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 Internet Engineering Task Force                    Saravanan Shanmugham
 Internet-Draft                                       Cisco Systems Inc.
 draft-ietf-speechsc-mrcpv2-01                          January 16, 2004
 Expires: July 16, 2004
 
 
 
 
 
 
              Media Resource Control Protocol Version 2(MRCPv2)
 
 
 Status of this Memo
 
    This document is an Internet-Draft and is in full conformance with
    all provisions of Section 10 of RFC2026.
 
    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.
 
 Copyright Notice
 
    Copyright (C) The Internet Society (1999).  All Rights Reserved.
 
 
 Abstract
 
    This document describes a proposal for a Media Resource Control
    Protocol Version 2(MRCPv2) and aims to meet the requirements
    specified in the SPEECHSC working group requirements document. It is
    based on the Media Resource Control Protocol (MRCP), also called
    MRCPv1 developed jointly by Cisco Systems, Inc., Nuance
    Communications, and Speechworks Inc.
 
    The MRCPv2 protocol will control media service resources like speech
    synthesizers, recognizers, signal generators, signal detectors, fax
    servers etc. over a network. This protocol depends on a session
    management protocol such as the Session Initiation Protocol (SIP) to
 
 S. Shanmugham, et. al.                                          Page 1
 
                            MRCPv2 Protocol               January 2004
 
    establish a separate MRCPv2 control session between the client and
    the media server. It also depends on SIP to establish the media pipe
    and associated parameters between the media source or sink and the
    media server. Once this is done, the MRCPv2 protocol exchange can
    happen over the control session established above allowing the
    client to command and control the media processing resources that
    may exist on the media server.
 
 
 Table of Contents
 
      Status of this Memo..............................................1
      Copyright Notice.................................................1
      Abstract.........................................................1
      Table of Contents................................................2
      1.   Introduction:...............................................4
      2.   Architecture:...............................................5
      2.1.  MRCPv2 Media Resources:...................................6
      2.2.  Server and Resource Addressing............................7
      3.   MRCPv2 Protocol Basics......................................7
      3.1.  Connecting to the Media Server............................7
      3.2.  Managing Resource Control Channels........................8
      3.3.  Media Streams and RTP Ports..............................14
      3.4.  MRCPv2 Message Transport.................................15
      4.   Notational Conventions.....................................16
      5.   MRCPv2 Specification.......................................16
      5.1.  Request..................................................17
      5.2.  Response.................................................18
      5.2.1. Status Codes.............................................18
      5.3.  Event....................................................19
      5.4.  Message Headers..........................................20
      5.4.1. Channel-Identifier.......................................21
      5.4.2. Active-Request-Id-List...................................21
      5.4.3. Proxy-Sync-Id............................................22
      5.4.4. Accept-Charset...........................................22
      5.4.5. Content-Type.............................................22
      5.4.6. Content-Id...............................................22
      5.4.7. Content-Base.............................................22
      5.4.8. Content-Encoding.........................................23
      5.4.9. Content-Location.........................................23
      5.4.10. Content-Length.........................................24
      5.4.11. Cache-Control..........................................24
      5.4.12. Logging-Tag............................................25
      6.   Resource Discovery.........................................26
      7.   Speech Synthesizer Resource................................27
      7.1.  Synthesizer State Machine................................27
      7.2.  Synthesizer Methods......................................28
      7.3.  Synthesizer Events.......................................28
      7.4.  Synthesizer Header Fields................................28
      7.4.1. Jump-Target..............................................29
      7.4.2. Kill-On-Barge-In.........................................30
 
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                            MRCPv2 Protocol               January 2004
 
      7.4.3. Speaker Profile..........................................30
      7.4.4. Completion Cause.........................................30
      7.4.5. Voice-Parameters.........................................31
      7.4.6. Prosody-Parameters.......................................31
      7.4.7. Vendor Specific Parameters...............................32
      7.4.8. Speech Marker............................................32
      7.4.9. Speech Language..........................................32
      7.4.10. Fetch Hint.............................................33
      7.4.11. Audio Fetch Hint.......................................33
      7.4.12. Fetch Timeout..........................................33
      7.4.13. Failed URI.............................................33
      7.4.14. Failed URI Cause.......................................34
      7.4.15. Speak Restart..........................................34
      7.4.16. Speak Length...........................................34
      7.5.  Synthesizer Message Body.................................35
      7.5.1. Synthesizer Speech Data..................................35
      7.6.  SET-PARAMS...............................................36
      7.7.  GET-PARAMS...............................................37
      7.8.  SPEAK....................................................38
      7.9.  STOP.....................................................39
      7.10. BARGE-IN-OCCURRED........................................40
      7.11. PAUSE....................................................41
      7.12. RESUME...................................................42
      7.13. CONTROL..................................................43
      7.14. SPEAK-COMPLETE...........................................45
      7.15. SPEECH-MARKER............................................46
      8.   Speech Recognizer Resource.................................47
      8.1.  Recognizer State Machine.................................47
      8.2.  Recognizer Methods.......................................48
      8.3.  Recognizer Events........................................48
      8.4.  Recognizer Header Fields.................................48
      8.4.1. Confidence Threshold.....................................49
      8.4.2. Sensitivity Level........................................50
      8.4.3. Speed Vs Accuracy........................................50
      8.4.4. N Best List Length.......................................50
      8.4.5. No Input Timeout.........................................50
      8.4.6. Recognition Timeout......................................51
      8.4.7. Waveform URL.............................................51
      8.4.8. Completion Cause.........................................51
      8.4.9. Recognizer Context Block.................................52
      8.4.10. Recognition Start Timers...............................52
      8.4.11. Vendor Specific Parameters.............................53
      8.4.12. Speech Complete Timeout................................53
      8.4.13. Speech Incomplete Timeout..............................54
      8.4.14. DTMF Interdigit Timeout................................54
      8.4.15. DTMF Term Timeout......................................54
      8.4.16. DTMF-Term-Char.........................................55
      8.4.17. Fetch Timeout..........................................55
      8.4.18. Failed URI.............................................55
      8.4.19. Failed URI Cause.......................................55
      8.4.20. Save Waveform..........................................55
 
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                            MRCPv2 Protocol               January 2004
 
      8.4.21. New Audio Channel......................................56
      8.4.22. Speech Language........................................56
      8.5.  Recognizer Message Body..................................56
      8.5.1. Recognizer Grammar Data..................................56
      8.5.2. Recognizer Result Data...................................59
      8.5.3. Recognizer Context Block.................................60
      8.6.  SET-PARAMS...............................................60
      8.7.  GET-PARAMS...............................................61
      8.8.  DEFINE-GRAMMAR...........................................61
      8.9.  RECOGNIZE................................................65
      8.10. STOP.....................................................67
      8.11. GET-RESULT...............................................68
      8.12. START-OF-SPEECH..........................................69
      8.13. RECOGNITION-START-TIMERS.................................69
      8.14. RECOGNITON-COMPLETE......................................69
      8.15. DTMF Detection...........................................71
      9.   Examples:..................................................71
      10.  Reference Documents........................................78
      11.  Appendix...................................................79
      ABNF Message Definitions........................................79
      Full Copyright Statement........................................87
      Authors' Addresses..............................................88
 
 
 1.   Introduction:
 
    The MRCPv2 protocol is designed to provide a mechanism for a client
    device requiring audio/video stream processing to control media
    processing resources on the network. Some of these media processing
    resources could be speech recognition, speech synthesis engines,
    speaker verification or speaker identification engines. This allows
    a vendor to implement distributed Interactive Voice Response
    platforms such as VoiceXML [7] browsers.
 
       This protocol is designed to leverage and build upon a session
    management protocols such as Session Initiation Protocol (SIP) and
    Session Description Protocol (SDP). The SIP protocol described in
    [2] defines session control messages used during the setup and tear
    down stages of a SIP session. In addition, the SIP re-INVITE can be
    used during a SIP session to change the characteristics of the
    session.  This is generally to create or delete media/control
    channels or to change the properties of existing media/control
    channels related to the SIP session. In this SIP exchange, SDP is
    used to describe the parameters of the media pipe associated with
    that session.
 
       The MRCPv2 protocol depends on SIP and SDP to create the session,
    and setup the media channels to the media server. It also depends on
    SIP and SDP to establish a MRCPv2 control channel between the client
    and the server for every media processing resource that thee client
 
 
 S Shanmugham                  IETF-Draft                        Page 4
 
                            MRCPv2 Protocol               January 2004
 
    requires for that session. The MRCPv2 protocol exchange between the
    client and the media resource can then happen on that control
    channel. The MRCPv2 protocol exchange happening on this control
    channel does not change the state of the SIP session, the media or
    other parameters of the session SIP initiated. It merely controls
    and affects the state of the media processing resource associated
    with that MRCPv2 channel.
 
       The MRCPv2 protocol 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 such as TCP or SCTP.
 
    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[9].
 
 
 2.   Architecture:
 
    The system consists of a client that requires the generation of
    media streams or requires the processing of media streams and a
    media resource server that has the resources or engines to process
    or generate these streams. The client establishes a session using
    SIP and SDP with the server to use its media processing resources. A
    SIP URI refers to the MRCPv2 media server.
 
    The session management protocol (SIP) will use SDP with the
    offer/answer model described RFC 3264 to describe and setup the
    MRCPv2 control channels. Separate MRCPv2 control channels are need
    for controlling the different media processing resources associated
    with that session. Within a SIP session, the individual resource
    control channels for the different resources are added or removed
    through the SDP offer/answer model and the SIP re-INVITE dialog.
 
    The server, through the SDP exchange, provides the client with a
    unique channel identifier and a TCP port number. The client MAY then
    open a new TCP connection with the server using 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 will also carry the specified channel
    identifier that MUST be unique among all MRCPv2 control channels
    that are active on that server. The client can use this channel to
    control the media processing resource associated with that channel.
 
    The session management protocol (SIP) will also establish media
    pipes between the client (or source/sink of media) and the media
    server using SDP m-lines. A media pipe maybe shared by one or more
    media processing resources under that SIP session or each media
    processing resource may have its own media pipe.
 
 
 S Shanmugham                  IETF-Draft                        Page 5
 
                            MRCPv2 Protocol               January 2004
 
         MRCPv2 client                  MRCPv2 Media Resource Server
      |--------------------|             |-----------------------------|
      ||------------------||             ||---------------------------||
      || Application Layer||             || TTS  | ASR  | SV   | SI   ||
      ||------------------||             ||Engine|Engine|Engine|Engine||
      ||Media Resource API||             ||---------------------------||
      ||------------------||             || Media Resource Management ||
      || SIP  |  MRCPv2   ||             ||---------------------------||
      ||Stack |           ||             ||   SIP  |    MRCPv2        ||
      ||      |           ||             ||  Stack |                  ||
      ||------------------||             ||---------------------------||
      ||   TCP/IP Stack   ||----MRCPv2---||       TCP/IP Stack        ||
      ||                  ||             ||                           ||
      ||------------------||-----SIP-----||---------------------------||
      |--------------------|             |-----------------------------|
               |                             /
              SIP                           /
               |                           /
      |-------------------|              RTP
      |                   |              /
      | Media Source/Sink |-------------/
      |                   |
      |-------------------|
 
 
 
 2.1. MRCPv2 Media Resources:
 
    The MRCPv2 media server may offer one or more of the following media
    processing resources to its clients.
 
    Speech Recognition
    The media server may offer speech recognition engines that the
    client can allocate, control and have it recognize the spoken input
    contained in the audio stream.
 
    Speech Synthesis
    The media server may offer speech synthesis engines that the client
    can allocate, control and have it generate synthesized voice into
    the audio stream.
 
    Speaker Identification
    The media server may offer speaker recognition engines that the
    client can allocate, control and have it recognize the speaker from
    voice in the audio stream.
 
    Speaker Verification
    The media server may offer speaker Verification engines that the
    client can allocate, control and have it verify and authenticate the
    speaker based on his voice.
 
 
 S Shanmugham                  IETF-Draft                        Page 6
 
                            MRCPv2 Protocol               January 2004
 
 2.2. Server and Resource Addressing
 
    The MRCPv2 server as a whole is a generic SIP server and the MRCPv2
    media processing resources it offers are addressed by specific SIP
    URL registered by the server.
 
    Example:
 
      sip:mrcpv2@mediaserver.com
 
 
 3.   MRCPv2 Protocol Basics
 
    MRCPv2 requires the use of a transport layer protocol such as TCP or
    SCTP to guarantee reliable sequencing and delivery of MRCPv2 control
    messages between the client and the server. One or more TCP or SCTP
    connections between the client and the server can be shared between
    different MRCPv2 channels to the server. The individual messages
    carry the channel identifier to differentiate messages on different
    channels. The message format for MRCPv2 is text based with
    mechanisms to carry embedded binary data. This allows data like
    recognition grammars, recognition results, synthesizer speech markup
    etc. to be carried in the MRCPv2 message between the client and the
    server resource. The protocol does not address session and media
    establishment and management and relies of SIP and SDP to do this.
 
 3.1. Connecting to the Media Server
 
    The MRCPv2 protocol depends on a session establishment and
    management protocol such as SIP in conjunction with SDP. The client
    finds and reaches a MRCPv2 server across the SIP network using the
    INVITE and other SIP dialog exchanges. The SDP offer/answer exchange
    model over SIP is used to establish resource control channels for
    each resource. The SDP offer/answer exchange is also used to
    establish media pipes between the source or sink of audio and the
    media server.
 
    Example 1:
    Opening a session to the media server. This does not immediately
    allocate any resource control channels yet.
 
    C->S:
           INVITE sip:mresources@mediaserver.com SIP/2.0
           Via: SIP/2.0/TCP client.atlanta.example.com:5060;
                branch=z9hG4bK74bf9
           Max-Forwards: 70
           To: MediaServer <sip:mresources@mediaserver.com>
           From: sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314161 INVITE
           Contact: <sip:sarvi@cisco.com>
 
 S Shanmugham                  IETF-Draft                        Page 7
 
                            MRCPv2 Protocol               January 2004
 
           Content-Type: application/sdp
           Content-Length: ...
 
           v=0
           o=sarvi 2890844526 2890842808 IN IP4 126.16.64.4
           s=-
           c=IN IP4 224.2.17.12
 
    S->C:
           SIP/2.0 200 OK
           Via: SIP/2.0/TCP client.atlanta.example.com:5060;
                branch=z9hG4bK74bf9
           To: MediaServer <sip:mresources@mediaserver.com>
           From: sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314161 INVITE
           Contact: <sip:sarvi@cisco.com>
           Content-Type: application/sdp
           Content-Length: ...
 
           v=0
           o=sarvi 2890844526 2890842808 IN IP4 126.16.64.4
           s=-
           c=IN IP4 224.2.17.12
 
    C->S:
           ACK sip:mresources@mediaserver.com SIP/2.0
           Via: SIP/2.0/TCP client.atlanta.example.com:5060;
                branch=z9hG4bK74bf9
           Max-Forwards: 70
           To: MediaServer <sip:mresources@mediaserver.com>;tag=a6c85cf
           From: Sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314162 ACK
           Content-Length: 0
 
 3.2. Managing Resource Control Channels
 
    The client needs a separate MRCPv2 resource control channel to
    control each media processing resource under the SIP session. A
    unique channel identifier string identifies these resource control
    channels. The channel identifier string consists of a hexadecimal
    number specifying the channel ID followed by a string token
    specifying the type of resource separated by an "@". The server
    generates the hexadecimal channel ID and MUST make sure it does not
    clash with any other MRCP channel allocated to that server. MRCPv2
    defines the following type of media processing resources. Additional
    resource types, their associated methods/events and state machines
    can be added by future specification proposing to extend the
    capabilities of MRCPv2.
 
 
 S Shanmugham                  IETF-Draft                        Page 8
 
                            MRCPv2 Protocol               January 2004
 
           Resource Type       Resource Description
                speechrecog    Speech Recognition
                dtmfrecog      DTMF Recognition
                speechsynth    Speech Synthesis
                simplesynth    Poor Speech Synthesizer
                audioplayer    Simple Audio Player
                speakidentify  Speaker Identification
                speakverify    Speaker Verification
 
    Additional resource types, their associated methods/events and state
    machines can be added by future specification proposing to extend
    the capabilities of MRCPv2.
 
    The SIP INVITE or re-INVITE dialog exchange and the SDP offer/answer
    exchange it carries, will contain m-lines describing the resource
    control channel it wants to allocate. There MUST be one SDP m-line
    for each MRCPv2 resource that needs to be controlled. This m-line
    will have a media type field of "control" and a transport type field
    of "TCP" or "SCTP". The port number field of the m-line MUST contain
    9 in the SDP offer from the client and MUST contain the TCP listen
    port on the server in the SDP answer. The client MAY then setup a
    TCP or TLS connection to that server port or share an already
    established connection to that port. The format field of the m-line
    MUST contain "application/mrcpv2". The client must specify the
    resource type identifier in the resource attribute associated with
    the control m-line of the SDP offer. The server MUST respond with
    the full Channel-Identifier (which includes the resource type
    identifier and an unique hexadecimal identifier), in the "channel"
    attribute associated with the control m-line of the SDP answer.
 
    When the client wants to add a media processing resource to the
    session, it MUST initiate a re-INVITE dialog. The SDP offer/answer
    exchange contained in this SIP dialog will contain an additional
    control m-line for the new resource that needs to be allocated. The
    media server, on seeing the new m-line, will allocate the resource
    and respond with a corresponding control m-line in the SDP answer
    response.
 
    When the client wants to de-allocate the resource from this session,
    it MUST initiate a SIP re-INVITE dialog with the media server and
    MUST offer the control m-line with a port 0. The server MUST then
    answer the control m-line with a response of port 0.
 
 
    Example 2:
    This exchange continues from example 1 and adds a resource control
    channel for a synthesizer. Since a synthesizer would be generating
    an audio stream, this interaction also creates a receive-only audio
    stream for the server to send audio to.
 
    C->S:
 
 S Shanmugham                  IETF-Draft                        Page 9
 
                            MRCPv2 Protocol               January 2004
 
           INVITE sip:mresources@mediaserver.com SIP/2.0
           Via: SIP/2.0/TCP client.atlanta.example.com:5060;
                branch=z9hG4bK74bf9
           Max-Forwards: 70
           To: MediaServer <sip:mresources@mediaserver.com>
           From: sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314161 INVITE
           Contact: <sip:sarvi@cisco.com>
           Content-Type: application/sdp
           Content-Length: ...
 
           v=0
           o=sarvi 2890844526 2890842808 IN IP4 126.16.64.4
           s=-
           c=IN IP4 224.2.17.12
           m=control 9 TCP application/mrcpv2
           a=resource:speechsynth
           a=cmid:1
           m=audio 49170 RTP/AVP 0 96
           a=rtpmap:0 pcmu/8000
           a=recvonly
           a=mid:1
 
    S->C:
           SIP/2.0 200 OK
           Via: SIP/2.0/TCP client.atlanta.example.com:5060;
                branch=z9hG4bK74bf9
           To: MediaServer <sip:mresources@mediaserver.com>
           From: sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314161 INVITE
           Contact: <sip:sarvi@cisco.com>
           Content-Type: application/sdp
           Content-Length: ...
 
           v=0
           o=sarvi 2890844526 2890842808 IN IP4 126.16.64.4
           s=-
           c=IN IP4 224.2.17.12
           m=control 32416 TCP application/mrcpv2
           a=channel:32AECB234338@speechsynth
           a=cmid:1
           m=audio 48260 RTP/AVP 00 96
           a=rtpmap:0 pcmu/8000
           a=sendonly
           a=mid:1
 
    C->S:
           ACK sip:mresources@mediaserver.com SIP/2.0
           Via: SIP/2.0/TCP client.atlanta.example.com:5060;
 
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                            MRCPv2 Protocol               January 2004
 
                branch=z9hG4bK74bf9
           Max-Forwards: 70
           To: MediaServer <sip:mresources@mediaserver.com>;tag=a6c85cf
           From: Sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314162 ACK
           Content-Length: 0
 
    Example 3:
    This exchange continues from example 2 allocates an additional
    resource control channel for a recognizer. Since a recognizer would
    need to receive an audio stream for recognition, this interaction
    also updates the audio stream to sendrecv making it a 2-way audio
    stream.
 
    C->S:
           INVITE sip:mresources@mediaserver.com SIP/2.0
           Via: SIP/2.0/TCP client.atlanta.example.com:5060;
                branch=z9hG4bK74bf9
           Max-Forwards: 70
           To: MediaServer <sip:mresources@mediaserver.com>
           From: sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314163 INVITE
           Contact: <sip:sarvi@cisco.com>
           Content-Type: application/sdp
           Content-Length: ...
 
           v=0
           o=sarvi 2890844526 2890842809 IN IP4 126.16.64.4
           s=-
           c=IN IP4 224.2.17.12
           m=control 9 TCP application/mrcpv2
           a=resource:speechrecog
           a=cmid:1
           m=control 9 TCP application/mrcpv2
           a=resource:speechsynth
           a=cmid:1
           m=audio 49170 RTP/AVP 0 96
           a=rtpmap:0 pcmu/8000
           a=rtpmap:96 telephone-event/8000
           a=fmtp:96 0-15
           a=sendrecv
           a=mid:1
 
    S->C:
           SIP/2.0 200 OK
           Via: SIP/2.0/TCP client.atlanta.example.com:5060;
                branch=z9hG4bK74bf9
           To: MediaServer <sip:mresources@mediaserver.com>
           From: sarvi <sip:sarvi@cisco.com>;tag=1928301774
 
 S Shanmugham                  IETF-Draft                       Page 11
 
                            MRCPv2 Protocol               January 2004
 
           Call-ID: a84b4c76e66710
           CSeq: 314163 INVITE
           Contact: <sip:sarvi@cisco.com>
           Content-Type: application/sdp
           Content-Length: 131
 
           v=0
           o=sarvi 2890844526 2890842809 IN IP4 126.16.64.4
           s=-
           c=IN IP4 224.2.17.12
           m=control 32416 TCP application/mrcpv2
           a=channel:32AECB234338@speechrecog
           a=cmid:1
           m=control 32416 TCP application/mrcpv2
           a=channel:32AECB234339@speechsynth
           a=cmid:1
           m=audio 48260 RTP/AVP 0 96
           a=rtpmap:0 pcmu/8000
           a=rtpmap:96 telephone-event/8000
           a=fmtp:96 0-15
           a=sendrecv
           a=mid:1
 
    C->S:
           ACK sip:mresources@mediaserver.com SIP/2.0
           Via: SIP/2.0/TCP client.atlanta.example.com:5060;
                branch=z9hG4bK74bf9
           Max-Forwards: 70
           To: MediaServer <sip:mresources@mediaserver.com>;tag=a6c85cf
           From: Sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314164 ACK
           Content-Length: 0
 
 
    Example 4:
    This exchange continues from example 3 and de-allocates recognizer
    channel. Since a recognizer would not need to receive an audio
    stream any more, this interaction also updates the audio stream to
    recvonly.
 
    C->S:
           INVITE sip:mresources@mediaserver.com SIP/2.0
           Via: SIP/2.0/TCP client.atlanta.example.com:5060;
                branch=z9hG4bK74bf9
           Max-Forwards: 70
           To: MediaServer <sip:mresources@mediaserver.com>
           From: sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314163 INVITE
           Contact: <sip:sarvi@cisco.com>
 
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                            MRCPv2 Protocol               January 2004
 
           Content-Type: application/sdp
           Content-Length: ...
 
           v=0
           o=sarvi 2890844526 2890842809 IN IP4 126.16.64.4
           s=-
           c=IN IP4 224.2.17.12
           m=control 0 TCP application/mrcpv2
           a=resource:speechrecog
           a=cmid:1
           m=control 9 TCP application/mrcpv2
           a=resource:speechsynth
           a=cmid:1
           m=audio 49170 RTP/AVP 0 96
           a=rtpmap:0 pcmu/8000
           a=recvonly
           a=mid:1
 
    S->C:
           SIP/2.0 200 OK
           Via: SIP/2.0/TCP client.atlanta.example.com:5060;
                branch=z9hG4bK74bf9
           To: MediaServer <sip:mresources@mediaserver.com>
           From: sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314163 INVITE
           Contact: <sip:sarvi@cisco.com>
           Content-Type: application/sdp
           Content-Length: 131
 
           v=0
           o=sarvi 2890844526 2890842809 IN IP4 126.16.64.4
           s=-
           c=IN IP4 224.2.17.12
           m=control 0 TCP application/mrcpv2
           a=channel:32AECB234338@speechrecog
           a=cmid:1
           m=control 32416 TCP application/mrcpv2
           a=channel:32AECB234339@speechsynth
           a=cmid:1
           m=audio 48260 RTP/AVP 0 96
           a=rtpmap:0 pcmu/8000
           a=sendonly
           a=mid:1
 
    C->S:
           ACK sip:mresources@mediaserver.com SIP/2.0
           Via: SIP/2.0/TCP client.atlanta.example.com:5060;
                branch=z9hG4bK74bf9
           Max-Forwards: 70
           To: MediaServer <sip:mresources@mediaserver.com>;tag=a6c85cf
 
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                            MRCPv2 Protocol               January 2004
 
           From: Sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314164 ACK
           Content-Length: 0
 
 3.3. Media Streams and RTP Ports
 
    The client or the server would need to add audio (or other media)
    pipes between the client and the server and associate them with the
    resource that would process or generate the media. One or more
    resources could be associated with a single media channel or each
    resource could be assigned a separate media channel. For example, a
    synthesizer and a recognizer could be associated to the same media
    pipe(m=audio line), if it is opened in "sendrecv" mode.
    Alternatively, the recognizer could have its own "sendonly" audio
    pipe and the synthesizer could have its own "recvonly" audio pipe.
 
    The association between control channels and their corresponding
    media channels is established through the mid attribute defined in
    RFC 3388[20]. If there are more than 1 audio m-line, then each audio
    m-line MUST have a "mid" attribute. Each control m-line MUST have a
    "cmid" attribute that matches the "mid" attribute of the audio m-
    line it is associated with.
 
      cmid-attribute      =    "a=cmid:" identification-tag
 
      identification-tag = token
 
    A single audio m-line can be associated with multiple resources or
    each resource can have its own audio m-line. For example, if the
    client wants to allocate a recognizer and a synthesizer and
    associate them to a single 2-way audio pipe, the SDP offer should
    contain two control m-lines and a single audio m-line with an
    attribute of "sendrecv". Each of the control m-lines should have a
    "cmid" attribute whose value matches the "mid" of the audio m-line.
    If the client wants to allocate a recognizer and a synthesizer each
    with its own separate audio pipe, the SDP offer would carry two
    control m-lines (one for the recognizer and another for the
    synthesizer) and two audio m-lines (one with the attribute
    "sendonly" and another with attribute "recvonly"). The "cmid"
    attribute of the recognizer control m-line would match the "mid"
    value of the "sendonly" audio m-line and the "cmid" attribute of the
    synthesizer control m-line would match the "mid" attribute of the
    "recvonly" m-line.
 
    When a server receives media(say audio) on a media pipe that is
    associated with more than one media processing resource, it is the
    responsibility of the server to receive and fork it to the resources
    that need it. If the multiple resources in a session are generating
    audio (or other media), that needs to be sent on a single associated
    media pipe, it is the responsibility of the server to mix the
 
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                            MRCPv2 Protocol               January 2004
 
    streams before sending on the media pipe. The media stream in either
    direction may contain more than one Synchronized Source (SSRC)
    identifier due to multiple sources contributing to the media on the
    pipe and the client server SHOULD be able to deal with it.
 
    If a media server does not have the capability to mix or fork media,
    in the above cases, then the server SHOULD disallow the client from
    associating multiple such resources to a single audio pipe, by
    rejecting the SDP offer.
 
 3.4. MRCPv2 Message Transport
 
    The MRCPv2 resource messages defined in this document are
    transported over a TCP or SCTP pipe between the client and the
    server. The setting up of this TCP pipe and the resource control
    channel is discussed in Section 3.2. Multiple resource control
    channels between a client and a server that belong to different SIP
    sessions can share one or more TCP or SCTP pipes between them. The
    individual MRCPv2 messages carry the MRCPv2 channel identifier in
    their Channel-Identifier header field MUST be used to differentiate
    MRCPv2 messages from different resource channels. All MRCPv2 based
    media servers MUST support TCP for transport and MAY support SCTP.
 
    Example 1:
 
    C->S:  MRCP/2.0 483 SPEAK 543257
           Channel-Identifier: 32AECB23433802@speechsynth
           Voice-gender: neutral
           Voice-category: teenager
           Prosody-volume: medium
           Content-Type: application/synthesis+ssml
           Content-Length: 104
 
           <?xml version="1.0"?>
           <speak>
            <paragraph>
              <sentence>You have 4 new messages.</sentence>
              <sentence>The first is from <say-as
              type="name">Stephanie Williams</say-as>
              and arrived at <break/>
              <say-as type="time">3:45pm</say-as>.</sentence>
 
              <sentence>The subject is <prosody
              rate="-20%">ski trip</prosody></sentence>
            </paragraph>
           </speak>
 
    S->C:  MRCP/2.0 81 543257 200 IN-PROGRESS
           Channel-Identifier: 32AECB23433802@speechsynth
 
    S->C:  MRCP/2.0 89 SPEAK-COMPLETE 543257 COMPLETE
 
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                            MRCPv2 Protocol               January 2004
 
           Channel-Identifier: 32AECB23433802@speechsynth
 
    Most examples from here on show only the MRCPv2 messages and do not
    show the SIP messages and headers that may have been used to
    establish the MRCPv2 control channel.
 
 4.   Notational Conventions
 
    Since many of the definitions and syntax are identical to HTTP/1.1,
    this specification only points 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 the current HTTP/1.1 specification (RFC 2616 [1]).
 
    All the mechanisms specified in this document are described in both
    prose and an augmented Backus-Naur form (ABNF). It is described in
    detail in RFC 2234 [3].
 
    The complete message format in ABNF form is provided in Appendix
    section 12.1 and is the normative format definition.
 
 5.   MRCPv2 Specification
 
    The MRCPv2 PDU is textual using an ISO 10646 character set in the
    UTF-8 encoding (RFC 2044) to allow many different languages to be
    represented. However, to assist in compact representations, MRCPv2
    also allows other character sets such as ISO 8859-1 to be used when
    desired. The MRCPv2 protocol headers and field names use only the
    US-ASCII subset of UTF-8. Internationalization only applies to
    certain fields like grammar, results, speech markup etc, and not to
    MRCPv2 as a whole.
 
    Lines are terminated by CRLF, but receivers SHOULD be prepared to
    also interpret CR and LF by themselves as line terminators. Also,
    some parameters in the PDU may contain binary data or a record
    spanning multiple lines. Such fields have a length value associated
    with the parameter, which indicates the number of octets immediately
    following the parameter.
 
    All MRCPv2 messages, responses and events MUST carry the Channel-
    Identifier header field in it for the server or client to
    differentiate messages from different control channels that may
    share the same TCP connection.
 
    The MRCPv2 message set consists of requests from the client to the
    server, responses from the server to the client and asynchronous
    events from the server to the client. All these messages consist of
    a start-line, one or more header fields (also known as "headers"),
    an empty line (i.e. a line with nothing preceding the CRLF)
    indicating the end of the header fields, and an optional message
    body.
      generic-message  =    start-line
 
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                            MRCPv2 Protocol               January 2004
 
                            message-header
                            CRLF
                            [ message-body ]
 
      start-line       =    request-line | response-line | event-line
 
      message-header   =   1*(generic-header | resource-header)
 
      resource-header  =    recognizer-header
                       |    synthesizer-header
 
    The message-body contains resource-specific and message-specific
    data that needs to be carried between the client and server as a
    MIME entity. The information contained here and the actual MIME-
    types used to carry the data are specified later when addressing the
    specific messages.
 
    If a message contains data in the message body, the header fields
    will contain content-headers indicating the MIME-type and encoding
    of the data in the message body.
 
 5.1. Request
 
    A MRCPv2 request consists of a Request line followed by zero or more
    parameters as part of the message headers and an optional message
    body containing data specific to the request message.
 
    The Request message from a client to the server includes within the
    first line, the method to be applied, a method tag for that request
    and the version of protocol in use.
 
      request-line   =    mrcp-version SP message-length SP method-name
                          SP request-id CRLF
 
    The mrcp-version field is the MRCPv2 protocol version that is being
    used by the client.
 
      mrcp-version   =    "MRCP" "/" 1*DIGIT "." 1*DIGIT
 
    The message-length field specifies the length of the message and                                nd                  MUST be the 2   token from the beginning of the message. This is to
    make the framing and parsing of the message simpler to do.
 
      Message-length =    1*DIGIT
 
    The request-id field is a unique identifier created by the client
    and sent to the server. The server resource MUST use this identifier
    in its response to this request. If the request does not complete
    with the response future asynchronous events associated with this
    request MUST carry the request-id.
 
 
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                            MRCPv2 Protocol               January 2004
 
      request-id    =    1*DIGIT
 
    The method-name field identifies the specific request that the
    client is making to the server. Each resource supports a certain
    list of requests or methods that can be issued to it, and will be
    addressed in later sections.
 
      method-name    =    synthesizer-method
                     |    recognizer-method
 
 5.2. Response
 
    After receiving and interpreting the request message, the server
    resource responds with an MRCPv2 response message. It consists of a
    status line optionally followed by a message body.
 
      response-line  =    mrcp-version SP message-length SP request-id
                          SP status-code SP request-state CRLF
 
    The mrcp-version field used here is similar to the one used in the
    Request Line and indicates the version of MRCPv2 protocol running on
    the server.
 
    The request-id used in the response MUST match the one sent in the
    corresponding request message.
 
    The status-code field is a 3-digit code representing the success or
    failure or other status of the request.
 
    The request-state field indicates if the job initiated by the
    Request is PENDING, IN-PROGRESS or COMPLETE. The COMPLETE status
    means that the Request was processed to completion and that there
    are will be no more events from that resource to the client with
    that request-id. The PENDING status means that the job has been
    placed on a queue and will be processed in first-in-first-out order.
    The IN-PROGRESS status means that the request is being processed and
    is not yet complete. A PENDING or IN-PROGRESS status indicates that
    further Event messages will be delivered with that request-id.
 
      request-state    =  "COMPLETE"
                       |  "IN-PROGRESS"
                       |  "PENDING"
 Status Codes
 
    The status codes are classified under the Success(2XX) codes and the
    Failure(4XX) codes.
 
 Success 2xx
 
       200       Success
       201       Success with some optional parameters ignored.
 
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                            MRCPv2 Protocol               January 2004
 
 
 Failure 4xx
 
       401       Method not allowed
       402       Method not valid in this state
       403       Unsupported Parameter
       404       Illegal Value for Parameter
       405       Not found (e.g. Resource URI not initialized
                 or doesn't exist)
       406       Mandatory Parameter Missing
       407       Method or Operation Failed(e.g. Grammar compilation
                 failed in the recognizer. Detailed cause codes MAY BE
                 available through a resource specific header field.)
       408       Unrecognized or unsupported message entity
       409       Unsupported Parameter Value
       421-499   Resource specific Failure codes
 
 
 5.3. Event
 
    The server resource may need to communicate a change in state or the
    occurrence of a certain event to the client. These messages are used
    when a request does not complete immediately and the response
    returns a status of PENDING or IN-PROGRESS. The intermediate results
    and events of the request are indicated to the client through the
    event message from the server. Events have the request-id of the
    request that is in progress and generating these events and status
    value. The status value is COMPLETE if the request is done and this
    was the last event, else it is IN-PROGRESS.
 
      event-line       =  mrcp-version SP message-length SP event-name
                          SP request-id SP request-state CRLF
 
    The mrcp-version used here is identical to the one used in the
    Request/Response Line and indicates the version of MRCPv2 protocol
    running on the server.
 
    The request-id used in the event MUST match the one sent in the
    request that caused this event.
 
    The request-state indicates if the Request/Command causing this
    event is complete or still in progress, and is the same as the one
    mentioned in section 5.3. The final event will contain a COMPLETE
    status indicating the completion of the request.
 
    The event-name identifies the nature of the event generated by the
    media resource. The set of valid event names are dependent on the
    resource generating it, and will be addressed in later sections.
 
      event-name       =  synthesizer-event
                       |  recognizer-event
 
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                            MRCPv2 Protocol               January 2004
 
 
 5.4. Message Headers
 
    MRCPv2 header fields, which include general-header (section 5.5) and
    resource-specific-header (section 7.4 and section 8.4), follow the
    same generic format as that given in Section 3.1 of RFC 822 [8].
    Each header field consists of a name followed by a colon (":") and
    the field value. Field names are case-insensitive. The field value
    MAY be preceded by any amount of LWS, though a single SP is
    preferred. Header fields can be extended over multiple lines by
    preceding each extra line with at least one SP or HT.
 
      message-header = field-name ":" [ field-value ]
      field-name     = token
      field-value    = *( field-content | LWS )
      field-content  = <the OCTETs making up the field-value
                        and consisting of either *TEXT or combinations
                        of token, separators, and quoted-string>
 
    The field-content does not include any leading or trailing LWS:
    linear white space occurring before the first non-whitespace
    character of the field-value or after the last non-whitespace
    character of the field-value. Such leading or trailing LWS MAY be
    removed without changing the semantics of the field value. Any LWS
    that occurs between field-content MAY be replaced with a single SP
    before interpreting the field value or forwarding the message
    downstream.
 
    The order in which header fields with differing field names are
    received is not significant. However, it is "good practice" to send
    general-header fields first, followed by request-header or response-
    header fields, and ending with the entity-header fields.
 
    Multiple message-header fields with the same field-name MAY be
    present in a message if and only if the entire field-value for that
    header field is defined as a comma-separated list [i.e., #(values)].
 
    It MUST be possible to combine the multiple header fields into one
    "field-name: field-value" pair, without changing the semantics of
    the message, by appending each subsequent field-value to the first,
    each separated by a comma. The order in which header fields with the
    same field-name are received is therefore significant to the
    interpretation of the combined field value, and thus a proxy MUST
    NOT change the order of these field values when a message is
    forwarded.
 
    Generic Headers
 
      generic-header      =    channel-identifier
                          |    active-request-id-list
                          |    proxy-sync-id
 
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                            MRCPv2 Protocol               January 2004
 
                          |    content-id
                          |    content-type
                          |    content-length
                          |    content-base
                          |    content-location
                          |    content-encoding
                          |    cache-control
                          |    logging-tag
 
    All headers in MRCPv2 will be case insensitive consistent with HTTP
    and SIP protocol header definitions.
 
 Channel-Identifier
 
    All MRCPv2 methods, responses and events MUST contain the Channel-
    Identifier header field. The value of this field is a hexadecimal
    string and is allocated by the media server when the control channel
    was added to the session through a SDP offer/answer exchange. The
    last 2 digits of the Channel-Identifier field specify one of the
    media processing resource types listed in Section 3.2.
 
      channel-identifier  = "Channel-Identifier" ":" channel-id CRLF
 
      Channel-id          = 1*HEXDIG "@" 1*ALPHA
 
 Active-Request-Id-List
 
    In a request, this field indicates the list of request-ids that it
    should apply to. This is useful when there are multiple Requests
    that are PENDING or IN-PROGRESS and you want this request to apply
    to one or more of these specifically.
 
    In a response, this field returns the list of request-ids that the
    operation modified or were in progress or just completed. There
    could be one or more requests that returned a request-state of
    PENDING or IN-PROGRESS. When a method affecting one or more PENDING
    or IN-PROGRESS requests is sent from the client to the server, the
    response MUST contain the list of request-ids that were affected in
    this header field.
 
    The active-request-id-list is only used in requests and responses,
    not in events.
 
    For example, if a STOP request with no active-request-id-list is
    sent to a synthesizer resource(a wildcard STOP) which has one or
    more SPEAK requests in the PENDING or IN-PROGRESS state, all SPEAK
    requests MUST be cancelled, including the one IN-PROGRESS and the
    response to the STOP request would contain the request-id of all the
    SPEAK requests that were terminated in the active-request-id-list.
    In this case, no SPEAK-COMPLETE or RECOGNITION-COMPLETE events will
    be sent for these terminated requests.
 
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                            MRCPv2 Protocol               January 2004
 
 
      active-request-id-list  =  "Active-Request-Id-List" ":"
                                  request-id *("," request-id) CRLF
 
 Proxy-Sync-Id
 
    When any server resource generates a barge-in-able event, it will
    generate a unique Tag and send it as a header field in an event to
    the client. The client then acts as a proxy to the server resource
    and sends a BARGE-IN-OCCURRED method to the synthesizer server
    resource with the Proxy-Sync-Id it received from the server
    resource. When the recognizer and synthesizer resources are part of
    the same session, they may choose to work together to achieve
    quicker interaction and response. Here the proxy-sync-id helps the
    resource receiving the event, proxied by the client, to decide if
    this event has been processed through a direct interaction of the
    resources.
 
      proxy-sync-id    =  "Proxy-Sync-Id" ":" 1*ALPHA CRLF
 
 Accept-Charset
 
    See [H14.2]. This specifies the acceptable character set for
    entities returned in the response or events associated with this
    request. This is useful in specifying the character set to use in
    the NLSML results of a RECOGNITON-COMPLETE event.
 
 Content-Type
 
    See [H14.17]. Note that the content types suitable for MRCPv2 are
    restricted to speech markup, grammar, recognition results etc. and
    are specified later in this document. The multi-part content type
    "multi-part/mixed" is supported to communicate multiple of the above
    mentioned contents, in which case the body parts cannot contain any
    MRCPv2 specific headers.
 
 Content-Id
 
    This field contains an ID or name for the content, by which it can
    be referred to.  The definition of this field is available in RFC
    2111 and is needed in multi-part messages. In MRCPv2 whenever the
    content needs to be stored, by either the client or the server, it
    is stored associated with this ID. Such content can be referenced
    during the session in URI form using the session: URI scheme
    described in a later section.
 
 Content-Base
 
    The content-base entity-header field may be used to specify the base
    URI for resolving relative URLs within the entity.
 
 
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                            MRCPv2 Protocol               January 2004
 
      content-base      = "Content-Base" ":" absoluteURI CRLF
 
    Note, however, that the base URI of the contents within the entity-
    body may be redefined within that entity-body. An example of this
    would be a multi-part MIME entity, which in turn can have multiple
    entities within it.
 
 Content-Encoding
 
    The content-encoding entity-header field is used as a modifier to
    the media-type. When present, its value indicates what additional
    content coding have been applied to the entity-body, and thus what
    decoding mechanisms must be applied in order to obtain the media-
    type referenced by the content-type header field. Content-encoding
    is primarily used to allow a document to be compressed without
    losing the identity of its underlying media type.
 
      content-encoding  = "Content-Encoding" ":"
                          1#content-coding CRLF
 
    Content coding is defined in [H3.5]. An example of its use is
 
      Content-Encoding: gzip
 
    If multiple encoding have been applied to an entity, the content
    coding MUST be listed in the order in which they were applied.
 
 Content-Location
 
    The content-location entity-header field MAY BE used to supply the
    resource location for the entity enclosed in the message when that
    entity is accessible from a location separate from the requested
    resource's URI.
 
      content-location =  "Content-Location" ":"
                          ( absoluteURI | relativeURI ) CRLF
 
    The content-location value is a statement of the location of the
    resource corresponding to this particular entity at the time of the
    request. The media server MAY use this header field to optimize
    certain operations. When providing this header field the entity
    being sent should not have been modified, from what was retrieved
    from the content-location URI.
 
    For example, if the client provided a grammar markup inline, and it
    had previously retrieved it from a certain URI, that URI can be
    provided as part of the entity, using the content-location header
    field. This allows a resource like the recognizer to look into its
    cache to see if this grammar was previously retrieved, compiled and
    cached. In which case, it might optimize by using the previously
    compiled grammar object.
 
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                            MRCPv2 Protocol               January 2004
 
 
    If the content-location is a relative URI, the relative URI is
    interpreted relative to the content-base URI.
 
 
 Content-Length
 
    This field contains the length of the content of the message body
    (i.e. after the double CRLF following the last header field). Unlike
    HTTP, it MUST be included in all messages that carry content beyond
    the header portion of the message. If it is missing, a default value
    of zero is assumed. It is interpreted according to [H14.13].
 
 Cache-Control
 
    If the media server plans on implementing caching it MUST adhere to
    the cache correctness rules of HTTP 1.1 (RFC2616), when accessing
    and caching HTTP URI. In particular, the expires and cache-control
    headers of the cached URI or document must be honored and will
    always take precedence over the Cache-Control defaults set by this
    header field. The cache-control directives are used to define the
    default caching algorithms on the media server for the session or
    request. The scope of the directive is based on the method it is
    sent on. If the directives are sent on a SET-PARAMS method, it
    SHOULD apply for all requests for documents the media server may
    make in that session. If the directives are sent on any other
    messages they MUST only apply to document requests the media server
    needs to make for that method. An empty cache-control header on the
    GET-PARAMS method is a request for the media server to return the
    current cache-control directives setting on the server.
 
      cache-control       = "Cache-Control" ":" 1#cache-directive CRLF
 
      cache-directive     = "max-age" "=" delta-seconds
                          | "max-stale" "=" delta-seconds
                          | "min-fresh" "=" delta-seconds
 
      delta-seconds       = 1*DIGIT
 
    Here delta-seconds is a time value to be specified as an integer
    number of seconds, represented in decimal, after the time that the
    message response or data was received by the media server.
 
    These directives allow the media server to override the basic
    expiration mechanism.
 
    max-age
 
    Indicates that the client is ok with the media server using a
    response whose age is no greater than the specified time in seconds.
 
 
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                            MRCPv2 Protocol               January 2004
 
    Unless a max-stale directive is also included, the client is not
    willing to accept the media server using a stale response.
 
    min-fresh
 
    Indicates that the client is willing to accept the media server
    using a response whose freshness lifetime is no less than its
    current age plus the specified time in seconds. That is, the client
    wants the media server to use a response that will still be fresh
    for at least the specified number of seconds.
 
    max-stale
 
    Indicates that the client is willing to accept the media server
    using a response that has exceeded its expiration time. If max-stale
    is assigned a value, then the client is willing to accept the media
    server using a response that has exceeded its expiration time by no
    more than the specified number of seconds. If no value is assigned
    to max-stale, then the client is willing to accept the media server
    using a stale response of any age.
 
 
    The media server cache MAY BE requested to use stale response/data
    without validation, but only if this does not conflict with any
    "MUST"-level requirements concerning cache validation (e.g., a
    "must-revalidate" cache-control directive) in the HTTP 1.1
    specification pertaining the URI.
 
    If both the MRCPv2 cache-control directive and the cached entry on
    the media server include "max-age" directives, then the lesser of
    the two values is used for determining the freshness of the cached
    entry for that request.
 
 Logging-Tag
 
    This header field MAY BE sent as part of a SET-PARAMS/GET-PARAMS
    method to set the logging tag for logs generated by the media
    server. Once set, the value persists until a new value is set or the
    session is ended.  The MRCPv2 server SHOULD provide a mechanism to
    subset its output logs so that system administrators can examine or
    extract only the log file portion during which the logging tag was
    set to a certain value.
 
    MRCPv2 clients using this feature SHOULD take care to ensure that no
    two clients specify the same logging tag.  In the event that two
    clients specify the same logging tag, the effect on the MRCPv2
    server's output logs in undefined.
 
      logging-tag    =    "Logging-Tag" ":" 1*ALPHA CRLF
 
 
 
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                            MRCPv2 Protocol               January 2004
 
 6.   Resource Discovery
 
    The capability of media server resources can be found using the SIP
    OPTIONS method requesting the capability of the media server. The
    media server SHOULD respond to such a request with an SDP
    description of its capabilities according to RFC 3264. The MRCPv2
    capabilities are described by a single m-line containing the media
    type Ÿcontrol÷, transport type ŸTCP÷ or "SCTP" and a format of
    "application/mrcpv2". There should be one "resource" attribute for
    each resource that the media server supports with the resource type
    identifier as its value.
 
    The SDP description SHOULD also contain m-lines describing the audio
    capabilities, and the coders it supports.
 
 
    Example 4:
    The client uses the SIP OPTIONS method to query the capabilities of
    the MRCPv2 media server.
 
    C->S:
           OPTIONS sip:mrcp@mediaserver.com SIP/2.0
           Max-Forwards: 70
           To: <sip:mrcp@mediaserver.com>
           From: Sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 63104 OPTIONS
           Contact: <sip:sarvi@cisco.com>
           Accept: application/sdp
           Content-Length: 0
 
 
    S->C:
           SIP/2.0 200 OK
           To: <sip:mrcp@mediaserver.com>;tag=93810874
           From: Sarvi <sip:sarvi@Cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 63104 OPTIONS
           Contact: <sip:mrcp@mediaserver.com>
           Allow: INVITE, ACK, CANCEL, OPTIONS, BYE
           Accept: application/sdp
           Accept-Encoding: gzip
           Accept-Language: en
           Supported: foo
           Content-Type: application/sdp
           Content-Length: 274
 
           v=0
           o=sarvi 2890844526 2890842807 IN IP4 126.16.64.4
           s=SDP Seminar
           i=A session for processing media
 
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                            MRCPv2 Protocol               January 2004
 
           c=IN IP4 224.2.17.12/127
           m=control 9 TCP application/mrcpv2
           a=resource:speechsynth
           a=resource:speechrecog
           a=resource:speakverify
           m=audio 0 RTP/AVP 0 1 3
           a=rtpmap:0 PCMU/8000
           a=rtpmap:1 1016/8000
           a=rtpmap:3 GSM/8000
 
 
 
 7.   Speech Synthesizer Resource
 
    This resource is capable of converting text provided by the client
    and generating a speech stream in real-time.  Depending on the
    implementation and capability of this resource, the client can
    control parameters like voice characteristics, speaker speed, etc.
 
    The synthesizer resource is controlled by MRCPv2 requests from the
    client. Similarly the resource can respond to these requests or
    generate asynchronous events to the server to indicate certain
    conditions during the processing of the stream.
 
    This section applies for the following resource types.
           1. speechsynth
           2. basicsynth
           3. audioplayer
    The difference between the above three resources is in their level
    of support in rendering SSML. The "audioplayer" resource MUST
    support the <audio> and <marker> tags of SSML at minimum. The
    "basicsynth" in addition to the "audioplayer" MUST support the
    <sayas> tag and be able to render it using concatenated audio files.
    The "speechsynth" resource is advanced speech synthesizer capable of
    synthesizing speech and SHOULD support the rest of the SSML tags as
    well.
 
 7.1. Synthesizer State Machine
 
    The synthesizer maintains states to correlate MRCPv2 requests from
    the client. The state transitions shown below describe the states of
    the synthesizer and reflect the request at the head of the queue. A
    SPEAK request in the PENDING state can be deleted or stopped by a
    STOP request and does not affect the state of the resource.
 
         Idle                   Speaking                  Paused
         State                  State                     State
          |                       |                          |
          |----------SPEAK------->|                 |--------|
          |<------STOP------------|             CONTROL      |
          |<----SPEAK-COMPLETE----|                 |------->|
 
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                            MRCPv2 Protocol               January 2004
 
          |<----BARGE-IN-OCCURRED-|                          |
          |              |--------|                          |
          |          CONTROL      |-----------PAUSE--------->|
          |              |------->|<----------RESUME---------|
          |                       |               |----------|
          |                       |              PAUSE       |
          |                       |               |--------->|
          |              |--------|----------|               |
          |      BARGE-IN-OCCURED |      SPEECH-MARKER       |
          |              |------->|<---------|               |
          |----------|            |             |------------|
          |         STOP          |          SPEAK           |
          |          |            |             |----------->|
          |<---------|                                       |
          |<-------------------STOP--------------------------|
 
 
 7.2. Synthesizer Methods
 
    The synthesizer supports the following methods.
 
      synthesizer-method  =  "SET-PARAMS"
                          |  "GET-PARAMS"
                          |  "SPEAK"
                          |  "STOP"
                          |  "PAUSE"
                          |  "RESUME"
                          |  "BARGE-IN-OCCURRED"
                          |  "CONTROL"
 
 7.3. Synthesizer Events
 
    The synthesizer may generate the following events.
 
      synthesizer-event   =  "SPEECH-MARKER"
                          |  "SPEAK-COMPLETE"
 
 7.4. Synthesizer Header Fields
 
    A synthesizer message may contain header fields containing request
    options and information to augment the Request, Response or Event
    the message it is associated with.
 
      synthesizer-header  =  jump-target       ; Section 7.4.1
                          |  kill-on-barge-in  ; Section 7.4.2
                          |  speaker-profile   ; Section 7.4.3
                          |  completion-cause  ; Section 7.4.4
                          |  voice-parameter   ; Section 7.4.5
                          |  prosody-parameter ; Section 7.4.6
                          |  vendor-specific   ; Section 7.4.7
                          |  speech-marker     ; Section 7.4.8
 
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                            MRCPv2 Protocol               January 2004
 
                          |  speech-language   ; Section 7.4.9
                          |  fetch-hint        ; Section 7.4.10
                          |  audio-fetch-hint  ; Section 7.4.11
                          |  fetch-timeout     ; Section 7.4.12
                          |  failed-uri        ; Section 7.4.13
                          |  failed-uri-cause  ; Section 7.4.14
                          |  speak-restart     ; Section 7.4.15
                          |  speak-length      ; Section 7.4.16
 
 
      Parameter           Support        Methods/Events/Response
 
      jump-target         MANDATORY      SPEAK, CONTROL
      logging-tag         MANDATORY      SET-PARAMS, GET-PARAMS
      kill-on-barge-in    MANDATORY      SPEAK
      speaker-profile     OPTIONAL       SET-PARAMS, GET-PARAMS,
                                         SPEAK, CONTROL
      completion-cause    MANDATORY      SPEAK-COMPLETE
      voice-parameter     MANDATORY      SET-PARAMS, GET-PARAMS,
                                         SPEAK, CONTROL
      prosody-parameter   MANDATORY      SET-PARAMS, GET-PARAMS,
                                         SPEAK, CONTROL
      vendor-specific     MANDATORY      SET-PARAMS, GET-PARAMS
      speech-marker       MANDATORY      SPEECH-MARKER
      speech-language     MANDATORY      SET-PARAMS, GET-PARAMS, SPEAK
      fetch-hint          MANDATORY      SET-PARAMS, GET-PARAMS, SPEAK
      audio-fetch-hint    MANDATORY      SET-PARAMS, GET-PARAMS, SPEAK
      fetch-timeout       MANDATORY      SET-PARAMS, GET-PARAMS, SPEAK
      failed-uri          MANDATORY      Any
      failed-uri-cause    MANDATORY      Any
      speak-restart       MANDATORY      CONTROL
      speak-length        MANDATORY      SPEAK, CONTROL
 
 
 Jump-Target
 
    This parameter MAY BE specified in a CONTROL method and controls the
    jump size to move forward or rewind backward on an active SPEAK
    request. A + or - indicates a relative value to what is being
    currently played. This MAY BE specified in a SPEAK request to
    indicate an offset into the speech markup that the SPEAK request
    should start speaking from. The different speech length units
    supported are dependent on the synthesizer implementation. If it
    does not support a unit or the operation the resource SHOULD respond
    with a status code of 404 "Illegal or Unsupported value for
    parameter".
 
      jump-target         =    "Jump-Size" ":" speech-length-value CRLF
      speech-length-value =    numeric-speech-length
                          |    text-speech-length
      text-speech-length  =    1*ALPHA SP "Tag"
 
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                            MRCPv2 Protocol               January 2004
 
 
      numeric-speech-length=   ("+" | "-") 1*DIGIT SP
                               numeric-speech-unit
      numeric-speech-unit =    "Second"
                          |    "Word"
                          |    "Sentence"
                          |    "Paragraph"
 
 Kill-On-Barge-In
 
    This parameter MAY BE sent as part of the SPEAK method to enable
    kill-on-barge-in support. If enabled, the SPEAK method is
    interrupted by DTMF input detected by a signal detector resource or
    by the start of speech sensed or recognized by the speech recognizer
    resource.
 
      kill-on-barge-in    =    "Kill-On-Barge-In" ":" boolean-value CRLF
      boolean-value       =    "true" | "false"
 
    If the recognizer or signal detector resource is on the same server
    as the synthesizer, the server should be intelligent enough to
    recognize their interactions by their common MRCPv2 channel
    identifier (ignoring the last 2 hexadecimal digits) and work with
    each other to provide kill-on-barge-in support.
    The client needs to send a BARGE-IN-OCCURRED method to the
    synthesizer resource when it receives a bargin-in-able event from
    the synthesizer resource or signal detector resource. These
    resources MAY BE local or distributed. If this field is not
    specified, the value defaults to "true".
 
 Speaker Profile
 
    This parameter MAY BE part of the SET-PARAMS/GET-PARAMS or SPEAK
    request from the client to the server and specifies the profile of
    the speaker by a uri, which may be a set of voice parameters like
    gender, accent etc.
 
      speaker-profile     =    "Speaker-Profile" ":" uri CRLF
 
 Completion Cause
 
    This header field MUST be specified in a SPEAK-COMPLETE event coming
    from the synthesizer resource to the client. This indicates the
    reason behind the SPEAK request completion.
 
      completion-cause    =    "Completion-Cause" ":" 1*DIGIT SP
                               1*ALPHA CRLF
 
    Cause-Code  Cause-Name     Description
      000       normal         SPEAK completed normally.
      001       barge-in       SPEAK request was terminated because
 
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                            MRCPv2 Protocol               January 2004
 
                               of barge-in.
      002       parse-failure  SPEAK request terminated because of a
                               failure to parse the speech markup text.
      003       uri-failure    SPEAK request terminated because, access
                               to one of the URIs failed.
      004       error          SPEAK request terminated prematurely due
                               to synthesizer error.
      005       language-unsupported
                               Language not supported.
 
 Voice-Parameters
 
    This set of parameters defines the voice of the speaker.
 
      voice-parameter     =    "Voice-" voice-param-name ":"
                               voice-param-value CRLF
 
    voice-param-name is any one of the attribute names under the voice
    element specified in W3C's Speech Synthesis Markup Language
    Specification[10]. The voice-param-value is any one of the value
    choices of the corresponding voice element attribute specified in
    the above section.
 
    These header fields MAY BE sent in SET-PARAMS/GET-PARAMS request to
    define/get default values for the entire session or MAY BE sent in
    the SPEAK request to define default values for that speak request.
    Furthermore these attributes can be part of the speech text marked
    up in SML.
 
    These voice parameter header fields can also be sent in a CONTROL
    method to affect a SPEAK request in progress and change its behavior
    on the fly. If the synthesizer resource does not support this
    operation, it should respond back to the client with a status of
    unsupported.
 
 Prosody-Parameters
 
    This set of parameters defines the prosody of the speech.
 
      prosody-parameter   =    "Prosody-" prosody-param-name ":"
                               prosody-param-value CRLF
 
    prosody-param-name is any one of the attribute names under the
    prosody element specified in W3C's Speech Synthesis Markup Language
    Specification[10]. The prosody-param-value is any one of the value
    choices of the corresponding prosody element attribute specified in
    the above section.
 
    These header fields MAY BE sent in SET-PARAMS/GET-PARAMS request to
    define/get default values for the entire session or MAY BE sent in
    the SPEAK request to define default values for that speak request.
 
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                            MRCPv2 Protocol               January 2004
 
    Further more these attributes can be part of the speech text marked
    up in SML.
 
    The prosody parameter header fields in the SET-PARAMS or SPEAK
    request only apply if the speech data is of type text/plain and does
    not use a speech markup format.
 
    These prosody parameter header fields MAY also be sent in a CONTROL
    method to affect a SPEAK request in progress and change its behavior
    on the fly. If the synthesizer resource does not support this
    operation, it should respond back to the client with a status of
    unsupported.
 
 Vendor Specific Parameters
 
    This set of headers allows for the client to set Vendor Specific
    parameters.
 
      vendor-specific     =    "Vendor-Specific-Parameters" ":"
                               vendor-specific-av-pair
                               *[";" vendor-specific-av-pair] CRLF
      vendor-specific-av-pair = vendor-av-pair-name "="
                               vendor-av-pair-value
 
    This header MAY BE sent in the SET-PARAMS/GET-PARAMS method and is
    used to set vendor-specific parameters on the server side. The
    vendor-av-pair-name can be any Vendor specific field name and
    conforms to the XML vendor-specific attribute naming convention. The
    vendor-av-pair-value is the value to set the attribute to and needs
    to be quoted.
 
    When asking the server to get the current value of these parameters,
    this header can be sent in the GET-PARAMS method with the list of
    vendor-specific attribute names to get separated by a semicolon.
 
 Speech Marker
 
    This header field contains a marker tag that may be embedded in the
    speech data. Most speech markup formats provide mechanisms to embed
    marker fields between speech texts. The synthesizer will generate
    SPEECH-MARKER events when it reaches these marker fields. This field
    SHOULD be part of the SPEECH-MARKER event and will contain the
    marker tag values.
 
      speech-marker =          "Speech-Marker" ":" 1*ALPHA CRLF
 
 Speech Language
 
    This header field specifies the default language of the speech data
    if it is not specified in it. The value of this header field should
 
 
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                            MRCPv2 Protocol               January 2004
 
    follow RFC 1766 for its values. This MAY occur in SPEAK, SET-PARAMS
    or GET-PARAMS request.
 
      speech-language          =    "Speech-Language" ":" 1*ALPHA CRLF
 
 Fetch Hint
 
    When the synthesizer needs to fetch documents or other resources
    like speech markup or audio files, etc., this header field controls
    URI access properties. This defines when the synthesizer should
    retrieve content from the server. A value of "prefetch" indicates a
    file may be downloaded when the request is received, whereas "safe"
    indicates a file that should only be downloaded when actually
    needed. The default value is "prefetch". This header field MAY occur
    in SPEAK, SET-PARAMS or GET-PARAMS requests.
 
      fetch-hint               =    "Fetch-Hint" ":" 1*ALPHA CRLF
 
 Audio Fetch Hint
 
    When the synthesizer needs to fetch documents or other resources
    like speech audio files, etc., this header field controls URI access
    properties. This defines whether or not the synthesizer can attempt
    to optimize speech by pre-fetching audio. The value is either "safe"
    to say that audio is only fetched when it is needed, never before;
    "prefetch" to permit, but not require the platform to pre-fetch the
    audio; or "stream" to allow it to stream the audio fetches. The
    default value is "prefetch". This header field MAY occur in SPEAK,
    SET-PARAMS or GET-PARAMS. requests.
 
      audio-fetch-hint         =    "Audio-Fetch-Hint" ":" 1*ALPHA CRLF
 
 Fetch Timeout
 
    When the synthesizer needs to fetch documents or other resources
    like speech audio files, etc., this header field controls URI access
    properties. This defines the synthesizer timeout for resources the
    media server may need to fetch from the network. This is specified
    in milliseconds. The default value is platform-dependent. This
    header field MAY occur in SPEAK, SET-PARAMS or GET-PARAMS.
 
      fetch-timeout            =    "Fetch-Timeout" ":" 1*DIGIT CRLF
 
 Failed URI
 
    When a synthesizer method needs a synthesizer to fetch or access a
    URI and the access fails the media server SHOULD provide the failed
    URI in this header field in the method response.
 
      failed-uri               =    "Failed-URI" ":" Url CRLF
 
 
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                            MRCPv2 Protocol               January 2004
 
 Failed URI Cause
 
    When a synthesizer method needs a synthesizer to fetch or access a
    URI and the access fails the media server SHOULD provide the URI
    specific or protocol specific response code through this header
    field in the method response. This field has been defined as
    alphanumeric to accommodate all protocols, some of which might have
    a response string instead of a numeric response code.
 
      failed-uri-cause         =    "Failed-URI-Cause" ":" 1*ALPHA CRLF
 
 Speak Restart
 
    When a CONTROL jump backward request is issued to a currently
    speaking synthesizer resource and the jumps beyond the start of the
    speech, the current SPEAK request re-starts from the beginning of
    its speech data and the response to the CONTROL request would
    contain this header indicating a restart. This header MAY occur in
    the CONTROL response.
 
      speak-restart       =    "Speak-Restart" ":" boolean-value CRLF
 
 Speak Length
 
    This parameter MAY BE specified in a CONTROL method to control the
    length of speech to speak, relative to the current speaking point in
    the currently active SPEAK request. A - value is illegal in this
    field. If a field with a Tag unit is specified, then the media must
    speak till the tag is reached or the SPEAK request complete, which
    ever comes first. This MAY BE specified in a SPEAK request to
    indicate the length to speak in the speech data and is relative to
    the point in speech the SPEAK request starts. The different speech
    length units supported are dependent on the synthesizer
    implementation. If it does not support a unit or the operation the
    resource SHOULD respond with a status code of 404 "Illegal or
    Unsupported value for parameter".
 
      speak-length        =    "Speak-Length" ":" speech-length-value
                               CRLF
      speech-length-value =    numeric-speech-length
                          |    text-speech-length
      text-speech-length  =    1*ALPHA SP "Tag"
 
      numeric-speech-length=   ("+" | "-") 1*DIGIT SP
                               numeric-speech-unit
      numeric-speech-unit =    "Second"
                          |    "Word"
                          |    "Sentence"
                          |    "Paragraph"
 
 
 
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                            MRCPv2 Protocol               January 2004
 
 7.5. Synthesizer Message Body
 
    A synthesizer message may contain additional information associated
    with the Method, Response or Event in its message body.
 
 Synthesizer Speech Data
 
    Marked-up text for the synthesizer to speak is specified as a MIME
    entity in the message body. The message to be spoken by the
    synthesizer can be specified inline by embedding the data in the
    message body or by reference by providing the URI to the data. In
    either case the data and the format used to markup the speech needs
    to be supported by the media server.
 
    All media servers MUST support plain text speech data and W3C's
    Speech Synthesis Markup Language[10] as a minimum and hence MUST
    support the MIME types text/plain and application/synthesis+ssml at
    a minimum.
    If the speech data needs to be specified by URI reference the MIME
    type text/uri-list is used to specify the one or more URI that will
    list what needs to be spoken. If a list of speech URI is specified,
    speech data provided by each URI must be spoken in the order in
    which the URI are specified.
 
    If the data to be spoken consists of a mix of URI and inline speech
    data the multipart/mixed MIME-type is used and embedded with the
    MIME-blocks for text/uri-list, application/synthesis+ssml or
    text/plain. The character set and encoding used in the speech data
    may be specified according to standard MIME-type definitions. The
    multi-part MIME-block can contain actual audio data in .wav or sun
    audio format. This is used when the client has audio clips that it
    may have recorded and has it stored in memory or a local device and
    it needs to play it as part of the SPEAK request. The audio MIME-
    parts, can be sent by the client as part of the multi-part MIME-
    block. This audio will be referenced in the speech markup data that
    will be another part in the multi-part MIME-block according to the
    multipart/mixed MIME-type specification.
 
    Example 1:
         Content-Type: text/uri-list
         Content-Length: 176
 
         http://www.example.com/ASR-Introduction.sml
         http://www.example.com/ASR-Document-Part1.sml
         http://www.example.com/ASR-Document-Part2.sml
         http://www.example.com/ASR-Conclusion.sml
 
    Example 2:
         Content-Type: application/synthesis+ssml
         Content-Length: 104
 
 
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                            MRCPv2 Protocol               January 2004
 
         <?xml version="1.0"?>
         <speak>
         <paragraph>
                  <sentence>You have 4 new messages.</sentence>
                  <sentence>The first is from <say-as
                  type="name">Stephanie Williams</say-as>
                  and arrived at <break/>
                  <say-as type="time">3:45pm</say-as>.</sentence>
 
                  <sentence>The subject is <prosody
                  rate="-20%">ski trip</prosody></sentence>
         </paragraph>
         </speak>
 
    Example 3:
         Content-Type: multipart/mixed; boundary="--break"
 
         --break
         Content-Type: text/uri-list
         Content-Length: 176
 
         http://www.example.com/ASR-Introduction.sml
         http://www.example.com/ASR-Document-Part1.sml
         http://www.example.com/ASR-Document-Part2.sml
         http://www.example.com/ASR-Conclusion.sml
 
         --break
         Content-Type: application/synthesis+ssml
         Content-Length: 104
 
         <?xml version="1.0"?>
         <speak>
         <paragraph>
                  <sentence>You have 4 new messages.</sentence>
                  <sentence>The first is from <say-as
                  type="name">Stephanie Williams</say-as>
                  and arrived at <break/>
                  <say-as type="time">3:45pm</say-as>.</sentence>
 
                  <sentence>The subject is <prosody
                  rate="-20%">ski trip</prosody></sentence>
         </paragraph>
         </speak>
          --break
 
 
 7.6. SET-PARAMS
 
    The SET-PARAMS method, from the client to server, tells the
    synthesizer resource to define default synthesizer context
    parameters, like voice characteristics and prosody etc. If the
 
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                            MRCPv2 Protocol               January 2004
 
    server accepted and set all parameters it MUST return a Response-
    Status of 200. If it chose to ignore some optional parameters it
    MUST return 201.
 
    If some of the parameters being set are unsupported or have illegal
    values, the server accept and set the remaining parameters and MUST
    respond with a Response-Status of 403 or 404, and MUST include in
    the response the header fields that could not be set.
 
    Example:
      C->S:MRCP/2.0 124 SET-PARAMS 543256
           Channel-Identifier: 32AECB23433802@speechsynth
           Voice-gender: female
           Voice-category: adult
           Voice-variant: 3
 
 
      S->C:MRCP/2.0 47 543256 200 COMPLETE
           Channel-Identifier: 32AECB23433802@speechsynth
 
 7.7. GET-PARAMS
 
    The GET-PARAMS method, from the client to server, asks the
    synthesizer resource for its current synthesizer context parameters,
    like voice characteristics and prosody etc. The client SHOULD send
    the list of parameter it wants to read from the server by listing a
    set of empty parameter header fields. If a specific list is not
    specified then the server SHOULD return all the settable parameters
    including vendor-specific parameters and their current values. The
    wild card use can be very intensive as the number of settable
    parameters can be large depending on the vendor.  Hence it is
    RECOMMENDED that the client does not use the wildcard GET-PARAMS
    operation very often.
 
    Example:
      C->S:MRCP/2.0 136 GET-PARAMS 543256
           Channel-Identifier: 32AECB23433802@speechsynth
           Voice-gender:
           Voice-category:
           Voice-variant:
           Vendor-Specific-Parameters:com.mycorp.param1;
                       com.mycorp.param2
 
      S->C:MRCP/2.0 163 543256 200 COMPLETE
           Channel-Identifier: 32AECB23433802
           Voice-gender:female
           Voice-category: adult
           Voice-variant: 3
           Vendor-Specific-Parameters:com.mycorp.param1="Company Name";
                          com.mycorp.param2="124324234@mycorp.com"
 
 
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                            MRCPv2 Protocol               January 2004
 
 7.8. SPEAK
 
    The SPEAK method from the client to the server provides the
    synthesizer resource with the speech text and initiates speech
    synthesis and streaming. The SPEAK method can carry voice and
    prosody header fields that define the behavior of the voice being
    synthesized, as well as the actual marked-up text to be spoken. If
    specific voice and prosody parameters are specified as part of the
    speech markup text, it will take precedence over the values
    specified in the header fields and those set using a previous SET-
    PARAMS request.
 
    When applying voice parameters there are 3 levels of scope. The
    highest precedence are those specified within the speech markup
    text, followed by those specified in the header fields of the SPEAK
    request and hence apply for that SPEAK request only, followed by the
    session default values which can be set using the SET-PARAMS request
    and apply for the whole session moving forward.
 
    If the resource is idle and the SPEAK request is being actively
    processed the resource will respond with a success status code and a
    request-state of IN-PROGRESS.
 
    If the resource is in the speaking or paused states, i.e. it is in
    the middle of processing a previous SPEAK request, the status
    returns success and a request-state of PENDING. This means that this
    SPEAK request is in queue and will be processed after the currently
    active SPEAK request is completed.
 
    For the synthesizer resource, this is the only request that can
    return a request-state of IN-PROGRESS or PENDING.
    When the text to be synthesized is complete, the resource will issue
    a SPEAK-COMPLETE event with the request-id of the SPEAK message and
    a request-state of COMPLETE.
 
    Example:
      C->S:MRCP/2.0 489 SPEAK 543257
           Channel-Identifier: 32AECB23433802@speechsynth
           Voice-gender: neutral
           Voice-category: teenager
           Prosody-volume: medium
           Content-Type: application/synthesis+ssml
           Content-Length: 104
 
           <?xml version="1.0"?>
           <speak>
           <paragraph>
             <sentence>You have 4 new messages.</sentence>
             <sentence>The first is from <say-as
             type="name">Stephanie Williams</say-as>
             and arrived at <break/>
 
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                            MRCPv2 Protocol               January 2004
 
             <say-as type="time">3:45pm</say-as>.</sentence>
 
             <sentence>The subject is <prosody
             rate="-20%">ski trip</prosody></sentence>
           </paragraph>
           </speak>
 
 
      S->C:MRCP/2.0 28 543257 200 IN-PROGRESS
           Channel-Identifier: 32AECB23433802@speechsynth
 
 
      S->C:MRCP/2.0 79 SPEAK-COMPLETE 543257 COMPLETE
           Channel-Identifier: 32AECB23433802@speechsynth
           Completion-Cause: 000 normal
 
 
 7.9. STOP
 
    The STOP method from the client to the server tells the resource to
    stop speaking if it is speaking something.
 
    The STOP request can be sent with an active-request-id-list header
    field to stop the zero or more specific SPEAK requests that may be
    in queue and return a response code of 200(Success). If no active-
    request-id-list header field is sent in the STOP request it will
    terminate all outstanding SPEAK requests.
 
    If a STOP request successfully terminated one or more PENDING or IN-
    PROGRESS SPEAK requests, then the response message body contains an
    active-request-id-list header field listing the SPEAK request-ids
    that were terminated. Otherwise there will be no active-request-id-
    list header field in the response. No SPEAK-COMPLETE events will be
    sent for these terminated requests.
 
    If a SPEAK request that was IN-PROGRESS and speaking was stopped the
    next pending SPEAK request, if any, would become IN-PROGRESS and
    move to the speaking state.
 
    If a SPEAK request that was IN-PROGRESS and in the paused state was
    stopped the next pending SPEAK request, if any, would become IN-
    PROGRESS and move to the paused state.
 
    Example:
      C->S:MRCP/2.0 423 SPEAK 543258
           Channel-Identifier: 32AECB23433802@speechsynth
           Content-Type: application/synthesis+ssml
           Content-Length: 104
 
           <?xml version="1.0"?>
           <speak>
 
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                            MRCPv2 Protocol               January 2004
 
           <paragraph>
             <sentence>You have 4 new messages.</sentence>
             <sentence>The first is from <say-as
             type="name">Stephanie Williams</say-as>
             and arrived at <break/>
             <say-as type="time">3:45pm</say-as>.</sentence>
 
             <sentence>The subject is <prosody
             rate="-20%">ski trip</prosody></sentence>
           </paragraph>
           </speak>
 
 
      S->C:MRCP/2.0 48 543258 200 IN-PROGRESS
           Channel-Identifier: 32AECB23433802@speechsynth
 
      C->S:MRCP/2.0 44 STOP 543259 200
           Channel-Identifier: 32AECB23433802@speechsynth
 
      S->C:MRCP/2.0 66 543259 200 COMPLETE
           Channel-Identifier: 32AECB23433802@speechsynth
           Active-Request-Id-List: 543258
 
 
 7.10.     BARGE-IN-OCCURRED
 
    The BARGE-IN-OCCURRED method is a mechanism for the client to
    communicate a barge-in-able event it detects to the speech resource.
 
    This event is useful in two scenarios,
 
    1. The client has detected some events like DTMF digits or other
    barge-in-able events and wants to communicate that to the
    synthesizer.
    2. The recognizer resource and the synthesizer resource are in
    different servers. In which case the client MUST act as a Proxy and
    receive event from the recognition resource, and then send a BARGE-
    IN-OCCURRED method to the synthesizer. In such cases, the BARGE-IN-
    OCCURRED method would also have a proxy-sync-id header field
    received from the resource generating the original event.
 
    If a SPEAK request is active with kill-on-barge-in enabled, and the
    BARGE-IN-OCCURRED event is received, the synthesizer should stop
    streaming out audio. It should also terminate any speech requests
    queued behind the current active one, irrespective of whether they
    have barge-in enabled or not. If a barge-in-able prompt was playing
    and it was terminated, the response MUST contain the request-ids of
    all SPEAK requests that were terminated in its active-request-id-
    list. There will be no SPEAK-COMPLETE events generated for these
    requests.
 
 
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                            MRCPv2 Protocol               January 2004
 
    If the synthesizer and the recognizer are on the same server they
    could be optimized for a quicker kill-on-barge-in response by the
    recognizer and synthesizer interacting directly based on a MRCPv2
    channel identifier ignoring the last 2 hexadecimal digits. In these
    cases, the client MUST still proxy the recognition event through a
    BARGE-IN-OCCURRED method, but the synthesizer resource may have
    already stopped and sent a SPEAK-COMPLETE event with a barge in
    completion cause code.  If there were no SPEAK requests terminated
    as a result of the BARGE-IN-OCCURRED method, the response would
    still be a 200 success but MUST not contain an active-request-id-
    list header field.
 
      C->S:MRCP/2.0 433 SPEAK 543258
           Channel-Identifier: 32AECB23433802@speechsynth
           Voice-gender: neutral
           Voice-category: teenager
           Prosody-volume: medium
           Content-Type: application/synthesis+ssml
           Content-Length: 104
 
           <?xml version="1.0"?>
           <speak>
           <paragraph>
             <sentence>You have 4 new messages.</sentence>
             <sentence>The first is from <say-as
             type="name">Stephanie Williams</say-as>
             and arrived at <break/>
             <say-as type="time">3:45pm</say-as>.</sentence>
 
             <sentence>The subject is <prosody
             rate="-20%">ski trip</prosody></sentence>
           </paragraph>
           </speak>
 
      S->C:MRCP/2.0 47 543258 200 IN-PROGRESS
           Channel-Identifier: 32AECB23433802@speechsynth
 
      C->S:MRCP/2.0 69 BARGE-IN-OCCURRED 543259 200
           Channel-Identifier: 32AECB23433802@speechsynth
           Proxy-Sync-Id: 987654321
 
      S->C:MRCP/2.0 72 543259 200 COMPLETE
           Channel-Identifier: 32AECB23433802@speechsynth
           Active-Request-Id-List: 543258
 
 
 7.11.     PAUSE
 
    The PAUSE method from the client to the server tells the resource to
    pause speech, if it is speaking something. If a PAUSE method is
    issued on a session when a SPEAK is not active the server SHOULD
 
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                            MRCPv2 Protocol               January 2004
 
    respond with a status of 402 or "Method not valid in this state". If
    a PAUSE method is issued on a session when a SPEAK is active and
    paused the server SHOULD respond with a status of 200 or "Success".
    If a SPEAK request was active the server MUST return an active-
    request-id-list header with the request-id of the SPEAK request that
    was paused.
 
      C->S:MRCP/2.0 434 SPEAK 543258
           Channel-Identifier: 32AECB23433802@speechsynth
           Voice-gender: neutral
           Voice-category: teenager
           Prosody-volume: medium
           Content-Type: application/synthesis+ssml
           Content-Length: 104
 
           <?xml version="1.0"?>
           <speak>
           <paragraph>
             <sentence>You have 4 new messages.</sentence>
             <sentence>The first is from <say-as
             type="name">Stephanie Williams</say-as>
             and arrived at <break/>
             <say-as type="time">3:45pm</say-as>.</sentence>
 
             <sentence>The subject is <prosody
             rate="-20%">ski trip</prosody></sentence>
           </paragraph>
           </speak>
 
      S->C:MRCP/2.0 48 543258 200 IN-PROGRESS
           Channel-Identifier: 32AECB23433802@speechsynth
 
      C->S:MRCP/2.0 43 PAUSE 543259
           Channel-Identifier: 32AECB23433802@speechsynth
 
      S->C:MRCP/2.0 68 543259 200 COMPLETE
           Channel-Identifier: 32AECB23433802@speechsynth
           Active-Request-Id-List: 543258
 
 7.12.     RESUME
 
    The RESUME method from the client to the server tells a paused
    synthesizer resource to continue speaking. If a RESUME method is
    issued on a session when a SPEAK is not active the server SHOULD
    respond with a status of 402 or "Method not valid in this state". If
    a RESUME method is issued on a session when a SPEAK is active and
    speaking(i.e. not paused) the server SHOULD respond with a status of
    200 or "Success". If a SPEAK request was active the server MUST
    return an active-request-id-list header with the request-id of the
    SPEAK request that was resumed
 
 
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                            MRCPv2 Protocol               January 2004
 
    Example:
      C->S:MRCP/2.0 434 SPEAK 543258
           Channel-Identifier: 32AECB23433802@speechsynth
           Voice-gender: neutral
           Voice-category: teenager
           Prosody-volume: medium
           Content-Type: application/synthesis+ssml
           Content-Length: 104
 
           <?xml version="1.0"?>
           <speak>
           <paragraph>
               <sentence>You have 4 new messages.</sentence>
               <sentence>The first is from <say-as
               type="name">Stephanie Williams</say-as>
               and arrived at <break/>
               <say-as type="time">3:45pm</say-as>.</sentence>
 
               <sentence>The subject is <prosody
               rate="-20%">ski trip</prosody></sentence>
           </paragraph>
           </speak>
 
      S->C:MRCP/2.0 48 543258 200 IN-PROGRESS@speechsynth
           Channel-Identifier: 32AECB23433802
 
      C->S:MRCP/2.0 44 PAUSE 543259
           Channel-Identifier: 32AECB23433802@speechsynth
 
      S->C:MRCP/2.0 47 543259 200 COMPLETE
           Channel-Identifier: 32AECB23433802@speechsynth
           Active-Request-Id-List: 543258
 
      C->S:MRCP/2.0 44 RESUME 543260
           Channel-Identifier: 32AECB23433802@speechsynth
 
      S->C:MRCP/2.0 66 543260 200 COMPLETE
           Channel-Identifier: 32AECB23433802@speechsynth
           Active-Request-Id-List: 543258
 
 7.13.     CONTROL
 
    The CONTROL method from the client to the server tells a synthesizer
    that is speaking to modify what it is speaking on the fly.  This
    method is used to make the synthesizer jump forward or backward in
    what it is speaking, change speaker rate, and speaker parameters,
    etc. It affects the active or IN-PROGRESS SPEAK request. Depending
    on the implementation and capability of the synthesizer resource it
    may allow this operation or one or more of its parameters.
 
 
 
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                            MRCPv2 Protocol               January 2004
 
    When a CONTROL to jump forward is issued and the operation goes
    beyond the end of the active SPEAK method's text, the request
    succeeds. A SPEAK-COMPLETE event follows the response to the CONTROL
    method. If there are more SPEAK requests in the queue, the
    synthesizer resource will continue to process the next SPEAK method.
    When a CONTROL to jump backwards is issued and the operation jumps
    to the beginning of the speech data of the active SPEAK request, the
    response to the CONTROL request contains the speak-restart header.
 
    These two behaviors can be used to rewind or fast-forward across
    multiple speech requests, if the client wants to break up a speech
    markup text to multiple SPEAK requests.
 
    If a SPEAK request was active when the CONTROL method was received
    the server MUST return an active-request-id-list header with the
    Request-id of the SPEAK request that was active.
 
    Example:
      C->S:MRCP/2.0 434 SPEAK 543258
           Channel-Identifier: 32AECB23433802@speechsynth
           Voice-gender: neutral
           Voice-category: teenager
           Prosody-volume: medium
           Content-Type: application/synthesis+ssml
           Content-Length: 104
 
           <?xml version="1.0"?>
           <speak>
           <paragraph>
             <sentence>You have 4 new messages.</sentence>
             <sentence>The first is from <say-as
             type="name">Stephanie Williams</say-as>
             and arrived at <break/>
             <say-as type="time">3:45pm</say-as>.</sentence>
 
             <sentence>The subject is <prosody
             rate="-20%">ski trip</prosody></sentence>
           </paragraph>
           </speak>
 
 
      S->C:MRCP/2.0 47 543258 200 IN-PROGRESS
           Channel-Identifier: 32AECB23433802@speechsynth
 
      C->S:MRCP/2.0 63 CONTROL 543259
           Channel-Identifier: 32AECB23433802@speechsynth
           Prosody-rate: fast
 
      S->C:MRCP/2.0 67 543259 200 COMPLETE
           Channel-Identifier: 32AECB23433802@speechsynth
           Active-Request-Id-List: 543258
 
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                            MRCPv2 Protocol               January 2004
 
 
      C->S:MRCP/2.0 68 CONTROL 543260
           Channel-Identifier: 32AECB23433802@speechsynth
           Jump-Size: -15 Words
 
      S->C:MRCP/2.0 69 543260 200 COMPLETE
           Channel-Identifier: 32AECB23433802@speechsynth
           Active-Request-Id-List: 543258
 
 7.14.     SPEAK-COMPLETE
 
    This is an Event message from the synthesizer resource to the client
    indicating that the SPEAK request was completed. The request-id
    header field WILL match the request-id of the SPEAK request that
    initiated the speech that just completed. The request-state field
    should be COMPLETE indicating that this is the last Event with that
    request-id, and that the request with that request-id is now
    complete. The completion-cause header field specifies the cause code
    pertaining to the status and reason of request completion such as
    the SPEAK completed normally or because of an error or kill-on-
    barge-in etc.
 
    Example:
      C->S:MRCP/2.0 434 SPEAK 543260
           Channel-Identifier: 32AECB23433802@speechsynth
           Voice-gender: neutral
           Voice-category: teenager
           Prosody-volume: medium
           Content-Type: application/synthesis+ssml
           Content-Length: 104
 
           <?xml version="1.0"?>
           <speak>
           <paragraph>
             <sentence>You have 4 new messages.</sentence>
             <sentence>The first is from <say-as
             type="name">Stephanie Williams</say-as>
             and arrived at <break/>
             <say-as type="time">3:45pm</say-as>.</sentence>
 
             <sentence>The subject is <prosody
             rate="-20%">ski trip</prosody></sentence>
           </paragraph>
           </speak>
 
      S->C:MRCP/2.0 48 543260 200 IN-PROGRESS
           Channel-Identifier: 32AECB23433802@speechsynth
 
      S->C:MRCP/2.0 73 SPEAK-COMPLETE 543260 COMPLETE
           Channel-Identifier: 32AECB23433802@speechsynth
           Completion-Cause: 000 normal
 
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                            MRCPv2 Protocol               January 2004
 
 
 7.15.     SPEECH-MARKER
 
    This is an event generated by the synthesizer resource to the client
    when it hits a marker tag in the speech markup it is currently
    processing. The request-id field in the header matches the SPEAK
    request request-id that initiated the speech. The request-state
    field should be IN-PROGRESS as the speech is still not complete and
    there is more to be spoken. The actual speech marker tag hit,
    describing where the synthesizer is in the speech markup, is
    returned in the speech-marker header field.
 
    Example:
      C->S:MRCP/2.0 434 SPEAK 543261
           Channel-Identifier: 32AECB23433802@speechsynth
           Voice-gender: neutral
           Voice-category: teenager
           Prosody-volume: medium
           Content-Type: application/synthesis+ssml
           Content-Length: 104
 
           <?xml version="1.0"?>
           <speak>
           <paragraph>
             <sentence>You have 4 new messages.</sentence>
             <sentence>The first is from <say-as
             type="name">Stephanie Williams</say-as>
             and arrived at <break/>
             <say-as type="time">3:45pm</say-as>.</sentence>
             <mark name="here"/>
             <sentence>The subject is
                <prosody rate="-20%">ski trip</prosody>
             </sentence>
             <mark name="ANSWER"/>
           </paragraph>
           </speak>
 
 
      S->C:MRCP/2.0 48 543261 200 IN-PROGRESS
           Channel-Identifier: 32AECB23433802@speechsynth
 
      S->C:MRCP/2.0 73 SPEECH-MARKER 543261 IN-PROGRESS
           Channel-Identifier: 32AECB23433802@speechsynth
           Speech-Marker: here
 
      S->C:MRCP/2.0 74 SPEECH-MARKER 543261 IN-PROGRESS
           Channel-Identifier: 32AECB23433802@speechsynth
           Speech-Marker: ANSWER
 
      S->C:MRCP/2.0 73 SPEAK-COMPLETE 543261 COMPLETE
           Channel-Identifier: 32AECB23433802@speechsynth
 
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                            MRCPv2 Protocol               January 2004
 
           Completion-Cause: 000 normal
 
 
 8.   Speech Recognizer Resource
 
    The speech recognizer resource is capable of receiving an incoming
    voice stream and providing the client with an interpretation of what
    was spoken in textual form.
 
    This section applies for the following resource types.
           1. speechrecog
           2. dtmfrecog
 
    The difference between the above two resources is in their level of
    support for recognition grammars. The "dtmfrecog" resource is
    capable of recognizing DTMF digits only and hence will accept DTMF
    grammars only. The "speechrecog" can recognize regular speech as
    well as DTMF digits and hence SHOULD support grammars describing
    speech or DTMF.
 
 8.1. Recognizer State Machine
 
    The recognizer resource is controlled by MRCPv2 requests from the
    client. Similarly the resource can respond to these requests or
    generate asynchronous events to the server to indicate certain
    conditions during the processing of the stream. Hence the recognizer
    maintains states to correlate MRCPv2 requests from the client. The
    state transitions are described below.
 
         Idle                   Recognizing               Recognized
         State                  State                     State
          |                       |                          |
          |---------RECOGNIZE---->|---RECOGNITION-COMPLETE-->|
          |<------STOP------------|<-----RECOGNIZE-----------|
          |                       |                          |
          |                       |              |-----------|
          |              |--------|       GET-RESULT         |
          |       START-OF-SPEECH |              |---------->|
          |------------| |------->|                          |
          |            |          |----------|               |
          |      DEFINE-GRAMMAR   | RECOGNITION-START-TIMERS |
          |<-----------|          |<---------|               |
          |                       |                          |
          |                       |                          |
          |-------|               |                          |
          |      STOP             |                          |
          |<------|               |                          |
          |                                                  |
          |<-------------------STOP--------------------------|
          |<-------------------DEFINE-GRAMMAR----------------|
 
 
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                            MRCPv2 Protocol               January 2004
 
 8.2. Recognizer Methods
 
    The recognizer supports the following methods.
      recognizer-Method   =    "SET-PARAMS"
                          |    "GET-PARAMS"
                          |    "DEFINE-GRAMMAR"
                          |    "RECOGNIZE"
                          |    "GET-RESULT"
                          |    "RECOGNITION-START-TIMERS"
                          |    "STOP"
 
 8.3. Recognizer Events
 
    The recognizer may generate the following events.
      recognizer-Event    =    "START-OF-SPEECH"
                          |    "RECOGNITION-COMPLETE"
 
 8.4. Recognizer Header Fields
 
    A recognizer message may contain header fields containing request
    options and information to augment the Method, Response or Event
    message it is associated with.
 
      recognizer-header   =    confidence-threshold     ; Section 8.4.1
                          |    sensitivity-level        ; Section 8.4.2
                          |    speed-vs-accuracy        ; Section 8.4.3
                          |    n-best-list-length       ; Section 8.4.4
                          |    no-input-timeout         ; Section 8.4.5
                          |    recognition-timeout      ; Section 8.4.6
                          |    waveform-url             ; Section 8.4.7
                          |    completion-cause         ; Section 8.4.8
                          |    recognizer-context-block ; Section 8.4.9
                          |    recognizer-start-timers  ; Section 8.4.10
                          |    vendor-specific          ; Section 8.4.11
                          |    speech-complete-timeout  ; Section 8.4.12
                          |    speech-incomplete-timeout; Section 8.4.13
                          |    dtmf-interdigit-timeout  ; Section 8.4.14
                          |    dtmf-term-timeout        ; Section 8.4.15
                          |    dtmf-term-char           ; Section 8.4.16
                          |    fetch-timeout            ; Section 8.4.17
                          |    failed-uri               ; Section 8.4.18
                          |    failed-uri-cause         ; Section 8.4.19
                          |    save-waveform            ; Section 8.4.20
                          |    new-audio-channel        ; Section 8.4.21
                          |    speech-language          ; Section 8.4.22
 
      Parameter                Support   Methods/Events
 
      confidence-threshold     MANDATORY SET-PARAMS, RECOGNIZE
                                         GET-RESULT
      sensitivity-level        Optional  SET-PARAMS, GET-PARAMS,
 
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                            MRCPv2 Protocol               January 2004
 
                                         RECOGNIZE
      speed-vs-accuracy        Optional  SET-PARAMS, GET-PARAMS,
                                         RECOGNIZE
      n-best-list-length       Optional  SET-PARAMS, GET-PARAMS,
                                         RECOGNIZE, GET-RESULT
      no-input-timeout         MANDATORY SET-PARAMS, GET-PARAMS,
                                         RECOGNIZE
      recognition-timeout      MANDATORY SET-PARAMS, GET-PARAMS,
                                         RECOGNIZE
      waveform-url             MANDATORY RECOGNITION-COMPLETE
      completion-cause         MANDATORY DEFINE-GRAMMAR, RECOGNIZE,
                                         RECOGNITON-COMPLETE
      recognizer-context-block Optional  SET-PARAMS, GET-PARAMS
      recognizer-start-timers  MANDATORY RECOGNIZE
      vendor-specific          MANDATORY SET-PARAMS, GET-PARAMS
      speech-complete-timeout  MANDATORY SET-PARAMS, GET-PARAMS
                                         RECOGNIZE
      speech-incomplete-timeout MANDATORY SET-PARAMS, GET-PARAMS
                                         RECOGNIZE
      dtmf-interdigit-timeout  MANDATORY SET-PARAMS, GET-PARAMS
                                         RECOGNIZE
      dtmf-term-timeout        MANDATORY SET-PARAMS, GET-PARAMS
                                         RECOGNIZE
      dtmf-term-char           MANDATORY SET-PARAMS, GET-PARAMS
                                         RECOGNIZE
      fetch-timeout            MANDATORY SET-PARAMS, GET-PARAMS
                                         RECOGNIZE, DEFINE-GRAMMAR
      failed-uri               MANDATORY DEFINE-GRAMMAR response,
                                         RECOGNITION-COMPLETE
      failed-uri-cause         MANDATORY DEFINE-GRAMMAR response,
                                         RECOGNITION-COMPLETE
      save-waveform            MANDATORY SET-PARAMS, GET-PARAMS,
                                         RECOGNIZE
      new-audio-channel        MANDATORY RECOGNIZE
      speech-language          MANDATORY SET-PARAMS, GET-PARAMS,
                                         RECOGNIZE, DEFINE-GRAMMAR
 
 
 Confidence Threshold
 
    When a recognition resource recognizes or matches a spoken phrase
    with some portion of the grammar, it associates a confidence level
    with that conclusion. The confidence-threshold parameter tells the
    recognizer resource what confidence level should be considered a
    successful match. This is an integer from 0-100 indicating the
    recognizer's confidence in the recognition. If the recognizer
    determines that its confidence in all its recognition results is
    less than the confidence threshold, then it MUST return no-match as
    the recognition result. This header field MAY occur in RECOGNIZE,
    SET-PARAMS or GET-PARAMS. The default value for this field is
    platform specific.
 
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                            MRCPv2 Protocol               January 2004
 
 
      confidence-threshold=    "Confidence-Threshold" ":" 1*DIGIT CRLF
 
 Sensitivity Level
 
    To filter out background noise and not mistake it for speech, the
    recognizer may support a variable level of sound sensitivity. The
    sensitivity-level parameter allows the client to set this value on
    the recognizer. This header field MAY occur in RECOGNIZE, SET-PARAMS
    or GET-PARAMS. A higher value for this field means higher
    sensitivity. The default value for this field is platform specific.
 
      sensitivity-level   =    "Sensitivity-Level" ":" 1*DIGIT CRLF
 
 Speed Vs Accuracy
 
    Depending on the implementation and capability of the recognizer
    resource it may be tunable towards Performance or Accuracy. Higher
    accuracy may mean more processing and higher CPU utilization,
    meaning less calls per media server and vice versa. This parameter
    on the resource can be tuned by the speed-vs-accuracy header. This
    header field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS. A
    higher value for this field means higher speed. The default value
    for this field is platform specific.
 
      speed-vs-accuracy   =     "Speed-Vs-Accuracy" ":" 1*DIGIT CRLF
 
 N Best List Length
 
    When the recognizer matches an incoming stream with the grammar, it
    may come up with more than one alternative matches because of
    confidence levels in certain words or conversation paths.  If this
    header field is not specified, by default, the recognition resource
    will only return the best match above the confidence threshold. The
    client, by setting this parameter, could ask the recognition
    resource to send it more than 1 alternative. All alternatives must
    still be above the confidence-threshold. A value greater than one
    does not guarantee that the recognizer will send the requested
    number of alternatives. This header field MAY occur in RECOGNIZE,
    SET-PARAMS or GET-PARAMS. The minimum value for this field is 1. The
    default value for this field is 1.
 
      n-best-list-length  =    "N-Best-List-Length" ":" 1*DIGIT CRLF
 
 No Input Timeout
 
    When recognition is started and there is no speech detected for a
    certain period of time, the recognizer can send a RECOGNITION-
    COMPLETE event to the client and terminate the recognition
    operation. The no-input-timeout header field can set this timeout
    value. The value is in milliseconds. This header field MAY occur in
 
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                            MRCPv2 Protocol               January 2004
 
    RECOGNIZE, SET-PARAMS or GET-PARAMS. The value for this field ranges
    from 0 to MAXTIMEOUT, where MAXTIMEOUT is platform specific. The
    default value for this field is platform specific.
 
      no-input-timeout    =    "No-Input-Timeout" ":" 1*DIGIT CRLF
 
 Recognition Timeout
 
    When recognition is started and there is no match for a certain
    period of time, the recognizer can send a RECOGNITION-COMPLETE event
    to the client and terminate the recognition operation. The
    recognition-timeout parameter field sets this timeout value. The
    value is in milliseconds. The value for this field ranges from 0 to
    MAXTIMEOUT, where MAXTIMEOUT is platform specific. The default value
    is 10 seconds. This header field MAY occur in RECOGNIZE, SET-PARAMS
    or GET-PARAMS.
 
      recognition-timeout =    "Recognition-Timeout" ":" 1*DIGIT CRLF
 
 Waveform URL
 
    If the save-waveform header field is set to true, the recognizer
    MUST record the incoming audio stream of the recognition into a file
    and provide a URI for the client to access it. This header MUST be
    present in the RECOGNITION-COMPLETE event if the save-waveform
    header field was set to true. The URL value of the header MUST be
    NULL if there was some error condition preventing the server from
    recording. Otherwise, the URL generated by the server SHOULD be
    globally unique across the server and all its recognition sessions.
    The URL SHOULD BE available until the session is torn down.
 
      waveform-url        =    "Waveform-URL" ":" Url CRLF
 
 Completion Cause
 
    This header field MUST be part of a RECOGNITION-COMPLETE, event
    coming from the recognizer resource to the client. This indicates
    the reason behind the RECOGNIZE method completion. This header field
    MUST BE sent in the DEFINE-GRAMMAR and RECOGNIZE responses, if they
    return with a failure status and a COMPLETE state.
 
      completion-cause    =    "Completion-Cause" ":" 1*DIGIT SP
                               1*ALPHA CRLF
 
      Cause-Code     Cause-Name     Description
 
        000           success       RECOGNIZE completed with a match or
                                    DEFINE-GRAMMAR succeeded in
                                    downloading and compiling the
                                    grammar
        001           no-match      RECOGNIZE completed, but no match
 
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                            MRCPv2 Protocol               January 2004
 
                                    was found
         002          no-input-timeout
                                    RECOGNIZE completed without a match
                                    due to a no-input-timeout
         003          recognition-timeout
                                    RECOGNIZE completed without a match
                                    due to a recognition-timeout
        004           gram-load-failure
                                    RECOGNIZE failed due grammar load
                                    failure.
        005           gram-comp-failure
                                    RECOGNIZE failed due to grammar
                                    compilation failure.
        006           error         RECOGNIZE request terminated
                                    prematurely due to a recognizer
                                    error.
        007           speech-too-early
                                    RECOGNIZE request terminated because
                                    speech was too early.
        008           too-much-speech-timeout
                                    RECOGNIZE request terminated because
                                    speech was too long.
        009           uri-failure   Failure accessing a URI.
        010           language-unsupported
                                    Language not supported.
 
 Recognizer Context Block
 
    This parameter MAY BE sent as part of the SET-PARAMS or GET-PARAMS
    request. If the GET-PARAMS method, contains this header field with
    no value, then it is a request to the recognizer to return the
    recognizer context block. The response to such a message MAY contain
    a recognizer context block as a message entity.  If the server
    returns a recognizer context block, the response MUST contain this
    header field and its value MUST match the content-id of that entity.
 
    If the SET-PARAMS method contains this header field, it MUST contain
    a message entity containing the recognizer context data, and a
    content-id matching this header field.
    This content-id should match the content-id that came with the
    context data during the GET-PARAMS operation.
 
      recognizer-context-block =    "Recognizer-Context-Block" ":"
                                    1*ALPHA CRLF
 
 Recognition Start Timers
 
    This parameter MAY BE sent as part of the RECOGNIZE request. A value
    of false tells the recognizer to start recognition, but not to start
    the no-input timer yet. The recognizer should not start the timers
    until the client sends a RECOGNITION-START-TIMERS request to the
 
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    recognizer. This is useful in the scenario when the recognizer and
    synthesizer engines are not part of the same session. Here when a
    kill-on-barge-in prompt is being played, you want the RECOGNIZE
    request to be simultaneously active so that it can detect and
    implement kill-on-barge-in. But at the same time you don't want the
    recognizer to start the no-input timers until the prompt is
    finished. The default value is "true".
 
      recognizer-start-timers  =    "Recognizer-Start-Timers" ":"
                                    boolean-value CRLF
 
 Vendor Specific Parameters
 
    This set of headers allows the client to set Vendor Specific
    parameters.
 
      vendor-specific     =    "Vendor-Specific-Parameters" ":"
                               vendor-specific-av-pair
                               *[";" vendor-specific-av-pair] CRLF
      vendor-specific-av-pair= vendor-av-pair-name "="
                               vendor-av-pair-value
 
    This header can be sent in the SET-PARAMS method and is used to set
    vendor-specific parameters on the server. The vendor-av-pair-name
    can be any vendor-specific field name and conforms to the XML
    vendor-specific attribute naming convention. The vendor-av-pair-
    value is the value to set the attribute to, and needs to be quoted.
 
    When asking the server to get the current value of these parameters,
    this header can be sent in the GET-PARAMS method with the list of
    vendor-specific attribute names to get separated by a semicolon.
    This header field MAY occur in SET-PARAMS or GET-PARAMS.
 
 Speech Complete Timeout
 
    This header field specifies the length of silence required following
    user speech before the speech recognizer finalizes a result (either
    accepting it or throwing a nomatch event). The speech-complete-
    timeout value is used when the recognizer currently has a complete
    match of an active grammar, and specifies how long it should wait
    for more input declaring a match.  By contrast, the incomplete
    timeout is used when the speech is an incomplete match to an active
    grammar. The value is in milliseconds.
 
      speech-complete-timeout= "Speech-Complete-Timeout" ":"
                               1*DIGIT CRLF
 
    A long speech-complete-timeout value delays the result completion
    and therefore makes the computer's response slow. A short speech-
    complete-timeout may lead to an utterance being broken up
    inappropriately. Reasonable complete timeout values are typically in
 
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    the range of 0.3 seconds to 1.0 seconds.  The value for this field
    ranges from 0 to MAXTIMEOUT, where MAXTIMEOUT is platform specific.
    The default value for this field is platform specific. This header
    field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS.
 
 Speech Incomplete Timeout
 
    This header field specifies the required length of silence following
    user speech after which a recognizer finalizes a result.  The
    incomplete timeout applies when the speech prior to the silence is
    an incomplete match of all active grammars.  In this case, once the
    timeout is triggered, the partial result is rejected (with a nomatch
    event). The value is in milliseconds. The value for this field
    ranges from 0 to MAXTIMEOUT, where MAXTIMEOUT is platform specific.
    The default value for this field is platform specific.
 
      speech-incomplete-timeout= "Speech-Incomplete-Timeout" ":"
                               1*DIGIT CRLF
 
    The speech-incomplete-timeout also applies when the speech prior to
    the silence is a complete match of an active grammar, but where it
    is possible to speak further and still match the grammar.  By
    contrast, the complete timeout is used when the speech is a complete
    match to an active grammar and no further words can be spoken.
 
    A long speech-incomplete-timeout value delays the result completion
    and therefore makes the computer's response slow. A short speech-
    incomplete-timeout may lead to an utterance being broken up
    inappropriately.
 
    The speech-incomplete-timeout is usually longer than the speech-
    complete-timeout to allow users to pause mid-utterance (for example,
    to breathe). This header field MAY occur in RECOGNIZE, SET-PARAMS or
    GET-PARAMS.
 
 DTMF Interdigit Timeout
 
    This header field specifies the inter-digit timeout value to use
    when recognizing DTMF input. The value is in milliseconds.  The
    value for this field ranges from 0 to MAXTIMEOUT, where MAXTIMEOUT
    is platform specific. The default value is 5 seconds. This header
    field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS.
 
      dtmf-interdigit-timeout= "DTMF-Interdigit-Timeout" ":"
                               1*DIGIT CRLF
 
 DTMF Term Timeout
 
    This header field specifies the terminating timeout to use when
    recognizing DTMF input. The value is in milliseconds. The value for
    this field ranges from 0 to MAXTIMEOUT, where MAXTIMEOUT is platform
 
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    specific. The default value is 10 seconds. This header field MAY
    occur in RECOGNIZE, SET-PARAMS or GET-PARAMS.
 
      dtmf-term-timeout   =    "DTMF-Term-Timeout" ":" 1*DIGIT CRLF
 
 DTMF-Term-Char
 
    This header field specifies the terminating DTMF character for DTMF
    input recognition. The default value is NULL which is specified as
    an empty header field. This header field MAY occur in RECOGNIZE,
    SET-PARAMS or GET-PARAMS.
 
      dtmf-term-char      =    "DTMF-Term-Char" ":" CHAR CRLF
 
 Fetch Timeout
 
    When the recognizer needs to fetch grammar documents this header
    field controls URI access properties. This defines the recognizer
    timeout for completing the fetch of the resources the media server
    needs from the network. The value is in milliseconds.  The value for
    this field ranges from 0 to MAXTIMEOUT, where MAXTIMEOUT is platform
    specific. The default value for this field is platform specific.
    This header field MAY occur in RECOGNIZE, SET-PARAMS or GET-PARAMS.
 
      fetch-timeout       =    "Fetch-Timeout" ":" 1*ALPHA CRLF
 
 Failed URI
 
    When a recognizer method needs a recognizer to fetch or access a URI
    and the access fails the media server SHOULD provide the failed URI
    in this header field in the method response.
 
      failed-uri               =    "Failed-URI" ":" Url CRLF
 
 Failed URI Cause
 
    When a recognizer method needs a recognizer to fetch or access a URI
    and the access fails the media server SHOULD provide the URI
    specific or protocol specific response code through this header
    field in the method response. This field has been defined as
    alphanumeric to accommodate all protocols, some of which might have
    a response string instead of a numeric response code.
 
      failed-uri-cause         =    "Failed-URI-Cause" ":" 1*ALPHA CRLF
 
 Save Waveform
 
    This header field allows the client to indicate to the recognizer
    that it MUST save the audio stream that was recognized. The
    recognizer MUST then record the recognized audio and make it
    available to the client in the form of a URI returned in the
 
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    waveform-uri header field in the RECOGNITION-COMPLETE event. If
    there was an error in recording the stream or the audio clip is
    otherwise not available, the recognizer MUST return an empty
    waveform-uri header field. The default value for this fields is
    "false".
 
      save-waveform       =    "Save-Waveform" ":" boolean-value CRLF
 
 New Audio Channel
 
    This header field MAY BE specified in a RECOGNIZE message and allows
    the client to tell the media server that, from that point on, it
    will be sending audio data from a new audio source, channel or
    speaker. If the recognition resource had collected any line
    statistics or information, it MUST discard it and start fresh for
    this RECOGNIZE. This helps in the case where the client MAY want to
    reuse an open recognition session with the media server for multiple
    telephone calls.
 
      new-audio-channel   =    "New-Audio-Channel" ":" boolean-value
                               CRLF
 
 Speech Language
 
    This header field specifies the language of recognition grammar data
    within a session or request, if it is not specified within the data.
    The value of this header field should follow RFC 1766 for its
    values. This MAY occur in DEFINE-GRAMMAR, RECOGNIZE, SET-PARAMS or
    GET-PARAMS request.
 
      speech-language          =    "Speech-Language" ":" 1*ALPHA CRLF
 
 
 8.5. Recognizer Message Body
 
    A recognizer message may carry additional data associated with the
    method, response or event. The client may send the grammar to be
    recognized in DEFINE-GRAMMAR or RECOGNIZE requests. When the grammar
    is sent in the DEFINE-GRAMMAR method, the server should be able to
    download compile and optimize the grammar. The RECOGNIZE request
    MUST contain a list of grammars that need to be active during the
    recognition. The server resource may send the recognition results in
    the RECOGNITION-COMPLETE event or the GET-RESULT response. This data
    will be carried in the message body of the corresponding MRCPv2
    message.
 
 Recognizer Grammar Data
 
    Recognizer grammar data from the client to the server can be
    provided inline or by reference. Either way they are carried as MIME
    entities in the message body of the MRCPv2 request message. The
 
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    grammar specified inline or by reference specifies the grammar used
    to match in the recognition process and this data is specified in
    one of the standard grammar specification formats like W3C's XML or
    ABNF or Sun's Java Speech Grammar Format etc.  All media servers
    MUST support W3C's XML based grammar markup format [12](MIME-type
    application/grammar+xml) and SHOULD support the ABNF form (MIME-type
    application/grammar).
 
    When a grammar is specified in-line in the message, the client MUST
    provide a content-id for that grammar as part of the content
    headers. The server MUST store the grammar associated with that
    content-id for the duration of the session. A stored grammar can be
    overwritten by defining a new grammar with the same content-id.
    Grammars that have been associated with a content-id can be
    referenced through a special "session:" URI scheme.
 
    Example:
      session:help@root-level.store
 
    If grammar data needs to be specified by external URI reference, the
    MIME-type text/uri-list is used to list the one or more URI that
    will specify the grammar data. All media servers MUST support the
    HTTP uri access mechanism.
 
    If the data to be defined consists of a mix of URI and inline
    grammar data the multipart/mixed MIME-type is used and embedded with
    the MIME-blocks for text/uri-list, application/grammar or
    application/grammar+xml. The character set and encoding used in the
    grammar data may be specified according to standard MIME-type
    definitions.
 
    When more than one grammar URI or inline grammar block is specified
    in a message body of the RECOGNIZE request, it is an active list of
    grammar alternatives to listen.  The ordering of the list implies
    the precedence of the grammars, with the first grammar in the list
    having the highest precedence.
 
    Example 1:
         Content-Type: application/grammar+xml
         Content-Id: request1@form-level.store
         Content-Length: 104
 
         <?xml version="1.0"?>
 
         <!-- the default grammar language is US English -->
         <grammar xml:lang="en-US" version="1.0">
 
         <!-- single language attachment to tokens -->
         <rule id="yes">
                    <one-of>
                        <item xml:lang="fr-CA">oui</item>
 
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                            MRCPv2 Protocol               January 2004
 
                        <item xml:lang="en-US">yes</item>
                    </one-of>
            </rule>
 
         <!-- single language attachment to a rule expansion -->
            <rule id="request">
                    may I speak to
                    <one-of xml:lang="fr-CA">
                        <item>Michel Tremblay</item>
                        <item>Andre Roy</item>
                    </one-of>
            </rule>
 
            <!-- multiple language attachment to a token -->
            <rule id="people1">
                    <token lexicon="en-US,fr-CA"> Robert </token>
            </rule>
 
            <!-- the equivalent single-language attachment expansion -->
            <rule id="people2">
                    <one-of>
                        <item xml:lang="en-US">Robert</item>
                        <item xml:lang="fr-CA">Robert</item>
                    </one-of>
            </rule>
 
            </grammar>
 
    Example 2:
        Content-Type: text/uri-list
        Content-Length: 176
 
        session:help@root-level.store
        http://www.example.com/Directory-Name-List.grxml
        http://www.example.com/Department-List.grxml
        http://www.example.com/TAC-Contact-List.grxml
        session:menu1@menu-level.store
 
    Example 3:
        Content-Type: multipart/mixed; boundary="--break"
 
        --break
        Content-Type: text/uri-list
        Content-Length: 176
        http://www.example.com/Directory-Name-List.grxml
        http://www.example.com/Department-List.grxml
        http://www.example.com/TAC-Contact-List.grxml
 
        --break
        Content-Type: application/grammar+xml
        Content-Id: request1@form-level.store
 
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                            MRCPv2 Protocol               January 2004
 
        Content-Length: 104
 
        <?xml version="1.0"?>
 
        <!-- the default grammar language is US English -->
        <grammar xml:lang="en-US" version="1.0">
 
        <!-- single language attachment to tokens -->
        <rule id="yes">
                    <one-of>
                        <item xml:lang="fr-CA">oui</item>
                        <item xml:lang="en-US">yes</item>
                    </one-of>
           </rule>
 
        <!-- single language attachment to a rule expansion -->
           <rule id="request">
                    may I speak to
                    <one-of xml:lang="fr-CA">
                        <item>Michel Tremblay</item>
                        <item>Andre Roy</item>
                    </one-of>
           </rule>
 
           <!-- multiple language attachment to a token -->
           <rule id="people1">
                    <token lexicon="en-US,fr-CA"> Robert </token>
           </rule>
 
           <!-- the equivalent single-language attachment expansion -->
           <rule id="people2">
                    <one-of>
                        <item xml:lang="en-US">Robert</item>
                        <item xml:lang="fr-CA">Robert</item>
                    </one-of>
           </rule>
 
           </grammar>
         --break
 
 Recognizer Result Data
 
    Recognition result data from the server is carried in the MRCPv2
    message body of the RECOGNITION-COMPLETE event or the GET-RESULT
    response message as MIME entities. All media servers MUST support
    W3C's Natural Language Semantics Markup Language (NLSML)[11] as the
    default standard for returning recognition results back to the
    client, and hence MUST support the MIME-type application/x-nlsml.
 
    Example 1:
        Content-Type: application/x-nlsml
 
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                            MRCPv2 Protocol               January 2004
 
        Content-Length: 104
 
        <?xml version="1.0"?>
        <result grammar="http://theYesNoGrammar>
            <interpretation>
                <instance>
                    <myApp:yes_no>
                        <response>yes</response>
                    </myApp:yes_no>
                </instance>
                <input>ok</input>
            </interpretation>
        </result>
 
 
 Recognizer Context Block
 
    When the client has to change recognition servers within a call,
    this is a block of data that the client MAY collect from the first
    media server and provide to the second media server. This may be
    because the client needs a different language support or because the
    media server issued a redirect. Here the first recognizer may have
    collected acoustic and other data during its recognition. When we
    switch recognition servers, communicating this data may allow the
    second recognition server to provide better recognition based on the
    acoustic data collected by the previous recognizer. This block of
    data is vendor-specific and MUST be carried as MIME-type
    application/octets in the body of the message.
 
    This block of data is communicated in the SET-PARAMS and GET-PARAMS
    method/response messages. In the GET-PARAMS method, if an empty
    recognizer-context-block header field is present, then the
    recognizer should return its vendor-specific context block in the
    message body as a MIME-entity with a specific content-id.  The
    content-id value should also be specified in the recognizer-context-
    block header field in the GET-PARAMS response.  The SET-PARAMS
    request wishing to provide this vendor-specific data should send it
    in the message body as a MIME-entity with the same content-id that
    it received from the GET-PARAMS.  The content-id should also be sent
    in the recognizer-context-block header field of the SET-PARAMS
    message.
 
    Each automatic speech recognition (ASR) vendor choosing to use this
    mechanism to handoff recognizer context data among its servers
    should distinguish its vendor-specific block of data from other
    vendors by choosing a unique content-id that they should recognize.
 
 8.6. SET-PARAMS
 
    The SET-PARAMS method, from the client to the server, tells the
    recognizer resource to set and modify recognizer context parameters
 
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                            MRCPv2 Protocol               January 2004
 
    like recognizer characteristics, result detail level, etc. In the
    following sections some standard parameters are discussed.   If the
    server resource does not recognize an OPTIONAL parameter it MUST
    ignore that field. Many of the parameters in the SET-PARAMS method
    can also be used in another method like the RECOGNIZE method. But
    the difference is that when you set something like the sensitivity-
    level using the SET-PARAMS it applies for all future requests,
    whenever applicable. On the other hand, when you pass sensitivity-
    level in a RECOGNIZE request it applies only to that request.
 
    Example:
      C->S:MRCP/2.0 123 SET-PARAMS 543256
           Channel-Identifier: 32AECB23433801@speechrecog
           Sensitivity-Level: 20
           Recognition-Timeout: 30
           Confidence-Threshold: 85
 
      S->C:MRCP/2.0 48 543256 200 COMPLETE
           Channel-Identifier: 32AECB23433801@speechrecog
 
 8.7. GET-PARAMS
 
    The GET-PARAMS method, from the client to the server, asks the
    recognizer resource for its current default parameters, like
    sensitivity-level, n-best-list-length etc. The client can request
    specific parameters from the server by sending it one or more empty
    parameter headers with no values. The server should then return the
    settings for those specific parameters only. When the client does
    not send a specific list of empty parameter headers, the recognizer
    should return the settings for all parameters. The wild card use can
    be very intensive as the number of settable parameters can be large
    depending on the vendor.  Hence it is RECOMMENDED that the client
    does not use the wildcard GET-PARAMS operation very often.
 
    Example:
      C->S:MRCP/2.0 112 GET-PARAMS 543256
           Channel-Identifier: 32AECB23433801@speechrecog
           Sensitivity-Level:
           Recognition-Timeout:
           Confidence-threshold:
 
 
      S->C:MRCP/2.0 136 543256 200 COMPLETE
           Channel-Identifier: 32AECB23433801@speechrecog
           Sensitivity-Level: 20
           Recognition-Timeout: 30
           Confidence-Threshold: 85
 
 8.8. DEFINE-GRAMMAR
 
 
 
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                            MRCPv2 Protocol               January 2004
 
    The DEFINE-GRAMMAR method, from the client to the server, provides a
    grammar and tells the server to define, download if needed and
    compile the grammar.
 
    If the server resource is in the recognition state, the DEFINE-
    GRAMMAR request MUST respond with a failure status.
 
    If the resource is in the idle state and is able to successfully
    load and compile the grammar the status MUST return a success code
    and the request-state MUST be COMPLETE.
 
    If the recognizer could not define the grammar for some reason, say
    the download failed or the grammar failed to compile, or the grammar
    was in an unsupported form, the MRCPv2 response for the DEFINE-
    GRAMMAR method MUST contain a failure status code of 407, and a
    completion-cause header field describing the failure reason.
 
    Example:
      C->S:MRCP/2.0 589 DEFINE-GRAMMAR 543257
           Channel-Identifier: 32AECB23433801@speechrecog
           Content-Type: application/grammar+xml
           Content-Id: request1@form-level.store
           Content-Length: 104
 
           <?xml version="1.0"?>
 
           <!-- the default grammar language is US English -->
           <grammar xml:lang="en-US" version="1.0">
 
           <!-- single language attachment to tokens -->
           <rule id="yes">
               <one-of>
                   <item xml:lang="fr-CA">oui</item>
                   <item xml:lang="en-US">yes</item>
               </one-of>
           </rule>
 
           <!-- single language attachment to a rule expansion -->
           <rule id="request">
               may I speak to
               <one-of xml:lang="fr-CA">
                   <item>Michel Tremblay</item>
                   <item>Andre Roy</item>
               </one-of>
           </rule>
 
           </grammar>
 
      S->C:MRCP/2.0 73 543257 200 COMPLETE
           Channel-Identifier: 32AECB23433801@speechrecog
           Completion-Cause: 000 success
 
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                            MRCPv2 Protocol               January 2004
 
 
 
      C->S:MRCP/2.0 334 DEFINE-GRAMMAR 543258
           Channel-Identifier: 32AECB23433801@speechrecog
           Content-Type: application/grammar+xml
           Content-Id: helpgrammar@root-level.store
           Content-Length: 104
 
           <?xml version="1.0"?>
 
           <!-- the default grammar language is US English -->
           <grammar xml:lang="en-US" version="1.0">
 
           <rule id="request">
               I need help
           </rule>
 
      S->C:MRCP/2.0 73 543258 200 COMPLETE
           Channel-Identifier: 32AECB23433801@speechrecog
           Completion-Cause: 000 success
 
      C->S:MRCP/2.0 723 DEFINE-GRAMMAR 543259
           Channel-Identifier: 32AECB23433801@speechrecog
           Content-Type: application/grammar+xml
           Content-Id: request2@field-level.store
           Content-Length: 104
 
           <?xml version="1.0"?>
 
                <grammar xml:lang="en">
 
                <import uri="session:politeness@form-level.store"
                        name="polite"/>
 
                <rule id="basicCmd" scope="public">
                <example> please move the window </example>
                <example> open a file </example>
 
                <ruleref import="polite#startPolite"/>
                <ruleref uri="#command"/>
                <ruleref import="polite#endPolite"/>
                </rule>
 
                <rule id="command">
                <ruleref uri="#action"/> <ruleref uri="#object"/>
                </rule>
 
                <rule id="action">
                     <choice>
                     <item weight="10" tag="OPEN">   open </item>
                     <item weight="2"  tag="CLOSE">  close </item>
 
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                            MRCPv2 Protocol               January 2004
 
                     <item weight="1"  tag="DELETE"> delete </item>
                     <item weight="1"  tag="MOVE">   move </item>
                     </choice>
                </rule>
 
                <rule id="object">
                <count number="optional">
                     <choice>
                          <item> the </item>
                          <item> a </item>
                     </choice>
                </count>
                <choice>
                     <item> window </item>
                     <item> file </item>
                     <item> menu </item>
                </choice>
                </rule>
 
                </grammar>
 
      S->C:MRCP/2.0 69 543259 200 COMPLETE
           Channel-Identifier: 32AECB23433801@speechrecog
           Completion-Cause: 000 success
 
      C->S:MRCP/2.0 155 RECOGNIZE 543260
           Channel-Identifier: 32AECB23433801@speechrecog
           N-Best-List-Length: 2
           Content-Type: text/uri-list
           Content-Length: 176
 
           session:request1@form-level.store
           session:request2@field-level.store
           session:helpgramar@root-level.store
 
      S->C:MRCP/2.0 48 543260 200 IN-PROGRESS
           Channel-Identifier: 32AECB23433801@speechrecog
 
      S->C:MRCP/2.0 48 START-OF-SPEECH 543260 IN-PROGRESS
           Channel-Identifier: 32AECB23433801@speechrecog
 
      S->C:MRCP/2.0 486 RECOGNITION-COMPLETE 543260 COMPLETE
           Channel-Identifier: 32AECB23433801@speechrecog
           Completion-Cause: 000 success
           Waveform-URL: http://web.media.com/session123/audio.wav
           Content-Type: applicationt/x-nlsml
           Content-Length: 276
 
           <?xml version="1.0"?>
           <result x-model="http://IdentityModel"
             xmlns:xf="http://www.w3.org/2000/xforms"
 
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                            MRCPv2 Protocol               January 2004
 
             grammar="session:request1@form-level.store>
                <interpretation>
                     <xf:instance name="Person">
                       <Person>
                           <Name> Andre Roy </Name>
                       </Person>
                     </xf:instance>
                     <input>   may I speak to Andre Roy </input>
                </interpretation>
           </result>
 
 8.9. RECOGNIZE
 
    The RECOGNIZE method from the client to the server tells the
    recognizer to start recognition and provides it with a grammar to
    match for. The RECOGNIZE method can carry parameters to control the
    sensitivity, confidence level and the level of detail in results
    provided by the recognizer. These parameters override the current
    defaults set by a previous SET-PARAMS method.
 
    If the resource is in the recognition state, the RECOGNIZE request
    MUST respond with a failure status.
    If the resource is in the Idle state and was able to successfully
    start the recognition, the server MUST return a success code and a
    request-state of IN-PROGRESS. This means that the recognizer is
    active and that the client should expect further events with this
    request-id.
 
    If the resource could not start a recognition, it MUST return a
    failure status code of 407 and contain a completion-cause header
    field describing the cause of failure.
 
    For the recognizer resource, this is the only request that can
    return request-state of IN-PROGRESS, meaning that recognition is in
    progress. When the recognition completes by matching one of the
    grammar alternatives or by a time-out without a match or for some
    other reason, the recognizer resource MUST send the client a
    RECOGNITON-COMPLETE event with the result of the recognition and a
    request-state of COMPLETE.
 
    For large grammars that can take a long time to compile and for
    grammars which are used repeatedly, the client could issue a DEFINE-
    GRAMMAR request with the grammar ahead of time. In such a case the
    client can issue the RECOGNIZE request and reference the grammar
    through the "session:" special URI. This also applies in general if
    the client wants to restart recognition with a previous inline
    grammar.
 
    Note that since the audio and the messages are carried over separate
    communication paths there may be a race condition between the start
    of the flow of audio and the receipt of the RECOGNIZE method. For
 
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                            MRCPv2 Protocol               January 2004
 
    example, if audio flow is started by the client at the same time as
    the RECOGNIZE method is sent, either the audio or the RECOGNIZE will
    arrive at the recognizer first. As another example, the client may
    chose to continuously send audio to the Media server and signal the
    Media server to recognize using the RECOGNIZE method.  A number of
    mechanisms exist to resolve this condition and the mechanism chosen
    is left to the implementers of recognizer Media servers. The
    recognizer should expect the media to start flowing when it receives
    the recognize request, and shouldn't buffer anything it receives
    beforehand.
 
 
    Example:
      C->S:MRCP/2.0 479 RECOGNIZE 543257
           Channel-Identifier: 32AECB23433801@speechrecog
           Confidence-Threshold: 90
           Content-Type: application/grammar+xml
           Content-Id: request1@form-level.store
           Content-Length: 104
 
           <?xml version="1.0"?>
 
           <!-- the default grammar language is US English -->
           <grammar xml:lang="en-US" version="1.0">
 
           <!-- single language attachment to tokens -->
           <rule id="yes">
                    <one-of>
                             <item xml:lang="fr-CA">oui</item>
                             <item xml:lang="en-US">yes</item>
                    </one-of>
                </rule>
 
           <!-- single language attachment to a rule expansion -->
                <rule id="request">
                    may I speak to
                    <one-of xml:lang="fr-CA">
                             <item>Michel Tremblay</item>
                             <item>Andre Roy</item>
                    </one-of>
                </rule>
 
             </grammar>
 
      S->C:MRCP/2.0 48 543257 200 IN-PROGRESS
           Channel-Identifier: 32AECB23433801@speechrecog
 
      S->C:MRCP/2.0 49 START-OF-SPEECH 543257 IN-PROGRESS
           Channel-Identifier: 32AECB23433801@speechrecog
 
      S->C:MRCP/2.0 467 RECOGNITION-COMPLETE 543257 COMPLETE
 
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                            MRCPv2 Protocol               January 2004
 
           Channel-Identifier: 32AECB23433801@speechrecog
           Completion-Cause: 000 success
           Waveform-URL: http://web.media.com/session123/audio.wav
           Content-Type: application/x-nlsml
           Content-Length: 276
 
           <?xml version="1.0"?>
           <result x-model="http://IdentityModel"
             xmlns:xf="http://www.w3.org/2000/xforms"
             grammar="session:request1@form-level.store>
               <interpretation>
                   <xf:instance name="Person">
                       <Person>
                           <Name> Andre Roy </Name>
                       </Person>
                   </xf:instance>
                     <input>   may I speak to Andre Roy </input>
               </interpretation>
           </result>
 
 8.10.     STOP
 
    The STOP method from the client to the server tells the resource to
    stop recognition if one is active. If a RECOGNIZE request is active
    and the STOP request successfully terminated it, then the response
    header contains an active-request-id-list header field containing
    the request-id of the RECOGNIZE request that was terminated. In this
    case, no RECOGNITION-COMPLETE event will be sent for the terminated
    request. If there was no recognition active, then the response MUST
    NOT contain an active-request-id-list header field. Either way the
    response MUST contain a status of 200(Success).
 
    Example:
      C->S:MRCP/2.0 573 RECOGNIZE 543257
           Channel-Identifier: 32AECB23433801@speechrecog
           Confidence-Threshold: 90
           Content-Type: application/grammar+xml
           Content-Id: request1@form-level.store
           Content-Length: 104
 
           <?xml version="1.0"?>
 
           <!-- the default grammar language is US English -->
           <grammar xml:lang="en-US" version="1.0">
 
           <!-- single language attachment to tokens -->
           <rule id="yes">
                    <one-of>
                             <item xml:lang="fr-CA">oui</item>
                             <item xml:lang="en-US">yes</item>
                    </one-of>
 
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                            MRCPv2 Protocol               January 2004
 
                </rule>
 
           <!-- single language attachment to a rule expansion -->
                <rule id="request">
                    may I speak to
                    <one-of xml:lang="fr-CA">
                             <item>Michel Tremblay</item>
                             <item>Andre Roy</item>
                    </one-of>
                </rule>
 
           </grammar>
 
      S->C:MRCP/2.0 47 543257 200 IN-PROGRESS
           Channel-Identifier: 32AECB23433801@speechrecog
 
      C->S:MRCP/2.0 28 STOP 543258 200
           Channel-Identifier: 32AECB23433801@speechrecog
 
      S->C:MRCP/2.0 67 543258 200 COMPLETE
           Channel-Identifier: 32AECB23433801@speechrecog
           Active-Request-Id-List: 543257
 
 8.11.     GET-RESULT
 
    The GET-RESULT method from the client to the server can be issued
    when the recognizer is in the recognized state. This request allows
    the client to retrieve results for a completed recognition.  This is
    useful if the client decides it wants more alternatives or more
    information. When the media server receives this request it should
    re-compute and return the results according to the recognition
    constraints provided in the GET-RESULT request.
 
    The GET-RESULT request could specify constraints like a different
    confidence-threshold, or n-best-list-length. This feature is
    optional and the automatic speech recognition (ASR) engine may
    return a status of unsupported feature.
 
    Example:
      C->S:MRCP/2.0 73 GET-RESULT 543257
           Channel-Identifier: 32AECB23433801@speechrecog
           Confidence-Threshold: 90
 
 
      S->C:MRCP/2.0 487 543257 200 COMPLETE
           Channel-Identifier: 32AECB23433801@speechrecog
           Content-Type: application/x-nlsml
           Content-Length: 276
 
           <?xml version="1.0"?>
           <result x-model="http://IdentityModel"
 
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                            MRCPv2 Protocol               January 2004
 
             xmlns:xf="http://www.w3.org/2000/xforms"
             grammar="session:request1@form-level.store>
               <interpretation>
                   <xf:instance name="Person">
                       <Person>
                           <Name> Andre Roy </Name>
                       </Person>
                   </xf:instance>
                             <input>   may I speak to Andre Roy </input>
               </interpretation>
           </result>
 
 8.12.     START-OF-SPEECH
 
    This is an event from the recognizer to the client indicating that
    it has detected speech or a DTMF digit. This event is useful in
    implementing kill-on-barge-in scenarios when the synthesizer
    resource is in a different session than the recognizer resource and
    hence is not aware of an incoming audio source. In these cases, it
    is up to the client to act as a proxy and turn around and issue the
    BARGE-IN-OCCURRED method to the synthesizer resource. The recognizer
    resource also sends a unique proxy-sync-id in the header for this
    event, which is sent to the synthesizer in the BARGE-IN-OCCURRED
    method to the synthesizer.
 
    This event should be generated irrespective of whether the
    synthesizer and recognizer are in the same media server or not.
 
 8.13.     RECOGNITION-START-TIMERS
 
    This request is sent from the client to the recognition resource
    when it knows that a kill-on-barge-in prompt has finished playing.
    This is useful in the scenario when the recognition and synthesizer
    engines are not in the same session. Here when a kill-on-barge-in
    prompt is being played, you want the RECOGNIZE request to be
    simultaneously active so that it can detect and implement kill on
    barge-in. But at the same time you don't want the recognizer to
    start the no-input timers until the prompt is finished. The
    parameter recognizer-start-timers header field in the RECOGNIZE
    request will allow the client to say if the timers should be started
    or not. The recognizer should not start the timers until the client
    sends a RECOGNITION-START-TIMERS method to the recognizer.
 
 8.14.     RECOGNITON-COMPLETE
 
    This is an Event from the recognizer resource to the client
    indicating that the recognition completed. The recognition result is
    sent in the MRCPv2 body of the message. The request-state field MUST
    be COMPLETE indicating that this is the last event with that
    request-id, and that the request with that request-id is now
    complete. The recognizer context still holds the results and the
 
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                            MRCPv2 Protocol               January 2004
 
    audio waveform input of that recognition till the next RECOGNIZE
    request is issued. A URL to the audio waveform MAY BE returned to
    the client in a waveform-url header field in the RECOGNITION-
    COMPLETE event. The client can use this URI to retrieve or playback
    the audio.
 
    Example:
      C->S:MRCP/2.0 487 RECOGNIZE 543257
           Channel-Identifier: 32AECB23433801@speechrecog
           Confidence-Threshold: 90
           Content-Type: application/grammar+xml
           Content-Id: request1@form-level.store
           Content-Length: 104
 
           <?xml version="1.0"?>
 
           <!-- the default grammar language is US English -->
           <grammar xml:lang="en-US" version="1.0">
 
           <!-- single language attachment to tokens -->
           <rule id="yes">
                    <one-of>
                             <item xml:lang="fr-CA">oui</item>
                             <item xml:lang="en-US">yes</item>
                    </one-of>
                </rule>
 
           <!-- single language attachment to a rule expansion -->
                <rule id="request">
                    may I speak to
                    <one-of xml:lang="fr-CA">
                             <item>Michel Tremblay</item>
                             <item>Andre Roy</item>
                    </one-of>
                </rule>
 
           </grammar>
 
      S->C:MRCP/2.0 48 543257 200 IN-PROGRESS
           Channel-Identifier: 32AECB23433801@speechrecog
 
      S->C:MRCP/2.0 49 START-OF-SPEECH 543257 IN-PROGRESS
           Channel-Identifier: 32AECB23433801@speechrecog
 
      S->C:MRCP/2.0 465 RECOGNITION-COMPLETE 543257 COMPLETE
           Channel-Identifier: 32AECB23433801@speechrecog
           Completion-Cause: 000 success
           Waveform-URL: http://web.media.com/session123/audio.wav
           Content-Type: application/x-nlsml
           Content-Length: 276
 
 
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                            MRCPv2 Protocol               January 2004
 
           <?xml version="1.0"?>
           <result x-model="http://IdentityModel"
             xmlns:xf="http://www.w3.org/2000/xforms"
             grammar="session:request1@form-level.store>
               <interpretation>
                   <xf:instance name="Person">
                       <Person>
                           <Name> Andre Roy </Name>
                       </Person>
                   </xf:instance>
                             <input>   may I speak to Andre Roy </input>
               </interpretation>
           </result>
 
 
 8.15.     DTMF Detection
 
    Digits received as DTMF tones will be delivered to the automatic
    speech recognition (ASR) engine in the RTP stream according to RFC
    2833. The automatic speech recognizer (ASR) needs to support RFC
    2833 to recognize digits. If it does not support RFC 2833, it will
    have to process the audio stream and extract the audio tones from
    it.
 
 9.   Examples:
 
    The following is an example of a typical MRCPv2 session of speech
    synthesis and recognition between a client and a server.
 
    Opening a session to the MRCPv2 server. This is exchange does not
    allocate a resource or setup media. It simply establishes a SIP
    session with the MRCPv2 server.
 
    C->S:
           INVITE sip:mresources@mediaserver.com SIP/2.0
           Max-Forwards: 70
           To: MediaServer <sip:mresources@mediaserver.com>
           From: sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314159 INVITE
           Contact: <sip: sarvi@cisco.com>
           Content-Type: application/sdp
           Content-Length: 142
 
           v=0
           o=sarvi 2890844526 2890842807 IN IP4 126.16.64.4
           s=SDP Seminar
           i=A session for processing media
           c=IN IP4 224.2.17.12/127
 
    S->C:
 
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                            MRCPv2 Protocol               January 2004
 
           SIP/2.0 200 OK
           To: MediaServer <sip:mresources@mediaserver.com>
           From: sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314159 INVITE
           Contact: <sip: sarvi@cisco.com>
           Content-Type: application/sdp
           Content-Length: 131
 
           v=0
           o=sarvi 2890844526 2890842807 IN IP4 126.16.64.4
           s=SDP Seminar
           i=A session for processing media
           c=IN IP4 224.2.17.12/127
 
    C->S:
           ACK sip:mrcp@mediaserver.com SIP/2.0
           Max-Forwards: 70
           To: MediaServer <sip:mrcp@mediaserver.com>;tag=a6c85cf
           From: Sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314160 ACK
           Content-Length: 0
 
    The client requests the server to create synthesizer resource
    control channel to do speech synthesis. This also adds a media pipe
    to send the generated speech.
 
    C->S:
           INVITE sip:mresources@mediaserver.com SIP/2.0
           Max-Forwards: 70
           To: MediaServer <sip:mresources@mediaserver.com>
           From: sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314161 INVITE
           Contact: <sip: sarvi@cisco.com>
           Content-Type: application/sdp
           Content-Length: 142
 
           v=0
           o=sarvi 2890844526 2890842808 IN IP4 126.16.64.4
           s=SDP Seminar
           i=A session for processing media
           c=IN IP4 224.2.17.12/127
           m=control 9 SCTP application/mrcpv2
           a=resource:speechsynth
           a=cmid:1
           m=audio 49170 RTP/AVP 0 96
           a=rtpmap:0 pcmu/8000
           a=recvonly
           a=mid:1
 
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                            MRCPv2 Protocol               January 2004
 
 
 
    S->C:
           SIP/2.0 200 OK
           To: MediaServer <sip:mresources@mediaserver.com>
           From: sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314161 INVITE
           Contact: <sip: sarvi@cisco.com>
           Content-Type: application/sdp
           Content-Length: 131
 
           v=0
           o=sarvi 2890844526 2890842808 IN IP4 126.16.64.4
           s=SDP Seminar
           i=A session for processing media
           c=IN IP4 224.2.17.12/127
           m=control 32416 SCTP application/mrcpv2
           a=channel:32AECB23433802@speechsynth
           a=cmid:1
           m=audio 48260 RTP/AVP 0
           a=rtpmap:0 pcmu/8000
           a=sendonly
           a=mid:1
 
    C->S:
           ACK sip:mrcp@mediaserver.com SIP/2.0
           Max-Forwards: 70
           To: MediaServer <sip:mrcp@mediaserver.com>;tag=a6c85cf
           From: Sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314162 ACK
           Content-Length: 0
 
    This exchange allocates an additional resource control channel for a
    recognizer. Since a recognizer would need to receive an audio stream
    for recognition, this interaction also updates the audio stream to
    sendrecv making it a 2-way audio stream.
 
    C->S:
           INVITE sip:mresources@mediaserver.com SIP/2.0
           Max-Forwards: 70
           To: MediaServer <sip:mresources@mediaserver.com>
           From: sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314163 INVITE
           Contact: <sip: sarvi@cisco.com>
           Content-Type: application/sdp
           Content-Length: 142
 
           v=0
 
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                            MRCPv2 Protocol               January 2004
 
           o=sarvi 2890844526 2890842809 IN IP4 126.16.64.4
           s=SDP Seminar
           i=A session for processing media
           c=IN IP4 224.2.17.12/127
           m=control 9 SCTP application/mrcpv2
           a=resource:speechsynth
           a=cmid:1
           m=audio 49170 RTP/AVP 0 96
           a=rtpmap:0 pcmu/8000
           a=recvonly
           a=mid:1
           m=control 9 SCTP application/mrcpv2
           a=resource:speechrecog
           a=cmid:2
           m=audio 49180 RTP/AVP 0 96
           a=rtpmap:0 pcmu/8000
           a=rtpmap:96 telephone-event/8000
           a=fmtp:96 0-15
           a=sendonly
           a=mid:2
 
 
    S->C:
           SIP/2.0 200 OK
           To: MediaServer <sip:mresources@mediaserver.com>
           From: sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314163 INVITE
           Contact: <sip: sarvi@cisco.com>
           Content-Type: application/sdp
           Content-Length: 131
 
           v=0
           o=sarvi 2890844526 2890842809 IN IP4 126.16.64.4
           s=SDP Seminar
           i=A session for processing media
           c=IN IP4 224.2.17.12/127
           m=control 32416 SCTP application/mrcpv2
           a=channel:32AECB23433801@speechsynth
           a=cmid:1
           m=audio 48260 RTP/AVP 0
           a=rtpmap:0 pcmu/8000
           a=sendonly
           a=mid:1
           m=control 32416 SCTP application/mrcpv2
           a=channel:32AECB23433802@speechrecog
           a=cmid:2
           m=audio 48260 RTP/AVP 0
           a=rtpmap:0 pcmu/8000
           a=rtpmap:96 telephone-event/8000
           a=fmtp:96 0-15
 
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                            MRCPv2 Protocol               January 2004
 
           a=recvonly
           a=mid:2
 
    C->S:
           ACK sip:mrcp@mediaserver.com SIP/2.0
           Max-Forwards: 70
           To: MediaServer <sip:mrcp@mediaserver.com>;tag=a6c85cf
           From: Sarvi <sip:sarvi@cisco.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 314164 ACK
           Content-Length: 0
 
    A MRCPv2 SPEAK request initiates speech.
 
      C->S:MRCP/2.0 386 SPEAK 543257
           Channel-Identifier: 32AECB23433802@speechsynth
           Kill-On-Barge-In: false
           Voice-gender: neutral
           Voice-category: teenager
                     Prosody-volume: medium
           Content-Type: application/synthesis+ssml
           Content-Length: 104
 
           <?xml version="1.0"?>
           <speak>
           <paragraph>
                    <sentence>You have 4 new messages.</sentence>
                    <sentence>The first is from <say-as
                    type="name">Stephanie Williams</say-as> <mark
           name="Stephanie"/>
                    and arrived at <break/>
                    <say-as type="time">3:45pm</say-as>.</sentence>
 
                    <sentence>The subject is <prosody
                    rate="-20%">ski trip</prosody></sentence>
           </paragraph>
           </speak>
 
      S->C:MRCP/2.0 49 543257 200 IN-PROGRESS
           Channel-Identifier: 32AECB23433802@speechsynth
 
    The synthesizer hits the special marker in the message to be spoken
    and faithfully informs the client of the event.
 
      S->C:MRCP/2.0 46 SPEECH-MARKER 543257 IN-PROGRESS
           Channel-Identifier: 32AECB23433802@speechsynth
           Speech-Marker: Stephanie
 
    The synthesizer finishes with the SPEAK request.
 
      S->C:MRCP/2.0 48 SPEAK-COMPLETE 543257 COMPLETE
 
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                            MRCPv2 Protocol               January 2004
 
           Channel-Identifier: 32AECB23433802@speechsynth
 
    The recognizer is issued a request to listen for the customer
    choices.
 
      C->S:MRCP/2.0 343 RECOGNIZE 543258
           Channel-Identifier: 32AECB23433801@speechrecog
           Content-Type: application/grammar+xml
           Content-Length: 104
 
           <?xml version="1.0"?>
 
           <!-- the default grammar language is US English -->
           <grammar xml:lang="en-US" version="1.0">
 
           <!-- single language attachment to a rule expansion -->
                <rule id="request">
                    Can I speak to
                    <one-of xml:lang="fr-CA">
                             <item>Michel Tremblay</item>
                             <item>Andre Roy</item>
                    </one-of>
                </rule>
 
           </grammar>
 
      S->C:MRCP/2.0 49 543258 200 IN-PROGRESS
           Channel-Identifier: 32AECB23433801@speechrecog
 
    The client issues the next MRCPv2 SPEAK method. It is generally
    RECOMMENDED when playing a prompt to the user with kill-on-barge-in
    and asking for input, that the client issue the RECOGNIZE request
    ahead of the SPEAK request for optimum performance and user
    experience. This way, it is guaranteed that the recognizer is online
    before the prompt starts playing and the user's speech will not be
    truncated at the beginning (especially for power users).
 
      C->S:MRCP/2.0 289 SPEAK 543259
           Channel-Identifier: 32AECB23433802@speechsynth
           Kill-On-Barge-In: true
           Content-Type: application/sml
           Content-Length: 104
 
           <?xml version="1.0"?>
           <speak>
           <paragraph>
                    <sentence>Welcome to ABC corporation.</sentence>
                    <sentence>Who would you like Talk to.</sentence>
           </paragraph>
           </speak>
 
 
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                            MRCPv2 Protocol               January 2004
 
      S->C:MRCP/2.0 52 543259 200 IN-PROGRESS
           Channel-Identifier: 32AECB23433802@speechsynth
 
    Since the last SPEAK request had Kill-On-Barge-In set to "true", the
    message synthesizer is interrupted when the user starts speaking.
    And the client is notified.
 
    Now, since the recognition and synthesizer resources are in the same
    session, they worked with each other to deliver kill-on-barge-in. If
    the resources were in different sessions it would have taken a few
    more messages before the client got the SPEAK-COMPLETE event from
    the synthesizer resource. Whether the synthesizer and recognizer are
    in the same session or not the recognizer MUST generate the START-
    OF-SPEECH event to the client.
 
    The client should have then blindly turned around and issued a
    BARGE-IN-OCCURRED method to the synthesizer resource. The
    synthesizer, if kill-on-barge-in was enabled on the current SPEAK
    request, would have then interrupted it and issued SPEAK-COMPLETE
    event to the client. In this example since the synthesizer and
    recognizer are in the same session, the client did not issue the
    BARGE-IN-OCCURRED method to the synthesizer and assumed that kill-
    on-barge-in was implemented between the two resources in the same
    session and worked.
 
    The completion-cause code differentiates if this is normal
    completion or a kill-on-barge-in interruption.
 
      S->C:MRCP/2.0 49 START-OF-SPEECH 543258 IN-PROGRESS
           Channel-Identifier: 32AECB23433801@speechrecog
 
      S->C:MRCP/2.0 73 SPEAK-COMPLETE 543259 COMPLETE
           Channel-Identifier: 32AECB23433802@speechsynth
           Completion-Cause: 000 normal
 
    The recognition resource matched the spoken stream to a grammar and
    generated results. The result of the recognition is returned by the
    server as part of the RECOGNITION-COMPLETE event.
 
      S->C:MRCP/2.0 412 RECOGNITION-COMPLETE 543258 COMPLETE
           Channel-Identifier: 32AECB23433801@speechrecog
           Completion-Cause: 000 success
           Waveform-URL: http://web.media.com/session123/audio.wav
           Content-Type: application/x-nlsml
           Content-Length: 104
 
           <?xml version="1.0"?>
           <result x-model="http://IdentityModel"
             xmlns:xf="http://www.w3.org/2000/xforms"
             grammar="session:request1@form-level.store>
               <interpretation>
 
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                            MRCPv2 Protocol               January 2004
 
                   <xf:instance name="Person">
                       <Person>
                           <Name> Andre Roy </Name>
                       </Person>
                   </xf:instance>
                             <input>   may I speak to Andre Roy </input>
               </interpretation>
           </result>
 
    When the client wants to tear down the whole session and all its
    resources, it MUST issue a SIP BYE to close the SIP session. This
    will de-allocate all the control channels and resources allocated
    under the session.
 
      C->S:BYE sip:mrcp@mediaserver.com SIP/2.0
           Max-Forwards: 70
           From: Sarvi <sip:sarvi@cisco.com>;tag=a6c85cf
           To: MediaServer <sip:mrcp@mediaserver.com>;tag=1928301774
           Call-ID: a84b4c76e66710
           CSeq: 231 BYE
           Content-Length: 0
 
 
 10.  Reference Documents
 
    [1]    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.
 
    [2]    Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time
           Streaming Protocol (RTSP)", RFC 2326, April 1998
 
    [3]    Crocker, D. and P. Overell, "Augmented BNF for syntax
           specifications: ABNF", RFC 2234, November 1997.
 
    [4]    Handley, M., Schulzrinne, H., Schooler, E., and J. Rosenberg,
           "SIP: Session Initiation Protocol", RFC 2543, March 1999.
 
    [6]    Handley, M. and V. Jacobson, "SDP: session description
           protocol", RFC 2327, April 1998.
 
    [7]    Robinson, F., Marquette, B., and R. Hernandez, "Using Media
           Resource Control Protocol with SIP", draft-robinson-mrcp-sip-
           00, (work in progress), September 2001.
 
     [8]   World Wide Web Consortium, ŸVoice Extensible Markup Language
           (VoiceXML) Version 2.0÷, (work in progress), October 2001.
 
     [9]   Crocker, D., ŸSTANDARD FOR THE FORMAT OF ARPA INTERNET TEXT
           MESSAGES÷, RFC 822, August 1982.
 
 
 S Shanmugham                  IETF-Draft                       Page 78
 
                            MRCPv2 Protocol               January 2004
 
     [10]  Bradner, S., ŸKey words for use in RFCs to Indicate
           Requirement Levels÷, RFC 2119, March 1997.
 
     [11]  World Wide Web Consortium, ŸSpeech Synthesis Markup Language
           (SSML)÷, W3C Working Draft, 3 January 2001.
 
     [12]  World Wide Web Consortium, ŸNatural Language Semantics Markup
           Language (NLSML) for the Speech Interface Framework÷, W3C
           Working Draft, 30 May 2001.
 
     [13]  World Wide Web Consortium, ŸSpeech Recognition Grammar
           Specification Version 1.0÷, W3C Candidate Recommendation, 26
           June 2002.
 
     [14]  Bradner, S., "The Internet Standards Process “ Revision 3",
           RFC 2026, October 1996
 
     [15]  Yergeau, F., "UTF-8, a transformation format of Unicode and
           ISO 10646", RFC 2044, October 1996
 
     [16]  Freed, N., Borenstein, N., "Multipupose Internet Mail
           Extensions (MIME) Part Two: Media Types", RFC 2046, November
           1996
 
     [17]  Levinson, E., "Content-ID and Message-ID Uniform Resource
           Locators", RFC 2111, March 1997
 
     [18]  Schulzrinne, H., Petrack, S., "RTP Payload for DTMF Digits,
           Telephony Tones and Telephony Signals", RFC 2833, May 2000
 
     [19]  Alvestrand, H., "Tags for the Identification of Languages",
           RFC 1766, March 1995
     [20]  Camarillo, G., Eriksson, G., Holler, J., "Grouping of Media
           Lines in the Session Description Protocol (SDP) ", RFC 3388,
           December 2002
 
 
 11.  Appendix
 
      ABNF Message Definitions
 
           LWS            =    [*WSP CRLF] 1*WSP ; linear whitespace
 
           SWS            =    [LWS] ; sep whitespace
 
           UTF8-NONASCII  =    %xC0-DF 1UTF8-CONT
                          /  %xE0-EF 2UTF8-CONT
                          /  %xF0-F7 3UTF8-CONT
                          /  %xF8-Fb 4UTF8-CONT
                          /  %xFC-FD 5UTF8-CONT
 
 
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                            MRCPv2 Protocol               January 2004
 
           UTF8-CONT      =    %x80-BF
 
           param          =    *pchar
 
           quoted-string  =    SWS DQUOTE *(qdtext / quoted-pair )
                               DQUOTE
 
           qdtext         =    LWS / %x21 / %x23-5B / %x5D-7E
                               / UTF8-NONASCII
 
           quoted-pair    =    "\" (%x00-09 / %x0B-0C
                               / %x0E-7F)
 
           token          =    1*(alphanum / "-" / "." / "!" / "%" / "*"
                                / "_" / "+" / "`" / "'" / "~" )
 
           reserved       =    ";" / "/" / "?" / ":" / "@" / "&" / "="
                               / "+" / "$" / ","
 
           mark           =    "-" / "_" / "." / "!" / "~" / "*" / "'"
                               / "(" / ")"
 
           unreserved     =    alphanum / mark
 
           pchar          =  unreserved / escaped /
                             ":" / "@" / "&" / "=" / "+" / "$" / ","
 
           alphanum       =    ALPHA / DIGIT
 
           escaped        =    "%" HEXDIG HEXDIG
 
           absoluteURI    =    scheme ":" ( hier-part / opaque-part )
 
           relativeURI    =    ( net-path / abs-path / rel-path )
                               [ "?" query ]
 
           hier-part      =    ( net-path / abs-path ) [ "?" query ]
 
           net-path       =    "//" authority [ abs-path ]
 
           abs-path       =    "/" path-segments
 
           rel-path       =    rel-segment [ abs-path ]
 
           rel-segment    =    1*( unreserved / escaped / ";" / "@"
                               / "&" / "=" / "+" / "$" / "," )
 
           opaque-part    =    uric-no-slash *uric
 
           uric           =    reserved / unreserved / escaped
 
 
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                            MRCPv2 Protocol               January 2004
 
           uric-no-slash  =    unreserved / escaped / ";" / "?" / ":"
                               / "@" / "&" / "=" / "+" / "$" / ","
 
           path-segments  =    segment *( "/" segment )
 
           segment        =    *pchar *( ";" param )
 
           scheme         =  ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
 
           authority      =  srvr / reg-name
 
           srvr           =  [ [ userinfo "@" ] hostport ]
 
           reg-name       =  1*( unreserved / escaped / "$" / ","
                             / ";" / ":" / "@" / "&" / "=" / "+" )
 
           query          =  *uric
 
           userinfo         =  ( user ) [ ":" password ] "@"
 
           user             =  1*( unreserved / escaped
                                    / user-unreserved )
 
           user-unreserved  =  "&" / "=" / "+" / "$" / "," / ";"
                               / "?" / "/"
 
           password         =  *( unreserved / escaped /
                               "&" / "=" / "+" / "$" / "," )
 
           hostport         =  host [ ":" port ]
 
           host             =  hostname / IPv4address / IPv6reference
 
           hostname         =  *( domainlabel "." ) toplabel [ "." ]
 
           domainlabel      =  alphanum
                               / alphanum *( alphanum / "-" ) alphanum
 
           toplabel       =    ALPHA / ALPHA *( alphanum / "-" )
                               alphanum
 
           IPv4address    =    1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT "."
                               1*3DIGIT
 
           IPv6reference  =    "[" IPv6address "]"
 
           IPv6address    =    hexpart [ ":" IPv4address ]
 
           hexpart        =    hexseq / hexseq "::" [ hexseq ] / "::"
                               [ hexseq ]
 
 
 S Shanmugham                  IETF-Draft                       Page 81
 
                            MRCPv2 Protocol               January 2004
 
           hexseq         =    hex4 *( ":" hex4)
 
           hex4           =    1*4HEXDIG
 
           port           =    1*DIGIT
 
           cmid-attribute      =    "a=cmid:" identification-tag
 
           identification-tag  =    token
 
           generic-message =   start-line
                               message-header
                               CRLF
                               [ message-body ]
 
           message-body   =    *OCTET
 
           start-line     =    request-line / status-line / event-line
 
           request-line   =    method-name SP request-id SP
                               mrcp-version CRLF
 
           status-line    =    mrcp-version SP request-id SP
                               status-code SP request-state CRLF
 
           event-line     =    event-name SP request-id SP
                               request-state SP mrcp-version CRLF
 
           message-header =    1*(generic-header / resource-header)
 
           generic-header =    channel-identifier
                          /    active-request-id-list
                          /    proxy-sync-id
                          /    content-id
                          /    content-type
                          /    content-length
                          /    content-base
                          /    content-location
                          /    content-encoding
                          /    cache-control
                          /    logging-tag
           ; -- content-id is as defined in RFC 2111, RFC2046 and RFC822
 
           mrcp-version   =    "MRCP" "/" 1*DIGIT "." 1*DIGIT
 
           request-id     =    1*DIGIT
 
           status-code    =    1*DIGIT
 
           channel-identifier  =    "Channel-Identifier" ":"
                                    channel-id CRLF
 
 S Shanmugham                  IETF-Draft                       Page 82
 
                            MRCPv2 Protocol               January 2004
 
 
           channel-id          = 1*HEXDIG "@" 1*ALPHA
 
           active-request-id-list =  "Active-Request-Id-List" ":"
                               request-id *("," request-id) CRLF
 
           proxy-sync-id  =    "Proxy-Sync-Id" ":" 1*ALPHA CRLF
 
           content-length =    "Content-Length" ":" 1*DIGIT CRLF
 
           content-base   =    "Content-Base" ":" absoluteURI CRLF
 
           Content-Type   =    "Content-Type" ":" media-type
 
           media-type     =    type "/" subtype *( ";" parameter )
 
           type           =    token
 
           subtype        =    token
 
           parameter      =    attribute "=" value
 
           attribute      =    token
 
           value          =    token / quoted-string
 
           content-encoding =  "Content-Encoding" ":"
                               *WSP content-coding
                               *(*WSP "," *WSP content-coding *WSP )
                               CRLF
 
           content-coding   =  token
 
 
           content-location =  "Content-Location" ":"
                               ( absoluteURI / relativeURI )  CRLF
 
           cache-control  =    "Cache-Control" ":"
                               *WSP cache-directive
                               *( *WSP "," *WSP cache-directive *WSP )
                               CRLF
 
           cache-directive =   "max-age" "=" delta-seconds
                          /    "max-stale" "=" delta-seconds
                          /    "min-fresh" "=" delta-seconds
 
           logging-tag    =    "Logging-Tag" ":" 1*ALPHA CRLF
 
 
           resource-header =   recognizer-header
                          /    synthesizer-header
 
 S Shanmugham                  IETF-Draft                       Page 83
 
                            MRCPv2 Protocol               January 2004
 
 
           method-name    =    synthesizer-method
                          /    recognizer-method
 
           event-name     =    synthesizer-event
                          /    recognizer-event
 
           request-state  =    "COMPLETE"
                          /    "IN-PROGRESS"
                          /    "PENDING"
 
           synthesizer-method = "SET-PARAMS"
                          /    "GET-PARAMS"
                          /    "SPEAK"
                          /    "STOP"
                          /    "PAUSE"
                          /    "RESUME"
                          /    "BARGE-IN-OCCURRED"
                          /    "CONTROL"
 
           synthesizer-event = "SPEECH-MARKER"
                          /    "SPEAK-COMPLETE"
 
           synthesizer-header = jump-target
                          /    kill-on-barge-in
                          /    speaker-profile
                          /    completion-cause
                          /    voice-parameter
                          /    prosody-parameter
                          /    vendor-specific
                          /    speech-marker
                          /    speech-language
                          /    fetch-hint
                          /    audio-fetch-hint
                          /    fetch-timeout
                          /    failed-uri
                          /    failed-uri-cause
                          /    speak-restart
                          /    speak-length
 
           recognizer-method = "SET-PARAMS"
                          /    "GET-PARAMS"
                          /    "DEFINE-GRAMMAR"
                          /    "RECOGNIZE"
                          /    "GET-RESULT"
                          /    "RECOGNITION-START-TIMERS"
                          /    "STOP"
 
           recognizer-event  = "START-OF-SPEECH"
                          /    "RECOGNITION-COMPLETE"
 
 
 S Shanmugham                  IETF-Draft                       Page 84
 
                            MRCPv2 Protocol               January 2004
 
           recognizer-header = confidence-threshold
                          /    sensitivity-level
                          /    speed-vs-accuracy
                          /    n-best-list-length
                          /    no-input-timeout
                          /    recognition-timeout
                          /    waveform-url
                          /    completion-cause
                          /    recognizer-context-block
                          /    recognizer-start-timers
                          /    vendor-specific
                          /    speech-complete-timeout
                          /    speech-incomplete-timeout
                          /    dtmf-interdigit-timeout
                          /    dtmf-term-timeout
                          /    dtmf-term-char
                          /    fetch-timeout
                          /    failed-uri
                          /    failed-uri-cause
                          /    save-waveform
                          /    new-audio-channel
                          /    speech-language
 
           jump-target    =    "Jump-Size" ":" speech-length-value CRLF
 
           speech-length-value = numeric-speech-length
                          /    text-speech-length
 
           text-speech-length =     1*ALPHA SP "Tag"
 
           numeric-speech-length =("+" / "-") 1*DIGIT SP
                               numeric-speech-unit
 
           numeric-speech-unit ="Second"
                          /    "Word"
                          /    "Sentence"
                          /    "Paragraph"
 
           delta-seconds  =    1*DIGIT
 
           kill-on-barge-in =  "Kill-On-Barge-In" ":" boolean-value CRLF
 
           boolean-value  =    "true" / "false"
 
           speaker-profile =    "Speaker-Profile" ":" absoluteURI CRLF
 
           completion-cause =  "Completion-Cause" ":" 1*DIGIT SP
                               1*ALPHA CRLF
 
           voice-parameter =   "Voice-" voice-param-name ":"
                               voice-param-value CRLF
 
 S Shanmugham                  IETF-Draft                       Page 85
 
                            MRCPv2 Protocol               January 2004
 
 
           voice-param-name =  1*ALPHA
 
           voice-param-value = 1*alphanum
 
           prosody-parameter = "Prosody-" prosody-param-name ":"
                               prosody-param-value CRLF
 
           prosody-param-name= 1*ALPHA
 
           prosody-param-value=1*alphanum
 
           vendor-specific =   "Vendor-Specific-Parameters" ":"
                               vendor-specific-av-pair
                               *[";" vendor-specific-av-pair] CRLF
 
           vendor-specific-av-pair = vendor-av-pair-name "="
                               vendor-av-pair-value
 
           vendor-av-pair-name = 1*ALPHA
 
           vendor-av-pair-value = 1*alphanum
 
           speech-marker  =    "Speech-Marker" ":" 1*ALPHA CRLF
 
           speech-language =   "Speech-Language" ":" 1*ALPHA CRLF
 
           fetch-hint     =    "Fetch-Hint" ":" 1*ALPHA CRLF
 
           audio-fetch-hint =  "Audio-Fetch-Hint" ":" 1*ALPHA CRLF
 
           fetch-timeout  =    "Fetch-Timeout" ":" 1*DIGIT CRLF
 
           failed-uri     =    "Failed-URI" ":" absoluteURI CRLF
 
           failed-uri-cause =  "Failed-URI-Cause" ":" 1*ALPHA CRLF
 
           speak-restart  =    "Speak-Restart" ":" boolean-value CRLF
 
           speak-length   =    "Speak-Length" ":" speech-length-value
                                       CRLF
           speech-length-value = numeric-speech-length
                          /    text-speech-length
 
           text-speech-length = 1*ALPHA SP "Tag"
 
           numeric-speech-length = ("+" / "-") 1*DIGIT SP
                                       numeric-speech-unit
 
           numeric-speech-unit = "Second"
                          /    "Word"
 
 S Shanmugham                  IETF-Draft                       Page 86
 
                            MRCPv2 Protocol               January 2004
 
                          /    "Sentence"
                          /    "Paragraph"
 
           confidence-threshold = "Confidence-Threshold" ":"
                               1*DIGIT CRLF
 
           sensitivity-level = "Sensitivity-Level" ":" 1*DIGIT CRLF
 
           speed-vs-accuracy = "Speed-Vs-Accuracy" ":" 1*DIGIT CRLF
 
           n-best-list-length = "N-Best-List-Length" ":" 1*DIGIT CRLF
 
           no-input-timeout =  "No-Input-Timeout" ":" 1*DIGIT CRLF
 
           recognition-timeout = "Recognition-Timeout" ":" 1*DIGIT CRLF
 
           waveform-url   =    "Waveform-URL" ":" absoluteURI CRLF
 
           completion-cause=   "Completion-Cause" ":" 1*DIGIT SP
                               1*ALPHA CRLF
 
           recognizer-context-block = "Recognizer-Context-Block" ":"
                               1*ALPHA CRLF
 
           recognizer-start-timers = "Recognizer-Start-Timers" ":"
                               boolean-value CRLF
 
           speech-complete-timeout = "Speech-Complete-Timeout" ":"
                               1*DIGIT CRLF
 
           speech-incomplete-timeout = "Speech-Incomplete-Timeout" ":"
                               1*DIGIT CRLF
 
           dtmf-interdigit-timeout = "DTMF-Interdigit-Timeout" ":"
                               1*DIGIT CRLF
 
           dtmf-term-timeout = "DTMF-Term-Timeout" ":" 1*DIGIT CRLF
 
           dtmf-term-char =    "DTMF-Term-Char" ":" CHAR CRLF
 
           fetch-timeout  =    "Fetch-Timeout" ":" 1*DIGIT CRLF
 
           save-waveform  =    "Save-Waveform" ":" boolean-value CRLF
 
           new-audio-channel = "New-Audio-Channel" ":"
                               boolean-value CRLF
 
 Full Copyright Statement
 
       Copyright (C) The Internet Society (1999).  All Rights Reserved.
 
 
 S Shanmugham                  IETF-Draft                       Page 87
 
                            MRCPv2 Protocol               January 2004
 
       This document and translations of it may be copied and furnished
    to others, and derivative works that comment on or otherwise explain
    it or assist in its implementation may be prepared, copied,
    published and distributed, in whole or in part, without restriction
    of any kind, provided that the above copyright notice and this
    paragraph are included on all such copies and derivative works.
    However, this document itself may not be modified in any way, such
    as by removing the copyright notice or references to the Internet
    Society or other Internet organizations, except as needed for the
    purpose of developing Internet standards in which case the
    procedures for copyrights defined in the Internet Standards process
    must be followed, or as required to translate it into languages
    other than English.
 
       The limited permissions granted above are perpetual and will not
    be revoked by the Internet Society or its successors or assigns.
 
       This document and the information contained herein is provided on
    an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
    ENGINEERING TASK FORCE DISCLAIMS 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.
 
 Acknowledgements
 
    Andre Gillet (Nuance Communications)
    Andrew Hunt (SpeechWorks)
    Aaron Kneiss (SpeechWorks)
    Brian Eberman (SpeechWorks)
    Kristian Finlator (SpeechWorks)
    Martin Dragomirecky (Cisco Systems Inc)
    Peter Monaco (Nuance Communications)
    Pierre Forgues (Nuance Communications)
    Suresh Kaliannan (Cisco Systems Inc.)
    Corey Stohs (Cisco Systems Inc)
    Dan Burnett (Nuance Communications)
 
 
 Authors' Addresses
 
    Saravanan Shanmugham
    Cisco Systems Inc.
    170 W Tasman Drive,
    San Jose,
    CA 95134
 
    Email: sarvi@cisco.com
 
 
 
 
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