Editing ISDN User Part (section)

== ISUP variants ==
Different ISUP variants exist. ITU-T specifies the variant used in the international network. In Europe [[ETSI]] releases its own ISUP specification which is close that of the ITU-T.<ref name="isupv4">{{Citation | url = http://webapp.etsi.org/workprogram/Report_Workitem.asp?WKI_ID=8105 | publisher = ETSI | title = EN 300 356-1, ISUP Version 4 for the International Interface}}.</ref> ITU-T ISUP is used for international connections and is the base for some national ISUP variants. Most countries have their own variation of ISUP to cover national requirements. [[ANSI]] specifies variations of ISUP utilized under the [[North American Numbering Plan]]; however, some countries under the NANP differ in their support of some procedures (for example, [[Local access and transport area|LATA]] is meaningless within Canada. Also, [[Regional Bell Operating Company|RBOC]]s support [[Telcordia Technologies|Telcordia]] procedures not fully specified by ANSI.) Some countries outside the NANP support ANSI-based variants (e.g. Mexico).

While these variations of ISUP differ in subtle ways, the vast majority of ISUP message type, parameter type, and parameter field code-points, and related fundamental call processing procedures, agree across all variants.

=== ITU-T specification versions ===
* 1980 – ISUP Yellow Book
* 1984 – ISUP Red Book
* 1988 – ISUP Blue Book
* 1991 – ISUP Q.767<ref name= "q767">{{Citation | url = http://www.itu.int/rec/T-REC-Q.767/en | publisher = ITU-T | title = Recommendation Q.767}}.</ref>
* 1992 – ISUP'92 White Book (segmentation, compatibility, new supplementary services)
* 1997 – ISUP'97 (new procedures, IN CS1, new supplementary services)

According to ITU-T Q.761 section 2.4.1 ''ISUP interworking'' ISUP'92 is backwards compatible with ISUP Blue Book and Q.767<ref name = "q767"/> for basic call procedures and supplementary services except for some procedures (e.g. number portability).<ref name = "q761">{{Citation | url = http://www.itu.int/rec/T-REC-Q.761/en | publisher = ITU-T | title = Recommendation Q.761}}.</ref> Additionally the compatibility features introduced in this version ensure forward compatibility with newer versions.