TSCTSF

Time Sensitive Communication and Time Synchronization Function

Services →
Introduced in Rel-17 Also in: Management, Services

TSCTSF is a 5G Core Network function that provides deterministic, low-latency, and reliable communication with precise time synchronization to support industrial IoT and other time-sensitive applications.

Category
Services
Introduced
Rel-17
Where
Core Network › 5G Core
Also touches
2 segments
Specifications
17 specs
TSCTSF Description Purpose Detected Changes Specifications

Description

The Time Sensitive Communication and Time Synchronization Function (TSCTSF) is a pivotal 5G Core Network (5GC) Network Function (NF) standardized from 3GPP Release 17 onwards. It is the central architectural entity designed to enable Time Sensitive Networking (TSN) capabilities and precise time distribution over 5G systems. The TSCTSF resides in the 5GC control plane and interacts with other core functions like the Policy Control Function (PCF), Network Exposure Function (NEF), and the User Plane Function (UPF) to orchestrate end-to-end deterministic communication services.

Architecturally, the TSCTSF has several key roles. First, it acts as a bridge between the 5G system and an external TSN network (or a TSN-aware application), often represented by a TSN Translator or a Centralized Network Controller (CNC). It exchanges TSN-specific configuration and requirements, such as gate control lists for scheduled traffic and time synchronization information, via the NEF or direct interfaces. Second, the TSCTSF is responsible for managing and configuring the 5G system as a virtual TSN bridge. This involves translating TSN requirements into 5G-specific QoS parameters and policies, which it provisions to the PCF and subsequently to the Session Management Function (SMF) and UPF. For time synchronization, the TSCTSF participates in distributing precise timing from a grandmaster clock (which could be inside or outside the 5G network) to User Equipment (UE) and UPFs, ensuring all nodes in the communication path are aligned to a common time reference, often using the IEEE 802.1AS (gPTP) profile.

From an operational perspective, the TSCTSF works in conjunction with the 5G system's QoS framework to create dedicated QoS Flows with guaranteed flow bit rate (GFBR) and maximum flow bit rate (MFBR), along with strict priority scheduling to meet latency and reliability bounds. It configures the UPF to act as a TSN talker/listener and bridge, implementing traffic shaping (e.g., per-queue gate control as per IEEE 802.1Qbv) on the N6 interface towards the data network. The TSCTSF also supports mechanisms for redundancy and seamless redundancy as defined in IEEE 802.1CB (Frame Replication and Elimination for Reliability) by coordinating multiple UPF paths. Its interfaces, such as Ntsctsf, are defined for service-based interaction within the 5GC, allowing other NFs to request time-sensitive communication services.

Purpose & Motivation

The creation of the TSCTSF was motivated by the industrial sector's demand to use 5G as a unified communication backbone for critical applications like factory automation, motion control, and process monitoring. These applications have stringent requirements for deterministic latency (often sub-millisecond), ultra-high reliability (up to 99.9999%), and precise synchronization (microsecond accuracy) that traditional best-effort mobile networks could not guarantee. Previous 3GPP releases focused on enhanced Mobile Broadband (eMBB) and ultra-reliable low-latency communication (URLLC) but lacked specific support for the scheduling and synchronization paradigms standardized in the IEEE TSN suite.

The TSCTSF specifically addresses the problem of integrating 5G systems into TSN-aware industrial networks. Before its introduction, there was no standardized way for a 5G network to appear as a virtual, deterministic bridge within a TSN domain, nor to participate in TSN's centralized configuration model. The TSCTSF bridges this gap, allowing 5G to be managed as a component within a larger TSN-controlled network. It solves the challenge of translating TSN's time-aware shaping and scheduled traffic concepts into actionable 5G QoS and user plane configurations, enabling end-to-end deterministic flows that traverse both wired TSN and wireless 5G segments seamlessly. This enables the convergence of Operational Technology (OT) and Information Technology (IT) networks over a single 5G infrastructure.

Detected Changes Across Releases

from 3GPP Change Requests

Specific changes extracted from the „Change history“ tables of 3GPP specifications (193 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.

Rel-16 38 changes

In Release 16, the TSCTSF (Time Sensitive Communication and Time Synchronization Function) was newly introduced as a network function to support Time Sensitive Communication (TSC), a service providing deterministic communication with bounds on latency and high reliability. The release also introduced the Time Sensitive Networking AF (TSN AF) and defined 5G Access Stratum-based Time Distribution as a method for the NG-RAN to provide time synchronization to UEs. Furthermore, it specified handling for TSN Time Synchronization Traffic and QoS information for Time Sensitive Networking to integrate with industrial automation standards.

  • Introduction of indirect communication between NF services and implicit discovery TS 23.501CR0736
  • eSBA communication schemas related to general discovery and selection TS 23.501CR0799
  • eSBA communication schemas related to UDM and UDR discovery and selection TS 23.501CR0800
  • eSBA communication schemas related to SMF discovery and selection TS 23.501CR0801
  • eSBA communication schemas related to PCF discovery and selection TS 23.501CR0802
  • eSBA communication schemas related to AUSF discovery and selection TS 23.501CR0803

+ 32 more changes

Rel-17 66 changes

In Release 17, the 3GPP specifications introduced the Time Sensitive Communication and Time Synchronization Function (TSCTSF) as a new network function to centrally support Time Sensitive Communication (TSC) and time synchronization services. This release expanded support beyond Time Sensitive Networking (TSN) to include other time-sensitive communication architectures and enhanced time synchronization by integrating support for IEEE 1588 Precision Time Protocol (PTP) and Boundary Clock functionality. Furthermore, the specifications defined procedures for TSCTSF registration, discovery, and interaction with an Application Function (AF) to request TSC support.

  • Introduction of the architectures for Time Sensing Communication other than TSN. TS 23.501CR2573
  • KI#3B-1: Exposure of Time synchronization as a service TS 23.501CR2629
  • Support for PTP in time synchronization service and BMCA TS 23.501CR2668
  • Support for IEEE 1588 Boundary Clocks in time synchronization service TS 23.501CR2690
  • Update for PTP in time synchronization service and BMCA TS 23.501CR2773
  • Introduction of architecture for AF requested support of Time Sensitive Communication and Time Synchronization TS 23.501CR2833

+ 60 more changes

Rel-18 73 changes

In Release 18, the TSCTSF was enhanced with new subscription-based time synchronization services and coverage area filters for that service. It gained the ability to receive direct reports on RAN timing synchronization status changes from the AMF and network timing status from the NW-TT, and to instruct UEs to reconnect to the network upon such status changes. Furthermore, support was added for direct reporting of TSC management information from the UPF and for PCC decisions based on TSCTSF input.

  • Adding time synchronization service based on subscription TS 23.501CR3762
  • Support for coverage area filters for time synchronization service TS 23.501CR3767
  • Reporting the RAN timing synchronization status change from AMF to TSCTSF TS 23.501CR3807
  • Support for network timing synchronization status and reporting KI1 - description TS 23.501CR3892
  • PIN communication configuration TS 23.501CR3897
  • CN based MT communication capability indication TS 23.501CR4081

+ 67 more changes

Rel-19 15 changes

In Release 19, the TSCTSF was enhanced to specifically support UE-Satellite-UE (UE-SAT-UE) communication, including procedures for when the serving satellite changes and for store-and-forward satellite operation. The release introduced support for serving satellite identification within this communication scheme and added required features for Ultra-Reliable Low Latency Communication (URLLC) to these satellite-based links. Furthermore, updates were made to clarify the User Plane path event reporting and the overall UE-SAT-UE communication procedure.

  • Support of UE-Satellite-UE communication TS 23.501CR5583
  • Support of UE-satellite-UE communications when serving satellite changes TS 23.501CR5518
  • Update for support of UE-Satellite-UE communication TS 23.501CR6144
  • Support of serving satellite identification in UE-SAT-UE communication TS 29.512CR1311
  • Support of serving satellite identification in UE-SAT-UE communication TS 29.514CR0704
  • Support of serving satellite identification in UE-SAT-UE communication TS 29.514CR0722

+ 9 more changes

Rel-20 1 change

In Release 20, the TSCTSF function was enhanced to support UE-Satellite-UE (UE-SAT-UE) communication for non-IMS services, enabling direct user traffic transfer between UEs under satellite coverage without transiting through the ground segment. This addition specifically addresses time-sensitive communication within the architecture for 5G LAN-type services and private communication scenarios. The enhancement facilitates deterministic communication for these direct satellite links, aligning with the TSCTSF's role in supporting bounded latency and synchronization.

  • Support of UE-SAT-UE communication for non-IMS services TS 23.501CR6520

Explore further

Broader topics and technologies where TSCTSF plays a role.

Topics
MEC (Edge Computing)Lawful InterceptSMS & Messaging5G Core (5GC)IoT & MTCServices & Applications
Technologies
5G

Defining Specifications

3GPP specifications that define or reference TSCTSF, with the latest known release. Sourced from the 3GPP document catalog — see methodology.

SpecificationTitleRelease
TS 23.501 vk00 5G System Architecture Stage 2 Rel-20
TS 24.501 vj50 5G NAS Protocols Specification Rel-19
TS 24.539 vj30 NW-TT Protocol Aspects Rel-19
TR 28.839 vi10 Technical Report Rel-18
TS 29.244 vj40 PFCP Specification for Control/User Plane Separation Rel-19
TS 29.510 vj50 NRF Service Based Interface Protocol Rel-19
TS 29.512 vj40 5G Session Management Policy Control Service Rel-19
TS 29.514 vj40 5G System; Policy Authorization Service; Stage 3 Rel-19
TS 29.518 vj50 AMF Service Based Interface Protocol Rel-19
TS 29.521 vj40 5G Binding Support Management Service Stage 3 Rel-19
TS 29.522 vj40 5G NEF Northbound APIs Stage 3 Rel-19
TS 29.534 vj20 5G Access & Mobility Policy Authorization Service Rel-19
TS 29.564 vj50 Nupf Service Based Interface Protocol Rel-19
TS 29.565 vj40 Time Synchronization Function Services Rel-19
TS 32.240 vj40 Charging Management Architecture & Principles Rel-19
TS 32.282 vi20 Charging management; Time Sensitive Networking Rel-18
TS 32.290 vj50 5G Charging for Service Based Interface Rel-19