 Voice Over Internet Protocol, also known as Voice over IP or Internet Telephony, is a general term for the technologies that use the Internet Protocol's packet-switched connections to exchange voice, fax, and other forms of information that have traditionally been carried over the dedicated circuit-switched connections of the public switched telephone network (PSTN).
Using the Internet, calls travel as packets of data on shared lines, avoiding the tolls of the PSTN. The challenge in IP telephony is to deliver the voice, fax, or video packets in a dependable flow to the user. Much of IP telephony focuses on that challenge.
VOIP uses established data communication networks to provide telephone services between users. The user phone (or multimedia package on a PC) is attached to a specialized Digital Signal Processing (DSP) device where the voice signal is converted into data packets. Special software on the conversion device translates the destination phone number into an IP address, attaches the appropriate IP header information to the packet, and forwards it to the nearest IP data router to be forwarded to the destination address. The destination system utilizes its DSP to convert the data packets into a voice signal that can be heard on a regular phone receiver or PC speakers.
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