Multimedia Policy Engine Devices

The Multimedia Policy Engine (MPE) device provides a policy and charging rules function (PCRF) as defined in the 3rd Generation Partnership Project (3GPP) technical specification “Policy and charging control architecture” (TS 23.203). It fully supports 3GPP Releases, 7 through 11, policy and charging control (PCC) interfaces. The MPE device includes a simple, powerful, and flexible policy rules engine. The policy rules engine operates on triggers from any interface or from internal timers; evaluates conditions; and then performs appropriate actions. Through the use of policy rules, you can modify the behavior of an MPE device dynamically as it processes protocol messages.

A policy is a set of operator-created business rules. These business rules control how subscribers, applications, and network resources are used. Policies define the conditions and actions used by a carrier network to determine:

How network resources are allocated and used
How applications and subscribers are treated

See the Policy Wizard Reference for information on how to create, organize, and manage policies and the elements they control.

Figure 1 shows the various interfaces to external devices and functions supported by an MPE device. These interfaces include the following:

A Policy and Charging Enforcement Function (PCEF) receives and processes requests to start new sessions for subscribers. Examples of PCEFs include a Gateway GPRS Support Node (GGSN), a Packet Data Network Gateway (PGW), and a High-Speed Gateway (HSGW). MPE devices act as servers for PCEFs, using the Diameter Gx and Gxx interfaces to:
- Receive requests for policy decisions
- Send those policy decisions, as PCC rules, to PCEFs for implementation
- Remove PCC rules from PCEFs
- Receive traffic plane events from PCEFs
(Additionally, gateways can communicate with online charging systems using the Diameter Gy interface, or offline charging systems using the Diameter Rf interface.) When a PCEF initiates a Gx session, it is assigned to an MPE device. Sessions for other Diameter applications, such as Gxa, Rx, and Gx Lite, that must reference the Gx session have their initial requests correlated to the same MPE device that hosts the Gx session.
An Application Function (AF) is a network element offering applications that require dynamic policy or charging control over the IP Connectivity Access Network (IP-CAN) user plane. An example of an AF is a Proxy Call Session Control Function (P-CSCF) device. MPE devices act as servers for AFs, using the Diameter Rx interface, to obtain dynamic session information and to send IP-CAN specific information and notifications about bearer-level events. When an AF initiates an Rx session, it is correlated to the same MPE device that hosts the Gx session for that subscriber based on the IP address, which must be globally unique and routable. (If a correlated Gx session cannot be found, the request is rejected with an error code.)
A Traffic Detection Function (TDF) permits, gates, shapes, or redirects service traffic. An example of a TDF is a deep packet inspection (DPI) device. MPE devices act as servers for TDFs, using the Diameter Sd or Gx Lite interfaces, to receive requests for policy decisions; to send those policy decisions, as PCC rules, to TDFs for implementation; to remove PCC rules from TDFs; and to receive traffic plane events from TDFs. When a TDF initiates an Sd or Gx Lite session, it is correlated to the same MPE device that hosts the Gx session for that subscriber based on the IP address. (If a correlated Gx session cannot be found, the request is rejected with an error code.)
A Bearer Binding and Event Reporting Function (BBERF) maps a PCC rule to an IP-CAN bearer. Examples of BBERFs are serving gateways (SGW) and HSGWs. MPE devices act as servers for BBERFs, using the Diameter Gxx interface, to receive requests for policy decisions; to send those policy decisions, as PCC rules, to BBERFs for implementation; to remove PCC rules from BBERFs; and to receive traffic plane events from BBERFs. When a BBERF initiates a Gxx session, it is correlated to the same MPE device that hosts the Gx session for that subscriber based on the IMSI. If a correlated Gxa session cannot be found, an MPE device is assigned for the session and the request is processed.
A Subscriber Profile Repository (SPR) contains subscriber or subscription information. MPE devices act as clients for SPRs, using the Diameter Sh interface, to retrieve subscriber profiles and to register for notification of changes to a subscriber's profile. MPE devices support the Oracle Communications Enhanced Subscriber Profile Repository (ESPR) application.
A directory services database provides distributed directory information, such as user account IDs, email and equipment addresses, and phone numbers, over an IP network. MPE devices communicate with directory servers using the Lightweight Directory Access Protocol (LDAP).
In support of voice roaming, the S9 Diameter application installs PCC rules generated in a home public land mobile network (HPLMN) into a visited PLMN (VPLMN) and report the events that may occur in the VPLMN to the HPLMN. When an AF is in the VPLMN, The Diameter Rx protocol is used over the S9 interface to exchange service session information from the visited PCRF to the home PCRF.
An Online Charging System (OCS) calculates charges against a prepaid account for an event and returns information on how long the subscriber can use the service; this can affect, in real time, the service rendered. MPE devices communicate with OCSes using the Diameter Sy interface. (By contrast, an Offline Charging System (OFCS) calculates charges for a service to an account, and does not affect, in real time, the service rendered.) MPE devices act as clients for OCSes, using the Diameter Sy interface, to retrieve subscriber policy counters and policy counter statuses and to register for notification of changes to a subscriber's policy counters.
The Multi-Protocol Routing Agent (MRA) (also referred to as the Policy Front End) is an optional product deployed in a large Policy Management network that maintains bindings between subscribers and MPE devices. MPE devices communicate with MRAs as proxy Diameter Routing Agents, so they exchange Diameter messages. For more information on the MRA product, refer to Policy Front End Wireless User's Guide.
The CMP system is required to configure, manage, and provision MPE devices. MPE and CMP devices communicate using a proprietary protocol.

Diameter Interfaces to the MPE Device

Each active MPE device establishes a connection to data sources (such as SPRs and LDAP servers). An MPE device can establish connections to multiple data sources, prioritized as primary, secondary, and tertiary. Each data source can also be configured with a primary and secondary connection. The MPE device uses the highest priority connection available.

MPE and MRA devices implement a load-shedding mechanism to protect themselves during times of severe overload. The devices enter a "too busy" state when the amount of queued traffic exceeds a predefined threshold. While in this state of busyness, requests may be responded to with Diameter TOO_BUSY result codes or silently discarded.