Handover Interface

Description

The Handover Interface (HI) is a critical component within the 3GPP lawful interception architecture. It serves as the standardized communication link between the network operator's interception infrastructure and the Law Enforcement Agency's (LEA) monitoring facility. The HI is not a single physical port but a logical interface encompassing a set of protocols, data formats, and delivery mechanisms defined in specifications such as TS 33.107 and TS 33.108. Its primary function is to transport intercepted communication content (CC) and intercepted communication-related information (IRI) from the network's Mediation Function (MF) to the LEA's Collection Function (CF).

The HI operates based on a request-response model initiated by the LEA. Following a lawful authorization, the LEA sends an interception request via the HI1 (Administrative Interface) to the network operator. Once activated, the network's targeted node (e.g., a MSC, SGSN, or PGW) begins generating IRI and CC data. This data is processed and formatted by the Mediation Function according to HI specifications. The actual delivery of the intercepted data to the LEA occurs over the HI2 and HI3 interfaces. HI2 is dedicated to delivering IRI, which includes metadata like call setup times, participant identities, and location information. HI3 is dedicated to delivering the CC, which is the actual voice, data, or message content.

The architecture of the HI ensures secure, reliable, and standardized delivery. It defines requirements for data encoding, sequencing, and timestamping to maintain evidential integrity. Security measures, including encryption and secure transport protocols, are mandated to protect the sensitive intercepted data during transmission. The HI's role is pivotal in separating the network's interception capabilities from the LEA's collection systems, providing a clear demarcation point that ensures compliance with legal frameworks while maintaining network security and operational independence.

Purpose & Motivation

The HI was created to address the growing need for a standardized, secure, and legally compliant method for lawful interception across global telecommunications networks. Prior to its standardization, interception mechanisms were often proprietary, country-specific, or non-existent, creating challenges for law enforcement operating across borders and for network operators managing multi-vendor environments. The lack of standardization hindered interoperability and increased the cost and complexity of implementing interception capabilities.

The introduction of the HI in 3GPP Release 8 provided a unified framework. It solves the problem of how to reliably and securely deliver intercepted data from any compliant 3GPP network (from 3G UMTS onwards) to any compliant LEA system. Its creation was motivated by legal requirements in many jurisdictions that mandate telecommunications providers to assist in lawful interception for national security, criminal investigations, and emergency situations. The HI ensures that this assistance can be provided efficiently without compromising the network's core functionality or security, and that the evidence collected is formatted and delivered in a consistent, admissible manner.