Advice Of Charge - During the communication

Description

Advice Of Charge - During the communication (AOC-D) is a standardized service within the 3GPP framework that delivers charging-related information to a user while a communication session is ongoing. It operates as part of the broader Advice of Charge (AoC) supplementary service family, which also includes AOC-E (at the end of a session) and AOC-S (for special services). AOC-D is specifically designed to provide periodic or event-triggered updates on accumulated charges during a session, such as a circuit-switched voice call, packet-switched data session, or multimedia telephony service. The service is implemented through interactions between network elements like the Mobile Switching Center (MSC), Serving GPRS Support Node (SGSN), and Online Charging System (OCS), ensuring that charging data is collected, processed, and relayed to the user's device in near real-time.

Architecturally, AOC-D leverages the core network's charging and signaling infrastructure. For circuit-switched services, it integrates with the CAMEL (Customized Applications for Mobile networks Enhanced Logic) or IMS (IP Multimedia Subsystem) charging mechanisms. When a session is established, the network initiates charging based on predefined tariff models. The charging function, often interfacing with an OCS for prepaid scenarios, monitors usage parameters like call duration, data volume, or service events. At configured intervals or upon specific triggers (e.g., reaching a charge threshold), the network generates an AOC-D message containing details such as current charge amount, currency, and tariff time. This message is then transmitted to the user equipment (UE) via in-band signaling (e.g., using User-to-User Information elements in ISUP) or out-of-band methods (e.g., via SIP messages in IMS), depending on the service type and network architecture.

Key components involved in AOC-D include the UE, which must support AOC-D presentation capabilities to display charges to the user; the MSC or Call Session Control Function (CSCF) for session control and signaling; and the charging system (e.g., OCS or Charging Data Function (CDF)). The service works by the charging system calculating incremental charges based on real-time usage data and instructing the session control node to send advice to the UE. For example, in a prepaid voice call, the OCS deducts credit as the call progresses and may trigger AOC-D notifications when credit reaches warning levels. In IMS-based services, AOC-D can be implemented using SIP INFO messages or as part of the Session Description Protocol (SDP) updates, allowing for flexible integration with multimedia sessions.

AOC-D's role in the network is to enhance user experience and operational efficiency by providing transparency in charging. It supports various billing models, including time-based, volume-based, and event-based charging, and is essential for compliance with regulatory requirements in many regions. The service also interacts with other network functions like policy control for QoS-aware charging, ensuring that charges reflect the quality of service delivered. By enabling real-time feedback, AOC-D helps reduce customer disputes and support cost control, particularly in roaming scenarios where charges can be higher.

Purpose & Motivation

AOC-D was created to address the need for real-time charging transparency in telecommunications networks, particularly as services evolved beyond simple voice calls to include data and multimedia. Prior to its introduction, users often received charging information only at the end of a session (via AOC-E) or on periodic bills, leading to surprises like 'bill shock' when usage exceeded expectations. This was especially problematic with the rise of mobile data and premium services, where costs could accumulate quickly. AOC-D solves this by providing ongoing updates during a session, allowing users to monitor expenses and make informed decisions, such as ending a call or limiting data use.

Historically, the motivation for AOC-D stemmed from operator requirements to improve customer satisfaction and reduce churn, as well as regulatory pressures for clearer billing practices. In 3GPP Release 7, it was standardized as part of the broader AoC enhancements to support emerging IMS and prepaid services. The service addresses limitations of previous approaches by integrating with online charging systems, enabling dynamic updates without disrupting the session. For operators, AOC-D facilitates better revenue assurance and reduces support costs related to billing inquiries, while for users, it empowers control over spending, particularly in prepaid or roaming contexts where budget management is critical.

Furthermore, AOC-D supports the evolution toward more complex service bundles and network slicing in 5G, where charging may vary based on slice type or QoS. By providing real-time advice, it helps users understand the cost implications of different service levels, aligning with trends in personalized and transparent telecom offerings. The service also enables innovative use cases, such as parental controls or enterprise spending limits, by allowing real-time notifications that can trigger user actions.