Here’s an extremely detailed primer on VoIP, with special attention paid to Linux VoIP implementations:
What is Voice over IP really? What do you need for Voice over IP? What do you mean, I can’t call my girlfriend? What’s all that buzz about open and proprietary protocols? Can I start my own telecom service? This article addresses these questions and compares the most popular Linux applications for calling and conferencing.
Read the full story from Linux Journal.
Here’s a good article from the NY Times, especially for beginners, on using VoIP service to save money when calling from abroad:
While internationally capable cell phones make calling home from abroad convenient, they’re not always the most economical choice.
For travelers looking for inexpensive alternatives, there are several options: new Internet-based voice services, callback services and one of the most low-tech–and low-cost–options: prepaid calling cards.
Internet-based services
The big news in calling home cheaply is voice over Internet protocol (VoIP) services like Vonage, which is based in Holmdel, N.J., or Skype, a company based in Luxembourg that was recently purchased by eBay.
Since VoIP services generally work best with a broadband or wireless Internet connection, they are recommended for travelers who want to make calls from fixed locations, such as their hotel rooms or a conference room–although they can also be used from Internet cafes, or wireless hot spots if you have a notebook computer. (Some specialized VoIP services or phones like Vonage’s Wi-Fi Utstarcom F1000 phone will only work at ‘open’ hot spots that do not require a user name or credit card.)
VoIP works by digitizing your voice and sending it via the Internet to the other caller, who hears it on his PC’s speakers, or by routing it through regular telephone lines to anyone’s standard phone line.
"VoIP is great if you know you’ll be close to high-speed data lines," says David Rowell, founder of the Travel Insider, a Web site and online newsletter that focuses on travel and travel-related technologies. But, Rowell adds, "it’s problematic if you’re on dial-up," in part because of insufficient bandwidth and speed, which may result in voice distortions.
This article from the Long Beach Press-Telegram provides a simple explanation of VoIP for our less experienced visitors, though some of the details could have been better researched (for example, VoIP service providers charge as little as $15 per month, not $30 as the article claims):
Haven’t heard about VoIP? You will
Voice Over Internet Protocol revolutionizes the phone call.
By Don Jergler
Staff writer
LONG BEACH — Say you own a call center in the Philippines, and you’re looking for a way to cut down on the cost of the 300,000 or so phone calls your employees make daily to the United States.
The solution: have each call converted into a digital format and sent over the World Wide Web. Once in the United States, the calls can be converted back to a standard format and heard on the other end of the line.
Your costs are cut in half because the transmission of data via the Internet is cheaper. And it’s nearly instantaneous, no matter the distance.
Voice Over Internet protocol, or VoIP for short, is making phone calls cheaper. With VoIP, a person can make a call from anywhere with broadband. Because the information is broadcast over the Internet, calls can be administered by the provider anywhere there is a connection.
Similar to cell phone pricing plans, many VoIP companies offer plans for as little as $30 a month.
The buzz about VoIP is growing louder.
Type the abbreviation into Google and up comes dramatic headlines: * "VoIP Market To Hit $4 Billion By 2010: Report’
* "Residential VoIP markets to see revenue rise’
* "Cable TV (system operators) Seek To Offer VoIP Service’
Full Story
by Jim Sherman
Session Initiation Protocol (SIP) is a signaling protocol for establishing sessions in an IP network. But if you are like most of us, that means nothing to you. In layman’s terms, SIP is a method by which various computers can talk to one another so that they can complete voice calls. The protocol is increasingly being adopted as the standard means by which computers communicate to facilitate VoIP or Voice Over Internet Protocol. So you can imagine SIP as a common language for new generation operators to speak to connect calls. However, there are no operators there is only your computer (or other hardware) and that of the person you are speaking with. That brings this introduction to some of the many benefits of SIP communication.
The goal of SIP was to provide users with many of the functions and features they typically expect with making phone calls, such as familiar rings, hearing the ring back tone when a call is placed, and the process of dialing a number. SIP goes beyond this however, also implementing a number of advanced features. Despite its’ convenient interface that mirrors that of a typical telephone call, SIP is based on an internet protocol rather than that of the telephone industry. Because of this, SIP is able to work seamlessly alongside other internet based protocols. This has allowed the technology to uniquely establish a user location, meaning that you can tell the IP address or "location" from which a person is making a call, something vital for offering emergency services. It also allows for coordination amongst the various participants in deciding upon what call features will be supported, as well as providing the protocol for call management which allows for adding, dropping, or transferring call participants.
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VoIP is an acronym for Voice Over Internet Protocol (IP).
What does that mean? VoIP is a way of using your high speed Internet connection as a telephone. Rather than using the wires your telephone company has run into your house to make and receive phone calls, a VoIP service provider will provide you with equipment to make those phone calls - in the same way - over your Internet connection.
Why would someone want this? There are two primary benefits of VoIP service. First, it tends to be cheaper than traditional "landline" telephone service, for both domestic and international calling.
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