A VoIP phone or IP phone uses

voice over IP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of speech, voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms In ...

technologies for placing and transmitting

telephone call A telephone call is a connection over a telephone network A telephone network is a telecommunications network that connects telephones, which allows telephone calls between two or more parties, as well as newer features such as fax and interne ...

s over an IP network, such as the

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...

. This is in contrast to a standard phone which uses the traditional

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 ...

(PSTN). Digital IP-based telephone service uses control protocols such as the Session Initiation Protocol (SIP),

Skinny Client Control Protocol The Skinny Client Control Protocol (SCCP) is a proprietary network terminal control protocol originally developed by Selsius Systems, which was acquired by Cisco Systems in 1998. SCCP is a lightweight IP-based protocol for session signaling with C ...

(SCCP) or various other

proprietary protocol In telecommunications, a proprietary protocol is a communications protocol owned by a single organization or individual. Intellectual property rights and enforcement Ownership by a single organization gives the owner the ability to place restricti ...

Types

VoIP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...

phones can be simple software-based

softphone A softphone is a software program for making telephone calls over the Internet using a general purpose computer rather than dedicated hardware. The softphone can be installed on a piece of equipment such as a desktop, mobile device, or other comp ...

s or purpose-built hardware devices that appear much like an ordinary

telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...

or a

cordless phone A cordless telephone or portable telephone has a portable telephone handset that connects by radio to a base station connected to the public telephone network. The operational range is limited, usually to the same building or within some short ...

. Traditional PSTN phones can be used as VoIP phones with

analog telephone adapter An analog telephone adapter (ATA) is a device for connecting traditional analog telephones, fax machines, and similar customer-premises devices to a digital telephone system or a voice over IP telephony network. An ATA is often built into a sma ...

s (ATA). A VoIP phone or application may have many features an analog phone doesn't support, such as e-mail-like IDs for contacts that may be easier to remember than names or phone numbers, or easy sharing of contact lists among multiple accounts. Generally the features of VoIP phones follow those of

Skype Skype () is a proprietary telecommunications application operated by Skype Technologies, a division of Microsoft, best known for VoIP-based videotelephony, videoconferencing and voice calls. It also has instant messaging, file transfer, deb ...

and other PC-based phone services, which have richer feature sets but may experience latency-related problems, because they rely on mainstream operating systems' IP and audio support. As mainstream operating systems became better at voice applications with appropriate

quality of service Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network, or a cloud computing service, particularly the performance seen by the users of the network. To quantitat ...

(QoS) guarantees, and 5G handoff ( IEEE 802.21 etc.) becomes available from wireless carriers, tablets and

smartphone A smartphone is a portable computer device that combines mobile telephone and computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities and extensive mobile operating systems, whic ...

s became the dominant interfaces. iPhone, Android and the

QNX QNX ( or ) is a commercial Unix-like real-time operating system, aimed primarily at the embedded systems market. QNX was one of the first commercially successful microkernel operating systems. The product was originally developed in the early ...

OS used in 2012-and-later

BlackBerry The blackberry is an edible fruit produced by many species in the genus ''Rubus'' in the family Rosaceae, hybrids among these species within the subgenus ''Rubus'', and hybrids between the subgenera ''Rubus'' and ''Idaeobatus''. The taxonomy of ...

phones are widely capable of VoIP performance. Besides wireless, they also typically support USB, but not Ethernet or Power over Ethernet interfaces. The smartphone became the dominant VoIP phone because it works both indoors and outdoors, and shifts base stations/protocols easily. It achieves this by accepting higher access costs and call clarity, and other factors personal to the user. The PoE/USB VoIP phone was thus relegated to the role of a transitional device, except in traditional business office, where it is still widely used as a desk phone.

Components and software

A VoIP telephone consist of the hardware and software components. The software requires standard networking components such as a

TCP/IP The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...

network stack, client implementation for

DHCP The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on Internet Protocol (IP) networks for automatically assigning IP addresses and other communication parameters to devices connected to the network using a cli ...

, and the

Domain Name System The Domain Name System (DNS) is a hierarchical and distributed naming system for computers, services, and other resources in the Internet or other Internet Protocol (IP) networks. It associates various information with domain names assigned t ...

(DNS). In addition, a VoIP signalling protocol stack, such as for the Session Initiation Protocol (SIP), H.323,

(Cisco), and/or

, is needed. For media streams, the

Real-time Transport Protocol The Real-time Transport Protocol (RTP) is a network protocol for delivering audio and video over IP networks. RTP is used in communication and entertainment systems that involve streaming media, such as telephony, video teleconference applicati ...

(RTP) is used in most VoIP systems. For voice and media encoding, a variety of codecs are available, such as for audio:

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 ...

GSM The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such ...

iLBC Internet Low Bitrate Codec (iLBC) is a royalty-free narrowband speech audio coding format and an open-source reference implementation (codec), developed by Global IP Solutions (GIPS) formerly Global IP Sound (acquired by Google Inc in 2011). ...

Speex Speex is an audio compression codec specifically tuned for the reproduction of human speech and also a free software speech codec that may be used on VoIP applications and podcasts. It is based on the CELP speech coding algorithm.Xiph.OrIntro ...

G.729 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 ...

G.722 G.722 is an ITU-T standard 7 kHz wideband audio codec operating at 48, 56 and 64 kbit/s. It was approved by ITU-T in November 1988. Technology of the codec is based on sub-band ADPCM (SB-ADPCM). The corresponding narrow-band codec based on ...

, G.722.2 (AMR-WB), other audio codecs, and for video H.263, H.263+,

H.264 Advanced Video Coding (AVC), also referred to as H.264 or MPEG-4 Part 10, is a video compression standard based on block-oriented, motion-compensated coding. It is by far the most commonly used format for the recording, compression, and distr ...

. User interface software controls the operation of the hardware components, and may respond to user actions with messages to a display screen.

STUN client

To enable the VoIP communications, the SIP/RTP packets should be utilised and STUN client would be the key component for VoIP communications with management of the SIP/RTP packets. A

Session Traversal Utilities for NAT STUN (Session Traversal Utilities for NAT; originally Simple Traversal of User Datagram Protocol (UDP) through Network Address Translators) is a standardized set of methods, including a network protocol, for traversal of network address transl ...

(STUN) client is used on some SIP-based VoIP phones as firewalls on network interface sometimes block SIP/RTP packets. Some special mechanism is required in this case to enable routing of SIP packets from one network to other. STUN is used in some of the sip phones to enable the SIP/RTP packets to cross boundaries of two different IP networks. A packet becomes unroutable between two sip elements if one of the networks uses private IP address range and other is in public IP address range. Stun is a mechanism to enable this border traversal. There are alternate mechanisms for traversal of NAT, STUN is just one of them. STUN or any other NAT traversal mechanism is not required when the two SIP phones connecting are routable from each other and no firewall exists in between.

DHCP client

DHCP client software simplifies connection of a device to an IP network. The software automatically configures the network and VoIP service parameters.

Hardware

The overall hardware may look like a telephone or mobile phone. A VoIP phone has the following hardware components *An handset with a headphone and a

microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public ...

, unless the whole telephone is a hand-held device containing these *A

loudspeaker A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or " ...

to act as a speakerphone *

Keypad A keypad is a block or pad of buttons set with an arrangement of digits, symbols, or alphabetical letters. Pads mostly containing numbers and used with computers are numeric keypads. Keypads are found on devices which require mainly numeric in ...

touchpad A touchpad or trackpad is a pointing device featuring a tactile sensor, a specialized surface that can translate the motion and position of a user's fingers to a relative position on the operating system that is made output to the screen. Touchp ...

to enter phone number and text *

Display Display may refer to: Technology * Display device, output device for presenting information, including: ** Cathode ray tube, video display that provides a quality picture, but can be very heavy and deep ** Electronic visual display, output devi ...

hardware to feedback user input and show caller-id/messages * General-purpose microprocessor (GPP) to control the device *A

voice engine A voice engine is a software subsystem for bidirectional audio communication, typically used as part of a telecommunications system to simulate a telephone. It functions like a data pump for audio data, specifically voice data. The voice engine ...

or a

digital signal processor A digital signal processor (DSP) is a specialized microprocessor chip, with its architecture optimized for the operational needs of digital signal processing. DSPs are fabricated on MOS integrated circuit chips. They are widely used in audio si ...

(DSP) to process RTP messages. Some IC manufacturers provides GPP and DSP in single

chip Chromatin immunoprecipitation (ChIP) is a type of immunoprecipitation experimental technique used to investigate the interaction between proteins and DNA in the cell. It aims to determine whether specific proteins are associated with specific genom ...

* AD and DA converters: To convert voice to digital data and vice versa *

Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...

wireless network A wireless network is a computer network that uses wireless data connections between network nodes. Wireless networking is a method by which homes, telecommunications networks and business installations avoid the costly process of introducing ...

hardware to send and receive messages on

data network A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...

*Power source - a battery or DC/AC source; some VoIP phones receive electricity from

Power over Ethernet Power over Ethernet, or PoE, describes any of several Technical standard, standards or ad hoc systems that pass electric power along with data on Ethernet over twisted pair, twisted-pair Ethernet cabling. This allows a single cable to provide ...

*Some VoIP phones include an RJ-11 port to connect the phone to the

PSTN The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local teleph ...

Other devices

There are several

Wi-Fi Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio wave ...

enabled

mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link whil ...

s and PDAs that have pre-installed SIP client software, or are capable of running IP telephony clients, including most smartphones.

Analog telephone adapter An analog telephone adapter (ATA) is a device for connecting traditional analog telephones, fax machines, and similar customer-premises devices to a digital telephone system or a voice over IP telephony network. An ATA is often built into a sma ...

s provide an interface for traditional analog telephones to a voice-over-IP network. They connect to the Internet or

local area network A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building. By contrast, a wide area network (WAN) not only covers a larger ...

using an

port and have jacks that provide a standard RJ11 interface that can accommodate a standard analog telephone. Another type of gateway device acts as a simple cellular base station. Regular

s can connect to this device, and make VoIP calls. While a license is required to run a cellular base station in most countries, these can be useful on

ship A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research, and fishing. Ships are generally distinguished ...

s, or in remote areas where a low-powered gateway transmitting on unused frequencies is likely to go unnoticed. Some VoIP phones and ATAs also support PSTN phone lines directly.

Common functionality and features

Caller ID Caller identification (Caller ID) is a telephone service, available in analog and digital telephone systems, including voice over IP (VoIP), that transmits a caller's telephone number to the called party's telephone equipment when the call i ...

display * Call transfer and call hold * Dialing using name/ID (differs from

speed dial Speed dial is a function available on many telephone systems allowing the user to place a call by pressing a reduced number of keys. This function is particularly useful for phone users who dial certain numbers on a regular basis. In most case ...

in that no number is stored on the client) * Locally stored and network-based directories *

Conference calling A conference call is a telephone call in which someone talks to several people at the same time. The conference call may be designed to allow the called party to participate during the call or set up so that the called party merely listens into ...

and multiparty calls * Call park * Call blocking feature. * Support for multiple VoIP accounts – the phone may register with more than one VoIP server/provider. ** Accounts are usually set and memorized on the phone itself. A more sophisticated feature is dynamic download of account settings, also known as " extension mobility". This feature allows settings stored on a server to be downloaded to the phone, based on user login. The user logs into the phone and that phone becomes the user's extension. This feature requires both a client (phone) and a server, usually in the context of unifVoIP — Vulnerability over Internet Protocol
/ref> ied communications systems. * Secure encrypted communications

References

{{Authority control Phone Network appliances