RFC 6917
Media Resource Brokering
Pages: 136
Proposed Standard
Proposed Standard
Part 2 of 6 – Pages 12 to 38
5. MRB Interface Definitions
The intention of this specification is to provide a toolkit for a variety of deployment architectures where media resource brokering can take place. Two main interfaces are required to support the differing requirements. The two interfaces are described in the remainder of this section and have been named the Media Server Resource Publish and Media Server Resource Consumer interfaces. It is beyond the scope of this document to define exactly how to construct an MRB using the interfaces described. It is, however, important that the two interfaces are complimentary so that development of appropriate MRB functionality is supported.5.1. Media Server Resource Publish Interface
The Media Server Resource Publish interface is responsible for providing an MRB with appropriate Media Server resource information. As such, this interface is assumed to provide both general and specific details related to Media Server resources. This information needs to be conveyed using an industry standard mechanism to provide increased levels of adoption and interoperability. A Control Package for the Media Control Channel Framework will be specified to fulfill this interface requirement. It provides an establishment and monitoring mechanism to enable a Media Server to report appropriate statistics to an MRB. The Publish interface is used with both the Query mode and In-line mode of MRB operation. As already discussed in Section 1, the MRB view of Media Server resource availability will in reality be approximate -- i.e., partial and imperfect. The MRB Publish interface does not provide an exhaustive view of current Media Server resource consumption; the Media Server may in some cases provide a best-effort computed view of resource consumption parameters conveyed in the Publish interface (e.g., Digital Signal Processors (DSPs) with a fixed number of
streams versus Graphics Processing Units (GPUs) with CPU availability). Media resource information may only be reported periodically over the Publish interface to an MRB. It is also worth noting that while the scope of the MRB is in providing interested Application Servers with the available resources, the MRB also allows for the retrieval of information about consumed resources. While this is of course a relevant piece of information (e.g., for monitoring purposes), such functionality inevitably raises security considerations, and implementations should take this into account. See Section 12 for more details. The MRB Publish interface uses the Media Control Channel Framework ([RFC6230]) as the basis for interaction between a Media Server and an MRB. The Media Control Channel Framework uses an extension mechanism to allow specific usages that are known as Control Packages. Section 5.1.1 defines the Control Package that MUST be implemented by any Media Server wanting to interact with an MRB entity.5.1.1. Control Package Definition
This section fulfills the requirement for information that must be specified during the definition of a Control Framework package, as detailed in Section 8 of [RFC6230].5.1.1.1. Control Package Name
The Media Channel Control Framework requires a Control Package definition to specify and register a unique name and version. The name and version of this Control Package is "mrb-publish/1.0".5.1.1.2. Framework Message Usage
The MRB Publish interface allows a Media Server to convey available capabilities and resources to an MRB entity. This package defines XML elements in Section 5.1.2 and provides an XML schema in Section 10. The XML elements in this package are split into requests, responses, and event notifications. Requests are carried in CONTROL message bodies; the <mrbrequest> element is defined as a package request. This request can be used for creating new subscriptions and updating/ removing existing subscriptions. Event notifications are also carried in CONTROL message bodies; the <mrbnotification> element is
defined for package event notifications. Responses are carried either in REPORT message or Control Framework 200 response bodies; the <mrbresponse> element is defined as a package-level response. Note that package responses are different from framework response codes. Framework error response codes (see Section 7 of [RFC6230]) are used when the request or event notification is invalid; for example, a request has invalid XML (400) or is not understood (500). Package-level responses are carried in framework 200 response or REPORT message bodies. This package's response codes are defined in Section 5.1.4.5.1.1.3. Common XML Support
The Media Control Channel Framework [RFC6230] requires a Control Package definition to specify if the attributes for media dialog or conference references are required. The Publish interface defined in Section 10 does import and make use of the common XML schema defined in the Media Control Channel Framework. The Consumer interface defined in Section 11 does import and make use of the common XML schema defined in the Media Control Channel Framework.5.1.1.4. CONTROL Message Body
A valid CONTROL message body MUST conform to the schema defined in Section 10 and described in Section 5.1.2. XML messages appearing in CONTROL messages MUST contain either an <mrbrequest> or <mrbnotification> element.5.1.1.5. REPORT Message Body
A valid REPORT message body MUST conform to the schema defined in Section 10 and described in Section 5.1.2. XML messages appearing in REPORT messages MUST contain an <mrbresponse> element.5.1.1.6. Audit
The 'mrb-publish/1.0' Media Control Channel Framework package does not require any additional auditing capability.
5.1.2. Element Definitions
This section defines the XML elements for the Publish interface Media Control Channel package defined in Section 5.1. The formal XML schema definition for the Publish interface can be found in Section 10. The root element is <mrbpublish>. All other XML elements (requests, responses, notifications) are contained within it. The MRB Publish interface request element is detailed in Section 5.1.3. The MRB Publish interface notification element is detailed in Section 5.1.5. The MRB Publish interface response element is detailed in Section 5.1.4. The <mrbpublish> element has the following attributes: version: a token specifying the mrb-publish package version. The value is fixed as '1.0' for this version of the package. The attribute MUST be present. The <mrbpublish> element has the following child elements, and there MUST NOT be more than one such child element in any <mrbpublish> message: <mrbrequest> for sending an MRB request. See Section 5.1.3. <mrbresponse> for sending an MRB response. See Section 5.1.4. <mrbnotification> for sending an MRB notification. See Section 5.1.5.5.1.3. <mrbrequest>
This section defines the <mrbrequest> element used to initiate requests from an MRB to a Media Server. The element describes information relevant for the interrogation of a Media Server. The <mrbrequest> element has no defined attributes. The <mrbrequest> element has the following child element: <subscription> for initiating a subscription to a Media Server from an MRB. See Section 5.1.3.1.
5.1.3.1. <subscription>
The <subscription> element is included in a request from an MRB to a Media Server to provide the details relating to the configuration of updates (known as a subscription session). This element can be used either to request a new subscription or to update an existing one (e.g., to change the frequency of the updates), and to remove ongoing subscriptions as well (e.g., to stop an indefinite update). The MRB will inform the Media Server regarding how long it wishes to receive updates and the frequency that updates should be sent. Updates related to the subscription are sent using the <mrbnotification> element. The <subscription> element has the following attributes: id: Indicates a unique token representing the subscription session between the MRB and the Media Server. The attribute MUST be present. seqnumber: Indicates a sequence number to be used in conjunction with the subscription session ID to identify a specific subscription command. The first subscription MUST contain a non-zero number 'seqnumber', and subsequent subscriptions MUST contain a higher number than the previous 'seqnumber' value. If a subsequent 'seqnumber' is not higher, a 405 response code is generated as per Section 5.1.4. The attribute MUST be present. action: Provides the operation that should be carried out on the subscription: * The value of 'create' instructs the Media Server to attempt to set up a new subscription. * The value of 'update' instructs the Media Server to attempt to update an existing subscription. * The value of 'remove' instructs the Media Server to attempt to remove an existing subscription and consequently stop any ongoing related notification. The attribute MUST be present.
The <subscription> element has zero or more of the following child
elements:
<expires>: Provides the amount of time in seconds that a
subscription should be installed for notifications at the Media
Server. Once the amount of time has passed, the subscription
expires, and the MRB has to subscribe again if it is still
interested in receiving notifications from the Media Server. The
element MAY be present.
<minfrequency>: Provides the minimum frequency in seconds that the
MRB wishes to receive notifications from the Media Server. The
element MAY be present.
<maxfrequency>: Provides the maximum frequency in seconds that the
MRB wishes to receive notifications from the Media Server. The
element MAY be present.
Please note that these three optional pieces of information provided
by the MRB only act as a suggestion: the Media Server MAY change the
proposed values if it considers the suggestions unacceptable (e.g.,
if the MRB has requested a notification frequency that is too high).
In such a case, the request would not fail, but the updated,
acceptable values would be reported in the <mrbresponse> accordingly.
5.1.4. <mrbresponse>
Responses to requests are indicated by an <mrbresponse> element.
The <mrbresponse> element has the following attributes:
status: numeric code indicating the response status. The attribute
MUST be present.
reason: string specifying a reason for the response status. The
attribute MAY be present.
The <mrbresponse> element has a single child element:
<subscription> for providing details related to a subscription
requested by a Media Server (see below in this section).
The following status codes are defined for 'status': +-----------+-------------------------------------------------------+ | code | description | +-----------+-------------------------------------------------------+ | 200 | OK | | | | | 400 | Syntax error | | | | | 401 | Unable to create Subscription | | | | | 402 | Unable to update Subscription | | | | | 403 | Unable to remove Subscription | | | | | 404 | Subscription does not exist | | | | | 405 | Wrong sequence number | | | | | 406 | Subscription already exists | | | | | 420 | Unsupported attribute or element | +-----------+-------------------------------------------------------+ Table 1: <mrbresponse> Status Codes If a new subscription request made by an MRB (action='create') has been accepted, the Media Server MUST reply with an <mrbresponse> with status code 200. The same rule applies whenever a request to update (action='update') or remove (action='remove') an existing transaction can be fulfilled by the Media Server. A subscription request, nevertheless, may fail for several reasons. In such a case, the status codes defined in Table 1 must be used instead. Specifically, if the Media Server fails to handle a request due to a syntax error in the request itself (e.g., incorrect XML, violation of the schema constraints, or invalid values in any of the attributes/elements), the Media Server MUST reply with an <mrbresponse> with status code 400. If a syntactically correct request fails because the request also includes any attribute/element the Media Server doesn't understand, the Media Server MUST reply with an <mrbresponse> with status code 420. If a syntactically correct request fails because the MRB wants to create a new subscription, but the provided unique 'id' for the subscription already exists, the Media Server MUST reply with an <mrbresponse> with status code 406. If a syntactically correct request fails because the MRB wants to update/remove a subscription that doesn't exist, the Media Server MUST reply with an <mrbresponse> with status code 404. If the Media
Server is unable to accept a request for any other reason (e.g., the MRB has no more resources to fulfill the request), the Media Server MUST reply with an <mrbresponse> with status code 401/402/403, depending on the action the MRB provided in its request: o action='create' --> 401; o action='update' --> 402; o action='remove' --> 403; A response to a subscription request that has a status code of 200 indicates that the request is successful. The response MAY also contain a <subscription> child that describes the subscription. The <subscription> child MAY contain 'expires', 'minfrequency', and 'maxfrequency' values even if they were not contained in the request. The Media Server can choose to change the suggested 'expires', 'minfrequency', and 'maxfrequency' values provided by the MRB in its <mrbrequest> if it considers them unacceptable (e.g., the requested frequency range is too high). In such a case, the response MUST contain a <subscription> element describing the subscription as the Media Server accepted it, and the Media Server MUST include in the <subscription> element all of those values that it modified relative to the request, to inform the MRB about the change.5.1.5. <mrbnotification>
The <mrbnotification> element is included in a request from a Media Server to an MRB to provide the details relating to current status. The Media Server will inform the MRB of its current status as defined by the information in the <subscription> element. Updates are sent using the <mrbnotification> element. The <mrbnotification> element has the following attributes: id: indicates a unique token representing the session between the MRB and the Media Server and is the same as the one appearing in the <subscription> element. The attribute MUST be present. seqnumber: indicates a sequence number to be used in conjunction with the subscription session ID to identify a specific notification update. The first notification update MUST contain a non-zero number 'seqnumber', and subsequent notification updates MUST contain a higher number than the previous 'seqnumber' value. If a subsequent 'seqnumber' is not higher, the situation should be
considered an error by the entity receiving the notification
update. How the receiving entity deals with this situation is
implementation specific. The attribute MUST be present.
It's important to point out that the 'seqnumber' that appears in an
<mrbnotification> is not related to the 'seqnumber' appearing in a
<subscription>. In fact, the latter is associated with subscriptions
and would increase at every command issued by the MRB, while the
former is associated with the asynchronous notifications the Media
Server would trigger according to the subscription and as such would
increase at every notification message to enable the MRB to keep
track of them.
The following sub-sections provide details of the child elements that
make up the contents of the <mrbnotification> element.
5.1.5.1. <media-server-id>
The <media-server-id> element provides a unique system-wide
identifier for a Media Server instance. The element MUST be present
and MUST be chosen such that it is extremely unlikely that two
different Media Servers would present the same id to a given MRB.
5.1.5.2. <supported-packages>
The <supported-packages> element provides the list of Media Control
Channel packages supported by the Media Server. The element MAY be
present.
The <supported-packages> element has no attributes.
The <supported-packages> element has a single child element:
<package>: Gives the name of a package supported by the Media
Server. The <package> element has a single attribute, 'name',
which provides the name of the supported Media Control Channel
Framework package, compliant with Section 13.1.1 of [RFC6230].
5.1.5.3. <active-rtp-sessions>
The <active-rtp-sessions> element provides information detailing the
current active Real-time Transport Protocol (RTP) sessions. The
element MAY be present.
The <active-rtp-sessions> element has no attributes.
The <active-rtp-sessions> element has a single child element:
<rtp-codec>: Describes a supported codec and the number of active
sessions using that codec. The <rtp-codec> element has one
attribute. The value of the attribute, 'name', is a media type
(which can include parameters per [RFC6381]). The <rtp-codec>
element has two child elements. The child element <decoding> has
as content the decimal number of RTP sessions being decoded using
the specified codec, and the child element <encoding> has as
content the decimal number of RTP sessions being encoded using the
specified codec.
5.1.5.4. <active-mixer-sessions>
The <active-mixer-sessions> element provides information detailing
the current active mixed RTP sessions. The element MAY be present.
The <active-mixer-sessions> element has no attributes.
The <active-mixer-sessions> element has a single child element:
<active-mix>: Describes a mixed active RTP session. The
<active-mix> element has one attribute. The value of the
attribute, 'conferenceid', is the name of the mix. The
<active-mix> element has one child element. The child element,
<rtp-codec>, contains the same information relating to RTP
sessions as that defined in Section 5.1.5.3. The element MAY be
present.
5.1.5.5. <non-active-rtp-sessions>
The <non-active-rtp-sessions> element provides information detailing
the currently available inactive RTP sessions, that is, how many more
RTP streams this Media Server can support. The element MAY be
present.
The <non-active-rtp-sessions> element has no attributes.
The <non-active-rtp-sessions> element has a single child element:
<rtp-codec>: Describes a supported codec and the number of
non-active sessions for that codec. The <rtp-codec> element has
one attribute. The value of the attribute, 'name', is a media
type (which can include parameters per [RFC6381]). The
<rtp-codec> element has two child elements. The child element
<decoding> has as content the decimal number of RTP sessions
available for decoding using the specified codec, and the child
element <encoding> has as content the decimal number of RTP
sessions available for encoding using the specified codec.
5.1.5.6. <non-active-mixer-sessions>
The <non-active-mixer-sessions> element provides information
detailing the current inactive mixed RTP sessions, that is, how many
more mixing sessions this Media Server can support. The element MAY
be present.
The <non-active-mixer-sessions> element has no attributes.
The <non-active-mixer-sessions> element has a single child element:
<non-active-mix>: Describes available mixed RTP sessions. The
<non-active-mix> element has one attribute. The value of the
attribute, 'available', is the number of mixes that could be used
using that profile. The <non-active-mix> element has one child
element. The child element, <rtp-codec>, contains the same
information relating to RTP sessions as that defined in
Section 5.1.5.5. The element MAY be present.
5.1.5.7. <media-server-status>
The <media-server-status> element provides information detailing the
current status of the Media Server. The element MUST be present. It
can return one of the following values:
active: Indicates that the Media Server is available for service.
deactivated: Indicates that the Media Server has been withdrawn from
service, and as such requests should not be sent to it before it
becomes 'active' again.
unavailable: Indicates that the Media Server continues to process
past requests but cannot accept new requests, and as such should
not be contacted before it becomes 'active' again.
The <media-server-status> element has no attributes.
The <media-server-status> element has no child elements.
5.1.5.8. <supported-codecs>
The <supported-codecs> element provides information detailing the current codecs supported by a Media Server and associated actions. The element MAY be present. The <supported-codecs> element has no attributes. The <supported-codecs> element has a single child element: <supported-codec>: Has a single attribute, 'name', which provides the name of the codec about which this element provides information. A valid value is a media type that, depending on its definition, can include additional parameters (e.g., [RFC6381]). The <supported-codec> element then has a further child element, <supported-codec-package>. The <supported-codec-package> element has a single attribute, 'name', which provides the name of the Media Control Channel Framework package, compliant with Section 13.1.1 of [RFC6230], for which the codec support applies. The <supported-codec-package> element has zero or more <supported-action> children, each one of which describes an action that a Media Server can apply to this codec: * 'decoding', meaning a decoder for this codec is available; * 'encoding', meaning an encoder for this codec is available; * 'passthrough', meaning the Media Server is able to pass a stream encoded using that codec through, without re-encoding.5.1.5.9. <application-data>
The <application-data> element provides an arbitrary string of characters as application-level data. This data is meant to only have meaning at the application-level logic and as such is not otherwise restricted by this specification. The set of allowed characters is the same as those in XML (viz., tab, carriage return, line feed, and the legal characters of Unicode and ISO/IEC 10646 [ISO.10646.2012] (see also Section 2.2 of <http://www.w3.org/TR/xml/>)). The element MAY be present. The <application-data> element has no attributes. The <application-data> element has no child elements.
5.1.5.10. <file-formats>
The <file-formats> element provides a list of file formats supported for the purpose of playing media. The element MAY be present. The <file-formats> element has no attributes. The <file-formats> element has zero of more the following child elements: <supported-format>: Has a single attribute, 'name', which provides the type of file format that is supported. A valid value is a media type that, depending on its definition, can include additional parameters (e.g., [RFC6381]). The <supported-format> element then has a further child element, <supported-file-package>. The <supported-file-package> element provides the name of the Media Control Channel Framework package, compliant with Section 13.1.1 of [RFC6230], for which the file format support applies.5.1.5.11. <max-prepared-duration>
The <max-prepared-duration> element provides the maximum amount of time a media dialog will be kept in the prepared state before timing out (see Section 4.4.2.2.6 of RFC 6231 [RFC6231]. The element MAY be present. The <max-prepared-duration> element has no attributes. The <max-prepared-duration> element has a single child element: <max-time>: Has a single attribute, 'max-time-seconds', which provides the amount of time in seconds that a media dialog can be in the prepared state. The <max-time> element then has a further child element, <max-time-package>. The <max-time-package> element provides the name of the Media Control Channel Framework package, compliant with Section 13.1.1 of [RFC6230], for which the time period applies.
5.1.5.12. <dtmf-support>
The <dtmf-support> element specifies the supported methods to detect Dual-Tone Multi-Frequency (DTMF) tones and to generate them. The element MAY be present. The <dtmf-support> element has no attributes. The <dtmf-support> element has zero of more of the following child elements: <detect>: Indicates the support for DTMF detection. The <detect> element has no attributes. The <detect> element then has a further child element, <dtmf-type>. The <dtmf-type> element has two attributes: 'name' and 'package'. The 'name' attribute provides the type of DTMF being used, and it can only be a case- insensitive string containing either 'RFC4733' [RFC4733] or 'Media' (detecting tones as signals from the audio stream). The 'package' attribute provides the name of the Media Control Channel Framework package, compliant with Section 13.1.1 of [RFC6230], for which the DTMF type applies. <generate>: Indicates the support for DTMF generation. The <generate> element has no attributes. The <generate> element then has a further child element, <dtmf-type>. The <dtmf-type> element has two attributes: 'name' and 'package'. The 'name' attribute provides the type of DTMF being used, and it can only be a case- insensitive string containing either 'RFC4733' [RFC4733] or 'Media' (generating tones as signals in the audio stream). The 'package' attribute provides the name of the Media Control Channel Framework package, compliant with Section 13.1.1 of [RFC6230], for which the DTMF type applies. <passthrough>: Indicates the support for passing DTMF through without re-encoding. The <passthrough> element has no attributes. The <passthrough> element then has a further child element, <dtmf-type>. The <dtmf-type> element has two attributes: 'name' and 'package'. The 'name' attribute provides the type of DTMF being used, and it can only be a case-insensitive string containing either 'RFC4733' [RFC4733] or 'Media' (passing tones as signals through the audio stream). The 'package' attribute provides the name of the Media Control Channel Framework package, compliant with Section 13.1.1 of [RFC6230], for which the DTMF type applies.
5.1.5.13. <mixing-modes>
The <mixing-modes> element provides information about the support for audio and video mixing of a Media Server, specifically a list of supported algorithms to mix audio and a list of supported video presentation layouts. The element MAY be present. The <mixing-modes> element has no attributes. The <mixing-modes> element has zero or more of the following child elements: <audio-mixing-modes>: Describes the available algorithms for audio mixing. The <audio-mixing-modes> element has no attributes. The <audio-mixing-modes> element has one child element. The child element, <audio-mixing-mode>, contains a specific available algorithm. Valid values for the <audio-mixing-mode> element are algorithm names, e.g., 'nbest' and 'controller' as defined in [RFC6505]. The element has a single attribute, 'package'. The attribute 'package' provides the name of the Media Control Channel Framework package, compliant with Section 13.1.1 of [RFC6230], for which the algorithm support applies. <video-mixing-modes>: Describes the available video presentation layouts and the supported functionality related to video mixing. The <video-mixing-modes> element has two attributes: 'vas' and 'activespeakermix'. The 'vas' attribute is of type boolean with a value of 'true' indicating that the Media Server supports automatic Voice Activated Switching. The 'activespeakermix' is of type boolean with a value of 'true' indicating that the Media Server is able to prepare an additional video stream for the loudest speaker participant without its contribution. The <video-mixing-modes> element has one child element. The child element, <video-mixing-mode>, contains the name of a specific video presentation layout. The name may refer to one of the predefined video layouts defined in the XCON conference information data model [RFC6501], or to non-XCON layouts as well, as long as they are properly prefixed according to the schema they belong to. The <video-mixing-mode> element has a single attribute, 'package'. The attribute 'package' provides the name of the Media Control Channel Framework package, compliant with Section 13.1.1 of [RFC6230], for which the algorithm support applies.
5.1.5.14. <supported-tones>
The <supported-tones> element provides information about which tones a Media Server is able to play and recognize. In particular, the support is reported by referring to both support for country codes (ISO 3166-1 [ISO.3166-1]) and supported functionality (ITU-T Recommendation Q.1950 [ITU-T.Q.1950]). The element MAY be present. The <supported-tones> element has no attributes. The <supported-tones> element has zero or more of the following child elements: <supported-country-codes>: Describes the supported country codes with respect to tones. The <supported-country-codes> element has no attributes. The <supported-country-codes> element has one child element. The child element, <country-code>, reports support for a specific country code, compliant with the ISO 3166-1 [ISO.3166-1] specification. The <country-code> element has a single attribute, 'package'. The attribute 'package' provides the name of the Media Control Channel Framework package, compliant with Section 13.1.1 of [RFC6230], in which the tones from the specified country code are supported. <supported-h248-codes>: Describes the supported H.248 codes with respect to tones. The <supported-h248-codes> element has no attributes. The <supported-h248-codes> element has one child element. The child element, <h248-code>, reports support for a specific H.248 code, compliant with the ITU-T Recommendation Q.1950 [ITU-T.Q.1950] specification. The codes can be either specific (e.g., cg/dt to only report the Dial Tone from the Call Progress Tones package) or generic (e.g., cg/* to report all the tones from the Call Progress Tones package), using wildcards. The <h248-code> element has a single attribute, 'package'. The attribute 'package' provides the name of the Media Control Channel Framework package, compliant with Section 13.1.1 of [RFC6230], in which the specified codes are supported.5.1.5.15. <file-transfer-modes>
The <file-transfer-modes> element allows the Media Server to specify which scheme names are supported for transferring files to a Media Server for each Media Control Channel Framework package type, for example, whether the Media Server supports fetching resources via HTTP, HTTPS, NFS, etc. The element MAY be present. The <file-transfer-modes> element has no attributes.
The <file-transfer-modes> element has a single child element:
<file-transfer-mode>: Has two attributes: 'name' and 'package'. The
'name' attribute provides the scheme name of the protocol that can
be used for file transfer (e.g., HTTP, HTTPS, NFS, etc.); the
value of the attribute is case insensitive. The 'package'
attribute provides the name of the Media Control Channel Framework
package, compliant with the specification in the related IANA
registry (e.g., "msc-ivr/1.0"), for which the scheme name applies.
It is important to point out that this element provides no
information about whether or not the Media Server supports any flavor
of live streaming: for instance, a value of "HTTP" for the IVR
(Interactive Voice Response) Package would only mean the 'http'
scheme makes sense to the Media Server within the context of that
package. Whether or not the Media Server can make use of HTTP to
only fetch resources, or also to attach an HTTP live stream to a
call, is to be considered implementation specific to the Media Server
and irrelevant to the Application Server and/or MRB. Besides, the
Media Server supporting a scheme does not imply that it also supports
the related secure versions: for instance, if the Media Server
supports both HTTP and HTTPS, both the schemes will appear in the
element. A lack of the "HTTPS" value would need to be interpreted as
a lack of support for the 'https' scheme.
5.1.5.16. <asr-tts-support>
The <asr-tts-support> element provides information about the support
for Automatic Speech Recognition (ASR) and Text-to-Speech (TTS)
functionality in a Media Server. The functionality is reported by
referring to the supported languages (using ISO 639-1 [ISO.639.2002]
codes) regarding both ASR and TTS. The element MAY be present.
The <asr-tts-support> element has no attributes.
The <asr-tts-support> element has zero or more of the following child
elements:
<asr-support>: Describes the available languages for ASR. The
<asr-support> element has no attributes. The <asr-support>
element has one child element. The child element, <language>,
reports that the Media Server supports ASR for a specific
language. The <language> element has a single attribute,
'xml:lang'. The attribute 'xml:lang' contains the ISO 639-1
[ISO.639.2002] code of the supported language.
<tts-support>: Describes the available languages for TTS. The
<tts-support> element has no attributes. The <tts-support>
element has one child element. The child element, <language>,
reports that the Media Server supports TTS for a specific
language. The <language> element has a single attribute,
'xml:lang'. The attribute 'xml:lang' contains the ISO 639-1
[ISO.639.2002] code of the supported language.
5.1.5.17. <vxml-support>
The <vxml-support> element specifies if the Media Server supports
VoiceXML (VXML) and, if it does, through which protocols the support
is exposed (e.g., via the control framework, RFC 4240 [RFC4240], or
RFC 5552 [RFC5552]). The element MAY be present.
The <vxml-support> element has no attributes.
The <vxml-support> element has a single child element:
<vxml-mode>: Has two attributes: 'package' and 'support'. The
'package' attribute provides the name of the Media Control Channel
Framework package, compliant with Section 13.1.1 of [RFC6230], for
which the VXML support applies. The 'support' attribute provides
the type of VXML support provided by the Media Server (e.g.,
RFC 5552 [RFC5552], RFC 4240 [RFC4240], or the IVR Package
[RFC6231]), and valid values are case-insensitive RFC references
(e.g., "rfc6231" to specify that the Media Server supports
VoiceXML as provided by the IVR Package [RFC6231]).
The presence of at least one <vxml-mode> child element would indicate
that the Media Server does support VXML as specified by the child
element itself. An empty <vxml> element would otherwise indicate
that the Media Server does not support VXML at all.
5.1.5.18. <media-server-location>
The <media-server-location> element provides information about the
civic location of a Media Server. Its description makes use of the
Civic Address Schema standardized in RFC 5139 [RFC5139]. The element
MAY be present. More precisely, this section is entirely optional,
and it's implementation specific to fill it with just the details
each implementer deems necessary for any optimization that may be
needed.
The <media-server-location> element has no attributes.
The <media-server-location> element has a single child element:
<civicAddress>: Describes the civic address location of the Media
Server, whose representation refers to Section 4 of RFC 5139
[RFC5139].
5.1.5.19. <label>
The <label> element allows a Media Server to declare a piece of
information that will be understood by the MRB. For example, the
Media Server can declare if it's a blue or green one. It's a string
to allow arbitrary values to be returned to allow arbitrary
classification. The element MAY be present.
The <label> element has no attributes.
The <label> element has no child elements.
5.1.5.20. <media-server-address>
The <media-server-address> element allows a Media Server to provide a
direct SIP URI where it can be reached (e.g., the URI that the
Application Server would call in order to set up a Control Channel
and relay SIP media dialogs). The element MAY be present.
The <media-server-address> element has no attributes.
The <media-server-address> element has no child elements.
5.1.5.21. <encryption>
The <encryption> element allows a Media Server to declare support for
encrypting RTP media streams using RFC 3711 [RFC3711]. The element
MAY be present. If the element is present, then the Media Server
supports DTLS-SRTP (a Secure Real-time Transport Protocol (SRTP)
extension for Datagram Transport Layer Security (DTLS)) [RFC5763].
The <encryption> element has no attributes.
The <encryption> element has no child elements.
5.2. Media Service Resource Consumer Interface
The Media Server Consumer interface provides the ability for clients
of an MRB, such as Application Servers, to request an appropriate
Media Server to satisfy specific criteria. This interface allows a
client to pass detailed meta-information to the MRB to help select an
appropriate Media Server. The MRB is then able to make an informed
decision and provide the client with an appropriate Media Server resource. The MRB Consumer interface includes both 1) the In-line Aware MRB Mode (IAMM), which uses the Session Initiation Protocol (SIP) and 2) the Query mode, which uses the Hypertext Transfer Protocol (HTTP) [RFC2616]. The MRB Consumer interface does not include the In-line Unaware Mode (IUMM), which is further explained in Section 5.3. The following sub-sections provide guidance on using the Consumer interface, which is represented by the 'application/mrb-consumer+xml' media type in Section 11, with HTTP and SIP.5.2.1. Query Mode/HTTP Consumer Interface Usage
An appropriate interface for such a 'query' style interface is in fact an HTTP usage. Using HTTP and XML combined reduces complexity and encourages the use of common tools that are widely available in the industry today. The following information explains the primary operations required to request and then receive information from an MRB, by making use of HTTP [RFC2616] and HTTPS [RFC2818] as transport for a query for a media resource, and the appropriate response. The media resource query, as defined by the <mediaResourceRequest> element from Section 11, MUST be carried in the body of an HTTP/HTTPS POST request. The media type contained in the HTTP/HTTPS request/ response MUST be 'application/mrb-consumer+xml'. This value MUST be reflected in the appropriate HTTP headers, such as 'Content-Type' and 'Accept'. The body of the HTTP/HTTPS POST request MUST only contain an <mrbconsumer> root element with only one child <mediaResourceRequest> element as defined in Section 11. The media resource response to a query, as defined by the <mediaResourceResponse> element from Section 11, MUST be carried in the body of an HTTP/HTTPS 200 response to the original HTTP/HTTPS POST request. The media type contained in the HTTP/HTTPS request/ response MUST be 'application/mrb-consumer+xml'. This value MUST be reflected in the appropriate HTTP headers, such as 'Content-Type' and 'Accept'. The body of the HTTP/HTTPS 200 response MUST only contain an <mrbconsumer> root element with only one child <mediaResourceResponse> element as defined in Section 11. When an Application Server wants to release previously awarded media resources granted through a prior request/response exchange with an MRB, it will send a new request with an <action> element with value 'remove', as described in Section 5.2.3 ("Consumer Interface Lease Mechanism").
5.2.2. In-Line Aware Mode/SIP Consumer Interface Usage
This document provides a complete toolkit for MRB deployment that includes the ability to interact with an MRB using SIP for the Consumer interface. The following information explains the primary operations required to request and then receive information from an MRB, by making use of SIP [RFC3261] as transport for a request for media resources, and the appropriate response when using IAMM as the mode of operation (as discussed in Section 5.2.2.1). The use of IAMM, besides having the MRB select appropriate media resources on behalf of a client application, includes setting up either a Control Framework Control Channel between an Application Server and one of the Media Servers (Section 5.2.2.1) or a media dialog session between an Application Server and one of the Media Servers (Section 5.2.2.2). Note that in either case the SIP URIs of the selected Media Servers are made known to the requesting Application Server in the SIP 200 OK response by means of one or more <media-server-address> child elements in the <response-session-info> element (Section 5.2.6).5.2.2.1. IAMM and Setting Up a Control Framework Control Channel
The media resource request information, as defined by the <mediaResourceRequest> element from Section 11, is carried in a SIP INVITE request. The INVITE request will be constructed as it would have been to connect to a Media Server, as defined by the Media Control Channel Framework [RFC6230]. It should be noted that this specification does not exclude the use of an offerless INVITE as defined in RFC 3261 [RFC3261]. Using offerless INVITE messages to an MRB can potentially cause confusion when applying resource selection algorithms, and an MRB, like any other SIP device, can choose to reject with a 4xx response. For an offerless INVITE to be treated appropriately, additional contextual information would need to be provided with the request; this is out of scope for this document. The following additional steps MUST be followed when using the Consumer interface: o The Consumer client will include a payload in the SIP INVITE request of type 'multipart/mixed' [RFC2046]. One of the parts to be included in the 'multipart/mixed' payload MUST be the 'application/sdp' format, which is constructed as specified in the Media Control Channel Framework [RFC6230]. o Another part of the 'multipart/mixed' payload MUST be of type 'application/mrb-consumer+xml', as specified in this document and defined in Section 11. The body part MUST be an XML document without prolog and whose root element is <mediaResourceRequest>.
o The INVITE request will then be dispatched to the MRB, as defined
by [RFC6230].
On receiving a SIP INVITE request containing the multipart/mixed
payload as specified previously, the MRB will complete a number of
steps to fulfill the request. It will:
o Extract the multipart MIME payload from the SIP INVITE request.
It will then use the contextual information provided by the client
in the 'application/mrb-consumer+xml' part to determine which
Media Server (or Media Servers, if more than one is deemed to be
needed) should be selected to service the request.
o Extract the 'application/sdp' part from the payload and use it as
the body of a new SIP INVITE request for connecting the client to
one of the selected Media Servers, as defined in the Media Channel
Control Framework [RFC6230]. The policy the MRB follows to pick a
specific Media Server out of the Media Servers it selects is
implementation specific and out of scope for this document. It is
important to configure the SIP elements between the MRB and the
Media Server in such a way that the INVITE will not fork. In the
case of a failure in reaching the chosen Media Server, the MRB
SHOULD proceed to the next one, if available.
If none of the available Media Servers can be reached, the MRB MUST
reply with a SIP 503 error message that includes a Retry-After header
with a non-zero value. The Application Server MUST NOT attempt to
set up a new session before the time that the MRB asked it to wait
has passed.
If at least one Media Server is reachable, the MRB acts as a Back-to-
Back User Agent (B2BUA) that extracts the 'application/
mrb-consumer+xml' information from the SIP INVITE request and then
sends a corresponding SIP INVITE request to the Media Server it has
selected, to negotiate a Control Channel as defined in the Media
Channel Control Framework [RFC6230].
In the case of a failure in negotiating the Control Channel with the
Media Server, the MRB SHOULD proceed to the next one, if available,
as explained above. If none of the available Media Servers can be
reached, or the negotiations of the Control Channel with all of them
fail, the MRB MUST reply with a SIP 503 error message that includes a
Retry-After header with a non-zero value. The Application Server
MUST NOT attempt to set up a new session before the time that the MRB
asked it to wait has expired.
Once the MRB receives the SIP response from the selected media resource (i.e., Media Server), it will in turn respond to the requesting client (i.e., Application Server). The media resource response generated by an MRB to a request, as defined by the <mediaResourceResponse> element from Section 11, MUST be carried in the payload of a SIP 200 OK response to the original SIP INVITE request. The SIP 200 OK response will be constructed as it would have been to connect from a Media Server, as defined by the Media Control Channel Framework [RFC6230]. The following additional steps MUST be followed when using the Consumer interface: o Include a payload in the SIP 200 response of type 'multipart/ mixed' as per RFC 2046 [RFC2046]. One of the parts to be included in the 'multipart/mixed' payload MUST be the 'application/sdp' format, which is constructed as specified in the Media Control Channel Framework [RFC6230] and based on the incoming response from the selected media resource. o Another part of the 'multipart/mixed' payload MUST be of type 'application/mrb-consumer+xml', as specified in this document and defined in Section 11. Only the <mediaResourceResponse> and its child elements can be included in the payload. o The SIP 200 response will then be dispatched from the MRB. o A SIP ACK to the 200 response will then be sent back to the MRB. Considering that the use of SIP as a transport for Consumer transactions may result in failure, the IAMM relies on a successful INVITE transaction to address the previously discussed sequence (using the 'seq' XML element) increment mechanism. This means that if the INVITE is unsuccessful for any reason, the Application Server MUST use the same 'seq' value as previously used for the next Consumer request that it may want to send to the MRB for the same session. An MRB implementation may be programmed to conclude that the requested resources are no longer needed when it receives a SIP BYE from the Application Server or Media Server that concludes the SIP dialog that initiated the request, or when the lease (Section 5.2.3) interval expires.
5.2.2.2. IAMM and Setting Up a Media Dialog
This scenario is identical to the description in the previous section for setting up a Control Framework Control Channel, with the exception that the application/sdp payload conveys content appropriate for setting up the media dialog to the media resource, as per RFC 3261 [RFC3261], instead of setting up a Control Channel.5.2.3. Consumer Interface Lease Mechanism
The Consumer interface defined in Sections 5.2 and 11 allows a client to request an appropriate media resource based on information included in the request (either an HTTP POST or SIP INVITE message). In the case of success, the response that is returned to the client MUST contain a <response-session-info> element in either the SIP 200 or HTTP 200 response. The success response contains the description of certain resources that have been reserved to a specific Consumer client in a (new or revised) "resource session", which is identified in the <response-session-info>. The resource session is a "lease", in that the reservation is scheduled to expire at a particular time in the future, releasing the resources to be assigned for other uses. The lease may be extended or terminated earlier by future Consumer client requests that identify and reference a specific resource session. Before delving into the details of such a lease mechanism, it is worth clarifying its role within the context of the Consumer interface. As explained in Section 5.1, the knowledge the MRB has of the resources of all the Media Servers it is provisioned to manage is not real-time. How an MRB actually manages such resources is implementation specific -- for example, an implementation may choose to have the MRB keeping track and state of the allocated resources, or simply rely on the Media Servers themselves to provide the information using the Publish interface. Further information may also be inferred by the signaling, in the case where an MRB is in the path of media dialogs.
The <mediaResourceResponse> element returned from the MRB contains a
<response-session-info> element if the request is successful. The
<response-session-info> element has zero or more of the following
child elements, which provide the appropriate resource session
information:
o <session-id> is a unique identifier that enables a Consumer client
and MRB to correlate future media resource requests related to an
initial media resource request. The <session-id> MUST be included
in all future related requests (see the <session-id> paragraph
later in this section, where constructing a subsequent request is
discussed).
o <seq> is a numeric value returned to the Consumer client. On
issuing any future requests related to the media resource session
(as determined by the <session-id> element), the Consumer client
MUST increment the value returned in the <seq> element and include
it in the request (see the <seq> paragraph later in this section,
where constructing a subsequent request is discussed). Its value
is a non-negative integer that MUST be limited within the
0..2^31-1 range.
o <expires> provides a value indicating the number of seconds that
the request for media resources is deemed alive. The Consumer
client should issue a refresh of the request, as discussed later
in this section, if the expiry is due to fire and the media
resources are still required.
o <media-server-address> provides information representing an
assigned Media Server. More instances of this element may appear
should the MRB assign more Media Servers to a Consumer request.
The <mediaResourceRequest> element is used in subsequent Consumer
interface requests if the client wishes to manipulate the session.
The Consumer client MUST include the <session-info> element, which
enables the receiving MRB to determine an existing media resource
allocation session. The <session-info> element has the following
child elements, which provide the appropriate resource session
information to the MRB:
o <session-id> is a unique identifier that allows a Consumer client
to indicate the appropriate existing media resource session to be
manipulated by the MRB for this request. The value was provided
by the MRB in the initial request for media resources, as
discussed earlier in this section (<session-id> element included
as part of the <session-info> element in the initial
<mediaResourceResponse>).
o <seq> is a numeric value returned to the Consumer client in the
initial request for media resources, as discussed earlier in this
section (<seq> element included as part of the <session-info>
element in the initial <mediaResourceResponse>). On issuing any
future requests related to the specific media resource session (as
determined by the <session-id> element), the Consumer client MUST
increment the value returned in the <seq> element from the initial
response (contained in the <mediaResourceResponse>) for every new
request. The value of the <seq> element in requests acts as a
counter and when used in conjunction with the unique <session-id>
allows for unique identification of a request. As anticipated
before, the <seq> value is limited to the 0..2^31-1 range: in the
unlikely case that the counter increases to reach the highest
allowed value, the <seq> value MUST be set to 0. The first
numeric value for the <seq> element is not meant to be '1' but
SHOULD be generated randomly by the MRB: this is to reduce the
chances of a malicious MRB disrupting the session created by this
MRB, as explained in Section 12.
o <action> provides the operation to be carried out by the MRB on
receiving the request:
* The value of 'update' is a request by the Consumer client to
update the existing session on the MRB with alternate media
resource requirements. If the requested resource information
is identical to the existing MRB session, the MRB will attempt
a session refresh. If the information has changed, the MRB
will attempt to update the existing session with the new
information. If the operation is successful, the 200 status
code in the response is returned in the status attribute of the
<mediaResourceResponseType> element. If the operation is not
successful, a 409 status code in the response is returned in
the status attribute of the <mediaResourceResponseType>
element.
* The value of 'remove' is a request by the Consumer client to
remove the session on the MRB. This provides a mechanism for
Consumer clients to release unwanted resources before they
expire. If the operation is successful, a 200 status code in
the response is returned in the status attribute of the
<mediaResourceResponseType> element. If the operation is not
successful, a 410 status code in the response is returned in
the status attribute of the <mediaResourceResponseType>
element.
Omitting the 'action' attribute means requesting a new set of
resources.
When used with HTTP, the <session-info> element MUST be included in an HTTP POST message (as defined in [RFC2616]). When used with SIP, the <session-info> element MUST instead be included in either a SIP INVITE or a SIP re-INVITE (as defined in [RFC3261]), or in a SIP UPDATE (as defined in [RFC3311]) request: in fact, any SIP dialog, be it a new or an existing one, can be exploited to carry leasing information, and as such new SIP INVITE messages can update other leases as well as request a new one. With IAMM, the Application Server or Media Server will eventually send a SIP BYE to end the SIP session, whether it was for a Control Channel or a media dialog. That BYE contains no Consumer interface lease information.5.2.4. <mrbconsumer>
This section defines the XML elements for the Consumer interface. The formal XML schema definition for the Consumer interface can be found in Section 11. The root element is <mrbconsumer>. All other XML elements (requests, responses) are contained within it. The MRB Consumer interface request element is detailed in Section 5.2.5.1. The MRB Consumer interface response element is detailed in Section 5.2.6.1. The <mrbconsumer> element has the following attributes: version: a token specifying the mrb-consumer package version. The value is fixed as '1.0' for this version of the package. The attribute MUST be present. The <mrbconsumer> element may have zero or more children of one of the following child element types: <mediaResourceRequest> for sending a Consumer request. See Section 5.2.5.1. <mediaResourceResponse> for sending a Consumer response. See Section 5.2.6.1.
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