| Voice over Internet Protocol (VoIP) is a protocol | | | | in sequential order, or provide Quality of Service |
| optimized for the communication of voice through the | | | | (known as QoS) guarantees, VoIP implementations |
| Internet or other packet switched networks. VoIP is | | | | face problems dealing with latency and jitter. This is |
| often used theoretically to refer to the actual | | | | true when satellite circuits are involved, due to long |
| transmission of voice (rather than the protocol | | | | round trip broadcast delay (400 milliseconds to 600 |
| implementing it). VoIP is also known as IP Telephony, | | | | milliseconds for geostationary satellite). The receiving |
| Internet telephony, Broadband telephony, Voice over | | | | node must restructure IP packets that may be out of |
| Broadband and Broadband Phone. | | | | order, delayed or missing, while ensuring that the audio |
| Voice over IP protocols carry telephonic signals as | | | | stream maintains a proper time consistency. This |
| digital audio, typically reduced in data rate using speech | | | | functionality is usually accomplished by means of a |
| data compression techniques, encapsulated in a data | | | | jitter buffer in the voice engine. |
| packet stream over IP. | | | | Landline phones are connected directly to telephone |
| Companies providing VoIP service are commonly | | | | company phone lines, which in the event of a power |
| referred to as providers, and protocol which are used | | | | failure are kept functioning by back-up generators or |
| to carry voice signals over the IP network are | | | | batteries located at the telephone exchange. However, |
| commonly referred to as Voice over IP or VoIP | | | | household VoIP hardware uses broadband modems |
| protocols. They may be viewed as commercial | | | | and other equipment powered by household electricity, |
| realizations of the experimental Network Voice | | | | which may be subject to outages in the absence of |
| Protocol (1973) invented for the ARPANET providers. | | | | an uninterruptible power supply or generator. Early |
| Some cost savings are due to utilizing a single network | | | | adopters of VoIP may also be users of other phone |
| to cart voice and data, especially where users have | | | | equipment, such as PBX and cordless phone bases, |
| existing underutilized network capacity that can carry | | | | which rely on power not provided by the telephone |
| VoIP at no additional cost. VoIP to VoIP phone calls | | | | company. Even with local power still available, the |
| are sometimes free, while VoIP to public switched | | | | broadband carrier itself may experience outages as |
| telephone networks, PSTN, may have a cost that is | | | | well. While the PSTN has been matured over decades |
| borne by the VoIP user. | | | | and is typically reliable, most broadband networks are |
| Basically there are two types of PSTN to VoIP | | | | less than 10 years old, and even the best are still |
| services: Direct Inward Dialing (DID) and access | | | | subject to intermittent outages. Furthermore, consumer |
| numbers. DID will connect the caller directly to the VoIP | | | | network technologies such as cable and DSL often |
| user while access numbers require the caller to input | | | | are not subject to the same restoration service levels |
| the extension number of the VoIP user. | | | | as the PSTN or business technologies such as T-1 |
| As UDP (user datagram protocol) does not provide a | | | | connection. |
| mechanism to ensure that data packets are delivered | | | | |