Subscribed Quality of Service

Description

Subscribed QoS refers to the quality of service profile that is associated with a user's subscription in the home subscriber database, such as the Home Location Register (HLR), Home Subscriber Server (HSS), or Unified Data Management (UDM). It defines the maximum QoS parameters that the network is authorized to grant to the user. These parameters include maximum bit rates, guaranteed bit rates, QoS class identifiers (QCIs), allocation and retention priority (ARP), and other attributes that control how the user's traffic is treated in the network. The core principle is that the network will not grant a QoS greater than what is subscribed; any request for higher QoS will be either rejected or downgraded to the subscribed level.

The subscription profile is provisioned by the operator and cannot be modified directly by the end user for security reasons. This prevents users from self-provisioning higher QoS and ensures fair usage of network resources. The subscribed QoS profile may include multiple QoS profiles for different services (e.g., one for voice, one for data) or may be a single set of parameters. In 3GPP, the subscribed QoS is part of the subscription data that is downloaded to the serving node (e.g., SGSN, MME, SMF) during attach or PDN connection establishment. The serving node uses this information to enforce QoS policies, often in conjunction with a Policy and Charging Control (PCC) framework that may further restrict QoS based on dynamic policies.

The enforcement of subscribed QoS occurs at multiple levels. For example, in EPS, the MME receives the subscribed QoS from the HSS and includes it in the default bearer context. The PGW can further apply PCRF policies. If the UE requests a dedicated bearer with QoS above the subscribed, the network may reject the request with an appropriate cause code. Similarly, in 5G, the SMF retrieves the subscribed QoS from the UDM and uses it to authorize PDU session QoS flows. The SMF may also interact with the PCF for dynamic policy control. Thus, the subscribed QoS acts as a ceiling for the QoS that can be granted.

The concept was introduced in Release 4 as part of the early packet-switched core network specifications. Over the releases, the location of the subscription data has evolved: from HLR in 2G/3G, to HSS in 4G, and to UDM in 5G. The definitions in 21.905 and 23.057 reflect these changes. The Rel-19 definition explicitly mentions HLR/HSS/UDM to cover all generations. This evolution mirrors the architectural shift towards a unified data management framework in 5G.

Subscribed QoS is critical for ensuring that users receive the service level they have paid for while protecting the network from overload. It enables differentiated services and is a key enabler for operator business models. Without subscribed QoS, the network would have no basis to deny excessive QoS requests, leading to potential abuse and degradation for other users.

Purpose & Motivation

The Subscribed QoS concept exists to enforce a contractual limit on the quality of service that a user can receive. It solves the problem of users demanding more network resources than they are entitled to, which could lead to congestion and unfair usage. Before its introduction, there was no standardized way to prevent a user from requesting high QoS without authorization. By storing the QoS profile in the subscription database, the network can consistently apply the same limits across different access technologies and serving nodes. This also supports roaming, as the visited network can retrieve the subscribed QoS from the home network and enforce it. The evolution from HLR to HSS to UDM reflects the need for a centralized, multi-technology subscription repository in increasingly complex networks.