Barring of All Outgoing Calls

Description

Barring of All Outgoing Calls (BAOC) is a standardized supplementary service defined within the 3GPP specifications for circuit-switched telephony services. It operates as part of the call control functions managed by the network's core domain, specifically interacting with the Mobile Switching Center (MSC) in GSM/UMTS networks or the MSC Server in IMS-based networks for legacy circuit-switched fallback scenarios. The service is invoked during the call establishment phase; when a subscriber with active BAOC attempts to originate a voice call, the MSC intercepts the call setup request, checks the subscriber's service profile, and applies the barring logic, resulting in the call being rejected before any radio resources are allocated for the outgoing leg.

The architecture for BAOC relies on the Home Location Register (HLR) as the central repository for the subscriber's service data. The HLR stores the BAOC subscription information as part of the subscriber's profile and transmits this data to the serving MSC/VLR (Visitor Location Register) when the subscriber registers on the network. This transfer occurs via the Mobile Application Part (MAP) protocol, specifically using the Insert Subscriber Data operation. The MSC/VLR then holds this data locally for rapid access during call processing. The service is typically activated, deactivated, or interrogated by the subscriber using standardized Unstructured Supplementary Service Data (USSD) codes or, in later releases, via the IP Multimedia Subsystem (IMS) service control mechanisms.

From a procedural standpoint, the MSC's Call Control function performs the barring check. Upon receiving a call origination request (e.g., a CM_SERVICE_REQUEST), the MSC consults its local VLR record for the subscriber. If the BAOC indicator is active, the MSC generates a call control rejection message back to the mobile station, often with a specific cause code indicating 'outgoing calls barred'. The service is distinct from operator-initiated barring and is intended for subscriber control. Its implementation is tightly integrated with other supplementary services like Barring of Outgoing International Calls (BOIC) and Barring of Outgoing International Calls except those directed to the Home PLMN Country (BOIC-exHC), forming a hierarchy of barring options.

In the evolution towards all-IP networks, the principles of BAOC are maintained for emergency calls and other essential services. Notably, BAOC must not bar emergency calls (to numbers like 112 or 911), as mandated by regulatory requirements. The network's call control logic includes an exception check for emergency numbers before applying the BAOC restriction. In 5G systems, where native voice is delivered over IMS (VoNR), traditional circuit-switched supplementary services like BAOC are not directly defined. However, equivalent service control for outgoing voice sessions is provided by IMS application servers and policy control, ensuring continuity of user-controlled call barring functionalities in the packet-switched domain.

Purpose & Motivation

BAOC was created to provide mobile subscribers with direct control over their ability to place outgoing voice calls, addressing needs for cost management, parental control, and device usage restrictions. In the early GSM era, post-paid and especially pre-paid billing models created a demand for tools to prevent unexpected charges from outgoing calls. A subscriber could activate BAOC to avoid making calls, perhaps when lending a phone to a child or to control usage on a corporate-liable device. This subscriber-initiated control differentiated it from network-operator barring services used for administrative reasons like debt management.

The service solved the limitation of having only operator-side barring capabilities. Before such supplementary services were standardized, any call restriction had to be applied manually by the network operator on the HLR, which was inefficient for temporary, user-driven needs. BAOC, as part of the GSM Phase 2+ supplementary services portfolio, empowered the user. Its creation was motivated by the broader 3GPP goal of providing feature parity with, and superiority to, the digital fixed-line networks (ISDN), which offered similar call barring supplementary services. It formed a foundational element for a suite of call-barring options, giving users granular control.

Furthermore, BAOC established a standardized, network-centric implementation that ensured reliability and interoperability across different network vendors and operators. By handling the barring in the core network's MSC, it provided a secure and tamper-resistant method compared to potential client-side solutions on the mobile equipment. The service's design also inherently respected regulatory requirements by ensuring emergency call access, balancing user control with essential safety mandates. Its longevity through 3GPP releases underscores its utility as a basic but vital telecommunication service for consumer protection and managed mobility.

Key Features

• Subscriber-controlled activation and deactivation via USSD or network menus
• Network-based enforcement at the MSC/VLR during call origination
• Storage of subscription data in the HLR with propagation to the VLR
• Explicit exemption for emergency call origination (e.g., 112, 911)
• Integration with the MAP protocol for subscriber data management
• Part of a complementary set of outgoing call barring services (BOIC, BOIC-exHC)

Evolution Across Releases

Defining Specifications