Barring of Outgoing International Calls

Description

Barring of Outgoing International Calls (BOIC) is a standardized supplementary service defined within the 3GPP framework, operating within the core network's service layer. It functions by intercepting call setup requests from a subscriber and applying a screening logic based on the dialed number. The service is typically managed by the Home Location Register (HLR) in GSM/UMTS or the Home Subscriber Server (HSS) in LTE/5G systems, which stores the subscriber's service profile including the BOIC activation status. When a mobile-originated call attempt is made, the Mobile Switching Center (MSC) or the IP Multimedia Subsystem (IMS) Call Session Control Function (CSCF) queries the HLR/HSS to verify if BOIC is active for that subscriber. If active, the network analyzes the dialed digits against international numbering formats (e.g., numbers starting with a '+' prefix or an international access code like '00'). If the number is identified as an international destination, the call setup is terminated, and a notification (such as an announcement or tone) is provided to the calling party.

The architectural implementation involves close interaction between the call control entities (MSC, MSC Server, CSCF) and the subscriber data repositories (HLR/HSS). The service logic is executed during the initial call routing phase. Key components include the service control point (the HLR/HSS), the service switching point (the MSC/CSCF performing the detection and interrogation), and the signaling protocols that carry the interrogation, such as Mobile Application Part (MAP) for circuit-switched domains or Diameter for IMS-based services. The BOIC service can be provisioned on a per-subscriber basis, allowing for individual control, and can also be applied as a network-wide policy for specific subscriber groups, such as prepaid users or corporate accounts with restricted international dialing privileges.

BOIC's role extends beyond simple call blocking; it is integrated into the broader suite of call barring services (e.g., BAOC, BOIC-exHC) which together form a comprehensive set of tools for service management. Its operation is transparent to the radio access network (RAN), as it is a core network and service layer function. The service supports both operator-initiated barring (e.g., for fraud prevention or unpaid bills) and subscriber-initiated barring (e.g., via USSD codes or customer care to control usage, especially useful for parents managing a child's phone or travelers wanting to avoid roaming charges). In modern IMS-based networks, BOIC logic may also be enforced by the Telephony Application Server (TAS) or other application servers, applying the same principles to Voice over LTE (VoLTE) and Voice over NR (VoNR) calls.

Purpose & Motivation

BOIC was introduced to address several operational and commercial challenges in mobile networks. Primarily, it serves as a cost-control mechanism for both subscribers and network operators. For subscribers, especially in the era of high international calling rates, it provided a way to proactively prevent accidental or unauthorized international calls that could lead to unexpectedly high bills. This was particularly important for corporate accounts, shared phone users, and parents managing family plans. For operators, BOIC is a critical tool for credit management and fraud prevention. It allows operators to bar international dialing for subscribers with outstanding debts or suspected fraudulent activity, thereby limiting financial exposure.

Historically, before such standardized supplementary services, controlling call types was more cumbersome, often requiring manual intervention by customer service or complex switch configurations. The standardization of BOIC in 3GPP Release 5, as part of the broader Intelligent Network (IN) and Customised Applications for Mobile network Enhanced Logic (CAMEL) service frameworks, provided a uniform, scalable, and remotely manageable method. It solved the limitation of having only basic, all-or-nothing call barring, by enabling granular control over specific call categories (international calls). This granularity allowed for more flexible service offerings and better customer experience, as users could bar expensive international calls while still making domestic and local calls.

The service's creation was also motivated by regulatory and competitive factors. In some regions, operators are required to offer tools for spending control. Furthermore, as mobile services expanded globally and roaming became more common, the risk of 'bill shock' from international calls (including calls made while roaming) increased. BOIC, along with related services like Barring of Outgoing International Calls except those directed to the Home PLMN Country (BOIC-exHC), provided a technical solution to mitigate this risk, enhancing subscriber trust and reducing customer care complaints related to billing disputes.

Key Features

• Prevents placement of calls to international number formats
• Integrates with HLR/HSS for subscriber profile management
• Can be activated/deactivated by subscriber via USSD or operator via OSS
• Works across circuit-switched (CS) and IMS-based voice domains
• Provides call setup interception and termination with user notification
• Supports both operator-enforced and subscriber-requested barring

Evolution Across Releases

Defining Specifications