SM

MT Short Message Mobile Terminated Point‑to‑Point

Services →
Introduced in R99 Also in: Core Network, User Equipment, Security, Testing, Radio Access Network

SM is the core network service for delivering a text message (SMS) from the network to a mobile device, encompassing the protocols and procedures to route, store, and forward it.

Category
Services
Introduced
R99
Where
Services › IMS
Also touches
5 segments
Specifications
39 specs
SM Description Purpose Related Classification Detected Changes Specifications

Description

MT Short Message Mobile Terminated Point‑to‑Point (SM-MT) refers to the complete process and service for delivering a Short Message Service (SMS) from the network to a Mobile Station (MS). It is one of the two fundamental SMS transfer mechanisms, the other being Mobile Originated (MO). The service is architected around a store-and-forward model centered on the Short Message Service Center (SMSC). The process begins when an SMSC receives a message destined for a subscriber. The SMSC queries the Home Location Register (HLR) to obtain routing information, specifically the address of the Mobile Switching Center/Visitor Location Register (MSC/VLR) or the Serving GPRS Support Node (SGSN) currently serving the subscriber. The SMSC then forwards the message to this serving node via the MAP (Mobile Application Part) protocol over SS7 or IP-based signalling.

Upon receipt, the serving network node (MSC or SGSN) performs several key functions. It first checks the subscriber's status (e.g., attached, reachable, not barred for SMS). If the device is available and idle, the node initiates a paging procedure to locate it on the radio access network. It then establishes a secure signalling connection (if not already present) and delivers the message over the control channel using specific protocols: the CP-DATA message within the Connection Management (CM) sublayer for circuit-switched delivery via an MSC, or within the GPRS session management for packet-switched delivery via an SGSN. The protocol stack involves layers like CM, MM (Mobility Management), and the radio resource layer, all ensuring reliable transfer. The mobile device acknowledges successful receipt, and this acknowledgment is propagated back to the SMSC, which then marks the message as delivered. If the device is unavailable, the network employs mechanisms like message waiting flags and retry schedules.

The role of SM-MT is critical as the delivery leg of the ubiquitous SMS service. It involves tight integration across multiple network domains: the service layer (SMSC), the core network signalling (HLR, MSC, SGSN), and the radio access network. Its design prioritizes reliability and efficiency, using control channels to avoid dedicating a traffic channel for a small payload. The service supports both circuit-switched and packet-switched delivery methods, adapting to the subscriber's attached domain. This seamless integration makes SMS a highly reliable, low-latency data service that operates in parallel with voice and packet data, forming a foundational messaging utility in all generations of 3GPP networks.

Purpose & Motivation

The SM-MT service was created to enable a reliable, network-initiated messaging capability, completing the two-way SMS system. The original GSM specifications included SMS as a value-added service to leverage unused capacity on the control channels. The Mobile Terminated component was essential to make SMS a true interactive communication tool, allowing messages from any source (other mobiles, web applications, operators) to reach a subscriber.

Historically, before SMS, simple text-based communication to a mobile device was not standardized. The creation of the SM-MT process solved the problem of how to locate a potentially mobile recipient, deliver a small data packet efficiently without a dedicated call, and confirm delivery—all within the constraints of 2G network architecture. It addressed the limitations of one-way paging systems by adding delivery confirmation and integration with subscriber identity and mobility management. The store-and-forward model of the SMSC, coupled with HLR queries, elegantly solved the challenge of subscriber mobility, ensuring messages could be delivered regardless of the user's current location within the network.

The motivation extended beyond person-to-person messaging. SM-MT became the carrier for a vast array of services: notifications (voicemail alerts), two-factor authentication, machine-to-machine commands, and broadcast information services. Its reliability and universality made it a critical channel for operators to communicate with subscribers. The continuous evolution through 3GPP releases has focused on enhancing its efficiency, integrating with IP networks, increasing security, and supporting new use cases like SMS over IMS, all while maintaining backward compatibility with the billions of devices that rely on this fundamental service.

Classification

Part ofSMS
Related approachesSMSCHLRMAP

Detected Changes Across Releases

from 3GPP Change Requests

Specific changes extracted from the „Change history“ tables of 3GPP specifications (133 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.

Rel-15 23 changes

In Release 15, the MT Short Message Mobile Terminated Point‑to‑Point function was enhanced for 5GS with the definition of a new 5GS NAS message type and a specification for its security-protected NAS message header. Key introductions included the support for MT SMS domain selection by the IP-SM-GW and the definition of N2 SM signalling procedures, including the creation of SM context and PDU session resource URIs within the UE context.

  • For 5GS – message and security headers and PDU session identities TS 24.007CR0104
  • Definition of 5GS NAS message type for 5GS TS 24.007CR0110
  • Specification of security protected 5GS NAS message header TS 24.007CR0111
  • EPS bearer identity in NAS message header TS 24.007CR0112
  • SM policy data resource definition TS 29.519CR0011
  • MT SMS domain selection by IP-SM-GW TS 23.204CR0109

+ 17 more changes

Rel-16 41 changes

In Release 16, the SM (Short Message) function was enhanced to support dynamic SMF (Session Management Function) deployment scenarios, specifically introducing and refining procedures for the Intermediate SMF (I-SMF). Key updates included new service operations for SM context creation, retrieval, update, release, and transfer between SMFs (including I-SMFs and V-SMFs) to manage I-SMF insertion, change, and removal. These changes facilitated improved handling of PDU Session establishment and NAS SM information transfer within the 5G Core architecture.

  • Update SM context service operation for additional PDU Session Anchor and Branching Point or UL CL controlled by I-SMF TS 29.502CR0124
  • Update Retrieve SM Context service operation from Source I-SMF or SMF TS 29.502CR0123
  • SM context transfer between I-SMFs or V-SMFs TS 29.502CR0110
  • Update Release SM Context service operation for I-SMF change and removal TS 29.502CR0122
  • Update Create SM context service operation for the I-SMF insertion and change TS 29.502CR0121
  • Update Create SM context service operation for the I-SMF insertion and change TS 29.502CR0134

+ 35 more changes

Rel-17 17 changes

In Release 17, enhancements for the SM function included the introduction of SM Context Consistency Validation and the inclusion of User location information in session management messages. The release also added support for indicating the possible use of OAuth2 authorization in the Create SM Context procedure and introduced a requestType Information Element in the Create SM Context service request.

  • Notification for SM Policy Association Events TS 29.502CR0492
  • Sending UUAA Authentication message TS 29.502CR0493
  • Indicating the possible use of OAuth2 authorization in Create SM Context TS 29.502CR0515
  • Notification for SM Policy Association Events TS 29.518CR0623
  • SM Context Consistency Validation TS 29.518CR0699
  • Message filters for SEAL groups TS 29.549CR0030

+ 11 more changes

Rel-18 23 changes

In Release 18, key enhancements for the SM (Mobile Terminated Short Message) function included the introduction of a dedicated Create SM Context service operation to support multicast MBS session procedures and the addition of HR-SBO information for SM context retrieval. The release also expanded support for Mobile Base Station Relay (including mobile IAB) within SMF services and introduced the capability to include an Alternative S-NSSAI within the SM Context. Furthermore, procedures were updated to convey the Access Type within N1/N2 information during the Update SM Context Request and to define specific release causes for mobility or access restrictions.

  • MO SM delivery application error codes alignment TS 23.540CR0009
  • Add SBI support Indication in S6c Routing Info for SM Answer TS 29.338CR0043
  • Retrieval of SM context with HR-SBO information TS 29.502CR0675
  • Support of Mobile Base Station Relay in SMF services TS 29.502CR0678
  • Alternative S-NSSAI in SM Context TS 29.502CR0751
  • Support of Mobile Base Station Relay in AMF services TS 29.518CR0942

+ 17 more changes

Rel-19 22 changes

In Release 19, key enhancements for the SM (MT Short Message Mobile Terminated Point‑to‑Point) function included the support for SM delivery HPLMN routing via SMS Router and SMSF addresses in RDR/RDA, and the introduction of the SMF Set Information procedure during SM Context Creation. Additionally, corrections were made to the handling of N1 SM information and to the sequenced message transfer operation.

  • Enhancements to SM data source services TS 23.437CR0016
  • AIoT NAS message type extension for future use TS 24.007CR0172
  • SMF Set Information During SM Context Creation TS 29.502CR0813
  • N1/N2 SM Rejection in 502 Response TS 29.502CR0821
  • Support of Short-Range based positioning information procedure TS 29.549CR0385
  • MPS for Messaging IP-SM-GW SBI TS 29.577CR0023

+ 16 more changes

Rel-20 7 changes

In Release 20, the enhancements for the SM (MT Short Message Mobile Terminated Point‑to‑Point) function focused on its data source services and subscription management. This included new procedures for SM data source triggering and updates to the SM data source subscription mechanisms. The work also provided corrections and updates to the relevant core network protocols governing these short message services.

  • Enhancements to SM data source services TS 23.437CR0036
  • Enhancements to SM data source events TS 23.437CR0037
  • SM data source triggering TS 23.437CR0070
  • Updates to SM Data Source subscription procedures TS 23.437CR0080
  • Updates to the SM data source subscription TS 23.437CR0096
  • SM data source subscription APIs TS 23.437CR0078

+ 1 more changes

Explore further

Broader topics and technologies where SM plays a role.

Topics
SON (Self-Organizing Networks)Authentication (5G-AKA, EAP)IMS & Voice (VoLTE, VoNR)MEC (Edge Computing)Lawful InterceptSMS & Messaging

Defining Specifications

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

SpecificationTitleRelease
TS 21.810 v1300 Multi-mode UE Issues - Categories, principles and procedures Rel-4
TR 21.905 vj00 3GPP Technical Terms and Definitions Rel-19
TR 21.910 v1300 Multi-mode UE Operation Principles Rel-4
TS 22.142 vj00 Value-added Services for SMS Requirements Rel-19
TR 22.942 vj00 SMS Value-Added Services Requirements Rel-19
TR 22.944 vj00 UE Functionality Split Scenarios and Requirements Rel-19
TS 23.039 v1400 SMSC to SME Interface Protocols Rel-5
TS 23.040 vj00 SMS Technical Realization Rel-19
TS 23.048 v1400 Secured Packets for UICC Remote Management Rel-5
TS 23.060 vj00 GPRS Service Description Stage 2 Rel-19
TS 23.078 vj00 CAMEL Phase 4 Stage 2 Specification Rel-19
TS 23.204 vj10 SMS over generic IP access; Stage 2 Rel-19
TS 23.437 vk10 SEAL Spatial Map & Anchors Rel-20
TS 23.540 vj20 5G Service Based SMS Stage 2 Rel-19
TS 23.824 va00 IP-SM-GW enhancements for CPM-SMS Interworking Rel-10
TS 23.840 v1700 SMS Inter-PLMN Architecture Study Rel-7
TS 24.007 vj40 GSM Um Interface Layer 3 Architecture Rel-19
TS 24.065 v1310 GPRS Subnetwork Dependent Convergence Protocol Rel-4
TS 24.237 vj00 IMS Service Continuity Protocol Details Rel-19
TS 24.305 vj00 Selective Disabling of 3GPP UE Capabilities Rel-19
TS 29.078 vj00 CAMEL Phase 4 CAP Specification Rel-19
TS 29.311 vj00 Service Level Interworking for Messaging Rel-19
TS 29.338 vj30 Diameter protocols for SMS in MME/5GS Rel-19
TS 29.437 vj00 Spatial Anchor & Map Management APIs Rel-19
TS 29.502 vj50 5G System; Nsmf Service Based Interface; Stage 3 Rel-19
TS 29.518 vj50 AMF Service Based Interface Protocol Rel-19
TS 29.519 vj40 UDR Usage for Policy & Exposure Data Rel-19
TS 29.541 vj30 NEF Service-Based Interfaces for NIDD & SMS Rel-19
TS 29.549 vj40 SEAL API Specification for Vertical Applications Rel-19
TS 29.577 vj40 IP-SM-GW & SMS Router SBI Protocol Rel-19
TS 29.579 vj40 5G SMS-IWMSC Service Based Interface Protocol Rel-19
TS 31.115 vj00 Secured Packet Structure for UICC Applications Rel-19
TS 31.121 vi50 UICC-terminal interface test specification Rel-18
TS 31.829 vd00 ISIM Conformance Requirements Technical Report Rel-13
TS 32.899 vf10 5G Charging Architecture Study Rel-15
TS 33.434 vj00 Security aspects of SEAL for verticals Rel-19
TS 38.401 vj10 NG-RAN Architecture Specification Rel-19
TR 43.901 vj00 Generic Access to A/Gb Interface Feasibility Study Rel-19
TS 44.065 vj00 GPRS SNDCP Specification Rel-19