Short Message origination

Description

SM origination, or Short Message origination, is the process by which a Short Message (SM) is originated by an SMS-capable User Equipment (UE). This includes both traditional SMS sent over circuit-switched or packet-switched networks and SMS over IP, which allows SMS to be sent over IP-based access networks such as LTE and 5G. The term is defined in 3GPP TS 23.040, which specifies the Short Message Service (SMS) technical realization, and in TS 23.204, which covers support of Short Message Service (SMS) over generic 3GPP Internet Protocol (IP) access networks. SM origination is a core service in mobile networks, providing text messaging capabilities that are used for person-to-person communication, machine-to-machine (M2M) communication, and various value-added services such as notifications, two-factor authentication, and mobile marketing.

The architecture for SM origination involves several key components. When a UE originates a short message, it sends the message to the network via the control plane or user plane, depending on the access technology. In traditional GSM/UMTS networks, the UE sends the message to the Mobile Switching Center (MSC) via the Short Message Service Center (SMSC) using signaling protocols such as MAP or SIP. In LTE and 5G networks, SMS is typically supported over IP using the IP Multimedia Subsystem (IMS) or via the NAS signaling. The UE must be registered with the network and have an active PDN connection or bearer to send the message. The SMSC is responsible for storing and forwarding the message to the recipient. The SM origination procedure includes the submission of the short message by the UE, the acknowledgment from the network, and the subsequent delivery to the SMSC.

For SMS over IP, the UE uses IMS to send the short message. The UE establishes an IMS session and sends the message using the SIP MESSAGE method. The IMS core network, including the Call Session Control Function (CSCF) and the SMSC, handles the message. The SMSC then forwards the message to the recipient's network. SMS over IP is particularly important in LTE and 5G networks where circuit-switched fallback is not available or not desired. It allows operators to offer SMS services without maintaining a circuit-switched network, simplifying network architecture and reducing costs. The 3GPP specifications TS 23.204 and TS 23.040 define the procedures and protocols for SMS over IP, ensuring interoperability across different vendors and networks.

SM origination is also relevant for machine-type communication (MTC) and IoT devices. Many IoT devices use SMS for remote configuration, alerts, and control. The 3GPP has defined optimizations for MTC devices, such as the use of SMS for small data transmissions and the support of SMS in narrowband IoT (NB-IoT) and LTE-M. These optimizations ensure that SMS remains a viable service for the massive number of IoT devices expected in 5G networks. The SM origination procedure for IoT devices may differ slightly from that of human users, with considerations for power saving, extended discontinuous reception (eDRX), and coverage enhancement.

In terms of standardization, the definition of SM origination has remained stable across releases from Rel-8 to Rel-19. The core concept of originating a short message by an SMS-capable UE, including SMS over IP, has not changed. However, the underlying technologies and procedures have evolved to support new access technologies and use cases. For example, the introduction of 5G has brought new requirements for SMS over IP, such as support for network slicing and enhanced security. The stability of the definition reflects the maturity of SMS as a service and its continued importance in mobile networks, even as newer messaging services like RCS (Rich Communication Services) emerge.

Purpose & Motivation

SM origination exists to enable the sending of Short Messages from a User Equipment (UE) to the network, which is a fundamental service in mobile communications. SMS was originally introduced in GSM networks as a way to send text messages between mobile subscribers. Over time, it became a ubiquitous service used for personal communication, business notifications, and value-added services. The purpose of defining SM origination is to standardize the procedure by which a UE submits a short message to the network, ensuring interoperability across different networks and devices. This standardization is crucial for enabling global SMS roaming and for supporting new access technologies like LTE and 5G, where SMS is delivered over IP.

Before the formal definition of SM origination, the procedure was implicit in the SMS specifications, but as networks evolved to support multiple access technologies and IP-based delivery, a clear definition became necessary. The introduction of SMS over IP in 3GPP Release 8 addressed the need to support SMS in LTE networks, which do not have a circuit-switched domain. Without SMS over IP, operators would have had to rely on circuit-switched fallback (CSFB) to deliver SMS, which is inefficient and adds latency. SM origination over IP allows SMS to be delivered natively over the packet-switched network, simplifying network architecture and improving user experience. It also enables SMS to be used in 5G networks, where circuit-switched fallback is not available.

The limitations of previous approaches that SM origination addresses include the lack of a standardized way to originate SMS over IP and the inability to support SMS in packet-switched-only networks. By defining SM origination, 3GPP provided a clear framework for UE manufacturers and network operators to implement SMS over IP, ensuring that SMS remains a reliable and ubiquitous service. Additionally, the definition supports the use of SMS for machine-type communication and IoT, which is essential for many vertical industries. As mobile networks continue to evolve, SM origination remains a key enabler for messaging services, and its stable definition ensures backward compatibility and interoperability.