The Media Resource Broker (MRB) is a functional entity that is responsible for both collection of appropriate published MRF information and supplying of appropriate MRF information to consuming entities such as the AS. Therefore, the MRB is responsible for supporting the identification and selection of appropriate MRF resources. The MRB supports the sharing of a pool of heterogeneous MRF resources by multiple heterogeneous applications. MRB assigns (and later releases) specific suitable MRF resources to calls as requested by the consuming applications, based on MRF attributes specified by the applications as well as other criteria. The MRB may take the following kinds of information into account when assigning MRF resources to an application:

• the specific characteristics of the media resources required for the call or calls;
• the identity of the application;
• rules for allocating MRF resources across different applications;
• per-application or per-subscriber SLA or QoS criteria;
• capacity models of particular MRF resources; and
• if it can use the services of another (visited network) MRB.

There are two modes in which MRB can be utilized - Query and In-Line, as explained below. An instance of an MRB may simultaneously operate in both modes. Likewise, a given AS/application could employ Query mode on some calls and In-Line mode on others. Query and In-Line modes of MRB have the following in common:

• the role of MRB is the same - assignment of MRF resources to calls as requested by applications;
• an application server provides the same kind of information to MRB on MRF attributes needed for a given call; and
• the way MRB acquires knowledge of MRF resources and other information needed to perform its role is the same (see subclause 13.3).

Query mode allows the application to:

• be the entity that determines when an MRF resource can be released;
• request and be assigned MRF resources for multiple calls in advance; and do that in a single request/response; and
• incrementally request more MRF resources or release resources that it determines aren't in fact needed.

An MRB can use the services of another MRB, either in In-Line mode or in Query mode, using the Mr, Mr' and Rc interfaces appropriately.

With Query mode, the AS queries the MRB with a request for media resources with certain attributes using the Rc interface. The MRB selects suitable MRF Resources, assigns them to that AS/application, and responds to the AS with the addresses of the selected MRF resources. Once the AS receives the response from MRB, it sets up the call or calls to the MRFC either through the S-CSCF (ISC and Mr interface) or directly to the MRFC (Mr' interface), using the MRF address information supplied by MRB. Control packages are supported over the Cr interface. When the AS/application is done using a MRF resource, it sends another message to MRB indicating so, and MRB returns that resource to the idle pool and acknowledges to the AS/application.

With In-Line mode, the MRB is between the AS and the MRFC. The AS sends a request to establish a dialog to the MRB (using the Mr' interface, or via the S-CSCF using the ISC and Mr interface). The request can contain information relating to the kind of MRF required to handle that particular call. The MRB selects an appropriate MRF resource and sends the request along to the MRF (using the Mr' interface, or via the S-CSCF using the ISC and Mr interface). Subsequent messages in the same dialog between the AS and MRFC traverse the MRB (as well as the S-CSCF if that was in the path between the AS and the MRB, or between the MRB and the MRFC). Control packages are supported over the Cr interface directly between AS and MRFC. The MRB infers that the media resource is no longer needed when it sees a session release request from either the AS or MRFC.

In order to perform its function, MRB may need the following kinds of information (this is not necessarily an exhaustive list):

• available MRF resources and their attributes; current and future. This may take into account planned and unplanned downtime and the scheduled addition/deletion or availability of MRF resources;
• rules for fair-share allocation across applications;
• capacity models for particular MRF resources; and
• reservations for future use of media resources (for example, for conferencing, or for anticipated traffic spikes for other applications such as a FreePhone application).

The above information can all acquired by MRB through operations interfaces. However, it the MRB can also learn of available MRF resources and their characteristics via a direct MRB-MRF interface.