Packet Flow Context

Description

The Packet Flow Context (PFC) is a fundamental concept within the GPRS and UMTS packet core architecture, specifically managed by the Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN). It represents the logical state and associated parameters for a specific packet data flow belonging to a user's Packet Data Protocol (PDP) context. A single PDP context, which establishes an IP session for a user, can contain multiple PFCs, each corresponding to a distinct traffic flow with unique requirements, such as a VoIP call, web browsing session, or video stream. The PFC contains all the necessary information to handle this specific flow, including its Traffic Flow Template (TFT) for packet filtering, the associated QoS profile, and charging identifiers.

Operationally, the PFC is created, modified, or deleted through signaling between the User Equipment (UE), the SGSN, and the GGSN, typically triggered by an application's need for a specific bearer. When uplink packets arrive from the UE, the SGSN uses the TFT stored in the PFC to classify them into the correct flow. The GGSN performs a similar classification for downlink packets received from the external Packet Data Network (PDN). Once classified, the network applies the QoS parameters (like guaranteed bit rate, priority, and delay) defined in the PFC's QoS profile to ensure the flow receives the appropriate treatment through scheduling and admission control mechanisms in both the core and radio access network.

The PFC's role is tightly integrated with charging systems. Each PFC is linked to a specific Charging ID, allowing the network to generate separate, detailed charging records (CDRs) for each service flow. This enables sophisticated charging models, such as billing a video stream differently from background email synchronization. The PFC thus acts as the central anchor point for policy enforcement, tying together packet filtering (TFT), quality of service (QoS), and charging for an individual data stream, enabling the fine-grained service differentiation that is a hallmark of 3GPP packet-switched networks.

Purpose & Motivation

The Packet Flow Context was introduced to address the limitation of having only a single, monolithic bearer (the PDP context) per IP address for a user. Early GPRS implementations could only apply a uniform QoS and charging policy to all of a user's traffic. This was insufficient for enabling multiple concurrent services with divergent requirements, such as a voice call requiring low latency and a file download requiring high bandwidth, over the same IP connection.

The creation of the PFC concept allowed for the establishment of multiple dedicated logical bearers within a single PDP context. This solved the critical problem of service differentiation. Network operators could now offer sophisticated services with guaranteed performance by allocating specific network resources and billing plans to individual application flows. It provided the necessary granularity for traffic management and monetization, forming the foundation for the IP Multimedia Subsystem (IMS) and other real-time services in 3GPP networks. The PFC mechanism was a key evolution from a best-effort data pipe to a managed, multi-service network capable of supporting diverse Quality of Service.

Key Features

• Enables multiple distinct packet flows within a single PDP context
• Stores the Traffic Flow Template (TFT) for uplink and downlink packet filtering and classification
• Associates a specific QoS profile (e.g., ARP, GBR, MBR) to each individual flow
• Links to a unique Charging ID for flow-specific accounting and billing
• Managed via signaling procedures between UE, SGSN, and GGSN (PFC operations)
• Allows independent activation, modification, and deactivation of flows

Evolution Across Releases

Defining Specifications