Voice Over IP

Voice over IP (VoIP) is a branch of technologies, methodologies, communication protocols, and transmission techniques for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. Related terms and those commonly used in conjunction with Voice over IP include IP telephony, Internet telephony, voice over broadband (VoBB), broadband telephony, and internet phone.

Internet telephony encompasses all communication services that are transported over the web rather than the public switched telephone network (PSTN) – this includes voice, fax, SMS and voice messaging services. The process of originating a VoIP telephone includes several key stages. These are – signalling and media channel configuration, digitization of the analogue voice signal, encoding, packetization, and transmission as Internet Protocol (IP) packets via a packet-switched network.

On the receiving end, the process is reversed and reception of the IP packets, decoding those packets and digital-to-analog conversion reproduce the original voice stream. Despite being used interchangeably, the terms IP Telephony and Voice over IP actually refer to different systems; IP telephony refers to digital telephony systems that use IP protocols for voice communication while VoIP is actually a subset of IP Telephony. VoIP technology is used by IP telephony to facilitate the transportation of phone calls.

Voice over IP systems use session control protocols to manage the set-up and tear-down of calls. Audio codecs then cipher speech granting transmission over an IP network as digital audio via an audio stream.

Which codec is used varies between different implementations of Voice over IP depending on the usage requirements and available network bandwidth. Some set-ups use narrow-band and compressed speech whereas others utilize high fidelity stereo codecs.

Voice over IP is now common on smart phones – commonly referred to as mobile VoIP – and many web enabled devices meaning people using portable devices that aren’t phones can still call or use SMS text messaging via 3G or Wi-Fi networks.

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