Understanding Active Mediation: The Bridge Between 5G, 4G, and Legacy Networks
Active Mediation: Complete Overview
Active Mediation
This article is part of our series on Telecom Mediation and Charging, focusing on the evolution of real-time usage processing as we transition to 5G Standalone (SA) architectures. In our previous discussions, we looked at how Online Charging mechanisms work for upfront balance checks and reservations.
Now, let us understand the concept of Active Mediation and how it acts as a real-time protocol gateway for both modern 4G/5G and legacy networks.
What is Active Mediation?
Whenever a Customer uses services like high-speed data, VoLTE, or 5G data, the network must ensure the usage is authorized in real-time. In traditional setups, mediation is a passive layer used mostly for collecting CDRs for offline billing. However, in modern 4G and 5G networks, we use Active Mediation to act as an "In-line" signal processing engine that participates directly in the signalling path.
As per the architecture, Active Mediation sits directly between the Network Element/Quota Server (managing Legacy network-side triggers) and the Charging Server, which is the OCS in 4G or the Converged Charging System (CCS) in 5G. The basic idea is to translate various network protocols into standardized messages, allowing the charging engine to perform credit control operations regardless of the network generation.
Core Components of Active Mediation
To understand the charging flow as per 3GPP standards, we look at three logical blocks inside the Active Mediation layer:
- Protocol Plugin: This serves as the real-time entry point for network triggers across all generations. It is designed to terminate connections from various sources, ranging from legacy GPRS/3G nodes using GTP' to 4G PGWs using Diameter, and modern 5G Network Functions (like the SMF) using Service-Based Architecture (SBA) triggers. The plugin ensures that whether the data comes from a legacy GPRS tunnel or a modern REST API, it is normalized for the mapping engine.
- Mapping Engine: This is the heart of the system. It performs the logic of converting proprietary or generation-specific network attributes into standardized data. For example, it maps 5G JSON-based triggers into a format the internal charging logic can process.
- DCCA/Service Plugin: This plugin communicates with the Charging Server. In 4G, it uses the Ro/Gy interfaces (Diameter), while in 5G, it uses the Nchf interface (HTTP/2 REST APIs) to interact with the Charging Function (CHF).
Legacy Interworking: Handling CAP (CAMEL) for 2G/3G
Even during the rollout of 5G, supporting legacy GSM/GPRS services is vital for roaming and fallback. In these networks, real-time charging is handled by CAMEL (CAP) for Voice and GTP' for Data Services.
fig. Active Mediation - Legacy To 4G Charging Interworking
Active Mediation translates these legacy triggers into Diameter (Ro/Gy) or 5G (Nchf) protocols:
- Triggering and Translation: A legacy CAP InitialDP or GTP' message is translated by Active Mediation into a Diameter CCR-I or a 5G Charging Data Request for a unified charging experience.
- Asset Life Extension: This allows Operators to upgrade to a 5G Converged Charging System while continuing to use existing legacy network infrastructure.
Sample Protocol Mapping (Legacy to 4G)
fig. Legacy-To-4G Protocol Mapping
Bridging 4G Diameter and 5G HTTP/2 REST APIs
fig. Active Mediation - 4G To 5G Charging Interworking
As Operators transition toward 5G Standalone (SA), the biggest challenge is the coexistence of 4G and 5G charging. While 4G relies on Diameter, 5G introduces the Service Based Architecture (SBA) using HTTP/2 and RESTful APIs.
Active Mediation acts as a critical Interworking Function (IWF) here:
- Protocol Translation: It can receive a Diameter CCR from a 4G node and map it into a JSON structure for an HTTP POST request toward the 5G Charging Function (CHF).
- Stateless vs. Stateful Handling: Diameter is stateful, requiring session maintenance, whereas 5G REST APIs are designed to be stateless. Active Mediation manages this "State" so that legacy nodes can communicate seamlessly with modern 5G systems.
- Converged Quota Models: It ensures that 4G Multiple Services Credit Control (MSCC) requests are correctly translated into 5G MultipleUnitUsage JSON structures, providing a unified view of the customer's balance across generations.
Sample Protocol Mapping (4G to 5G)
fig. 4G-To-5G Protocol Mapping
Summary and Future Outlook
Active Mediation has evolved into a high-performance, real-time gateway that enables Converged Charging. Whether it is translating CAP/GTP' to Diameter or Diameter to HTTP/2, it ensures that an Operator can maintain a single, 5G-ready BSS stack while the underlying network evolves.
The transition from 4G Diameter-based charging to 5G HTTP/2-based Convergent Charging is one of the steepest learning curves in the industry today. My book "The 5G Core: Architecture and Functions Explained" was written specifically to help Architects, Product Managers, and Billing Professionals master this shift with a clear, step-by-step mental model.
Get your copy on Amazon →Kindly share this article with your friends and colleagues. Feel free to like and comment. Happy learning.
Glossary
GTP': GTP Prime - Protocol used for charging data transfer in 2G/3G networks
CAMEL: Customised Applications for Mobile network Enhanced Logic
CAP: CAMEL Application Part
CCS: Converged Charging System
SMF: Session Management Function
CHF: Charging Function
DCCA: Diameter Credit Control Application
SBA: Service Based Architecture
Nchf: 5G Charging Interface
OCS: Online Charging System
BSS: Business Support System
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