3GPP Glossary

Alternate Connectivity

Alternate Connectivity (ALTC) is a 3GPP feature enabling user equipment to maintain multiple simultaneous connections to different access networks. It allows traffic to be routed through alternative paths when primary connectivity is degraded, enhancing reliability and service continuity. This is crucial for mission-critical applications requiring uninterrupted communication.

Base Station System - Anchor

BSS-A is the originating Base Station System during a GSM handover procedure. It serves as the anchor point that maintains the connection while coordinating the transfer of a mobile station to a target BSS. This concept is fundamental for seamless mobility in 2G/GSM networks.

Base Station Subsystem - B

The target Base Station Subsystem (BSS) to which a Mobile Station (MS) is being handed over during a handover procedure in GSM/UMTS networks. It represents the destination network element that will take over radio communication with the mobile device after successful handover execution, ensuring continuous service during mobility.

Binding Update List Entry

A data structure in the Packet Data Network Gateway (PGW) that maintains binding information for mobile nodes using Dual-Stack Mobile IPv6 (DSMIPv6). It stores the association between a mobile node's home address and its current care-of address, enabling IP mobility management and session continuity as devices move between networks.

Conditional Handover

A handover procedure where preparation occurs in advance, but execution is conditional on specific radio conditions being met at the UE. It enhances handover reliability and reduces failures in challenging mobility scenarios like high-speed or cell-edge environments by providing a prepared alternative target cell.

Conditional L1/L2 Triggered Mobility

Conditional L1/L2 Triggered Mobility (CLTM) is a 5G NR mobility enhancement introduced in Release 19. It enables faster and more reliable handovers by allowing the UE to autonomously execute a pre-configured handover based on real-time physical layer (L1) and MAC layer (L2) measurements, bypassing slower RRC signaling. This is critical for supporting ultra-reliable low-latency communication (URLLC) and high-mobility scenarios.

Circuit Mobility Management

Circuit Mobility Management (CMM) is a 3GPP protocol responsible for managing mobility and location tracking of mobile devices in circuit-switched networks. It handles procedures like location updates, handovers, and authentication within GSM and UMTS networks, ensuring continuous connectivity for voice calls and circuit-switched data services.

Conditional PSCell Addition or Change

A mobility enhancement in 5G NR Dual Connectivity (EN-DC, NR-DC) and Multi-RAT Dual Connectivity (MR-DC) that allows a UE to prepare and evaluate candidate PSCells before execution. It improves handover reliability and reduces service interruption by enabling conditional execution based on radio measurements.

Call Re-establishment

A Radio Resource Control (RRC) procedure that allows a User Equipment (UE) to quickly re-establish a dropped radio link and resume an ongoing call or data session. It is triggered by radio link failure (RLF) to minimize service interruption and improve user experience by avoiding a full call drop and re-establishment.

Circuit Switched Fallback

Circuit Switched Fallback (CSFB) is a 3GPP mechanism enabling LTE devices to access legacy circuit-switched voice and SMS services by temporarily falling back to 2G/3G networks. It was crucial for early LTE deployments that lacked native voice-over-IP solutions, ensuring service continuity for operators transitioning from legacy networks. CSFB bridges the gap between all-IP LTE networks and traditional circuit-switched telephony during network evolution.

Dual Active Protocol Stacks

Dual Active Protocol Stacks (DAPS) is a 5G handover enhancement that maintains two simultaneous protocol stacks during handover, one for the source cell and one for the target cell. This enables seamless, zero-interruption data transfer, which is critical for ultra-reliable low-latency communication (URLLC) services. It eliminates packet loss and reduces latency by allowing the UE to receive data from both cells until the handover is fully completed.

Diversity Handover

DHO is a soft handover technique used in WCDMA-based UMTS networks where a UE maintains simultaneous radio links with multiple NodeBs during a cell transition. This provides seamless connectivity, reduces call drops, and improves link quality through macro-diversity combining. It is a key feature of 3G UMTS that enhances mobility performance.

Dual Radio Voice Call Continuity

A mechanism for maintaining a voice call when a user equipment moves between a 3GPP network (like LTE) and a non-3GPP network (like CDMA 1x). It enables seamless handover for single radio voice call continuity (SRVCC) incapable devices by utilizing dual radios. This ensures voice service continuity in heterogeneous network environments.

Dual Stack Mobile IP

DSMIP is a mobility management protocol that enables seamless handover for IPv4 and IPv6 dual-stack devices in 3GPP networks. It extends Mobile IP to support both IP versions simultaneously, allowing devices to maintain connectivity while moving across networks. It is crucial for transitioning to IPv6 and ensuring backward compatibility in evolving mobile infrastructures.

Emergency Single Radio Voice Call Continuity

A specific subset of the SR-VCC (Single Radio Voice Call Continuity) feature that ensures the continuity of an emergency voice call when a UE moves from a packet-switched LTE/5G network to a legacy circuit-switched 2G/3G network. It guarantees that a critical emergency call (e.g., to 911/112) is not dropped during handover, even if the UE lacks a valid UICC (SIM card) or is in limited service state.

Extended Access Barring

Extended Access Barring (EAB) is a network congestion control mechanism introduced in 3GPP to manage random access attempts from low-priority or machine-type devices during overload conditions. It prevents network overload by barring specific categories of UEs from initiating access, ensuring critical services remain available.

Evolved Mobility Management

EMM is a protocol and state machine in the EPS and 5GS that manages the mobility and security context of a UE. It handles procedures like attach, detach, tracking area updates, and authentication, ensuring the device is reachable and secure for network services.

Equivalent PLMN

A list of Public Land Mobile Networks (PLMNs) considered equivalent to the registered PLMN for cell selection and reselection. It allows a User Equipment (UE) to treat these networks as 'home' for access purposes, facilitating seamless mobility and load balancing between operator partners.

Fast BSS Transition

A set of protocols and procedures defined by 3GPP to enable a User Equipment (UE) to rapidly and securely transition between different Base Station Subsystems (BSS) or access points, minimizing service interruption. It is crucial for supporting seamless mobility, especially for real-time services like Voice over IP (VoIP) and for Wi-Fi integration.

GPRS Mobility Management and Session Management

GMM/SM encompasses the protocols and procedures for managing a mobile device's mobility and packet data sessions in GPRS and UMTS networks. It handles functions like attach/detach, location area updates, and PDP context activation, enabling IP connectivity and mobility.

GERAN Registration Area

A GERAN Registration Area (GRA) is a logical grouping of cells within a 2G GSM/EDGE Radio Access Network (GERAN). It defines an area for which a mobile device performs location registration and paging, enabling efficient mobility management and reducing signaling load during idle mode movements within the area.

Host Based Mobility

A network-based mobility management protocol where the mobility signaling and IP address management are handled by a mobility anchor in the network, not by the mobile host itself. The host uses a stable Home Address (HoA) while the network manages the routing via a Care-of Address (CoA).

Hard Handover

Hard Handover (HHO) is a handover procedure where the radio connection to the current cell is broken before a new connection to the target cell is established. It is characterized by a 'break-before-make' operation, resulting in a brief interruption in data transmission. This classic handover type is fundamental to mobility management in cellular networks, especially in early GSM and in technologies without soft handover capabilities.

High Mobility

High Mobility (HM) is a 3GPP feature set enabling reliable communication for users moving at very high speeds, such as on high-speed trains. It addresses challenges like severe Doppler shift and rapid cell changes to maintain service continuity and quality. This is critical for delivering consistent data and voice services in high-velocity scenarios.

HandOver Failure

A failure event that occurs when a handover procedure is unsuccessful, causing a radio link failure. It is a critical Key Performance Indicator (KPI) for network optimization, directly impacting user experience through call drops or service interruption. Minimizing HOF rates is a primary goal of mobility robustness optimization in cellular networks.

Handover Path Switching

Handover Path Switching is a core mobility management procedure that redirects a user's data path during a handover between base stations or access technologies. It ensures seamless service continuity by updating routing anchors and tunnel endpoints within the core network. This is fundamental for maintaining active sessions while a user moves.

Handover Resource Reservation

HRR is a network-controlled mobility mechanism where radio resources are proactively reserved in a target cell before a handover is executed. This pre-reservation aims to guarantee resource availability, minimize service interruption, and reduce the probability of handover failure, thereby enhancing the reliability and quality of service during user mobility.

IP Flow Mobility

A 3GPP feature enabling the simultaneous use of 3GPP and non-3GPP access networks (like Wi-Fi) for different IP data flows from a single UE. It allows operators to steer specific application traffic to the most suitable access based on policy, optimizing network resources and user experience.

Intra Frequency Reselection Indication

A mechanism in 5G NR that provides explicit network control over a UE's cell reselection behavior on the same frequency. It prevents unnecessary reselections, enhancing mobility robustness and reducing signaling overhead, especially in dense or heterogeneous network deployments.

IP Mobility management Selection

IPMS is a network function that selects the appropriate IP mobility management protocol (e.g., DSMIPv6, PMIPv6) for a UE based on operator policies and UE capabilities. It ensures seamless IP session continuity as the UE moves across different access networks, such as between 3GPP and non-3GPP systems.

Inter-Radio Access Technology

Inter-RAT (IRAT) refers to the mobility and interaction between different generations or types of radio access networks (RANs) within a 3GPP system or between 3GPP and non-3GPP networks. It enables seamless handovers, measurements, and connectivity management as a user device moves across heterogeneous network technologies.

Inter-System Mobility Policy

Inter-System Mobility Policy (ISMP) is a set of network-provided rules that guide a User Equipment (UE) in selecting and prioritizing between different 3GPP and non-3GPP radio access technologies (e.g., LTE, NR, Wi-Fi). It enables seamless, network-controlled traffic steering and handover decisions based on operator policies and real-time conditions.

Idle mode Signalling Reduction

ISR is a mobility management mechanism that allows a UE to be simultaneously registered in both the E-UTRAN (LTE) and UTRAN/GERAN (2G/3G) packet domains. It reduces signaling overhead during idle mode mobility between these systems by minimizing Tracking Area Update (TAU) and Routing Area Update (RAU) procedures.

Location Area Update

A procedure performed by a mobile device to inform the network of its current Location Area (LA), enabling efficient paging and mobility management. It is triggered when the device moves into a new LA or periodically, ensuring the network can locate the device for incoming calls or messages.

Legacy Handover

A network management function for handovers involving legacy network nodes, such as 2G/3G base stations, within a 5G network context. It ensures backward compatibility and seamless mobility for User Equipment (UE) moving between 5G New Radio (NR) and older RATs during network evolution and optimization.

Location Management

Location Management (LM) is a core mobility function that tracks and maintains the current location of a mobile device (UE) within the network. It enables the network to route calls and data sessions to the correct cell or tracking area, and is fundamental for subscriber reachability, paging, and mobility procedures. Its efficient operation is critical for network performance and user experience.

Limited Service Mode

A UE operating state where it can only access emergency services and, optionally, other legally mandated services like earthquake and tsunami warnings. It is entered when normal registration fails, ensuring users can always make emergency calls even without valid subscription or in a forbidden network.

Lower-layer Triggered Mobility

Lower-layer Triggered Mobility (LTM) is a 5G NR mobility enhancement where handover decisions are initiated by the Radio Access Network based on lower-layer (PHY/MAC) measurements, reducing latency. It enables faster, more reliable cell transitions, crucial for high-mobility and ultra-reliable low-latency communication scenarios.

Location Update

Location Update (LU) is a core mobility management procedure where a mobile device informs the network of its current location area. It enables the network to track the subscriber's approximate location for efficient call and message delivery. This procedure is fundamental for subscriber reachability in cellular networks.

Mobile Assisted Handover

A handover mechanism where the mobile station (MS) assists the network by performing radio measurements on neighboring cells. The MS reports these measurements to the network, which then makes the final handover decision. This is fundamental for maintaining call quality and network-controlled mobility in GSM and UMTS.

Measurement Assistance Information

Information provided by the network to a mobile device to assist it in performing efficient and accurate radio measurements on neighboring cells, particularly in heterogeneous network (HetNet) and carrier aggregation scenarios. It optimizes measurement performance and device battery life.

Mobile Evaluated Handover

A handover decision mechanism where the mobile station (UE) evaluates measurements and can initiate or influence the handover process. It enhances mobility management by distributing decision-making intelligence, improving responsiveness to rapid radio condition changes.

Measurement Gap

A configured period during which a User Equipment (UE) temporarily suspends communication with its serving cell to perform radio measurements on other frequencies or Radio Access Technologies (RATs). It is essential for mobility procedures like handover and cell reselection in multi-RAT and carrier aggregation scenarios.

Mobility History Information

MHI is a data record containing a UE's past mobility patterns, such as previous cell associations and handover history. It is used by the network to predict future mobility, enabling more efficient handover decisions, load balancing, and network optimization, particularly in complex 5G-NR deployments.

Minimization of Service Interruption

A set of 3GPP features and procedures designed to reduce the duration of service interruption experienced by a User Equipment during mobility events, such as handovers between cells or access technologies. It is crucial for supporting seamless mobility for latency-sensitive and mission-critical services.

Mobility Management

Mobility Management (MM) is a fundamental layer-3 protocol in 3GPP networks responsible for tracking and maintaining the location of a mobile device (UE). It enables the network to know the UE's reachability state (e.g., idle, connected) and is essential for functions like paging, registration, and handover. Its context information is crucial for session continuity and efficient network resource utilization.

Mobile station Not Reachable Flag

A flag stored in the HLR or HSS indicating that a mobile device is currently unreachable by the network. It is set when network-initiated procedures like paging fail, preventing unnecessary signaling attempts and allowing for optimized message storage and delivery mechanisms like SMS waiting.

Mobile Not Reachable Flag in MME for SMS

A flag set in the MME when a UE is unreachable for SMS delivery in EPS. It prevents unnecessary paging and signaling for SMS when the UE is known to be unavailable, optimizing network resources.

Mobile station Not Reachable for GPRS flag

A flag in the SGSN indicating a UE is unreachable for packet-switched services in GPRS/UMTS. It optimizes network efficiency by preventing paging attempts for data sessions when the UE is known to be unavailable.

Mobile station Not Reachable Reason

A parameter indicating why a UE is marked as unreachable in the SGSN (e.g., implicit detach). It provides diagnostic information for network management and helps differentiate between types of unreachability for improved handling.

Mobile Originated Handover

A handover procedure initiated by the mobile station (MS) or User Equipment (UE), typically based on its own radio measurements, to request a transfer to a new cell or channel. It is a key mobility management function that allows the network to leverage UE-side radio condition awareness for optimized connection maintenance.

Mobility Speed Estimation

Mobility Speed Estimation (MSE) is a network function that determines the speed category (e.g., stationary, pedestrian, vehicular) of a User Equipment (UE). It is crucial for optimizing handover parameters, radio resource management, and power-saving features based on the user's mobility state.

Non 5G Capable over WLAN

N5CW is a UE capability indicator signifying that the device supports connectivity to a 5G Core Network but is not capable of using 5G radio access (NG-RAN) over a WLAN interface. Essentially, it indicates a UE that can access 5GC services via non-3GPP access (like Wi-Fi) but cannot use 5G-NR radio when connected to a WLAN. This affects network selection and mobility policies.

Network Assisted Cell Change

A feature in GERAN (GSM/EDGE Radio Access Network) that enables the network to assist a mobile station during a cell reselection or handover by providing it with system information of the target cell in advance. This significantly reduces service interruption time.

Network Access Mode

A UE configuration parameter that determines which radio access technologies (RATs) it can use for network access. It controls whether a device can operate in single-mode (e.g., 3G-only) or dual/multi-mode (e.g., 3G and 2G). This is crucial for managing device capabilities, network selection, and service continuity.

Network Based Mobility Management

A mobility management architecture where the network controls and manages the mobility of user equipment (UE). It is a core concept in 3GPP Evolved Packet Core (EPC) and 5G Core (5GC), enabling seamless handovers and session continuity without requiring the UE to be heavily involved in the signaling process.

Neighbour Cell List

A list of neighboring cells configured by the network and provided to a UE to assist in cell measurement and handover procedures. It contains essential parameters like physical cell identities and frequencies, enabling efficient mobility management and seamless connectivity.

Network Evaluated Handover

Network Evaluated Handover (NEHO) is a handover decision mechanism where the network (e.g., the base station or RNC) primarily evaluates measurements and makes the handover decision for a User Equipment (UE). This contrasts with Mobile Evaluated Handover (MEHO), where the UE plays a larger role in the decision process.

Offload Preference Indicator

The Offload Preference Indicator (OPI) is a parameter used by the network to influence a UE's access network selection, particularly between 3GPP (e.g., LTE, 5G) and non-3GPP (e.g., Wi-Fi) networks. It helps manage traffic steering and load balancing based on operator policies. This is key for optimizing network resource utilization and user experience.

Pedestrian User Equipment

A UE mobility state classification indicating a user moving at pedestrian speeds. It enables the network to apply optimized radio resource management and mobility procedures, improving handover performance and battery life for walking users.

Proxy Binding Update

Proxy Binding Update (PBU) is a key signaling message in Proxy Mobile IPv6 (PMIPv6), sent by the Mobile Access Gateway (MAG) to the Local Mobility Anchor (LMA). It establishes or updates a binding between the mobile node's home network prefix and its current point of attachment, enabling network-based mobility.

Proxy Mobile Internet Protocol version 6

Proxy Mobile IPv6 (PMIPv6) is a network-based mobility management protocol standardized by IETF and adopted by 3GPP. It enables IP mobility for a mobile node without requiring its involvement in mobility signaling. The network entities, the Mobile Access Gateway (MAG) and the Local Mobility Anchor (LMA), handle all mobility-related signaling on behalf of the mobile node.

Packet Mobility Management

Packet Mobility Management (PMM) is a core network state model for GPRS and UMTS packet-switched services. It tracks the mobility and connectivity state of User Equipment (UE) between the Serving GPRS Support Node (SGSN) and the UE itself. This state management is fundamental for efficient resource allocation, enabling packet data sessions, and supporting mobility procedures like routing area updates.

Paging Proceed Flag

A network-side flag used in mobility management to control whether paging attempts for a mobile device should continue. It helps optimize paging procedures and manage network resources by indicating if further paging attempts are warranted based on the device's state and location.

Presence Reporting Area

A Presence Reporting Area (PRA) is a logical, configurable geographical area defined within a mobile network, used to track and report the presence or movement of User Equipment (UE). It enables location-based services and optimizations without requiring continuous, precise GPS-like tracking. The network can be configured to trigger reports when a UE enters, leaves, or is within a PRA, supporting applications like targeted broadcasting, lawful interception, and mobility load balancing.

Preferred Roaming List

A list stored on a mobile device (e.g., in the USIM or device memory) that defines the preferred networks and frequencies for roaming. It guides the device's network selection process, prioritizing certain operators or technologies to ensure seamless service, avoid roaming charges, or comply with regulatory requirements.

RAN-based Notification Area Code

RAN-based Notification Area Code (RANAC) is an identifier used in 5G to define a RAN-based Notification Area (RNA) for UEs in RRC_INACTIVE state. It allows the RAN to efficiently page and locate these UEs within a specific area without involving the core network, reducing signaling overhead and improving battery life for IoT and mobile devices.

Routeing Area Update

A GPRS/UMTS procedure where a mobile device updates the network with its current location within a Routeing Area (RA). It enables efficient packet-switched mobility management, allowing the network to page the device and route data correctly while conserving device battery and signaling resources.

RAT/Frequency Selection Priority

RAT/Frequency Selection Priority (RFSP) is a network-controlled index used to influence a UE's cell selection and reselection behavior. It allows the network to steer UEs to preferred radio access technologies (RATs) and frequency layers based on subscription, service requirements, or network load. This enables efficient traffic management, load balancing, and service-aware mobility.

RAN-based Notification Area

A concept in LTE and NR where a UE in RRC_INACTIVE state is assigned a specific area, comprising one or more cells, within which it can move without performing a location update. It enables efficient power saving and signaling reduction for infrequent data transmitters.

RAN-based Notification Area Update

A procedure in 5G NR for a UE in RRC_INACTIVE state to update its location within a RAN Notification Area (RNA) without transitioning to RRC_CONNECTED. It enables efficient, network-controlled mobility and paging for inactive UEs, reducing signaling overhead and power consumption compared to full core network tracking area updates.

Registered Public Land Mobile Network

The Public Land Mobile Network (PLMN) where a User Equipment (UE) is currently registered and allowed to receive service. It is a fundamental concept for network selection, roaming, and mobility management, ensuring the UE can access authorized cellular services.

RAN Registration Area

A RAN Registration Area (RRA) is a logical area within the Radio Access Network used for tracking and paging User Equipment in connected or inactive states. It enables efficient mobility management by reducing signaling overhead compared to cell-level tracking. The RRA is a key concept in LTE and 5G NR for managing UE location at a granularity between a single cell and the entire tracking area.

MIPv4 Registration Response

The MIPv4 Registration Response (RRP) is a protocol message sent by a Home Agent (HA) in response to a Registration Request (RRQ) from a Mobile Node (MN) in Mobile IPv4. It confirms or denies the MN's request to register its current care-of address, enabling IP mobility by allowing the MN to maintain its home address while moving. It is a critical component for session continuity in IP-based networks.

MIPv4 Registration Request

The MIPv4 Registration Request (RRQ) is a protocol message sent by a Mobile Node (MN) to its Home Agent (HA) in Mobile IPv4. It requests the creation or renewal of a binding between the MN's home address and its current care-of address, enabling the HA to tunnel packets to the MN's new location. It initiates the process that allows a device to move across IP networks without changing its IP address, maintaining session continuity.

Subsequent Conditional PSCell Addition or Change

S-CPAC is a 5G NR Dual Connectivity (EN-DC, NR-DC) enhancement that allows a UE to execute a conditional PSCell addition or change after an initial conditional handover or PSCell change has been prepared. It improves mobility robustness and reduces interruption time in complex multi-connectivity scenarios.

Service Area Restriction Information

A set of data used by the 5G Core Network to control where a User Equipment (UE) is permitted to obtain service. It defines allowed and non-allowed tracking areas, preventing access in restricted zones for reasons like regulatory compliance, network slicing, or localized service policies.

Successful Handover Report

Successful Handover Report (SHR) is a data collection and reporting mechanism introduced in 5G. It provides detailed, post-event information about a completed handover procedure from the target base station to the source, enabling network optimization and troubleshooting. This enhances mobility robustness and user experience.

Steering of Roaming Connected Mode Control Information

SOR-CMCI is a parameter sent to a UE in connected mode, instructing it to apply Steering of Roaming information immediately or at the next idle mode. It ensures timely execution of network steering policies, crucial for dynamic traffic management and optimizing the user's roaming experience without unnecessary delays.

Subscriber Profile ID for RAT/Frequency Priority

A network-configured identifier used to apply specific Radio Access Technology (RAT) and frequency selection priorities to a subscriber. It enables operators to steer user equipment towards preferred networks (e.g., 4G over 3G) based on subscription, optimizing network load and user experience.

Successful PSCell Addition/Change Report

A report generated by a UE upon successful completion of a PSCell addition or change procedure in dual connectivity (DC) or carrier aggregation (CA) scenarios. It provides the network with confirmation and details of the secondary cell group (SCG) configuration, enabling efficient mobility management and radio resource optimization in multi-connectivity setups.

Single Radio Voice Call Continuity

SR-VCC is a 3GPP standard for seamlessly handing over a voice call from a packet-switched LTE/5G network (using VoLTE or VoNR) to a legacy circuit-switched 2G/3G network. It ensures voice service continuity when a user moves out of LTE/NR coverage, maintaining the active call without interruption.

Single Radio Voice Call Continuity

SRVCC is a 3GPP feature enabling seamless handover of a voice call from LTE/5G NR (using VoLTE or VoNR) to legacy 2G/3G CS networks when the user moves out of LTE/5G coverage. It ensures voice call continuity for subscribers with a single radio transceiver, preventing call drops during mobility. This was crucial for the initial deployment of LTE, which lacked a native circuit-switched domain for voice.

Session Transfer Number - Single Radio

STN-SR is a unique identifier assigned to a user equipment (UE) to support Voice Call Continuity (VCC) and, more specifically, Single Radio Voice Call Continuity (SRVCC). It enables the network to seamlessly transfer an ongoing voice call from the LTE/5G packet-switched domain to the legacy circuit-switched domain (e.g., 2G/3G) when the user moves out of LTE coverage. This is critical for maintaining voice service continuity in early VoLTE deployments.

Tracking Area Update

A procedure performed by a User Equipment (UE) in LTE and 5G networks to update the network with its current Tracking Area (TA) location. It enables efficient paging and mobility management, ensuring the network can locate the UE for incoming calls or data sessions while it moves.

Target BSS

TBSS refers to the Base Station Subsystem (BSS) that a mobile station is transitioning to during a handover procedure in GSM or UMTS networks. It is the destination network element that prepares resources and accepts the connection from the serving BSS.

Time To Trigger

TTT is a timer used in handover and cell reselection procedures in LTE and 5G NR. It defines how long a measurement condition (e.g., signal strength of a neighbor cell being better than the serving cell) must be persistently true before the UE initiates a mobility event. It prevents ping-pong handovers caused by rapid signal fluctuations, ensuring network stability.

Unified Access Control

A mechanism that manages access attempts from User Equipment (UE) to the radio network during congestion or emergency situations. It uses Access Class Barring (ACB), Service Specific Access Control (SSAC), and Extended Access Barring (EAB) to prioritize access for specific users or services, ensuring network stability and availability for critical communications.

Visited Public Land Mobile Network

The VPLMN is the mobile network a subscriber is currently roaming in, which is different from their Home PLMN (HPLMN). It provides radio access and core network services to the visiting user, while the HPLMN handles subscription and authentication.

Visited Public Land Mobile Network of the A subscriber

VPLMNA identifies the mobile network (PLMN) that the calling party (A-subscriber) is currently roaming in during a call setup. It is a critical parameter for routing, billing, and applying roaming policies, ensuring calls are correctly handled when subscribers are outside their home network.

Visited Public Land Mobile Network of the B subscriber

VPLMNB identifies the mobile network (PLMN) where the called party (B-subscriber) is currently roaming when a call is delivered. It is crucial for terminating call routing, roaming billing, and applying location-based services for the recipient of a call.

WiMAX Network Discovery and Selection

WNDS is a 3GPP mechanism defined for early LTE/EPC networks to enable User Equipment (UE) to discover and select WiMAX networks as a non-3GPP access technology. It provides the UE with necessary network information and policies to facilitate seamless attachment and potential handover to WiMAX networks.