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rfc:rfc4463

Network Working Group S. Shanmugham Request for Comments: 4463 Cisco Systems, Inc. Category: Informational P. Monaco

                                                 Nuance Communications
                                                            B. Eberman
                                                      Speechworks Inc.
                                                            April 2006
              A Media Resource Control Protocol (MRCP)
            Developed by Cisco, Nuance, and Speechworks

Status of This Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2006).

IESG Note

 This RFC is not a candidate for any level of Internet Standard.  The
 IETF disclaims any knowledge of the fitness of this RFC for any
 purpose and in particular notes that the decision to publish is not
 based on IETF review for such things as security, congestion control,
 or inappropriate interaction with deployed protocols.  The RFC Editor
 has chosen to publish this document at its discretion.  Readers of
 this document should exercise caution in evaluating its value for
 implementation and deployment.  See RFC 3932 for more information.
 Note that this document uses a MIME type 'application/mrcp' which has
 not been registered with the IANA, and is therefore not recognized as
 a standard IETF MIME type.  The historical value of this document as
 an ancestor to ongoing standardization in this space, however, makes
 the publication of this document meaningful.

Shanmugham, et al. Informational [Page 1] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

Abstract

 This document describes a Media Resource Control Protocol (MRCP) that
 was developed jointly by Cisco Systems, Inc., Nuance Communications,
 and Speechworks, Inc.  It is published as an RFC as input for further
 IETF development in this area.
 MRCP controls media service resources like speech synthesizers,
 recognizers, signal generators, signal detectors, fax servers, etc.,
 over a network.  This protocol is designed to work with streaming
 protocols like RTSP (Real Time Streaming Protocol) or SIP (Session
 Initiation Protocol), which help establish control connections to
 external media streaming devices, and media delivery mechanisms like
 RTP (Real Time Protocol).

Table of Contents

 1. Introduction ....................................................3
 2. Architecture ....................................................4
    2.1. Resources and Services .....................................4
    2.2. Server and Resource Addressing .............................5
 3. MRCP Protocol Basics ............................................5
    3.1. Establishing Control Session and Media Streams .............5
    3.2. MRCP over RTSP .............................................6
    3.3. Media Streams and RTP Ports ................................8
 4. Notational Conventions ..........................................8
 5. MRCP Specification ..............................................9
    5.1. Request ...................................................10
    5.2. Response ..................................................10
    5.3. Event .....................................................12
    5.4. Message Headers ...........................................12
 6. Media Server ...................................................19
    6.1. Media Server Session ......................................19
 7. Speech Synthesizer Resource ....................................21
    7.1. Synthesizer State Machine .................................22
    7.2. Synthesizer Methods .......................................22
    7.3. Synthesizer Events ........................................23
    7.4. Synthesizer Header Fields .................................23
    7.5. Synthesizer Message Body ..................................29
    7.6. SET-PARAMS ................................................32
    7.7. GET-PARAMS ................................................32
    7.8. SPEAK .....................................................33
    7.9. STOP ......................................................34
    7.10. BARGE-IN-OCCURRED ........................................35
    7.11. PAUSE ....................................................37
    7.12. RESUME ...................................................37
    7.13. CONTROL ..................................................38
    7.14. SPEAK-COMPLETE ...........................................40

Shanmugham, et al. Informational [Page 2] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

    7.15. SPEECH-MARKER ............................................41
 8. Speech Recognizer Resource .....................................42
    8.1. Recognizer State Machine ..................................42
    8.2. Recognizer Methods ........................................42
    8.3. Recognizer Events .........................................43
    8.4. Recognizer Header Fields ..................................43
    8.5. Recognizer Message Body ...................................51
    8.6. SET-PARAMS ................................................56
    8.7. GET-PARAMS ................................................56
    8.8. DEFINE-GRAMMAR ............................................57
    8.9. RECOGNIZE .................................................60
    8.10. STOP .....................................................63
    8.11. GET-RESULT ...............................................64
    8.12. START-OF-SPEECH ..........................................64
    8.13. RECOGNITION-START-TIMERS .................................65
    8.14. RECOGNITON-COMPLETE ......................................65
    8.15. DTMF Detection ...........................................67
 9. Future Study ...................................................67
 10. Security Considerations .......................................67
 11. RTSP-Based Examples ...........................................67
 12. Informative References ........................................74
 Appendix A. ABNF Message Definitions ..............................76
 Appendix B. Acknowledgements ......................................84

1. Introduction

 The Media Resource Control Protocol (MRCP) is designed to provide a
 mechanism for a client device requiring audio/video stream processing
 to control processing resources on the network.  These media
 processing resources may be speech recognizers (a.k.a. Automatic-
 Speech-Recognition (ASR) engines), speech synthesizers (a.k.a. Text-
 To-Speech (TTS) engines), fax, signal detectors, etc.  MRCP allows
 implementation of distributed Interactive Voice Response platforms,
 for example VoiceXML [6] interpreters.  The MRCP protocol defines the
 requests, responses, and events needed to control the media
 processing resources.  The MRCP protocol defines the state machine
 for each resource and the required state transitions for each request
 and server-generated event.
 The MRCP protocol does not address how the control session is
 established with the server and relies on the Real Time Streaming
 Protocol (RTSP) [2] to establish and maintain the session.  The
 session control protocol is also responsible for establishing the
 media connection from the client to the network server.  The MRCP
 protocol and its messaging is designed to be carried over RTSP or
 another protocol as a MIME-type similar to the Session Description
 Protocol (SDP) [5].

Shanmugham, et al. Informational [Page 3] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 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 [8].

2. Architecture

 The system consists of a client that requires media streams generated
 or needs media streams processed and a server that has the resources
 or devices to process or generate the streams.  The client
 establishes a control session with the server for media processing
 using a protocol such as RTSP.  This will also set up and establish
 the RTP stream between the client and the server or another RTP
 endpoint.  Each resource needed in processing or generating the
 stream is addressed or referred to by a URL.  The client can now use
 MRCP messages to control the media resources and affect how they
 process or generate the media stream.
   |--------------------|
   ||------------------||                   |----------------------|
   || Application Layer||                   ||--------------------||
   ||------------------||                   || TTS  | ASR  | Fax  ||
   ||  ASR/TTS API     ||                   ||Plugin|Plugin|Plugin||
   ||------------------||                   ||  on  |  on  |  on  ||
   ||    MRCP Core     ||                   || MRCP | MRCP | MRCP ||
   ||  Protocol Stack  ||                   ||--------------------||
   ||------------------||                   ||   RTSP Stack       ||
   ||   RTSP Stack     ||                   ||                    ||
   ||------------------||                   ||--------------------||
   ||   TCP/IP Stack   ||========IP=========||  TCP/IP Stack      ||
   ||------------------||                   ||--------------------||
   |--------------------|                   |----------------------|
      MRCP client                             Real-time Streaming MRCP
                                               media server

2.1. Resources and Services

 The server is set up to offer a certain set of resources and services
 to the client.  These resources are of 3 types.
 Transmission Resources
 These are resources that are capable of generating real-time streams,
 like signal generators that generate tones and sounds of certain
 frequencies and patterns, and speech synthesizers that generate
 spoken audio streams, etc.

Shanmugham, et al. Informational [Page 4] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 Reception Resources
 These are resources that receive and process streaming data like
 signal detectors and speech recognizers.
 Dual Mode Resources
 These are resources that both send and receive data like a fax
 resource, capable of sending or receiving fax through a two-way RTP
 stream.

2.2. Server and Resource Addressing

 The server as a whole is addressed using a container URL, and the
 individual resources the server has to offer are reached by
 individual resource URLs within the container URL.
 RTSP Example:
 A media server or container URL like,
   rtsp://mediaserver.com/media/
 may contain one or more resource URLs of the form,
   rtsp://mediaserver.com/media/speechrecognizer/
   rtsp://mediaserver.com/media/speechsynthesizer/
   rtsp://mediaserver.com/media/fax/

3. MRCP Protocol Basics

 The message format for MRCP 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 MRCP message between the client and the server resource.  The
 protocol does not address session control management, media
 management, reliable sequencing, and delivery or server or resource
 addressing.  These are left to a protocol like SIP or RTSP.  MRCP
 addresses the issue of controlling and communicating with the
 resource processing the stream, and defines the requests, responses,
 and events needed to do that.

3.1. Establishing Control Session and Media Streams

 The control session between the client and the server is established
 using a protocol like RTSP.  This protocol will also set up the
 appropriate RTP streams between the server and the client, allocating
 ports and setting up transport parameters as needed.  Each control

Shanmugham, et al. Informational [Page 5] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 session is identified by a unique session-id.  The format, usage, and
 life cycle of the session-id is in accordance with the RTSP protocol.
 The resources within the session are addressed by the individual
 resource URLs.
 The MRCP protocol is designed to work with and tunnel through another
 protocol like RTSP, and augment its capabilities.  MRCP relies on
 RTSP headers for sequencing, reliability, and addressing to make sure
 that messages get delivered reliably and in the correct order and to
 the right resource.  The MRCP messages are carried in the RTSP
 message body.  The media server delivers the MRCP message to the
 appropriate resource or device by looking at the session-level
 message headers and URL information.  Another protocol, such as SIP
 [4], could be used for tunneling MRCP messages.

3.2. MRCP over RTSP

 RTSP supports both TCP and UDP mechanisms for the client to talk to
 the server and is differentiated by the RTSP URL.  All MRCP based
 media servers MUST support TCP for transport and MAY support UDP.
 In RTSP, the ANNOUNCE method/response MUST be used to carry MRCP
 request/responses between the client and the server.  MRCP messages
 MUST NOT be communicated in the RTSP SETUP or TEARDOWN messages.
 Currently all RTSP messages are request/responses and there is no
 support for asynchronous events in RTSP.  This is because RTSP was
 designed to work over TCP or UDP and, hence, could not assume
 reliability in the underlying protocol.  Hence, when using MRCP over
 RTSP, an asynchronous event from the MRCP server is packaged in a
 server-initiated ANNOUNCE method/response communication.  A future
 RTSP extension to send asynchronous events from the server to the
 client would provide an alternate vehicle to carry such asynchronous
 MRCP events from the server.
 An RTSP session is created when an RTSP SETUP message is sent from
 the client to a server and is addressed to a server URL or any one of
 its resource URLs without specifying a session-id.  The server will
 establish a session context and will respond with a session-id to the
 client.  This sequence will also set up the RTP transport parameters
 between the client and the server, and then the server will be ready
 to receive or send media streams.  If the client wants to attach an
 additional resource to an existing session, the client should send
 that session's ID in the subsequent SETUP message.

Shanmugham, et al. Informational [Page 6] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 When a media server implementing MRCP over RTSP receives a PLAY,
 RECORD, or PAUSE RTSP method from an MRCP resource URL, it should
 respond with an RTSP 405 "Method not Allowed" response.  For these
 resources, the only allowed RTSP methods are SETUP, TEARDOWN,
 DESCRIBE, and ANNOUNCE.
 Example 1:
 C->S:  ANNOUNCE rtsp://media.server.com/media/synthesizer RTSP/1.0
        CSeq:4
        Session:12345678
        Content-Type:application/mrcp
        Content-Length:223
        SPEAK 543257 MRCP/1.0
        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:  RTSP/1.0 200 OK
        CSeq: 4
        Session:12345678
        RTP-Info:url=rtsp://media.server.com/media/synthesizer;
                  seq=9810092;rtptime=3450012
        Content-Type:application/mrcp
        Content-Length:52
        MRCP/1.0 543257 200 IN-PROGRESS
 S->C:  ANNOUNCE rtsp://media.server.com/media/synthesizer RTSP/1.0
        CSeq:6
        Session:12345678

Shanmugham, et al. Informational [Page 7] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

        Content-Type:application/mrcp
        Content-Length:123
        SPEAK-COMPLETE 543257 COMPLETE MRCP/1.0
 C->S:  RTSP/1.0 200 OK
        CSeq:6
 For the sake of brevity, most examples from here on show only the
 MRCP messages and do not show the RTSP message and headers in which
 they are tunneled.  Also, RTSP messages such as response that are not
 carrying an MRCP message are also left out.

3.3. Media Streams and RTP Ports

 A single set of RTP/RTCP ports is negotiated and shared between the
 MRCP client and server when multiple media processing resources, such
 as automatic speech recognition (ASR) engines and text to speech
 (TTS) engines, are used for a single session.  The individual
 resource instances allocated on the server under a common session
 identifier will feed from/to that single RTP stream.
 The client can send multiple media streams towards the server,
 differentiated by using different synchronized source (SSRC)
 identifier values.  Similarly the server can use multiple
 Synchronized Source (SSRC) identifier values to differentiate media
 streams originating from the individual transmission resource URLs if
 more than one exists.  The individual resources may, on the other
 hand, work together to send just one stream to the client.  This is
 up to the implementation of the media server.

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] refers 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) similar to that used
 in [H2.1].  It is described in detail in RFC 4234 [3].
 The ABNF provided along with the descriptive text is informative in
 nature and may not be complete.  The complete message format in ABNF
 form is provided in Appendix A and is the normative format
 definition.

Shanmugham, et al. Informational [Page 8] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

5. MRCP Specification

 The MRCP PDU is textual using an ISO 10646 character set in the UTF-8
 encoding (RFC 3629 [12]) to allow many different languages to be
 represented.  However, to assist in compact representations, MRCP
 also allows other character sets such as ISO 8859-1 to be used when
 desired.  The MRCP 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
 MRCP 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.
 The whole MRCP PDU is encoded in the body of the session level
 message as a MIME entity of type application/mrcp.  The individual
 MRCP messages do not have addressing information regarding which
 resource the request/response are to/from.  Instead, the MRCP message
 relies on the header of the session level message carrying it to
 deliver the request to the appropriate resource, or to figure out who
 the response or event is from.
 The MRCP 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
                            message-header
                            CRLF
                            [ message-body ]
        message-body    =   *OCTET
        start-line      =   request-line / status-line / event-line
 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.

Shanmugham, et al. Informational [Page 9] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 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

 An MRCP 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   =    method-name SP request-id SP
                       mrcp-version CRLF
 The request-id field is a unique identifier created by the client and
 sent to the server.  The server resource should 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.
   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
 The mrcp-version field is the MRCP protocol version that is being
 used by the client.
   mrcp-version   =    "MRCP" "/" 1*DIGIT "." 1*DIGIT

5.2. Response

 After receiving and interpreting the request message, the server
 resource responds with an MRCP response message.  It consists of a
 status line optionally followed by a message body.
   response-line  =    mrcp-version SP request-id SP status-code SP
                       request-state CRLF

Shanmugham, et al. Informational [Page 10] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 The mrcp-version field used here is similar to the one used in the
 Request Line and indicates the version of MRCP 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 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"

5.2.1. Status Codes

 The status codes are classified under the Success(2XX) codes and the
 Failure(4XX) codes.

5.2.1.1. Success 2xx

    200       Success
    201       Success with some optional parameters ignored.

5.2.1.2. 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

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    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 is 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       =  event-name SP request-id SP request-state SP
                       mrcp-version CRLF
 The mrcp-version used here is identical to the one used in the
 Request/Response Line and indicates the version of MRCP protocol
 running on the server.
 The request-id used in the event should 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 5.2.  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

5.4. Message Headers

 MRCP header fields, which include general-header (Section 5.4) and
 resource-specific-header (Sections 7.4 and 8.4), follow the same
 generic format as that given in Section 2.1 of RFC 2822 [7].  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 linear whitespace (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.

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        message-header =    1*(generic-header / resource-header)
 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.  Therefore, the order in which header fields
 with the same field-name are received is 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      =    active-request-id-list
                       /    proxy-sync-id
                       /    content-id
                       /    content-type
                       /    content-length
                       /    content-base
                       /    content-location
                       /    content-encoding
                       /    cache-control
                       /    logging-tag
 All headers in MRCP will be case insensitive, consistent with HTTP
 and RTSP protocol header definitions.

5.4.1. Active-Request-Id-List

 In a request, this field indicates the list of request-ids to which
 it should apply.  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

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 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) that has one or more
 SPEAK requests in the PENDING or IN-PROGRESS state, all SPEAK
 requests MUST be cancelled, including the one IN-PROGRESS.  In
 addition, 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.
   active-request-id-list  =  "Active-Request-Id-List" ":" request-id
                               *("," request-id) CRLF

5.4.2. 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 (Section 7.10) 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

5.4.3. 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 Natural Language Semantics Markup Language (NLSML) results of a
 RECOGNITON-COMPLETE event.

Shanmugham, et al. Informational [Page 14] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

5.4.4. Content-Type

 See [H14.17].  Note that the content types suitable for MRCP 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
 MRCP specific headers.

5.4.5. Content-Id

 This field contains an ID or name for the content, by which it can be
 referred to.  The definition of this field conforms to RFC 2392 [14],
 RFC 2822 [7], RFC 2046 [13] and is needed in multi-part messages.  In
 MRCP 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.

5.4.6. Content-Base

 The content-base entity-header field may be used to specify the base
 URI for resolving relative URLs within the entity.
   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.

5.4.7. 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 has 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" ":"
                            *WSP content-coding
                            *(*WSP "," *WSP content-coding *WSP )
                            CRLF
        content-coding   =  token

Shanmugham, et al. Informational [Page 15] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

        token            =  1*(alphanum / "-" / "." / "!" / "%" / "*"
                            / "_" / "+" / "`" / "'" / "~" )
 Content coding is defined in [H3.5].  An example of its use is
   Content-Encoding:gzip
 If multiple encodings have been applied to an entity, the content
 codings MUST be listed in the order in which they were applied.

5.4.8. 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.
 If the content-location is a relative URI, the relative URI is
 interpreted relative to the content-base URI.

5.4.9. 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].

Shanmugham, et al. Informational [Page 16] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

5.4.10. 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" ":" *WSP cache-directive
                            *( *WSP "," *WSP cache-directive *WSP )
                            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.  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

Shanmugham, et al. Informational [Page 17] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

    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 MRCP 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.

5.4.11. 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 MRCP 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.
 MRCP 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 MRCP server's
 output logs in undefined.
   logging-tag    =    "Logging-Tag" ":" 1*ALPHA CRLF

Shanmugham, et al. Informational [Page 18] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

6. Media Server

 The capability of media server resources can be found using the RTSP
 DESCRIBE mechanism.  When a client issues an RTSP DESCRIBE method for
 a media resource URI, the media server response MUST contain an SDP
 description in its body describing the capabilities of the media
 server resource.  The SDP description MUST contain at a minimum the
 media header (m-line) describing the codec and other media related
 features it supports.  It MAY contain another SDP header as well, but
 support for it is optional.
 The usage of SDP messages in the RTSP message body and its
 application follows the SIP RFC 2543 [4], but is limited to media-
 related negotiation and description.

6.1. Media Server Session

 As discussed in Section 3.2, a client/server should share one RTSP
 session-id for the different resources it may use under the same
 session.  The client MUST allocate a set of client RTP/RTCP ports for
 a new session and MUST NOT send a Session-ID in the SETUP message for
 the first resource.  The server then creates a Session-ID and
 allocates a set of server RTP/RTCP ports and responds to the SETUP
 message.
 If the client wants to open more resources with the same server under
 the same session, it will send the session-id (that it got in the
 earlier SETUP response) in the SETUP for the new resource.  A SETUP
 message with an existing session-id tells the server that this new
 resource will feed from/into the same RTP/RTCP stream of that
 existing session.
 If the client wants to open a resource from a media server that is
 not where the first resource came from, it will send separate SETUP
 requests with no session-id header field in them.  Each server will
 allocate its own session-id and return it in the response.  Each of
 them will also come back with their own set of RTP/RTCP ports.  This
 would be the case when the synthesizer engine and the recognition
 engine are on different servers.
 The RTSP SETUP method SHOULD contain an SDP description of the media
 stream being set up.  The RTSP SETUP response MUST contain an SDP
 description of the media stream that it expects to receive and send
 on that session.
 The SDP description in the SETUP method from the client SHOULD
 describe the required media parameters like codec, Named Signaling
 Event (NSE) payload types, etc.  This could have multiple media

Shanmugham, et al. Informational [Page 19] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 headers (i.e., m-lines) to allow the client to provide the media
 server with more than one option to choose from.
 The SDP description in the SETUP response should reflect the media
 parameters that the media server will be using for the stream.  It
 should be within the choices that were specified in the SDP of the
 SETUP method, if one was provided.
 Example:
   C->S:
     SETUP rtsp://media.server.com/recognizer/ RTSP/1.0
     CSeq:1
     Transport:RTP/AVP;unicast;client_port=46456-46457
     Content-Type:application/sdp
     Content-Length:190
     v=0
     o=- 123 456 IN IP4 10.0.0.1
     s=Media Server
     p=+1-888-555-1212
     c=IN IP4 0.0.0.0
     t=0 0
     m=audio 46456 RTP/AVP 0 96
     a=rtpmap:0 pcmu/8000
     a=rtpmap:96 telephone-event/8000
     a=fmtp:96 0-15
   S->C:
     RTSP/1.0 200 OK
     CSeq:1
     Session:0a030258_00003815_3bc4873a_0001_0000
     Transport:RTP/AVP;unicast;client_port=46456-46457;
                server_port=46460-46461
     Content-Length:190
     Content-Type:application/sdp
     v=0
     o=- 3211724219 3211724219 IN IP4 10.3.2.88
     s=Media Server
     c=IN IP4 0.0.0.0
     t=0 0
     m=audio 46460 RTP/AVP 0 96
     a=rtpmap:0 pcmu/8000
     a=rtpmap:96 telephone-event/8000
     a=fmtp:96 0-15

Shanmugham, et al. Informational [Page 20] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 If an SDP description was not provided in the RTSP SETUP method, then
 the media server may decide on parameters of the stream but MUST
 specify what it chooses in the SETUP response.  An SDP announcement
 is only returned in a response to a SETUP message that does not
 specify a Session.  That is, the server will not return an SDP
 announcement for the synthesizer SETUP of a session already
 established with a recognizer.
   C->S:
     SETUP rtsp://media.server.com/recognizer/ RTSP/1.0
     CSeq:1
     Transport:RTP/AVP;unicast;client_port=46498
   S->C:
     RTSP/1.0 200 OK
     CSeq:1
     Session:0a030258_000039dc_3bc48a13_0001_0000
     Transport:RTP/AVP;unicast; client_port=46498;
                server_port=46502-46503
     Content-Length:193
     Content-Type:application/sdp
     v=0
     o=- 3211724947 3211724947 IN IP4 10.3.2.88
     s=Media Server
     c=IN IP4 0.0.0.0
     t=0 0
     m=audio 46502 RTP/AVP 0 101
     a=rtpmap:0 pcmu/8000
     a=rtpmap:101 telephone-event/8000
     a=fmtp:101 0-15

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 MRCP 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.

Shanmugham, et al. Informational [Page 21] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

7.1. Synthesizer State Machine

 The synthesizer maintains states because it needs to correlate MRCP
 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----|                 |------->|
      |<----BARGE-IN-OCCURRED-|                          |
      |              |--------|                          |
      |          CONTROL      |-----------PAUSE--------->|
      |              |------->|<----------RESUME---------|
      |                       |               |----------|
      |                       |              PAUSE       |
      |                       |               |--------->|
      |              |--------|----------|               |
      |     BARGE-IN-OCCURRED |      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"

Shanmugham, et al. Informational [Page 22] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

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 of
 the message with which it is associated.
   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
                       /  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

Shanmugham, et al. Informational [Page 23] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

   failed-uri          MANDATORY      Any
   failed-uri-cause    MANDATORY      Any
   speak-restart       MANDATORY      CONTROL
   speak-length        MANDATORY      SPEAK, CONTROL

7.4.1. 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"
   numeric-speech-length=   ("+" / "-") 1*DIGIT SP
                            numeric-speech-unit
   numeric-speech-unit =    "Second"
                       /    "Word"
                       /    "Sentence"
                       /    "Paragraph"

7.4.2. 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 RTSP session-id 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 barge-in-able event from the synthesizer resource

Shanmugham, et al. Informational [Page 24] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 or signal detector resource.  These resources MAY BE local or
 distributed.  If this field is not specified, the value defaults to
 "true".

7.4.3. 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

7.4.4. 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
                            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.

7.4.5. 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 [9].  The voice-param-value is any one of the value
 choices of the corresponding voice element attribute specified in the
 above section.

Shanmugham, et al. Informational [Page 25] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 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 Speech Synthesis Markup Language (SSML).
 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.

7.4.6. 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 [9].  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.
 Furthermore, these attributes can be part of the speech text marked
 up in SSML.
 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 to 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.

Shanmugham, et al. Informational [Page 26] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

7.4.7. 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.

7.4.8. 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

7.4.9. Speech Language

 This header field specifies the default language of the speech data
 if it is not specified in the speech data.  The value of this header
 field should follow RFC 3066 [16] for its values.  This MAY occur in
 SPEAK, SET-PARAMS, or GET-PARAMS request.
   speech-language          =    "Speech-Language" ":" 1*ALPHA CRLF

Shanmugham, et al. Informational [Page 27] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

7.4.10. 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

7.4.11. 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

7.4.12. 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

7.4.13. 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

Shanmugham, et al. Informational [Page 28] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

7.4.14. 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

7.4.15. 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

7.4.16. 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 until the tag is reached or the SPEAK request complete,
 whichever 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 where 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

7.5. Synthesizer Message Body

 A synthesizer message may contain additional information associated
 with the Method, Response, or Event in its message body.

Shanmugham, et al. Informational [Page 29] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

7.5.1. 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 [9] at 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 URIs that will
 list what needs to be spoken.  If a list of speech URIs 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, then stored in memory or a local device, and that
 it currently needs to play 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.cisco.com/ASR-Introduction.sml
     http://www.cisco.com/ASR-Document-Part1.sml
     http://www.cisco.com/ASR-Document-Part2.sml
     http://www.cisco.com/ASR-Conclusion.sml
 Example 2:
     Content-Type:application/synthesis+ssml
     Content-Length:104
     <?xml version="1.0"?>

Shanmugham, et al. Informational [Page 30] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

     <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"
  1. -break

Content-Type:text/uri-list

     Content-Length:176
     http://www.cisco.com/ASR-Introduction.sml
     http://www.cisco.com/ASR-Document-Part1.sml
     http://www.cisco.com/ASR-Document-Part2.sml
     http://www.cisco.com/ASR-Conclusion.sml
  1. -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

Shanmugham, et al. Informational [Page 31] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

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
 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 accepts and sets 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:SET-PARAMS 543256 MRCP/1.0
       Voice-gender:female
       Voice-category:adult
       Voice-variant:3
   S->C:MRCP/1.0 543256 200 COMPLETE

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 parameters 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:GET-PARAMS 543256 MRCP/1.0
        Voice-gender:
        Voice-category:
        Voice-variant:
        Vendor-Specific-Parameters:com.mycorp.param1;
                    com.mycorp.param2
   S->C:MRCP/1.0 543256 200 COMPLETE
        Voice-gender:female
        Voice-category:adult
        Voice-variant:3

Shanmugham, et al. Informational [Page 32] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

        Vendor-Specific-Parameters:com.mycorp.param1="Company Name";
                       com.mycorp.param2="124324234@mycorp.com"

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 that 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:SPEAK 543257 MRCP/1.0
        Voice-gender:neutral
        Voice-category:teenager
        Prosody-volume:medium
        Content-Type:application/synthesis+ssml
        Content-Length:104

Shanmugham, et al. Informational [Page 33] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

        <?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/1.0 543257 200 IN-PROGRESS
   S->C:SPEAK-COMPLETE 543257 COMPLETE MRCP/1.0
        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.

Shanmugham, et al. Informational [Page 34] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 Example:
   C->S:SPEAK 543258 MRCP/1.0
        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/1.0 543258 200 IN-PROGRESS
   C->S:STOP 543259 200 MRCP/1.0
   S->C:MRCP/1.0 543259 200 COMPLETE
        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

Shanmugham, et al. Informational [Page 35] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 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.
 If the synthesizer and the recognizer are on the same server, they
 could be optimized for a quicker kill-on-barge-in response by having
 them interact directly based on a common RTSP session-id.  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:SPEAK 543258 MRCP/1.0
        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/1.0 543258 200 IN-PROGRESS
   C->S:BARGE-IN-OCCURRED 543259 200 MRCP/1.0
        Proxy-Sync-Id:987654321
   S->C:MRCP/1.0 543259 200 COMPLETE
        Active-Request-Id-List:543258

Shanmugham, et al. Informational [Page 36] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

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
 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:SPEAK 543258 MRCP/1.0
        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/1.0 543258 200 IN-PROGRESS
   C->S:PAUSE 543259 MRCP/1.0
   S->C:MRCP/1.0 543259 200 COMPLETE
        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

Shanmugham, et al. Informational [Page 37] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 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
 Example:
   C->S:SPEAK 543258 MRCP/1.0
        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/1.0 543258 200 IN-PROGRESS
   C->S:PAUSE 543259 MRCP/1.0
   S->C:MRCP/1.0 543259 200 COMPLETE
        Active-Request-Id-List:543258
   C->S:RESUME 543260 MRCP/1.0
   S->C:MRCP/1.0 543260 200 COMPLETE
        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 being spoken, 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.

Shanmugham, et al. Informational [Page 38] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 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 into 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:SPEAK 543258 MRCP/1.0
        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/1.0 543258 200 IN-PROGRESS
   C->S:CONTROL 543259 MRCP/1.0
        Prosody-rate:fast
   S->C:MRCP/1.0 543259 200 COMPLETE
        Active-Request-Id-List:543258
   C->S:CONTROL 543260 MRCP/1.0

Shanmugham, et al. Informational [Page 39] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

        Jump-Size:-15 Words
   S->C:MRCP/1.0 543260 200 COMPLETE
        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:SPEAK 543260 MRCP/1.0
        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/1.0 543260 200 IN-PROGRESS
   S->C:SPEAK-COMPLETE 543260 COMPLETE MRCP/1.0
        Completion-Cause:000 normal

Shanmugham, et al. Informational [Page 40] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

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:SPEAK 543261 MRCP/1.0
        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/1.0 543261 200 IN-PROGRESS
   S->C:SPEECH-MARKER 543261 IN-PROGRESS MRCP/1.0
        Speech-Marker:here
   S->C:SPEECH-MARKER 543261 IN-PROGRESS MRCP/1.0
        Speech-Marker:ANSWER
   S->C:SPEAK-COMPLETE 543261 COMPLETE MRCP/1.0
        Completion-Cause:000 normal

Shanmugham, et al. Informational [Page 41] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

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.

8.1. Recognizer State Machine

 The recognizer resource is controlled by MRCP 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 MRCP 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----------------|

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

Shanmugham, et al. Informational [Page 42] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

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,
                                      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

Shanmugham, et al. Informational [Page 43] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

   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

8.4.1. 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.
   confidence-threshold =    "Confidence-Threshold" ":" 1*DIGIT CRLF

Shanmugham, et al. Informational [Page 44] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

8.4.2. 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

8.4.3. 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

8.4.4. N Best List Length

 When the recognizer matches an incoming stream with the grammar, it
 may come up with more than one alternative match 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

8.4.5. 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 RECOGNIZE,

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 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

8.4.6. 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

8.4.7. 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

8.4.8. 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.
   Cause-Code     Cause-Name     Description
     000           success       RECOGNIZE completed with a match or
                                 DEFINE-GRAMMAR succeeded in
                                 downloading and compiling the
                                 grammar

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     001           no-match      RECOGNIZE completed, but no match
                                 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.

8.4.9. 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

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8.4.10. 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
 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

8.4.11. Vendor Specific Parameters

 This set of headers allows the client to set Vendor Specific
 parameters.
 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.

8.4.12. 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 before 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

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 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
 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.

8.4.13. 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.

8.4.14. 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.

Shanmugham, et al. Informational [Page 49] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

   dtmf-interdigit-timeout = "DTMF-Interdigit-Timeout" ":"
                             1*DIGIT CRLF

8.4.15. 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
 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

8.4.16. 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

8.4.17. 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.

8.4.18. 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.

8.4.19. 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.

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8.4.20. 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
 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

8.4.21. 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

8.4.22. 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 3066 [16] for its
 values.  This MAY occur in DEFINE-GRAMMAR, RECOGNIZE, SET-PARAMS, or
 GET-PARAMS request.

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 MRCP
 message.

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8.5.1. 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 MRCP request message.  The
 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 [11] (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"?>

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     <!-- 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>
 Example 2:
    Content-Type:text/uri-list
    Content-Length:176
    session:help@root-level.store
    http://www.cisco.com/Directory-Name-List.grxml
    http://www.cisco.com/Department-List.grxml
    http://www.cisco.com/TAC-Contact-List.grxml
    session:menu1@menu-level.store
 Example 3:
    Content-Type:multipart/mixed; boundary="--break"

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  1. -break

Content-Type:text/uri-list

    Content-Length:176
    http://www.cisco.com/Directory-Name-List.grxml
    http://www.cisco.com/Department-List.grxml
    http://www.cisco.com/TAC-Contact-List.grxml
  1. -break

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>
       <!-- 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>

Shanmugham, et al. Informational [Page 54] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

       </grammar>
     --break

8.5.2. Recognizer Result Data

 Recognition result data from the server is carried in the MRCP
 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) [10] 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
    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>

8.5.3. 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 different language support or because the media
 server issued an RTSP RE-DIRECT.  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

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 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
 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:SET-PARAMS 543256 MRCP/1.0
        Sensitivity-Level:20
        Recognition-Timeout:30
        Confidence-Threshold:85
   S->C:MRCP/1.0 543256 200 COMPLETE

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.

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 Example:
   C->S:GET-PARAMS 543256 MRCP/1.0
        Sensitivity-Level:
        Recognition-Timeout:
        Confidence-threshold:
   S->C:MRCP/1.0 543256 200 COMPLETE
        Sensitivity-Level:20
        Recognition-Timeout:30
        Confidence-Threshold:85

8.8. DEFINE-GRAMMAR

 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 MRCP 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:DEFINE-GRAMMAR 543257 MRCP/1.0
        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>

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        <!-- 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/1.0 543257 200 COMPLETE
        Completion-Cause:000 success
   C->S:DEFINE-GRAMMAR 543258 MRCP/1.0
        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>
        </grammar>
   S->C:MRCP/1.0 543258 200 COMPLETE
        Completion-Cause:000 success
   C->S:DEFINE-GRAMMAR 543259 MRCP/1.0
        Content-Type:application/grammar+xml
        Content-Id:request2@field-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/1.0 543258 200 COMPLETE

Shanmugham, et al. Informational [Page 58] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

        Completion-Cause:000 success
   C->S:DEFINE-GRAMMAR 543259 MRCP/1.0
        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>
                  <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>

Shanmugham, et al. Informational [Page 59] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

             </rule>
             </grammar>
   S->C:MRCP/1.0 543259 200 COMPLETE
        Completion-Cause:000 success
   C->S:RECOGNIZE 543260 MRCP/1.0
        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/1.0 543260 200 IN-PROGRESS
   S->C:START-OF-SPEECH 543260 IN-PROGRESS MRCP/1.0
   S->C:RECOGNITION-COMPLETE 543260 COMPLETE MRCP/1.0
        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"
          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.

Shanmugham, et al. Informational [Page 60] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 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 that 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
 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.
 Example:
   C->S:RECOGNIZE 543257 MRCP/1.0
        Confidence-Threshold:90
        Content-Type:application/grammar+xml
        Content-Id:request1@form-level.store
        Content-Length:104
        <?xml version="1.0"?>

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        <!-- 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/1.0 543257 200 IN-PROGRESS
   S->C:START-OF-SPEECH 543257 IN-PROGRESS MRCP/1.0
   S->C:RECOGNITION-COMPLETE 543257 COMPLETE MRCP/1.0
        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>

Shanmugham, et al. Informational [Page 62] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

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,method the response MUST contain a status of 200(Success).
 Example:
   C->S:RECOGNIZE 543257 MRCP/1.0
        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/1.0 543257 200 IN-PROGRESS
   C->S:STOP 543258 200 MRCP/1.0

Shanmugham, et al. Informational [Page 63] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

   S->C:MRCP/1.0 543258 200 COMPLETE
        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:GET-RESULT 543257 MRCP/1.0
        Confidence-Threshold:90
   S->C:MRCP/1.0 543257 200 COMPLETE
        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>

8.12. START-OF-SPEECH

 This is an event from the recognizer to the client indicating that it
 has detected speech.  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

Shanmugham, et al. Informational [Page 64] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 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 MRCP 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
 audio waveform input of that recognition until 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:RECOGNIZE 543257 MRCP/1.0
        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">

Shanmugham, et al. Informational [Page 65] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

        <!-- 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/1.0 543257 200 IN-PROGRESS
   S->C:START-OF-SPEECH 543257 IN-PROGRESS MRCP/1.0
   S->C:RECOGNITION-COMPLETE 543257 COMPLETE MRCP/1.0
        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>

Shanmugham, et al. Informational [Page 66] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

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 [15].  The automatic speech recognizer (ASR) needs to support
 RFC 2833 [15] to recognize digits.  If it does not support RFC 2833
 [15], it will have to process the audio stream and extract the audio
 tones from it.

9. Future Study

 Various sections of the recognizer could be distributed into Digital
 Signal Processors (DSPs) on the Voice Browser/Gateway or IP Phones.
 For instance, the gateway might perform voice activity detection to
 reduce network bandwidth and CPU requirement of the automatic speech
 recognition (ASR) server.  Such extensions are deferred for further
 study and will not be addressed in this document.

10. Security Considerations

 The MRCP protocol may carry sensitive information such as account
 numbers, passwords, etc.  For this reason it is important that the
 client have the option of secure communication with the server for
 both the control messages as well as the media, though the client is
 not required to use it.  If all MRCP communications happens in a
 trusted domain behind a firewall, this may not be necessary.  If the
 client or server is deployed in an insecure network, communication
 happening across this insecure network needs to be protected.  In
 such cases, the following additional security functionality MUST be
 supported on the MRCP server.  MRCP servers MUST implement Transport
 Layer Security (TLS) to secure the RTSP communication, i.e., the RTSP
 stack SHOULD support the rtsps: URI form.  MRCP servers MUST support
 Secure Real-Time Transport Protocol (SRTP) as an option to send and
 receive media.

11. RTSP-Based Examples

 The following is an example of a typical session of speech synthesis
 and recognition between a client and the server.
 Opening the synthesizer.  This is the first resource for this
 session.  The server and client agree on a single Session ID 12345678
 and set of RTP/RTCP ports on both sides.
   C->S:SETUP rtsp://media.server.com/media/synthesizer RTSP/1.0
        CSeq:2
        Transport:RTP/AVP;unicast;client_port=46456-46457
        Content-Type:application/sdp

Shanmugham, et al. Informational [Page 67] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

        Content-Length:190
        v=0
        o=- 123 456 IN IP4 10.0.0.1
        s=Media Server
        p=+1-888-555-1212
        c=IN IP4 0.0.0.0
        t=0 0
        m=audio 0 RTP/AVP 0 96
        a=rtpmap:0 pcmu/8000
        a=rtpmap:96 telephone-event/8000
        a=fmtp:96 0-15
   S->C:RTSP/1.0 200 OK
        CSeq:2
        Transport:RTP/AVP;unicast;client_port=46456-46457;
                  server_port=46460-46461
        Session:12345678
        Content-Length:190
        Content-Type:application/sdp
        v=0
        o=- 3211724219 3211724219 IN IP4 10.3.2.88
        s=Media Server
        c=IN IP4 0.0.0.0
        t=0 0
        m=audio 46460 RTP/AVP 0 96
        a=rtpmap:0 pcmu/8000
        a=rtpmap:96 telephone-event/8000
        a=fmtp:96 0-15
 Opening a recognizer resource.  Uses the existing session ID and
 ports.
   C->S:SETUP rtsp://media.server.com/media/recognizer RTSP/1.0
        CSeq:3
        Transport:RTP/AVP;unicast;client_port=46456-46457;
                   mode=record;ttl=127
        Session:12345678
   S->C:RTSP/1.0 200 OK
        CSeq:3
        Transport:RTP/AVP;unicast;client_port=46456-46457;
                   server_port=46460-46461;mode=record;ttl=127
        Session:12345678

Shanmugham, et al. Informational [Page 68] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 An ANNOUNCE message with the MRCP SPEAK request initiates speech.
   C->S:ANNOUNCE rtsp://media.server.com/media/synthesizer RTSP/1.0
        CSeq:4
        Session:12345678
        Content-Type:application/mrcp
        Content-Length:456
        SPEAK 543257 MRCP/1.0
        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:RTSP/1.0 200 OK
        CSeq:4
        Session:12345678
        RTP-Info:url=rtsp://media.server.com/media/synthesizer;
                   seq=9810092;rtptime=3450012
        Content-Type:application/mrcp
        Content-Length:456
        MRCP/1.0 543257 200 IN-PROGRESS
 The synthesizer hits the special marker in the message to be spoken
 and faithfully informs the client of the event.
   S->C:ANNOUNCE rtsp://media.server.com/media/synthesizer RTSP/1.0
        CSeq:5
        Session:12345678

Shanmugham, et al. Informational [Page 69] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

        Content-Type:application/mrcp
        Content-Length:123
        SPEECH-MARKER 543257 IN-PROGRESS MRCP/1.0
        Speech-Marker:Stephanie
   C->S:RTSP/1.0 200 OK
        CSeq:5
 The synthesizer finishes with the SPEAK request.
   S->C:ANNOUNCE rtsp://media.server.com/media/synthesizer RTSP/1.0
        CSeq:6
        Session:12345678
        Content-Type:application/mrcp
        Content-Length:123
        SPEAK-COMPLETE 543257 COMPLETE MRCP/1.0
   C->S:RTSP/1.0 200 OK
        CSeq:6
 The recognizer is issued a request to listen for the customer
 choices.
   C->S:ANNOUNCE rtsp://media.server.com/media/recognizer RTSP/1.0
        CSeq:7
        Session:12345678
        RECOGNIZE 543258 MRCP/1.0
        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>

Shanmugham, et al. Informational [Page 70] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

   S->C:RTSP/1.0 200 OK
        CSeq:7
        Content-Type:application/mrcp
        Content-Length:123
        MRCP/1.0 543258 200 IN-PROGRESS
 The client issues the next MRCP SPEAK method in an ANNOUNCE message,
 asking the user the question.  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:ANNOUNCE rtsp://media.server.com/media/synthesizer RTSP/1.0
        CSeq:8 Session:12345678 Content-Type:application/mrcp
        Content-Length:733
        SPEAK 543259 MRCP/1.0
        Kill-On-Barge-In:true
        Content-Type:application/synthesis+ssml
        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>
   S->C:RTSP/1.0 200 OK
        CSeq:8
        Content-Type:application/mrcp
        Content-Length:123
        MRCP/1.0 543259 200 IN-PROGRESS
 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

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 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:ANNOUNCE rtsp://media.server.com/media/recognizer RTSP/1.0
        CSeq:9
        Session:12345678
        Content-Type:application/mrcp
        Content-Length:273
        START-OF-SPEECH 543258 IN-PROGRESS MRCP/1.0
   C->S:RTSP/1.0 200 OK
        CSeq:9
   S->C:ANNOUNCE rtsp://media.server.com/media/synthesizer RTSP/1.0
        CSeq:10
        Session:12345678
        Content-Type:application/mrcp
        Content-Length:273
        SPEAK-COMPLETE 543259 COMPLETE MRCP/1.0
        Completion-Cause:000 normal
   C->S:RTSP/1.0 200 OK
        CSeq:10
 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:ANNOUNCE rtsp://media.server.com/media/recognizer RTSP/1.0
        CSeq:11
        Session:12345678
        Content-Type:application/mrcp

Shanmugham, et al. Informational [Page 72] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

        Content-Length:733
        RECOGNITION-COMPLETE 543258 COMPLETE MRCP/1.0
        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>
                <xf:instance name="Person">
                    <Person>
                        <Name> Andre Roy </Name>
                    </Person>
                </xf:instance>
                          <input>   may I speak to Andre Roy </input>
            </interpretation>
        </result>
   C->S:RTSP/1.0 200 OK
        CSeq:11
   C->S:TEARDOWN rtsp://media.server.com/media/synthesizer RTSP/1.0
        CSeq:12
        Session:12345678
   S->C:RTSP/1.0 200 OK
        CSeq:12
 We are done with the resources and are tearing them down.  When the
 last of the resources for this session are released, the Session-ID
 and the RTP/RTCP ports are also released.
   C->S:TEARDOWN rtsp://media.server.com/media/recognizer RTSP/1.0
        CSeq:13
        Session:12345678
   S->C:RTSP/1.0 200 OK
        CSeq:13

Shanmugham, et al. Informational [Page 73] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

12. Informative References

 [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 4234, October 2005.
 [4]   Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
       Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
       Session Initiation Protocol", RFC 3261, June 2002.
 [5]   Handley, M. and V. Jacobson, "SDP: Session Description
       Protocol", RFC 2327, April 1998.
 [6]   World Wide Web Consortium, "Voice Extensible Markup Language
       (VoiceXML) Version 2.0", W3C Candidate Recommendation, March
       2004.
 [7]   Resnick, P., "Internet Message Format", RFC 2822, April 2001.
 [8]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
       Levels", BCP 14, RFC 2119, March 1997.
 [9]   World Wide Web Consortium, "Speech Synthesis Markup Language
       (SSML) Version 1.0", W3C Candidate Recommendation, September
       2004.
 [10]  World Wide Web Consortium, "Natural Language Semantics Markup
       Language (NLSML) for the Speech Interface Framework", W3C
       Working Draft, 30 May 2001.
 [11]  World Wide Web Consortium, "Speech Recognition Grammar
       Specification Version 1.0", W3C Candidate Recommendation, March
       2004.
 [12]  Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD
       63, RFC 3629, November 2003.
 [13]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
       Extensions (MIME) Part Two: Media Types", RFC 2046, November
       1996.

Shanmugham, et al. Informational [Page 74] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 [14]  Levinson, E., "Content-ID and Message-ID Uniform Resource
       Locators", RFC 2392, August 1998.
 [15]  Schulzrinne, H. and S. Petrack, "RTP Payload for DTMF Digits,
       Telephony Tones and Telephony Signals", RFC 2833, May 2000.
 [16]  Alvestrand, H., "Tags for the Identification of Languages", BCP
       47, RFC 3066, January 2001.

Shanmugham, et al. Informational [Page 75] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

Appendix A. ABNF Message Definitions

 ALPHA          =  %x41-5A / %x61-7A   ; A-Z / a-z
 CHAR           =  %x01-7F     ; any 7-bit US-ASCII character,
                               ;    excluding NUL
 CR             =  %x0D        ; carriage return
 CRLF           =  CR LF       ; Internet standard newline
 DIGIT          =  %x30-39     ; 0-9
 DQUOTE         =  %x22        ; " (Double Quote)
 HEXDIG         =  DIGIT / "A" / "B" / "C" / "D" / "E" / "F"
 HTAB           =  %x09        ; horizontal tab
 LF             =  %x0A        ; linefeed
 OCTET          =  %x00-FF     ; 8 bits of data
 SP             =  %x20        ; space
 WSP            =  SP / HTAB   ; white space
 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
 UTF8-CONT      =  %x80-BF
 param          =  *pchar
 quoted-string  =  SWS DQUOTE *(qdtext / quoted-pair )
                   DQUOTE
 qdtext         =  LWS / %x21 / %x23-5B / %x5D-7E
                   / UTF8-NONASCII

Shanmugham, et al. Informational [Page 76] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 quoted-pair    =  "\" (%x00-09 / %x0B-0C
                   / %x0E-7F)
 token          =  1*(alphanum / "-" / "." / "!" / "%" / "*"
                    / "_" / "+" / "`" / "'" / "~" )
 reserved       =  ";" / "/" / "?" / ":" / "@" / "&" / "="
                   / "+" / "$" / ","
 mark           =  "-" / "_" / "." / "!" / "~" / "*" / "'"
                   / "(" / ")"
 unreserved     =  alphanum / mark
 char           =  unreserved / escaped /
                   ":" / "@" / "&" / "=" / "+" / "$" / ","
 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 / ";" / "@"
                   / "&" / "=" / "+" / "$" / "," )
 opaque-part    =  uric-no-slash *uric
 uric           =  reserved / unreserved / escaped
 uric-no-slash  =  unreserved / escaped / ";" / "?" / ":"
                   / "@" / "&" / "=" / "+" / "$" / ","
 path-segments  =  segment *( "/" segment )
 segment        =  *pchar *( ";" param )

Shanmugham, et al. Informational [Page 77] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 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 ]
 hexseq         =    hex4 *( ":" hex4)
 hex4           =    1*4HEXDIG

Shanmugham, et al. Informational [Page 78] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 port           =    1*DIGIT
 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 =    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 2392 and RFC 2046
 mrcp-version   =    "MRCP" "/" 1*DIGIT "." 1*DIGIT
 request-id     =    1*DIGIT
 status-code    =    1*DIGIT
 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

Shanmugham, et al. Informational [Page 79] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 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
 method-name    =    synthesizer-method
                     /    recognizer-method
 event-name     =    synthesizer-event
                     /    recognizer-event

Shanmugham, et al. Informational [Page 80] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 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"
 recognizer-header =      confidence-threshold
                   /      sensitivity-level
                   /      speed-vs-accuracy
                   /      n-best-list-length

Shanmugham, et al. Informational [Page 81] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

                   /      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

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 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
 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

Shanmugham, et al. Informational [Page 83] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

 no-input-timeout =  "No-Input-Timeout" ":" 1*DIGIT CRLF
 recognition-timeout = "Recognition-Timeout" ":" 1*DIGIT CRLF
 waveform-url   =    "Waveform-URL" ":" absoluteURI 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
 save-waveform  =    "Save-Waveform" ":" boolean-value CRLF
 new-audio-channel = "New-Audio-Channel" ":"
                     boolean-value CRLF

Appendix B. Acknowledgements

 Andre Gillet (Nuance Communications)
 Andrew Hunt (SpeechWorks)
 Aaron Kneiss (SpeechWorks)
 Kristian Finlator (SpeechWorks)
 Martin Dragomirecky (Cisco Systems, Inc.)
 Pierre Forgues (Nuance Communications)
 Suresh Kaliannan (Cisco Systems, Inc.)
 Corey Stohs (Cisco Systems, Inc.)
 Dan Burnett (Nuance Communications)

Shanmugham, et al. Informational [Page 84] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

Authors' Addresses

 Saravanan Shanmugham
 Cisco Systems, Inc.
 170 W. Tasman Drive
 San Jose, CA 95134
 EMail: sarvi@cisco.com
 Peter Monaco
 Nuasis Corporation
 303 Bryant St.
 Mountain View, CA 94041
 EMail: peter.monaco@nuasis.com
 Brian Eberman
 Speechworks, Inc.
 695 Atlantic Avenue
 Boston, MA 02111
 EMail: brian.eberman@speechworks.com

Shanmugham, et al. Informational [Page 85] RFC 4463 MRCP by Cisco, Nuance, and Speechworks April 2006

Full Copyright Statement

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 This document is subject to the rights, licenses and restrictions
 contained in BCP 78 and at www.rfc-editor.org/copyright.html, and
 except as set forth therein, the authors retain all their rights.
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