SIP-ISUP Interworking
SIP-I, or the Session Initiation Protocol with encapsulated ISUP, is a protocol used to create, modify, and terminate communication sessions based on ISUP using SIP and IP networks. Services using SIP-I include voice, video telephony, fax and data. SIP-I and SIP-T are two protocols with similar features, notably to allow ISUP messages to be transported over SIP networks. This preserves all of the detail available in the ISUP header, which is important as there are many country-specific variants of ISUP that have been implemented over the last 30 years, and it is not always possible to express all of the same detail using a native SIP message. SIP-I was defined by the ITU-T, where SIP-T was defined via the IETF RFC route. A Session Initiation Protocol (SIP) connection is a Voice over Internet Protocol (VoIP) service offered by many Internet telephony service providers (ITSPs) that connects a company's private branch exchange (PBX) telephone system to the public switched telephone network (PSTN) via the Internet.
Using a SIP connection may simplify administration for the organization as the SIP connection typically uses the same Internet access that is used for data. This often removes the need to install Basic Rate Interface (BRI) or Primary Rate Interface (PRI) telephone circuits.
Read more about this topic: SIP Connection