SPEECHSC D. Burnett Internet-Draft Voxeo Intended status: Standards Track S. Shanmugham Expires: March 1, 2013 Cisco Systems, Inc. August 28, 2012 Media Resource Control Protocol Version 2 (MRCPv2) draft-ietf-speechsc-mrcpv2-28 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 March 1, 2013. Copyright Notice Copyright (c) 2012 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 March 1, 2013 [Page 1] Internet-Draft MRCPv2 August 2012 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 March 1, 2013 [Page 2] Internet-Draft MRCPv2 August 2012 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 . . . . . . . . . . . . . . . . . . . . . . . . 12 3.1. MRCPv2 Media Resource Types . . . . . . . . . . . . . . 13 3.2. Server and Resource Addressing . . . . . . . . . . . . . 14 4. MRCPv2 Protocol Basics . . . . . . . . . . . . . . . . . . . 15 4.1. Connecting to the Server . . . . . . . . . . . . . . . . 15 4.2. Managing Resource Control Channels . . . . . . . . . . . 15 4.3. SIP session example . . . . . . . . . . . . . . . . . . 18 4.4. Media Streams and RTP Ports . . . . . . . . . . . . . . 23 4.5. MRCPv2 Message Transport . . . . . . . . . . . . . . . . 24 4.6. MRCPv2 Session Termination . . . . . . . . . . . . . . . 25 5. MRCPv2 Specification . . . . . . . . . . . . . . . . . . . . 25 5.1. Common Protocol Elements . . . . . . . . . . . . . . . . 25 5.2. Request . . . . . . . . . . . . . . . . . . . . . . . . 28 5.3. Response . . . . . . . . . . . . . . . . . . . . . . . . 29 5.4. Status Codes . . . . . . . . . . . . . . . . . . . . . . 30 5.5. Events . . . . . . . . . . . . . . . . . . . . . . . . . 31 6. MRCPv2 Generic Methods, Headers, and Result Structure . . . . 32 6.1. Generic Methods . . . . . . . . . . . . . . . . . . . . 33 6.1.1. SET-PARAMS . . . . . . . . . . . . . . . . . . . . . 33 6.1.2. GET-PARAMS . . . . . . . . . . . . . . . . . . . . . 34 6.2. Generic Message Headers . . . . . . . . . . . . . . . . 35 6.2.1. Channel-Identifier . . . . . . . . . . . . . . . . . 36 6.2.2. Accept . . . . . . . . . . . . . . . . . . . . . . . 36 6.2.3. Active-Request-Id-List . . . . . . . . . . . . . . . 37 6.2.4. Proxy-Sync-Id . . . . . . . . . . . . . . . . . . . 37 6.2.5. Accept-Charset . . . . . . . . . . . . . . . . . . . 38 6.2.6. Content-Type . . . . . . . . . . . . . . . . . . . . 38 6.2.7. Content-ID . . . . . . . . . . . . . . . . . . . . . 38 6.2.8. Content-Base . . . . . . . . . . . . . . . . . . . . 39 6.2.9. Content-Encoding . . . . . . . . . . . . . . . . . . 39 6.2.10. Content-Location . . . . . . . . . . . . . . . . . . 39 6.2.11. Content-Length . . . . . . . . . . . . . . . . . . . 40 6.2.12. Fetch Timeout . . . . . . . . . . . . . . . . . . . 40 6.2.13. Cache-Control . . . . . . . . . . . . . . . . . . . 41 6.2.14. Logging-Tag . . . . . . . . . . . . . . . . . . . . 42 6.2.15. Set-Cookie . . . . . . . . . . . . . . . . . . . . . 42 6.2.16. Vendor Specific Parameters . . . . . . . . . . . . . 45 6.3. Generic Result Structure . . . . . . . . . . . . . . . . 46 6.3.1. Natural Language Semantics Markup Language . . . . . 47 7. Resource Discovery . . . . . . . . . . . . . . . . . . . . . 47 8. Speech Synthesizer Resource . . . . . . . . . . . . . . . . . 49 Burnett & Shanmugham Expires March 1, 2013 [Page 3] Internet-Draft MRCPv2 August 2012 8.1. Synthesizer State Machine . . . . . . . . . . . . . . . 49 8.2. Synthesizer Methods . . . . . . . . . . . . . . . . . . 50 8.3. Synthesizer Events . . . . . . . . . . . . . . . . . . . 50 8.4. Synthesizer Header Fields . . . . . . . . . . . . . . . 51 8.4.1. Jump-Size . . . . . . . . . . . . . . . . . . . . . 51 8.4.2. Kill-On-Barge-In . . . . . . . . . . . . . . . . . . 52 8.4.3. Speaker Profile . . . . . . . . . . . . . . . . . . 53 8.4.4. Completion Cause . . . . . . . . . . . . . . . . . . 53 8.4.5. Completion Reason . . . . . . . . . . . . . . . . . 54 8.4.6. Voice-Parameter . . . . . . . . . . . . . . . . . . 54 8.4.7. Prosody-Parameters . . . . . . . . . . . . . . . . . 55 8.4.8. Speech Marker . . . . . . . . . . . . . . . . . . . 55 8.4.9. Speech Language . . . . . . . . . . . . . . . . . . 56 8.4.10. Fetch Hint . . . . . . . . . . . . . . . . . . . . . 56 8.4.11. Audio Fetch Hint . . . . . . . . . . . . . . . . . . 57 8.4.12. Failed URI . . . . . . . . . . . . . . . . . . . . . 57 8.4.13. Failed URI Cause . . . . . . . . . . . . . . . . . . 57 8.4.14. Speak Restart . . . . . . . . . . . . . . . . . . . 57 8.4.15. Speak Length . . . . . . . . . . . . . . . . . . . . 58 8.4.16. Load-Lexicon . . . . . . . . . . . . . . . . . . . . 58 8.4.17. Lexicon-Search-Order . . . . . . . . . . . . . . . . 58 8.5. Synthesizer Message Body . . . . . . . . . . . . . . . . 59 8.5.1. Synthesizer Speech Data . . . . . . . . . . . . . . 59 8.5.2. Lexicon Data . . . . . . . . . . . . . . . . . . . . 61 8.6. SPEAK Method . . . . . . . . . . . . . . . . . . . . . . 62 8.7. STOP . . . . . . . . . . . . . . . . . . . . . . . . . . 64 8.8. BARGE-IN-OCCURRED . . . . . . . . . . . . . . . . . . . 65 8.9. PAUSE . . . . . . . . . . . . . . . . . . . . . . . . . 67 8.10. RESUME . . . . . . . . . . . . . . . . . . . . . . . . . 68 8.11. CONTROL . . . . . . . . . . . . . . . . . . . . . . . . 70 8.12. SPEAK-COMPLETE . . . . . . . . . . . . . . . . . . . . . 72 8.13. SPEECH-MARKER . . . . . . . . . . . . . . . . . . . . . 73 8.14. DEFINE-LEXICON . . . . . . . . . . . . . . . . . . . . . 75 9. Speech Recognizer Resource . . . . . . . . . . . . . . . . . 75 9.1. Recognizer State Machine . . . . . . . . . . . . . . . . 77 9.2. Recognizer Methods . . . . . . . . . . . . . . . . . . . 77 9.3. Recognizer Events . . . . . . . . . . . . . . . . . . . 78 9.4. Recognizer Header Fields . . . . . . . . . . . . . . . . 78 9.4.1. Confidence Threshold . . . . . . . . . . . . . . . . 80 9.4.2. Sensitivity Level . . . . . . . . . . . . . . . . . 80 9.4.3. Speed Vs Accuracy . . . . . . . . . . . . . . . . . 81 9.4.4. N Best List Length . . . . . . . . . . . . . . . . . 81 9.4.5. Input Type . . . . . . . . . . . . . . . . . . . . . 81 9.4.6. No Input Timeout . . . . . . . . . . . . . . . . . . 82 9.4.7. Recognition Timeout . . . . . . . . . . . . . . . . 82 9.4.8. Waveform URI . . . . . . . . . . . . . . . . . . . . 82 9.4.9. Media Type . . . . . . . . . . . . . . . . . . . . . 83 9.4.10. Input-Waveform-URI . . . . . . . . . . . . . . . . . 83 Burnett & Shanmugham Expires March 1, 2013 [Page 4] Internet-Draft MRCPv2 August 2012 9.4.11. Completion Cause . . . . . . . . . . . . . . . . . . 83 9.4.12. Completion Reason . . . . . . . . . . . . . . . . . 85 9.4.13. Recognizer Context Block . . . . . . . . . . . . . . 85 9.4.14. Start Input Timers . . . . . . . . . . . . . . . . . 86 9.4.15. Speech Complete Timeout . . . . . . . . . . . . . . 86 9.4.16. Speech Incomplete Timeout . . . . . . . . . . . . . 87 9.4.17. DTMF Interdigit Timeout . . . . . . . . . . . . . . 87 9.4.18. DTMF Term Timeout . . . . . . . . . . . . . . . . . 88 9.4.19. DTMF-Term-Char . . . . . . . . . . . . . . . . . . . 88 9.4.20. Failed URI . . . . . . . . . . . . . . . . . . . . . 88 9.4.21. Failed URI Cause . . . . . . . . . . . . . . . . . . 88 9.4.22. Save Waveform . . . . . . . . . . . . . . . . . . . 89 9.4.23. New Audio Channel . . . . . . . . . . . . . . . . . 89 9.4.24. Speech-Language . . . . . . . . . . . . . . . . . . 89 9.4.25. Ver-Buffer-Utterance . . . . . . . . . . . . . . . . 90 9.4.26. Recognition-Mode . . . . . . . . . . . . . . . . . . 90 9.4.27. Cancel-If-Queue . . . . . . . . . . . . . . . . . . 90 9.4.28. Hotword-Max-Duration . . . . . . . . . . . . . . . . 91 9.4.29. Hotword-Min-Duration . . . . . . . . . . . . . . . . 91 9.4.30. Interpret-Text . . . . . . . . . . . . . . . . . . . 91 9.4.31. DTMF-Buffer-Time . . . . . . . . . . . . . . . . . . 92 9.4.32. Clear-DTMF-Buffer . . . . . . . . . . . . . . . . . 92 9.4.33. Early-No-Match . . . . . . . . . . . . . . . . . . . 92 9.4.34. Num-Min-Consistent-Pronunciations . . . . . . . . . 92 9.4.35. Consistency-Threshold . . . . . . . . . . . . . . . 93 9.4.36. Clash-Threshold . . . . . . . . . . . . . . . . . . 93 9.4.37. Personal-Grammar-URI . . . . . . . . . . . . . . . . 93 9.4.38. Enroll-Utterance . . . . . . . . . . . . . . . . . . 94 9.4.39. Phrase-Id . . . . . . . . . . . . . . . . . . . . . 94 9.4.40. Phrase-NL . . . . . . . . . . . . . . . . . . . . . 94 9.4.41. Weight . . . . . . . . . . . . . . . . . . . . . . . 94 9.4.42. Save-Best-Waveform . . . . . . . . . . . . . . . . . 95 9.4.43. New-Phrase-Id . . . . . . . . . . . . . . . . . . . 95 9.4.44. Confusable-Phrases-URI . . . . . . . . . . . . . . . 95 9.4.45. Abort-Phrase-Enrollment . . . . . . . . . . . . . . 95 9.5. Recognizer Message Body . . . . . . . . . . . . . . . . 96 9.5.1. Recognizer Grammar Data . . . . . . . . . . . . . . 96 9.5.2. Recognizer Result Data . . . . . . . . . . . . . . . 100 9.5.3. Enrollment Result Data . . . . . . . . . . . . . . . 101 9.5.4. Recognizer Context Block . . . . . . . . . . . . . . 101 9.6. Recognizer Results . . . . . . . . . . . . . . . . . . . 101 9.6.1. Markup Functions . . . . . . . . . . . . . . . . . . 102 9.6.2. Overview of Recognizer Result Elements and their Relationships . . . . . . . . . . . . . . . . . . . 103 9.6.3. Elements and Attributes . . . . . . . . . . . . . . 103 9.7. Enrollment Results . . . . . . . . . . . . . . . . . . . 108 9.7.1. NUM-CLASHES Element . . . . . . . . . . . . . . . . 108 9.7.2. NUM-GOOD-REPETITIONS Element . . . . . . . . . . . . 109 Burnett & Shanmugham Expires March 1, 2013 [Page 5] Internet-Draft MRCPv2 August 2012 9.7.3. NUM-REPETITIONS-STILL-NEEDED Element . . . . . . . . 109 9.7.4. CONSISTENCY-STATUS Element . . . . . . . . . . . . . 109 9.7.5. CLASH-PHRASE-IDS Element . . . . . . . . . . . . . . 109 9.7.6. TRANSCRIPTIONS Element . . . . . . . . . . . . . . . 109 9.7.7. CONFUSABLE-PHRASES Element . . . . . . . . . . . . . 109 9.8. DEFINE-GRAMMAR . . . . . . . . . . . . . . . . . . . . . 109 9.9. RECOGNIZE . . . . . . . . . . . . . . . . . . . . . . . 113 9.10. STOP . . . . . . . . . . . . . . . . . . . . . . . . . . 119 9.11. GET-RESULT . . . . . . . . . . . . . . . . . . . . . . . 120 9.12. START-OF-INPUT . . . . . . . . . . . . . . . . . . . . . 121 9.13. START-INPUT-TIMERS . . . . . . . . . . . . . . . . . . . 122 9.14. RECOGNITION-COMPLETE . . . . . . . . . . . . . . . . . . 122 9.15. START-PHRASE-ENROLLMENT . . . . . . . . . . . . . . . . 124 9.16. ENROLLMENT-ROLLBACK . . . . . . . . . . . . . . . . . . 125 9.17. END-PHRASE-ENROLLMENT . . . . . . . . . . . . . . . . . 126 9.18. MODIFY-PHRASE . . . . . . . . . . . . . . . . . . . . . 126 9.19. DELETE-PHRASE . . . . . . . . . . . . . . . . . . . . . 127 9.20. INTERPRET . . . . . . . . . . . . . . . . . . . . . . . 127 9.21. INTERPRETATION-COMPLETE . . . . . . . . . . . . . . . . 128 9.22. DTMF Detection . . . . . . . . . . . . . . . . . . . . . 130 10. Recorder Resource . . . . . . . . . . . . . . . . . . . . . . 130 10.1. Recorder State Machine . . . . . . . . . . . . . . . . . 131 10.2. Recorder Methods . . . . . . . . . . . . . . . . . . . . 131 10.3. Recorder Events . . . . . . . . . . . . . . . . . . . . 131 10.4. Recorder Header Fields . . . . . . . . . . . . . . . . . 131 10.4.1. Sensitivity Level . . . . . . . . . . . . . . . . . 132 10.4.2. No Input Timeout . . . . . . . . . . . . . . . . . . 132 10.4.3. Completion Cause . . . . . . . . . . . . . . . . . . 132 10.4.4. Completion Reason . . . . . . . . . . . . . . . . . 133 10.4.5. Failed URI . . . . . . . . . . . . . . . . . . . . . 133 10.4.6. Failed URI Cause . . . . . . . . . . . . . . . . . . 134 10.4.7. Record URI . . . . . . . . . . . . . . . . . . . . . 134 10.4.8. Media Type . . . . . . . . . . . . . . . . . . . . . 134 10.4.9. Max Time . . . . . . . . . . . . . . . . . . . . . . 135 10.4.10. Trim-Length . . . . . . . . . . . . . . . . . . . . 135 10.4.11. Final Silence . . . . . . . . . . . . . . . . . . . 135 10.4.12. Capture On Speech . . . . . . . . . . . . . . . . . 135 10.4.13. Ver-Buffer-Utterance . . . . . . . . . . . . . . . . 136 10.4.14. Start Input Timers . . . . . . . . . . . . . . . . . 136 10.4.15. New Audio Channel . . . . . . . . . . . . . . . . . 136 10.5. Recorder Message Body . . . . . . . . . . . . . . . . . 136 10.6. RECORD . . . . . . . . . . . . . . . . . . . . . . . . . 137 10.7. STOP . . . . . . . . . . . . . . . . . . . . . . . . . . 138 10.8. RECORD-COMPLETE . . . . . . . . . . . . . . . . . . . . 139 10.9. START-INPUT-TIMERS . . . . . . . . . . . . . . . . . . . 140 10.10. START-OF-INPUT . . . . . . . . . . . . . . . . . . . . . 140 11. Speaker Verification and Identification . . . . . . . . . . . 141 11.1. Speaker Verification State Machine . . . . . . . . . . . 142 Burnett & Shanmugham Expires March 1, 2013 [Page 6] Internet-Draft MRCPv2 August 2012 11.2. Speaker Verification Methods . . . . . . . . . . . . . . 144 11.3. Verification Events . . . . . . . . . . . . . . . . . . 145 11.4. Verification Header Fields . . . . . . . . . . . . . . . 145 11.4.1. Repository-URI . . . . . . . . . . . . . . . . . . . 146 11.4.2. Voiceprint-Identifier . . . . . . . . . . . . . . . 146 11.4.3. Verification-Mode . . . . . . . . . . . . . . . . . 147 11.4.4. Adapt-Model . . . . . . . . . . . . . . . . . . . . 148 11.4.5. Abort-Model . . . . . . . . . . . . . . . . . . . . 148 11.4.6. Min-Verification-Score . . . . . . . . . . . . . . . 148 11.4.7. Num-Min-Verification-Phrases . . . . . . . . . . . . 148 11.4.8. Num-Max-Verification-Phrases . . . . . . . . . . . . 149 11.4.9. No-Input-Timeout . . . . . . . . . . . . . . . . . . 149 11.4.10. Save-Waveform . . . . . . . . . . . . . . . . . . . 149 11.4.11. Media Type . . . . . . . . . . . . . . . . . . . . . 150 11.4.12. Waveform-URI . . . . . . . . . . . . . . . . . . . . 150 11.4.13. Voiceprint-Exists . . . . . . . . . . . . . . . . . 150 11.4.14. Ver-Buffer-Utterance . . . . . . . . . . . . . . . . 151 11.4.15. Input-Waveform-Uri . . . . . . . . . . . . . . . . . 151 11.4.16. Completion-Cause . . . . . . . . . . . . . . . . . . 151 11.4.17. Completion Reason . . . . . . . . . . . . . . . . . 153 11.4.18. Speech Complete Timeout . . . . . . . . . . . . . . 153 11.4.19. New Audio Channel . . . . . . . . . . . . . . . . . 153 11.4.20. Abort-Verification . . . . . . . . . . . . . . . . . 153 11.4.21. Start Input Timers . . . . . . . . . . . . . . . . . 153 11.5. Verification Message Body . . . . . . . . . . . . . . . 154 11.5.1. Verification Result Data . . . . . . . . . . . . . . 154 11.5.2. Verification Result Elements . . . . . . . . . . . . 154 11.6. START-SESSION . . . . . . . . . . . . . . . . . . . . . 158 11.7. END-SESSION . . . . . . . . . . . . . . . . . . . . . . 159 11.8. QUERY-VOICEPRINT . . . . . . . . . . . . . . . . . . . . 160 11.9. DELETE-VOICEPRINT . . . . . . . . . . . . . . . . . . . 161 11.10. VERIFY . . . . . . . . . . . . . . . . . . . . . . . . . 162 11.11. VERIFY-FROM-BUFFER . . . . . . . . . . . . . . . . . . . 162 11.12. VERIFY-ROLLBACK . . . . . . . . . . . . . . . . . . . . 165 11.13. STOP . . . . . . . . . . . . . . . . . . . . . . . . . . 165 11.14. START-INPUT-TIMERS . . . . . . . . . . . . . . . . . . . 166 11.15. VERIFICATION-COMPLETE . . . . . . . . . . . . . . . . . 167 11.16. START-OF-INPUT . . . . . . . . . . . . . . . . . . . . . 167 11.17. CLEAR-BUFFER . . . . . . . . . . . . . . . . . . . . . . 168 11.18. GET-INTERMEDIATE-RESULT . . . . . . . . . . . . . . . . 168 12. Security Considerations . . . . . . . . . . . . . . . . . . . 169 12.1. Rendezvous and Session Establishment . . . . . . . . . . 170 12.2. Control channel protection . . . . . . . . . . . . . . . 170 12.3. Media session protection . . . . . . . . . . . . . . . . 170 12.4. Indirect Content Access . . . . . . . . . . . . . . . . 171 12.5. Protection of stored media . . . . . . . . . . . . . . . 172 12.6. DTMF and recognition buffers . . . . . . . . . . . . . . 172 12.7. Client-set server parameters . . . . . . . . . . . . . . 172 Burnett & Shanmugham Expires March 1, 2013 [Page 7] Internet-Draft MRCPv2 August 2012 12.8. DELETE-VOICEPRINT and authorization . . . . . . . . . . 172 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 173 13.1. New registries . . . . . . . . . . . . . . . . . . . . . 173 13.1.1. MRCPv2 resource types . . . . . . . . . . . . . . . 173 13.1.2. MRCPv2 methods and events . . . . . . . . . . . . . 173 13.1.3. MRCPv2 header fields . . . . . . . . . . . . . . . . 175 13.1.4. MRCPv2 status codes . . . . . . . . . . . . . . . . 177 13.1.5. Grammar Reference List Parameters . . . . . . . . . 177 13.1.6. MRCPv2 vendor-specific parameters . . . . . . . . . 178 13.2. NLSML-related registrations . . . . . . . . . . . . . . 178 13.2.1. application/nlsml+xml Media Type registration . . . 178 13.3. NLSML XML Schema registration . . . . . . . . . . . . . 179 13.4. MRCPv2 XML Namespace registration . . . . . . . . . . . 179 13.5. text Media Type Registrations . . . . . . . . . . . . . 179 13.5.1. text/grammar-ref-list . . . . . . . . . . . . . . . 180 13.6. session URI scheme registration . . . . . . . . . . . . 180 13.7. SDP parameter registrations . . . . . . . . . . . . . . 181 13.7.1. sub-registry "proto" . . . . . . . . . . . . . . . . 182 13.7.2. sub-registry "att-field (media-level)" . . . . . . . 182 14. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 183 14.1. Message Flow . . . . . . . . . . . . . . . . . . . . . . 183 14.2. Recognition Result Examples . . . . . . . . . . . . . . 193 14.2.1. Simple ASR Ambiguity . . . . . . . . . . . . . . . . 193 14.2.2. Mixed Initiative . . . . . . . . . . . . . . . . . . 194 14.2.3. DTMF Input . . . . . . . . . . . . . . . . . . . . . 195 14.2.4. Interpreting Meta-Dialog and Meta-Task Utterances . 195 14.2.5. Anaphora and Deixis . . . . . . . . . . . . . . . . 196 14.2.6. Distinguishing Individual Items from Sets with One Member . . . . . . . . . . . . . . . . . . . . . 197 14.2.7. Extensibility . . . . . . . . . . . . . . . . . . . 198 15. ABNF Normative Definition . . . . . . . . . . . . . . . . . . 198 16. XML Schemas . . . . . . . . . . . . . . . . . . . . . . . . . 213 16.1. NLSML Schema Definition . . . . . . . . . . . . . . . . 213 16.2. Enrollment Results Schema Definition . . . . . . . . . . 214 16.3. Verification Results Schema Definition . . . . . . . . . 216 17. References . . . . . . . . . . . . . . . . . . . . . . . . . 219 17.1. Normative References . . . . . . . . . . . . . . . . . . 219 17.2. Informative References . . . . . . . . . . . . . . . . . 222 Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 224 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 225 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 225 Burnett & Shanmugham Expires March 1, 2013 [Page 8] Internet-Draft MRCPv2 August 2012 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. Although some of the method names are similar, the way in which these methods are communicated is different. There are also more resources and more methods for each resource. The first version of MRCP was essentially taken only as input to the development of this protocol. There is no expectation that an MRCPv2 client will work with an MRCPv1 server or vice versa. There is no migration plan or gateway definition between the two protocols. 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. The proprietary version of MRCP ran over the Real Time Streaming Protocol (RTSP) [RFC2326]. At the time work on MRCPv2 was begun, the consensus was that this use of RTSP would break the RTSP protocol or cause backward-compatibility problems, something forbidden by Section 3.2 of the above mentioned requirements document. This is the reason why MRCPv2 does not 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 Burnett & Shanmugham Expires March 1, 2013 [Page 9] Internet-Draft MRCPv2 August 2012 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 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 the Transmission Control Protocol (TCP) [RFC0793] or the Transport Layer Security (TLS) Protocol [RFC5246] (Note: the Stream Control Transmission Protocol (SCTP) [RFC4960] 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 RFC 2119 [RFC2119]. Since many of the definitions and syntax are identical to those for the HTTP/1.1 (Hypertext Transfer Protocol (HTTP/1.1) [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 RFC 2616. 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. Note that productions may be duplicated within the main body of the document for reading convenience. If a production in the body of the text conflicts with one in the normative definition, the latter rules. 2.1. Definitions Media Resource An entity on the speech processing server that can be controlled through the MRCPv2 protocol. Burnett & Shanmugham Expires March 1, 2013 [Page 10] Internet-Draft MRCPv2 August 2012 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 (RFC 4733 [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. 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 (Uniform Resource Identifier (URI) [RFC3986]) or lists of URIs for referencing media. The entire document, including the Security Considerations section (Section 12), assumes that HTTP or HTTP over TLS (HTTPS) [RFC2818] 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. Burnett & Shanmugham Expires March 1, 2013 [Page 11] Internet-Draft MRCPv2 August 2012 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 carried in a SIP re-INVITE transaction. The server, through the SDP exchange, provides the client with a difficult to guess, unambiguous channel identifier and a TCP port number (see Section 4.2). 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 initiation 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. 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 March 1, 2013 [Page 12] Internet-Draft MRCPv2 August 2012 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 the Speech Synthesis Markup Language (SSML) [W3C.REC-speech-synthesis-20040907] elements. A basic synthesizer MUST support the SSML tags ,