Editing Session Initiation Protocol (section)

==SIP-ISUP interworking==
SIP-I, Session Initiation Protocol with encapsulated [[ISDN User Part|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<ref name="RFC 3372">{{cite IETF |rfc=3372 |title=SIP-T Context and Architectures |date=September 2002}}</ref> 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.{{efn|ISUP detail 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]], whereas SIP-T was defined by the [[IETF]].<ref>{{cite web |url=http://www.4gamericas.org/documents/3G_Americas_SIP-I_White_Paper_August_2007-FINAL.pdf |title=Why SIP-I? A Switching Core Protocol Recommendation |archive-url=https://web.archive.org/web/20120317091603/http://www.4gamericas.org/documents/3G_Americas_SIP-I_White_Paper_August_2007-FINAL.pdf |archive-date=2012-03-17 |url-status=dead}}</ref>