A VoIP gateway is a gateway device that uses

Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. IP h ...

s to transmit and receive voice communications (VoIP).

Setup

A typical VoIP gateway has interfaces to both IP networks and PSTN (

Public switched telephone network The public switched telephone network (PSTN) provides Communications infrastructure, infrastructure and services for public Telecommunications, telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that ...

) or POTS (Plain old telephone service) telephone services. The gateway may be configured to use these in several ways, including: * An internal telephone instrument or nmnbm , with external game connectivity through VoIP via the Internet. * The PSTN interface to a telephone network, with IP connectivity to an in-house VoIP phone system. * Both PSTN and VoIP interfaces externally, sometimes to offer a connection at local call charges to a remote call centre. The PSTN interface is often either duplicated as, or can act as, connections for both a

foreign exchange station Foreign exchange service (FX) is an access service in a telecommunications network in which a telephone in a given exchange area is connected, via a private line, as opposed to a switched line, to a telephone exchange or central office in another e ...

(FXS) and a

foreign exchange office Foreign exchange service (FX) is an access service in a telecommunications network in which a telephone in a given exchange area is connected, via a private line, as opposed to a switched line, to a telephone exchange or central office in another e ...

(FXO). An FXS interface connects to FXO devices, such as local analogue telephone handsets or the exchange side of a PABX. The FXO interface connects to FXS devices, such as the PSTN. A relatively potent device is needed to use better compression formats, such as

G.729a G.729 is a royalty-free narrow-band vocoder-based audio data compression algorithm using a frame length of 10 milliseconds. It is officially described as ''Coding of speech at 8 kbit/s using code-excited linear prediction'' speech coding (CS-ACEL ...

; a relatively inexpensive and simple device can easily handle a similar function using more bandwidth over

G.711 G.711 is a narrowband audio codec originally designed for use in telephony that provides toll-quality audio at 64 kbit/s. G.711 passes audio signals in the range of 300–3400 Hz and samples them at the rate of 8,000 samples per second ...

. Any device capable of delivering audio in G.711 via Internet in either way can be considered a VOIP Gateway, but one that is capable of sending and receiving simultaneously will perform better. One with support for more

codecs A codec is a device or computer program that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder. In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or da ...

will usually be able to perform better in a range of situations, such as restricted bandwidth, though doing so is not always easy to differentiate. The packets of data are quickly sent (as little as a few milliseconds between packets), most often using

User Datagram Protocol In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages (transported as datagrams in packets) to other hosts on an Internet Protocol (IP) network. ...

(UDP). A lost packet or two will not usually result in any noticeable degradation of the signal. Using G.711 as the codec, it is possible to use a fax machine or modem via these devices without issues. This is mostly due to G.711 being a relatively simple compression audio stream. Other codecs will not usually perform this task. Any modern PC with a microphone and speakers (or a headset serving both those tasks) is capable of acting as a VoIP gateway. This still requires an Internet connection and a

Session Initiation Protocol The Session Initiation Protocol (SIP) is a signaling protocol used for initiating, maintaining, and terminating communication sessions that include voice, video and messaging applications. SIP is used in Internet telephony, in private IP telepho ...

(SIP) relay which adds to the disadvantages of VoIP. Most SIP relays are commercial and charge either pay-per-minute or a flat rate for unlimited service on a number of channels.

References

{{Reflist Voice over IP