User Parts Signaling System Number 7

www.pragsoft.com Chapter 10: Telephone Networks 137 interconnected to other public and private networks, such as a public X.25 network or a corporate LAN. Figure 10.Error Bookmark not defined. illustrates a sample PBX system connected to a variety of other systems. Figure 10.15 Sample PBX configuration. Extensions Voice Services Data Services LAN Services Admin. Services PBX LAN WAN Cetral Office Exchange Trunks Telephone companies have also attempted to gain a share of the PBX market by offering PBX-equivalent services on their public networks. The Centrex service in North America is an example. It provides the same features as a typical PBX system but uses the public network for handling calls. Given that most PBX installations represent significant investments with continued upgrading and reconfiguration costs, the Centrex approach has obvious economic attractions.

10.4.2. Corporate Networks

Many large corporations operate their own distributed private telephone network, which consists of a number of PBX systems at different sites, interconnected through leased trunk lines. Each user is provided with a network-wide number which can be used to contact them, independent of their geographic location. The network also provides an interface to the public network for contacting people outside the corporation. By concentrating traffic on leased trunk lines, significant reductions in running costs can be achieved. Figure 10.Error Bookmark not defined. illustrates the structure of a simple corporate network. 138 Communication Networks Copyright © 2005 PragSoft Figure 10.16 A corporate network. Melbourne London New York PBX PBX PBX International Telephone Network Trunks Leased Lines Central Office Exchange

10.4.3. Intelligent Networks

SS7 opens the scope for user-defined procedures for the way calls are handled. This leads to the concept of Intelligent Networks IN. A conceptual view of an intelligent network is shown in Figure 10.Error Bookmark not defined.. The various components in the diagram are explained below.. Network access is facilitated through a set of Service Switching Points SSPs. The signaling link between the switches is controlled through a set of Signaling Transfer Points STPs. A Service Control Point SCP is in charge of dictating how calls should be handled and routed. For its operation, the SCP uses a service database which contains service profile definitions provided by the customer. Service profiles use a number of network-provided parameters e.g., time and date of the call, origin of the call, network-related conditions to determine how to handle calls. An Support Management System SMS provides network management and customer control capabilities. Figure 10.17 An intelligent network. SSP SSP SSP STP SCP STP STP SMS IN applications include: Call Management Services CMS, Customer Local Area Signaling Service CLASS, Personal Communications Service PCS, Centrex, Automatic Calling Card Service ACCS, and basic and enhanced 800 service. The 800 or 008 service is available in many countries. A typical 800