Instant Message

Description

An Instant Message (IM) is a communication service that allows users to exchange text or multimedia content in near real-time, as opposed to store-and-forward messaging like SMS or MMS. In 3GPP, the term is defined by reference to the OMA SIMPLE IM specification (OMA-TS-SIMPLE_IM-V1_0) and 3GPP TS 24.247, which specifies the message service using IP Multimedia Subsystem (IMS). The service is built on the IMS core network, leveraging SIP for session and message signaling. The architecture includes an IM client on the user equipment (UE), which communicates with an IM server (application server) in the IMS domain. The IM server handles message routing, storage, and delivery, and may also provide presence and group management functions. The protocol used for IM is typically the Message Session Relay Protocol (MSRP) for session-based messaging, or SIP MESSAGE for page-mode messaging. 3GPP TS 24.247 defines the procedures for IM within the IMS, including registration, message sending, and delivery reports. The service supports one-to-one and group chats, and can be integrated with other IMS services like voice and video sharing. In later releases, the term Instant Message is also used to designate a CPM Message, reflecting the convergence of messaging services under the Converged IP Messaging (CPM) framework defined by OMA. CPM aims to unify various messaging services (SMS, MMS, IM, email) into a single, interoperable platform. The IM service in 3GPP is part of the broader IMS-based messaging enablers, and its evolution is tied to the enhancements in IMS and service layer specifications. Key components include the IM client, the IM server (often part of the IMS application layer), the SIP core (P-CSCF, S-CSCF, etc.), and the MSRP media plane. The service relies on the IMS registration and authentication procedures for security and charging. IM is a fundamental service for mobile operators to offer rich communication services (RCS) and to compete with over-the-top (OTT) messaging applications. Its standardization ensures interoperability between different vendors and operators, enabling seamless messaging across networks.

Purpose & Motivation

The Instant Message service was created to provide a standardized, interoperable messaging solution over 3GPP networks, moving beyond the limitations of SMS and MMS. SMS, while ubiquitous, is limited to 160 characters, lacks support for rich media, and is not session-based. MMS improved media support but still operates in a store-and-forward manner, not suitable for real-time conversations. The IM service, built on IMS, enables near-real-time text and multimedia messaging, presence, and group communication, aligning with the capabilities of popular OTT messaging apps. It solves the problem of fragmented messaging services by providing a standardized framework that operators can deploy to offer feature-rich messaging, ensuring interoperability and quality of service. The inclusion of CPM in later releases further addresses the need for convergence, allowing a single messaging client to handle multiple message types and providing a unified user experience. This standardization is crucial for operators to maintain relevance in the messaging market and to integrate messaging with other IMS services like voice and video calling.