VoIP ( Voice Over IP) Overview The VoIP technology enables a variety of Internet-based appliances and devices to send voice, real-time fax and data over the IP network. Voice over IP (VoIP) uses the Internet Protocol (IP) to transmit voice as packets over an IP network. So VoIP can be achieved on any data network that uses IP, like Internet, Intranets and Local Area Networks (LAN). Here the voice signal is digitized, compressed and converted to IP packets and then transmitted over the IP network. Signaling protocols are used to set up and tear down calls, carry information required to locate users and negotiate capabilities. One of the main motivations for Internet telephony is the very low cost involved. Some other motivations are demands for multimedia communication and for integration of voice and data networks. Although audio and video services are available on the Internet, most forms of audio and video transfer over the Internet are not in real time. Jitter through the network is compensated for by buffering (or spooling) large time segments of the audio or video resulting in large lag times. This essentially eliminates interactive services such as videoconferencing or telephony. Voice over IP technology enables many multimedia applications at the desktop, including desktop videoconferencing, Internet and video telephony, white boarding, distance learning, support and help-desk applications, interactive shopping, and much more. Working The user dials a gateway connected to the Internet. The gateway, via an interactive voice response (IVR) interface, prompts the user to enter the number they want to reach. The first gateway connects across the Net to the gateway closest to the dialed number, and establishes a VoIP connection via the H.323 protocol, which is the de facto VoIP standard. The second gateway dials the recipient’s number and the call is established. Transmitting voice and fax over the Internet results in a drastic drop in international telecommunications rates. Encryption is used at the gateway to make the VoIP call secure so that an unauthorized entity cannot intercept the call on the Internet. Additionally, VoIP compresses calls significantly, permitting more calls, and more packets, to be transmitted on the same circuit. The Internet PhoneJACK is an audio card designed from the ground up, to improve the quality and performance of Internet telephony applications. Fax over IP (FoIP) Another immediate application for IP telephony is real time facsimile transmission. Fax transmission quality is typically affected by network delays, machine compatibility and analog signal quality. To send faxes over packet networks, an interface unit must convert the data to packet form, handle the conversion of signaling and control protocols, and ensure complete delivery of the scanned data in the correct order. Packet loss and end-to-end delay are even more critical here than in voice applications.