EPC-level Proximity Services Discovery

Description

EPC-level ProSe Discovery is a network-controlled proximity discovery procedure defined in 3GPP specifications for Proximity Services (ProSe). In this procedure, the Evolved Packet Core (EPC) determines the proximity of two ProSe-enabled User Equipments (UEs) and informs them of their mutual proximity. This enables various proximity-based applications and services, such as social networking, public safety, and commercial services, without requiring the UEs to directly discover each other over the radio interface.

The procedure involves several network elements, including the ProSe Function, the Home Subscriber Server (HSS), the Mobility Management Entity (MME), and the Serving Gateway (SGW) / Packet Data Network Gateway (PGW). The ProSe Function is a logical function that handles ProSe-related control plane procedures, including authorization, discovery, and match reporting. When a UE wants to discover another UE, it sends a Discovery Request to the ProSe Function, which then checks the target UE's ProSe profile and location information.

The EPC-level discovery can operate in two modes: open discovery and restricted discovery. In open discovery, no explicit permission is required from the target UE, while restricted discovery requires the target UE's consent. The ProSe Function uses location information from the EPC (e.g., from the MME or SGW) to determine if the UEs are within a certain proximity threshold. If proximity is detected, the ProSe Function sends a Match Report to the requesting UE, indicating that the target UE is nearby.

This procedure is particularly useful for applications that require network assistance for discovery, such as finding friends nearby or public safety communications where direct discovery might be unreliable. It also supports privacy features, allowing users to control who can discover them. The EPC-level ProSe Discovery is specified in 3GPP TS 23.303 (Proximity-based services), TS 23.703 (Study on architecture enhancements), TS 29.343 (ProSe Function interfaces), TS 32.277 (ProSe charging), and TS 33.833 (Security aspects).

The procedure relies on the EPC's ability to track UE locations and manage subscriptions. It can be used in conjunction with direct discovery (PC5-based) to provide a comprehensive discovery solution. The network can also use EPC-level discovery to trigger direct discovery or to assist in establishing direct communication paths.

Purpose & Motivation

EPC-level ProSe Discovery was created to enable network-controlled proximity discovery for UEs, addressing the limitations of direct radio-based discovery. Direct discovery (also known as PC5-based discovery) allows UEs to discover each other by broadcasting and monitoring discovery messages over the PC5 interface. However, direct discovery has limitations: it requires UEs to be within radio range, it may consume battery power, and it may not be reliable in all scenarios (e.g., when UEs are in different cells or when radio conditions are poor).

EPC-level discovery leverages the cellular network's infrastructure to determine proximity based on location information and other network data. This provides a more reliable and energy-efficient discovery mechanism, especially for applications that do not require immediate direct communication. It also enables network operators to control and monetize proximity services, as they can manage discovery requests and apply policies.

The introduction of EPC-level ProSe Discovery in Release 12 was part of the broader ProSe work item, which aimed to support public safety and commercial applications. It complements direct discovery by providing an alternative when direct discovery is not feasible or when network assistance is desired. The procedure has evolved with subsequent releases, incorporating enhancements for security, privacy, and efficiency.