SIPi

SIPi is a term used in telecommunications to describe methods and extensions that enable signaling interoperability between Session Initiation Protocol (SIP) networks and traditional circuit-switched networks such as those based on SS7 and ISUP. In this sense, SIP-i (also written as SIP-I or SIP for IP) refers to a family of approaches for carrying legacy telephony signaling within SIP signaling to support end-to-end call setup, routing, and charging across IP and PSTN domains.

Key concepts associated with SIPi include signaling interworking, where ISUP or similar telephony signaling elements are conveyed or mapped into SIP messages at network borders. This often involves gateways or border controllers that translate between ISUP-level information and SIP signaling, allowing a call originated in a SIP network to be completed on a PSTN network and vice versa while preserving core call control semantics.

SIPi is typically discussed in the context of IP-based telephony deployments that connect to traditional telephony systems, such as those using an IP Multimedia Subsystem (IMS), PSTN interconnections, or wholesale voice networks. Variants and related approaches include SIP-T and other interworking schemes that aim to preserve legacy signaling semantics within SIP, enabling compatibility with existing SS7-based infrastructure.

Over time, the practical emphasis in industry has shifted toward standardized interworking solutions such as SIP-T, but SIPi concepts have influenced the design of interworking mechanisms and gateway equipment. The term may be used variably, and in some contexts it denotes a general family of interworking techniques rather than a single formal specification.

See also: SIP, ISUP, SS7, SIP-T, IMS.