SPEECHSC D. Burnett Internet-Draft Voxeo Intended status: Standards Track S. Shanmugham Expires: January 10, 2011 Cisco Systems, Inc. July 9, 2010 Media Resource Control Protocol Version 2 (MRCPv2) draft-ietf-speechsc-mrcpv2-21 Abstract The MRCPv2 protocol allows client hosts to control media service resources such as speech synthesizers, recognizers, verifiers and identifiers residing in servers on the network. MRCPv2 is not a "stand-alone" protocol - it relies on other protocols, such as Session Initiation Protocol (SIP) to rendezvous MRCPv2 clients and servers and manage sessions between them, and the Session Description Protocol (SDP) to describe, discover and exchange capabilities. It also depends on SIP and SDP to establish the media sessions and associated parameters between the media source or sink and the media server. Once this is done, the MRCPv2 protocol exchange operates over the control session established above, allowing the client to control the media processing resources on the speech resource server. 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 10, 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 Burnett & Shanmugham Expires January 10, 2011 [Page 1] Internet-Draft MRCPv2 July 2010 Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Burnett & Shanmugham Expires January 10, 2011 [Page 2] Internet-Draft MRCPv2 July 2010 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 9 2. Document Conventions . . . . . . . . . . . . . . . . . . . . 10 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . 10 2.2. State-Machine Diagrams . . . . . . . . . . . . . . . . . 11 2.3. URI Schemes . . . . . . . . . . . . . . . . . . . . . . 11 3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 11 3.1. MRCPv2 Media Resource Types . . . . . . . . . . . . . . 13 3.2. Server and Resource Addressing . . . . . . . . . . . . . 14 4. MRCPv2 Protocol Basics . . . . . . . . . . . . . . . . . . . 14 4.1. Connecting to the Server . . . . . . . . . . . . . . . . 15 4.2. Managing Resource Control Channels . . . . . . . . . . . 15 4.3. SIP session example . . . . . . . . . . . . . . . . . . 17 4.4. Media Streams and RTP Ports . . . . . . . . . . . . . . 22 4.5. MRCPv2 Message Transport . . . . . . . . . . . . . . . . 24 5. MRCPv2 Specification . . . . . . . . . . . . . . . . . . . . 24 5.1. Common Protocol Elements . . . . . . . . . . . . . . . . 24 5.2. Request . . . . . . . . . . . . . . . . . . . . . . . . 26 5.3. Response . . . . . . . . . . . . . . . . . . . . . . . . 27 5.4. Status Codes . . . . . . . . . . . . . . . . . . . . . . 28 5.5. Events . . . . . . . . . . . . . . . . . . . . . . . . . 29 6. MRCPv2 Generic Methods, Headers, and Result Structure . . . . 30 6.1. Generic Methods . . . . . . . . . . . . . . . . . . . . 30 6.1.1. SET-PARAMS . . . . . . . . . . . . . . . . . . . . . 30 6.1.2. GET-PARAMS . . . . . . . . . . . . . . . . . . . . . 31 6.2. Generic Message Headers . . . . . . . . . . . . . . . . 32 6.2.1. Channel-Identifier . . . . . . . . . . . . . . . . . 33 6.2.2. Accept . . . . . . . . . . . . . . . . . . . . . . . 34 6.2.3. Active-Request-Id-List . . . . . . . . . . . . . . . 34 6.2.4. Proxy-Sync-Id . . . . . . . . . . . . . . . . . . . 35 6.2.5. Accept-Charset . . . . . . . . . . . . . . . . . . . 35 6.2.6. Content-Type . . . . . . . . . . . . . . . . . . . . 35 6.2.7. Content-ID . . . . . . . . . . . . . . . . . . . . . 35 6.2.8. Content-Base . . . . . . . . . . . . . . . . . . . . 36 6.2.9. Content-Encoding . . . . . . . . . . . . . . . . . . 36 6.2.10. Content-Location . . . . . . . . . . . . . . . . . . 36 6.2.11. Content-Length . . . . . . . . . . . . . . . . . . . 37 6.2.12. Fetch Timeout . . . . . . . . . . . . . . . . . . . 37 6.2.13. Cache-Control . . . . . . . . . . . . . . . . . . . 38 6.2.14. Logging-Tag . . . . . . . . . . . . . . . . . . . . 39 6.2.15. Set-Cookie and Set-Cookie2 . . . . . . . . . . . . . 39 6.2.16. Vendor Specific Parameters . . . . . . . . . . . . . 41 6.3. Generic Result Structure . . . . . . . . . . . . . . . . 42 6.3.1. Natural Language Semantics Markup Language . . . . . 42 7. Resource Discovery . . . . . . . . . . . . . . . . . . . . . 43 8. Speech Synthesizer Resource . . . . . . . . . . . . . . . . . 45 8.1. Synthesizer State Machine . . . . . . . . . . . . . . . 45 Burnett & Shanmugham Expires January 10, 2011 [Page 3] Internet-Draft MRCPv2 July 2010 8.2. Synthesizer Methods . . . . . . . . . . . . . . . . . . 46 8.3. Synthesizer Events . . . . . . . . . . . . . . . . . . . 46 8.4. Synthesizer Header Fields . . . . . . . . . . . . . . . 47 8.4.1. Jump-Size . . . . . . . . . . . . . . . . . . . . . 47 8.4.2. Kill-On-Barge-In . . . . . . . . . . . . . . . . . . 48 8.4.3. Speaker Profile . . . . . . . . . . . . . . . . . . 48 8.4.4. Completion Cause . . . . . . . . . . . . . . . . . . 49 8.4.5. Completion Reason . . . . . . . . . . . . . . . . . 49 8.4.6. Voice-Parameter . . . . . . . . . . . . . . . . . . 50 8.4.7. Prosody-Parameters . . . . . . . . . . . . . . . . . 50 8.4.8. Speech Marker . . . . . . . . . . . . . . . . . . . 51 8.4.9. Speech Language . . . . . . . . . . . . . . . . . . 52 8.4.10. Fetch Hint . . . . . . . . . . . . . . . . . . . . . 52 8.4.11. Audio Fetch Hint . . . . . . . . . . . . . . . . . . 52 8.4.12. Failed URI . . . . . . . . . . . . . . . . . . . . . 53 8.4.13. Failed URI Cause . . . . . . . . . . . . . . . . . . 53 8.4.14. Speak Restart . . . . . . . . . . . . . . . . . . . 53 8.4.15. Speak Length . . . . . . . . . . . . . . . . . . . . 53 8.4.16. Load-Lexicon . . . . . . . . . . . . . . . . . . . . 54 8.4.17. Lexicon-Search-Order . . . . . . . . . . . . . . . . 54 8.5. Synthesizer Message Body . . . . . . . . . . . . . . . . 54 8.5.1. Synthesizer Speech Data . . . . . . . . . . . . . . 54 8.5.2. Lexicon Data . . . . . . . . . . . . . . . . . . . . 57 8.6. SPEAK Method . . . . . . . . . . . . . . . . . . . . . . 58 8.7. STOP . . . . . . . . . . . . . . . . . . . . . . . . . . 60 8.8. BARGE-IN-OCCURED . . . . . . . . . . . . . . . . . . . . 61 8.9. PAUSE . . . . . . . . . . . . . . . . . . . . . . . . . 63 8.10. RESUME . . . . . . . . . . . . . . . . . . . . . . . . . 64 8.11. CONTROL . . . . . . . . . . . . . . . . . . . . . . . . 66 8.12. SPEAK-COMPLETE . . . . . . . . . . . . . . . . . . . . . 68 8.13. SPEECH-MARKER . . . . . . . . . . . . . . . . . . . . . 69 8.14. DEFINE-LEXICON . . . . . . . . . . . . . . . . . . . . . 71 9. Speech Recognizer Resource . . . . . . . . . . . . . . . . . 71 9.1. Recognizer State Machine . . . . . . . . . . . . . . . . 73 9.2. Recognizer Methods . . . . . . . . . . . . . . . . . . . 73 9.3. Recognizer Events . . . . . . . . . . . . . . . . . . . 74 9.4. Recognizer Header Fields . . . . . . . . . . . . . . . . 74 9.4.1. Confidence Threshold . . . . . . . . . . . . . . . . 76 9.4.2. Sensitivity Level . . . . . . . . . . . . . . . . . 76 9.4.3. Speed Vs Accuracy . . . . . . . . . . . . . . . . . 77 9.4.4. N Best List Length . . . . . . . . . . . . . . . . . 77 9.4.5. Input Type . . . . . . . . . . . . . . . . . . . . . 77 9.4.6. No Input Timeout . . . . . . . . . . . . . . . . . . 78 9.4.7. Recognition Timeout . . . . . . . . . . . . . . . . 78 9.4.8. Waveform URI . . . . . . . . . . . . . . . . . . . . 78 9.4.9. Media Type . . . . . . . . . . . . . . . . . . . . . 79 9.4.10. Input-Waveform-URI . . . . . . . . . . . . . . . . . 79 9.4.11. Completion Cause . . . . . . . . . . . . . . . . . . 79 Burnett & Shanmugham Expires January 10, 2011 [Page 4] Internet-Draft MRCPv2 July 2010 9.4.12. Completion Reason . . . . . . . . . . . . . . . . . 81 9.4.13. Recognizer Context Block . . . . . . . . . . . . . . 81 9.4.14. Start Input Timers . . . . . . . . . . . . . . . . . 82 9.4.15. Speech Complete Timeout . . . . . . . . . . . . . . 82 9.4.16. Speech Incomplete Timeout . . . . . . . . . . . . . 83 9.4.17. DTMF Interdigit Timeout . . . . . . . . . . . . . . 83 9.4.18. DTMF Term Timeout . . . . . . . . . . . . . . . . . 84 9.4.19. DTMF-Term-Char . . . . . . . . . . . . . . . . . . . 84 9.4.20. Failed URI . . . . . . . . . . . . . . . . . . . . . 84 9.4.21. Failed URI Cause . . . . . . . . . . . . . . . . . . 84 9.4.22. Save Waveform . . . . . . . . . . . . . . . . . . . 85 9.4.23. New Audio Channel . . . . . . . . . . . . . . . . . 85 9.4.24. Speech-Language . . . . . . . . . . . . . . . . . . 85 9.4.25. Ver-Buffer-Utterance . . . . . . . . . . . . . . . . 86 9.4.26. Recognition-Mode . . . . . . . . . . . . . . . . . . 86 9.4.27. Cancel-If-Queue . . . . . . . . . . . . . . . . . . 86 9.4.28. Hotword-Max-Duration . . . . . . . . . . . . . . . . 87 9.4.29. Hotword-Min-Duration . . . . . . . . . . . . . . . . 87 9.4.30. Interpret-Text . . . . . . . . . . . . . . . . . . . 87 9.4.31. DTMF-Buffer-Time . . . . . . . . . . . . . . . . . . 87 9.4.32. Clear-DTMF-Buffer . . . . . . . . . . . . . . . . . 88 9.4.33. Early-No-Match . . . . . . . . . . . . . . . . . . . 88 9.4.34. Num-Min-Consistent-Pronunciations . . . . . . . . . 88 9.4.35. Consistency-Threshold . . . . . . . . . . . . . . . 89 9.4.36. Clash-Threshold . . . . . . . . . . . . . . . . . . 89 9.4.37. Personal-Grammar-URI . . . . . . . . . . . . . . . . 89 9.4.38. Enroll-Utterance . . . . . . . . . . . . . . . . . . 90 9.4.39. Phrase-Id . . . . . . . . . . . . . . . . . . . . . 90 9.4.40. Phrase-NL . . . . . . . . . . . . . . . . . . . . . 90 9.4.41. Weight . . . . . . . . . . . . . . . . . . . . . . . 90 9.4.42. Save-Best-Waveform . . . . . . . . . . . . . . . . . 91 9.4.43. New-Phrase-Id . . . . . . . . . . . . . . . . . . . 91 9.4.44. Confusable-Phrases-URI . . . . . . . . . . . . . . . 91 9.4.45. Abort-Phrase-Enrollment . . . . . . . . . . . . . . 91 9.5. Recognizer Message Body . . . . . . . . . . . . . . . . 92 9.5.1. Recognizer Grammar Data . . . . . . . . . . . . . . 92 9.5.2. Recognizer Result Data . . . . . . . . . . . . . . . 96 9.5.3. Enrollment Result Data . . . . . . . . . . . . . . . 97 9.5.4. Recognizer Context Block . . . . . . . . . . . . . . 97 9.6. Recognizer Results . . . . . . . . . . . . . . . . . . . 97 9.6.1. Markup Functions . . . . . . . . . . . . . . . . . . 98 9.6.2. Overview of Recognizer Result Elements and their Relationships . . . . . . . . . . . . . . . . . . . 99 9.6.3. Elements and Attributes . . . . . . . . . . . . . . 99 9.7. Enrollment Results . . . . . . . . . . . . . . . . . . . 104 9.7.1. NUM-CLASHES Element . . . . . . . . . . . . . . . . 104 9.7.2. NUM-GOOD-REPETITIONS Element . . . . . . . . . . . . 105 9.7.3. NUM-REPETITIONS-STILL-NEEDED Element . . . . . . . . 105 Burnett & Shanmugham Expires January 10, 2011 [Page 5] Internet-Draft MRCPv2 July 2010 9.7.4. CONSISTENCY-STATUS Element . . . . . . . . . . . . . 105 9.7.5. CLASH-PHRASE-IDS Element . . . . . . . . . . . . . . 105 9.7.6. TRANSCRIPTIONS Element . . . . . . . . . . . . . . . 105 9.7.7. CONFUSABLE-PHRASES Element . . . . . . . . . . . . . 105 9.8. DEFINE-GRAMMAR . . . . . . . . . . . . . . . . . . . . . 105 9.9. RECOGNIZE . . . . . . . . . . . . . . . . . . . . . . . 109 9.10. STOP . . . . . . . . . . . . . . . . . . . . . . . . . . 115 9.11. GET-RESULT . . . . . . . . . . . . . . . . . . . . . . . 116 9.12. START-OF-INPUT . . . . . . . . . . . . . . . . . . . . . 117 9.13. START-INPUT-TIMERS . . . . . . . . . . . . . . . . . . . 118 9.14. RECOGNITION-COMPLETE . . . . . . . . . . . . . . . . . . 118 9.15. START-PHRASE-ENROLLMENT . . . . . . . . . . . . . . . . 120 9.16. ENROLLMENT-ROLLBACK . . . . . . . . . . . . . . . . . . 121 9.17. END-PHRASE-ENROLLMENT . . . . . . . . . . . . . . . . . 122 9.18. MODIFY-PHRASE . . . . . . . . . . . . . . . . . . . . . 122 9.19. DELETE-PHRASE . . . . . . . . . . . . . . . . . . . . . 123 9.20. INTERPRET . . . . . . . . . . . . . . . . . . . . . . . 123 9.21. INTERPRETATION-COMPLETE . . . . . . . . . . . . . . . . 124 9.22. DTMF Detection . . . . . . . . . . . . . . . . . . . . . 126 10. Recorder Resource . . . . . . . . . . . . . . . . . . . . . . 126 10.1. Recorder State Machine . . . . . . . . . . . . . . . . . 127 10.2. Recorder Methods . . . . . . . . . . . . . . . . . . . . 127 10.3. Recorder Events . . . . . . . . . . . . . . . . . . . . 127 10.4. Recorder Header Fields . . . . . . . . . . . . . . . . . 127 10.4.1. Sensitivity Level . . . . . . . . . . . . . . . . . 128 10.4.2. No Input Timeout . . . . . . . . . . . . . . . . . . 128 10.4.3. Completion Cause . . . . . . . . . . . . . . . . . . 128 10.4.4. Completion Reason . . . . . . . . . . . . . . . . . 129 10.4.5. Failed URI . . . . . . . . . . . . . . . . . . . . . 129 10.4.6. Failed URI Cause . . . . . . . . . . . . . . . . . . 129 10.4.7. Record URI . . . . . . . . . . . . . . . . . . . . . 130 10.4.8. Media Type . . . . . . . . . . . . . . . . . . . . . 130 10.4.9. Max Time . . . . . . . . . . . . . . . . . . . . . . 130 10.4.10. Trim-Length . . . . . . . . . . . . . . . . . . . . 131 10.4.11. Final Silence . . . . . . . . . . . . . . . . . . . 131 10.4.12. Capture On Speech . . . . . . . . . . . . . . . . . 131 10.4.13. Ver-Buffer-Utterance . . . . . . . . . . . . . . . . 131 10.4.14. Start Input Timers . . . . . . . . . . . . . . . . . 132 10.4.15. New Audio Channel . . . . . . . . . . . . . . . . . 132 10.5. Recorder Message Body . . . . . . . . . . . . . . . . . 132 10.6. RECORD . . . . . . . . . . . . . . . . . . . . . . . . . 132 10.7. STOP . . . . . . . . . . . . . . . . . . . . . . . . . . 133 10.8. RECORD-COMPLETE . . . . . . . . . . . . . . . . . . . . 134 10.9. START-INPUT-TIMERS . . . . . . . . . . . . . . . . . . . 135 10.10. START-OF-INPUT . . . . . . . . . . . . . . . . . . . . . 135 11. Speaker Verification and Identification . . . . . . . . . . . 136 11.1. Speaker Verification State Machine . . . . . . . . . . . 137 11.2. Speaker Verification Methods . . . . . . . . . . . . . . 139 Burnett & Shanmugham Expires January 10, 2011 [Page 6] Internet-Draft MRCPv2 July 2010 11.3. Verification Events . . . . . . . . . . . . . . . . . . 140 11.4. Verification Header Fields . . . . . . . . . . . . . . . 140 11.4.1. Repository-URI . . . . . . . . . . . . . . . . . . . 141 11.4.2. Voiceprint-Identifier . . . . . . . . . . . . . . . 141 11.4.3. Verification-Mode . . . . . . . . . . . . . . . . . 142 11.4.4. Adapt-Model . . . . . . . . . . . . . . . . . . . . 143 11.4.5. Abort-Model . . . . . . . . . . . . . . . . . . . . 143 11.4.6. Min-Verification-Score . . . . . . . . . . . . . . . 143 11.4.7. Num-Min-Verification-Phrases . . . . . . . . . . . . 143 11.4.8. Num-Max-Verification-Phrases . . . . . . . . . . . . 144 11.4.9. No-Input-Timeout . . . . . . . . . . . . . . . . . . 144 11.4.10. Save-Waveform . . . . . . . . . . . . . . . . . . . 144 11.4.11. Media Type . . . . . . . . . . . . . . . . . . . . . 145 11.4.12. Waveform-URI . . . . . . . . . . . . . . . . . . . . 145 11.4.13. Voiceprint-Exists . . . . . . . . . . . . . . . . . 145 11.4.14. Ver-Buffer-Utterance . . . . . . . . . . . . . . . . 146 11.4.15. Input-Waveform-Uri . . . . . . . . . . . . . . . . . 146 11.4.16. Completion-Cause . . . . . . . . . . . . . . . . . . 146 11.4.17. Completion Reason . . . . . . . . . . . . . . . . . 148 11.4.18. Speech Complete Timeout . . . . . . . . . . . . . . 148 11.4.19. New Audio Channel . . . . . . . . . . . . . . . . . 148 11.4.20. Abort-Verification . . . . . . . . . . . . . . . . . 148 11.4.21. Start Input Timers . . . . . . . . . . . . . . . . . 149 11.5. Verification Message Body . . . . . . . . . . . . . . . 149 11.5.1. Verification Result Data . . . . . . . . . . . . . . 149 11.5.2. Verification Result Elements . . . . . . . . . . . . 149 11.6. START-SESSION . . . . . . . . . . . . . . . . . . . . . 153 11.7. END-SESSION . . . . . . . . . . . . . . . . . . . . . . 154 11.8. QUERY-VOICEPRINT . . . . . . . . . . . . . . . . . . . . 155 11.9. DELETE-VOICEPRINT . . . . . . . . . . . . . . . . . . . 156 11.10. VERIFY . . . . . . . . . . . . . . . . . . . . . . . . . 157 11.11. VERIFY-FROM-BUFFER . . . . . . . . . . . . . . . . . . . 157 11.12. VERIFY-ROLLBACK . . . . . . . . . . . . . . . . . . . . 160 11.13. STOP . . . . . . . . . . . . . . . . . . . . . . . . . . 160 11.14. START-INPUT-TIMERS . . . . . . . . . . . . . . . . . . . 161 11.15. VERIFICATION-COMPLETE . . . . . . . . . . . . . . . . . 162 11.16. START-OF-INPUT . . . . . . . . . . . . . . . . . . . . . 162 11.17. CLEAR-BUFFER . . . . . . . . . . . . . . . . . . . . . . 163 11.18. GET-INTERMEDIATE-RESULT . . . . . . . . . . . . . . . . 163 12. Security Considerations . . . . . . . . . . . . . . . . . . . 164 12.1. Rendezvous and Session Establishment . . . . . . . . . . 165 12.2. Control channel protection . . . . . . . . . . . . . . . 165 12.3. Media session protection . . . . . . . . . . . . . . . . 165 12.4. Indirect Content Access . . . . . . . . . . . . . . . . 165 12.5. Protection of stored media . . . . . . . . . . . . . . . 166 12.6. DTMF and recognition buffers . . . . . . . . . . . . . . 167 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 167 13.1. New registries . . . . . . . . . . . . . . . . . . . . . 167 Burnett & Shanmugham Expires January 10, 2011 [Page 7] Internet-Draft MRCPv2 July 2010 13.1.1. MRCPv2 resource types . . . . . . . . . . . . . . . 167 13.1.2. MRCPv2 methods and events . . . . . . . . . . . . . 167 13.1.3. MRCPv2 header fields . . . . . . . . . . . . . . . . 168 13.1.4. MRCPv2 status codes . . . . . . . . . . . . . . . . 171 13.1.5. Grammar Reference List Parameters . . . . . . . . . 171 13.1.6. MRCPv2 vendor-specific parameters . . . . . . . . . 171 13.2. NLSML-related registrations . . . . . . . . . . . . . . 172 13.2.1. application/nlsml+xml Media Type registration . . . 172 13.3. NLSML XML Schema registration . . . . . . . . . . . . . 173 13.4. MRCPv2 XML Namespace registration . . . . . . . . . . . 173 13.5. text Media Type Registrations . . . . . . . . . . . . . 173 13.5.1. text/grammar-ref-list . . . . . . . . . . . . . . . 173 13.6. session URL scheme registration . . . . . . . . . . . . 174 13.7. SDP parameter registrations . . . . . . . . . . . . . . 175 13.7.1. sub-registry "proto" . . . . . . . . . . . . . . . . 175 13.7.2. sub-registry "att-field (session-level)" . . . . . . 176 13.7.3. sub-registry "att-field (media-level)" . . . . . . . 176 14. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 177 14.1. Message Flow . . . . . . . . . . . . . . . . . . . . . . 177 14.2. Recognition Result Examples . . . . . . . . . . . . . . 186 14.2.1. Simple ASR Ambiguity . . . . . . . . . . . . . . . . 186 14.2.2. Mixed Initiative . . . . . . . . . . . . . . . . . . 187 14.2.3. DTMF Input . . . . . . . . . . . . . . . . . . . . . 188 14.2.4. Interpreting Meta-Dialog and Meta-Task Utterances . 188 14.2.5. Anaphora and Deixis . . . . . . . . . . . . . . . . 189 14.2.6. Distinguishing Individual Items from Sets with One Member . . . . . . . . . . . . . . . . . . . . . 190 14.2.7. Extensibility . . . . . . . . . . . . . . . . . . . 191 15. ABNF Normative Definition . . . . . . . . . . . . . . . . . . 191 16. XML Schemas . . . . . . . . . . . . . . . . . . . . . . . . . 206 16.1. NLSML Schema Definition . . . . . . . . . . . . . . . . 206 16.2. Enrollment Results Schema Definition . . . . . . . . . . 207 16.3. Verification Results Schema Definition . . . . . . . . . 209 17. References . . . . . . . . . . . . . . . . . . . . . . . . . 212 17.1. Normative References . . . . . . . . . . . . . . . . . . 212 17.2. Informative References . . . . . . . . . . . . . . . . . 214 Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 216 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 217 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 217 Burnett & Shanmugham Expires January 10, 2011 [Page 8] Internet-Draft MRCPv2 July 2010 1. Introduction The MRCPv2 protocol is designed to allow a client device to control media processing resources on the network. Some of these media processing resources include speech recognition engines, speech synthesis engines, speaker verification and speaker identification engines. MRCPv2 enables the implementation of distributed Interactive Voice Response platforms using VoiceXML [W3C.REC-voicexml20-20040316] browsers or other client applications while maintaining separate back-end speech processing capabilities on specialized speech processing servers. MRCPv2 is based on the earlier Media Resource Control Protocol (MRCP) [RFC4463] developed jointly by Cisco Systems, Inc., Nuance Communications, and Speechworks Inc. The protocol requirements of SPEECHSC [RFC4313] include that the solution be capable of reaching a media processing server and setting up communication channels to the media resources, and sending and receiving control messages and media streams to/from the server. The Session Initiation Protocol (SIP) [RFC3261] meets these requirements. Note the above mentioned requirements document, RFC 4313, goes into detail on alternatives to SIP, such as RTSP [RFC2326], and why MRCPv2 does not use RTSP, even though the proprietary version of MRCP did run over RTSP. MRCPv2 leverages these capabilities by building upon SIP and the Session Description Protocol (SDP) [RFC4566]. MRCPv2 uses SIP to setup and tear down media and control sessions with the server. In addition, the client can use a SIP re-INVITE method (an INVITE dialog sent within an existing SIP Session) to change the characteristics of these media and control session while maintaining the SIP dialog between the client and server. SDP is used to describe the parameters of the media sessions associated with that dialog. It is mandatory to support SIP as the session establishment protocol to ensure interoperability. Other protocols can be used for session establishment by prior agreement. This document only describes the use of SIP and SDP. MRCPv2 uses SIP and SDP to create the speech client/server dialog and set up the media channels to the server. It also uses SIP and SDP to establish MRCPv2 control sessions between the client and the server for each media processing resource required for that dialog. The MRCPv2 protocol exchange between the client and the media resource is carried on that control session. MRCPv2 protocol exchanges do not change the state of the SIP dialog, the media sessions, or other parameters of the dialog initiated via SIP. It controls and affects the state of the media processing resource associated with the MRCPv2 Burnett & Shanmugham Expires January 10, 2011 [Page 9] Internet-Draft MRCPv2 July 2010 session(s). MRCPv2 defines the messages to control the different media processing resources and the state machines required to guide their operation. It also describes how these messages are carried over a transport layer protocol such as TCP or TLS (Note: SCTP is a viable transport for MRCPv2 as well, but the mapping onto SCTP is not described in this specification). 2. Document 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 RFC2119 [RFC2119]. Since many of the definitions and syntax are identical to HTTP/1.1 (RFC2616 [RFC2616]), this specification refers to the section where they are defined rather than copying it. For brevity, [HX.Y] is to be taken to refer to Section X.Y of RFC2616. All the mechanisms specified in this document are described in both prose and an augmented Backus-Naur form (ABNF [RFC5234]). The complete message format in ABNF form is provided in Section 15 and is the normative format definition. 2.1. Definitions Media Resource An entity on the speech processing server that can be controlled through the MRCPv2 protocol. MRCP Server Aggregate of one or more "Media Resource" entities on a Server, exposed through the MRCPv2 protocol ("Server" for short). MRCP Client An entity controlling one or more Media Resources through the MRCPv2 protocol ("Client" for short). DTMF Dual Tone Multi-Frequency; a method of transmitting key presses in-band, either as actual tones (Q.23 [Q.23]) or as named tone events (RFC4733 [RFC4733]). Endpointing The process of automatically detecting the beginning and end of speech in an audio stream. This is critical both for speech recognition and for automated recording as one would find in voice mail systems. Burnett & Shanmugham Expires January 10, 2011 [Page 10] Internet-Draft MRCPv2 July 2010 Hotword Mode A mode of speech recognition where a stream of utterances is evaluated for match against a small set of command words. This is generally employed to either trigger some action, or to control the subsequent grammar to be used for further recognition 2.2. State-Machine Diagrams The state-machine diagrams in this document do not show every possible method call. Rather, they reflect the state of the resource based on the methods that have moved to IN-PROGRESS or COMPLETE states (see Section 5.3). Note that since PENDING requests essentially have not affected the resource yet and are in queue to be processed, they are not reflected in the state-machine diagrams. 2.3. URI Schemes This document defines many protocol headers that contain URIs or lists of URIs for referencing media. The entire document, including the Security Considerations section (Section 12), assumes that HTTP/ HTTPS will be used as the URI addressing scheme unless otherwise stated. However, implementations MAY support other schemes (such as "file") provided they have addressed any security considerations described in this document and any others particular to the specific scheme. For example, implementations where the client and server both reside on the same physical hardware and the file system is secured by traditional user-level file access controls could be reasonable candidates for supporting the "file" scheme. 3. Architecture A system using MRCPv2 consists of a client that requires the generation and/or consumption of media streams and a media resource server that has the resources or "engines" to process these streams as input or generate these streams as output. The client uses SIP and SDP to establish an MRCPv2 control channel with the server to use its media processing resources. MRCPv2 servers are addressed using SIP URIs. The session initiation protocol (SIP) uses SDP with the offer/answer model described in RFC3264 [RFC3264] to set up the MRCPv2 control channels and describe their characteristics. A separate MRCPv2 session is needed to control each of the media processing resources associated with the SIP dialog between the client and server. Within a SIP dialog, the individual resource control channels for the different resources are added or removed through SDP offer/answer Burnett & Shanmugham Expires January 10, 2011 [Page 11] Internet-Draft MRCPv2 July 2010 carried in a SIP re-INVITE transaction. The server, through the SDP exchange, provides the client with an unambiguous channel identifier and a TCP port number. The client MAY then open a new TCP connection with the server on this port number. Multiple MRCPv2 channels can share a TCP connection between the client and the server. All MRCPv2 messages exchanged between the client and the server carry the specified channel identifier that the server MUST ensure is unambiguous among all MRCPv2 control channels that are active on that server. The client uses this channel identifier to indicate the media processing resource associated with that channel. For information on message framing, see Section 5. The session management protocol (SIP) also establishes the media sessions between the client (or other source/sink of media) and the MRCPv2 server using SDP m-lines. One or more media processing resources may share a media session under a SIP session, or each media processing resource may have its own media session. An MRCP client that merely relays results from one MRCP server to another MRCP server can be considered an MCRP Proxy. This could be useful in cases where different resources have their own MRCP servers that a service aggregator would like to present via a single MRCP server. The following diagram shows the general architecture of a system that uses MRCPv2. To simplify the diagram only a few resources are shown. Burnett & Shanmugham Expires January 10, 2011 [Page 12] Internet-Draft MRCPv2 July 2010 MRCPv2 client MRCPv2 Media Resource Server |--------------------| |------------------------------------| ||------------------|| ||----------------------------------|| || Application Layer|| ||Synthesis|Recognition|Verification|| ||------------------|| || Engine | Engine | Engine || ||Media Resource API|| || || | || | || || ||------------------|| ||Synthesis|Recognizer | Verifier || || SIP | MRCPv2 || ||Resource | Resource | Resource || ||Stack | || || Media Resource Management || || | || ||----------------------------------|| ||------------------|| || SIP | MRCPv2 || || TCP/IP Stack ||---MRCPv2---|| Stack | || || || ||----------------------------------|| ||------------------||----SIP-----|| TCP/IP Stack || |--------------------| || || | ||----------------------------------|| SIP |------------------------------------| | / |-------------------| RTP | | / | Media Source/Sink |------------/ | | |-------------------| Figure 1: Architectural Diagram 3.1. MRCPv2 Media Resource Types An MRCPv2 server may offer one or more of the following media processing resources to its clients. Basic Synthesizer A speech synthesizer resource with very limited capabilities, that can generate its media stream exclusively from concatenated audio clips. The speech data is described using a limited subset of SSML [W3C.REC-speech-synthesis-20040907] elements. A basic synthesizer MUST support the SSML tags ,