Instant Message Origination

Description

IM origination is defined as the origination of an Instant Message by an IMS UE (User Equipment). It is a term used in 3GPP specifications, particularly in TS 23.204 (Support of Short Message Service (SMS) over generic 3GPP Internet Protocol (IP) access) and TS 23.824 (Study on Instant Message and Session-based Messaging). The term describes the action or process by which an IMS UE initiates the sending of an instant message within the IMS framework.

In the context of IMS, instant messaging is a service that allows users to exchange messages in near real-time. IM origination is the first step in this process, where the UE generates a message and sends it towards the network. This typically involves the UE using SIP (Session Initiation Protocol) to send a MESSAGE request, which carries the instant message content. The message is routed through the IMS core network, specifically via the P-CSCF, I-CSCF, and S-CSCF, and may be processed by an Application Server (AS) that provides the instant messaging service.

The term is important for distinguishing between origination (sending) and termination (receiving) of instant messages. IM origination covers the procedures and requirements for the sender side, including authentication, authorization, and charging. It ensures that the UE can properly initiate an instant message session, and that the network can handle the message appropriately, including store-and-forward if the recipient is offline.

IM origination is part of the broader IMS messaging framework, which includes SMS over IMS, instant messaging, and session-based messaging (e.g., chat). The specifications TS 23.204 and TS 23.824 provide details on how IM origination should be supported, including interworking with legacy messaging systems. The term is used in the context of service definition and is not a network element itself, but rather a concept that describes a user action and the corresponding network procedures.

In practice, IM origination involves the UE constructing a SIP MESSAGE request with the appropriate headers and body, and sending it to the P-CSCF. The P-CSCF forwards it to the S-CSCF, which may invoke an AS based on initial Filter Criteria. The AS handles the message, possibly storing it if the recipient is not available, and then delivers it to the recipient's network. The origination side is responsible for ensuring the message is correctly formatted and that the user is authorized to send it. Charging records are generated for the origination event.

The term has been stable in 3GPP specifications since its introduction in Rel-8, with only minor formatting changes in the definition text. It remains relevant as IMS messaging continues to evolve, including RCS (Rich Communication Services) which builds on instant messaging capabilities.

Purpose & Motivation

IM origination exists to define and standardize the procedures for a user to send an instant message within the IMS framework. Before IMS, instant messaging was largely proprietary and not standardized across mobile networks. 3GPP introduced IMS-based messaging to provide a standardized, interoperable, and operator-controlled messaging service that could compete with OTT messaging apps. IM origination is a key concept in this standardization effort, ensuring that the origination side of instant messaging is well-defined and can be implemented consistently by different vendors and operators.

The term helps in specifying requirements for UE behavior, network procedures, and interworking with other messaging systems. It allows for proper charging, security, and policy control for instant messages. By defining IM origination, 3GPP enables features such as message delivery reports, store-and-forward, and interoperability with SMS. It also facilitates roaming and ensures that instant messages can be sent across networks.

Historically, IM origination was introduced in Rel-8 as part of the broader effort to support messaging over IMS, including SMS over IMS and instant messaging. It addresses the need for a clear distinction between origination and termination in messaging, which is essential for network design and service implementation. The term continues to be used in later releases, reflecting its ongoing relevance in IMS messaging.