Disregard Incoming Call

Description

The Disregard Incoming Call (DIC) supplementary service is a network-based feature that enables a subscriber to instruct the network to reject all incoming circuit-switched voice calls destined for their line. When the service is activated by the user, the Mobile Switching Center (MSC) or MSC Server intercepts any incoming call setup request (e.g., an IAM message in SS7) intended for that subscriber. Instead of completing the call, the network returns a specific cause value to the calling party's network, typically indicating that the user is busy or that the call is rejected. This results in the calling party hearing a busy tone or being routed to a voice mail system if subscribed.

Architecturally, the service logic resides in the Home Location Register (HLR) and is executed by the MSC serving the user. The HLR stores the subscriber's service profile, including the DIC activation status. When the user activates or deactivates DIC, this status is updated in the HLR. During call termination procedures, the serving MSC queries the HLR (via MAP messages) or uses locally cached profile information to check if DIC is active. If active, the MSC applies the service logic and rejects the call. The service can be invoked by the user through Unstructured Supplementary Service Data (USSD) codes (e.g., *#43#), via a handset menu that generates the appropriate signaling, or through an interactive voice response system.

Key components involved are the UE (for service invocation), the MSC/MSC Server (for service execution), and the HLR (for service profile storage). The service works on a per-user basis and applies to all incoming voice calls regardless of the caller's identity. It does not typically affect SMS or packet-switched data sessions. Its role in the network is to provide a basic but essential user-controlled call management feature, enhancing subscriber convenience and privacy. It operates independently of, but can be complementary to, other call barring services like Call Deflection or Call Forwarding on Busy.

Purpose & Motivation

The DIC service was created to give mobile subscribers direct and immediate control over their call reception, fulfilling a basic need for privacy and uninterrupted time. Before the widespread adoption of sophisticated smartphones with 'do not disturb' modes, network-based services like DIC were the primary means for users to temporarily block all incoming calls without turning off the phone or removing the SIM card. It solved the problem of unwanted interruptions during meetings, sleep, or personal time.

Historically, it was part of the suite of GSM supplementary services standardized from the early phases (Phase 1/2) and carried forward into 3GPP UMTS and LTE circuit-switched domains. It addressed a limitation of earlier telephony systems where rejecting calls required manual intervention (not answering) or physical disconnection. DIC provides a network-enforced guarantee that no calls will ring through. The motivation was to increase subscriber satisfaction and mimic landline features, while also allowing network operators to offer differentiated service packages. It is a simpler alternative to conditional call forwarding, as it requires no configuration of destination numbers.

Key Features

• Network-based rejection of all incoming circuit-switched voice calls
• Activation/Deactivation via USSD codes (e.g., *#43#) or handset menus
• Status stored in the subscriber's profile in the HLR
• Causes the network to return a 'user busy' or similar cause to the caller
• Does not affect outgoing calls, SMS, or data sessions
• Provides an immediate 'do not disturb' function without phone shutdown

Evolution Across Releases

Defining Specifications