Traffic Flow Template

Description

The Traffic Flow Template (TFT) is a core policy and traffic management construct in 3GPP packet core networks, including GPRS, UMTS, and Evolved Packet System (EPS). It operates at the Gateway GPRS Support Node (GGSN) in UMTS or the Packet Data Network Gateway (P-GW) in EPS. A TFT is essentially a collection of up to eight packet filters (in the downlink direction) that are installed as part of a PDP context (UMTS) or PDN connection/EPS bearer (EPS). Each packet filter contains matching criteria such as source/destination IP addresses and port numbers, protocol type (e.g., TCP/UDP), IPsec Security Parameter Index (SPI), and Type of Service (TOS) field bits.

Architecturally, the TFT is created by the UE or the network (via the Policy and Charging Rules Function - PCRF) and is signaled to the gateway node (GGSN/P-GW) during PDP context activation or modification procedures. In the downlink, when a packet arrives from the external packet data network (e.g., the internet), the GGSN/P-GW performs packet classification by evaluating the packet header against all active TFT filters associated with the user's PDP contexts. The packet is then directed to the specific PDP context (and its associated radio bearer) whose TFT contains the matching filter. This creates a binding between an IP flow (e.g., a VoIP call, a video stream) and a specific bearer that has the requisite Quality of Service (QoS) characteristics (e.g., guaranteed bit rate, priority).

Its role is critical for enabling multiple simultaneous services with different QoS requirements over a single user's IP address. For example, a user can have a default bearer for best-effort internet browsing and a dedicated bearer with a TFT matching their VoIP traffic to ensure low latency and jitter. The TFT mechanism allows the network to apply distinct QoS policies, charging rules, and even routing treatments (like offload to a local breakout) on a per-service-flow basis. In the uplink direction, the UE uses the TFT packet filters to map its own outgoing IP traffic to the correct bearer. The TFT is thus the fundamental tool for implementing flow-based QoS and policy control in 3GPP networks.

Purpose & Motivation

The TFT was introduced to solve the problem of supporting multiple IP-based services, each with distinct Quality of Service (QoS) needs, within a single Packet Data Protocol (PDP) context that traditionally had only one IP address and one set of QoS parameters. Early GPRS/UMTS data services primarily offered a single 'pipe' for all traffic, which was insufficient for real-time services like Voice over IP (VoIP) or video conferencing that require guaranteed bandwidth and low delay amidst other background traffic.

The creation of the TFT, standardized from Release 99 onwards, was motivated by the vision of All-IP networks and multimedia services. It enables the network to identify and differentiate between individual traffic flows (e.g., separate TCP connections for email, web, and a VoIP stream) originating from the same user equipment. By classifying packets into flows, the network can then map each flow to a dedicated bearer with optimized QoS characteristics, a process essential for the 3GPP's standardized QoS architecture. This addressed the limitations of the earlier, service-agnostic 'best-effort' data pipe, allowing operators to offer tiered services, implement sophisticated charging models (e.g., different rates for video vs. chat), and ensure a consistent user experience for latency-sensitive applications.