IP Telephony, IP Telephony And Voice-Over IP (Voip)

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The terms Internet telephony, IP telephony and voice-over-IP (VoIP) are often used interchangeably. Some people consider IP telephony a superset of Internet telephony, as it refers to all telephony services over IP, rather than just those carried across the Internet. Similarly, IP telephony is sometimes taken to be a more generic term than VoIP, as it de-emphasizes the voice component.
While some consider telephony to be restricted to voice services, common usage today includes all services that have been using the telephone network in the recent past, such as modems, TTY, facsimile, application sharing, whiteboards and text messaging. This usage is particularly appropriate for IP telephony, since one of the strengths of Internet telephony …show more content…

For enterprises, the current cost of a traditional circuit-switched PBX and a VoIP system are roughly similar, at about $500 a seat, due to the larger cost of IP phones. However, enterprises with branch offices can re-use their VPN or leased lines for intra-company voice communications and can avoid having to lease small numbers of phone circuits at each branch office. It is well known that a single large trunk for a large user population is more efficient than dividing the user population among smaller trunks, due to the higher statistical multiplexing gain. Enterprises can realize operational savings since moves, additions and changes for IP phones are much simpler, only requiring that the phone be plugged in at its new location.
Architecture:
IP telephony, unlike other Internet applications, is still dominated by concerns about interworking with older technology, here, the PSTN. Thus, we can define three classes [21] of IP telephony operation as shown in Fig. 1.1, depending on the number of IP and traditional telephone end systems. Figure 1.1: Internet Telephony

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