3GPP Glossary

ATM End System Address

AESA is the unique network address for an ATM (Asynchronous Transfer Mode) end system, such as a network node or terminal. It is used for routing and identifying endpoints within an ATM-based transport network, which was foundational for early 3GPP core network interfaces. It enabled reliable, connection-oriented communication between network elements like RNCs and core nodes.

Application Interface

AI is a prefix used in 3GPP specifications to denote an Application Interface, specifically a class method within an interface. It standardizes the naming of application-level interfaces for network functions and services, ensuring consistent implementation across vendors and systems.

Application Programming Interface

A standardized set of definitions and protocols for building and integrating software applications within 3GPP systems. It enables service exposure, network function interaction, and third-party access, forming the foundation for programmability and innovation in mobile networks.

Access Transport Parameter

ATP is a parameter used in 3GPP networks to characterize the transport capabilities of an access network, particularly for IP-based services. It provides information about the underlying transport network's characteristics, such as bandwidth, latency, and reliability, enabling more efficient service delivery and QoS management across heterogeneous access technologies.

Common API Framework

CAPIF is a standardized framework for exposing 3GPP network capabilities via northbound APIs. It provides a common, secure, and discoverable interface for third-party applications and service providers to consume network functions. This enables innovation, simplifies integration, and fosters an ecosystem of value-added services on top of 5G and beyond.

Cell Broadcast Centre - Base Station Controller Interface

The CBC-BSC is the standardized interface between the Cell Broadcast Centre (CBC) and the Base Station Controller (BSC) in 2G/GSM networks. It enables the delivery of Cell Broadcast Service (CBS) messages to mobile devices within specific geographical areas. This interface is crucial for public warning systems and location-based information services.

Cell Broadcast Centre - Serving Mobile Location Centre Interface

The CBC-SMLC is a standardized interface defined in 3GPP for communication between the Cell Broadcast Centre (CBC) and the Serving Mobile Location Centre (SMLC). It enables the CBC to request location information from the SMLC for location-based cell broadcast services, such as geographically targeted public warning messages. This interface is crucial for ensuring that emergency alerts and other broadcast messages are delivered only to users within specific, relevant geographical areas.

Communication Service Interface

CSIF is a standardized northbound interface defined in 3GPP for exposing network capabilities to third-party communication service providers. It enables the integration of 3GPP networks with external applications and services, facilitating the creation of new business models and service offerings. This interface is crucial for enabling network-as-a-service (NaaS) concepts and supporting vertical industry applications.

Contributing Source

CSRC is a 3GPP interface defined between the Serving Gateway (S-GW) and the Packet Data Network Gateway (P-GW) in the Evolved Packet Core (EPC). It carries user plane traffic and control plane signaling for GTP-based S5/S8 interfaces, enabling the separation of gateway functions for flexible network deployment. This interface is fundamental for LTE/EPC architecture, supporting mobility and bearer management.

Interchange Circuit 105

CT105 is a control circuit defined in ITU-T V.24 and referenced in 3GPP specifications for modem and data terminal equipment (DTE) interfaces. It carries the Request to Send (RTS) signal, which controls data transmission direction in half-duplex communication. This standardized interface ensures reliable data flow control between network equipment and modems in legacy and some specialized 3GPP implementations.

Interchange Circuit 107

CT107 is a standardized data set ready (DSR) control circuit defined by ITU-T V.24 and referenced in 3GPP for modem and terminal equipment interfaces. It signals when the data terminal equipment (DTE) is ready to operate, ensuring proper handshaking and data flow control in legacy telecommunications systems. Its inclusion in 3GPP specifications supports backward compatibility and interoperability with traditional circuit-switched data services.

Circuit 109 (Interchange Circuit 109 per ITU-T V.24)

CT109 is a standardized control circuit defined by ITU-T V.24 and adopted in 3GPP for modem and data terminal equipment (DTE) interfaces. It carries the Received Line Signal Detector (RLSD) signal, indicating the presence of a valid carrier signal from the remote modem. This circuit is fundamental for establishing and maintaining reliable data communication sessions in legacy circuit-switched data services.

Circuit 114 (Interchange Circuit 114)

CT114 is a standardized interchange circuit defined by ITU-T V.24, adopted in 3GPP specifications for modem control signaling. It corresponds to the Data Terminal Ready (DTR) signal, used to indicate the readiness of data terminal equipment (DTE) for communication. Its inclusion in 3GPP specs ensures compatibility with legacy telecommunication interfaces and modem-based data services.

Interchange Circuit 115

CT115 is a standardized electrical interface circuit defined by ITU-T V.24, adopted by 3GPP for specific signaling and control functions. It provides a secondary channel for transmitting signals, such as receiver signal element timing, between data terminal equipment (DTE) and data circuit-terminating equipment (DCE). Its inclusion in 3GPP specifications ensures interoperability for legacy and specialized equipment interfaces within telecommunications networks.

Data Circuit-terminating Equipment

DCE is a network interface device that terminates a data circuit, providing the physical connection and signal conversion between Data Terminal Equipment (DTE) and the telecommunications network. It is essential for establishing reliable point-to-point data communications, such as in legacy circuit-switched data services and some fixed-line interfaces within 3GPP architectures.

E1 Application Protocol

The control plane protocol operating over the E1 interface in a disaggregated 5G RAN (NG-RAN). It facilitates communication between the Central Unit (CU) and the Distributed Unit (DU), enabling control and management of radio resources in a split architecture.

F1 Control Plane Interface

The F1-C is the control plane interface between a gNB-Central Unit (gNB-CU) and a gNB-Distributed Unit (gNB-DU) in a disaggregated 5G NR RAN. It carries signaling for UE context management, bearer setup, and mobility procedures, enabling flexible and scalable RAN deployments.

F1 User Plane Interface

The F1-U is the user plane interface between a gNB-Central Unit (gNB-CU) and a gNB-Distributed Unit (gNB-DU) in 5G NR. It transports user data packets (IP packets) over GTP-U tunnels, enabling the separation of data processing from radio transmission for flexible RAN deployments.

Frame Quality Classification

Frame Quality Classification (FQC) is a mechanism used on the Iu (between RNC and Core Network) and Nb (between MSC Servers) interfaces in 3GPP UMTS networks. It classifies the quality of received speech frames (e.g., as 'Good', 'Bad', or 'Erased') to enable selective frame processing and error concealment, optimizing voice quality across network nodes.

High-Definition Multimedia Interface

A proprietary audio/video interface standard for transmitting uncompressed video data and compressed/uncompressed digital audio from an HDMI-compliant source device to a compatible display. In 3GPP, it is referenced in the context of device capabilities and multimedia service requirements for high-definition content delivery.

Handover Interface

The Handover Interface (HI) is a standardized interface defined by 3GPP for the exchange of information between Law Enforcement Agencies (LEAs) and telecommunications networks. It enables lawful interception, allowing authorized entities to monitor specific communications for legal and security purposes.

Handover Interface Port 1 (for Administrative Information)

HI1 is the administrative port of the Handover Interface (HI) used for lawful interception. It carries the interception orders and administrative data from the Law Enforcement Agency to the network operator, activating and managing the interception session.

Handover Interface Port 2

HI2 is a standardized interface for lawful interception, specifically for delivering Intercept Related Information (IRI) from a network operator to a Law Enforcement Monitoring Facility (LEMF). It is a critical component for legal compliance, enabling the authorized delivery of call-associated data like numbers, time, and location.

Handover Interface Port 3

HI3 is the standardized interface for lawful interception that delivers the actual Content of Communication (CC), such as voice call audio or user data packets, from the network operator to a Law Enforcement Monitoring Facility. It is essential for capturing the substantive material of intercepted communications.

IMS Application Server Interface (MSC Server enhanced for ICS to IMS)

A reference point defined between a Circuit-Switched (CS) network element, specifically an MSC Server enhanced for IMS Centralized Services (ICS), and the home IP Multimedia Subsystem (IMS). It enables the delivery of IMS services to legacy CS-attached user equipment by allowing the MSC to act as an IMS Application Server.

Interface Control Document

A 3GPP specification document that defines the detailed control procedures, message formats, and information flows for a specific interface between network elements. It ensures interoperability between equipment from different vendors by providing a standardized implementation blueprint.

Interface Device

A standardized interface device defined in 3GPP for testing and conformance purposes. It provides a physical and logical reference point for connecting test equipment to network elements or user equipment, ensuring interoperability and compliance with specifications. This is crucial for certification and validation of network components.

Inter-IMS Network to Network Interface

A standardized reference point between two IP Multimedia Subsystem (IMS) networks from different operators or administrative domains. It enables secure, feature-rich interconnection for IMS-based services like VoLTE, video calling, and rich communication services (RCS) between networks.

Internal Network Interface

INI is an internal network interface defined in 3GPP for secure communication between network functions within an operator's domain. It facilitates trusted exchanges, such as authentication and key management, ensuring that sensitive data remains protected from external threats. This interface is critical for maintaining network integrity and security in mobile systems.

Internetwork Packet Exchange

A standardized, secure, and QoS-enabled IP-based interconnect framework for exchanging traffic between mobile network operators and service providers. It enables global roaming, interconnect billing, and reliable delivery of services like voice, SMS, and data across administrative domains.

IMS Access Gateway to P-CSCF Reference Point

The IQ reference point is a standardized interface between the Proxy-Call Session Control Function (P-CSCF) in the IMS core and an IMS Access Gateway. It facilitates the transport of SIP signaling and media for IMS-based services, such as VoLTE, over non-3GPP access networks like fixed broadband or Wi-Fi.

IP multimedia subsystem Service Control interface

The ISC interface is the standardized reference point between a Call Session Control Function (CSCF) and an application server (AS) within the IMS core. It is based on the Session Initiation Protocol (SIP) and is used for service control, enabling the CSCF to delegate session handling to external service logic for features like VoIP, video calling, and supplementary services.

Interworking Unit

A functional unit that provides adaptation between different network protocols or interfaces, enabling communication between heterogeneous systems. It is often referenced for interworking with legacy or external networks based on CCITT (now ITU-T) standards like X.71 and X.75.

LLC to GPRS Mobility Management service access point

LLGMM is a specific Service Access Point (SAP) between the LLC layer and the GMM sublayer in GPRS/UMTS. It provides the interface for transporting GPRS mobility management signaling messages over the reliable LLC link. It ensures secure and ordered delivery of critical signaling like attach, routing area updates, and security procedures.

Mobile Station – Supported Codec List

MS-SCL (Mobile Station – Supported Codec List) is a UE capability transmitted to the network detailing the audio and speech codecs the device supports. It is crucial for efficient codec negotiation during call setup, ensuring compatible media is selected and avoiding transcoding where possible.

Multi Technology Operations System Interface

A standardized, web services-based interface defined by the TM Forum and adopted by 3GPP for communication between Operations Support Systems (OSS) and network management systems. It enables automated, interoperable service and resource management across multi-vendor, multi-technology networks.

Reference point between the NG-RAN and the AMF

The N2 is a critical reference point in the 5G system architecture that connects the Next Generation Radio Access Network (NG-RAN) to the Access and Mobility Management Function (AMF) in the core network. It carries signaling for registration, connection management, mobility, and session management, enabling control-plane separation and flexible deployment.

Non-3GPP Access Network

A standardized reference point connecting a 5G Core Network to a non-3GPP access network, such as Wi-Fi or fixed broadband. It enables secure, seamless integration of alternative access technologies into the 5G system, supporting unified authentication, policy, and mobility.

Network Digital Interface

A standardized digital interface specification for connecting network elements within mobile networks, particularly between radio access and core network components. It defines the physical, electrical, and logical characteristics for reliable data and control signal transmission.

Next Generation Service Interfaces

NGSI is a set of standardized, northbound APIs that enable external applications to discover, request, and interact with 3GPP network capabilities and data. It provides a unified, secure, and programmable interface for service exposure, which is fundamental for creating new vertical applications and enabling network-as-a-service business models in 5G.

Network to Network Interfaces

NNI refers to standardized interfaces between different networks or network elements in 3GPP systems. They enable interoperability, signaling, and data exchange across network boundaries, essential for multi-network operations.

Network Service Service Access Point

NS-SAP is a service access point defined in 3GPP specifications for the interface between a Base Station Controller (BSC) and a Packet Control Unit (PCU) in GSM/EDGE Radio Access Network (GERAN). It provides the logical point for packet-switched data services. This matters as it was a key architectural element enabling GPRS and EDGE data services over legacy GSM networks.

Network Service Virtual Connection

A logical connection defined in the Iur-g interface between a BSC and a BSS Network Synchronization Server (NSS). It transports synchronization information, such as timing and phase alignment data, between network elements to ensure coordinated operation of the radio access network.

Network Service Virtual Link

A logical link that aggregates multiple Network Service Virtual Connections (NS-VCs) between a BSC and a BSS Network Synchronization Server (NSS) over the Iur-g interface. It represents a higher-level transport path for synchronization data, facilitating efficient management and resource allocation.

Network Service Access Point

A conceptual point within the network layer architecture where services are provided to the layer above. It defines the interface for data transfer and control between the network layer and the transport layer in the 3GPP protocol stack, ensuring standardized communication.

Packet Handler Interface

An internal interface within the UMTS packet-switched core network (PS-CN), specifically between the SGSN and GGSN. It standardizes the communication for packet handling and routing functions, ensuring interoperability between network elements from different vendors. Its role was crucial for the early deployment and scaling of 3G data services.

Physical Service Access Point

The Physical Service Access Point (PHY-SAP) is a conceptual service interface between the Physical Layer (PHY) and the Medium Access Control (MAC) layer in the 3GPP protocol stack. It defines the primitives and data units exchanged, such as transport blocks and HARQ feedback. This abstraction is crucial for maintaining layer independence and enabling interoperability between different PHY and MAC implementations.

Point Of Interconnection

POI is the physical and logical interface where a 3GPP mobile network connects to the Public Switched Telephone Network (PSTN) or other external networks. It enables interoperability for voice and data services, ensuring seamless call routing and signaling between cellular and traditional telephony systems, which is essential for global communication.

Physical Termination Point

A conceptual point representing the physical boundary of a 3GPP network, typically the user equipment (UE) or a network termination. It is a fundamental reference point for defining network interfaces, service access points, and protocol termination, crucial for architectural modeling and standardization.

Reference Point

A Reference Point (RP) is a conceptual point in the network architecture representing a standardized interface between two distinct functional entities. It defines the protocols, procedures, and information exchanged, ensuring interoperability between network components from different vendors in 3GPP systems.

S1 Control Plane

The S1-C is the control plane interface between the eNodeB (base station) and the Mobility Management Entity (MME) in LTE/EPC networks. It carries signaling messages for functions like bearer establishment, handover, and paging, enabling core network control over radio resources.

S1 Control Plane Interface to the Mobility Management Entity

S1-MME is the logical control plane interface between the eNodeB and the MME in LTE networks. It carries signaling for mobility management, session establishment, and security, separating control functions from user data to optimize network performance and scalability.

S1 User Plane Interface

S1-U is the user plane interface between the eNodeB (base station) and the Serving Gateway (SGW) in LTE networks. It carries actual user data packets, such as internet traffic, using GTP-U tunneling to ensure seamless mobility and efficient data forwarding across the network.

S101 Interface

The S101 is a standardized reference point between the LTE Evolved Packet Core's Mobility Management Entity (MME) and a CDMA2000 High Rate Packet Data (HRPD) Access Network. It enables optimized handovers and seamless mobility for dual-mode LTE/CDMA devices, ensuring service continuity during network transitions.

S103 Interface

The S103 is a user plane reference point between the Serving Gateway (SGW) in an LTE network and the HRPD Serving Gateway (HSGW) in a CDMA network. It enables the forwarding of downlink data packets during an active handover from LTE to HRPD, minimizing packet loss and service disruption.

Service Based Interfaces

A modern architectural paradigm for 5G Core Network (5GC) where Network Functions (NFs) expose their capabilities as reusable services through HTTP/2 APIs. It replaces traditional point-to-point interfaces, enabling cloud-native design, automation, and flexible service composition, which is foundational for network slicing and edge computing.

Service Interface

A standardized prefix used to denote interface class methods within 3GPP specifications. It provides a consistent naming convention for service-based interfaces, facilitating interoperability and clear architectural definitions between network functions. Its consistent use is crucial for unambiguous specification development and implementation.

Signalling Transport Converter

STC is a network element that converts signalling protocols between different transport layers, such as between SS7-based signalling and IP-based transport. It facilitates interworking in core networks, ensuring seamless communication between legacy and modern systems during network evolution.

Transceiver Speech & Data Interface

A standardized interface specification within 3GPP that defines the electrical and logical characteristics for connecting a mobile terminal's transceiver unit (RF part) to its baseband processing and application unit. It enables modular terminal design and interoperability between components from different vendors.

User to Network Interface

The UNI is the demarcation point or reference point between user equipment (or customer premises equipment) and a public telecommunications network. It defines the technical, operational, and often contractual boundary, specifying protocols, physical connections, and service characteristics.

Uniform Pulse Code Modulation Interface (13-bit)

A specific 13-bit linear PCM interface standard defined for connecting network elements in 3GPP systems. It specifies the electrical and logical characteristics for transmitting high-quality, uniformly quantized digital voice signals between equipment like base stations and controllers.

Video Decoding Interface

A standardized interface within the 3GPP Multimedia Broadcast Multicast Service (MBMS) architecture that defines how a client application or user equipment requests and receives decoded video streams from a network-based decoding function. It enables efficient video delivery by offloading complex decoding tasks.

VLAN Identifier

A 12-bit field in Ethernet frames used to identify Virtual Local Area Networks (VLANs), enabling network segmentation and traffic isolation. In 3GPP, it is used in 5G networks to separate user plane traffic for different network slices or services over Ethernet-based interfaces.

Web Services Description Language

WSDL is an XML-based interface description language standardized by the W3C and extensively used in 3GPP to define the operations, data types, and network endpoints of web services. It serves as a machine-readable contract between service providers and consumers, enabling automated client generation and ensuring interoperability for management, provisioning, and policy interfaces.

Wireless Telephony Applications Interface

The programming interface library for WTA, providing the specific function calls that allow applications to control telephony features on a mobile device. It defines how software interacts with network and device functions like making calls or handling messages.

X2 Interface

The X2 interface is a logical, direct point-to-point interface between two eNodeBs in LTE or two gNBs in NR. It enables direct inter-base-station communication for critical functions like handover preparation and interference coordination without routing through the core network.

X2-Control Plane

The control plane interface between two eNodeBs in LTE and 5G NR. It enables direct signaling exchange for functions like handover preparation, load management, and interference coordination, reducing latency and core network load compared to routing all signaling through the core.

X2-User Plane

The user plane interface between eNodeBs in LTE and 5G NR, used to forward user data packets during inter-base station handovers. It establishes GTP-U tunnels to ensure data delivery is not interrupted while the UE changes its serving cell, providing seamless mobility.

10-Gigabit-capable Passive Optical Network (type 1)

XGPON1 is a 3GPP-specified optical access network technology for the wireline part of fixed-mobile convergence. It provides a shared fiber infrastructure with downstream speeds up to 10 Gbps and upstream speeds up to 2.5 Gbps. It serves as a high-bandwidth backhaul for base stations and a residential broadband access for IMS-based services.