Service Data Flow Template

Description

The Service Data Flow (SDF) Template is a fundamental concept in 3GPP Policy and Charging Control (PCC) architecture, defined primarily in TS 23.203 for EPS and TS 23.501/23.503 for 5GS. An SDF represents a group of IP packets that are treated with the same QoS and charging policies. The SDF Template provides the means to identify which packets belong to that SDF. It consists of either a set of Service Data Flow Filters or an Application Identifier that references an Application Detection Filter. The SDF Filters are typically IP 5-tuple based (source/destination IP address, source/destination port, protocol) and may include additional parameters like ToS/Traffic Class or SPI. When an Application Identifier is used, the actual packet classification is performed by deep packet inspection (DPI) in the UPF (or PGW-U in EPC), based on the Application Detection Filter. The SDF Template is a key component of a PCC Rule, which also includes charging and QoS parameters. The PCRF (in EPC) or PCF (in 5GC) generates PCC rules and installs them into the PCEF (PGW) or SMF/UPF. The SMF then translates the PCC rule into a Packet Detection Rule (PDR) for the UPF, where the SDF Template becomes the PDR's Packet Detection Information (PDI). The UPF uses the PDI to match incoming packets and apply the associated FAR (Forwarding Action Rule), QER (QoS Enforcement Rule), and URR (Usage Reporting Rule). This architecture allows dynamic policy control based on application detection, user subscription, and network conditions. The SDF Template concept has evolved from Rel-7 to Rel-20, with the introduction of application detection filters in Rel-11 and the extension to 5G in later releases, where the SMF and UPF play key roles in enforcing the template.

Purpose & Motivation

The SDF Template exists to solve the problem of identifying and classifying IP traffic flows in a mobile network so that differentiated QoS and charging can be applied. Before its introduction, networks could only apply coarse-grained policies based on bearer-level QoS, without the ability to distinguish between different applications or services within the same bearer. This limited the ability to offer tailored services, such as zero-rating for specific apps, guaranteed bit rates for VoLTE, or blocking of certain traffic. The SDF Template provides a flexible and extensible mechanism to define traffic filters, either statically via 5-tuples or dynamically via application detection. It enables operators to enforce policy decisions from the PCRF/PCF, such as gating, QoS modification, and usage monitoring, on a per-SDF basis. It also supports charging differentiation, allowing online and offline charging systems to bill based on the service data flow. The introduction of application identifiers in Rel-11 further enhanced this by allowing policy control based on application detection, even when the traffic is encrypted or uses dynamic ports. In 5G, the SDF Template is integrated into the PDR concept, ensuring that the same policy framework applies to both 4G and 5G networks, facilitating smooth migration and consistent service experience.