■ Enterprise iPBX Solution ·PBX application in enterprise Most enterprises currently adopt PSTN-based PBX to set up internal telephone system, as shown in the figure below: 　　Legacy telephony system is a centralized enterprise communication system. It has a complicated layout and limited expandability. One office needs one system, and one telephony system cannot be shared among several branch offices. With the rapid development and application of Internet and IP telephony, legacy telephony system thus meets its bottleneck to accommodate a corporation's growing communication needs. [Migrated Solution for PBX to iPBX ]   The enterprise, once decides to establish its own iPBX system, needs to take the PBX system that has been fully or partially used into account to protect investments, therefore, there must be a solution seeking to fulfill the steady transition and switch from co-existing of PBX and iPBX system to total iPBX system. Based on product features, Voipack puts forward the Migrated Solution for enterprise PBX to iPBX as below:Schematic diagram for system configuration: As shown in the above figure, PBX system has been installed in the headquarters, and iPBX interconnects with PBX system by voice gateway via FXS or FXO. Headquarters- based departments continue to communicate internally and externally centering the PBX, while branch offices establish local telephony systems by voice gateway, however those departments equipped with PBX system may establish their communication systems the way their headquarters does. The interconnections between branches access headquarters PBX system through voice gateway of the headquarters. Taking the diagram for example, each branch office can utilize all iPBX functions directly, and the headquarters uses iPBX functions indirectly by way of voice gateway, in which the iPBX functions may be restricted. It is time to replace the PBX system, when it fails to accommodate the growing demand of telecommunications of enterprises. In an all iPBX system where internal telecommunication system of an enterprise completely centers on iPBX, iPBX seamlessly connects Internet with PSTN and builds up new IP communication platform for the enterprise. The advantage, flexibility, expandability and openness that distinguish IPBX will be fully demonstrated in Total iPBX Solution for Enterprise as below.   [Total iPBX Solution] iPBX system for enterprise is built upon the basis of IP network to offer enterprise the reliability equal to that of circuit exchange of telephony system, the flexibility of service promotion and the advantage of IP telephone in cost and mobility. IP telephone enables enterprise to reduce the number of lines and telephone costs by integrating voice and mobility into general infrastructure. VoIP integration requires no special training for 　　 users, for they may dial an IP extension the same way as they use an analog extension.   ■Single Point iPBX Application in LAN For typical iPBX single node configuration, enterprises may perform “external” voice communication through PSTN and “internal” voice communication through VoIP. A telephone system comprises the server equipped with iPBX software system, IP telephone, VoIP gateway, regular analog fax machine, intranet and PSTN. Schematic 　 Diagram for System Configuration　　 　　 This solution adopts iPBX, taking the role of traditional PBX, to establish telephone system based on IP network inside enterprise and provide voice and fax service by seamless connection with PSTN. VCM/VMS is the core of the system. 　　 ■Multi-point iPBX Application Across Area Enterprises having two or more branch offices interconnected via Intranet or Internet are seeking a solution both to reduce toll call expenditure and to provide service grade communication among offices. Voipack iPBX platform provides enterprise with a solution featuring high performance/price ratio and high expandability to achieve such a goal. Users may enjoy powerful functions of iPBX without geographical restriction. Calls are relayed through IP network seamlessly, achieving zero call charge within enterprise. The telephone system comprises the server equipped with iPBX software system, IP telephone, VoIP telephone gateway, analog fax machine, intranet, Internet, ISP VoIP network and PSTN. The core of the system consists of VCM, VMS, VSBC and VBS. VCM conducts call control over the system; VMS provides interactive voice reply service; VSBC provides private network traversal function for terminal equipment based on different broadband accesses; VBS provides all calls with authentication and billing function. Baed on different scale of system, they can either co-work over hardware equipment or work independently over different hardware equipment.　 In multi-point iPBX solution connected via Internet, the core system equipment is required to use the public IP 　　 address.