Extended Traffic Flow Template Support User Equipment

Description

The Extended Traffic Flow Template Support User Equipment (ETFTU) is a capability indicator within the User Equipment (UE) that signals to the network the UE's ability to handle an extended number and complexity of packet filters within a Traffic Flow Template (TFT). A TFT is a fundamental construct in 3GPP packet core networks (GPRS, EPS, 5GS) used to associate IP traffic flows with specific bearers, enabling differentiated Quality of Service (QoS) and policy enforcement. The TFT contains packet filter sets that classify uplink and downlink IP packets based on parameters like source/destination IP addresses, port numbers, protocol type (e.g., TCP/UDP), and Type of Service (TOS) fields. Each packet filter is essentially a rule that matches specific IP traffic.

In the core network architecture, specifically in the Packet Data Network Gateway (PGW) in EPS or the User Plane Function (UPF) in 5GC, TFTs are used to map classified IP flows to the appropriate Evolved Packet System (EPS) bearer or QoS Flow. The network establishes dedicated bearers with specific QoS characteristics (like guaranteed bitrate, priority) for traffic that matches the TFT filters. The standard TFT has a defined limit on the number of packet filters it can contain. The ETFTU capability indicates that the UE can support an extended set beyond this baseline limit, allowing for more sophisticated traffic differentiation.

The ETFTU capability is exchanged during UE capability transfer procedures, such as during Attach or Tracking Area Update procedures. The network (e.g., the Mobility Management Entity (MME) or Access and Mobility Management Function (AMF)) becomes aware of this UE capability. When the Policy and Charging Rules Function (PCRF) or Policy Control Function (PCF) dictates policy rules requiring complex traffic filtering, the network can utilize this extended capability. It allows the Session Management function to configure TFTs with a larger number of filters on the UE side for uplink traffic classification and on the network side for downlink traffic enforcement. This is crucial for services requiring multiple concurrent flows with distinct QoS, such as enterprise VPNs with multiple applications, advanced IP Multimedia Subsystem (IMS) services, or scenarios with simultaneous guaranteed and non-guaranteed bitrate flows.

Purpose & Motivation

ETFTU was introduced to address the limitation of the standard Traffic Flow Template's capacity for packet filters. As mobile services evolved, applications began generating more concurrent IP flows with diverse requirements. A standard VoIP call over IMS, for instance, might require separate flows for voice, video, and signaling (SIP), each needing different QoS. Enterprise scenarios could involve dozens of distinct application flows. The original TFT specification posed a constraint on how many such flows could be individually identified and mapped to dedicated bearers.

The primary problem ETFTU solves is enabling finer-grained traffic management and QoS differentiation. Without extended TFT support, the network might be forced to aggregate dissimilar traffic onto a single bearer, compromising the ability to provide optimal QoS for each flow, or it might be unable to establish all necessary dedicated bearers. This could lead to suboptimal user experience, especially for latency-sensitive or high-priority applications mixed with best-effort traffic. ETFTU provides the foundational capability in the UE to support the network's advanced policy enforcement, allowing for more precise traffic steering and resource allocation as defined by policy frameworks like Policy and Charging Control (PCC).

Its creation was motivated by the industry's move towards all-IP networks and the increasing demand for rich communication services. It future-proofed the UE capability set, ensuring that as network policies became more sophisticated, UEs would not become a bottleneck. It is a key enabler for the QoS and policy-driven architecture that is central to both 4G EPS and 5G 5GS, ensuring consistent service experience across different access technologies.

Key Features

• Signals UE support for an extended number of packet filters per TFT
• Enables creation of more complex traffic classification rules on the UE
• Facilitates advanced QoS mapping for a larger number of concurrent IP flows
• Works in conjunction with PCC architecture for dynamic policy enforcement
• Applicable to both EPS dedicated bearers and 5GS QoS Flows
• Backward compatible; networks can operate with or without ETFTU-capable UEs

Evolution Across Releases

Defining Specifications