Internet Telephony Gateways
IP (Internet Protocol) telephony is a technology that sends audio, using the Internet, between two or more computer users in real time, so they can converse. In early 1995 a company called VocalTec introduced the first IP telephony software product. The VocalTec Internet Phone (and the several other similar) lets users speak into their microphone and listen via their speakers on a a multimedia computer.
In less than a year after its development, IP telephony technology caught the world's attention. The technology has improved to a point where conversations are easily possible. And it continues to develop. Many companies have now introduced IP Telephony products, and many major telecommunications companies have launched research to better understand this new threat to their markets.
The original Internet telephone products based on multimedia PCs are tremendous -- offering the ability to combine voice and data on one network. They also offer low-cost long distance "telephone" service, that is, if the user already has a multimedia PC and a fixed-rate Internet service provider [ISP] account. This service can be limited though, so more work was needed.
In March of 1996, VocalTec announced it was teaming up with Dialogic to develop the first IP telephony gateway. Gateways are now bringing IP telephony into the mainstream. They bridge the traditional circuit-switched telephony world with the Internet, and therefore, they offer the advantages of IP telephony to the standard telephone, the most common, cheapest, most mobile, and easiest-to-use terminal in the world. Gateways also overcome the significant IP telephony problem of addressing. With a gateway product, instead of needing to know the user's Internet Protocol (IP) address, you only need to know their phone number.
The Way It Works
The basic concept of Internet telephone gateways is that on one side, the gateway connects to the telephone world, and it can communicate with any
phone in the world. A phone line plugs into the gateway on this end. On the other side, the gateway connects to the Internet world, and it can communicate with any computer in the world. A computer network plugs into the gateway on that end.
The gateway digitizes the standard telephone signal, if it is not already digital, compresses it, makes a packet out it for the Internet using Internet Protocol (IP), and sends it to a destination over the Internet. The gateway does the reverse operation when packets come in from the network, and it sends them out the phone. Both operations are happening at the same time, which allows a full-duplex or two-way conversation.
Various configurations can be built from this basic operation. Phone-to-Computer, or Computer-to-phone operation can take place with one gateway. Phone-to-phone Computer operation can occur with two gateways. An organization or service provider can offer international long distance service, using gateways, by hosting one gateway in each country. The configuration costs significantly less than traditional circuit-switched service because it bypasses the international connect charges even if in-country long distance charges are paid.
Quality of Transmission
The quality of the transmission is affected by voice quality and turnaround time, or latency.
Voice quality has improved considerably from earlier versions of this technology. As the voice coding and lost packet reconstruction technologies improve, they are yielding products which allow speech to be more easily understood.
Latency affects the pace of the conversation. Today's IP telephony products exceed the latency tolerance of about 250 milliseconds, so most calls sound like traditional ones routed over a satellite circuit (which are usable, but require some getting used to). Many of the current products are well suited to a number of applications. The latency will continue to improve, driven by the fact that gateways will improve, that they will be deployed on private circuits, which allows some control of the bandwidth utilization, and therefore the latency, and the Internet is being and will continue to be upgraded to accomodate more of these and other services.
The information on this page came from a page called IP Telephony Basics, which is on the Dialogic website. Please see that page for a more complete discussion of this topic.Home Internet Telephony Gateways Internet Phone
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