Send Information For Outgoing Call

Description

Send Information For Outgoing Call (SIFOC) is a supplementary service defined within the 3GPP specifications for GSM and UMTS networks. It operates as part of the call control and service interaction framework, allowing the calling party to provide supplementary information to the network during the establishment phase of an outgoing call. This information is typically used for authentication, billing, or routing purposes beyond the standard dialed digits. The service is invoked by the user equipment (UE) or the mobile station (MS) by sending specific signaling messages containing the SIFOC information element to the network. The network, specifically the Mobile Switching Center (MSC) or Visitor Location Register (VLR), processes this information. It may interact with other network entities like the Home Location Register (HLR) or service control points (e.g., for CAMEL) to validate the information and apply appropriate service logic, such as alternative charging or call routing based on the provided data. Architecturally, SIFOC is integrated into the call control protocols (e.g., in TS 24.008) and relies on the existing signaling infrastructure (e.g., MAP, ISUP). The information is carried transparently through the network until it reaches the entity responsible for service execution. Its role is crucial for enabling value-added services that require additional user input at call initiation, bridging the gap between basic telephony and intelligent network services.

Purpose & Motivation

SIFOC was created to support calling card services and other telephony applications where the caller needs to provide authentication or billing information separate from the dialed number. Before its introduction, such services often required complex dual-tone multi-frequency (DTMF) input after call connection, which was cumbersome and insecure. SIFOC allows this information to be sent securely within the initial call setup signaling, improving user experience and enabling network-based authentication. It addresses the limitation of basic call setup, which only carries the destination number, by providing a standardized mechanism for additional data. This was particularly important for GSM operators offering prepaid or corporate services, as it facilitated integration with intelligent network platforms for real-time billing and service control. The feature emerged in the early GSM releases to enhance service flexibility and has been maintained through subsequent 3GPP releases for backward compatibility and continued support of legacy service offerings.