Description
The Multicast/Broadcast User Plane Function (MB-UPF) is a specialized network function within the 5G Core (5GC) architecture, introduced to support point-to-multipoint delivery of data. It operates as part of the 5G Multicast-Broadcast Service (5MBS) framework. The MB-UPF is responsible for processing and forwarding user plane packets for multicast and broadcast traffic. It interfaces with the Radio Access Network (RAN) via the N3/N9 interfaces and with the Session Management Function (SMF) via the N4 interface for control. Its key role is to replicate and route data packets received from a multicast source (e.g., via N6 interface) towards the appropriate RAN nodes serving user equipment (UEs) subscribed to a specific multicast session. This differs from a standard UPF, which primarily handles unicast traffic, by optimizing for one-to-many distribution.
Architecturally, the MB-UPF can be deployed as a standalone function or integrated with a standard UPF. It supports both multicast and broadcast delivery modes. In multicast mode, it delivers content only to UEs that have explicitly joined a multicast group, managed via the Multicast Session Management Function (M-SMF) and Multicast Control Plane Function (M-CPF). In broadcast mode, it pushes content to all UEs within a designated service area. The MB-UPF performs packet replication based on multicast group identifiers and QoS flows, ensuring efficient use of transport and radio resources. It also handles traffic policing, forwarding rule enforcement, and charging data collection for multicast/broadcast sessions as per policies from the Policy Control Function (PCF).
From a protocol perspective, the MB-UPF utilizes GTP-U tunnels over the N3 interface towards the RAN. For multicast, it may establish a single GTP-U tunnel to a RAN node, which then further distributes the traffic over the air interface using Single-Cell Point-To-Multipoint (SC-PTM) or Multicast-Broadcast Single Frequency Network (MBSFN) techniques. The MB-UPF is a critical enabler for efficient content delivery, as it prevents the network from establishing separate unicast bearers for each user receiving the same content, thereby conserving core and RAN resources and reducing latency for simultaneous delivery to large audiences.
Purpose & Motivation
The MB-UPF was created to address the inherent inefficiency of using unicast connections for delivering popular live or on-demand content to many users simultaneously. Prior to its introduction in 3GPP Release 17, 5G networks lacked a standardized, efficient core network mechanism for multicast and broadcast services. While LTE had evolved Multimedia Broadcast Multicast Service (eMBMS), its integration with the 5G Core was not fully defined. The rise of applications like live sports streaming, emergency alerts, over-the-air software updates for IoT devices, and public safety communications created a clear need for a native 5G multicast/broadcast solution.
The primary problem the MB-UPF solves is network congestion and resource waste. In a unicast-only model, if 1,000 users in a stadium request the same live video stream, the network sets up 1,000 separate data flows from the content server, through the core, and over the radio, consuming significant bandwidth and processing power. The MB-UPF, as part of the 5MBS architecture, allows a single content flow from the source to be intelligently replicated at optimal points (in the core and RAN), dramatically reducing transport load and improving spectral efficiency on the radio interface. This enables scalable, high-quality service delivery to massive audiences, which is crucial for the commercial viability of new media services and for mission-critical public warnings.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (174 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the MB-UPF was introduced as a new functional element within the 5G Multicast-Broadcast Service (MBS) architecture to handle user plane data for multicast and broadcast sessions. Its definition includes its role in the 5GC Shared MBS traffic delivery method and its control by the MB-SMF, as specified for efficient point-to-multipoint data transmission. The release also established foundational procedures for MB-UPF management, such as user plane reporting and handling path failures, as indicated by the introduced Change Requests.
- Architectural solution for User Plane (UP) Security policy and User Plane Integrity Protection TS 23.501CR0066
- User Plane management to support interworking with EPS TS 23.501CR0122
- N4 User Plane Path TS 23.501CR0171
- Correction on Control Plane protocol stacks TS 23.501CR0240
- Providing AF with information on the N6 User Plane tunnelling information TS 23.501CR0265
- Clarification on the PDU Session handover procedure with the User Plane Security Enforcement TS 23.501CR0682
+ 8 more changes
In Release 16, the MB-UPF was introduced to support the forwarding of broadcast and multicast packets for Ethernet type PDU Sessions, enabling 5G-LAN multicast services. This included enhancements for data forwarding specifically for 5G-LAN multicast and clarifications on PDU Session management for these services. The updates established the MB-UPF's role within the 5G Multicast-Broadcast Service architecture for efficient point-to-multipoint user plane delivery.
- Introduction of data transfer in Control Plane CIoT 5GS Optimisation TS 23.501CR0889
- General description of solution 1 in 23.725 for user plane redundancy TS 23.501CR0753
- UPF Selection influenced by the indication of the identity/identities of 5G AN N3 User Plane capability TS 23.501CR0862
- Use of analytics for user plane function selection TS 23.501CR0899
- User Plane Forwarding with Control Plane CIoT 5GS Optimisation TS 23.501CR0916
- Network request re-activation of user-plane resources TS 23.501CR1351
+ 26 more changes
In Release 17, the MB-UPF was enhanced with new procedures for MBS session restoration upon its own failure or an NG-RAN failure, with options for scenarios with or without an MB-UPF restart. It also gained capabilities for User Plane (In)Activity Detection and Reporting over the N4mb interface and support for specific event reporting, such as Broadcast Delivery Status and Multicast Transport Address Change. Furthermore, the release introduced the N6mb, Nmb9, and Nmb8 protocols to support 5MBS data delivery.
- 5MBS architecture TS 23.501CR2689
- N4 extensions for 5MBS TS 23.501CR2696
- Enabling restricted PDU Session for remote provisioning of UE via User Plane TS 23.501CR2709
- User Plane Remote Provisioning of UEs if PLMN as ON TS 23.501CR2802
- Edge relocation considering user plane lantecy requirement TS 23.501CR2804
- PCF impacts of 5MBS TS 23.501CR2880
+ 52 more changes
In Release 18, key enhancements for the MB-UPF included enabling multicast MBS session data delivery to UEs in the RRC_INACTIVE state, with corresponding updates to mobility procedures like Mobility Registration Update and Service Request for local or location-dependent multicast services. The release also introduced comprehensive 5MBS charging architecture, principles, and procedures, and added support for user plane inactivity detection updates. Furthermore, it specified mechanisms for multicast MBS session activation, deactivation, or update following an AMF failure.
- Support of MBS multicast reception by UEs in RRC_INACTIVE state TS 23.247CR0149
- Support RRC_INACTIVE UE receiving multicast MBS data TS 23.247CR0159
- Mobility procedures for UEs receiving multicast MBS session data in RRC Inactive state TS 23.247CR0179
- Mobility Registration Update and Service Request procedures for local multicast service TS 23.247CR0226
- Mobility Registration Update and Service Request procedures for location dependent multicast service TS 23.247CR0227
- SNPN broadcast system information and manual network selection for localized service TS 23.501CR4095
+ 51 more changes
In Release 19, the MB-UPF saw enhancements for Non-Terrestrial Networks (NTN) to support MBS broadcast, along with clarifications and procedure updates for multicast MBS session restoration following an N3mb path failure or an NG-RAN restart. The release also included clarifications on the MBS broadcast service area and introduced reporting from the SMF for user-plane energy consumption calculation. Furthermore, support for broadcast reception was clarified for enhanced RedCap UEs, and user plane traffic flow information was updated.
- MBS broadcast support for NTN TS 23.247CR0372
- Exposure enhancements for static UE IP address assignment and 5G VN group's User Plane Security Policy TS 23.501CR5492
- Control Plane and User Plane Protocol stacks involving the MWAB node TS 23.501CR5561
- AMF event exposure for supporting on-demand broadcast of LCS assistant data TS 23.501CR5580
- Multicast MBS session restoration procedure for N3mb path failure TS 23.527CR0082
- Clarification on MBS broadcast service area TS 23.247CR0387
+ 6 more changes
In Release 20, the MB-UPF gained new capabilities for mitigation actions based on analytics of abnormal user plane traffic. This enhancement allows the network to proactively respond to irregularities in the multicast or broadcast data flow. The specific mitigation procedures are triggered by this new analytics function for user plane traffic.
- Mitigation actions based on New Abnormal user plane traffic Analytics TS 23.501CR6507
Explore further
Broader topics and technologies where MB-UPF plays a role.
Defining Specifications
3GPP specifications that define or reference MB-UPF, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.247 vj30 | 5G Multicast/Broadcast Service Architecture | Rel-19 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 23.527 vj50 | 5G System Restoration Procedures | Rel-19 |
| TS 29.244 vj40 | PFCP Specification for Control/User Plane Separation | Rel-19 |
| TS 29.532 vj30 | MB-SMF Service Based Interface Protocol | Rel-19 |
| TS 29.561 vj30 | 5G Interworking with External Data Networks | Rel-19 |
| TS 29.581 vj20 | MBSTF Service Based Interface Protocol Specification | Rel-19 |
| TS 32.255 vk10 | Telecom Management; Charging for 5G Data Connectivity | Rel-20 |
| TS 32.279 vj00 | 5G MBS Session Converged Charging | Rel-19 |
| TS 38.415 vj10 | PDU Session User Plane Protocol | Rel-19 |