Download

9.4 TUP SUPPORT OF ADDITIONAL SERVICES 2179.4 TUP SUPPORT OF ADDITIONAL SERVICESThis section describes a number of services that do not fall into the category of“basic” call control and the manner in which these services are supported in TUPsignaling [4,5].9.4.1 ServicesThe services to be described fall into one of the following classes.Malicious Call Identification. Multifrequency Compelled (MFC) signaling inmany national networks includes procedures to identify malicious callers (Section4.6). These are also included in TUP signaling.Digital Connectivity. Telecoms in France [8] and several other countries haveintroduced digital subscriber lines, without waiting for the completion of the specificationsfor digital subscriber lines in the integrated services digital network(ISDN).Normal subscriber signaling (Chapter 3) is used on these lines. When the connectionhas been set up, the subscribers communicate with 64-kb/s digital data.Supplementary Services. ITU-T has defined a number of supplementary services.These services require connections with SS7 (TUP or ISUP) signaling allthe way.Calling Line Identification. Subscribers marked for this service at their localexchanges have devices attached to their telephones that display the calling partynumber. In the United States this service is known as “caller ID” (Section 3.7.2).Call Forwarding Service. In this service, a subscriber can indicate to his localexchange that, until further notice, incoming calls should be forwarded to anothersubscriber.Closed User Group Service [5]. In this service (not offered in the United States), amultilocation business customer can register its lines as members of a closed usergroup (CUG). A CUG is identified worldwide by four digits that represent a particulartelecom and an interlock code assigned by the telecom to the CUG (Section9.2.2). A CUG restricts the calls that can be made and received by its members.A CUG has three characteristics that can be specified by the business customer:1. Outgoing Access. Members of a CUG with no outgoing access (NOA) canonly make calls to other members of their CUG. Members of a CUG with outgoingaccess (OA) have no restrictions on their outgoing calls.