This standard is aimed at defining the interworking relationship between the call control protocol of the ISDN User-Network Interface Protocol and the ISDN User Part of SS7. This standard defines in detail the relationship between signalling information conveyed via the User-Network Interface Protocol and similar signalling information conveyed via the ISDN User part of SS7. The above relationship is described within the context of supporting the establishment and clearing of call within an ISDN or mixed ISDN/non-ISDN environment. Formerly known as T1.609-1999(R2009).