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Thực hiện tiếng nói qua IP (P8)

VoIP FOR GLOBAL COMMUNICATIONS1 This Chapter discusses how IP-based voice communications can be deployed for global communications in multinational enterprises and for international calling by residential PSTN customers. In traditional PSTN networks, various countries use their own version of the ITU-T standards for signaling or for bearer or information transmission. When IP-based networks, protocols, interfaces, and terminals (PCs, IP phones, Web clients, etc.) are used, unification of transmission, signaling, management, and interfaces can be easily achieved | Implementing Voice over IP. Bhumip Khasnabish Copyright 2003 John Wiley Sons Inc. ISBN 0-471-21666-6 8 VoIP FOR GLOBAL COMMUNICATIONS1 This Chapter discusses how IP-based voice communications can be deployed for global communications in multinational enterprises and for international calling by residential PSTN customers. In traditional PSTN networks various countries use their own version of the ITU-T standards for signaling or for bearer or information transmission. When IP-based networks protocols interfaces and terminals PCs IP phones Web clients etc. are used unification of transmission signaling management and interfaces can be easily achieved. We discuss a possible hierarchical architecture for controlling IP-based global communications in a hypothetical multinational organization. VoIP IN MULTINATIONAL CORPORATE NETWORKS Large multinational companies with global operations usually manage multiple network infrastructures for voice and data services. For data networking they commonly use IP frame relay FR asynchronous transfer mode ATM and other networking technologies 1 . For voice communications depending on the number of employees in a location they either deploy PBX or use centrex services from telecoms local with for example Tl-based 24 DS0 lines over a 24 x 64 1.536 Mbps line PSTN connectivity in North America El-based 32 DS0 lines over a 32 x 64 2.048 Mbps line PSTN connectivity in Europe and so on 1 . 1 The ideas and viewpoints presented here belong solely to Bhumip Khasnabish Massachusetts USA. 117 118 VoIP FOR GLOBAL COMMUNICATIONS If PSTN centrex-based services are used for voice calls the costs for service from the telecom may be very high but the on-site maintenance costs will be low. If PBXs are deployed two different network infrastructures must be maintained one for data services and the other for voice services in every corporate location. This involves two different sets of monthly bills and two different sets of personnel for maintenance .