Voice over IP
Voice over IP (also called VoIP, IP Telephony, and Internet telephony) refers to technology that enables routing of voice conversations over the Internet or any other IP network. The voice data flows over a general-purpose packet-switched network, instead of the traditional dedicated, circuit-switched voice transmission lines.
This arrangement has several advantages over traditional telephony:
Wider range of features and facilities. In addition to the basic end-to-end voice conversation, more information and control about each call can easily be provided. This includes sending and receiving messages or data files in parallel with the voice conversation, audio conferencing, managing address books and passing presence information about whether friends/colleague are available online to interested parties.
Freer innovation. Innovation progresses at market rates rather than the slow pace of the multilateral International Telecommunications Union (ITU) committee process, resulting in more new advanced features.
Lower per-call costs. Once the capital costs of terminals and/or computers and the operating costs of a data network connection are in place, there are no additioanl charges for usage unless the destination is outside the IP network. However, this must be offset by the higher costs of telephony equipment. Prices from VoIP providers are not always cheaper than other carriers.
Higher quality voice is an option where higher bandwidth voice encoding can be selected to improve end-to-end quality. However, often high compression techniques are used to save bandwidth and potential result in slightly poorer quality than traditional telephony circuits.
Lower infrastructure costs. VoIP reduces the traditional scheme—two separate wiring systems, one for voice and one for network—to a single connection.
"Future proof" hardware. Functionality is software (protocol) based, allowing for changes in software coding without requiring a "forklift" or component upgrade.
However, there are several drawbacks which are being addressed as the technology matures:
Occasional drop-out of voice, where IP packets are lost or dropped in the network between end users. This is more noticeable in highly congested networks and/or where there is long distances and/or interworking between end points. Avoidance of this problem will require introduction of priority schemes for voice traffic, using Quality of Service mechanisms. These have been developed for IP Version 6, but rarely implemented.
Single point of calling. Typically a computer is used as the terminal for VoIP calls, although telephone adaptors and/or VoIP telephones are commercially available.
Unlike a standard POTS (Plain Old Telephone System) phone it is not possible to share a single line with 3 or 4 telephones. In many homes, these ring in parallel, and any may be used to answer and complete the call. This is typically not possible with VoIP where individual terminals are called, although new schemes with VoIP compatible cordless phones and routers with VoIP capability have been introduced.
Lack of global telephone number range. Whilst the standard POTS and mobile phone networks share a common global standard (E.164) which allocates and identifies any specific telephone line, there is no widely adopted similar standard for VoIP networks. Some allocate an E.164 number which can be used for VoIP as well as incoming/external calls. However, there are often different, incompatible schemes when calling between VoIP providers which use short codes that are provider specific.
Emergency Calls are usually barred from VoIP phones because their location cannot be determined. There have been examples of deaths due to home telephone services that had no emergency call service available.