element APi layer method. nw2 allows hosted networks (e.g., nw3) to use its own numbering system for addressing. We say that nw3 uses global routes and that nw2 views these addresses as global titles (GT). The 3.4 Route Type Examples term "global title" is used in SS7 and in PSTN/ISDN. It corresponds to the domain name in IP-based systems. Obviously, before a routing analysis in nw1 can take place, an address transla- tion must be done. For this purpose, a new type of table is needed, the T-GT table, to be handled by nodes of nw2. This table translates a GT (part of the numbering system of a hosted network) to an REi of a switched route, and a destination APi of nw2. Its T-RE table is then used for translating the REi to an nw1 network address. 3.4.5.2 Global Routes in SS7 Let's now look at how global titles are supported in some network systems, starting with SS7. In this system, SCCP has been assigned the task to support global routes (see Fig. 3.31). Global routes, Other realized by SCCP Other addrMethod, calledSSN, numbPlan, destGT {calledSSN,callingSSN,...} {SI=3, DPC, OPC, SLS,. T-ROs MTP L3 Signaling links T-GT(SCCP): destGT->{DPC,calledSSN) T-AP(SCCP): hostedNWi->calledSSN MTP L2 Fig. 3.31 Realization of global routes in SS7 Note that global title addressing in SCCP does not substitute socket addressing. It is just an alternative addressing method, i.e., the hosted node is identified by the same SSN, whether it uses socket or global routes. Global routes do, however, complicate the SCCP layer interface, since a hosted node must, for every invoca- tion, inform SCCP about which addressing method is used and which numbering system (of the hosted network) is referred (every hosted network may have its own numbering system). The SCCP protocol is not affected by the introduction of global title handling in SCCP, as long as every SCCP node has a relevant T-GT. However, SCCP does not stop there: in order to facilitate T-GT table management, SCCP also supports cen- tralized handling of T-GT tables, i.e. all T-GT t