Post Event Charging

Description

Post Event Charging (PEC) is a charging paradigm introduced in 3GPP Release 16 as part of the 5G system. It represents a shift from traditional online (OCS) and offline charging, where charging interactions occur during the session. In PEC, the network does not interact with the charging system in real-time during the service delivery. Instead, usage data is collected locally by the network function (e.g., SMF, PCF) serving the user. After the service data session or a specific service event is completed, the network function generates a Charging Data Record (CDR) or a similar usage report. This record is then forwarded to the Charging Function (CHF) for rating and billing in a post-processing manner. The architecture relies on pre-established policies and quotas agreed upon between the network and the CHF before service initiation. These policies define the charging rules, such as flat rates, event-based charges, or volume thresholds, which the network function applies locally. Key components include the PCF for policy control, the SMF for session management and CDR generation, and the CHF which acts as the billing domain. PEC is particularly managed within the Service Based Interface (SBI) framework of the 5G Core, using HTTP/2-based Nchf services. This method reduces signaling load and latency because it eliminates the need for real-time credit checks and quota updates during the session, which is ideal for machine-type communications and other services where immediate billing authorization is not critical.

Purpose & Motivation

PEC was developed to address the limitations of existing online charging systems (OCS) in handling massive numbers of low-cost, low-latency transactions expected in 5G, particularly for Internet of Things (IoT) and massive Machine-Type Communication (mMTC) scenarios. Traditional online charging requires real-time dialogue between network functions and the OCS for quota management and credit control, which introduces signaling overhead and latency that can be prohibitive for services involving billions of small, frequent events. Offline charging, while avoiding real-time interaction, still involves generating detailed records during the session and may not be flexible for new business models. PEC solves this by decoupling charging from the real-time service flow. It allows operators to implement simple, event-based charging models (e.g., per device, per transaction, or flat-rate) efficiently. The motivation stems from the need for scalable and cost-effective charging for 5G verticals like industrial IoT, where devices generate vast amounts of small data transactions. By processing charges after the fact based on pre-agreed policies, PEC reduces network signaling congestion, lowers operational costs, and enables new monetization strategies for high-volume, low-value services.