Communication Deflection

Description

Communication Deflection (CD) is a supplementary service defined in 3GPP specifications that enables a served user (the deflector) to redirect an incoming communication session, typically a voice call, to another target address. The redirection is invoked by the called party, not the calling party, and can be conditional or unconditional. It is a core component of traditional telephony services and has been carried forward into IP Multimedia Subsystem (IMS) environments.

The service operates within the call control logic of the network. When an incoming call arrives for a subscriber who has activated CD (e.g., Deflection when Busy), the serving network node (like a Mobile Switching Centre or IMS Call Session Control Function) evaluates the deflection criteria. If the condition is met (e.g., the subscriber's line is busy), the network deflects the call by re-routing it to a pre-defined or dynamically provided target address. The deflector's UE may also explicitly request deflection during an active call setup (e.g., by sending a specific signal). The network then releases the connection to the deflector and establishes a new connection to the deflection target.

Key aspects include the deflection reason (e.g., busy, no reply, unconditional), the target address (which can be a SIP URI, tel URI, or MSISDN), and the interaction with other supplementary services like Call Forwarding. While Call Forwarding is typically provisioned in the HSS and executed by the network proactively, Deflection is often an explicit, real-time action initiated by the called party. The service involves specific signaling messages between the UE and network (e.g., in ISDN User Part or SIP) to request and acknowledge the deflection. It enhances user control over incoming communications.

Purpose & Motivation

Communication Deflection was created to give subscribers direct, real-time control over the handling of incoming calls, complementing the more static, network-provisioned Call Forwarding services. Its development in early GSM/UMTS standards addressed the need for flexible call management where the decision to redirect a call could be made at the moment of arrival based on the called party's immediate situation or preference.

It solves specific user scenarios: for example, allowing a user to deflect a call to a colleague while already engaged in another call, or deflecting an unwanted call to voicemail without answering. This provides a more dynamic and user-driven experience compared to pre-set forwarding rules. The service was particularly important in the era of circuit-switched telephony and remains relevant in IMS for maintaining service parity and enriching IP-based communication offerings. It addresses the limitation of purely network-controlled forwarding by putting the redirection trigger in the hands of the served user.