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Versions: (draft-chen-rtp-bv) 00 01 02 03 04 RFC 4298

   Internet Draft                                        Juin-Hwey Chen
   draft-ietf-avt-rtp-bv-03.txt                              Winnie Lee
   February 17, 2005                                        Jes Thyssen
   Expires: August 17, 2005                        Broadcom Corporation





       RTP Payload and Storage Format for BroadVoice Speech Codecs



Status of This Memo

   By submitting this Internet-Draft, we certify that any applicable
   patent or other IPR claims of which we are aware have been
   disclosed, or will be disclosed, and any of which we become aware
   will be disclosed, in accordance with RFC 3668.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
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   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
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   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.


Abstract

   This document describes the RTP payload format and the storage
   format for the BroadVoice(TM) narrowband and wideband speech codecs
   developed by Broadcom Corporation.  The document also provides
   specifications for the use of BroadVoice with MIME and SDP.













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Table of Contents

   1. Introduction....................................................2
   2. Background......................................................2
   3. RTP Payload Format for BroadVoice16 Narrowband Codec............3
      3.1 BroadVoice16 Bit Stream Definition..........................4
      3.2 Multiple BroadVoice16 Frames in an RTP Packet...............5
   4. RTP Payload Format for BroadVoice32 Wideband Codec..............6
      4.1 BroadVoice32 Bit Stream Definition..........................6
      4.2 Multiple BroadVoice32 Frames in an RTP Packet...............8
   5. Storage Format..................................................8
   6. IANA Considerations.............................................9
      6.1 MIME Registration of BroadVoice16...........................9
      6.2 MIME Registration of BroadVoice32..........................10
   7. Mapping to SDP Parameters......................................11
      7.1 Offer-Answer Model Considerations..........................12
   8. Security Considerations........................................12
   9. Congestion Control.............................................12
  10. Acknowledgments................................................13
  11. References.....................................................13
      11.1 Normative References......................................13
      11.2 Informative References....................................13
  12. Authors' Addresses.............................................14
  13. RFC-Editor Consideration.......................................14


1. Introduction

   This document specifies the payload format for sending BroadVoice
   encoded speech or audio signals using the Real-time Transport
   Protocol (RTP) [1].  The sender may send one or more BroadVoice
   codec data frames per packet, depending on the application scenario,
   based on network conditions, bandwidth availability, delay
   requirements, and packet-loss tolerance.

   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 [2].


2. Background

   BroadVoice is a speech codec family developed by Broadcom for VoIP
   applications, including Voice over Cable, Voice over DSL, and IP
   phone applications.  BroadVoice achieves high speech quality with
   a low coding delay and relatively low codec complexity.

   The BroadVoice codec family contains two codec versions. The
   narrowband version of BroadVoice, called BroadVoice16 [3], or BV16
   for short, encodes 8 kHz-sampled narrowband speech at a bit rate of


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   16 kilobits/second, or 16 kbit/s.  The wideband version of
   BroadVoice, called BroadVoice32, or BV32, encodes 16 kHz-sampled
   wideband speech at a bit rate of 32 kbit/s.  The BV16 and BV32 use
   very similar (but not identical) coding algorithms; they share most
   of their algorithm modules.

   To minimize the delay in real-time two-way communications, both the
   BV16 and BV32 encode speech with a very small frame size of 5 ms
   without using any look ahead.  This allows VoIP systems based on
   BroadVoice to have a very low end-to-end system delay, by using a
   packet size as small as 5 ms if necessary.

   BroadVoice also has relatively low codec complexity when compared
   with ITU-T standard speech codecs based on CELP (Coded Excited
   Linear Prediction), such as G.728, G.729, G.723.1, G.722.2, etc.
   Full-duplex implementations of the BV16 and BV32 take around 12 and
   17 MIPS, respectively, on general-purpose 16-bit fixed-point DSPs.
   The total memory footprints of the BV16 and BV32, including program
   size, data tables, and data RAM, are around 12 kwords each, or 24
   kbytes.

   The PacketCable(TM) project of Cable Television Laboratories, Inc.
   (CableLabs(r)) has chosen the BV16 codec for use in VoIP (Voice
   over Internet Protocol) telephone services provided by cable
   operators.  More specifically, the BV16 codec was selected as one
   of the mandatory audio codecs in PacketCable (TM) 1.5 Audio/Video
   Codecs Specification [4].


3. RTP Payload Format for BroadVoice16 Narrowband Codec

   The BroadVoice16 uses 5 ms frames and a sampling frequency of 8 kHz,
   so the RTP timestamp MUST be in units of 1/8000 of a second.  The
   RTP timestamp indicates the sampling instant of the oldest audio
   sample represented by the frame(s) present in the payload.  The
   RTP payload for the BroadVoice16 has the format shown in the figure
   below.  No additional header specific to this payload format is
   required.


    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      RTP Header [1]                           |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |                                                               |
   |             one or more frames of BroadVoice16                |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   If BroadVoice16 is used for applications with silence compression,
   the first BroadVoice16 packet after a silence period during which
   packets have not been transmitted contiguously, SHOULD have the
   marker bit in the RTP data header set to one.  The marker bit
   in all other packets is zero.  Applications without silence
   suppression MUST set the marker bit to zero.

   The assignment of an RTP payload type for this new packet format is
   outside the scope of this document, and will not be specified here.
   It is expected that the RTP profile for a particular class of
   applications will assign a payload type for this encoding, or if
   that is not done then a payload type in the dynamic range shall be
   chosen.


3.1 BroadVoice16 Bit Stream Definition

   The BroadVoice16 encoder operates on speech frames of 5 ms
   corresponding to 40 samples at a sampling rate of 8000 samples per
   second.  For every 5 ms frame, the encoder encodes the 40
   consecutive audio samples into 80 bits, or 10 octets.  Thus, the
   80-bit bit stream produced by the BroadVoice16 for each 5 ms frame
   is octet-aligned, and no padding bits are required.  The bit
   allocation for the encoded parameters of the BroadVoice16 codec
   is listed in the following table.


      Encoded Parameter      Codeword     Number of bits per frame
      ------------------------------------------------------------
      Line Spectrum Pairs    L0,L1            7+7=14
      Pitch Lag              PL                    7
      Pitch Gain             PG                    5
      Log-Gain               LG                    4
      Excitation Vectors     V0,...,V9       5*10=50
      ------------------------------------------------------------
      Total:                                      80 bits


   The mapping of the encoded parameters in an 80-bit BroadVoice16 data
   frame is defined in the following figure.  This figure shows the bit
   packing in "network byte order", also known as big-endian order.
   The bits of each 32-bit word are numbered 0 to 31, with the most
   significant bit on the left and numbered 0.  The octets (bytes) of
   each word are transmitted most significant octet first.  The bits of
   data field for each encoded parameter are numbered in the same
   order, with the most significant bit on the left.






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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     L0      |     L1      |      PL     |   PG    |  LG   | V0|

    |             |             |             |         |       |   |
    |0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4 5 6|0 1 2 3 4|0 1 2 3|0 1|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | V0  |    V1   |    V2   |    V3   |    V4   |    V5   |   V6  |
    |     |         |         |         |         |         |       |
    |2 3 4|0 1 2 3 4|0 1 2 3 4|0 1 2 3 4|0 1 2 3 4|0 1 2 3 4|0 1 2 3|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |V|    V7   |    V8   |   V9    |
    |6|         |         |         |
    |4|0 1 2 3 4|0 1 2 3 4|0 1 2 3 4|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 1: BroadVoice16 bit packing


3.2 Multiple BroadVoice16 Frames in an RTP Packet

   More than one BroadVoice16 frame MAY be included in a single RTP
   packet by a sender.  Senders have the following additional
   restrictions:

     o  SHOULD NOT include more BroadVoice16 frames in a single RTP
        packet than will fit in the MTU of the RTP transport protocol.

     o  MUST NOT split a BroadVoice16 frame between RTP packets.

     o  BroadVoice16 frames in an RTP packet MUST be consecutive.

   Since multiple BroadVoice16 frames in an RTP packet MUST be
   consecutive, and since BroadVoice16 has a fixed frame size of 5 ms,
   recovering the timestamps of all frames within a packet is easy.
   The oldest frame within an RTP packet has the same timestamp as the
   RTP packet, as mentioned above.  To obtain the timestamp of the
   frame that is N frames later than the oldest frame in the packet,
   one simply adds 5*N ms worth of time units to the timestamp of the
   RTP packet.

   It is RECOMMENDED that the number of frames contained within an RTP
   packet is consistent with the application.  For example, in a
   telephony application where delay is important, the fewer frames per
   packet the lower the delay, whereas for a delay insensitive
   streaming or messaging application, many frames per packet would be
   acceptable.




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   Information describing the number of frames contained in an RTP
   packet is not transmitted as part of the RTP payload.  The only way
   to determine the number of BroadVoice16 frames is to count the total
   number of octets within the RTP payload, and divide the octet count
   by 10.


4. RTP Payload Format for BroadVoice32 Wideband Codec

   The BroadVoice32 uses 5 ms frames and a sampling frequency of 16
   kHz, so the RTP timestamp MUST be in units of 1/16000 of a second.
   The RTP timestamp indicates the sampling instant of the oldest
   audio sample represented by the frame(s) present in the payload.
   The RTP payload for the BroadVoice32 has the format shown in the
   figure below.  No additional header specific to this payload format
   is required.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      RTP Header [1]                           |
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
   |                                                               |
   |             one or more frames of BroadVoice32                |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   If BroadVoice32 is used for applications with silence compression,
   the first BroadVoice32 packet after a silence period during which
   packets have not been transmitted contiguously, SHOULD have the
   marker bit in the RTP data header set to one.  The marker bit
   in all other packets is zero.  Applications without silence
   suppression MUST set the marker bit to zero.

   The assignment of an RTP payload type for this new packet format is
   outside the scope of this document, and will not be specified here.
   It is expected that the RTP profile for a particular class of
   applications will assign a payload type for this encoding, or if
   that is not done then a payload type in the dynamic range shall be
   chosen.


4.1 BroadVoice32 Bit Stream Definition

   The BroadVoice32 encoder operates on speech frames of 5 ms
   corresponding to 80 samples at a sampling rate of 16000 samples per
   second.  For every 5 ms frame, the encoder encodes the 80
   consecutive audio samples into 160 bits, or 20 octets.  Thus, the



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   160-bit bit stream produced by the BroadVoice32 for each 5 ms frame
   is octet-aligned, and no padding bits are required.  The bit
   allocation for the encoded parameters of the BroadVoice32 codec
   is listed in the following table.
                                                      Number of bits
      Encoded Parameter                  Codeword       per frame
      ---------------------------------------------------------------
      Line Spectrum Pairs                L0,L1,L2       7+5+5=17
      Pitch Lag                          PL                    8
      Pitch Gain                         PG                    5
      Log-Gains (1st & 2nd subframes)    LG0,LG1          5+5=10
      Excitation Vectors (1st subframe)  VA0,...,VA9     6*10=60
      Excitation Vectors (2nd subframe)  VB0,...,VB9     6*10=60
      ---------------------------------------------------------------
      Total:                                                 160 bits

   The mapping of the encoded parameters in a 160-bit BroadVoice32 data
   frame is defined in the following figure.  This figure shows the bit
   packing in "network byte order", also known as big-endian order.
   The bits of each 32-bit word are numbered 0 to 31, with the most
   significant bit on the left and numbered 0.  The octets (bytes) of
   each word are transmitted most significant octet first.  The bits of
   data field for each encoded parameter are numbered in the same
   order, with the most significant bit on the left.

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     L0      |    L1   |    L2   |       PL      |    PG   |LG0|
    |             |         |         |               |         |   |
    |0 1 2 3 4 5 6|0 1 2 3 4|0 1 2 3 4|0 1 2 3 4 5 6 7|0 1 2 3 4|0 1|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | LG0 |   LG1   |    VA0    |    VA1    |    VA2    |    VA3    |
    |     |         |           |           |           |           |
    |2 3 4|0 1 2 3 4|0 1 2 3 4 5|0 1 2 3 4 5|0 1 2 3 4 5|0 1 2 3 4 5|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    VA4    |    VA5    |    VA6    |    VA7    |    VA8    |VA9|
    |           |           |           |           |           |   |
    |0 1 2 3 4 5|0 1 2 3 4 5|0 1 2 3 4 5|0 1 2 3 4 5|0 1 2 3 4 5|0 1|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | VA9   |    VB0    |    VB1    |    VB2    |    VB3    |  VB4  |
    |       |           |           |           |           |       |
    |2 3 4 5|0 1 2 3 4 5|0 1 2 3 4 5|0 1 2 3 4 5|0 1 2 3 4 5|0 1 2 3|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |VB4|    VB5    |    VB6    |    VB7    |    VB8    |   VB9     |
    |   |           |           |           |           |           |
    |4 5|0 1 2 3 4 5|0 1 2 3 4 5|0 1 2 3 4 5|0 1 2 3 4 5|0 1 2 3 4 5|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 2: BroadVoice32 bit packing


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4.2 Multiple BroadVoice32 Frames in an RTP Packet

   More than one BroadVoice32 frame MAY be included in a single RTP
   packet by a sender.  Senders have the following additional
   restrictions:

     o  SHOULD NOT include more BroadVoice32 frames in a single RTP
        packet than will fit in the MTU of the RTP transport protocol.

     o  MUST NOT split a BroadVoice32 frame between RTP packets.

     o  BroadVoice32 frames in an RTP packet MUST be consecutive.

   Since multiple BroadVoice32 frames in an RTP packet MUST be
   consecutive, and since BroadVoice16 has a fixed frame size of 5 ms,
   recovering the timestamps of all frames within a packet is easy.
   The oldest frame within an RTP packet has the same timestamp as the
   RTP packet, as mentioned above.  To obtain the timestamp of the
   frame that is N frames later than the oldest frame in the packet,
   one simply adds 5*N ms worth of time units to the timestamp of the
   RTP packet.

   It is RECOMMENDED that the number of frames contained within an RTP
   packet is consistent with the application.  For example, in a
   telephony application where delay is important, the fewer frames per
   packet the lower the delay, whereas for a delay insensitive
   streaming or messaging application, many frames per packet would be
   acceptable.

   Information describing the number of frames contained in an RTP
   packet is not transmitted as part of the RTP payload.  The only way
   to determine the number of BroadVoice32 frames is to count the total
   number of octets within the RTP payload, and divide the octet count
   by 20.


5. Storage Format

   The storage format is used for storing speech frames, e.g., as a
   file or e-mail attachment.

   The file begins with a header that includes only a magic number to
   identify the codec that is used.  The magic number for the
   BroadVoice16 narrowband codec MUST correspond to the ASCII character
   string "#!BV16\n", or "0x23 0x21 0x42 0x56 0x31 0x36 0x0A" in
   hexadecimal format.  The magic number for the BroadVoice32 wideband
   codec MUST correspond to the ASCII character string "#!BV32\n", or
   "0x23 0x21 0x42 0x56 0x33 0x32 0x0A".  A file contains the encoded
   bit stream of either BroadVoice16 or BroadVoice32, but not both.  In



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   other words, BroadVoice16 frames and BroadVoice32 frames MUST NOT be
   mixed in the same file.

   After the header that contains the magic number identifying the
   codec used, the encoded codec data frames are stored in a sequential
   order, as shown below.  All encoded codec data frames must be
   present, otherwise synchronization problems will arise.

   +--------+---------------+---------------+-----+---------------+
   | Header | Codec frame 1 | Codec frame 2 | ... | Codec frame N |
   +--------+---------------+---------------+-----+---------------+


6. IANA Considerations

   Two new MIME sub-types as described in this section are to be
   registered.

   The MIME names for the BV16 and BV32 codecs are to be allocated from
   the IETF tree since these two codecs are expected to be widely used
   for Voice-over-IP applications, especially in Voice over Cable
   applications.


6.1 MIME Registration of BroadVoice16 for RTP

   MIME media type name: audio

   MIME media subtype name: BV16

   Required parameter: none

   Optional parameters:
      The following parameters apply to RTP transfer only.

      ptime:    Defined as usual for RTP audio (see RFC 2327 [5]).

      maxptime: See RFC 2327 [5] for its definition. The maxptime
         SHOULD be a multiple of the duration of a single codec data
         frame (5 ms).

   Encoding considerations:
      This type is defined for transfer of BV16-encoded data via RTP
      using the payload format specified in Sections 3 of RFC XXXX.
      It is also defined for other transfer methods using the storage
      format specified in Section 5 of RFC XXXX. Audio data is binary
      data, and must be encoded for non-binary transport; the Base64
      encoding is suitable for Email.

   Security considerations:
      See Section 8 "Security Considerations" of RFC XXXX.

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   Public specification:
      The BroadVoice16 codec has been specified in [3].

   Additional information:
      The following information applies to storage format only.

      Magic number: ASCII character string "#!BV16\n" (or "0x23 0x21
         0x42 0x56 0x31 0x36 0x0A" in hexadecimal)

      File extensions: bvn, BVN (stands for "BroadVoice, Narrowband")

      Macintosh file type code: none

      Object identifier or OID: none

   Intended usage:
      COMMON. It is expected that many VoIP applications, especially
      Voice over Cable applications, will use this type.

   Person & email address to contact for further information:
      Juin-Hwey (Raymond) Chen
      rchen@broadcom.com

   Author/Change controller:
      Author: Juin-Hwey (Raymond) Chen, rchen@broadcom.com
      Change Controller: IETF Audio/Video Transport Working Group
         delegated from the IESG


6.2 MIME Registration of BroadVoice32 for RTP

   MIME media type name: audio

   MIME media subtype name: BV32

   Required parameter: none

   Optional parameters:
      The following parameters apply to RTP transfer only.

      ptime:    Defined as usual for RTP audio (see RFC 2327 [5]).

      maxptime: See RFC 2327 [5] for its definition. The maxptime
         SHOULD be a multiple of the duration of a single codec data
         frame (5 ms).

   Encoding considerations:
      This type is defined for transfer of BV32-encoded data via RTP
      using the payload format specified in Sections 4 of RFC XXXX.
      It is also defined for other transfer methods using the storage


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      format specified in Section 5 of RFC XXXX. Audio data is binary
      data, and must be encoded for non-binary transport; the Base64
      encoding is suitable for Email.

   Security considerations:
      See Section 8 "Security Considerations" of RFC XXXX.

   Additional information:
      The following information applies to storage format only.

      Magic number: ASCII character string "#!BV32\n" (or "0x23 0x21
         0x42 0x56 0x33 0x32 0x0A" in hexadecimal)

      File extensions: bvw, BVW (stands for "BroadVoice, Wideband")

      Macintosh file type code: none

      Object identifier or OID: none

   Intended usage:
      COMMON. It is expected that many VoIP applications, especially
      Voice over Cable applications, will use this type.

   Person & email address to contact for further information:
      Juin-Hwey (Raymond) Chen
      rchen@broadcom.com

   Author/Change controller:
      Author: Juin-Hwey (Raymond) Chen, rchen@broadcom.com
      Change Controller: IETF Audio/Video Transport Working Group
      delegated from the IESG


7. Mapping to SDP Parameters

   The information carried in the MIME media type specification has a
   specific mapping to fields in the Session Description Protocol (SDP)
   [5], which is commonly used to describe RTP sessions.  When SDP is
   used to specify sessions employing the BroadVoice16 or BroadVoice32
   codec, the mapping is as follows:

      -  The MIME type ("audio") goes in SDP "m=" as the media name.

      -  The MIME subtype (payload format name) goes in SDP "a=rtpmap"
         as the encoding name.  The RTP clock rate in "a=rtpmap" MUST
         be 8000 for BV16 and 16000 for BV32.

      -  The parameters "ptime" and "maxptime" go in the SDP "a=ptime"
         and "a=maxptime" attributes, respectively.



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   An example of the media representation in SDP for describing BV16
   might be:

     m=audio 49120 RTP/AVP 97
     a=rtpmap:97 BV16/8000

   An example of the media representation in SDP for describing BV32
   might be:

     m=audio 49122 RTP/AVP 99
     a=rtpmap:99 BV32/16000


7.1 Offer-Answer Model Considerations

   No special considerations are need for using the SDP Offer/Answer
   model [6] with the BV16 and BV32 RTP payload formats.


8. Security Considerations

   RTP packets using the payload format defined in this specification
   are subject to the security considerations discussed in the RTP
   specification [1] and any appropriate profile (for example, [7]).
   This implies that confidentiality of the media streams is achieved
   by encryption.  Because the data compression used with this payload
   format is applied end-to-end, encryption may be performed after
   compression so there is no conflict between the two operations.

   A potential denial-of-service threat exists for data encoding using
   compression techniques that have non-uniform receiver-end
   computational load. The attacker can inject pathological datagrams
   into the stream which are complex to decode and cause the receiver
   to become overloaded. However, the encodings covered in this
   document do not exhibit any significant non-uniformity.


9. Congestion Control

   The general congestion control considerations for transporting RTP
   data apply to BV16 and BV32 audio over RTP as well, see RTP [1]
   and any applicable RTP profile like AVP [7]. BV16 and BV32 do not
   have any built-in mechanism for reducing the bandwidth. Packing
   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 and reduced error robustness against
   packet losses.





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10. Acknowledgments

   The authors would like to thank Magnus Westerlung, Colin Perkins,
   Allison Mankin, and Jean-Francois Mule for their review of this
   document.


11. References


11.1 Normative References

   [1] H. Schulzrinne, S. Casner, R. Frederick, and V. Jacobson, "RTP:
       A Transport Protocol for Real-Time Applications", STD 64,
       RFC 3550, Internet Engineering Task Force, July 2003.

   [2] S. Bradner, "Key words for use in RFCs to Indicate requirement
       Levels", BCP 14, RFC 2119, Internet Engineering Task Force,
       March 1997.

   [3] Cable Television Laboratories, Inc., BroadVoice(TM)16 Speech
       Codec Specification, Revision 1.2, October 30, 2003.

   [5] M. Handley and V. Jacobson, "SDP: Session Description
       Protocol", RC 2327, April 1998.

   [6] J. Rosenberg and H. Schulzrinne, "An Offer/Answer Model with
       the Session Description Protocol (SDP)", RFC 3264, Internet
       Engineering Task Force, June 2002.

   [7] H. Schulzrinne and S. Casner, "RTP Profile for Audio and Video
       Conferences with Minimal Control", STD 65, RFC 3551, Internet
       Engineering Task Force, July 2003.


11.2 Informative References

   [4] Cable Television Laboratories, Inc., PacketCable(TM) 1.5
       Audio/Video Codecs Specification, PKT-SP-CODEC1.5-I01-050128,
       January 28, 2005.
       http://www.cablelabs.com/specifications/archives/











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12. Authors' Addresses

   Juin-Hwey (Raymond) Chen
   Broadcom Corporation
   Room A3032
   16215 Alton Parkway
   Irvine, CA 92618
   USA
   Phone: +1 949 926 6288
   Email: rchen@broadcom.com

   Winnie Lee
   Broadcom Corporation
   Room A2012E
   200-13711 International Place
   Richmond, British Columbia V6V 2Z8
   Canada
   Phone: +1 604 233 8605
   Email: wlee@broadcom.com

   Jes Thyssen
   Broadcom Corporation
   Room A3053
   16215 Alton Parkway
   Irvine, CA 92618
   USA
   Phone: +1 949 926 5768
   Email: jthyssen@broadcom.com


13. RFC-Editor Consideration

   The RFC-editor is kindly requested to perform the following
   modifications upon the publication of this specification:

     - Replace all occurrences of RFC XXXX with the RFC number this
       specification receives when being published.

     - Remove this Section.













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INTERNET DRAFT     RTP Payload format for BroadVoice      February 2005

Expires: August 17, 2005


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