Binding

Description

Binding is a core concept in 3GPP policy and charging control (PCC) architecture, defining the association between a service data flow (SDF) and the IP-CAN bearer (for GPRS, the PDP context) that transports it. In 5G, the term evolved to refer to the association between an SDF and the QoS Flow. This binding ensures that each service data flow receives the appropriate Quality of Service (QoS) treatment as defined by the policy and charging rules. The binding mechanism is the method for creating, modifying, and deleting these bindings. The binding process is typically performed by the Policy and Charging Rules Function (PCRF) in 4G or the Policy Control Function (PCF) in 5G, which evaluates policy rules and determines which bearer or QoS Flow should carry a particular SDF. The binding is based on various parameters, such as the QoS class identifier (QCI) or 5G QoS Identifier (5QI), allocation and retention priority (ARP), and other QoS parameters. When a new service data flow is detected, the PCRF/PCF decides whether to bind it to an existing bearer/QoS Flow or to create a new one. This decision is communicated to the Policy and Charging Enforcement Function (PCEF) or Session Management Function (SMF), which enforces the binding by installing the appropriate packet filters and QoS parameters. The binding mechanism also handles modifications, such as when QoS requirements change or when a bearer is modified, and deletions when a service data flow ends. The binding ensures efficient use of network resources by multiplexing multiple service data flows with similar QoS requirements onto the same bearer or QoS Flow, while isolating flows with different requirements. It is essential for maintaining end-to-end QoS and for enabling differentiated services. The concept has evolved from 4G to 5G, where the IP-CAN bearer is replaced by the QoS Flow, reflecting the more granular and flexible QoS framework in 5G. Despite this evolution, the fundamental principle of associating service data flows with transport resources remains the same.

Purpose & Motivation

The Binding concept exists to ensure that service data flows are transported over the appropriate network resources with the correct QoS treatment. In earlier networks, without a standardized binding mechanism, QoS enforcement was often static and based on bearer-level parameters, which limited the ability to differentiate services dynamically. The introduction of binding in 3GPP Release 7 as part of the PCC architecture allowed for dynamic and policy-driven QoS control, enabling operators to offer differentiated services and to enforce fair usage policies. The binding mechanism solves the problem of mapping application-level service requirements to network-level transport resources. It allows the network to decide how to group multiple service data flows onto bearers or QoS Flows based on their QoS characteristics, optimizing resource utilization while meeting each flow's requirements. This is particularly important in networks with diverse services, such as VoLTE, video streaming, and web browsing, each with different QoS needs. The evolution to 5G QoS Flows further enhances this by providing more granular QoS handling and supporting new use cases like ultra-reliable low-latency communications (URLLC) and massive machine-type communications (mMTC). The binding concept is fundamental to the 3GPP QoS framework and continues to be relevant in the 5G era.