Subscription

Description

In 3GPP terminology, a subscription has two primary meanings depending on the context. In a general sense, it describes the commercial relationship between the subscriber and the service provider, encompassing the agreed services, billing, and terms of use. In the context of presence services, a subscription refers to the mechanism by which a watcher can access presence data; before a watcher can access presence data, he has to subscribe to it. This dual meaning reflects the broad applicability of the term across different domains.

The commercial subscription is the foundation of the relationship between a user and a mobile network operator. It includes the subscriber's identity, the services they are entitled to, and the associated charging and billing arrangements. This subscription is represented technically by the subscriber profile, which is stored and managed by the operator's systems. The subscription may be postpaid or prepaid, and it can include various add-on services. The subscription is also the basis for roaming agreements, allowing subscribers to use services on visited networks.

In presence services, a subscription is an authorization granted by a presentity (the entity whose presence information is being shared) to a watcher (the entity requesting the presence information). The watcher must subscribe to the presence data, and the presentity can accept or reject the subscription. The subscription can be handled automatically by server policies edited by the presentity or other authorized users. The service/protocol to manage those policies is out of the scope of the present document. This subscription model is defined in specifications such as 3GPP TS 29.199, which covers the presence service.

The subscription concept is also used in other contexts, such as event subscriptions in the Service Capability Exposure Function (SCEF) or the Network Exposure Function (NEF), where an application can subscribe to notifications about certain events. In 5G, the Unified Data Repository (UDR) and UDM manage subscriptions to data changes. The term is thus pervasive in 3GPP, reflecting the need to manage relationships and access rights in a controlled manner.

The technical realization of subscriptions involves several network functions. For commercial subscriptions, the HSS/UDM stores the subscription data, and the PCRF/PCF enforces policies based on it. For presence subscriptions, the Presence Server (PS) handles subscription requests and notifications. The subscription lifecycle includes creation, modification, renewal, and termination, each with associated procedures and security considerations. The subscription is a key enabler of personalized services and is essential for charging and revenue generation.

Purpose & Motivation

The concept of a subscription exists to formalize the relationship between a subscriber and a service provider, ensuring that services are provided according to agreed terms and that the provider can charge for them. It solves the problem of access control and authorization: only entities with a valid subscription can access certain services or data. This is crucial for both commercial services and presence information.

In the commercial context, the subscription provides a legal and technical framework for service delivery. It allows operators to offer differentiated services, manage customer relationships, and comply with regulatory requirements. Without a subscription, there would be no basis for billing or for determining a user's entitlements.

In presence services, the subscription mechanism protects the privacy of the presentity. It ensures that only authorized watchers can access presence data, and it gives the presentity control over who can see their information. This is essential for user trust and for complying with privacy regulations. The subscription model also enables scalable presence systems, where policies can be automated to handle large numbers of watchers.

The motivation for defining subscriptions in 3GPP came from the need to support new services beyond voice, such as presence and instant messaging, which require fine-grained access control. The specifications were developed to standardize these mechanisms, ensuring interoperability between different vendors and networks. Over time, the subscription concept has been extended to new domains, such as IoT and network slicing, where subscriptions define the terms of service for devices and network resources.