nonIMS

Non-IMS refers to network architectures and service platforms that deliver IP-based multimedia services without relying on the IP Multimedia Subsystem as the central signaling and control framework. IMS, developed to unify and enhance IP multimedia services, provides a standardized control plane for voice, video, messaging, and presence. Non-IMS approaches implement service logic and session control outside the IMS core, often over legacy circuit-switched or non-IMS packet networks. Signaling may use traditional SS7/ISUP or operator-specific SIP, with application servers, media gateways, and service controllers connecting to the transport network. The media plane is typically handled by standalone gateways or by connections to the PSTN or internet, and QoS is managed by the operator’s network rather than by IMS QoS mechanisms.

Non-IMS deployments arose to reduce cost and complexity for operators with existing infrastructure, to support legacy devices, or to enable selective migration to IP-based services without a full IMS rollout. They have seen use in rural or early-market deployments, fixed-mobile convergence scenarios, and certain enterprise or vertical-market solutions where IMS was unnecessary or impractical.

As networks evolved toward IMS, many operators migrated to IMS to gain standardized service delivery and broader interworking. Nonetheless, non-IMS deployments persist in some regions or contexts, particularly where legacy interworking, vendor-specific features, or cost considerations continue to influence architecture choices. In contemporary discussions, non-IMS is often viewed alongside hybrid approaches that combine IMS and non-IMS elements to balance cost, interworking, and functionality.