Barring of Outgoing InterZonal Calls

Description

BOIZC (Barring of Outgoing InterZonal Calls) is a standardized supplementary service defined in 3GPP specifications that provides network operators with granular control over subscribers' ability to make outgoing calls across different geographical zones. The service operates at the core network level, specifically within the Home Location Register (HLR) and Visitor Location Register (VLR) architecture, where subscriber service profiles are maintained and enforced. When a subscriber attempts to place a call, the network checks the destination against predefined geographical zones and applies barring logic based on the subscriber's service subscription profile stored in the HLR.

The technical implementation involves several network elements working in coordination. The HLR stores the BOIZC subscription data as part of the subscriber's service profile, including the specific zones from which the subscriber is barred from making outgoing calls. When a subscriber initiates a call setup procedure, the Mobile Switching Center (MSC) queries the VLR (which contains a copy of the subscriber's service profile from the HLR) to determine if the call destination falls within a barred interzonal category. The MSC performs geographical analysis of the called party number against predefined zone definitions, which can be based on numbering plans, country codes, or specific network operator-defined zones.

The zone definitions are critical to BOIZC operation and are typically configured in network databases according to regional numbering plans. Zones may correspond to countries, specific area codes, or custom geographical regions defined by the operator for billing or regulatory purposes. When a call attempt matches a barred interzonal condition, the MSC rejects the call setup with an appropriate cause code, preventing the call from being established. The service supports both permanent barring (always active) and temporary barring (activated/deactivated by the subscriber or operator) modes of operation.

BOIZC integrates with other supplementary services and call control mechanisms in the network. It operates in conjunction with basic call procedures and interacts with charging systems to ensure proper billing for calls that are allowed. The service also works alongside other barring services like Barring of All Outgoing Calls (BAOC) and Barring of Outgoing International Calls (BOIC), with specific precedence rules defined in 3GPP specifications. From a signaling perspective, BOIZC utilizes MAP (Mobile Application Part) protocols for service profile transfer between HLR and VLR, and ISUP (ISDN User Part) or BICC (Bearer Independent Call Control) for call setup and teardown procedures when barring decisions are made.

The service plays a crucial role in network resource management and service differentiation. By controlling interzonal call origination, operators can implement differentiated service plans, prevent revenue leakage from unauthorized international calling, and comply with regulatory requirements for call restrictions in specific geographical areas. The implementation is transparent to the subscriber during normal operation but provides operators with powerful tools for service management and control across complex multi-zone network environments.

Purpose & Motivation

BOIZC was developed to address the growing need for geographical call control in increasingly complex mobile networks that span multiple countries and regions. As mobile networks expanded beyond national borders through roaming agreements and multinational operator partnerships, the need arose for more granular control over call origination based on geographical zones. Traditional call barring services like BAOC (Barring of All Outgoing Calls) and BOIC (Barring of Outgoing International Calls) provided only binary or overly broad controls that didn't match the nuanced geographical service areas that operators needed to manage.

Prior to BOIZC implementation, operators faced challenges in implementing zone-based billing plans and complying with regulatory requirements that varied by geographical region. For example, some regulatory frameworks required restrictions on calls to specific neighboring countries or regions, while allowing calls to others. Operators also needed to create service packages that allowed calls within certain zones while barring calls to others, enabling more sophisticated tariff structures and service offerings. The limitations of existing barring services forced operators to implement proprietary solutions that lacked interoperability and standardization across different network equipment vendors.

The creation of BOIZC in 3GPP Release 4 provided a standardized approach to geographical call barring that could be implemented consistently across multi-vendor networks. This standardization was particularly important as networks evolved toward more complex architectures with multiple service zones and increased roaming scenarios. BOIZC enabled operators to implement precise geographical controls that aligned with their business models, regulatory obligations, and service differentiation strategies, while maintaining interoperability and consistent subscriber experience across different network implementations.

Key Features

• Geographical zone-based call barring for outgoing calls
• Integration with HLR/VLR subscriber service profiles
• Support for operator-defined geographical zones
• Compatibility with existing call setup and signaling procedures
• Interworking with other supplementary barring services
• Standardized implementation across multi-vendor networks

Evolution Across Releases

Defining Specifications