Description
MCH Scheduling Information (MSI) is a critical control element within the LTE Radio Access Network (RAN) for Multimedia Broadcast Multicast Service (MBMS) operation. It is transmitted as part of the MCCH (MBMS Control Channel) information on the MCH (Multicast Channel). The MSI provides a detailed scheduling map for the associated MTCH (MBMS Traffic Channel) data transmissions. Specifically, it contains the MSI MAC Control Element, which lists the subframes allocated to each MBMS service (identified by a Temporary Mobile Group Identity or TMGI) within a specific MCH Scheduling Period (MSP). This allows the UE to know precisely when to wake its receiver to decode the desired MBMS service data without having to monitor the channel continuously, thus saving battery power.
The architecture for MSI is embedded within the LTE MAC layer for MBMS. The eNodeB, acting as the MBMS Gateway for the radio interface, determines the scheduling for MTCHs based on service requirements and network load. This scheduling information is then packaged into the MSI and broadcast periodically on the MCCH. The UE, after acquiring the MBMS control information including the MBSFN Area configuration and MCCH, decodes the MSI to build a reception schedule. The information includes the stop frame and stop subframe for each service's transmission, effectively defining a time window for reception.
Key components of the MSI mechanism include the MCH Scheduling Period (MSP), which is a configurable time interval (e.g., 160 ms, 320 ms) defining the repetition period of the scheduling pattern, and the MCH Subframe Allocation Pattern (MSAP), which is derived from the MSI and indicates the specific subframes used for MTCH. The MSI's role is to enable dynamic and efficient sharing of the MCH radio resources among multiple concurrent MBMS services. Without MSI, UEs would require semi-static, pre-configured scheduling or would need to blindly attempt decoding, leading to inefficient power consumption and potential service acquisition failures. Its operation is foundational for SC-PTM (Single Cell Point To Multipoint) as well, where similar scheduling principles apply on a per-cell basis.
Purpose & Motivation
MSI was created to address the specific challenge of efficiently delivering scheduled broadcast and multicast content in LTE networks. Prior to MBMS, cellular networks were optimized for unicast (point-to-point) communication. Broadcasting content, like mobile TV, would have been highly inefficient if treated as multiple simultaneous unicast streams. The MBMS framework introduced shared channels (MCH, MTCH), but a mechanism was needed to inform a potentially massive number of idle UEs about when their desired service data would be transmitted.
The purpose of MSI is to solve this scheduling notification problem. It allows the network to dynamically allocate radio resources among various MBMS services and communicate this allocation reliably to all UEs in the MBSFN area. This solves several key problems: it enables UE power saving through discontinuous reception (DRX) for multicast services, allows for flexible and network-controlled resource partitioning between MBMS and unicast traffic, and supports service multiplexing on a single radio channel. Its creation was motivated by the need to make broadcast services economically viable on cellular networks by maximizing spectral efficiency and minimizing UE power consumption, which are critical for user acceptance of services like live video broadcasting.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (48 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-9, normative work from Rel-15.
In Release 15, the MSI function was enhanced to support **MBMS reception in Receive Only Mode (ROM)**, enabling user equipment to receive Multimedia Broadcast Multicast Service transmissions without being attached to a network for unicast services. This was complemented by the introduction of **assistance information for local cache** to improve service acquisition and delivery. Furthermore, corrections and clarifications were made to ensure robust system information acquisition and scheduling for these MBMS features.
- Running 36.300 CR to introduce assistance information for local cache TS 36.300CR1076
- Enabling MBMS Bearer Event Notification TS 36.300CR1138
- MBMS reception in Receive Only Mode TS 36.300CR1207
- Introduce assistance information for local cache 36.331 CR TS 36.331CR3178
- MBMS reception in Receive Only Mode (ROM) TS 36.331CR3776
- Introduction of Geofencing information in CMAS TS 36.331CR3523
+ 19 more changes
In Release 16, the MSI function was updated to clarify the scheduling of System Information Blocks (SIBs) within the `schedulingInfoListExt` and `posSchedulingInfoList`. This included corrections and specific scheduling restrictions for positioning SI messages for eMTC and NB-IoT. These changes provided more precise rules for how this control channel information is organized and transmitted.
- Modification of SI scheduling for extended SIBs TS 36.331CR4445
- CP length and reference signal for MBSFN with sub-carrier spacing of 0.375 kHz and 2.5 kHz TS 36.300CR1322
- Correction on the configuration of subframe #0 and #5 for MCH in MBMS dedicated cell TS 36.331CR4259
- MBMS UE capabilities per band for subcarrier spacing of 2.5 kHz and 0.37 kHz TS 36.331CR4307
- Correction on MCCH configuration for 0.37kHz SCS TS 36.331CR4335
- Correction regarding placement of cell specific SSB QCL information TS 36.331CR4393
+ 6 more changes
In Release 17, the MSI function was updated with a clarification regarding the `schedulingInfoList` for NB-IoT operation. Furthermore, enhancements were made to introduce height information reporting within MDT (Minimization of Drive Tests) reports. These changes provided more detailed radio environment information and refined scheduling parameters for specific UE capabilities.
In Release 18, the MSI function was updated with corrections to the MBMS Interest Indication procedure. Furthermore, enhancements were made to system information broadcasting, specifically for the delivery of GNSS LOS/NLOS positioning assistance information. These changes refined the mechanisms for distributing control information and location-related data to user equipment.
- GNSS LOS/NLOS posSIB broadcast assistance information [GNSS LOS/NLOS] TS 36.331CR4931
- Correction on UE Location Information Reporting in IoT-NTN TS 36.300CR1410
- Coarse UE Location Information Reporting from MME to eNB for NB-IoT UEs TS 36.300CR1415
- Correction on MBMS Interest Indication TS 36.331CR5125
- Correction on UE location information in NB-IoT RLF report TS 36.331CR4997
- Correction to MIB-MBMS systemFrameNumber field description TS 36.331CR5046
In Release 19, the MSI function was updated to include the provision of Store-and-Forward Mode Indication Information. This enhancement specifically introduces NB-IoT satellite information for E-UTRAN, enabling the network to convey scheduling and mode details relevant to non-terrestrial networks.
Explore further
Broader topics and technologies where MSI plays a role.
Defining Specifications
3GPP specifications that define or reference MSI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 23.795 vg10 | V2X Application Architecture Study | Rel-16 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |