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Versions: (draft-zfang-avt-rtp-evrc-nw) 00 01 02 03 04 05 06 07 08 09 10 RFC 6884

Network Working Group                                            Z. Fang
Internet-Draft                                                  Qualcomm
Intended status: Standards Track                           July 26, 2010
Expires: January 27, 2011


RTP payload format for Enhanced Variable Rate Narrowband-Wideband Codec
                               (EVRC-NW)
                     draft-ietf-avt-rtp-evrc-nw-01

Abstract

   This document specifies real-time transport protocol (RTP) payload
   formats to be used for the Enhanced Variable Rate Narrowband-Wideband
   Codec (EVRC-NW).  Three media type registrations are included for
   EVRC-NW RTP payload formats.  In addition, a file format is specified
   for transport of EVRC-NW speech data in storage mode applications
   such as e-mail.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on January 27, 2011.

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
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   (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
   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  EVRC-NW codec  . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  RTP header usage . . . . . . . . . . . . . . . . . . . . . . .  7
   6.  Payload format . . . . . . . . . . . . . . . . . . . . . . . .  8
   7.  Congestion Control Considerations  . . . . . . . . . . . . . .  9
   8.  Storage format for the EVRC-NW Codec . . . . . . . . . . . . . 10
   9.  IANA considerations  . . . . . . . . . . . . . . . . . . . . . 11
     9.1.  Media Type Registrations . . . . . . . . . . . . . . . . . 11
       9.1.1.  Registration of Media Type audio/EVRCNW  . . . . . . . 11
       9.1.2.  Registration of Media Type audio/EVRCNW0 . . . . . . . 13
       9.1.3.  Registration of Media Type audio/EVRCNW1 . . . . . . . 14
   10. SDP mode attributes for EVRC-NW  . . . . . . . . . . . . . . . 17
   11. Mapping EVRC-NW media type parameters into SDP . . . . . . . . 18
   12. Offer-Answer Model Considerations for EVRC-NW  . . . . . . . . 19
   13. Declarative SDP Considerations . . . . . . . . . . . . . . . . 21
   14. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
   15. Security Considerations  . . . . . . . . . . . . . . . . . . . 25
   16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
     16.1. Normative References . . . . . . . . . . . . . . . . . . . 26
     16.2. Informative References . . . . . . . . . . . . . . . . . . 26
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 28






















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1.  Introduction

   This document specifies the payload formats for packetization of
   EVRC-NW encoded speech signals into the real-time transport protocol
   (RTP).  It defines support for the header-free, interleaved/bundled
   and compact bundle packet formats for the EVRC-NW codec as well as
   discontinuous transmission (DTX) support for EVRC-NW encoded speech
   transported via RTP.  The EVRC-NW codec offers better speech quality
   than the EVRC and EVRC-B codecs and better capacity than EVRC-WB
   codec.  EVRC-NW belongs to the EVRC family of codecs.









































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2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].














































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3.  Background

   EVRC-NW is an extension of both the EVRC-B [2] and EVRC-WB [3] speech
   codecs developed in 3GPP2 with support for discontinuous transmission
   (DTX).  It provides enhanced voice quality and high spectral
   efficiency.

   The EVRC-NW codec operates on 20 ms frames, and the default sampling
   rate is 16 kHz.  Input and output at 8 kHz sampling rate is also
   supported.  The EVRC-NW codec can operate in eight modes (0 to 7)
   defined in [4].  EVRC-NW modes 0, 1 and 7 are interoperable with
   EVRC-WB.  EVRC-NW modes 1 to 7 are interoperable with EVRC-B.
   EVRC-NW modes 0 to 6 use the full set or a subset of full rate, 1/2
   rate, 1/4 rate and 1/8 rate frames.  EVRC-NW mode 7 uses only 1/2
   rate and 1/8 rate frames.  By default, EVRC-NW supports all
   narrowband modes (modes 1 to 7).  The support of wideband mode (mode
   0) is optional.  Mode change among modes 1 to 7 (or among modes 0 to
   7 if the receiver supports wideband mode) results in codec output
   bit-rate change but does not cause any decoding problems at the
   receiver.  EVRC-NW provides a standardized solution for packetized
   voice applications that allow transitions between enhanced quality
   and increased capacity.  The most important service addressed is IP
   telephony.  Target devices can be IP phones or VoIP handsets, media
   gateways, voice messaging servers, etc.



























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4.  EVRC-NW codec

   The EVRC-NW codec operates on 20 ms frames.  It produces output
   frames of one of the four different sizes: 171 bits (Rate 1), 80 bits
   (Rate 1/2), 40 bits (Rate 1/4) or 16 bits (Rate 1/8 or Rate 1/8 Non-
   Critical).  In addition, there are two zero bit codec frame types:
   blank (null) frames and erasure frames.  For IP based traffic, the
   Rate 1/8 Non-Critical type frame shall be suppressed and denoted as
   blank (null) frame of 0 bit.  The default sampling rate is 16 kHz.
   Input and output at 8 kHz sampling rate is also supported.

   The frame type values and sizes of the associated codec data frames
   are listed in the table below:

   Value   Rate      Total codec data frame size in bytes (and in bits)
   --------------------------------------------------------------------
     0     Blank(Null)  0    (0 bit)
     1     1/8          2    (16 bits)
     2     1/4          5    (40 bits)
     3     1/2         10    (80 bits)
     4     1           22    (171 bits; 5 bits padded at the end)
     5     Erasure      0    (SHOULD NOT be transmitted by sender)





























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5.  RTP header usage

   The format of the RTP header is specified in RFC 3550 [5].  The
   EVRC-NW payload formats (Section 6) use the fields of the RTP header
   in a manner consistent with RFC 3550 [5].

   EVRC-NW has also the capability to operate with 8 kHz sampled input/
   output signals.  The decoder does not require a priori knowledge
   about the sampling rate of the original signal at the input of the
   encoder.  The decoder output can be at 8kHz or 16kHz regardless of
   the sampling rate used at the encoder.  Therefore, depending on the
   implementation and the electroacoustic audio capabilities of the
   devices, the input of the encoder and/or the output of the decoder
   can be configured at 8 kHz; however, a 16 kHz RTP clock rate MUST
   always be used.  The RTP timestamp is increased by 320 for each 20
   milliseconds.

   The RTP header marker bit (M) SHALL be set to 1 if the first frame
   carried in the packet contains a speech frame which is the first in a
   talkspurt.  For all other packets the marker bit SHALL be set to zero
   (M=0).






























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6.  Payload format

   Three RTP packet formats are supported for the EVRC-NW codec - the
   interleaved/bundled packet format, the header-free packet format and
   the compact bundled packet format.  For all these formats, the
   operational details and capabilities, such as ToC, interleaving, DTX,
   and bundling, of EVRC-NW are exactly the same as those of EVRC-B and
   EVRC-WB, as defined in [2] and [3], except that the mode change
   request field in the ToC MUST be interpreted according to the
   definition of the RATE_REDUC parameter as defined in EVRC-NW [4].
   The media type audio/EVRCNW maps to the interleaved/bundled packet
   format, audio/EVRCNW0 maps to the header-free packet format and
   audio/EVRCNW1 maps to the compact bundled packet format.






































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7.  Congestion Control Considerations

   Congestion control for RTP SHALL be used in accordance with RFC 3550
   [5], and with any applicable RTP profile; e.g., RFC 3551 [6].

   Due to the header overhead, the number of frames encapsulated in each
   RTP packet influences the overall bandwidth of the RTP stream.
   Packing more frames in each RTP packet can reduce the number of
   packets sent and hence the header overhead, at the expense of
   increased delay and reduced error robustness.









































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8.  Storage format for the EVRC-NW Codec

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

   The file begins with a magic number to identify the vocoder that is
   used.  The magic number for EVRC-NW corresponds to the ASCII
   character string "#!EVRCNW\n", i.e., "0x23 0x21 0x45 0x56 0x52 0x43
   0x4E 0x57 0x0A".

   The codec data frames are stored in consecutive order, with a single
   ToC entry field, extended to one octet, prefixing each codec data
   frame.  The ToC field is extended to one octet by setting the four
   most significant bits of the octet to zero.  For example, a ToC value
   of 4 (a full-rate frame) is stored as 0x04.  See Section 4 for the
   mapping from frame type to ToC value.

   Speech frames lost in transmission and non-received frames MUST be
   stored as erasure frames (ToC value of 5) to maintain synchronization
   with the original media.































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9.  IANA considerations

   This document introduces a new EVRC-NW 'audio' media subtype.

9.1.  Media Type Registrations

   Following the guidelines in RFC 4855 [7] and RFC 4288 [8], this
   section registers new 'audio' media subtypes for EVRC-NW.

9.1.1.  Registration of Media Type audio/EVRCNW

   Type name: audio

   Subtype names: EVRCNW

   Required parameters: None

   Optional parameters:

   These parameters apply to RTP transfer only.

   mode-set-recv: A subset of EVRC-NW modes.  Possible values are a
   comma separated list of modes from the set {0,1,2,3,4,5,6,7} (see
   Table 2.6.1.2-4 in 3GPP2 C.S0014-D).  A decoder can use this
   attribute to inform an encoder of its preference to operate in a
   specified subset of modes.  Absence of this parameter signals the
   mode set {1,2,3,4,5,6,7}.

   sendmode: A mode of the EVRC-NW codec.  An encoder can use this to
   signal its current mode of operation.  Possible values are
   0,1,2,3,4,5,6,7 (see Table 2.6.1.2-4 in 3GPP2 C.S0014-D).  Absence of
   this parameter signals mode 4.

   ptime: see RFC 4566 [9].

   maxptime: see RFC 4566.

   maxinterleave: Maximum number for interleaving length (field LLL in
   the Interleaving Octet)[0..7].  The interleaving lengths used in the
   entire session MUST NOT exceed this maximum value.  If not signaled,
   the maxinterleave length MUST be 5.

   silencesupp: see Section 6.1 in RFC 4788.

   dtxmax: see Section 6.1 in RFC 4788.

   dtxmin: see Section 6.1 in RFC 4788.




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   hangover: see Section 6.1 in RFC 4788.

   Encoding considerations:

   This media type is framed binary data (see RFC 4288, Section 4.8) and
   is defined for transfer of EVRC-NW encoded data via RTP using the
   Interleaved/Bundled packet format specified in RFC 3558.

   Security considerations: See Section 15.

   Interoperability considerations: None

   Published specification:

   The EVRC-NW vocoder is specified in 3GPP2 C.S0014-D.  The transfer
   method with the Interleaved/Bundled packet format via RTP is
   specified in RFC 3558.

   Applications that use this media type:

   It is expected that many VoIP applications (as well as mobile
   applications) will use this type.

   Additional information:

   The following applies to stored-file transfer methods:

   Magic number: #!EVRCNW\n (see Section 8)

   File extensions: enw, ENW

   Macintosh file type code: None

   Object identifier or OID: None

   EVRC-NW speech frames may also be stored in the file format "3g2"
   defined in 3GPP2 C.S0050-B, which is identified using the media types
   "audio/3gpp2" or "video/3gpp2" registered by RFC 4393 [10].

   Person & email address to contact for further information:

   Zheng Fang <zfang@qualcomm.com>

   Intended usage: COMMON

   Restrictions on usage:

   When this media type is used in the context of transfer over RTP, the



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   RTP payload format specified in Section 4.1 of RFC 3558 SHALL be
   used.  In all other contexts, the file format defined in Section 8
   SHALL be used.

   Author:

   Zheng Fang

   Change controller:

   IETF Audio/Video Transport working group delegated from the IESG.

9.1.2.  Registration of Media Type audio/EVRCNW0

   Type name: audio

   Subtype names: EVRCNW0

   Required parameters: None

   Optional parameters:

   These parameters apply to RTP transfer only.

   mode-set-recv: A subset of EVRC-NW modes.  Possible values are a
   comma separated list of modes from the set {0,1,2,3,4,5,6,7} (see
   Table 2.6.1.2-4 in 3GPP2 C.S0014-D).  A decoder can use this
   attribute to inform an encoder of its preference to operate in a
   specified subset of modes.  Absence of this parameter signals the
   mode set {1,2,3,4,5,6,7}.

   sendmode: A mode of the EVRC-NW codec.  An encoder can use this to
   signal its current mode of operation.  Possible values are
   0,1,2,3,4,5,6,7 (see Table 2.6.1.2-4 in 3GPP2 C.S0014-D).  Absence of
   this parameter signals mode 4.

   ptime: see RFC 4566.

   silencesupp: see Section 6.1 in RFC 4788.

   dtxmax: see Section 6.1 in RFC 4788.

   dtxmin: see Section 6.1 in RFC 4788.

   hangover: see Section 6.1 in RFC 4788.

   Encoding considerations:




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   This media type is framed binary data (see RFC 4288, Section 4.8) and
   is defined for transfer of EVRC-NW encoded data via RTP using the
   Header-Free packet format specified in RFC 3558.

   Security considerations: See Section 15.

   Interoperability considertaions: None

   Published specification:

   The EVRC-NW vocoder is specified in 3GPP2 C.S0014-D.  The transfer
   method with the Header-Free packet format via RTP is specified in RFC
   3558.

   Applications that use this media type:

   It is expected that many VoIP applications (as well as mobile
   applications) will use this type.

   Additional information: None

   Person & email address to contact for further information:

   Zheng Fang <zfang@qualcomm.com>

   Intended usage: COMMON

   Restrictions on usage:

   This media type depends on RTP framing, and hence is only defined for
   transfer via RTP [5], the RTP payload format specified in Section 4.2
   of RFC 3558 SHALL be used.  This media type SHALL NOT be used for
   storage or file transfer, instead audio/EVRCNW SHALL be used.

   Author:

   Zheng Fang

   Change controller:

   IETF Audio/Video Transport working group delegated from the IESG.

9.1.3.  Registration of Media Type audio/EVRCNW1

   Type name: audio

   Subtype names: EVRCNW1




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   Required parameters: None

   Optional parameters:

   These parameters apply to RTP transfer only.

   mode-set-recv: A subset of EVRC-NW modes.  Possible values are a
   comma separated list of modes from the set {0,1} (see Table 2.6.1.2-4
   in 3GPP2 C.S0014-D).  A decoder can use this attribute to inform an
   encoder of its preference to operate in a specified subset of modes.
   A value of 0 signals the support for wideband fixed rate (full or
   half rate, depending on the value of 'fixedrate' parameter).  A value
   of 1 signals narroband fixed rate (full or half rate, depending on
   the value of 'fixedrate' parameter).  Absence of this parameter
   signals the mode 1.

   sendmode: A mode of the EVRC-NW codec.  An encoder can use this to
   signal its current mode of operation.  Possible values are 0,1 (see
   Table 2.6.1.2-4 in 3GPP2 C.S0014-D). 'sendmode' with value 0 signals
   wideband fixed rate operation (full or half rate, depending on the
   value of the 'fixedrate' parameter). 'sendmode' with value 1 signals
   narrowband fixed rate operation (full or half rate, depending on the
   value of the 'fixedrate' parameter).  Absence of this parameter
   signals mode 1.

   ptime: see RFC 4566.

   maxptime: see RFC 4566.

   fixedrate: Indicates the EVRC-NW rate of the session while in single
   rate operation.  Valid values include: 0.5 and 1, where a value of
   0.5 indicates the 1/2 rate while a value of 1 indicates the full
   rate.  If this parameter is not present, 1/2 rate is assumed.

   silencesupp: see Section 6.1 in RFC 4788.

   dtxmax: see Section 6.1 in RFC 4788.

   dtxmin: see Section 6.1 in RFC 4788.

   hangover: see Section 6.1 in RFC 4788.

   Encoding considerations:

   This media type is framed binary data (see RFC 4288, Section 4.8) and
   is defined for transfer of EVRC-NW encoded data via RTP using the
   Compact Bundled packet format specified in RFC 4788.




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   Security considerations: See Section 15

   Interoperability considertaions: None

   Published specification:

   The EVRC-NW vocoder is specified in 3GPP2 C.S0014-D.  The transfer
   method with the Compact Bundled packet format via RTP is specified in
   RFC 4788.

   Applications that use this media type:

   It is expected that many VoIP applications (as well as mobile
   applications) will use this type.

   Additional information: None

   Person & email address to contact for further information:

   Zheng Fang <zfang@qualcomm.com>

   Intended usage: COMMON

   Restrictions on usage:

   This media type depends on RTP framing, and hence is only defined for
   transfer via RTP [5], the RTP payload format specified in Section 4
   of RFC 4788 SHALL be used.  This media type SHALL NOT be used for
   storage or file transfer, instead audio/EVRCNW SHALL be used.

   Author:

   Zheng Fang

   Change controller:

   IETF Audio/Video Transport working group delegated from the IESG.














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10.  SDP mode attributes for EVRC-NW

   'mode-set-recv' can be used by a decoder to inform an encoder of its
   preference to operate in a specified subset of modes.  Note that
   indicating a preference, implicitly indicates support for that
   capability.  Conversely, if mode 0 is not preferred, then there is no
   indication that mode 0 is supported.

   1.  To inform the capability of wideband mode support: A decoder can
       always decode all the narrowband modes (modes 1 to 7).  Unless
       the decoder indicates the support of mode 0 (i.e., preference) in
       this parameter, an encoder at the other side shall not operate in
       mode 0.

   2.  To inform the preference to operate in a subset of modes: A set
       has been defined so that several modes can be expressed as a
       preference in one attempt.  For instance, the set {4,5,6,7}
       signals that the receiver perfers the sender to operate in
       bandwidth-efficient narrowband modes of EVRC-NW.

   'sendmode' can be used by a sender to announce its encoder's current
   mode of operation.  A sender can change its mode among modes 1 to 7
   (or among modes 0 to 7 if the receiver supports wideband mode)
   anytime and this does not cause any decoding problems at the
   receiver.


























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11.  Mapping EVRC-NW media type parameters into SDP

   Information carried in the media type specification has a specific
   mapping to fields in the Session Description Protocol (SDP) [9],
   which is commonly used to describe RTP sessions.  When SDP is used to
   specify sessions employing EVRC-NW encoded speech, the mapping is as
   follows.

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

   o  The media subtype ("EVRCNW", "EVRCNW0" or "EVRCNW1") goes in SDP
      "a=rtpmap" as the encoding name.

   o  The optional parameters 'ptime and 'maxptime' (for subtypes
      EVRCNW, EVRCNW1) go in the SDP "a=ptime" and "a=maxptime"
      attributes, respectively.

   o  Any remaining parameters (for subtypes EVRCNW, EVRCNW0 and
      EVRCNW1) go in the SDP "a=fmtp" attribute by copying them from the
      media type string as a semicolon separated list of parameter=value
      pairs.






























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12.  Offer-Answer Model Considerations for EVRC-NW

   The following considerations apply when using the SDP offer-answer
   procedures of RFC 3264 [11] to negotiate the use of EVRC-NW payload
   in RTP:

   o  Since EVRC-NW is an extension of both EVRC-B and EVRC-WB, the
      offerer SHOULD also announce EVRC-B and EVRC-WB support in its
      "m=audio" lines, with EVRC-NW as the preferred codec.  This will
      allow interoperability with an answerer which supports only EVRC-B
      and/or EVRC-WB.

   Below is an example of such an offer:

          m=audio 55954 RTP/AVP 98 99 100
          a=rtpmap:98 EVRCNW0/16000
          a=rtpmap:99 EVRCWB0/16000
          a=rtpmap:100 EVRCB0/8000
          a=fmtp:98 mode-set-recv=0,1,2,3,4,5,6;sendmode=0
          a=fmtp:99 mode-set-recv=0,4;sendmode=0
          a=fmtp:100 recvmode=0;sendmode=4


   If the answerer supports EVRC-NW then the answerer can keep the
   payload type 98 in its answer and the conversation can be done using
   EVRC-NW.  Else, if the answerer supports only EVRC-WB and/or EVRC-B
   then the answerer will leave only the payload type 99 and/or 100
   respectively in its answer and the conversation will be done using
   EVRC-WB and/or EVRC-B respectively.

   An example answer for the above offer:

          m=audio 55954 RTP/AVP 98
          a=rtpmap:98 EVRCNW0/16000
          a=fmtp:98 mode-set-recv=4;sendmode=4


   o  'mode-set-recv' is a uni-directional receive only parameter.

   o  'sendmode' is a uni-directional send only parameter.

   o  Using 'sendmode', a sender can signal its current mode of
      operation.  Note that a receiver may receive RTP media well before
      the arrival of SDP with a (first time, or updated) 'sendmode'
      parameter.

   o  An offerer can use 'mode-set-recv' to request that the remote
      sender's encoder be limited to the list of modes signaled in



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      'mode-set-recv'.  A remote sender MAY ignore 'mode-set-recv'
      requests.  However, a remote sender shall not assume the other
      side can support mode 0, unless the offer includes mode 0
      explicitly in 'mode-set-recv'.

   o  The parameters 'maxptime' and 'ptime' will in most cases not
      affect interoperability, however the setting of the parameters can
      affect the performance of the application.  The SDP offer-answer
      handling of the 'ptime' parameter is described in RFC 3264 [11].
      The 'maxptime' parameter MUST be handled in the same way.

   o  For a sendonly stream, the 'mode-set-recv' parameter is not useful
      and SHOULD NOT be used.

   o  For a recvonly stream, the 'sendmode' parameter is not useful and
      SHOULD NOT be used.

   o  When using EVRCNW1, the entire session MUST use the same fixed
      rate and mode (0-Wideband or 1-Narrowband).

   o  For additional rules which MUST be followed while negotiating DTX
      parameters, see Section 6.8 in RFC 4788 [2].

   o  Any unknown parameter in an SDP offer MUST be ignored by the
      receiver and MUST NOT be included in the SDP answer.


























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13.  Declarative SDP Considerations

   For declarative use of SDP in SAP [13] and RTSP [14], the following
   considerations apply:

   o  Any 'maxptime' and 'ptime' values should be selected with care to
      ensure that the session's participants can achieve reasonable
      performance.

   o  The payload format configuration parameters are all declarative
      and a participant MUST use the configuration(s) that is provided
      for the session.  More than one configuration may be provided if
      necessary by declaring multiple RTP payload types, however the
      number of types should be kept small.  For declarative examples,
      see Section 14.




































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14.  Examples

   Some example SDP session descriptions utilizing EVRC-NW encodings
   follow.  In these examples, long a=fmtp lines are folded to meet the
   column width constraints of this document.  The backslash ("\") at
   the end of a line and the carriage return that follows it should be
   ignored.  Note that media subtype names are case-insensitive.
   Parameter names are case-insensitive both in media types and in the
   mapping to the SDP a=fmtp attribute.

   Example usage of EVRCNW if wideband mode is supported:

          m=audio 49120 RTP/AVP 97 98 99
          a=rtpmap:97 EVRCNW/16000
          a=rtpmap:98 EVRCWB/16000
          a=rtpmap:99 EVRCB/8000
          a=fmtp:97 mode-set-recv=0,1,2,3,4,5,6;sendmode=0
          a=fmtp:98 mode-set-recv=0,4;sendmode=0
          a=fmtp:99 recvmode=0;sendmode=0
          a=maxptime:120

   Example usage of EVRCNW if wideband mode is not supported:

          m=audio 49120 RTP/AVP 97 98 99
          a=rtpmap:97 EVRCNW/16000
          a=rtpmap:98 EVRCWB/16000
          a=rtpmap:99 EVRCB/8000
          a=fmtp:97 mode-set-recv=1,2,3,4,5,6;sendmode=4
          a=fmtp:98 mode-set-recv=4;sendmode=4
          a=fmtp:99 recvmode=0;sendmode=0
          a=maxptime:120

   Example usage of EVRCNW0:

          m=audio 49120 RTP/AVP 97 98 99
          a=rtpmap:97 EVRCNW0/16000
          a=rtpmap:98 EVRCWB0/16000
          a=rtpmap:99 EVRCB0/8000
          a=fmtp:97 mode-set-recv=0,1,2,3,4,5,6;sendmode=0
          a=fmtp:98 mode-set-recv=0,4;sendmode=0
          a=fmtp:99 recvmode=0;sendmode=0

   Example SDP answer from a media gateway requesting a terminal to
   limit its encoder operation to EVRC-NW mode 4.

          m=audio 49120 RTP/AVP 97
          a=rtpmap:97 EVRCNW0/16000
          a=fmtp:97 mode-set-recv=4;sendmode=4



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   Example usage of EVRCNW1:

          m=audio 49120 RTP/AVP 97 98 99
          a=rtpmap:97 EVRCNW1/16000
          a=rtpmap:98 EVRCWB1/16000
          a=rtpmap:99 EVRCB1/8000
          a=fmtp:97 fixedrate=0.5
          a=fmtp:98 fixedrate=0.5
          a=fmtp:99 fixedrate=0.5
          a=maxptime:100

   Example usage of EVRCNW with DTX with silencesupp=1:

          m=audio 49120 RTP/AVP 97 98 99
          a=rtpmap:97 EVRCNW/16000
          a=rtpmap:98 EVRCWB/16000
          a=rtpmap:99 EVRCB/8000
          a=fmtp:97 silencesupp=1;dtxmax=32;dtxmin=12;hangover=1 \
          mode-set-recv=0,1,2,3,4,5,6;sendmode=0
          a=fmtp:98 silencesupp=1;dtxmax=32;dtxmin=12;hangover=1 \
          mode-set-recv=0,4;sendmode=0
          a=fmtp:99 recvmode=0;sendmode=0
          a=maxptime:120

   Examples usage of EVRCNW with DTX with silencesupp=0:

          m=audio 49120 RTP/AVP 97 98 99
          a=rtpmap:97 EVRCNW/16000
          a=rtpmap:98 EVRCWB/16000
          a=rtpmap:99 EVRCB/8000
          a=fmtp:97 silencesupp=0;dtxmax=32;dtxmin=12;hangover=1 \
          mode-set-recv=0,1,2,3,4,5,6;sendmode=0
          a=fmtp:98 silencesupp=0;dtxmax=32;dtxmin=12;hangover=1 \
          mode-set-recv=0,4;sendmode=0
          a=fmtp:99 recvmode=0;sendmode=0
          a=maxptime:120

   Example offer answer exchange between EVRC-NW and legacy EVRC-B (RFC
   4788):












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         Offer:

           m=audio 55954 RTP/AVP 97 98 99
           a=rtpmap:97 EVRCNW0/16000
           a=rtpmap:98 EVRCWB0/16000
           a=rtpmap:99 EVRCB0/8000
           a=rtpmap:97 mode-set-recv=0,1,2,3,4,5,6;sendmode=0
           a=fmtp:98 mode-set-recv=0,4;sendmode=0
           a=fmtp:99 recvmode=0;sendmode=0

         Answer:

           m=audio 55954 RTP/AVP 99
           a=rtpmap:99 EVRCB0/8000

   Example offer answer exchange between EVRC-NW and legacy EVRC-WB (RFC
   5188):

         Offer:

           m=audio 55954 RTP/AVP 97 98 99
           a=rtpmap:97 EVRCNW0/16000
           a=rtpmap:98 EVRCWB0/16000
           a=rtpmap:99 EVRCB0/8000
           a=rtpmap:97 mode-set-recv=0,1,2,3,4,5,6;sendmode=0
           a=fmtp:98 mode-set-recv=0,4;sendmode=0
           a=fmtp:99 recvmode=0;sendmode=0

         Answer:

           m=audio 55954 RTP/AVP 98 99
           a=rtpmap:98 EVRCWB0/16000



















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15.  Security Considerations

   Since compression is applied to the payload formats end-to-end, and
   the encodings do not exhibit significant non-uniformity,
   implementations of this specification are subject to all the security
   considerations specified in RFC 3558 [12].  Implementations using the
   payload defined in this specification are subject to the security
   considerations discussed in RFC 3558 [12], RFC 3550 [5] and any
   appropriate profile (for example RFC 3551 [6]).










































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16.  References

16.1.  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [2]   Xie, Q. and R. Kapoor, "Enhancements to RTP Payload Formats for
         EVRC Family Codecs", RFC 4788, January 2007.

   [3]   Desineni, H. and Q. Xie, "RTP Payload Format for the Enhanced
         Variable Rate Wideband Codec (EVRC-WB) and the Media Subtype
         Updates for EVRC-B Codec", RFC 5188, February 2008.

   [4]   "Enhanced Variable Rate Codec, Speech Service Options 3, 68,
         70, and 73 for Wideband Spread Spectrum Digital Systems",
         3GPP2 C.S0014-D v1.0, May 2009.

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

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

   [7]   Casner, S., "Media Type Registration of RTP Payload Formats",
         RFC 4855, February 2007.

   [8]   Freed, N. and J. Klensin, "Media Type Specifications and
         Registration Procedures", BCP 13, RFC 4288, December 2005.

   [9]   Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
         Description Protocol", RFC 4566, July 2006.

   [10]  Garudadri, H., "MIME Type Registrations for 3GPP2 Multimedia
         Files", RFC 4393, March 2006.

   [11]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
         Session Description Protocol (SDP)", RFC 3264, June 2002.

   [12]  Li, A., "RTP Payload Format for Enhanced Variable Rate Codecs
         (EVRC) and Selectable Mode Vocoders (SMV)", RFC 3558,
         July 2003.

16.2.  Informative References

   [13]  Handley, M., Perkins, C., and E. Whelan, "Session Announcement
         Protocol", RFC 2974, October 2000.



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   [14]  Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming
         Protocol (RTSP)", RFC 2326, April 1998.

















































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Author's Address

   Zheng Fang
   Qualcomm
   5775 Morehouse Drive
   San Diego, CA  92126
   USA

   Phone: +1 858 651 9484
   Email: zfang@qualcomm.com
   URI:   http://www.qualcomm.com








































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