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MRCP Event Messages

Reference Number: AA-01632 Views: 4035 0 Rating/ Voters

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.  The event message consists of an event header line followed by the message header section and an optional message body containing data specific to the event message.  The header line has the request-id of the corresponding request and status value.  The request-state value is COMPLETE if the request is done and this was the last event, else it is IN-PROGRESS.

event-line         = mrcp-version SP message-length SP event-name
                                  SP request-id SP request-state CRLF


The mrcp-version used here is identical to the one used in the Request/Response Line and indicates the version of the MRCP protocol running on the server.

mrcp-version       = "MRCP" "/" 1*DIGIT "." 1*DIGIT


The message-length field describes the length of the message (in bytes), including the start-line:

message-length     = 1*19DIGIT


The request-id field is a unique identifier associated with each request. Clients should assign incremental numbers to each unique request, and the Media Server will use this request-id when responding to requests. In event messages, this value indicates which specific request the event relates to.

request-id         = 1*10DIGIT


The event-name identifies the nature of the event generated by the media resource.  The set of valid event names depends on the resource generating it.  See the corresponding resource-specific section of the article (below).

event-name         =  synthesizer-event
                   /  recognizer-event


The request-state field indicates whether the Request/Command causing this event is complete or still in progress. The final event for a request has a COMPLETE status indicating the completion of the request.

request-state      =  "COMPLETE"
                   /  "IN-PROGRESS"
                   /  "PENDING"


Recognizer Events

The recognizer can generate the following events.

recognizer-event    =  "START-OF-INPUT"
                    /  "RECOGNITION-COMPLETE"
                    /  "INTERPRETATION-COMPLETE"


The START-OF-INPUT event is issued whenever the recognizer detects the beginning of either speech or DTMF signal within the RTP audio stream associated with the session. The input-type header field of the START-OF-INPUT indicates whether the source of the event was speech or dtmf. Note that in the MRCPv1 specification, "START-OF-INPUT" is reported as "START-OF-SPEECH", so when using MRCPv1, the event will be "START-OF-SPEECH", not "START-OF-INPUT".

The RECOGNITION-COMPLETE event is issued when the Media Server finishes a recognition operation. The recognition result is sent in the body of the message. If the server is configured to return a URI to the audio waveform for this request, it will be indicated in the Waveform-URI header field. The client can use this URI to retrieve or playback the audio. The request-state for these events will be COMPLETE to indicate that no further messages will be associated with the associated request-id.

The INTERPRETATION-COMPLETE event from the recognizer resource to the client indicates that a INTERPRET operation is complete. The interpretation result is sent in the body of the message. The request-state for these events will be COMPLETE to indicate that no further messages will be associated with the associated request-id. The Completion-Cause header field will be included in this event and will be set to an appropriate value from the table below.


Recognizer Completion-Codes

The Completion-Code header field is part of a RECOGNITION-COMPLETE event coming from the recognizer resource to the client.  It indicates the reason behind the RECOGNIZE method completion.  This header field is sent in the DEFINE-GRAMMAR and RECOGNIZE responses, if they return with a failure status and a COMPLETE state.  In the ABNF below, the 'cause-code' contains a numerical value selected from the Cause-Code column of the following table.  The 'cause-name' contains the corresponding token selected from the Cause-Name column.

completion-cause    =  "Completion-Cause" ":" cause-code SP
                       cause-name CRLF
cause-code          =  3DIGIT
cause-name          =  *VCHAR

                                                                                                                                                                 

  

Cause-Code

  
  

Cause-Name

  
  

Description

  
  

000

  
  

success

  
  

RECOGNIZE completed with a match or   DEFINE-GRAMMAR succeeded in downloading and compiling the grammar

  
  

001

  
  

no-match

  
  

RECOGNIZE completed, but no match was found

  
  

002

  
  

no-input-timeout

  
  

RECOGNIZE completed without a match due to a   no-input-timeout

  
  

003

  
  

hotword-maxtime

  
  

RECOGNIZE in hotword mode completed without   a match due to a recognition-timeout

  
  

004

  
  

grammar-load-failure

  
  

RECOGNIZE failed due grammar load failure

  
  

005

  
  

grammar-compilation-failure

  
  

RECOGNIZE failed due to grammar compilation   failure

  
  

006

  
  

recognizer-error

  
  

RECOGNIZE request terminated prematurely due   to a recognizer error

  
  

007

  
  

speech-too-early

  
  

RECOGNIZE request terminated because speech   was too early. This happens when the audio stream is already “in-speech” when   the RECOGNIZE request was received.

  
  

008

  
  

success-maxtime

  
  

RECOGNIZE request terminated because speed   was too long but whatever was spoken till that point was a full match

  
  

009

  
  

uri-failure

  
  

Failure accessing a URI

  
  

010

  
  

language-unsupported

  
  

Language not supported

  
  

011

  
  

cancelled

  
  

A new RECOGNIZE cancelled this one, or a   prior RECOGNIZE failed while this one was still in the queue.

  
  

012

  
  

semantics-failure

  
  

Recognition succeeded but semantic   interpretation of the recognized input failed. The RECOGNITION-COMPLETE event   will contain the Recognition result with only input text and no   interpretation.

  
  

013

  
  

partial-match

  
  

Speech Incomplete timeout expired before   there was a full match.  But whatever that   was spoken till that point was a partial match to one or more grammars.

  
  

014

  
  

partial-match-maxtime

  
  

The Recognition-Timer expired before full   match was achieved.  But whatever was   spoken till that point was a partial match to one or more grammars.

  
  

015

  
  

no-match-maxtime

  
  

The Recognition-Timer expired.  Whatever was spoken till that point either   did not match any of the grammars.    This cause could also be returned if the recognizer does not support   detecting partial grammar matches.

  
  

016

  
  

grammar-definition-failure

  
  

Any DEFINE-GRAMMAR error other than grammar-load-failure   and grammar-compilation-failure.

  


Synthesizer Events

The synthesizer can generate the following events.

synthesizer-event  =  "SPEECH-MARKER"
                   /  "SPEAK-COMPLETE"


The SPEECH-MARKER event is issued whenever the synthesizer reaches a marker tag in the speech markup it is currently processing. The value of the request-id field will match that of the corresponding SPEAK request.  The request-state field will have the value "IN-PROGRESS" as the speech is still not complete.  The value of the speech marker hit, describing where the synthesizer is in the speech markup will be returned in the Speech-Marker header field, along with the timestamp indicating the instant in the output speech stream that the marker was encountered. 

The SPEAK-COMPLETE event is issued when the Media Server finishes a SPEAK operation. The request-state for these events will be COMPLETE to indicate that no further messages will be associated with the associated request-id. The Completion-Cause header field specifies the cause code pertaining to the status and reason of the request completion, such as SPEAK completed normally or because of an error, kill-on-barge-in etc. The Completion-Cause header field will be included in this event and will be set to an appropriate value from the table below.


Synthesizer Completion-Codes

The Completion-Code header field is part of a SPEAK-COMPLETE event coming from the synthesizer resource to the client.  It indicates the reason behind the SPEAK method completion.  This header field is sent in the SPEAK responses, if they return with a failure status and a COMPLETE state.  

completion-cause   =   "Completion-Cause" ":" 3DIGIT SP
                       1*VCHAR 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 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

  
  

006

  
  

lexicon-load-failure

  
  

Lexicon loading failed

  
  

007

  
  

Cancelled

  
  

A prior SPEAK request failed while this one   was still in the queue.