Service subscriber

Description

A Service subscriber, in the context of 3GPP specifications, is a mobile subscriber who has a subscription to the enhanced Multi-Level Precedence and Pre-emption (eMLPP) service. eMLPP is a supplementary service that provides priority handling for calls during network congestion or emergencies. The service subscriber is the entity that has explicitly subscribed to this service, allowing them to make and receive calls with different precedence levels. The subscription is typically managed by the home network and stored in the subscriber's profile in the Home Subscriber Server (HSS) or Home Location Register (HLR).

The eMLPP service is defined in 3GPP TS 22.067 and TS 23.067, and the term 'Service subscriber' is formally defined in TS 21.905 (Vocabulary for 3GPP Specifications). The definition states: 'Mobile subscriber which subscribes to the eMLPP service. In principle, if a network provides eMLPP service, all users are able to subscribe to this service.' This highlights that eMLPP is an optional service that a network may offer, and any user can subscribe to it if available. The service subscriber is thus a user who has opted in to receive priority treatment for their calls.

From an architectural perspective, the eMLPP service involves several network elements. The Service subscriber's subscription data includes the maximum precedence level they are allowed to use. When a call is set up, the network checks the subscriber's eMLPP subscription and the requested precedence level. The Mobile Switching Center (MSC) or Mobility Management Entity (MME) enforces the precedence and pre-emption rules. Precedence levels range from A (highest) to B, 0, 1, 2, 3, 4 (lowest), with level 4 being the default for normal calls. The Service subscriber can select a precedence level for each call, subject to their subscription.

The eMLPP service is particularly important for Public Protection and Disaster Relief (PPDR) organizations, such as police, fire, and ambulance services. These users need guaranteed access to network resources during emergencies when the network may be congested. By subscribing to eMLPP, they become Service subscribers and can make calls with high precedence, potentially pre-empting lower-priority calls if necessary. This ensures that critical communications can always get through.

In terms of operation, when a Service subscriber initiates a call with a certain precedence level, the network performs admission control based on the available resources and the precedence level. If resources are insufficient, the network may pre-empt ongoing calls with lower precedence to free up resources for the higher-precedence call. The Service subscriber's calls are also given priority in queueing and resource allocation. The subscription ensures that the user is authorized to use these capabilities and that the network can bill appropriately.

The term has remained stable across 3GPP releases from Rel-4 to Rel-19, indicating that the fundamental concept of a Service subscriber for eMLPP has not changed. The definition has been carried over unchanged, reflecting the maturity and stability of the eMLPP service. However, the underlying network technologies have evolved from GSM/UMTS to LTE and 5G, and the eMLPP service has been adapted to these new architectures, but the role of the Service subscriber remains the same: a user with a subscription to priority call handling.

Purpose & Motivation

The concept of a Service subscriber exists to identify and manage users who require priority treatment for their communications, particularly during emergencies or network congestion. The eMLPP service was created to provide a standardized way to offer different levels of precedence for calls, ensuring that critical users (e.g., emergency services) can communicate even when the network is overloaded. Before eMLPP, there was no standardized mechanism for priority handling in GSM networks, leading to potential denial of service for emergency calls during congestion. The Service subscriber designation allows the network to differentiate between users who have paid for or are authorized to use priority services and those who are not.

The eMLPP service builds upon the earlier Multi-Level Precedence and Pre-emption (MLPP) service defined for fixed networks, adapting it to mobile environments. The Service subscriber concept ensures that only authorized users can invoke high precedence levels, preventing abuse and ensuring that the priority mechanisms are used appropriately. It also enables charging and policy enforcement, as the network can track usage of the eMLPP service by each subscriber.

Over time, as networks evolved to support new technologies like LTE and 5G, the need for priority services has extended to these domains. The Service subscriber term remains relevant, though in 5G, the equivalent functionality is provided by the Mission Critical Push-to-Talk (MCPTT) and other mission-critical services, as well as the 5G Priority and QoS framework. The eMLPP service itself is primarily a circuit-switched service, but its principles have influenced packet-switched priority mechanisms. The Service subscriber concept thus represents an early standardization of priority user handling that continues to inform modern priority and QoS architectures.