relevant SS7 protocols in this regard. In the last specifications, ISUP included all the functionality supported by TUP, plus more features such as the capability to transfer user-to-user information, SO ISUP is sufficient for our discussion here. ISUP is actually a generic name for a protocol which has many flavors in many different countries. When carriers want to implement a new feature, they often use non-compatible extensions that cause interoperability problems, and in SO doing, create a variety of local ISUP flavors. Naturally, national variants of ISUP are incompatible, SO an international version of ISUP is used to inter- connect networks with ISUP variants. Gateway switches between them understand/support both international ISUP and the specific ISUP imple- mented in the network and perform translations between them. The drawback of this arrangement is that international ISUP is com- paratively feature-poor, limiting network services to users connected to the same network. For example, users in Spain must choose among an avail- able set of services for calls within Spain, because the signalling protocol used for those calls is the Spanish ISUP. Users in Brazil have another set of services available for their internal calls. But services can't extend to calls between both countries, because there's no feature transparency between both flavors. Supplementary Services Functionality provided by ISUP can be divided into three groups: basic services, circuit management, and supple- mentary services. Basic services include the basic call establishment to pro- vide voice service. ISUP circuit management functions include blocking and unblocking cir- cuits and establishing, releasing, and testing circuit-switched paths. The same protocol used for establishing calls is also used for managing network resources. Chapter 1 Spanish ISUP Brazilian ISUP Figure 1-18 Gateways perform translations between Gateway Gateway national flavors and international ISUP. International Supplementary services are more varied; example