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Thực hiện tiếng nói qua IP (P7)

VoIP IN THE PUBLIC NETWORKS1 VoIP technology is currently mature enough to be implemented in public networks (PSTN, cable TV [CATV], etc.), at least for long-distance telecommunications services to both residential and corporate customers. Either a private IP-based network (an Intranet) or an IP-based VPN can be used to guarantee the required QoS (call acceptance/drop rate, voice quality, etc.). In order to launch VoIP in the access loop, IP-based local access over digital subscriber line (DSL) or Ethernet in the first mile (EFM, IEEE P802.3ah) access, CATV networks, and wireless local loop (WLL) can be utilized | Implementing Voice over IP. Bhumip Khasnabish Copyright 2003 John Wiley Sons Inc. ISBN 0-471-21666-6 7 VoIP IN THE PUBLIC NETWORKS1 VoIP technology is currently mature enough to be implemented in public networks PSTN cable TV CATV etc. at least for long-distance telecommunications services to both residential and corporate customers. Either a private IP-based network an Intranet or an IP-based VPN can be used to guarantee the required QoS call acceptance drop rate voice quality etc. . In order to launch VoIP in the access loop IP-based local access over digital subscriber line DSL or Ethernet in the first mile EFM IEEE P802.3ah access CATV networks and wireless local loop WLL can be utilized. For corporate customers the PSTN network can provide a variety of DSL-based access links to offer centrex features and functions and intersite IP-PBX connectivity as discussed in Chapter 6. In this chapter we discuss evolution of various public network infrastructures e.g. PSTN CATV etc. to offer VoIP-based basic and advanced telephony services either by using new IP-based network elements that are capable of supporting PSTN interfaces or by upgrading or modernizing the existing Telco-grade i.e. the network equipment building system NEBS -compliant PSTN elements with IP-based line cards servers and so on. IP-BASED TANDEM OR CLASS-4 OR LONG-DISTANCE SERVICES In traditional PSTN terminology if the calling and called parties are not served by the same CLASS-5 central office CO switch or cloud then one or more i The ideas and viewpoints presented here belong solely to Bhumip Khasnabish Massachusetts USA. 93 94 VoIP IN THE PUBLIC NETWORKS CLASS-4 or tandem-level switches and a transport network see e.g. Fig. 1-1 of Chapter 1 are required for establishing the connection between the two parties. That transport switch-based intermediate network constitutes a multiconnected and highly protected network that is commonly known as a longdistance LD or inter-LATA network and the call .