Network Working Group Q. Xie Internet-Draft Motorola Updates: RFC 3558 (if approved) R. Kapoor Expires: December 10, 2006 Qualcomm June 8, 2006 Enhancements to RTP Payload Formats for EVRC Family Codecs draft-ietf-avt-compact-bundled-evrc-06.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 10, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This document updates the EVRC RTP payload formats defined in RFC 3558 with several enhancements and extensions. In particular, it defines support for the header-free and interleaved/bundled packet formats for the EVRC-B codec, a new compact bundled format for the EVRC and EVRC-B codecs, as well as discontinuous transmission (DTX) support for EVRC and EVRC-B encoded speech transported via RTP. VoIP applications operating over low bandwidth dial-up and wireless Xie & Kapoor Expires December 10, 2006 [Page 1]
Internet-Draft EVRC RTP Format Enhancements June 2006 networks require such enhancements for efficient use of the bandwidth. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Support of EVRC-B Codec . . . . . . . . . . . . . . . . . 3 1.2 Compact (Header-free) Bundled Format . . . . . . . . . . . 3 1.3 Discontinuous Transmission (DTX) . . . . . . . . . . . . . 4 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . 4 3. EVRC-B Codec . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1 Other Frame-Based Vocoders . . . . . . . . . . . . . . . . 5 4. Compact Bundled Format . . . . . . . . . . . . . . . . . . . 5 4.1 Single Rate Operation . . . . . . . . . . . . . . . . . . 6 5. Storage Format For EVRC-B Codec . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . 6 6.1 Registration of Media Type EVRC1 . . . . . . . . . . . . . 7 6.2 Registration of Media Type EVRCB . . . . . . . . . . . . . 9 6.3 Registration of Media Type EVRCB0 . . . . . . . . . . . . 11 6.4 Registration of Media Type EVRCB1 . . . . . . . . . . . . 12 6.5 Updated Registration of Media Type EVRC . . . . . . . . . 13 6.6 Updated Registration of Media Type EVRC0 . . . . . . . . . 15 6.7 Mapping MIME Parameters into SDP . . . . . . . . . . . . . 17 6.8 Usage in Offer/Answer . . . . . . . . . . . . . . . . . . 18 7. Backward Compatibility with RFC 3558 . . . . . . . . . . . . 19 8. Security Considerations . . . . . . . . . . . . . . . . . . 19 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 10.1 Normative References . . . . . . . . . . . . . . . . . . 19 10.2 Informative References . . . . . . . . . . . . . . . . . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 20 Intellectual Property and Copyright Statements . . . . . . . 21 Xie & Kapoor Expires December 10, 2006 [Page 2]
Internet-Draft EVRC RTP Format Enhancements June 2006 1. Introduction This document defines support for the header-free and interleaved/ bundled packet formats for the EVRC-B codec, a new compact bundled format for the EVRC and EVRC-B codecs, as well as discontinuous transmission (DTX) support for EVRC and EVRC-B encoded speech transported via RTP. VoIP applications operating over low bandwidth dial-up and wireless networks require such EVRC RTP payload capabilities for efficient use of the bandwidth. 1.1 Support of EVRC-B Codec EVRC-B [4] is an extension to [3] developed in 3GPP2. EVRC-B [4] compresses each 20 milliseconds of 8000Hz, 16-bit sampled speech input into output frames of one of the four different sizes: Rate 1 (171 bits), Rate 1/2 (80 bits), Rate 1/4 (40 bits), or Rate 1/8 (16 bits). In addition, there are two zero bit codec frame types: null frames and erasure frames, similar to EVRC [3]. One significant enhancement in EVRC-B is the use of 1/4 rate frames that were not used in EVRC. This provides lower average data rates (ADRs) compared to EVRC, for a given voice quality. Since speech frames encoded by EVRC-B are different from those encoded by EVRC, EVRC-B and EVRC codecs do not interoperate with each other. At the initiation of a RTP session, the RTP sender and receiver need to indicate (e.g., using MIME subtypes that are separate from those of EVRC) that EVRC-B is to be used for the ensuing session. 1.2 Compact (Header-free) Bundled Format The current interleaved/bundled packet format defined in RFC 3558 allows bundling of multiple speech frames of different rate in a single RTP packet, sending mode change requests, and interleaving. To support these functions, a Table of Contents (ToC) is used in each RTP packet in addition to the standard RTP header. The size of the ToC is variable, depending on the number of EVRC frames carried in the packet [5]. The current header-free packet format defined in RFC 3558 is more compact and optimized for use over wireless links. It eliminates the need for a ToC by requiring that each RTP packet contain only one speech frame (of any allowable rate), i.e., bundling is not allowed. Moreover, interleaving and mode change request are not supported in the header-free format [5]. The compact bundled format described in this document presents the user an alternative to the header-free format defined in RFC 3558. Xie & Kapoor Expires December 10, 2006 [Page 3]
Internet-Draft EVRC RTP Format Enhancements June 2006 This format allows bundling of multiple EVRC or EVRC-B frames without the addition of extra headers, as would be in case of the interleaved/bundled format. However, in order to use this compact bundled format, only one EVRC/EVRC-B rate (full rate or 1/2 rate) can be used in the session. Similar to the header-free format defined in RFC 3558, interleaving and mode change request are not supported in the compact bundled format. 1.3 Discontinuous Transmission (DTX) The EVRC and EVRC-B codecs do not use Silence Descriptor frames; instead, in variable rate operation mode the encoder sends 1/8 rate frames during periods of silence, while in single rate operation mode (see Section 4), silence is encoded and sent in frames of the same rate as that of speech frames. The DTX parameters defined in this document apply to 1/8th rate frames in the variable rate mode and to silence frames in the single rate operation mode. For simplicity, in the rest of this document the term "silence frame" refers either to an 1/8th rate frame in variable rate operation or a frame that contains only silence in the signal rate operation. Information carried in silence frames of EVRC and EVRC-B codecs varies little during periods of silence. The transmission of these silence frames across the radio interface in a wireless system is expensive in terms of capacity, and therefore, suppression of these frames is desirable. Suppression of silence frames is accomplished by using DTX. When DTX is applied, the first few silence frames may be transmitted to establish background noise during the period of silence. Then a portion of the stream of subsequent silence frames is not transmitted and is discarded at the sender. At the receiver, background or comfort noise may be generated by using the previously received silence frames. 2. Conventions The keywords MUST, MUST NOT, REQUIRED, MUST, MUST NOT, SHOULD, SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in [2]. 3. EVRC-B Codec Three RTP packet formats are supported for the EVRC-B codec - the interleaved/bundled packet format, the header-free packet format and the compact bundled packet format. For the interleaved/bundled and header-free packet formats, the operational details and capabilities, Xie & Kapoor Expires December 10, 2006 [Page 4]
Internet-Draft EVRC RTP Format Enhancements June 2006 such as ToC, interleaving, and bundling, of EVRC-B are exactly the same as those of EVRC, as defined in RFC3558 [5], except that the mode change request field in the ToC MUST be interpreted according to the definition of the RATE_REDUC parameter in EVRC-B [4]. The compact bundled packet format for EVRC-B is defined in Section 4 of this document. 3.1 Other Frame-Based Vocoders Other frame-based vocoders can be carried in the packet formats defined in this document, as long as they possess the following properties: o the codec is frame-based; o blank and erasure frames are supported; o the total number of rates is less than 17; o the maximum full rate frame can be transported in a single RTP packet using this specific format. Vocoders with the characteristics listed above can be transported using the packet format specified in this document with some additional specification work; the pieces that must be defined are listed in Section 15 of RFC 3558. 4. Compact Bundled Format A packet in the compact bundled format consists of an RTP header followed by a sequence of one or more consecutive EVRC/EVRC-B codec data frames of the same rate, as shown below: 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 [4] | +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ | | | One or more EVRC/EVRC-B data frames of same rate | | .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The codec data frames MUST be generated from the output of the codec following the procedure described in 5.2 in RFC 3558 [5] and all MUST be of the same rate and size. Xie & Kapoor Expires December 10, 2006 [Page 5]
Internet-Draft EVRC RTP Format Enhancements June 2006 4.1 Single Rate Operation As mentioned earlier, in order to use the compact bundled format, all the EVRC/EVRC-B data frames in the session MUST be of the same rate. This packet format may carry only full or half-rate frames. For a session that uses the compact bundled format, the rate for the session can be determined during the session setup signaling, for example, via SDP exchanges. See Section 6 below for more details. 5. Storage Format For EVRC-B Codec The storage format is used for storing EVRC-B 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-B corresponds to the ASCII character string "#!EVRC-B\n", i.e., "0x23 0x21 0x45 0x56 0x52 0x43 0x2D 0x42 0x0A". Note, the "\n" is an important part of the magic number and MUST be included in the comparison, since, otherwise, the EVRC-B magic number will become indistinguishable from magic number used for EVRC. 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. Speech frames lost in transmission and non-received frames MUST be stored as erasure frames to maintain synchronization with the original media. 6. IANA Considerations Four (4) new MIME subtype registrations - "EVRC1", "EVRCB", "EVRCB0", and "EVRCB1" - are defined in this document for EVRC-B and compact bundled payload format support. For all the EVRC and EVRC-B RTP payload formats defined in RFC 3558 [5] and RFC XXXX, four additional optional parameters - "silencesupp", "dtxmax", "dtxmin", and "hangover" - are defined and used in DTX. The MIME subtype registrations, "EVRC" and "EVRC0" originally defined in RFC 3558 [5], are updated with the optional DTX parameters. Xie & Kapoor Expires December 10, 2006 [Page 6]
Internet-Draft EVRC RTP Format Enhancements June 2006 6.1 Registration of Media Type EVRC1 Type name: audio Subtype names: EVRC1 Required parameters: none Optional parameters: ptime: see RFC 2327 [8]. maxptime: The maximum amount of media which can be encapsulated in each packet, expressed as time in milliseconds. The time MUST be calculated as the sum of the time the media present in the packet represents. The time SHOULD be a multiple of the duration of a single codec data frame (20 msec). If not signaled, the default maxptime value MUST be 200 milliseconds. fixedrate: Indicates the EVRC 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: Permissible values are 0 and 1. A value of 1 indicates that the sender of this parameter: a) is capable of receiving silence suppressed speech using DTX, AND b) is capable of and will send out silence suppressed speech using DTX, unless the other end indicates that it does not want to receive silence suppressed speech using DTX. A value of 0 indicates that the sender of this parameter: a) does NOT want to receive silence suppressed speech using DTX, AND b) will NOT send out silence suppressed speech using DTX. If this parameter is not present, the default value specified in [9] MUST be assumed. If the RTP receiver indicates through the use of SIP signaling or other means that it is incapable of or unwilling to use silence suppression using DTX, silence suppression using DTX as specified in this document MUST NOT be used for the session. dtxmax: Permissible values are from 0 to 255. Indicates the maximum DTX update interval in number of frames. During DTX, the RTP sender occasionally updates the RTP receiver about the change in background noise characteristics, etc., by sending a new silence frame to the RTP receiver. The RTP receiver may Xie & Kapoor Expires December 10, 2006 [Page 7]
Internet-Draft EVRC RTP Format Enhancements June 2006 use 'dtxmax' to indicate to the RTP sender the maximum interval (in number of frames) between any two DTX updates it expects to receive from the RTP sender. If this parameter is not present in a session that uses DTX, the default value, 32, as specified in [9] MUST be assumed (note, if a later version of [9] specifies a new, different value, the new value will take precedence). This parameter MUST be ignored if silence suppression using DTX is not used for the session. dtxmin: Permissible values are from 0 to 255. Indicates the minimum DTX update interval in number of frames. The RTP receiver may use 'dtxmin' to indicate to the RTP sender the minimal interval (in number of frames) between any two DTX updates it expects to receive from the RTP sender. If this parameter is not present, the default value, 12, as specified in [9] MUST be assumed (note, if a later version of [9] specifies a new, different value, the new value will take precedence). This parameter MUST be ignored if silence suppression using DTX is not used for the session. hangover: Permissible values are from 0 to 255. Indicates the number of consecutive silence frames transmitted at the end of an active speech interval but before the DTX interval begins. When setting up an RTP session that uses DTX, an RTP receiver can use this parameter to signal the number of silence frames it expects to receive before the beginning of DTX. While hangover=0 is allowed, it is RECOMMENDED that hangover be set to 1 or greater since the presence of silence frames at the end of active speech can help the RTP receiver to identify the beginning of the DTX period. If this parameter is not present for a session that uses DTX, the default value, 1, as specified in [9] MUST be assumed (note, if a later version of [9] specifies a new, different value, the new value will take precedence). This parameter MUST be ignored if silence suppression using DTX is not used for the session. Encoding considerations: This media type is framed binary data (see RFC 4288, Section 4.8) and is defined for transfer of EVRC encoded data via RTP using the compact bundled format as described in RFC XXXX. Xie & Kapoor Expires December 10, 2006 [Page 8]
Internet-Draft EVRC RTP Format Enhancements June 2006 Security considerations: See Section 8 of RFC XXXX. Interoperability considerations: none Published specification: The EVRC vocoder is specified in 3GPP2 C.S0014 [3]. Transfer method with compact bundled RTP format is specified in RFC XXXX. 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: Qiaobing Xie <Qiaobing.Xie@motorola.com> Intended usage: COMMON Restrictions on usage: This media type depends on RTP framing, and hence is only defined for transfer via RTP (RFC 3550 [6]). Transfer within other framing protocols is not defined at this time. Author: Qiaobing Xie Change controller: IETF Audio/Video Transport working group delegated from the IESG. 6.2 Registration of Media Type EVRCB Type name: audio Subtype names: EVRCB Required parameters: none Optional parameters: ptime: see RFC 2327 [8]. maxptime: The maximum amount of media which can be encapsulated in each packet, expressed as time in milliseconds. The time MUST be calculated as the sum of the time the media present in the packet represents. The time SHOULD be a multiple of the duration of a single codec data frame (20 msec). If not Xie & Kapoor Expires December 10, 2006 [Page 9]
Internet-Draft EVRC RTP Format Enhancements June 2006 signaled, the default maxptime value MUST be 200 milliseconds. maxinterleave: Maximum number for interleaving length (field LLL in the Interleaving Octet). 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 dtxmax: see Section 6.1 dtxmin: see Section 6.1 hangover: see Section 6.1 Encoding considerations: This media type is framed binary data (see RFC 4288, Section 4.8) and is defined for transfer of EVRC-B encoded data via RTP using the Interleaved/Bundled packet format specified in RFC 3558 [5]. Security considerations: See Section 8 of RFC XXXX. Interoperability considerations: none Published specification: The EVRC-B vocoder is specified in 3GPP2 C.S0014-B [4]. Transfer method with 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 information applies for storage format only. Magic number: #!EVRC-B\n (see Section 5 of RFC XXXX) File extensions: evb, EVB Macintosh file type code: none Object identifier or OID: none Person & email address to contact for further information: Qiaobing Xie <Qiaobing.Xie@motorola.com> Intended usage: COMMON Xie & Kapoor Expires December 10, 2006 [Page 10]
Internet-Draft EVRC RTP Format Enhancements June 2006 Restrictions on usage: This media type may be used with RTP framing (RFC 3550 [6]) and as a storage format. When used with RTP, the procedures in Section 3 MUST be followed. In all other contexts, the storage format defined in Section 5 MUST be used. Author: Qiaobing Xie Change controller: IETF Audio/Video Transport working group delegated from the IESG. 6.3 Registration of Media Type EVRCB0 Type name: audio Subtype names: EVRCB0 Required parameters: none Optional parameters: silencesupp: see Section 6.1 dtxmax: see Section 6.1 dtxmin: see Section 6.1 hangover: see Section 6.1 Encoding considerations: This media type is framed binary data (see RFC 4288, Section 4.8) and is defined for transfer of EVRC-B encoded data via RTP using the Header-Free packet format specified in RFC 3558 [5]. Security considerations: See Section 8 of RFC XXXX. Interoperability considerations: none Published specification: The EVRC-B vocoder is specified in 3GPP2 C.S0014-B [4]. Transfer method with Header-Free packet format via RTP is specified in RFC 3558 and RFC XXXX. Xie & Kapoor Expires December 10, 2006 [Page 11]
Internet-Draft EVRC RTP Format Enhancements June 2006 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: Qiaobing Xie <Qiaobing.Xie@motorola.com> Intended usage: COMMON Restrictions on usage: This media type depends on RTP framing, and hence is only defined for transfer via RTP (RFC 3550 [6]). Transfer within other framing protocols is not defined at this time. Author: Qiaobing Xie Change controller: IETF Audio/Video Transport working group delegated from the IESG. 6.4 Registration of Media Type EVRCB1 Type name: audio Subtype names: EVRCB1 Required parameters: none Optional parameters: ptime: see RFC 2327 [8]. maxptime: The maximum amount of media which can be encapsulated in each packet, expressed as time in milliseconds. The time MUST be calculated as the sum of the time the media present in the packet represents. The time SHOULD be a multiple of the duration of a single codec data frame (20 msec). If not signaled, the default maxptime value MUST be 200 milliseconds. fixedrate: Indicates the EVRC-B 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. Xie & Kapoor Expires December 10, 2006 [Page 12]
Internet-Draft EVRC RTP Format Enhancements June 2006 silencesupp: see Section 6.1 dtxmax: see Section 6.1 dtxmin: see Section 6.1 hangover: see Section 6.1 Encoding considerations: This media type is framed binary data (see RFC 4288, Section 4.8) and is defined for transfer of EVRC-B encoded data via RTP using the compact bundled format as described in RFC XXXX. Security considerations: See Section 8 of RFC XXXX. Interoperability considerations: none. Published specification: The EVRC-B vocoder is specified in 3GPP2 C.S0014-B [4]. Transfer method with compact bundled RTP format is specified in RFC XXXX. 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: Qiaobing Xie <Qiaobing.Xie@motorola.com> Intended usage: COMMON Restrictions on usage: This media type depends on RTP framing, and hence is only defined for transfer via RTP (RFC 3550 [6]). Transfer within other framing protocols is not defined at this time. Author: Qiaobing Xie Change controller: IETF Audio/Video Transport working group delegated from the IESG. 6.5 Updated Registration of Media Type EVRC (The definition is from RFC 3558, added with the optional DTX parameters, and updated with the new template specified in [11].) Xie & Kapoor Expires December 10, 2006 [Page 13]
Internet-Draft EVRC RTP Format Enhancements June 2006 Type name: audio Subtype names: EVRC Required parameters: none Optional parameters: ptime: Defined as usual for RTP audio (see RFC 2327). maxptime: The maximum amount of media which can be encapsulated in each packet, expressed as time in milliseconds. The time SHALL be calculated as the sum of the time the media present in the packet represents. The time SHOULD be a multiple of the duration of a single codec data frame (20 msec). If not signaled, the default maxptime value SHALL be 200 milliseconds. maxinterleave: Maximum number for interleaving length (field LLL in the Interleaving Octet). The interleaving lengths used in the entire session MUST NOT exceed this maximum value. If not signaled, the maxinterleave length SHALL be 5. silencesupp: see Section 6.1 dtxmax: see Section 6.1 dtxmin: see Section 6.1 hangover: see Section 6.1 Encoding considerations: This media type is framed binary data (see RFC 4288, Section 4.8) and is defined for transfer of EVRC-encoded data via RTP using the Interleaved/Bundled packet format specified in Sections 4.1, 6, and 7 of RFC 3558. It is also defined for other transfer methods using the storage format specified in Section 11 of RFC 3558. Security considerations: See Section 14 "Security Considerations" of RFC 3558. Interoperability considerations: The DTX parameters are receiver options. Existing RFC 3558 implementations will not send any of the DTX parameters in their SDP and will ignore any DTX parameters they receive. The adaptive DTX behavior of DTX-capable EVRC codecs (as detailed in [9], Section 4.3.5) ensures interoperability with non-DTX EVRC codecs. Xie & Kapoor Expires December 10, 2006 [Page 14]
Internet-Draft EVRC RTP Format Enhancements June 2006 Published specification: The EVRC vocoder is specified in 3GPP2 C.S0014. Transfer methods are 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 information applies for storage format only. Magic number: #!EVRC\n (see Section 11 of RFC 3558) File extensions: evc, EVC Macintosh file type code: none Object identifier or OID: none Person & email address to contact for further information: Qiaobing Xie <Qiaobing.Xie@motorola.com> Intended usage: COMMON Restrictions on usage: This media type may be used with RTP framing (RFC 3550 [6]) and as a storage format. When used with RTP, the procedures in RFC 3558, Section 4.1 MUST be followed. In all other contexts, the storage format defined in RFC 3558, Section 11 MUST be used. Author: Adam Li/Qiaobing Xie Change controller: IETF Audio/Video Transport working group delegated from the IESG. 6.6 Updated Registration of Media Type EVRC0 (The definition is from RFC 3558, added with the optional DTX parameters, and updated with the new template specified in [11].) Type name: audio Subtype names: EVRC0 Required parameters: none Optional parameters: Xie & Kapoor Expires December 10, 2006 [Page 15]
Internet-Draft EVRC RTP Format Enhancements June 2006 silencesupp: see Section 6.1 dtxmax: see Section 6.1 dtxmin: see Section 6.1 hangover: see Section 6.1 Encoding considerations: This media type is framed binary data (see RFC 4288, Section 4.8) and is only defined for transfer of EVRC-encoded data via RTP using the Header-Free packet format specified in Section 4.2 of RFC 3558. Security considerations: See Section 14 "Security Considerations" of RFC 3558. Interoperability considerations: The DTX parameters are receiver options. Existing RFC 3558 implementations will not send any of the DTX parameters in their SDP and will ignore any DTX parameters they receive. The adaptive DTX behavior of DTX-capable EVRC codecs (as detailed in [9], Section 4.3.5) ensures interoperability with non-DTX EVRC codecs. Published specification: The EVRC vocoder is specified in 3GPP2 C.S0014. Transfer methods are 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: Qiaobing Xie <Qiaobing.Xie@motorola.com> Intended usage: COMMON Restrictions on usage: This media type depends on RTP framing, and hence is only defined for transfer via RTP (RFC 3550 [6]). Transfer within other framing protocols is not defined at this time. Author: Adam Li/Qiaobing Xie Xie & Kapoor Expires December 10, 2006 [Page 16]
Internet-Draft EVRC RTP Format Enhancements June 2006 Change controller: IETF Audio/Video Transport working group delegated from the IESG. 6.7 Mapping MIME Parameters into SDP The information carried in the MIME media type specification has a specific mapping to fields in the Session Description Protocol (SDP) [8], which is commonly used to describe RTP sessions. When SDP is used to specify sessions employing the compact bundled format for EVRC/EVRC-B encoded speech, the mapping is as follows: o The MIME type ("audio") goes in SDP "m=" as the media name. o The MIME subtype ("EVRC", "EVRC0", "EVRC1", "EVRCB", EVRCB0", or "EVRCB1") goes in SDP "a=rtpmap" as the encoding name. o The optional parameters "ptime" and "maxptime" (for subtypes EVRC, EVRC1, EVRCB, and EVRCB1) go in the SDP "a=ptime" and "a=maxptime" attributes, respectively. o The optional parameter "maxinterleave" (for subtypes EVRC and EVRCB) goes in the SDP "a=fmtp" attribute by copying it directly from the MIME media type string as "maxinterleave=value". o The optional parameter "fixedrate" (for subtypes EVRC1 and EVRCB1) goes in "a=fmtp" attribute by copying it directly from the MIME media type string as "fixedrate=value". o The optional parameters "silencesupp", "dtxmax", "dtxmin", and "hangover" go in "a=fmtp" attribute by copying it directly from the MIME media type string as "silencesupp=value", "dtxmax=value", "dtxmin=value", and "hangover=value", respectively. Example of usage of EVRC1: m=audio 49120 RTP/AVP 97 a=rtpmap:97 EVRC1/8000 a=fmtp:97 fixedrate=0.5 a=maxptime:120 Example of usage of EVRCB: m=audio 49120 RTP/AVP 97 a=rtpmap:97 EVRCB/8000 a=maxptime:120 Example of usage of EVRCB0: Xie & Kapoor Expires December 10, 2006 [Page 17]
Internet-Draft EVRC RTP Format Enhancements June 2006 m=audio 49120 RTP/AVP 97 a=rtpmap:97 EVRCB0/8000 Example of usage of EVRCB1: m=audio 49120 RTP/AVP 97 a=rtpmap:97 EVRCB1/8000 a=fmtp:97 fixedrate=0.5 a=maxptime:100 Example of usage of EVRC with DTX with silencesupp=1: m=audio 49120 RTP/AVP 97 a=rtpmap:97 EVRC/8000 a=fmtp:97 silencesupp=1 dtxmax=32 dtxmin=12 hangover=1 Examples of usage of EVRC with DTX with silencesupp=0: m=audio 49120 RTP/AVP 97 a=rtpmap:97 EVRC/8000 a=fmtp:97 silencesupp=0 6.8 Usage in Offer/Answer All SDP parameters in this payload format are declarative, and all reasonable values are expected to be supported. In particular, when DTX is supported, the RTP sender implementation SHOULD support hangover, dtxmin, and dtxmax values from 0 to 255. Thus, the standard usage of Offer/Answer as described in RFC 3264 [7] SHOULD be followed. In addition, the following rules MUST be followed while negotiating DTX parameters: 1. If any DTX parameter is not present in either offer and/or answer, the default value of the DTX parameter MUST be assumed. 2. If silencesupp is present and set to 0 in either offer or answer, the values of all received DTX parameters other than silencesupp SHOULD be ignored. 3. In an offer or answer, the value of dtxmax SHOULD always be larger than or equal to the value of dtxmin, regardless of whether the values are indicated explicitly or implicitly by default. Moreover, if the indicated value of dtxmin is larger than that of dtxmax, an RTP sender MUST ignore the indicated values and MUST fall back on using the default dtxmin and dtxmax Xie & Kapoor Expires December 10, 2006 [Page 18]
Internet-Draft EVRC RTP Format Enhancements June 2006 values. 7. Backward Compatibility with RFC 3558 This document adds new optional DTX parameters to the original EVRC payload subtypes "EVRC" and "EVRC0" defined in RFC 3558. Since the new DTX parameters are receiver options, we expect the existing RFC 3558 implementations will not send any of the DTX parameters in their SDP and will ignore any DTX parameters they receive. The adaptive DTX behavior of DTX-capable EVRC codecs (as detailed in [9], Section 4.3.5) ensures the backward interoperability between the DTX-capable EVRC codec and non-DTX EVRC codecs. 8. Security Considerations Implementations using the payload defined in this specification are subject to the security considerations discussed in RFC 3558 [5], RFC 3550 [6], and any appropriate profile (for example RFC3551 [10]). This payload does not specify any different security services. 9. Acknowledgements The following people have made significant contributions to this document (in alphabetic order): Parag Agashe, Jim Ashley, Harikishan Desineni, Serafin Diaz, Harinath Garudadri, Gouri Johanssen, Ananth Kandhadai, Waqar Mohsin, Ashok Roy, Gino Scribano, and Gajinder Singh Vij. Special thanks to Colin Perkins for his careful review and comments that significantly improved the quality of this document. 10. References 10.1 Normative References [1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [3] "Enhanced Variable Rate Codec, Speech Service Option 3 for Wideband Spread Spectrum Digital Systems", 3GPP2 C.S0014, January 1997. [4] "Enhanced Variable Rate Codec, Speech Service Option 68 for Wideband Spread Spectrum Digital Systems", 3GPP2 C.S0014-B, in Xie & Kapoor Expires December 10, 2006 [Page 19]
Internet-Draft EVRC RTP Format Enhancements June 2006 progress. [5] Li, A., "RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV)", RFC 3558, July 2003. [6] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", RFC 3550, July 2003. [7] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with the Session Description Protocol (SDP)", RFC 3264, June 2002. [8] Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. [9] "Discontinuous Transmission (DTX) of Speech in cdma2000 Systems", 3GPP2 C.S0076-0, Version 1.0, December 2005. 10.2 Informative References [10] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video Conferences with Minimal Control", RFC 3551, July 2003. [11] Casner, S., "Media Type Registration of RTP Payload Formats", draft-ietf-avt-rfc3555bis-03.txt (work in progress), March 2006. Authors' Addresses Qiaobing Xie Motorola, Inc. 1501 W. Shure Drive, 2-F9 Arlington Heights, IL 60004 US Phone: +1-847-632-3028 Email: Qiaobing.Xie@Motorola.com Rohit Kapoor Qualcomm Inc. US Phone: +1-858-845-1161 Email: rkapoor@qualcomm.com Xie & Kapoor Expires December 10, 2006 [Page 20]
Internet-Draft EVRC RTP Format Enhancements June 2006 Intellectual Property Statement The IETF 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 this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR 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 rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY 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 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Xie & Kapoor Expires December 10, 2006 [Page 21]
