Advice Of Charge - Charging

Description

Advice Of Charge - Charging (AOC-C) is a comprehensive charging service defined in 3GPP standards that provides real-time charging information to mobile subscribers during their communication sessions. The service operates within the IP Multimedia Subsystem (IMS) architecture and works in conjunction with charging systems like Online Charging System (OCS) and Offline Charging System (OFCS). AOC-C enables operators to deliver charging notifications to users through various mechanisms including in-call announcements, SMS notifications, or visual indicators on user equipment, allowing subscribers to monitor their usage costs during active sessions.

Architecturally, AOC-C integrates with multiple network elements including the Serving-Call Session Control Function (S-CSCF), Application Server (AS), and charging functions. When a user initiates a call or data session, the network triggers charging events that are processed by the charging system. The AOC-C service then formats this charging information into user-friendly notifications that can be delivered through different interfaces. The service supports multiple charging models including time-based charging, volume-based charging, and event-based charging, with the ability to provide notifications at configurable intervals or upon reaching specific thresholds.

Key components of AOC-C include the AOC-Server function that processes charging data, the AOC-Client function in user equipment that receives and displays notifications, and the charging interfaces that connect to OCS/OFCS systems. The service uses standardized Diameter interfaces (Ro/Rf) for communication with charging systems and SIP signaling for delivering notifications within IMS sessions. AOC-C supports both prepaid and postpaid scenarios, with different notification strategies for each billing model. For prepaid users, it typically provides balance depletion warnings, while for postpaid users it offers usage accumulation notifications.

The service plays a critical role in the network by bridging the technical charging systems with user-facing billing transparency. It operates in real-time during active sessions, collecting charging data from multiple sources including the Policy and Charging Rules Function (PCRF) for data sessions and the Media Gateway Control Function (MGCF) for voice sessions. AOC-C notifications can include information such as accumulated charges, remaining balance, cost per minute/kilobyte, and estimated total session cost. The service also supports currency conversion and multiple tariff zones, making it suitable for international roaming scenarios where charging complexity increases significantly.

Purpose & Motivation

AOC-C was created to address the growing need for billing transparency in mobile telecommunications, particularly as services became more complex with the introduction of IMS and diverse charging models. Before AOC-C, subscribers often received unexpected bills (bill shock) due to lack of real-time charging information during usage. This was especially problematic for premium services, international roaming, and data services where costs could accumulate rapidly without user awareness. The service aimed to improve customer satisfaction and reduce billing disputes by providing proactive charging notifications.

Historically, mobile operators faced increasing customer complaints about unexpected charges, particularly with the transition to packet-switched networks and the introduction of value-added services. Traditional billing systems only provided information after service consumption, leaving users vulnerable to overspending. AOC-C addressed this by integrating real-time charging capabilities directly into the service delivery architecture, allowing operators to offer transparent billing as a competitive differentiator. The service was particularly important for prepaid markets where balance management is critical, and for postpaid markets where users needed better control over their spending.

The creation of AOC-C in Release 7 coincided with the broader rollout of IMS and the need for sophisticated charging mechanisms that could support converged services. It solved the limitation of previous approaches that either provided no real-time information or used proprietary solutions that weren't interoperable across networks. By standardizing AOC-C, 3GPP enabled consistent charging transparency across different operators and regions, facilitating international roaming and multi-vendor interoperability while giving users greater control over their telecommunications expenses.

Key Features

• Real-time charging notifications during active sessions
• Support for both prepaid and postpaid billing models
• Integration with Online Charging System (OCS) and Offline Charging System (OFCS)
• Multiple delivery mechanisms including in-call announcements and SMS
• Currency conversion and international roaming support
• Configurable notification thresholds and intervals

Evolution Across Releases

Defining Specifications