tailieunhanh - Future of Voice-over-Internet Protocol Telephony

Internet telephony refers to communications services—voice, facsimile, and/or voice-messaging applications—that are transported via the Internet, rather than the public switched telephone network (PSTN). The basic steps involved in originating an Internet telephone call are conversion of the analog voice signal to digital format and compression/translation of the signal into Internet protocol (IP) packets for transmission over the Internet; the process is reversed at the receiving end. | Voice over Internet Protocol Definition Internet telephony refers to communications services voice facsimile and or voice-messaging applications that are transported via the Internet rather than the public switched telephone network PSTN . The basic steps involved in originating an Internet telephone call are conversion of the analog voice signal to digital format and compression translation of the signal into Internet protocol IP packets for transmission over the Internet the process is reversed at the receiving end. Overview This tutorial discusses the ongoing but rapid evolution of Internet telephony the market forces fueling that evolution and the benefits that users can realize as well as the underlying technologies. It also examines the hurdles that must be overcome before Internet telephony can be adopted on a widespread basis. Topics 1. Introduction 2. Intranet Telephony Paves the Way for Internet Telephony 3. Technical Barriers 4. Standards 5. Future of VoIP Telephony Self-Test Correct Answers Glossary 1. Introduction The possibility of voice communications traveling over the Internet rather than the PSTN first became a reality in February 1995 when Vocaltec Inc. introduced Wei PnoFonjm futanats Capyncht me mien edorul Cc-iaortwrh 1 16 its Internet Phone software. Designed to run on a 486 33-MHz or higher personal computer PC equipped with a sound card speakers microphone and modem see Figure 1 the software compresses the voice signal and translates it into IP packets for transmission over the Internet. This PC-to-PC Internet telephony works however only if both parties are using Internet Phone software. Figure 1. PC Configuration for VoIP U i Pi outfit Mntw lArMQfnmA f In the relatively short period of time since then Internet telephony has advanced rapidly. Many software developers now offer PC telephony software but more importantly gateway servers are emerging to act as an interface between the Internet and the PSTn see Figure 2 . Equipped .