SUPL Enabled Terminal

Description

A SUPL Enabled Terminal (SET) is the client device in the OMA Secure User Plane Location (SUPL) architecture, adopted and profiled by 3GPP for location services. The SET is typically a User Equipment (UE) such as a smartphone or IoT device that incorporates a SUPL client software stack. This client communicates with a network server called the SUPL Location Platform (SLP) to compute the device's position. Unlike control-plane location methods which use signaling channels, SUPL carries all location protocol messages (e.g., from the LTE Positioning Protocol, LPP) embedded within a secure IP data connection (the user plane), such as a regular mobile data session.

The operation begins when a location request is triggered, either by the SET itself (Mobile Originated) or by the network (Mobile Terminated, e.g., for an emergency call). The SET establishes a secure TLS/SSL connection to the SLP. They then exchange capabilities to agree on supported positioning methods, which can include satellite-based methods like GPS, A-GPS, GLONASS, Galileo, and terrestrial methods like Observed Time Difference of Arrival (OTDOA) in LTE or Downlink Time Difference of Arrival (DL-TDoA) in 5G. The SLP may provide assistance data to the SET, such as satellite ephemeris or cell tower locations, to significantly speed up acquisition and improve accuracy (this is Assisted-GNSS).

The SET uses its internal GNSS receiver and/or measures signals from nearby cellular base stations. The actual position calculation can happen in the SET (SET-based mode), where it computes its own fix and sends it to the SLP, or in the SLP (SET-assisted mode), where the SET sends raw measurement data (e.g., pseudoranges) to the SLP for calculation. The SUPL protocol (specifically, SUPL versions like 1.0, 2.0, 3.0) defines the message flows for session initiation, capability negotiation, assistance data delivery, and position reporting. The SET's role is critical in enabling efficient, scalable, and accurate location services for consumer apps (maps), enterprise tracking, and regulatory services like E911/E112 without overloading the control-plane signaling network.

Purpose & Motivation

The SET and the SUPL framework were created to provide a standardized, efficient, and scalable method for delivering location services over cellular networks. Prior to SUPL, most network-based location services used the control plane, where positioning signaling was carried over SS7 or other circuit-switched signaling channels. This approach was inefficient for high-volume location requests (e.g., from countless smartphone apps), could slow down core network signaling, and was not well-suited for always-connected IP devices.

SUPL's user-plane approach solves these problems by leveraging the existing data connection. This makes location services easier to deploy (as it rides on IP infrastructure), more scalable, and accessible to a wider range of application developers. The purpose of defining the SET was to ensure interoperability between devices from different manufacturers and network servers (SLPs) from different vendors. It allows devices to obtain assistance data from the network to achieve faster Time-To-First-Fix (TTFF) and better indoor performance for GNSS, a key feature known as Assisted-GPS (A-GPS).

Furthermore, SUPL and the SET are essential for meeting regulatory emergency location requirements (e.g., FCC E911) in packet-switched networks. As networks evolved to LTE and 5G, which are all-IP, the control-plane for legacy location became obsolete. SUPL provided the path forward. The SET's evolution through 3GPP releases integrated support for new positioning technologies like OTDOA for LTE and NR positioning, ensuring continuous improvement in accuracy and reliability for services ranging from turn-by-turn navigation to location-based advertising and IoT asset tracking.