Business Data Communications and Networking, Eleventh Edition

APPENDIX C

IP TELEPHONY

IP Telephony refers to the use of Internet protocols to provide voice, video, and data in one integrated service over LANs, BNs, MANs, and WANs. When most people talk about IP Telephony, they mean Voice over IP (VoIP). Voice over ATM (VoATM) and Voice over Frame Relay (VoFR) are less common, and, as the names suggests, are close cousins to VoIP.

VoIP provides three key benefits compared to traditional voice telephone services. First, it minimizes the need for extra wiring in new buildings (there is one cable for both voice and data, not two). Second, it provides easy movement of telephones and the ability of phone numbers to move with the individual (the number is installed in the telephone, much like an IP address, so anywhere the phone is connected or the phone number programmed, the phone will connect, even if it is halfway around the world). Finally, VoIP is generally cheaper to operate because it requires less network capacity to transmit the same voice telephone call over an increasingly digital telephone network.

VoIP requires a VoIP Private Branch Exchange (PBX), which connects the organization's internal telephone network into the public switched telephone network (PSTN). The PBX can also be connected into the organization's WAN and be configured to route calls through the WAN to other organization locations (or even over the Internet), thereby bypassing any long-distance charges in the PSTN (although the call does use up network capacity on the ...