The X1 X2 X3 5G interface architecture represents a fundamental evolution in lawful interception design. The arrival of 5G has brought fundamental changes to how telecommunications networks are designed, deployed, and operated. For lawful interception, these changes are equally profound. The 3GPP LI architecture for 5G builds on the X1, X2 and X3 interfaces already known from 3G and 4G, but now with standardised protocols (ETSI TS 103 221-1 and TS 103 221-2) instead of the vendor-specific implementations used in previous network generations. For operators deploying 5G networks, understanding the X1/X2/X3 architecture is essential to building LI capabilities that meet regulatory requirements and function effectively in the new network environment.
이 기사에서는 5G를 위한 3GPP LI 아키텍처에 대해 상세히 설명하며, 특히 X1, X2, X3 인터페이스와 ETSI HI 인터페이스와의 관계, 그리고 통신 사업자에게 미치는 실질적인 영향 등에 중점을 둡니다. LI 솔루션 제공업체.
X1, X2, X3 5G 아키텍처
3GPP에서 정의한 5G 코어 네트워크는 3G 및 4G의 노드 기반 아키텍처와는 근본적으로 다른 서비스 기반 아키텍처(SBA)를 사용합니다. 특정 기능을 수행하는 전용 네트워크 요소 대신, 5G 코어는 서비스 기반 인터페이스를 통해 서로 통신하는 일련의 네트워크 기능(NF)으로 구성됩니다. 주요 네트워크 기능으로는 액세스 및 모빌리티 관리 기능(AMF), 세션 관리 기능(SMF), 사용자 플레인 기능(UPF) 등이 있으며, 그 외에도 다양한 기능이 있습니다.
이러한 아키텍처의 변화는 LI에 중대한 영향을 미칩니다. 이전 세대에서는 일반적으로 특정 네트워크 노드(3G의 경우 음성 신호의 MSC, 4G의 경우 데이터 신호의 P-GW 등)에서 감청이 구현되었는데, 이는 대상의 시그널링 및 사용자 플레인 트래픽이 수렴하는 명확히 정의된 지점이었습니다. 5G에서는 네트워크 기능의 분산 및 가상화 특성으로 인해 감청에 대한 접근 방식도 달라져야 합니다. 3GPP LI 아키텍처는 노드별 감청 메커니즘에 의존하기보다는 LI 시스템과 네트워크 기능 간의 표준화된 인터페이스를 정의함으로써 이 문제를 해결합니다.
3GPP TS 33.127 및 TS 33.128에 명시된 LI 아키텍처
The 3GPP LI architecture for 5G is defined primarily in three specifications: TS 33.126 (Lawful Interception requirements), TS 33.127 (Lawful Interception architecture and functions) and TS 33.128 (Lawful Interception protocols and procedures, stage 3). These specifications define the functional components of the LI system within the 5G network, the interfaces between them, and the interfaces to the law enforcement domain.
The key functional components defined in TS 33.127 are the Administration Function (ADMF), which receives warrants (in its LI Control Function, LICF) and provisions the LI system (through its LI Provisioning Function, LIPF); the Points of Interception (POIs) inside or alongside the network functions, split into IRI-POIs and CC-POIs; Triggering Functions (TFs), which activate interception at POIs such as the UPF on demand; and the Mediation and Delivery Function (MDF), split into MDF2 for IRI and MDF3 for content, which delivers the result to law enforcement.
The interfaces between these components are designated X1, X2, and X3. These interfaces are internal to the operator’s domain — they connect the LI management and delivery functions to the network functions — and are distinct from the ETSI HI interfaces, which connect the operator to the LEMF. In practice, X2 and X3 feed the handover interfaces: the MDF2 turns xIRI received over X2 into IRI for HI2, and the MDF3 turns xCC received over X3 into CC for HI3. X1 has no HI counterpart: it is the operator’s internal provisioning channel, while HI1 carries the warrant from the authority to the operator.
X1: 관리자 인터페이스
X1 is the interface over which the ADMF provisions and manages the POIs, the triggering functions and the MDF. Through X1, the ADMF sends instructions to the POIs to activate, modify, or deactivate interceptions. The X1 interface carries the target identification parameters, the scope of the interception, and any technology-specific configuration information needed by the POI.
X1 uses ETSI TS 103 221-1: XML messages sent as HTTP POST requests over HTTPS (HTTP/1.1 or HTTP/2), with mutual TLS authentication using X.509 certificates. X1, X2 and X3 are not new as concepts (3GPP TS 33.107 already used them for 3G and 4G), but in previous generations their protocols were left to vendors. For 5G, TS 33.128 mandates the standardised ETSI protocols TS 103 221-1 (X1) and TS 103 221-2 (X2/X3), which can also be used for 4G and IMS.
The X1 interface supports various target identification methods, including SUPI (Subscription Permanent Identifier), GPSI (Generic Public Subscription Identifier), PEI (Permanent Equipment Identifier), and IP addresses. Because 5G conceals the permanent identifier on the radio interface (SUCI, 5G-GUTI), TS 33.127 adds identifier-association functions (IEF, ICF and IQF) that let the operator and the LEA map temporary identifiers to the target’s SUPI.
X2: IRI 전달 인터페이스
X2 is the interface for delivering intercept-related information from the Points of Interception to the LI Mediation and Delivery Function. When a target’s communications trigger events at the POI — such as registration, session establishment, mobility events, or session termination — the IRI-POI generates xIRI records and sends them to the MDF2 over X2.
The X2 IRI records in the 5G architecture are significantly richer than those in previous generations, reflecting the more complex signalling and session management in 5G networks. X2 records may include information about PDU (Protocol Data Unit) session establishment, QoS (Quality of Service) flow creation and modification, handover events, network slice selection, and service-specific parameters. The X2 records (xIRI) are defined in TS 33.128 as BER-encoded ASN.1 and carried in the binary X2 PDU format of ETSI TS 103 221-2.
The X2 interface operates in a push model — the POI generates and sends xIRI records to the MDF2 as events occur, without waiting for a request. The delivery must be timely and reliable, as the IRI forms a critical part of the intercepted material delivered to law enforcement. The MDF2 receives X2 records from potentially multiple POIs across the network, correlates them, and formats them for delivery to the LEMF over the HI2 interface.
X3: CC 전달 인터페이스
X3 carries content (xCC) from the CC-POIs to the MDF3. For 5G data sessions the CC-POI is in the UPF: when the target’s PDU session is set up, the triggering function in the SMF instructs the UPF over LI_T3 to duplicate the session’s user-plane packets — IP packets carrying voice, data, messaging, and other services — and send them over X3.
The X3 interface handles potentially large volumes of data, particularly for data-heavy targets. The interface must be dimensioned to handle the throughput requirements without packet loss, and the delivery mechanism must maintain the integrity and ordering of the intercepted packets. The MDF3 receives the X3 traffic, processes it as needed, and delivers it to the LEMF over the HI3 interface.
In the 5G architecture, the UPF is the primary POI for user-plane interception. However, the UPF may be deployed in different locations within the network — at the edge, in regional data centres, or in central facilities — depending on the network architecture and the services being provided. The LI system must be capable of interacting with UPFs wherever they are deployed, which may require distributed X3 collection points and centralised processing at the MDF3.
네트워크 슬라이싱은 X3 차단 기능에 새로운 차원을 더합니다. 단일 대상의 트래픽이 여러 네트워크 슬라이스를 통해 흐를 수 있으며, 각 슬라이스에는 고유한 UPF 인스턴스가 있습니다. LI 시스템은 모든 관련 슬라이스에 걸쳐 대상의 트래픽을 식별하고 차단하여, 대상의 통신을 완벽하게 포괄해야 합니다.
X1/X2/X3와 HI1/HI2/HI3 간의 관계
The X interfaces and the HI interfaces serve different but complementary roles in the overall LI architecture. The X interfaces operate within the operator’s domain, connecting the LI management and delivery functions to the network infrastructure. The HI interfaces operate at the boundary between the operator and law enforcement: HI1 carries the warrant to the operator, and HI2 and HI3 deliver the intercepted IRI and content to the LEMF.
The LI Mediation and Delivery Function serves as the bridge between these two interface sets. It receives X2 IRI records from the POIs, processes and formats them, and delivers the resulting ETSI-compliant IRI over the HI2 interface to the LEMF. Similarly, it receives X3 content (xCC) from the CC-POIs, such as the UPF, processes it, and delivers it over the HI3 interface. On the administration side, the ADMF receives the warrant over HI1 (typically ETSI TS 103 120), and its provisioning function sends X1 messages (ETSI TS 103 221-1) to the POIs, the triggering functions and the MDF itself.
This layered architecture provides a clean separation between the internal network interception mechanisms and the external handover to law enforcement. It allows the network functions to implement interception using standardised X interfaces without needing to understand the specific requirements of the national HI interface implementation, and it allows the MDF to adapt between different internal and external interface versions as standards evolve.
운영자를 위한 실질적인 시사점
For operators deploying 5G networks, the X1/X2/X3 architecture has several practical implications. First, LI must be considered from the earliest stages of 5G network design. The POI interfaces within the network functions must be planned and provisioned, the MDF must be dimensioned for the expected interception volumes, and the connectivity between the POIs and the MDF must be established.
Second, operators must ensure that their 5G network function vendors support the X1, X2, and X3 interfaces as defined in TS 33.127 and TS 33.128 (ETSI TS 103 221-1/-2 as profiled by TS 33.128). TS 33.128 also makes ETSI TS 103 120 the HI1 protocol and ETSI TS 102 232-1/-7 the HI2/HI3 transport for 5G. Vendor support for the LI interfaces has historically been uneven, and operators should include LI interface compliance as a requirement in their procurement specifications.
Third, the virtualised and cloud-native nature of 5G networks introduces new challenges for LI deployment. The MDF and POIs may need to operate in containerised environments, scale dynamically, and maintain performance and reliability across distributed deployments. Operators must ensure that their LI solutions are designed for cloud-native operation and can keep pace with the dynamic nature of the 5G network.
결론
X1/X2/X3 인터페이스는 3GPP LI 아키텍처의 중대한 진화를 나타내며, 5G가 네트워크 설계 및 운영에 가져오는 근본적인 변화를 반영합니다. X1은 통신 감청을 관리하기 위한 관리 채널을 제공하며, X2는 법 집행 기관이 수사에 필요한 풍부한 메타데이터를 전달하고, X3는 감청된 통신의 내용을 전달합니다. 이 인터페이스들은 ETSI HI 인터페이스와 함께, 최첨단 통신 네트워크에서 합법적 감청을 가능하게 하는 포괄적이고 계층적인 아키텍처를 형성합니다. 통신 사업자의 경우, 법적 의무를 이행하고 5G 네트워크가 효과적이며 규정을 준수하는 합법적 감청 기능을 지원하도록 보장하기 위해서는 이러한 인터페이스를 이해하고 구현하는 것이 필수적입니다.
5G 독립형(SA) 구축이 가속화됨에 따라 X1, X2, X3 5G 인터페이스의 중요성이 점점 더 커지고 있습니다. 통신 사업자들은 자사의 X1, X2, X3 5G 구현이 최신 3GPP 사양을 준수하도록 보장해야 합니다.
관련 기사
관련 주제에 대한 자세한 내용은 다음 문서를 참조하세요:
- HI1 대 HI2 대 HI3: 세 가지 합법적 감청 인터페이스에 대한 이해
- SIPREC과 ETSI LI: 차이점은 무엇이며 각각 언제 적용되나요?
- 5G SA 환경에서의 네트워크 슬라이싱: LI 타겟팅을 어떻게 복잡하게 만들며(그리고 어떻게 단순화할 수 있는가)
외부 리소스
다음 외부 리소스에서 추가 컨텍스트와 공식 문서를 확인할 수 있습니다:
