Interactive / Background

Description

Interactive / Background (I/B) is a fundamental Quality of Service (QoS) traffic class defined within the 3GPP packet-switched domain, specifically for the Packet Data Protocol (PDP) context. It is one of the four primary QoS classes standardized, alongside Conversational, Streaming, and Background. The I/B class is designed for non-real-time, elastic applications where the end-to-end delay is not critically bounded but where the user expects a responsive interaction or predictable data transfer. The class is subdivided into two distinct traffic handling priorities: Interactive and Background. The Interactive sub-class is intended for applications like web browsing, database queries, or server access where a request-response pattern exists, and the user is actively waiting for a reply. The Background sub-class is for applications like email delivery, file downloads (FTP), or software updates where the transfer occurs without immediate user interaction and can tolerate longer delays.

Architecturally, the I/B class parameters are negotiated during the PDP Context Activation procedure between the User Equipment (UE) and the network's Gateway GPRS Support Node (GGSN) in the core network. Key QoS attributes for an I/B context include the Traffic Class itself, Allocation/Retention Priority (ARP), Traffic Handling Priority (THP) specifically for the Interactive sub-class, and Maximum Bit Rate (MBR) / Guaranteed Bit Rate (GBR) indicators. Notably, I/B traffic is non-GBR, meaning the network does not guarantee a constant bit rate but provides a 'best-effort' service with prioritization. The Traffic Handling Priority (THP), with values 1, 2, or 3 (where 1 is highest), is a key differentiator within the Interactive sub-class, allowing the Radio Access Network (RAN) scheduler to prioritize packets from one Interactive context over another during congestion.

Within the Radio Access Network (e.g., UTRAN or E-UTRAN), the NodeB or eNodeB uses the QoS parameters signaled for the bearer (mapped from the PDP context) to make scheduling decisions on the air interface. Packets marked with Interactive class and a high THP are typically scheduled before those with Background class or a lower THP, assuming similar channel conditions. This ensures that a user's web page request is served more promptly than a concurrent background file sync. The Serving GPRS Support Node (SGSN) and GGSN perform policing and shaping functions based on the agreed Maximum Bit Rate to prevent a single user from consuming excessive network resources. The I/B class is a cornerstone of 3GPP's QoS framework, enabling efficient statistical multiplexing of data traffic while providing a basic level of service differentiation that is crucial for managing network resources and perceived user experience for the vast majority of internet applications.

Purpose & Motivation

The I/B QoS class was created to address the fundamental challenge of efficiently supporting diverse internet data applications over cellular networks, which were originally designed for voice. Prior to standardized QoS classes, all packet data was treated as undifferentiated 'best-effort,' leading to poor user experience where latency-sensitive interactive applications could be starved by bulk background transfers. The introduction of the I/B class in Rel-8 (building on earlier GPRS/UMTS QoS concepts) provided a standardized mechanism for the network to distinguish between user-in-the-loop traffic and machine-initiated background traffic.

This differentiation solves the problem of resource contention and allows network operators to implement policies that improve the perceived performance for end-users. For example, during network congestion, a web browsing session can be prioritized over a peer-to-peer file download, ensuring responsive service for the interactive user. It also allows for the creation of differentiated service offerings or tariffs, where a premium data plan might assign a higher Traffic Handling Priority to a user's interactive traffic compared to a basic plan. The I/B class, as part of the broader QoS framework, was a critical enabler for the mobile data revolution, allowing cellular networks to transition from being mere connectivity pipes to intelligent platforms capable of managing application performance.

Key Features

• Defines non-real-time, non-Guaranteed Bit Rate (non-GBR) traffic class
• Subdivided into Interactive and Background traffic handling priorities
• Uses Traffic Handling Priority (THP) parameter (1,2,3) for granular scheduling of Interactive traffic
• Key parameters negotiated during PDP Context Activation (Traffic Class, ARP, THP, MBR)
• Enables differentiated radio scheduler treatment in RAN (e.g., UTRAN, E-UTRAN)
• Fundamental for statistical multiplexing and efficient resource utilization for data services

Evolution Across Releases

Defining Specifications