Description
Point to Multipoint (PTM) is a core network service architecture defined by 3GPP for delivering content from one source to multiple recipients. It operates across multiple network domains, including the Core Network (CN) and Radio Access Network (RAN). The architecture involves specific functional entities and interfaces for managing session establishment, bearer management, and data distribution. In the CN, the Broadcast-Multicast Service Center (BM-SC) acts as the entry point, handling service announcement, security, and charging. For the RAN, PTM defines specific radio bearers and transmission modes, such as Multimedia Broadcast Multicast Service (MBMS), which can use either a dedicated multicast channel or a shared broadcast channel depending on the number of users in a cell.
The operation begins with service announcement and user subscription. When a PTM session is activated, the network establishes a common bearer path for data delivery. In the RAN, this involves configuring multicast radio bearers. Data packets are replicated at optimal points in the network—often at the radio base station (NodeB/gNB)—to minimize core network traffic. Key protocols include the MBMS protocols (GTP for user plane, and specific control plane signaling) and RAN protocols for scheduling and transmission over the air interface.
PTM's role is critical for scalable group communication. It underpins services like mobile TV, public warning systems, and software updates. By utilizing shared network resources, it significantly improves spectral efficiency and reduces network load compared to establishing individual Point-to-Point (PTP) connections for each user, making it a foundational technology for broadcast and multicast services in cellular networks.
Purpose & Motivation
PTM technology was created to address the inefficiency of using multiple unicast (point-to-point) connections for delivering identical content to many users. Prior to PTM, services like video streaming to a group would consume excessive network bandwidth and core network resources, as the same data packets were sent individually to each subscriber. This approach does not scale and becomes prohibitively costly for mass-market services.
The historical motivation stemmed from the growing demand for multimedia group communication, such as mobile TV and live event broadcasting, in 3G UMTS networks. 3GPP introduced the Multimedia Broadcast Multicast Service (MBMS) framework, which relies on PTM principles, to enable efficient one-to-many data delivery. PTM solves the problem of network congestion and inefficient radio resource usage by allowing data replication at the edge of the network (the RAN) rather than at the core.
Furthermore, PTM supports essential services like emergency alerts and group calls for public safety and commercial applications. It provides a standardized mechanism for service providers to offer broadcast/multicast services, creating new revenue streams while optimizing infrastructure utilization. The evolution into 5G with further enhancements like MBS (Multicast and Broadcast Services) continues this purpose for new use cases like V2X and immersive media.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (16 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-4, normative work from Rel-15.
In Release 15, the Point to Multipoint (PTM) function was enhanced with the introduction of support for SAND for MBMS and measures to avoid security risks for RLC UM bearers during a termination point change. These updates were accompanied by corrections to the EUTRA-MBSFN-SubframeConfig and clarifications regarding the commonControlResourceSet frequency reference point. These changes refined the technical operation and security of the PTM service, which provides IP Multicast (IP-M) transmission to a specified group of subscribers.
In Release 16, the PTM function introduced specific enhancements for MBMS User Service Description (USD) data handling and security for RLC AM bearers. These changes included defining missing XML data types for MBMS USD attributes and implementing measures to avoid security risks during the termination point change procedure for RLC AM bearers.
In Release 17, the PTM function was enhanced to enable interworking with MBMS over E-UTRAN for broadcast service, clarifying its operation with legacy systems. Corrections were made to the description of epochTime and UTC time references for service timing, and to the F1-U context reference for PTM to ensure technical accuracy. Additionally, assumptions for CRS-IM default network configuration in non-DSS scenarios for MBSFN were specified.
- Interworking with MBMS over E-UTRAN for broadcast service TS 23.247CR0008
- CRS-IM default network configuration assumptions for MBSFN configuration in non-DSS scenario TS 38.331CR3497
- Corrections on description of epochTime and reference point of UTC time and t-Service TS 38.331CR4463
- Correction of F1-U context Reference for PTM TS 38.473CR1233
In Release 18, the enhancements for the Point-to-Multipoint (PTM) function specifically introduced support for PTM retransmission reception when operating with multicast DRX and with HARQ feedback disabled. This involved defining and correcting the related UE capabilities for handling these retransmissions. The release also provided a clarification regarding the applicable reference point for a procedure involving a hard satellite switch with resynchronization.
- PTM retransmission reception for multicast DRX with HARQ feedback disabled [PTM_ReTx_Mcast_HARQ_Disb] TS 38.321CR1727
- PTM retransmission reception for multicast DRX with HARQ feedback disabled [PTM_ReTx_Mcast_HARQ_Disb] TS 38.331CR4504
- Correction on the capabilities on PTM retransmission [PTM_ReTx_Mcast_HARQ_Disb] TS 38.331CR4867
- Clarification on reference point for hard satellite switch with resynchronization TS 38.331CR5372
In Release 19, the PTM (Point-to-Multipoint) function introduced an **in-session unicast repair** mechanism for MBMS object distribution and made improvements to **time synchronization** for MBMS. These enhancements specifically augment the existing IP Multicast (IP-M) PTM service, which transmits data to a specified group of subscribers. The new capabilities aim to improve the reliability and coordination of multicast content delivery within the defined service.
Explore further
Broader topics and technologies where PTM plays a role.
Defining Specifications
3GPP specifications that define or reference PTM, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 22.060 vj00 | GPRS Stage 1 Service Description | Rel-19 |
| TS 23.060 vj00 | GPRS Service Description Stage 2 | Rel-19 |
| TS 23.110 vj00 | Access Stratum Services Specification | Rel-19 |
| TS 23.247 vj30 | 5G Multicast/Broadcast Service Architecture | Rel-19 |
| TS 25.401 vj00 | UTRAN Overall Architecture | Rel-19 |
| TS 25.420 vj00 | Iur Interface Introduction for UTRAN | Rel-19 |
| TS 25.423 vj00 | UTRAN RNSAP Specification | Rel-19 |
| TR 25.931 vj00 | UTRAN Signalling Procedures Examples | Rel-19 |
| TS 26.346 vj20 | MBMS User Services Media Codecs & Protocols | Rel-19 |
| TR 26.946 vj00 | MBMS User Services Overview | Rel-19 |
| TS 27.060 vj00 | TE-MT Interworking for Packet Domain | Rel-19 |
| TS 37.480 vj00 | E1 Interface General Aspects and Principles | Rel-19 |
| TS 37.483 vj10 | E1 Application Protocol (E1AP) | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.321 vj00 | NR MAC Protocol Specification | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TS 38.401 vj10 | NG-RAN Architecture Specification | Rel-19 |
| TS 38.410 vj10 | NG Interface Introduction for NG-RAN to 5GC | Rel-19 |
| TS 38.413 vj10 | NG Application Protocol (NGAP) | Rel-19 |
| TS 38.425 vj10 | NR User Plane Protocol Specification | Rel-19 |
| TS 38.470 vj10 | F1 Interface Introduction | Rel-19 |
| TS 38.473 vj10 | 5G F1 Application Protocol (F1AP) | Rel-19 |