/ 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
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
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,
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
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
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
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.
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.
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.
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"?>
<!-- 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>