RFC 6917
Media Resource Brokering
Pages: 136
Proposed Standard
Proposed Standard
Part 1 of 6 – Pages 1 to 12
Internet Engineering Task Force (IETF) C. Boulton Request for Comments: 6917 NS-Technologies Category: Standards Track L. Miniero ISSN: 2070-1721 Meetecho G. Munson AT&T April 2013 Media Resource BrokeringAbstract
The MediaCtrl working group in the IETF has proposed an architecture for controlling media services. The Session Initiation Protocol (SIP) is used as the signaling protocol that provides many inherent capabilities for message routing. In addition to such signaling properties, a need exists for intelligent, application-level media service selection based on non-static signaling properties. This is especially true when considered in conjunction with deployment architectures that include 1:M and M:N combinations of Application Servers and Media Servers. This document introduces a Media Resource Broker (MRB) entity, which manages the availability of Media Servers and the media resource demands of Application Servers. The document includes potential deployment options for an MRB and appropriate interfaces to Application Servers and Media Servers. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6917.
Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.Table of Contents
1. Introduction ....................................................3 2. Conventions and Terminology .....................................6 3. Problem Discussion ..............................................6 4. Deployment Scenario Options .....................................7 4.1. Query MRB ..................................................8 4.1.1. Hybrid Query MRB ....................................9 4.2. In-Line MRB ...............................................11 5. MRB Interface Definitions ......................................12 5.1. Media Server Resource Publish Interface ...................12 5.1.1. Control Package Definition .........................13 5.1.2. Element Definitions ................................15 5.1.3. <mrbrequest> .......................................15 5.1.4. <mrbresponse> ......................................17 5.1.5. <mrbnotification> ..................................19 5.2. Media Service Resource Consumer Interface .................30 5.2.1. Query Mode/HTTP Consumer Interface Usage ...........31 5.2.2. In-Line Aware Mode/SIP Consumer Interface Usage ....32 5.2.3. Consumer Interface Lease Mechanism .................35 5.2.4. <mrbconsumer> ......................................38 5.2.5. Media Service Resource Request .....................39 5.2.6. Media Service Resource Response ....................51 5.3. In-Line Unaware MRB Interface .............................54 6. MRB Acting as a B2BUA ..........................................54 7. Multimodal MRB Implementations .................................55 8. Relative Merits of Query Mode, IAMM, and IUMM ..................56 9. Examples .......................................................58 9.1. Publish Example ...........................................58 9.2. Consumer Examples .........................................64 9.2.1. Query Example ......................................64 9.2.2. IAMM Examples ......................................68 10. Media Service Resource Publisher Interface XML Schema .........83
11. Media Service Resource Consumer Interface XML Schema .........106 12. Security Considerations ......................................127 13. IANA Considerations ..........................................130 13.1. Media Control Channel Framework Package Registration ....130 13.2. application/mrb-publish+xml Media Type ..................130 13.3. application/mrb-consumer+xml Media Type .................131 13.4. URN Sub-Namespace Registration for mrb-publish ..........132 13.5. URN Sub-Namespace Registration for mrb-consumer .........132 13.6. XML Schema Registration for mrb-publish .................132 13.7. XML Schema Registration for mrb-consumer ................133 14. Acknowledgements .............................................133 15. References ...................................................133 15.1. Normative References ....................................133 15.2. Informative References ..................................1351. Introduction
As IP-based multimedia infrastructures mature, the complexity and demands from deployments increase. Such complexity will result in a wide variety of capabilities from a range of vendors that should all be interoperable using the architecture and protocols produced by the MediaCtrl working group. It should be possible for a controlling entity to be assisted in Media Server selection so that the most appropriate resource is selected for a particular operation. The importance increases when one introduces a flexible level of deployment scenarios, as specified in RFC 5167 [RFC5167] and RFC 5567 [RFC5567]. These documents make statements like "it should be possible to have a many-to-many relationship between Application Servers and Media Servers that use this protocol". This leads to the following deployment architectures being possible when considering media resources, to provide what can be effectively described as media resource brokering. The simplest deployment view is illustrated in Figure 1. +---+-----+---+ +---+-----+---+ | Application | | Media | | Server |<-------MS Control------>| Server | +-------------+ +-------------+ Figure 1: Basic Architecture This simply involves a single Application Server and Media Server. Expanding on this view, it is also possible for an Application Server to control multiple (greater than 1) Media Server instances at any one time. This deployment view is illustrated in Figure 2. Typically, such architectures are associated with application logic that requires high-demand media services. It is more than possible
that each Media Server possesses a different media capability set. Media Servers may offer different media services as specified in the MediaCtrl architecture document [RFC5567]. A Media Server may have similar media functionality but may have different capacity or media codec support. +---+-----+---+ | Media | +----->| Server | | +-------------+ | +---+-----+---+ | +---+-----+---+ | Application | | | Media | | Server |<--MS Control-----+----->| Server | +-------------+ | +-------------+ | | +---+-----+---+ +----->| Media | | Server | +-------------+ Figure 2: Multiple Media Servers Figure 3 conveys the opposite view to that in Figure 2. In this model, there are a number of (greater than 1) Application Servers, possibly supporting dissimilar applications, controlling a single Media Server. Typically, such architectures are associated with application logic that requires low-demand media services. +---+-----+---+ | Application | | Server |<-----+ +-------------+ | | +---+-----+---+ | +---+-----+---+ | Application | | | Media | | Server |<-----+-----MS Control-->| Server | +-------------+ | +-------------+ | +---+-----+---+ | | Application | | | Server |<-----+ +-------------+ Figure 3: Multiple Application Servers
The final deployment view is the most complex (Figure 4). In this model (M:N), there exist any number of Application Servers and any number of Media Servers. It is again possible in this model that Media Servers might not be homogeneous, and they might have different capability sets and capacities. +---+-----+---+ +---+-----+---+ | Application | | Media | | Server |<-----+ +---->| Server | +-------------+ | | +-------------+ | | +---+-----+---+ | | +---+-----+---+ | Application | | | | Media | | Server |<-----+-MS Control-+---->| Server | +-------------+ | | +-------------+ | | +---+-----+---+ | | +---+-----+---+ | Application | | +---->| Media | | Server |<-----+ | Server | +-------------+ +---+-----+---+ Figure 4: Many-to-Many Architecture The remaining sections in this specification will focus on a new entity called a Media Resource Broker (MRB), which can be utilized in the deployment architectures described previously in this section. The MRB entity provides the ability to obtain media resource information and appropriately allocate (broker) on behalf of client applications. The high-level deployment options discussed in this section rely on network architecture and policy to prohibit inappropriate use. Such policies are out of scope for this document. This document will take a look at the specific problem areas related to such deployment architectures. It is recognized that the solutions proposed in this document should be equally adaptable to all of the previously described deployment models. It is also recognized that the solution is far more relevant to some of the previously discussed deployment models and can almost be viewed as redundant on others.
2. Conventions and Terminology
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 [RFC2119]. This document inherits terminology proposed in RFC 5567 [RFC5567] and in "Media Control Channel Framework" [RFC6230]. In addition, the following terms are defined for use in this document and for use in the context of the MediaCtrl working group in the IETF: Media Resource Broker (MRB): A logical entity that is responsible for both collection of appropriate published Media Server (MS) information and selecting appropriate Media Server resources on behalf of consuming entities. Query MRB: An instantiation of an MRB (see previous definition) that provides an interface for an Application Server to retrieve the address of an appropriate Media Server. The result returned to the Application Server can be influenced by information contained in the query request. In-line MRB: An instantiation of an MRB (see previous definition) that directly receives requests on the signaling path. There is no separate query. CFW: Media Control Channel Framework, as specified in [RFC6230]. Within the context of In-line MRBs, additional terms are defined: In-line Aware MRB Mode (IAMM): Defined in Section 5.2.2.1. In-line Unaware MRB Mode (IUMM): Defined in Section 5.3. The document will often specify when a specific identifier in a protocol message needs to be unique. Unless stated otherwise, such uniqueness will always be within the scope of the Media Servers controlled by the same MRB. The interaction between different MRB instances, e.g., the partitioning of a logical MRB, is out of scope for this document.3. Problem Discussion
As discussed in Section 1, a goal of the MediaCtrl working group is to produce a solution that will service a wide variety of deployment architectures. Such architectures range from the simplest 1:1 relationship between Media Servers and Application Servers to potentially linearly scaling 1:M, M:1, and M:N deployments.
Managing such deployments is itself non-trivial for the proposed solution until an additional number of factors that increase complexity are included in the equation. As Media Servers evolve, it must be taken into consideration that, where many can exist in a deployment, they may not have been produced by the same vendor and may not have the same capability set. It should be possible for an Application Server that exists in a deployment to select a media service based on a common, appropriate capability set. In conjunction with capabilities, it is also important to take available resources into consideration. The ability to select an appropriate media service function is an extremely useful feature but becomes even more powerful when considered with available resources for servicing a request. In conclusion, the intention is to create a toolkit that allows MediaCtrl deployments to effectively utilize the available media resources. It should be noted that in the simplest deployments where only a single Media Server exists, an MRB function is probably not required. Only a single capability set exists, and resource availability can be handled using the appropriate underlying signaling, e.g., SIP response. This document does not prohibit such uses of an MRB; it simply provides the tools for various entities to interact where appropriate. It is also worth noting that the functions specified in this document aim to provide a 'best effort' view of media resources at the time of request for initial Media Server routing decisions. Any dramatic change in media capabilities or capacity after a request has taken place should be handled by the underlying protocol. It should be noted that there may be additional information that is desirable for the MRB to have for purposes of selecting a Media Server resource, such as resource allocation rules across different applications, planned or unplanned downtime of Media Server resources, the planned addition of future Media Server resources, or Media Server resource capacity models. How the MRB acquires such information is outside the scope of this document. The specific techniques used for selecting an appropriate media resource by an MRB is also outside the scope of this document.4. Deployment Scenario Options
Research into media resource brokering concluded that a couple of high-level models provided an appropriate level of flexibility. The general principles of "in-line" and "query" MRB concepts are discussed in the rest of this section. It should be noted that while the interfaces are different, they both use common underlying mechanisms defined in this specification.
4.1. Query MRB
The "Query" model for MRB interactions provides the ability for a client of media services (for example, an Application Server) to "ask" an MRB for an appropriate Media Server, as illustrated in Figure 5. +---+-----+---+ +------------>| MRB |<----------+----<-----+---+ | +-------------+ (1)| | | | | | | |(2) +---+--+--+---+ | | | | Media | | | | +---->| Server | | | | | +-------------+ | | | | (1)| | +---+--+--+---+ | +---+-----+---+ | | | Application | | | Media | | | | Server |<-----+-MS Control-+---->| Server |->-+ | +-------------+ (3) | +-------------+ | | | | +---+-----+---+ (1)| +---->| Media | | | Server |--->---+ +---+-----+---+ Figure 5: Query MRB In this deployment, the Media Servers use the Media Server Resource Publish interface, as discussed in Section 5.1, to convey capability sets as well as resource information. This is depicted by (1) in Figure 5. It is then the MRB's responsibility to accumulate all appropriate information relating to media services in the logical deployment cluster. The Application Server (or other media services client) is then able to query the MRB for an appropriate resource (as identified by (2) in Figure 5). Such a query would carry specific information related to the media service required and enable the MRB to provide increased accuracy in its response. This particular interface is discussed in "Media Service Resource Consumer Interface" (Section 5.2). The Application Server is then able to direct control commands (for example, create a conference) and media dialogs to the appropriate Media Server, as shown by (3) in Figure 5. Additionally, with Query mode, the MRB is not directly in the signaling path between the Application Server and the selected Media Server resource.
4.1.1. Hybrid Query MRB
As mentioned previously, it is the intention that a toolkit is provided for MRB functionality within a MediaCtrl architecture. It is expected that in specific deployment scenarios the role of the MRB might be co-hosted as a hybrid logical entity with an Application Server, as shown in Figure 6. +------------<----------------<---------+----<-----+---+ | (1) | | | | | | | | +---+--+--+---+ | | | | Media | | | V +---->| Server | | | +------+------+ | +-------------+ | | | MRB | | | | +---+--+--+---+ | +---+-----+---+ | | | Application | | | Media | | | | Server |<-----+-MS Control-+---->| Server |->-+ | +-------------+ | +-------------+ | | | | +---+-----+---+ | +---->| Media | | | Server |--->---+ +---+-----+---+ Figure 6: Hybrid Query MRB - Application Server Hosted This diagram is identical to that in Figure 5 with the exception that the MRB is now hosted on the Application Server. The Media Server Publish interface is still being used to accumulate resource information at the MRB, but as it is co-hosted on the Application Server, the Media Server Consumer interface has collapsed. It might still exist within the Application Server/MRB interaction, but this is an implementation issue. This type of deployment suits a single Application Server environment, but it should be noted that a Media Server Consumer interface could then be offered from the hybrid if required.
In a similar manner, the Media Server could also act as a hybrid for the deployment cluster, as illustrated in Figure 7. (1) +---+-----+---+ +---+---+------------->---------------->----------->| MRB | | | | +---+--+--+---+ +---+-----+---+ | | +-<-| Application | | Media | | | | Server |<--+-MS Control-+------->| Server | | | +-------------+ | +-------------+ | | | | | +---+--+--+---+ | | +---<---| Application | | | | Server |<--+-MS Control-+--+ | +-------------+ | | | | +---+--+--+---+ | +---<-------| Application | | | Server |<--+-MS Control-+--+ +-------------+ Figure 7: Hybrid Query MRB - MS Hosted In this example, the MRB has collapsed and is co-hosted by the Media Server. The Media Server Consumer interface is still available to the Application Servers (1) to query Media Server resources. The Media Server Publish interface has collapsed onto the Media Server. It might still exist within the Media Server/MRB interaction, but this is an implementation issue. This type of deployment suits a single Media Server environment, but it should be noted that a Media Server Publish interface could then be offered from the hybrid if required. A typical use case scenario for such a topology would be a single Media Server representing a pool of MSs in a cluster. In this case, the MRB would actually be handling a cluster of Media Servers, rather than one.
4.2. In-Line MRB
The "In-line" MRB is architecturally different from the "Query" model discussed in the previous section. The concept of a separate query disappears. The client of the MRB simply uses the media resource control and media dialog signaling to involve the MRB. This type of deployment is illustrated in Figure 8. +-------<----------+----<-------+---+ | | (1) | | | | | | | +---+--+--+---+ | | | | Media | | | | +------>| Server | | | | |(3) +-------------+ | | | | (1)| | +---+--+--+---+ | | +---+-----+---+ | | | Application | (2) +---+--V--+---+ (3) | Media | | | | Server |----->| MRB |----->| Server |->-+ | +-------------+ +---+-----+---+ +-------------+ | | | | (3) +---+-----+---+ (1)| +------>| Media | | | Server |--->---+ +---+-----+---+ Figure 8: In-Line MRB The Media Servers still use the Media Server Publish interface to convey capabilities and resources to the MRB, as illustrated by (1). The Media Server Control Channels (and media dialogs as well, if required) are sent to the MRB (2), which then selects an appropriate Media Server (3) and remains in the signaling path between the Application Server and the Media Server resources. The In-line MRB can be split into two distinct logical roles that can be applied on a per-request basis. They are: In-line Unaware MRB Mode (IUMM): Allows an MRB to act on behalf of clients requiring media services who are not aware of an MRB or its operation. In this case, the Application Server does not provide explicit information on the kind of Media Server resource it needs (as in Section 5.2), and the MRB is left to deduce it by potentially inspecting other information in the request from the Application Server (for example, Session Description Protocol (SDP) content, or address of the requesting Application Server, or additional Request-URI parameters as per RFC 4240 [RFC4240]).
In-line Aware MRB Mode (IAMM): Allows an MRB to act on behalf of
clients requiring media services who are aware of an MRB and its
operation. In particular, it allows the Application Server to
explicitly convey matching characteristics to those provided by
Media Servers, as does the Query MRB mode (as in Section 5.2).
In either of the previously described roles, signaling as specified
by the Media Control Channel Framework ([RFC6230]) would be involved,
and the MRB would deduce that the selected Media Server resources are
no longer needed when the Application Server or Media Server
terminates the corresponding SIP dialog. The two modes are discussed
in more detail in Section 5.3.
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