MO

Mobile Originated Short Message Service

Services
Introduced in R99
MO (Mobile Originated) refers to the origination of a Short Message Service (SMS) from a mobile device. It is the fundamental process where a user sends a text message, involving the UE, the serving network, and the Short Message Service Centre (SMSC). This capability is a core telecommunication service enabling person-to-person messaging.

Description

Mobile Originated (MO) Short Message Service is a standardized mechanism for a User Equipment (UE) to initiate and transmit a short text message to a recipient via the mobile network. The process begins when the user composes and sends an SMS from the device. The UE packages the message, including the destination address (typically an MSISDN) and the text content, into a CP-DATA message as per the protocol defined in 3GPP TS 24.011. This message is sent over the signaling channels (e.g., using the Connection Management (CM) sublayer) to the Mobile Switching Centre (MSC) in circuit-switched networks or the Mobility Management Entity (MME)/Access and Mobility Management Function (AMF) in packet-switched networks for SMS over IP.

The MSC or MME/AMF, upon receiving the MO-SMS, forwards it to the Interworking MSC (IWMSC) or the IP-SM-GW, which acts as a gateway to the Short Message Service Centre (SMSC). The SMSC is the central hub responsible for store-and-forward functionality. It receives the MO message, stores it, and then initiates the Mobile Terminated (MT) process to deliver it to the intended recipient. The delivery involves querying the Home Location Register (HLR) or Home Subscriber Server (HSS) to determine the recipient's current serving network node.

Key architectural components involved in MO-SMS include the UE (with its SMS application and protocol stack), the radio access network (RAN) for transmission, the core network control plane nodes (MSC, MME, AMF, SMSC), and the necessary interfaces (e.g., the air interface, the interface to the SMSC). The service operates on the control plane, ensuring delivery even when no user-plane bearer is established, which is crucial for reliability. MO-SMS supports both circuit-switched (CS) and packet-switched (PS) domains, with evolution towards SMS over IP (IMS) as defined in later releases.

The role of MO-SMS in the network is foundational for text-based communication. It leverages existing signaling infrastructure, making it a low-bandwidth, highly reliable service. Its integration into the core network ensures widespread interoperability and forms the basis for value-added services like SMS-based authentication, notifications, and machine-to-machine (M2M) communication. The protocols ensure error handling, delivery reports, and concatenation for longer messages.

Purpose & Motivation

MO-SMS was created to provide a simple, efficient, and ubiquitous text messaging service for mobile subscribers. Prior to SMS, mobile communication was primarily voice-centric. The development of SMS, including the MO capability, leveraged unused capacity in the signaling channels of GSM networks (specifically the Stand-alone Dedicated Control Channel - SDCCH), allowing text messages to be sent without requiring a dedicated voice channel. This was a revolutionary, cost-effective way to enable asynchronous communication.

The technology solved the problem of enabling brief, non-voice communication between users and between networks and devices. It addressed the need for a reliable, store-and-forward messaging system that could work across different network operators and regions. Its creation was motivated by the desire to utilize network resources more efficiently and to open a new revenue stream and service offering for operators.

Over time, MO-SMS became the backbone for numerous applications beyond person-to-person messaging, including service activation, banking alerts, and two-factor authentication, due to its high reliability and nearly universal reach. It established the foundational architecture and protocols for mobile-originated data services that later evolved to support more complex messaging and IoT scenarios.

Key Features

  • Control Plane Transmission: Uses signaling channels (e.g., SDCCH in GSM, NAS signaling in LTE/NR) for message transfer, not requiring a dedicated traffic channel.
  • Store-and-Forward via SMSC: Messages are reliably stored in the Short Message Service Centre before delivery attempts to the recipient.
  • Support for Delivery Reports: Can provide sender confirmation of successful or failed message delivery to the network.
  • Concatenated SMS: Allows splitting and reassembly of messages longer than the 160-character limit into multiple segments.
  • Interworking between Domains: Supports origination from both Circuit-Switched (CS) and Packet-Switched (PS/IMS) core network domains.
  • International Roaming: Enables message origination while the UE is roaming in visited networks through standardized inter-operator interfaces.

Evolution Across Releases

R99 Initial

Introduced the foundational GSM/UMTS architecture for MO-SMS. Defined the protocol stack (CP-DATA/CP-ACK) over the CS domain, using the MSC to relay messages to the SMSC. Established basic features like delivery reports and alphanumeric addressing.

TS 21.905TS 21.978TS 22.031TS 22.034TS 22.101TS 22.105TS 23.018TS 23.031TS 23.035TS 23.078TS 23.107TS 23.207TS 23.218TS 23.278TS 23.540TS 23.725TS 23.887TS 24.008TS 24.116TS 24.117TS 24.166TS 24.167TS 24.175TS 24.216TS 24.235TS 24.275TS 24.285TS 24.286TS 24.302TS 24.305TS 24.312TS 24.323TS 24.333TS 24.368TS 24.385TS 24.391TS 24.417TS 24.424TS 24.483TS 24.484TS 25.222TS 26.114TS 26.130TS 26.238TS 26.849TS 28.510TS 28.606TS 28.616TS 28.622TS 28.629TS 28.632TS 28.652TS 28.653TS 28.656TS 28.659TS 28.663TS 28.673TS 28.676TS 28.702TS 28.703TS 28.705TS 28.706TS 28.708TS 28.709TS 28.733TS 28.735TS 28.736TS 28.816TS 29.078TS 29.502TS 29.541TS 32.111TS 32.153TS 32.240TS 32.251TS 32.270TS 32.271TS 32.272TS 32.276TS 32.293TS 32.300TS 32.523TS 32.526TS 32.602TS 32.603TS 32.606TS 32.607TS 32.612TS 32.613TS 32.616TS 32.622TS 32.623TS 32.626TS 32.632TS 32.633TS 32.636TS 32.641TS 32.642TS 32.643TS 32.646TS 32.651TS 32.652TS 32.653TS 32.656TS 32.662TS 32.663TS 32.666TS 32.667TS 32.692TS 32.712TS 32.713TS 32.716TS 32.721TS 32.722TS 32.723TS 32.726TS 32.732TS 32.733TS 32.736TS 32.741TS 32.742TS 32.743TS 32.746TS 32.752TS 32.753TS 32.756TS 32.762TS 32.763TS 32.766TS 32.773TS 32.776TS 32.783TS 32.786TS 32.796TS 32.818TS 32.849TS 32.851TS 36.331TS 43.802TS 43.901

Defining Specifications

SpecificationTitle
TS 21.905 3GPP TS 21.905
TS 21.978 3GPP TS 21.978
TS 22.031 3GPP TS 22.031
TS 22.034 3GPP TS 22.034
TS 22.101 3GPP TS 22.101
TS 22.105 3GPP TS 22.105
TS 23.018 3GPP TS 23.018
TS 23.031 3GPP TS 23.031
TS 23.035 3GPP TS 23.035
TS 23.078 3GPP TS 23.078
TS 23.107 3GPP TS 23.107
TS 23.207 3GPP TS 23.207
TS 23.218 3GPP TS 23.218
TS 23.278 3GPP TS 23.278
TS 23.540 3GPP TS 23.540
TS 23.725 3GPP TS 23.725
TS 23.887 3GPP TS 23.887
TS 24.008 3GPP TS 24.008
TS 24.116 3GPP TS 24.116
TS 24.117 3GPP TS 24.117
TS 24.166 3GPP TS 24.166
TS 24.167 3GPP TS 24.167
TS 24.175 3GPP TS 24.175
TS 24.216 3GPP TS 24.216
TS 24.235 3GPP TS 24.235
TS 24.275 3GPP TS 24.275
TS 24.285 3GPP TS 24.285
TS 24.286 3GPP TS 24.286
TS 24.302 3GPP TS 24.302
TS 24.305 3GPP TS 24.305
TS 24.312 3GPP TS 24.312
TS 24.323 3GPP TS 24.323
TS 24.333 3GPP TS 24.333
TS 24.368 3GPP TS 24.368
TS 24.385 3GPP TS 24.385
TS 24.391 3GPP TS 24.391
TS 24.417 3GPP TS 24.417
TS 24.424 3GPP TS 24.424
TS 24.483 3GPP TS 24.483
TS 24.484 3GPP TS 24.484
TS 25.222 3GPP TS 25.222
TS 26.114 3GPP TS 26.114
TS 26.130 3GPP TS 26.130
TS 26.238 3GPP TS 26.238
TS 26.849 3GPP TS 26.849
TS 28.510 3GPP TS 28.510
TS 28.606 3GPP TS 28.606
TS 28.616 3GPP TS 28.616
TS 28.622 3GPP TS 28.622
TS 28.629 3GPP TS 28.629
TS 28.632 3GPP TS 28.632
TS 28.652 3GPP TS 28.652
TS 28.653 3GPP TS 28.653
TS 28.656 3GPP TS 28.656
TS 28.659 3GPP TS 28.659
TS 28.663 3GPP TS 28.663
TS 28.673 3GPP TS 28.673
TS 28.676 3GPP TS 28.676
TS 28.702 3GPP TS 28.702
TS 28.703 3GPP TS 28.703
TS 28.705 3GPP TS 28.705
TS 28.706 3GPP TS 28.706
TS 28.708 3GPP TS 28.708
TS 28.709 3GPP TS 28.709
TS 28.733 3GPP TS 28.733
TS 28.735 3GPP TS 28.735
TS 28.736 3GPP TS 28.736
TS 28.816 3GPP TS 28.816
TS 29.078 3GPP TS 29.078
TS 29.502 3GPP TS 29.502
TS 29.541 3GPP TS 29.541
TS 32.111 3GPP TR 32.111
TS 32.153 3GPP TR 32.153
TS 32.240 3GPP TR 32.240
TS 32.251 3GPP TR 32.251
TS 32.270 3GPP TR 32.270
TS 32.271 3GPP TR 32.271
TS 32.272 3GPP TR 32.272
TS 32.276 3GPP TR 32.276
TS 32.293 3GPP TR 32.293
TS 32.300 3GPP TR 32.300
TS 32.523 3GPP TR 32.523
TS 32.526 3GPP TR 32.526
TS 32.602 3GPP TR 32.602
TS 32.603 3GPP TR 32.603
TS 32.606 3GPP TR 32.606
TS 32.607 3GPP TR 32.607
TS 32.612 3GPP TR 32.612
TS 32.613 3GPP TR 32.613
TS 32.616 3GPP TR 32.616
TS 32.622 3GPP TR 32.622
TS 32.623 3GPP TR 32.623
TS 32.626 3GPP TR 32.626
TS 32.632 3GPP TR 32.632
TS 32.633 3GPP TR 32.633
TS 32.636 3GPP TR 32.636
TS 32.641 3GPP TR 32.641
TS 32.642 3GPP TR 32.642
TS 32.643 3GPP TR 32.643
TS 32.646 3GPP TR 32.646
TS 32.651 3GPP TR 32.651
TS 32.652 3GPP TR 32.652
TS 32.653 3GPP TR 32.653
TS 32.656 3GPP TR 32.656
TS 32.662 3GPP TR 32.662
TS 32.663 3GPP TR 32.663
TS 32.666 3GPP TR 32.666
TS 32.667 3GPP TR 32.667
TS 32.692 3GPP TR 32.692
TS 32.712 3GPP TR 32.712
TS 32.713 3GPP TR 32.713
TS 32.716 3GPP TR 32.716
TS 32.721 3GPP TR 32.721
TS 32.722 3GPP TR 32.722
TS 32.723 3GPP TR 32.723
TS 32.726 3GPP TR 32.726
TS 32.732 3GPP TR 32.732
TS 32.733 3GPP TR 32.733
TS 32.736 3GPP TR 32.736
TS 32.741 3GPP TR 32.741
TS 32.742 3GPP TR 32.742
TS 32.743 3GPP TR 32.743
TS 32.746 3GPP TR 32.746
TS 32.752 3GPP TR 32.752
TS 32.753 3GPP TR 32.753
TS 32.756 3GPP TR 32.756
TS 32.762 3GPP TR 32.762
TS 32.763 3GPP TR 32.763
TS 32.766 3GPP TR 32.766
TS 32.773 3GPP TR 32.773
TS 32.776 3GPP TR 32.776
TS 32.783 3GPP TR 32.783
TS 32.786 3GPP TR 32.786
TS 32.796 3GPP TR 32.796
TS 32.818 3GPP TR 32.818
TS 32.849 3GPP TR 32.849
TS 32.851 3GPP TR 32.851
TS 36.331 3GPP TR 36.331
TS 43.802 3GPP TR 43.802
TS 43.901 3GPP TR 43.901