1016, GSA, Room 6654;
7th & D Street SW; Washington, DC 20407 (+1-202-708-9205), 1990. 7th & D Street SW; Washington, DC 20407 (+1-202-708-9205), 1990.
[3] J. P. Campbell, Jr., T. E. Tremain, and V. C. Welch, "The [4] J. P. Campbell, Jr., T. E. Tremain, and V. C. Welch, "The
proposed Federal Standard 1016 4800 bps voice coder: CELP," Speech proposed Federal Standard 1016 4800 bps voice coder: CELP," Speech
Technology , vol. 5, pp. 58--64, April/May 1990. Technology , vol. 5, pp. 58--64, April/May 1990.
[4] J. P. Campbell, Jr., T. E. Tremain, and V. C. Welch, "The federal [5] J. P. Campbell, Jr., T. E. Tremain, and V. C. Welch, "The federal
standard 1016 4800 bps CELP voice coder," Digital Signal Processing , standard 1016 4800 bps CELP voice coder," Digital Signal Processing ,
vol. 1, no. 3, pp. 145--155, 1991. vol. 1, no. 3, pp. 145--155, 1991.
[5] J. P. Campbell, Jr., T. E. Tremain, and V. C. Welch, "The dod 4.8 [6] J. P. Campbell, Jr., T. E. Tremain, and V. C. Welch, "The dod 4.8
kbps standard (proposed federal standard 1016)," in Advances in kbps standard (proposed federal standard 1016)," in Advances in
Speech Coding (B. Atal, V. Cuperman, and A. Gersho, eds.), ch. 12, Speech Coding (B. Atal, V. Cuperman, and A. Gersho, eds.), ch. 12,
pp. 121--133, Kluwer Academic Publishers, 1991. pp. 121--133, Kluwer Academic Publishers, 1991.
[6] IMA Digital Audio Focus and Technical Working Groups, [7] IMA Digital Audio Focus and Technical Working Groups,
"Recommended practices for enhancing digital audio compatibility in "Recommended practices for enhancing digital audio compatibility in
multimedia systems (version 3.00)," tech. rep., Interactive multimedia systems (version 3.00)," tech. rep., Interactive
Multimedia Association, Annapolis, Maryland, Oct. 1992. Multimedia Association, Annapolis, Maryland, Oct. 1992.
[7] D. Deléam and J.-P. Petit, "Real-time implementations of the [8] D. Deleam and J.-P. Petit, "Real-time implementations of the
recent ITU-T low bit rate speech coders on the TI TMS320C54X DSP: recent ITU-T low bit rate speech coders on the TI TMS320C54X DSP:
results, methodology, and applications," in Proc. of International results, methodology, and applications," in Proc. of International
Conference on Signal Processing, Technology, and Applications Conference on Signal Processing, Technology, and Applications
(ICSPAT) , (Boston, Massachusetts), pp. 1656--1660, Oct. 1996. (ICSPAT) , (Boston, Massachusetts), pp. 1656--1660, Oct. 1996.
[8] M. Mouly and M.-B. Pautet, The GSM system for mobile [9] M. Mouly and M.-B. Pautet, The GSM system for mobile
communications Lassay-les-Chateaux, France: Europe Media Duplication, communications Lassay-les-Chateaux, France: Europe Media Duplication,
1993. 1993.
[9] J. Degener, "Digital speech compression," Dr. Dobb's Journal , [10] J. Degener, "Digital speech compression," Dr. Dobb's Journal ,
Dec. 1994. Dec. 1994.
[10] S. M. Redl, M. K. Weber, and M. W. Oliphant, An Introduction to [11] S. M. Redl, M. K. Weber, and M. W. Oliphant, An Introduction to
GSM Boston: Artech House, 1995. GSM Boston: Artech House, 1995.
[11] D. Hoffman, G. Fernando, and V. Goyal, "RTP payload format for [12] D. Hoffman, G. Fernando, V. Goyal, and M. Civanlar, "RTP payload
MPEG1/MPEG2 video," Request for Comments (Proposed Standard) RFC format for MPEG1/MPEG2 video," Request for Comments (Proposed
2038, Internet Engineering Task Force, Oct. 1996. Standard) RFC 2250, Internet Engineering Task Force, Jan. 1998.
[12] N. S. Jayant and P. Noll, Digital Coding of Waveforms-- [13] N. S. Jayant and P. Noll, Digital Coding of Waveforms--
Principles and Applications to Speech and Video Englewood Cliffs, New Principles and Applications to Speech and Video Englewood Cliffs, New
PT encoding media type clock rate channels
name (Hz) (audio)
_______________________________________________________________
0 PCMU A 8000 1
1 1016 A 8000 1
2 G726-32 A 8000 1
3 GSM A 8000 1
4 G723 A 8000 1
5 DVI4 A 8000 1
6 DVI4 A 16000 1
7 LPC A 8000 1
8 PCMA A 8000 1
9 G722 A 16000 1
10 L16 A 44100 2
11 L16 A 44100 1
12 QCELP A 8000 1
13 unassigned A
14 MPA A 90000 (see text)
15 G728 A 8000 1
16 DVI4 A 11025 1
17 DVI4 A 22050 1
18 G729 A 8000 1
19 CN A 8000 1
20 unassigned A
21 unassigned A
22 unassigned A
23 unassigned A
24 unassigned V
25 CelB V 90000
26 JPEG V 90000
27 unassigned V
28 nv V 90000
29 unassigned V
30 unassigned V
31 H261 V 90000
32 MPV V 90000
33 MP2T AV 90000
34 H263 V 90000
35--71 unassigned ?
72--76 reserved N/A N/A N/A
77--95 unassigned ?
96--127 dynamic ?
dyn RED A
dyn MP1S V 90000
dyn MP2P V 90000
Table 4: Payload types (PT) for standard audio and video encodings
Jersey: Prentice-Hall, 1984. Jersey: Prentice-Hall, 1984.
[13] M. Speer and D. Hoffman, "RTP payload format of sun's CellB [14] K. McKay, "RTP Payload Format for PureVoice(tm) Audio", Internet
Draft, Internet Engineering Task Force, Oct. 1998. Work in progress.
[15] C. Perkins, I. Kouvelas, O. Hodson, V. Hardman, M. Handley, J.C.
Bolot, A. Vega-Garcia, and S. Fosse-Parisis, "RTP Payload for
Redundant Audio Data," Request for Comments (Proposed Standard) RFC
2198, Internet Engineering Task Force, Sep. 1997.
[16] M. Speer and D. Hoffman, "RTP payload format of sun's CellB
video encoding," Request for Comments (Proposed Standard) RFC 2029, video encoding," Request for Comments (Proposed Standard) RFC 2029,
Internet Engineering Task Force, Oct. 1996. Internet Engineering Task Force, Oct. 1996.
[14] L. Berc, W. Fenner, R. Frederick, and S. McCanne, "RTP payload [17] L. Berc, W. Fenner, R. Frederick, and S. McCanne, "RTP payload
format for JPEG-compressed video," Request for Comments (Proposed format for JPEG-compressed video," Request for Comments (Proposed
Standard) RFC 2035, Internet Engineering Task Force, Oct. 1996. Standard) RFC 2035, Internet Engineering Task Force, Oct. 1996.
[15] T. Turletti and C. Huitema, "RTP payload format for H.261 video [18] T. Turletti and C. Huitema, "RTP payload format for H.261 video
streams," Request for Comments (Proposed Standard) RFC 2032, Internet streams," Request for Comments (Proposed Standard) RFC 2032, Internet
Engineering Task Force, Oct. 1996. Engineering Task Force, Oct. 1996.
[16] C. C. Zhu, "RTP payload format for H.263 video streams," [19] C. Zhu, "RTP payload format for H.263 video streams," Request
Internet Draft, Internet Engineering Task Force, Mar. 1997. Work in for Comments (Proposed Standard) RFC 2190, Internet Engineering Task
progress. Force, Sep. 1997.
[17] H. Schulzrinne, A. Rao, and R. Lanphier, "Real time streaming [20] H. Schulzrinne, A. Rao, and R. Lanphier, "Real time streaming
protocol (RTSP)," Internet Draft, Internet Engineering Task Force, protocol (RTSP)," Request for Comments (Proposed Standard) RFC 2326,
July 1997. Work in progress. Internet Engineering Task Force, Apr. 1998.
10 Acknowledgements 10 Acknowledgements
The comments and careful review of Steve Casner, Simao Campos and The comments and careful review of Steve Casner, Simao Campos and
Richard Cox are gratefully acknowledged. The GSM description was Richard Cox are gratefully acknowledged. The GSM description was
adopted from the IMTC Voice over IP Forum Service Interoperability adopted from the IMTC Voice over IP Forum Service Interoperability
Implementation Agreement (January 1997). Fred Burg and Terry Lyons Implementation Agreement (January 1997). Fred Burg and Terry Lyons
helped with the G.729 description. helped with the G.729 description.
11 Address of Author 11 Address of Author
skipping to change at page 29, line 43 skipping to change at page 30, line 15
LPC LPC
An implementation is available at An implementation is available at
ftp://parcftp.xerox.com/pub/net-research/lpc.tar.Z ftp://parcftp.xerox.com/pub/net-research/lpc.tar.Z
PCMU, PCMA PCMU, PCMA
An implementation of these algorithm is available as part of the An implementation of these algorithm is available as part of the
ITU-T STL, described above. Code to convert between linear and mu-law ITU-T STL, described above. Code to convert between linear and mu-law
companded data is also available in [6]. companded data is also available in [7].
Table of Contents Table of Contents
1 Introduction ........................................ 2 1 Introduction ........................................ 2
2 RTP and RTCP Packet Forms and Protocol Behavior ..... 3 2 RTP and RTCP Packet Forms and Protocol Behavior ..... 3
3 Registering Payload Types ........................... 5 3 Registering Payload Types ........................... 5
4 Audio ............................................... 6 4 Audio ............................................... 6
4.1 Encoding-Independent Rules .......................... 6 4.1 Encoding-Independent Rules .......................... 6
4.2 Operating Recommendations ........................... 7 4.2 Operating Recommendations ........................... 7
4.3 Guidelines for Sample-Based Audio Encodings ......... 8 4.3 Guidelines for Sample-Based Audio Encodings ......... 8
4.4 Guidelines for Frame-Based Audio Encodings .......... 8 4.4 Guidelines for Frame-Based Audio Encodings .......... 8
4.5 Audio Encodings ..................................... 9 4.5 Audio Encodings ..................................... 9
4.5.1 1016 ................................................ 9 4.5.1 1016 ................................................ 10
4.5.2 CN .................................................. 9 4.5.2 CN .................................................. 10
4.5.3 DVI4 ................................................ 11 4.5.3 DVI4 ................................................ 11
4.5.4 G722 ................................................ 12 4.5.4 G722 ................................................ 12
4.5.5 G723 ................................................ 12 4.5.5 G723 ................................................ 12
4.5.6 G726-16, G726-24, G726-32, G726-40 .................. 13 4.5.6 G726-16, G726-24, G726-32, G726-40 .................. 13
4.5.7 G727-16, G727-24, G727-32, G727-40 .................. 14 4.5.7 G727-16, G727-24, G727-32, G727-40 .................. 13
4.5.8 G728 ................................................ 14 4.5.8 G728 ................................................ 13
4.5.9 G729 ................................................ 15 4.5.9 G729 ................................................ 14
4.5.10 GSM ................................................. 17 4.5.10 GSM ................................................. 16
4.5.10.1 General Packaging Issues ............................ 17 4.5.10.1 General Packaging Issues ............................ 16
4.5.10.2 GSM variable names and numbers ...................... 17 4.5.10.2 GSM variable names and numbers ...................... 17
4.5.11 L8 .................................................. 17 4.5.11 L8 .................................................. 17
4.5.12 L16 ................................................. 18 4.5.12 L16 ................................................. 17
4.5.13 LPC ................................................. 19 4.5.13 LPC ................................................. 17
4.5.14 MPA ................................................. 20 4.5.14 MPA ................................................. 17
4.5.15 PCMA and PCMU ....................................... 20 4.5.15 PCMA and PCMU ....................................... 17
4.5.16 RED ................................................. 20 4.5.16 QCELP ............................................... 19
4.5.17 SX7300P ............................................. 20 4.5.17 RED ................................................. 20
4.5.18 SX8300P ............................................. 20 4.5.18 SX* ................................................. 20
4.5.18.1 SX7300P ............................................. 20
4.5.18.2 SX8300P ............................................. 20
4.5.18.3 SX9600P ............................................. 20
4.5.19 VDVI ................................................ 21 4.5.19 VDVI ................................................ 21
5 Video ............................................... 21 5 Video ............................................... 21
5.1 CelB ................................................ 21 5.1 CelB ................................................ 21
5.2 JPEG ................................................ 21 5.2 JPEG ................................................ 21
5.3 H261 ................................................ 22 5.3 H261 ................................................ 21
5.4 H263 ................................................ 22 5.4 H263 ................................................ 22
5.5 MPV ................................................. 22 5.5 MPV ................................................. 22
5.6 MP2T ................................................ 22 5.6 MP2T ................................................ 22
5.7 nv .................................................. 22 5.7 MP1S ................................................ 22
5.8 MP2P ................................................ 22
5.9 nv .................................................. 22
6 Payload Type Definitions ............................ 22 6 Payload Type Definitions ............................ 22
7 RTP over TCP and Similar Byte Stream Protocols ...... 25 7 RTP over TCP and Similar Byte Stream Protocols ...... 24
8 Port Assignment ..................................... 25 8 Port Assignment ..................................... 24
9 Bibliography ........................................ 25 9 Bibliography ........................................ 24
10 Acknowledgements .................................... 27 10 Acknowledgements .................................... 27
11 Address of Author ................................... 27 11 Address of Author ................................... 27
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