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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 6262

Audio/Video Transport Working Group                            S. Ikonin
Internet Draft                                                SPIRIT DSP
Intended status: Proposed Standard                    September 20, 2010

               RTP Payload Format for IP-MR Speech Codec
                     draft-ietf-avt-rtp-ipmr-13.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
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   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



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   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 . . . . . . . . . . . . . . . . .  12
      7.2. Mapping Media Type Parameters into SDP  . . . . . . . . .  13
   8. IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  14
   9. Normative References . . . . . . . . . . . . . . . . . . . . .  14
   10. Disclaimer  . . . . . . . . . . . . . . . . . . . . . . . . .  14
   11. Legal Terms . . . . . . . . . . . . . . . . . . . . . . . . .  15
   12. Authors' Addresses  . . . . . . . . . . . . . . . . . . . . .  16
   APPENDIX A. RETRIEVING FRAME INFORMATION  . . . . . . . . . . . .  17
      A.1. get_frame_info.c  . . . . . . . . . . . . . . . . . . . .  17
















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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



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   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].






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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.




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      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.



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   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 aligned (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.












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                    +-------+--------------------+
                    |  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.




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   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.






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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |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.



















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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |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



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   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 [RFC3550] and in any applicable RTP profile. As this
   format transports encoded audio, the main security issues include
   confidentiality, integrity protection, and data origin authentication
   of the audio itself.

   The payload format itself does not have any built-in security
   mechanisms.  Any suitable external mechanisms, such as SRTP [RFC-
   3711], MAY be used.

   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.  Note, the IP-MR bitstream was frozen starting from
   internal release version of 2.5. Currently 'IP-MR' and 'IP-MR v2.5'
   terms are synonyms.

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.




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      ptime: The media packet length in in milliseconds. Allowed values
      are: 20, 40, 60 and 80.

   Encoding considerations:
      This media type is framed binary data (see RFC4288, 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
      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.



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      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.

   [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



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   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
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   Copies of Intellectual Property disclosures made to the IETF
   Secretariat and any assurances of licenses to be made available, or
   the result of an attempt made to obtain a general license or
   permission for the use of such proprietary rights by implementers or
   users of this specification can be obtained from the IETF on-line IPR
   repository at http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
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   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



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   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: info@spiritdsp.com





























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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 BE
   LIABLE 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

     Retrieving frame information for IP-MR Speech Codec

   ******************************************************************/




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   #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 *data, int curBit)
   {
     return ((data[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,
                               //    if base_rate > rate, then assumed
                               //    that base_rate = rate.
     unsigned char *pCoded,    // i: coded bit frame
     short pLayerBits          // o: number of bits in layers
         [RATES_NUM],
     short pSenseBits          // o: number of bits in sensitivity classes
         [SENSE_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;

     if (rate < 0 || rate > 5) {
       return 0; // incorrect stream
     }

     for(i = 0; i < SENSE_CLASSES; i++) {
       pSenseBits[i] = 0;
     }

     nBits = 0;
     // extract frame type bit if required
     FrType = GetBit(pCoded, nBits++) ? FT_SPEECH : FT_DTX_SID;




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     {
       int cw_0;
       int b[14];

       // extract meaning bits
       for(i = 0 ; i < 14; i++) {
           b[i] = GetBit(pCoded, 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++) {
           pLayerBits[i] = 4*(Bits_3[idx][i]);
         }
       }

       pLayerBits[0] = 0;



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       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;
     }
   }



































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