Multiple Services Credit Control

Description

Multiple Services Credit Control (MSCC) is a fundamental component of the 3GPP Online Charging System (OCS), implemented as a Diameter application based on IETF RFC 4006. It provides a standardized protocol for real-time credit authorization and control between network functions (like the GGSN, P-GW, or S-CSCF) and the OCS. The MSCC protocol enables the network to request credit quotas for a subscriber's usage of specific services before allowing that usage, and to report back consumed credit. Each MSCC message can contain multiple Service-Context-Id values and multiple Rating-Groups, allowing it to handle concurrent charging for different services (e.g., voice calls, data sessions, SMS messages) within a single subscriber session.

Architecturally, the network function acting as a Diameter client (e.g., a Charging Trigger Function, CTF) sends a Credit-Control-Request (CCR) command to the OCS (Diameter server). The request includes MSCC AVPs (Attribute-Value Pairs) that specify the service being requested, the requested quota, and relevant charging parameters. The OCS performs rating and balance management, then responds with a Credit-Control-Answer (CCA) containing granted quotas, validity times, and final-unit indications. The network function then allows the user to consume resources up to the granted quota. When the quota is exhausted or the service is terminated, the CTF sends an update CCR to report usage and request new quotas.

The MSCC protocol supports various credit control models: event-based charging for immediate services (like an SMS), session-based charging for continuous services (like a data session), and volume/time quota management. It includes mechanisms for graceful service termination when credit is depleted, redirecting the user to a top-up portal. MSCC is integral to 3GPP's Charging Data Record (CDR) generation and ensures accurate, real-time balance deductions, which is critical for prepaid services and spending limit controls in postpaid plans.

Purpose & Motivation

MSCC was created to provide a standardized, real-time credit control mechanism for modern telecommunications networks, replacing vendor-specific and less flexible prepaid solutions. Traditional offline charging (post-event) was insufficient for prepaid services, which require immediate credit authorization to prevent fraud and overspending. Early prepaid systems often used proprietary protocols, leading to integration complexity and limited service agility.

The adoption of MSCC, based on the extensible Diameter protocol, solved these problems by enabling a unified online charging interface for all network services (voice, data, messaging, IMS). It allows operators to offer real-time charging for multiple services concurrently, implement sophisticated rating plans, and provide instant notifications to subscribers. Its creation was motivated by the growth of prepaid markets and the need for convergence in charging systems as networks evolved to offer bundled multimedia services. MSCC is a cornerstone of 3GPP's converged charging architecture, supporting both prepaid and real-time postpaid business models.