Voice over IP

Voice over IP

From Wikipedia, the free encyclopedia

Voice-over-Internet protocol (VoIP) is a methodology and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. Other terms commonly associated with VoIP are IP telephony, Internet telephony, voice over broadband (VoBB), broadband telephony, IP communications, and broadband phone service.

The term Internet telephony specifically refers to the provisioning of communications services (voice, fax, SMS, voice-messaging) over the public Internet, rather than via the public switched telephone network (PSTN). The steps and principles involved in originating VoIP telephone calls are similar to traditional digital telephony and involve signaling, channel setup, digitization of the analog voice signals, and encoding. Instead of being transmitted over a circuit-switched network, however, the digital information is packetized, and transmission occurs as Internet Protocol (IP) packets over a packet-switched network. Such transmission entails careful considerations about resource management different from time-division multiplexing (TDM) networks.

Early providers of voice-over-IP services offered business models and technical solutions that mirrored the architecture of the legacy telephone network. Second-generation providers, such as Skype, have built closed networks for private user bases, offering the benefit of free calls and convenience while potentially charging for access to other communication networks, such as the PSTN. This has limited the freedom of users to mix-and-match third-party hardware and software. Third-generation providers, such as Google Talk, have adopted[1] the concept of federated VoIP—which is a departure from the architecture of the legacy networks. These solutions typically allow dynamic interconnection between users on any two domains on the Internet when a user wishes to place a call.

VoIP systems employ session control and signaling protocols to control the signaling, set-up, and tear-down of calls. They transport audio streams over IP networks using special media delivery protocols that encode voice, audio, video with audio codecs, and video codecs as Digital audio by streaming media. Various codecs exist that optimize the media stream based on application requirements and network bandwidth; some implementations rely on narrowband and compressed speech, while others support high fidelity stereo codecs. Some popular codecs include μ-law and a-law versions of G.711, G.722, which is a high-fidelity codec marketed as HD Voice by Polycom, a popular open source voice codec known as iLBC, a codec that only uses 8 kbit/s each way called G.729, and many others.

VoIP is available on many smartphones, personal computers, and on Internet access devices. Calls and SMS text messages may be sent over 3G or Wi-Fi.[2]

Contents [hide]

1 Pronunciation

2 Protocols

3 Adoption

3.1 Consumer market

3.2 PSTN and mobile network providers

3.3 Corporate use

4 Quality of service

4.1 Layer 2

5 PSTN integration

5.1 Number portability

5.2 Emergency calls

6 Fax support

7 Power requirements

8 Redundancy

9 Security

10 Caller ID

11 Compatibility with traditional analog telephone sets

12 Support for other telephony devices

13 User and administrative interfaces

14 Operational cost

15 Regulatory and legal issues

15.1 European Union

15.2 India

15.3 Middle East

15.4 South Korea

15.5 United States

16 Historical milestones

17 See also

18 References

19 External links

Pronunciation[edit]

The acronym "VoIP" has been pronounced variably since the inception of the term. Apart from spelling out the acronym letter by letter, /viːoʊaɪˈpiː/ (vee-oh-eye-pee), there are three likely possible pronunciations: /voʊaɪˈpiː/ (vo-eye-pee) and /voʊˈip/ (vo-ipp), have been used, but generally, the single syllable /ˈvɔjp/ (voyp, as in voice) may be the most common within the industry.[3]

Protocols[edit]

Voice over IP has been implemented in various ways using both proprietary protocols and protocols based on open standards. Examples of the VoIP protocols are:

H.323

Media Gateway Control Protocol (MGCP)

Session Initiation Protocol (SIP)

H.248 (also known as Media Gateway Control (Megaco))

Real-time Transport Protocol (RTP)

Real-time Transport Control Protocol (RTCP)

Secure Real-time Transport Protocol (SRTP)

Session Description Protocol (SDP)

Inter-Asterisk eXchange (IAX)

Jingle XMPP VoIP extensions

Skype protocol

Teamspeak

The H.323 protocol was one of the first VoIP protocols that found widespread implementation for long-distance traffic, as well as local area network services. However, since the development of newer, less complex protocols such as MGCP and SIP, H.323 deployments are increasingly limited to carrying existing long-haul network traffic. In particular, the Session Initiation Protocol (SIP) has gained widespread VoIP market penetration.

These protocols can be used by special-purpose software, such as Jitsi, or integrated into a web page (web-based VoIP), like Google Talk.

Adoption[edit]

Consumer market[edit]

Example of residential network including VoIP

A major development that started in 2004 was the introduction of mass-market VoIP services that utilize existing broadband Internet access, by which subscribers place and receive telephone calls in much the same manner as they would via the public switched telephone network (PSTN). Full-service VoIP phone companies provide inbound and outbound service with direct inbound dialing. Many offer unlimited domestic calling for a flat monthly subscription fee. This sometimes includes international calls to certain countries. Phone calls between subscribers of the same provider are usually free when flat-fee service is not available. A VoIP phone is necessary to connect to a VoIP service provider. This can be implemented in several ways:

Dedicated VoIP phones connect directly to the IP network using technologies such as wired Ethernet or Wi-Fi. They are typically designed in the style of traditional digital business telephones.

An analog telephone adapter is a device that connects to the network and implements the electronics and firmware to operate a conventional analog telephone attached through a modular phone jack. Some residential Internet gateways

...