IP telephony

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IP Telephony

(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.

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.)
References in periodicals archive ?
Within the Asia-Pacific region (excluding Japan), IP telephony will be driven by SMBs in Australia, Singapore, South Korea and New Zealand," says Cindy Sim, Singapore-based analyst at AMI-Partners.
New Version Features Enhanced Reporting and Extended IP Telephony System Data Analysis
VoiceCon(R), now in its 16th year, is the leading conference and exhibition for enterprise voice, IP Telephony and convergence in North America.
With the latest release of ClarusIPC Operations, customers can now proactively prevent security problems caused by incorrect or malicious configurations of the IP telephony security settings.
To support managed service providers (MSPs) with their IP telephony installations SilverBack Technologies announced today that it supports a family of Cisco IP telephony solutions.
Furthermore, the enhanced, robust reporting in Qovia IP Telephony Manager can indicate trends and identify potential problems that IT managers can correct before end-users are affected.
By expanding our IP telephony services, Norlight can now provide all of our customers a solution that meets their varied needs," explained Tom Szews, Norlight's category manager for IP telephony and voice services.
And yet more than half (52%) of these companies have experienced user complaints about the reliability, performance and quality of their IP telephony.
Cisco supports open, standards based architectures and shares a commitment to interoperable solutions with Clarus Systems, who has become an important player in the growing market for IP telephony testing and reporting," said Rick Tywoniak, marketing manager, Cisco IP Communications Business Unit.
The VoiceCon Spring exhibition floor is the only venue to feature all of the leading vendors and suppliers in enterprise IP Telephony and converged communications," said Fred Knight, VoiceCon General Manager.