RFC 4695
RTP Payload Format for MIDI
E. A MIDI Overview for Networking Specialists
This appendix presents an overview of the MIDI standard, for the benefit of networking specialists new to musical applications. Implementors should consult [MIDI] for a normative description of MIDI. Musicians make music by performing a controlled sequence of physical movements. For example, a pianist plays by coordinating a series of key presses, key releases, and pedal actions. MIDI represents a musical performance by encoding these physical gestures as a sequence of MIDI commands. This high-level musical representation is compact but fragile: one lost command may be catastrophic to the performance. MIDI commands have much in common with the machine instructions of a microprocessor. MIDI commands are defined as binary elements. Bitfields within a MIDI command have a regular structure and a specialized purpose. For example, the upper nibble of the first command octet (the opcode field) codes the command type. MIDI commands may consist of an arbitrary number of complete octets, but most MIDI commands are 1, 2, or 3 octets in length.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | Channel Voice Messages | Bitfield Pattern | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | NoteOff (end a note) | 1000cccc 0nnnnnnn 0vvvvvvv | |-------------------------------------------------------------| | NoteOn (start a note) | 1001cccc 0nnnnnnn 0vvvvvvv | |-------------------------------------------------------------| | PTouch (Polyphonic Aftertouch) | 1010cccc 0nnnnnnn 0aaaaaaa | |-------------------------------------------------------------| | CControl (Controller Change) | 1011cccc 0xxxxxxx 0yyyyyyy | |-------------------------------------------------------------| | PChange (Program Change) | 1100cccc 0ppppppp | |-------------------------------------------------------------| | CTouch (Channel Aftertouch) | 1101cccc 0aaaaaaa | |-------------------------------------------------------------| | PWheel (Pitch Wheel) | 1110cccc 0xxxxxxx 0yyyyyyy | ------------------------------------------------------------- Figure E.1 -- MIDI Channel Messages
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | System Common Messages | Bitfield Pattern | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | System Exclusive | 11110000, followed by a | | | list of 0xxxxxx octets, | | | followed by 11110111 | |-------------------------------------------------------------| | MIDI Time Code Quarter Frame | 11110001 0xxxxxxx | |-------------------------------------------------------------| | Song Position Pointer | 11110010 0xxxxxxx 0yyyyyyy | |-------------------------------------------------------------| | Song Select | 11110011 0xxxxxxx | |-------------------------------------------------------------| | Undefined | 11110100 | |-------------------------------------------------------------| | Undefined | 11110101 | |-------------------------------------------------------------| | Tune Request | 11110110 | |-------------------------------------------------------------| | System Exclusive End Marker | 11110111 | ------------------------------------------------------------- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | System Realtime Messages | Bitfield Pattern | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | Clock | 11111000 | |-------------------------------------------------------------| | Undefined | 11111001 | |-------------------------------------------------------------| | Start | 11111010 | |-------------------------------------------------------------| | Continue | 11111011 | |-------------------------------------------------------------| | Stop | 11111100 | |-------------------------------------------------------------| | Undefined | 11111101 | |-------------------------------------------------------------| | Active Sense | 11111110 | |-------------------------------------------------------------| | System Reset | 11111111 | ------------------------------------------------------------- Figure E.2 -- MIDI System Messages
Figure E.1 and E.2 show the MIDI command family. There are three major classes of commands: voice commands (opcode field values in the range 0x8 through 0xE), system common commands (opcode field 0xF, commands 0xF0 through 0xF7), and system real-time commands (opcode field 0xF, commands 0xF8 through 0xFF). Voice commands code the musical gestures for each timbre in a composition. Systems commands perform functions that usually affect all voice channels, such as System Reset (0xFF).E.1. Commands Types
Voice commands execute on one of 16 MIDI channels, as coded by its 4-bit channel field (field cccc in Figure E.1). In most applications, notes for different timbres are assigned to different channels. To support applications that require more than 16 channels, MIDI systems use several MIDI command streams in parallel, to yield 32, 48, or 64 MIDI channels. As an example of a voice command, consider a NoteOn command (opcode 0x9), with binary encoding 1001cccc 0nnnnnnn 0aaaaaaa. This command signals the start of a musical note on MIDI channel cccc. The note has a pitch coded by the note number nnnnnnn, and an onset amplitude coded by note velocity aaaaaaa. Other voice commands signal the end of notes (NoteOff, opcode 0x8), map a specific timbre to a MIDI channel (PChange, opcode 0xC), or set the value of parameters that modulate the timbral quality (all other voice commands). The exact meaning of most voice channel commands depends on the rendering algorithms the MIDI receiver uses to generate sound. In most applications, a MIDI sender has a model (in some sense) of the rendering method used by the receiver. System commands perform a variety of global tasks in the stream, including "sequencer" playback control of pre-recorded MIDI commands (the Song Position Pointer, Song Select, Clock, Start, Continue, and Stop messages), SMPTE time code (the MIDI Time Code Quarter Frame command), and the communication of device-specific data (the System Exclusive messages).E.2. Running Status
All MIDI command bitfields share a special structure: the leading bit of the first octet is set to 1, and the leading bit of all subsequent octets is set to 0. This structure supports a data compression system, called running status [MIDI], that improves the coding efficiency of MIDI.
In running status coding, the first octet of a MIDI voice command may be dropped if it is identical to the first octet of the previous MIDI voice command. This rule, in combination with a convention to consider NoteOn commands with a null third octet as NoteOff commands, supports the coding of note sequences using two octets per command. Running status coding is only used for voice commands. The presence of a system common message in the stream cancels running status mode for the next voice command. However, system real-time messages do not cancel running status mode.E.3. Command Timing
The bitfield formats in Figures E.1 and E.2 do not encode the execution time for a command. Timing information is not a part of the MIDI command syntax itself; different applications of the MIDI command language use different methods to encode timing. For example, the MIDI command set acts as the transport layer for MIDI 1.0 DIN cables [MIDI]. MIDI cables are short asynchronous serial lines that facilitate the remote operation of musical instruments and audio equipment. Timestamps are not sent over a MIDI 1.0 DIN cable. Instead, the standard uses an implicit "time of arrival" code. Receivers execute MIDI commands at the moment of arrival. In contrast, Standard MIDI Files (SMFs, [MIDI]), a file format for representing complete musical performances, add an explicit timestamp to each MIDI command, using a delta encoding scheme that is optimized for statistics of musical performance. SMF timestamps usually code timing using the metric notation of a musical score. SMF meta-events are used to add a tempo map to the file, so that score beats may be accurately converted into units of seconds during rendering.E.4. AudioSpecificConfig Templates for MMA Renderers
In Section 6.2 and Appendix C.6.5, we describe how session descriptions include an AudioSpecificConfig data block to specify a MIDI rendering algorithm for mpeg4-generic RTP MIDI streams. The bitfield format of AudioSpecificConfig is defined in [MPEGAUDIO]. StructuredAudioSpecificConfig, a key data structure coded in AudioSpecificConfig, is defined in [MPEGSA]. For implementors wishing to specify Structured Audio renderers, a full understanding of [MPEGSA] and [MPEGAUDIO] is essential. However, many implementors will limit their rendering options to the two MIDI Manufacturers Association renderers that may be specified in
AudioSpecificConfig: General MIDI (GM, [MIDI]) and Downloadable Sounds 2 (DLS 2, [DLS2]). To aid these implementors, we reproduce the AudioSpecificConfig bitfield formats for a GM renderer and a DLS 2 renderer below. We have checked these bitfields carefully and believe they are correct. However, we stress that the material below is informative, and that [MPEGAUDIO] and [MPEGSA] are the normative definitions for AudioSpecificConfig. As described in Section 6.2, a minimal mpeg4-generic session description encodes the AudioSpecificConfig binary bitfield as a hexadecimal string (whose format is defined in [RFC3640]) that is assigned to the "config" parameter. As described in Appendix C.6.3, a session description that uses the render parameter encodes the AudioSpecificConfig binary bitfield as a Base64-encoded string assigned to the "inline" parameter, or in the body of an HTTP URL assigned to the "url" parameter. Below, we show a simplified binary AudioSpecificConfig bitfield format, suitable for sending and receiving GM and DLS 2 data: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AOTYPE |FREQIDX|CHANNEL|SACNK| FILE_BLK 1 (required) ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|SACNK| FILE_BLK 2 (optional) ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... |1|SACNK| FILE_BLK N (optional) ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0|0| (first "0" bit terminates FILE_BLK list) +-+-+ Figure E.3 -- Simplified AudioSpecificConfig The 5-bit AOTYPE field specifies the Audio Object Type as an unsigned integer. The legal values for use with mpeg4-generic RTP MIDI streams are "15" (General MIDI), "14" (DLS 2), and "13" (Structured Audio). Thus, receivers that do not support all three mpeg4-generic renderers may parse the first 5 bits of an AudioSpecificConfig coded in a session description and reject sessions that specify unsupported renderers. The 4-bit FREQIDX field specifies the sampling rate of the renderer. We show the mapping of FREQIDX values to sampling rates in Figure E.4. Senders MUST specify a sampling frequency that matches the RTP clock rate, if possible; if not, senders MUST specify the escape
value. Receivers MUST consult the RTP clock parameter for the true sampling rate if the escape value is specified. FREQIDX Sampling Frequency 0x0 96000 0x1 88200 0x2 64000 0x3 48000 0x4 44100 0x5 32000 0x6 24000 0x7 22050 0x8 16000 0x9 12000 0xa 11025 0xb 8000 0xc reserved 0xd reserved 0xe reserved 0xf escape value Figure E.4 -- FreqIdx encoding The 4-bit CHANNEL field specifies the number of audio channels for the renderer. The values 0x1 to 0x5 specify 1 to 5 audio channels; the value 0x6 specifies 5+1 surround sound, and the value 0x7 specifies 7+1 surround sound. If the rtpmap line in the session description specifies one of these formats, CHANNEL MUST be set to the corresponding value. Otherwise, CHANNEL MUST be set to 0x0. The CHANNEL field is followed by a list of one or more binary file data blocks. The 3-bit SACNK field (the chunk_type field in class StructuredAudioSpecificConfig, defined in [MPEGSA]) specifies the type of each data block. For General MIDI, only Standard MIDI Files may appear in the list (SACNK field value 2). For DLS 2, only Standard MIDI Files and DLS 2 RIFF files (SACNK field value 4) may appear. For both of these file types, the FILE_BLK field has the format shown in Figure E.5: a 32- bit unsigned integer value (FILE_LEN) coding the number of bytes in the SMF or RIFF file, followed by FILE_LEN bytes coding the file data.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | FILE_LEN (32-bit, a byte count SMF file or RIFF file) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | FILE_DATA (file contents, a list of FILE_LEN bytes) ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure E.5 -- The FILE_BLK field format Note that several files may follow CHANNEL field. The "1" constant fields in Figure E.3 code the presence of another file; the "0" constant field codes the end of the list. The final "0" bit in Figure E.3 codes the absence of special coding tools (see [MPEGAUDIO] for details). Senders not using these tools MUST append this "0" bit; receivers that do not understand these coding tools MUST ignore all data following a "1" in this position. The StructuredAudioSpecificConfig bitfield structure requires the presence of one FILE_BLK. For mpeg4-generic RTP MIDI use of DLS 2, FILE_BLKs MUST code RIFF files or SMF files. For mpeg4-generic RTP MIDI use of General MIDI, FILE_BLKs MUST code SMF files. By default, this SMF will be ignored (Appendix C.6.4.1). In this default case, a GM StructuredAudioSpecificConfig bitfield SHOULD code a FILE_BLK whose FILE_LEN is 0, and whose FILE_DATA is empty. To complete this appendix, we derive the StructuredAudioSpecificConfig that we use in the General MIDI session examples in this memo. Referring to Figure E.3, we note that for GM, AOTYPE = 15. Our examples use a 44,100 Hz sample rate (FREQIDX = 4) and are in mono (CHANNEL = 1). For GM, a single SMF is encoded (SACNK = 2), using the SMF shown in Figure E.6 (a 26 byte file). -------------------------------------------- | MIDI File = <Header Chunk> <Track Chunk> | -------------------------------------------- <Header Chunk> = <chunk type> <length> <format> <ntrks> <divsn> 4D 54 68 64 00 00 00 06 00 00 00 01 00 60 <Track Chunk> = <chunk type> <length> <delta-time> <end-event> 4D 54 72 6B 00 00 00 04 00 FF 2F 00 Figure E.6 -- SMF file encoded in the example
Placing these constants in binary format into the data structure shown in Figure E.3 yields the constant shown in Figure E.7. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 1 1 1 1|0 1 0 0|0 0 0 1|0 1 0|0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 0 0 0 0 0 0 0 0 0 1 1 0 1 0|0 1 0 0|1 1 0 1|0 1 0 1|0 1 0 0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 1 1 0|1 0 0 0|0 1 1 0|0 1 0 0|0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 0 0|0 0 0 0|0 0 0 0|0 1 1 0|0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 1|0 0 0 0|0 0 0 0|0 1 1 0|0 0 0 0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 1 0 0|1 1 0 1|0 1 0 1|0 1 0 0|0 1 1 1|0 0 1 0|0 1 1 0|1 0 1 1| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0|0 0 0 0|0 1 1 0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0 0 0 0|0 0 0 0|1 1 1 1|1 1 1 1|0 0 1 0|1 1 1 1|0 0 0 0|0 0 0 0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0|0| +-+-+ Figure E.7 -- AudioSpecificConfig used in GM examples Expressing this bitfield as an ASCII hexadecimal string yields: 7A0A0000001A4D546864000000060000000100604D54726B0000000600FF2F000 This string is assigned to the "config" parameter in the minimal mpeg4-generic General MIDI examples in this memo (such as the example in Section 6.2). Expressing this string in Base64 [RFC2045] yields: egoAAAAaTVRoZAAAAAYAAAABAGBNVHJrAAAABgD/LwAA This string is assigned to the "inline" parameter in the General MIDI example shown in Appendix C.6.5.
References
Normative References
[MIDI] MIDI Manufacturers Association. "The Complete MIDI 1.0 Detailed Specification", 1996. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video Conferences with Minimal Control", STD 65, RFC 3551, July 2003. [RFC3640] van der Meer, J., Mackie, D., Swaminathan, V., Singer, D., and P. Gentric, "RTP Payload Format for Transport of MPEG-4 Elementary Streams", RFC 3640, November 2003. [MPEGSA] International Standards Organization. "ISO/IEC 14496 MPEG-4", Part 3 (Audio), Subpart 5 (Structured Audio), 2001. [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. [MPEGAUDIO] International Standards Organization. "ISO 14496 MPEG- 4", Part 3 (Audio), 2001. [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [DLS2] MIDI Manufacturers Association. "The MIDI Downloadable Sounds Specification", v98.2, 1998. [RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 4234, October 2005. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. [RFC3388] Camarillo, G., Eriksson, G., Holler, J., and H. Schulzrinne, "Grouping of Media Lines in the Session Description Protocol (SDP)", RFC 3388, December 2002. [RP015] MIDI Manufacturers Association. "Recommended Practice 015 (RP-015): Response to Reset All Controllers", 11/98. [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and Registration Procedures", BCP 13, RFC 4288, December 2005. [RFC3555] Casner, S. and P. Hoschka, "MIME Type Registration of RTP Payload Formats", RFC 3555, July 2003.Informative References
[NMP] Lazzaro, J. and J. Wawrzynek. "A Case for Network Musical Performance", 11th International Workshop on Network and Operating Systems Support for Digital Audio and Video (NOSSDAV 2001) June 25-26, 2001, Port Jefferson, New York. [GRAME] Fober, D., Orlarey, Y. and S. Letz. "Real Time Musical Events Streaming over Internet", Proceedings of the International Conference on WEB Delivering of Music 2001, pages 147-154. [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming Protocol (RTSP)", RFC 2326, April 1998.
[ALF] Clark, D. D. and D. L. Tennenhouse. "Architectural considerations for a new generation of protocols", SIGCOMM Symposium on Communications Architectures and Protocols , (Philadelphia, Pennsylvania), pp. 200--208, IEEE, Sept. 1990. [RFC4696] Lazzaro, J. and J. Wawrzynek, "An Implementation Guide for RTP MIDI", RFC 4696, November 2006. [RFC2205] Braden, R., Zhang, L., Berson, S., Herzog, S., and S. Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification", RFC 2205, September 1997. [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and Registration Procedures", BCP 13, RFC 4288, December 2005. [RFC4289] Freed, N. and J. Klensin, "Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures", BCP 13, RFC 4289, December 2005. [RFC4571] Lazzaro, J. "Framing Real-time Transport Protocol (RTP) and RTP Control Protocol (RTCP) Packets over Connection- Oriented Transport", RFC 4571, July 2006. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [SPMIDI] MIDI Manufacturers Association. "Scalable Polyphony MIDI, Specification and Device Profiles", Document Version 1.0a, 2002. [LCP] Apple Computer. "Logic 7 Dedicated Control Surface Support", Appendix B. Product manual available from www.apple.com.
Authors' Addresses
John Lazzaro (corresponding author) UC Berkeley CS Division 315 Soda Hall Berkeley CA 94720-1776 EMail: lazzaro@cs.berkeley.edu John Wawrzynek UC Berkeley CS Division 631 Soda Hall Berkeley CA 94720-1776 EMail: johnw@cs.berkeley.edu
Full Copyright Statement Copyright (C) The IETF Trust (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. 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, THE IETF TRUST, AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property 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. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society.