IP telephony


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IP Telephony

(communications)
(IPT, Internet Telephony) Use of IP data connections to exchange voice and fax data that have traditionally been carried over the public switched telephone network.

During the late 1990s, an increasing number of telephone calls have been routed over the Internet. Calls made in this way avoid PSTN charges. Unlike traditional telephony, IP telephony is relatively unregulated.

Companies providing these services are known as Internet Telephony Service Providers (ITSPs). They include telephone companies, cable TV companies and Internet Service Providers (ISPs).

There are still many problems with voice quality, latency, compression algorithms, and quality of service.

Voice over IP is an organised effort to standardise IP telephony.

See also Computer Telephone Integration.

Internet Telephony Overview.
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IP telephony

The two-way transmission of voice over a packet-switched IP network, which is part of the TCP/IP protocol suite. The terms "IP telephony" and "voice over IP" (VoIP) are synonymous. However, the term VoIP is widely used for the actual services offered (see VoIP for details), while IP telephony often refers to the technology behind it. In addition, IP telephony is an umbrella term for all real-time applications over IP, including voice over instant messaging (IM) and videoconferencing. See TCP/IP.

Starting in the late 1990s, the Internet and its TCP/IP protocol suite began to turn the data communications and telephone industry upside down. IP became the universal transport for data and video communications worldwide, and it is increasingly becoming the infrastructure for voice traffic as well. Today, every communications carrier has built or is using an IP backbone for some or all of its voice services. In addition, large enterprises are either already using IP for some amount of internal voice traffic or have plans to do so.

Data Over Voice Became Voice Over Data
Starting in the 1960s, data was transmitted over analog telephone networks, and by the late 1980s, data routinely traveled over digital voice circuits. By the 1990s, the majority of worldwide communications traffic had changed from voice to data, and as IP networks began to flourish, the economics of using IP for voice began to emerge.

Although the backbone of the global telephone network had been converted to digital for some time, the circuit-switched nature of the public switched telephone network (PSTN) is wasteful. Even though one person talks and the other listens, both "to" and "from" channels are always dedicated. In addition, newer voice codecs cut the digital requirement from the traditional 64 Kbps (PCM) down to 8 Kbps with respectable quality. Thus, the bandwidth requirement for voice on an IP network is 1/16th that of the PSTN's dedicated, digital circuits.

Varying Quality
Starting in the mid-1990s, advertiser-supported, free telephone service from PC to PC or between phones and PCs using the Internet became popular, especially for international calls. Call quality over the Internet can be erratic because the Internet provides no guarantee of quality of service (QoS). However, when an organization has control over its network, quality can be excellent. Private enterprises with their own IP networks, as well as major telcos and IP telephony carriers that have developed IP backbones, can provide voice quality that competes with the traditional PSTN.

Transport and Signaling
IP telephony uses two protocols: one for transport and another for signaling. Transport is provided by UDP over IP for voice packets and either UDP or TCP over IP for signals. Signaling commands that establish and terminate the call as well as provide special features such as call forwarding, call waiting and conference calling are defined in a signaling protocol such as SIP, H.323, MGCP or MEGACO (see IP telephony signaling protocol).

The integration of packet-switched IP with the traditional SS7-based telephone system was a complex undertaking with numerous protocols competing for attention. See ITXC and IP on Everything.


Integrating IP Telephony with the PSTN
This shows the interaction between the traditional telco system and IP carriers, which are often one and the same. Note the difference between voice packets (blue lines) and signaling (red lines). (Illustration assistance courtesy of GNP Computers and Pulver.com.)







Not Quite IP Telephony
We can be certain that they didn't have the IP protocol in mind when they set up this telephone switchboard in 1882. It was used to switch phone calls between all the lawyers in Richmond, Virginia. (Image courtesy of AT&T.)
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References in periodicals archive ?
FIRST AMENDMENT REGULATORY DIVERGENCE AND IP TELEPHONY
As a contributing author of the PacketCable IP Telephony Specification, Broadcom has incorporated this on-going work into its reference design.
Eventually, competition between IP telephony services will drive the price of the long-distance phone call down to 5 cents per minute, says McKnight.
"The new IP telephony infrastructure has given the bank its fastest-ever return on investment for an IT/telecoms deployment, which is important at a time when the financial services industry is making every effort to maximize its technology spend.
"In winning one of the largest managed IP telephony deployments ever, France Telecom and Equant now assume a leadership position in the global IP communications services market," added Charles Dehelly, CEO, Equant.
The 3Com VCX IP Telephony module was first introduced in 2003 for large enterprises.
* Research organization IDC estimates that IP communications are significantly hitting the mainstream market, with 14 percent of medium and large organizations having IP telephony equipment and software already implemented.
The integrated company will make use of Fusion's optical fiber-based IP telephony network and subscribers to each telecommunications company will be able to communicate free of charge with those located in other regions, starting April 1, the officials said.
"Verizon and Alcatel clearly demonstrated the ability to provide the level of support required to undertake an IP telephony deployment of this magnitude, and Alcatel's dual IP/TDM architecture gives us the flexibility to deploy a combination of digital and IP handsets throughout all district facilities."
IP telephony carries voice, video, facsimile and data over a network using IP, the same protocol used on the Internet.
The IPLink 2.0 platform supports up to 150 channels per PC chassis, each able to negotiate the G.723.1, G.711, or GSM voice coders, offering unmatched scalability and flexibility for high value IP telephony offerings.