Mobile Originated Mobile Terminated

Description

Mobile Originated Mobile Terminated (MOMT) is a foundational service category defined within the 3GPP service framework, specifically detailed in specifications such as TS 22.262 (Service Requirements) and TS 23.554 (Architecture). It describes the complete end-to-end communication scenario where a user equipment (UE) initiates a session (Mobile Originated, MO) towards another UE that is the target recipient (Mobile Terminated, MT). This encompasses the full signaling and user plane path establishment between two mobile subscribers. Architecturally, MOMT services rely on the core network's call session control functions, mobility management, and subscriber data management (e.g., in the HSS) to route the session correctly. The process involves the originating UE attaching to the network, performing service authorization, and initiating a session setup request (like an SIP INVITE for IMS-based calls). The network then queries routing information, often involving interrogation of the HSS to locate the terminating UE, and delivers the session request to the target UE, which responds to complete the establishment. For non-IMS circuit-switched services, similar principles apply through MSC servers. MOMT is not a protocol itself but a service characterization that dictates how network functions like the P-CSCF, S-CSCF, I-CSCF, MME, AMF, and SMF interact to fulfill the service logic for mobile-to-mobile communication. Its role is critical in defining billing, lawful interception, and quality of service policies specific to this most common communication pattern.

Purpose & Motivation

The MOMT service category exists to formally define and standardize the requirements and architectural behavior for the most fundamental cellular service: direct communication between two mobile subscribers. Prior to comprehensive service definitions, implementations could vary, leading to interoperability issues between different network operators and equipment vendors. By creating a standardized service description, 3GPP ensures that a call or message originating from a mobile phone and destined for another mobile phone behaves consistently across global networks. This solves problems related to service transparency, roaming compatibility, and consistent charging mechanisms. Historically, as networks evolved from circuit-switched 2G/3G to packet-switched 4G/5G with IMS, the need for a clear, access-agnostic definition of this basic service became paramount to ensure backward compatibility and a seamless user experience. It addresses the limitation of having service logic embedded in proprietary ways within network nodes, instead providing a reference model for service implementation that supports innovation on top of a stable base.

Key Features

• Defines end-to-end signaling flow for mobile-originated to mobile-terminated sessions
• Supports both IMS-based (VoLTE, VoNR) and legacy circuit-switched call models
• Integrates with subscriber location and routing procedures (e.g., HSS/UDM query)
• Forms the basis for charging data generation (e.g., for MO-MT calls)
• Enables consistent application of policy control (e.g., QoS, barring) for the service
• Provides a framework for lawful interception for mobile-to-mobile communications

Evolution Across Releases

Defining Specifications