Audio/Video Transport Working Group S. Ikonin
Internet Draft SPIRIT DSP
Intended status: Proposed Standard October 13, 2010
RTP Payload Format for IP-MR Speech Codec
draft-ietf-avt-rtp-ipmr-14.txt
Abstract
This document specifies the payload format for packetization of
SPIRIT IP-MR encoded speech signals into the real-time transport
protocol (RTP). The payload format supports transmission of multiple
frames per packet and introduced redundancy for robustness against
packet loss and bit errors.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and 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.
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/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
This Internet-Draft will expire on December 18, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
Ikonin Expires April 16, 2011 [Page 1]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
The source codes included in this document are provided under BSD
license (http://trustee.ietf.org/docs/IETF-Trust-License-Policy.pdf).
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. IP-MR Codec Description . . . . . . . . . . . . . . . . . . . . 3
3. Payload Format . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. RTP Header Usage . . . . . . . . . . . . . . . . . . . . . 4
3.2. RTP Payload Structure . . . . . . . . . . . . . . . . . . . 5
3.3. Speech Payload Header . . . . . . . . . . . . . . . . . . . 5
3.4. Speech Payload Table of Contents . . . . . . . . . . . . . 6
3.5. Speech Payload Data . . . . . . . . . . . . . . . . . . . . 6
3.6. Redundancy Payload Header . . . . . . . . . . . . . . . . . 7
3.7. Redundancy Payload Table of Contents . . . . . . . . . . . 8
3.8. Redundancy Payload Data . . . . . . . . . . . . . . . . . . 8
4. Payload Examples . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. Payload Carrying a Single Frame . . . . . . . . . . . . . . 9
4.2. Payload Carrying Multiple Frames with Redundancy . . . . 10
5. Congestion Control . . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. Payload Format Parameters . . . . . . . . . . . . . . . . . . 12
7.1. Media Type Registration . . . . . . . . . . . . . . . . . 13
7.2. Mapping Media Type Parameters into SDP . . . . . . . . . 14
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. Normative References . . . . . . . . . . . . . . . . . . . . . 14
10. Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . 15
11. Legal Terms . . . . . . . . . . . . . . . . . . . . . . . . . 15
12. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 16
APPENDIX A. RETRIEVING FRAME INFORMATION . . . . . . . . . . . . 17
A.1. get_frame_info.c . . . . . . . . . . . . . . . . . . . . 17
Ikonin Expires April 16, 2011 [Page 2]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
1. Introduction
This document specifies the payload format for packetization of
SPIRIT IP-MR encoded speech signals into the real-time transport
protocol (RTP). The payload format supports transmission of multiple
frames per packet and introduced redundancy for robustness against
packet loss and bit errors.
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 RFC 2119 [RFC 2119].
2. IP-MR Codec Description
IP-MR is a wideband speech codec designed by SPIRIT for conferencing
services over packet-switched networks such as the Internet.
IP-MR is a scalable codec. It means that not only source has the
ability to change transmission rate on a fly, but the gateway is also
able to decrease bandwidth at any time without performance overhead.
There are 6 coding rates from 7.7 to 34.2 kbps available.
Codec operates on a frame-by-frame basis with a frame size of 20 ms
at 16 kHz sampling rate with the total end-to-end delay of 25ms. Each
compressed frame represented as a sequence of layers. The first
(base) layer is mandatory while the other (enhancement) can be safely
discarded. Information about particular frame structure is available
from the payload header. In order to adjust outgoing bandwidth the
gateway MUST read frame(s) structure from the payload header, define
which enhancement layers to discard and compose new RTP packet
according to this specification.
In fact, not all of bits within a frame are equally tolerant to
distortion. IP-MR defines 6 classes ('A'-'F') of sensitivity to bit
errors. Any damage of class 'A' bits cause significant reconstruction
artifacts while the lost in class 'F' may be even not perceived by
the listener. Note, only base layer in a bitstream is represented as
a set of classes.
The IP-MR payload format allows frame duplicate through the packets
to improve robustness against packet loss (Section 3.6). Base layer
can be retransmitted completely or in several sensitive classes.
Enchantment layers are not retransmittable.
The fine-grained redundancy in conjunction with bitrate scalability
allows application adjust the trade-off between overhead and
robustness against packet loss. Note, this approach supported
natively within a packet and requires no out-of-band signals or
Ikonin Expires April 16, 2011 [Page 3]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
session initialization procedures.
Main IP-MR features are as the following:
o High quality wideband speech codec.
o Bitrate scalable with 6 average rates from 7.7 to 34.2 kbps.
o Built-in discontinuous transmission (DTX) and comfort noise
generation (CNG) support.
o Flexible in-band redundancy control scheme for packet loss
protection.
3. Payload Format
The payload format consists of the RTP header, and IP-MR payload.
3.1. RTP Header Usage
The format of the RTP header is specified in RFC 1889. This payload
format uses the fields of the header in a manner consistent with that
specification.
The RTP timestamp corresponds to the sampling instant of the first
sample encoded for the first frame-block in the packet. The timestamp
clock frequency SHALL be 16 kHz. The duration of one frame is 20 ms,
this corresponding to 320 samples per frame. Thus the timestamp is
increased by 320 for each consecutive frame. The timestamp is also
used to recover the correct decoding order of the frame-blocks.
The RTP header marker bit (M) SHALL be set to 1 whenever the first
frame-block carried in the packet is the first frame-block in a
talkspurt (see definition of the talkspurt in Section 4.1
[RFC 3551]). For all other packets, the marker bit SHALL be set to
zero (M=0).
The assignment of an RTP payload type for the format defined in this
memo is outside the scope of this document. The RTP profiles in use
currently mandate binding the payload type dynamically for this
payload format. This is basically necessary because the payload type
expresses the configuration of the payload itself, i.e. basic or
interleaved mode, and the number of channels carried.
The remaining RTP header fields are used as specified in [RFC 3550].
Ikonin Expires April 16, 2011 [Page 4]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
3.2. RTP Payload Structure
The IP-MR payload composed of two payloads, one for current (speech)
speech and one for redundancy. Both of payloads are represented in a
form of: Header, Table of contents (TOC) and Data. Redundancy payload
carries data for preceding and pre-preceding packets.
+--------+-----+----------------------+- - - - +- - +- - - - - +
| Header | TOC | Data | Header | TOC | Data |
+--------+-----+----------------------+- - - - +- - +- - - - - +
|<- Speech -------------------------->|<- Redundancy (opt) ---->|
3.3. Speech Payload Header
This header carries parameters which are common for all frames in the
packet:
0 1
0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+
|T| CR | BR |D|A|GR |R|
+-+-+-+-+-+-+-+-+-+-+-+-+
o T (1 bit): Reserved. MUST be always set to 0. Receiver SHOULD
discard packet if 'T' bit is not equal to 0.
o CR (3 bits): Coding rate index - top enchantment layer
available. The CR value 7 (NO_DATA) indicates that there is no
speech data (and speech TOC accordingly) in the payload. This MAY
be used to transmit redundancy data only.
o BR (3 bits): Base rate index - base layer bitrate. Speech
payload can be scaled to any rate index between BR and CR. Packets
with BR = 6 or BR > CR MUST be discarded. Redundancy data is also
considered as having a base rate of BR.
o D (1 bit): Reserved. MUST be always set to 1. Receiver MAY
discard packet if 'D' bit is zero.
o A (1 bit): Byte-alignment. The value of 1 specifies that padding
bits were added to enable each compressed frame (3.5) starts with
the byte (8 bit) boundary. The value of 0 specifies unaligned
frames. Note, speech payload is always padded to byte boundary
independently on 'A' bit value.
o GR (2 bits): Number of frames in packet (grouping size). Actual
grouping size is GR + 1, thus maximum grouping supported is 4.
Ikonin Expires April 16, 2011 [Page 5]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
o R (1 bit): Redundancy presence. Value of 1 indicates redundancy
payload presence.
Note, the values of 'T' and 'D' bits are fixed, any other values are
not allowed by specification. Note, the values of padding bit is not
specified.
The following table defines mapping between rate index and rate
value:
+------------+--------------+
| rate index | avg. bitrate |
+------------+--------------+
| 0 | 7.7 kbps |
| 1 | 9.8 kbps |
| 2 | 14.3 kbps |
| 3 | 20.8 kbps |
| 4 | 27.9 kbps |
| 5 | 34.2 kbps |
| 6 | (reserved) |
| 7 | NO_DATA |
+------------+--------------+
The value of 6 is reserved. If receiving this value the packet MUST
be discarded.
3.4. Speech Payload Table of Contents
The speech TOC is a bit mask indicating the presence of each frame in
the packet. TOC is only available if 'CR' value is not equal to 7
(NO_DATA).
0 1 2 3
+-+-+-+-+
|E|E|E|E|
+-+-+-+-+
|<----->| <-- #(GR+1)
o E (1 bit): Frame existence indicator. The value of 0 indicates
speech data does not present for corresponding frame. IP-MR
encoder sets E flag to 0 for the periods of silence in DTX mode.
Application MUST set this bit to 0 if the frame is known to be
damaged.
3.5. Speech Payload Data
Speech data contains (GR+1) compressed IP-MR frames (20ms of data).
Compressed frame have zero length if corresponding TOC flag is zero.
Ikonin Expires April 16, 2011 [Page 6]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
The beginning of each compressed frame is aligned if 'A' bit is
nonzero, while the end of speech payload is always aligned to a byte
(8 bit) boundary:
+- - -+------------+------------+------------+------------+
| TOC | Frame1 | Frame2 | Frame3 | Frame4 |
+- - -+------------+------------+------------+------------+ ALWAYS
|<- aligned |<- aligned |<- aligned |<- aligned |<- ALIGNED
Marked regions MUST be padded only if 'A' bit is set to '1'.
The compressed frame structure is the following:
|<---- sensitive classes ------>|<----- enchantment layers -------->|
+-------------------------------+----+-----+------+- - - - - +------+
| L1 (Base Layer) | L2 | L3 | L4 | | LN |
+-------------------------------+----+-----+------+- - - - - +------+
|<- A --->|<- B ->| ... |<- F ->| |
|<- BR rate ------------------->| |
|<- CR rate ------------------------------------------------------->|
The Annex A of this document provides helper routine written in "C"
which MUST be used to extract sensitivity classes and enchantment
layers bounds from the compressed frame data.
3.6. Redundancy Payload Header
The redundancy payload presence is signaled by R bit of speech
payload header. Redundancy header composed of two fields of 3 bits
each:
0 1 2 3 4 5
+-+-+-+-+-+-+
| CL1 | CL2 |
+-+-+-+-+-+-+
Both of 'CL1' and 'CL2' fields specify the sensitivity classes
available for preceding and pre-preceding packets correspondingly.
Ikonin Expires April 16, 2011 [Page 7]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
+-------+--------------------+
| CL | Redundancy classes |
| | available |
+-------+--------------------+
| 0 | NONE |
| 1 | A |
| 2 | A-B |
| 3 | A-C |
| 4 | A-D |
| 5 | A-E |
| 6 | A-F |
| 7 | (reserved) |
+-------+--------------------+
Receiver can reconstruct base layer of preceding packets completely
(CL=6) or partially (0<CL< 6) based on sensitivity classes delivered.
Decoder MUST discard redundancy payload if CL is equal to 0 or 7.
Note, the index of the base rate and grouping parameter are not
transmitted for redundancy payload. Application MUST assume that 'BR'
and 'GR' are the same as for current packet.
3.7. Redundancy Payload Table of Contents
The redundancy TOC is a bit mask indicating the presence of each
frame in the redundancy payload. Redundancy TOC is only available if
'CL' value is not equal to 0 or 7.
0 1 ...
+-+-+-+-+-+-+-+-+
|E|E|E|E|E|E|E|E|
+-+-+-+-+-+-+-+-+
| |<----->| pre-preceding payload #(GR+1)
|<----->| preceding payload #(GR+1)
o E (1 bit): Redundancy frame existence indicator. The value of 0
indicates redundancy data does not present for corresponding frame.
3.8. Redundancy Payload Data
IP-MR defines 6 classes ('A'-'F') of sensitivity to bit errors. Any
damage of class 'A' bits cause significant reconstruction artifacts
while the lost in class 'F' may be even not perceived by the
listener. Note, only base layer in a bitstream is represented as a
set of classes. Together, the set of sensitivity classes approach and
redundancy allows IP-MR duplicate frames through the packets to
improve robustness against packet loss.
Ikonin Expires April 16, 2011 [Page 8]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
Redundancy data carries a number of sensitivity classes for preceding
and pre-preceding packets as indicated by 'CL1' and 'CL2' fields of
redundancy header. The sensitivity classes data is available
individually for each frame only if corresponding 'E' bit of
redundancy TOC is nonzero:
+---+---+----+----|-----+-----+-----+-----+-----+-----+-----+
|A-C|A-B|1000|1001|cl_A1|cl_B1|cl_C1|cl_A1|cl_B1|cl_A4|cl_B4|
+---+---+----+----|-----+-----+-----+-----+-----+-----+-----+
|<- CL >|<- TOC ->|<- preceding --->|<- pre-preceding ----->|
Redundancy data only available if base (BR) and coding (CR) rates of
preceding and pre-preceding packets are the same as for the current
packet.
Receiver MAY use redundancy data to compensate packet loss, note this
case the 'CL' field MUST be also passed to decoder. Helper routine
provided in Annex A MUST be used to extract sensitivity classes
length for each frame. The following pseudo code describes the
sequence of operations:
int sensitivityBits[numOfRedundancyFrames][6];
int redundancyBits [numOfRedundancyFrames];
for(i = 0 ; i < numOfRedundancyFrames; i++) {
GetFrameInfo(CR, BR, pRedundancyPayloadData, dummy,
sensitivityBits[i], dummy);
redundancyBits[i] = 0;
for(j = 0; j < CL[i]; j++ ) {
redundancyBits[i] += sensitivityBits[i][j];
}
flushBits(pRedundancyPayloadData, redundancyBits[i]);
}
4. Payload Examples
This section provides detailed examples of IP-MR payload format.
4.1. Payload Carrying a Single Frame
The following diagram shows typical IP-MR payload carrying a one
(GR=0) non-aligned (A=0) speech frame without redundancy (R=0). The
base layer is coded at 7.8 kbps (BR=0) while the coding rate is 9.7
kbps (CR=1). The 'E' bit value of 1 signals that compressed frame
bits s(0) - s(193) are present. There is a padding bit 'P' to
maintain speech payload size alignment.
Ikonin Expires April 16, 2011 [Page 9]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|CR=1 |BR=0 |1|0|0 0|0|1|s(0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| s(193)|P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.2. Payload Carrying Multiple Frames with Redundancy
The following diagram shows a payload carrying 3 (GR=2) aligned (A=1)
speech frames with redundancy (R=1). The TOC value of '101' indicates
speech data presents for a first (bits sp1(0)-sp1(92)) and third
frames (bits sp3(0)-sp3(171)). There is no enchantment layers because
of base and coding rates are equal (BR=CR=0). Padding bit 'P' is
inserted to maintain necessary alignment.
The redundancy payload presents for both preceding and pre-preceding
payloads (CL1 = A-B, CL2=A), but redundancy data only available for a
5 (TOC='111011') of 6 (2*(GR+1)) frames. There are redundancy data of
20, 39 and 35 bits for each three frames of preceding packet and 15
and 19 bits for two frames of pre-preceding packet.
Ikonin Expires April 16, 2011 [Page 10]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|CR=0 |BR=0 |1|1|1 0|1|1 0 1|P|sp1(0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sp1(92)|P|P|P|sp3(0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sp3(171)|P|P|P|P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|CL1=2|CL2=1|1 1 1|0 1 1|red1_1_AB(0) red1_1_AB(19)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|red1_2_AB(0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|red1_2_AB(38)|red1_3_AB(0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| red1_3_AB(34)|red2_2_A(0) red2_2_A(14)|red2_3_A(0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| red2_3_A(18)|P|P|P|P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5. Congestion Control The general congestion control considerations for
transporting RTP data applicable to IP-MR speech over RTP (see RTP
[RFC 3550] and any applicable RTP profile like AVP [RFC 3551]).
However, the multi-rate capability of IP-MR speech coding provides a
mechanism that may help to control congestion, since the bandwidth
demand can be adjusted by selecting a different encoding mode.
The number of frames encapsulated in each RTP payload highly
influences the overall bandwidth of the RTP stream due to header
overhead constraints. Packetizing more frames in each RTP payload can
reduce the number of packets sent and hence the overhead from
IP/UDP/RTP headers, at the expense of increased delay.
Due to scalability nature of IP_MR codec the transmission rate can be
reduced at any transport stage to fit channel bandwidth. The minimal
rate is specified by BR field of payload header and can be is low as
Ikonin Expires April 16, 2011 [Page 11]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
7.7 kbps. It is up to application to keep balance between coding
quality (high BR) and bitstream scalability (small BR). Because of
coding quality depends rather on coding rate(CR) than base rate (BR),
it is NOT RECOMMENDED to use high BR values for real-time
communications.
Application MAY utilize bitstream redundancy to combat packet loss.
But the gateway is free to chose any option to reduce transmission
rate - coding layer or redundancy bits can be dropped. Due to this
fact it is NOT RECOMMENDED application to increase total bitrate when
adding redundancy in a response to packet loss.
6. Security Considerations
RTP packets using the payload format defined in this specification
are subject to the security considerations discussed in the RTP
specification [RFC 3550] and in any applicable RTP profile. The main
security considerations for the RTP packet carrying the RTP payload
format defined within this memo are confidentiality, integrity, and
source authenticity. Confidentiality is achieved by encryption of
the RTP payload. Integrity of the RTP packets is achieved through a
suitable cryptographic integrity protection mechanism. Such a
cryptographic system may also allow the authentication of the source
of the payload. A suitable security mechanism for this RTP payload
format should provide confidentiality, integrity protection, and at
least source authentication capable of determining if an RTP packet
is from a member of the RTP session.
Note that the appropriate mechanism to provide security to RTP and
payloads following this memo may vary. It is dependent on the
application, the transport, and the signaling protocol employed.
Therefore, a single mechanism is not sufficient, although if
suitable, usage of the Secure Real-time Transport Protocol (SRTP)
[RFC 3711] is recommended. Other mechanisms that may be used are
IPsec [RFC 4301] and Transport Layer Security (TLS) [RFC 5246] (RTP
over TCP); other alternatives may exist.
This payload format does not exhibit any significant non-uniformity
in the receiver side computational complexity for packet processing
and thus is unlikely to pose a denial-of-service threat due to the
receipt of pathological data.
7. Payload Format Parameters
This section describes the media types and names associated with this
payload format.
The IP-MR media subtype is defined as 'ip-mr_v2.5'. This subtype was
Ikonin Expires April 16, 2011 [Page 12]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
registered to specify internal codec version. Later, this version was
accepted as the final, the bitstream was frozen and IP-MR v2.5 was
published under the name of IP-MR. Currently 'IP-MR' and 'IP-MR v2.5'
terms are synonyms. The subtype name ip-mr_v2.5 is being uses in
implementations.
7.1. Media Type Registration
Media Type name: audio
Media Subtype name: ip-mr_v2.5
Required parameters: none
Optional parameters:
These parameters apply to RTP transfer only.
ptime: The media packet length in milliseconds. Allowed values
are: 20, 40, 60 and 80.
Encoding considerations:
This media type is framed binary data (see RFC 4288, Section 4.8).
Security considerations:
See section 6 of RFC XXXX (RFC editor please replace with this RFC
number).
Interoperability considerations:
none
Published specification:
RFC XXXX (RFC editor please replace with this RFC number)
Applications that use this media type:
Real-time audio applications like voice over IP and
teleconference, and multi-media streaming.
Additional information:
none
Person & email address to contact for further information:
Dmitry Yudin <yudin@spiritdsp.com>
Intended usage:
COMMON
Restrictions on usage:
This media type depends on RTP framing, and hence is only defined
Ikonin Expires April 16, 2011 [Page 13]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
fortransfer via RTP [RFC 3550].
Authors:
Sergey Ikonin <info@spiritdsp.com> Dmitry Yudin
<yudin@spiritdsp.com>
Change controller:
IETF Audio/Video Transport working group delegated from the IESG.
7.2. 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)
[RFC 4566], which is commonly used to describe RTP sessions. When SDP
is used to specify sessions employing the IP-MR codec, the mapping is
as follows:
o The media type ("audio") goes in SDP "m=" as the media name.
o The media subtype (payload format name) goes in SDP "a=rtpmap"
as the encoding name. The RTP clock rate in "a=rtpmap" MUST 16000.
o The parameter "ptime" goes in the SDP "a=ptime" attributes.
Any remaining parameters go in the SDP "a=fmtp" attribute by copying
them directly from the media type parameter string as a semicolon-
separated list of parameter=value pairs.
Note that the payload format (encoding) names are commonly shown in
upper case. Media subtypes are commonly shown in lower case. These
names are case-insensitive in both places.
8. IANA Considerations
One media type has been defined and needs registration in the media
types registry.
9. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC 3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", STD 65, RFC 3551,
July 2003.
Ikonin Expires April 16, 2011 [Page 14]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
[RFC 4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC 3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E.,
Norrman, K., "The Secure Real-Time Transport Protocol
(SRTP)", RFC 3711, March 2004.
[RFC 5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC 4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
10. Disclaimer
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
11. Legal Terms
All IETF Documents and the information contained therein are provided
on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL
WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY
WARRANTY THAT THE USE OF THE INFORMATION THEREIN WILL NOT INFRINGE
ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS
FOR A PARTICULAR PURPOSE.
The IETF Trust takes no position regarding the validity or scope of
any Intellectual Property Rights or other rights that might be
claimed to pertain to the implementation or use of the technology
described in any IETF Document or the extent to which any license
under such rights might or might not be available; nor does it
represent that it has made any independent effort to identify any
such rights.
Copies of Intellectual Property disclosures made to the IETF
Secretariat and any assurances of licenses to be made available, or
Ikonin Expires April 16, 2011 [Page 15]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
the result of an attempt made to obtain a general license or
permission for the use of such proprietary rights by implementers or
users of this specification can be obtained from the IETF on-line IPR
repository at http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
any standard or specification contained in an IETF Document. Please
address the information to the IETF at ietf-ipr@ietf.org.
The definitive version of an IETF Document is that published by, or
under the auspices of, the IETF. Versions of IETF Documents that are
published by third parties, including those that are translated into
other languages, should not be considered to be definitive versions
of IETF Documents. The definitive version of these Legal Provisions
is that published by, or under the auspices of, the IETF. Versions of
these Legal Provisions that are published by third parties, including
those that are translated into other languages, should not be
considered to be definitive versions of these Legal Provisions.
For the avoidance of doubt, each Contributor to the IETF Standards
Process licenses each Contribution that he or she makes as part of
the IETF Standards Process to the IETF Trust pursuant to the
provisions of RFC 5378. No language to the contrary, or terms,
conditions or rights that differ from or are inconsistent with the
rights and licenses granted under RFC 5378, shall have any effect and
shall be null and void, whether published or posted by such
Contributor, or included with or in such Contribution.
12. Authors' Addresses
SPIRIT DSP
Building 27, A. Solzhenitsyna street
109004, Moscow, RUSSIA
Tel: +7 495 661-2178
Fax: +7 495 912-6786
EMail: yudin@spiritdsp.com
Ikonin Expires April 16, 2011 [Page 16]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
APPENDIX A. RETRIEVING FRAME INFORMATION
This appendix contains the c-code for implementation of frame parsing
function. This function extracts information about coded frame
including frame size, number of layers, size of each layer and size
of perceptual sensitive classes.
A.1. get_frame_info.c
/*
Copyright (c) 2010
IETF Trust and the persons identified as authors of the code.
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
- Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
- Neither the name of Internet Society, IETF or IETF Trust, nor
the names of specific contributors, may be used to endorse or
promote products derived from this software without specific
prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
OWNER OR CONTRIBUTORS BELIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/******************************************************************
get_frame_info.c
Ikonin Expires April 16, 2011 [Page 17]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
Retrieving frame information for IP-MR Speech Codec
******************************************************************/
#define RATES_NUM 6 // number of codec rates
#define SENSE_CLASSES 6 // number of sensitivity classes (A..F)
// frame types
#define FT_SPEECH 0 // active speech
#define FT_DTX_SID 1 // silence insertion descriptor
// get specified bit from coded data
int GetBit(unsigned char *buf, int curBit)
{
return (buf[curBit>>3]>>(curBit%8))&1;
}
// retrieve frame information
int GetFrameInfo( // o: frame size in bits
short rate, // i: encoding rate (0..5)
short base_rate, // i: base (core) layer rate,
unsigned char *buf, // i: coded bit frame
int size, // i: coded bit frame size in bytes
short pLayerBits[RATES_NUM], // o: number of bits in layers
short pSenseBits[SENSE_CLASSES], // o: number of bits in
// sensitivity classes
short *nLayers // o: number of layers
)
{
static const short Bits_1[4] = { 0, 9, 9,15};
static const short Bits_2[16] = { 43,50,36,31,46,48,40,44,
47,43,44,45,43,44,47,36};
static const short Bits_3[2][6] = {{13,11,23,33,36,31},
{25, 0,23,32,36,31},};
int FrType;
int i,nBits = 0;
if (rate < 0 || rate > 5) {
return 0; // incorrect stream
}
// extract frame type bit if required
FrType = GetBit(buf, nBits++) ? FT_SPEECH : FT_DTX_SID;
if((FrType != FT_DTX_SID && size < 2) || size < 1) {
return 0; // not enough input data
}
Ikonin Expires April 16, 2011 [Page 18]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
for(i = 0; i < SENSE_CLASSES; i++) {
pSenseBits[i] = 0;
}
{
int cw_0;
int b[14];
// extract meaning bits
for(i = 0 ; i < 14; i++) {
b[i] = GetBit(buf, nBits++);
}
// parse
if(FrType == FT_DTX_SID) {
cw_0 = (b[0]<<0)|(b[1]<<1)|(b[2]<<2)|(b[3]<<3);
rate = 0;
pSenseBits[0] = 10 + Bits_2[cw_0];
} else {
int i, idx;
int nFlag_1, nFlag_2, cw_1, cw_2;
nFlag_1 = b[0] + b[2] + b[4] + b[6];
cw_1 = (cw_1 << 1) | b[0];
cw_1 = (cw_1 << 1) | b[2];
cw_1 = (cw_1 << 1) | b[4];
cw_1 = (cw_1 << 1) | b[6];
nFlag_2 = b[1] + b[3] + b[5] + b[7];
cw_2 = (cw_2 << 1) | b[1];
cw_2 = (cw_2 << 1) | b[3];
cw_2 = (cw_2 << 1) | b[5];
cw_2 = (cw_2 << 1) | b[7];
cw_0 = (b[10]<<0)|(b[11]<<1)|(b[12]<<2)|(b[13]<<3);
if (base_rate < 0) base_rate = 0;
if (base_rate > rate) base_rate = rate;
idx = base_rate == 0 ? 0 : 1;
pSenseBits[0] = 15+Bits_2[cw_0];
pSenseBits[1] = Bits_1[(cw_1>>0)&0x3] +
Bits_1[(cw_1>>2)&0x3];
pSenseBits[2] = nFlag_1*5;
pSenseBits[3] = nFlag_2*30;
pSenseBits[5] = (4 - nFlag_2)*(Bits_3[idx][0]);
for (i = 1; i < rate+1; i++) {
Ikonin Expires April 16, 2011 [Page 19]
Internet-Draft RTP Payload Format for IP-MR Speech CodecOctober 13, 2010
pLayerBits[i] = 4*Bits_3[idx][i];
}
}
pLayerBits[0] = 0;
for (i = 0; i < SENSE_CLASSES; i++) {
pLayerBits[0] += pSenseBits[i];
}
*nLayers = rate+1;
}
{
// count total frame size
int payloadBitCount = 0;
for (i = 0; i < *nLayers; i++) {
payloadBitCount += pLayerBits[i];
}
return payloadBitCount;
}
}
Ikonin Expires April 16, 2011 [Page 20]
