Description
Deflected To Number (DTN) is a supplementary service in telecommunication networks that enables a called party to redirect an incoming call to a different telephone number before the call is answered. This deflection occurs during the call setup phase, typically after the call is presented to the called party but before they pick up, allowing the user to manually or automatically forward the call to another destination. The service is part of the Call Deflection (CD) feature set, which provides dynamic call routing control to enhance user convenience and call management.
Architecturally, DTN operates within the core network of 3GPP systems, involving network entities such as the Mobile Switching Center (MSC) for circuit-switched networks or the Call Session Control Function (CSCF) in IMS-based networks. When a call arrives, the serving node checks if DTN is active for the called subscriber. If enabled, the network intercepts the call and redirects it to the pre-defined or dynamically specified number. Key components include the Home Location Register (HLR) or Home Subscriber Server (HSS), which stores deflection settings, and the service logic that executes the redirection. The deflection can be triggered by user input (e.g., pressing a key) or based on conditions like busy status or no answer.
The technical process begins when an incoming call is routed to the called party's device. The network signals the call setup, and if DTN is invoked, the called party's UE or network node sends a deflection request containing the target number. This request is processed by the core network, which then re-routes the call to the new number using standard call establishment procedures. In packet-switched domains, DTN may be implemented using SIP redirect messages within the IMS framework. The service ensures that the original caller remains unaware of the deflection, maintaining a seamless experience.
DTN's role in the network is to provide flexible call handling, reducing missed calls and improving accessibility. It is commonly used in scenarios where users are temporarily unavailable at their primary number, such as in office settings or during travel. The service integrates with other supplementary services like Call Forwarding, but differs in that deflection is typically initiated by the called party in real-time, rather than being pre-configured. Specifications like TS 23.078 detail the protocols and procedures for DTN, ensuring interoperability across different network generations and vendor equipment.
Purpose & Motivation
DTN was created to give called parties immediate control over call routing, addressing the need for dynamic call management without pre-setting forwarding rules. Before DTN, call forwarding services required pre-configuration (e.g., forward when busy or unanswered), which lacked flexibility for ad-hoc situations. DTN solves this by allowing users to deflect calls on a per-call basis, enabling them to redirect specific calls to colleagues, voicemail, or other numbers as needed, enhancing responsiveness and personalization.
Historically, call deflection emerged as part of supplementary services in GSM and was standardized in 3GPP Release 4 to support evolving telephony features. It addressed limitations of static forwarding by providing a real-time alternative, particularly useful in business environments where call handling requires agility. The service motivation includes improving user experience by reducing call abandonment and ensuring important calls are not missed, especially when the called party is aware they cannot answer but wants the call handled elsewhere.
In 3GPP networks, DTN's inclusion supports the transition to IP-based multimedia subsystems, maintaining feature parity with legacy circuit-switched services. It solves problems related to call congestion and user mobility, allowing seamless redirection across network boundaries. By enabling deflection to any valid number, DTN facilitates efficient call distribution in contact centers and personal use cases, contributing to overall network efficiency and subscriber satisfaction in modern telecommunications.
Key Features
- Real-time call redirection initiated by the called party
- Support for deflection to any valid telephone number
- Integration with circuit-switched and IMS-based networks
- Dynamic invocation without pre-configuration
- Seamless experience for the calling party
- Interoperability with other supplementary services like call forwarding
Evolution Across Releases
Introduced DTN as a standardized supplementary service in 3GPP, defining its procedures and network architecture for UMTS networks. Initial capabilities included manual deflection during call setup, with specifications in TS 23.078 outlining signaling flows and subscriber management.
Defining Specifications
| Specification | Title |
|---|---|
| TS 23.078 | 3GPP TS 23.078 |