Monitoring Event Charging Node

Description

The Monitoring Event Charging Node (MECN) is a functional entity defined within the 3GPP architecture for the purpose of collecting, processing, and reporting monitoring events that are relevant for charging. It is not a standalone physical node but a logical function integrated into existing core network elements, primarily the Mobility Management Entity (MME), the Serving GPRS Support Node (SGSN), and the Interworking SCEF (IWK-SCEF). Its primary role is to act as a source of detailed, event-based usage information that feeds into the offline and online charging systems (OFCS and OCS). The MECN monitors specific user and network activities, such as session establishment, mobility events, or service usage, and generates corresponding Charging Data Records (CDRs) or event reports. These records are then forwarded to the Charging Data Function (CDF) or Online Charging Function (OCF) via standardized interfaces like the Ga or Gy reference points.

Architecturally, the MECN function operates by intercepting and analyzing signaling and user plane messages within its host node. For instance, within the MME, it monitors Non-Access Stratum (NAS) signaling procedures like Attach, Tracking Area Update, and Service Request. It extracts relevant information such as user identity, time stamps, location details, and quality of service parameters. This data is then formatted according to 3GPP specifications (e.g., 3GPP TS 32.298 for charging data description) into a structured event report. The MECN's integration allows for granular, per-event charging rather than just session-based aggregation, enabling more flexible billing models like event-based charging or spending limit controls.

The MECN's operation is tightly coupled with policy control. It can be triggered by policies received from the Policy and Charging Rules Function (PCRF) via the MME's Gx interface (or equivalent). For example, a policy rule may instruct the MME to report every handover event for a specific subscriber. The MECN function within the MME would then generate a monitoring event for each handover, including details like the source and target cell IDs. This capability is crucial for implementing advanced charging scenarios in 4G and 5G networks, such as charging for mobility-as-a-service, location-based services, or IoT device event reporting. Its specification across releases 13 to 19 ensures backward compatibility and evolution to support new network functions and services.

Purpose & Motivation

The MECN was introduced to address the growing need for granular, event-driven charging in modern mobile networks. Traditional charging systems often relied on session-based CDRs generated by gateways (like PGW or GGSN), which provided a summary of data usage but lacked detail on specific network events or subscriber activities occurring within the control plane nodes. As networks evolved to offer more complex services (e.g., IoT, M2M, policy-driven services), operators required the ability to charge based on discrete events—such as a device attachment, a mobility update, or a specific service invocation—not just data volume. The MECN fulfills this need by turning control plane nodes into sources of chargeable events.

Historically, before MECN standardization, operators had limited visibility into charging-relevant events occurring in the MME or SGSN. Any event-based charging required proprietary implementations or indirect inference from gateway records, which was inefficient and inaccurate. The MECN, standardized from Release 13 onwards, provided a unified, standards-based method for these nodes to participate directly in the charging ecosystem. This was particularly motivated by the rise of IoT and Machine-Type Communication (MTC), where numerous small, event-driven transactions (like sensor readings) make volume-based charging impractical. MECN enables monetization of these transactions by reporting each as a discrete chargeable event.

Furthermore, MECN supports enhanced policy and charging control (PCC) by providing real-time event reports that can be used for immediate credit control or policy enforcement. For example, an operator can define a policy where the first ten mobility events per day are free, but subsequent ones incur a charge. The MECN in the MME can count these events and interact with the OCS to apply the correct charging logic. This solves the problem of implementing sophisticated, real-time charging schemes that are tightly integrated with network policy, a limitation of earlier architectures where charging and policy were more loosely coupled.

Key Features

• Integrated within MME, SGSN, and IWK-SCEF as a logical function
• Generates detailed monitoring event reports for charging
• Supports both offline (CDR-based) and online (event-based) charging models
• Triggers based on network events like attach, handover, or service requests
• Formats data according to 3GPP charging specifications (e.g., TS 32.298)
• Interworks with PCRF for policy-driven event reporting

Evolution Across Releases

Defining Specifications