Pin Me

Introduction To VoIP - An Overview Of VoIP Technology And Its History

written by: George Garza•edited by: Lamar Stonecypher•updated: 5/19/2011

One of the newest ways to transmit phone calls is to use the Internet. A technology known as Voice over Internet Protocol (VoIP) makes this possible. It is a family of transmission protocols that will deliver voice communications over IP networks, with the most common being the Internet.

  • slide 1 of 5

    An Introduction to VoIP - What is it

    VoIP is a form of digital telecommunication that takes place over the Internet. Early forms of communication were based on analog systems where frequencies were sent over distances and retransmitted again and again until they reached their destination. These were analog systems because they were "smooth" from source to destination. An example of an analog signal would be to take an elevator to go up to the next floor; it is a smooth transition. A digital signal, otherwise known as discrete, would be likened to taking the steps in a staircase to go to the next floor.

    The newer systems are digital. Digital transmissions take a signal and break it down into millions of packets for delivery. Each packet looks the same on the outside, but the data content in each one makes them different. The reason that digital transmissions are preferred over analog is that outside interference is minimized and the signal is steady and direct without fading or dropping.

    In VoIP, you are going to take an analog signal and turn it into a digital signal at the sending side, then turn the digital signal to an analog signal at the receiving side.

  • slide 2 of 5

    An Overview of VoIP

    Because the signals are transported over the Internet, VoIP systems employ different session control protocols that will govern the set-up and tear-down of calls. There are also audio codecs, which encode speech, allowing the transmission over an IP network as digital audio through an audio stream. A codec is a set of technology specifications for audio or video that are applied to a hardware device to allow it to interact with other devices.

    Some VoIP implementations rely on a feature called transmission narrowband. This is a way of controlling the signal by coherence to make it more uniform and compressed speech so that packets does not go over certain restrictions or limitations. This will affect voice quality. But other codecs support high fidelity stereo, so the voice quality will be different.

  • slide 3 of 5

    VoIP Technology

    The first technology challenge that had to be addressed was how to deal with the transmission of voice. The VoIP protocol specifies how the transmission and reception of audio occurs over the Internet. The critical connection between the call sender and the call recipient is established using the Session Initiation Protocol (SIP). This protocol has many functions, but the most important include negotiating the codecs used to make the call, how to transfer calls, and how to terminate a call.


    During a phone call, VoIP phones communicate directly over an IP and stream audio directly. But the problem is that analog phones and cellular phones cannot use SIP or peer-to-peer calling. So VoIP deployments use the Internet Protocol / Private Branch Exchange (IP PBX) service, which serves as a bridge between a phone using an IP-based calling function, and the Public Switched Telephone Network (PSTN) that is the regular public phone system.

    Here analog cell phones and regular phones can connect to the PSTN but VoIP phones cannot. So to make the call possible, routing the audio from a VoIP phone occurs through an IP PBX and then to the PSTN. This allows a VoIP phone to make a call to either an analog or cellular phone.

    VoIP How It Works 

    Image Credit: Dynaplex

  • slide 4 of 5

    History of VoIP

    Back in 1995 a small technology company, Vocaltec, released the first internet phone software. It was designed to run on a home PC, and it utilized sound cards, microphones and speakers much like the PC phones used today. "Internet Phone" was the name of the product, and it operated using the older H.323 protocol instead of SIP (Session Inititation Protocol), which is more commonly used today.

    The Company had some initial success with Internet Phone, and it even launched a successful IPO in 1996. But the lack of broadband availability in 1995 was a major drawback. Many people were using dial-up, not cable or DSL. Because of this, the software used modems, and this resulted in poor voice quality compared to a regular telephone call. However, it represented a milestone as the first IP Phone.

    Even though by 1998, VoIP traffic had grown to represent only 1% of all voice traffic in the United States, network engineers and companies saw a lot of potential. Networking manufacturers like Cisco and Lucent began to produce networking equipment that could route and switch the VoIP traffic. By 2000, VoIP traffic had grown to more than 3% of all voice traffic.

    By 2005, major voice quality issues had been addressed and resolved, and VoIP traffic could be prioritized over data traffic. This lead to reliable, clear sounding, and unbroken telephone calls. Revenue from VoIP equipment sales alone reached nearly $3 billion and over $8.5 billion by the end of 2008.

  • slide 5 of 5


    Communication technology continued to change throughout the '90s. The newest technology was VoIP (Voice over IP). The IP was the Internet Protocol used by computers to send information over the Internet. Now phones could do so as well. Because it was a low cost technology, and it used the existing Internet framework, individuals and businesses could save money by switching to this technology. It avoided some of the problems inherent in analog telephone service, like dropped calls or crosstalk. VoIP is resilient and it can be used with mobile or analog phones.

    For more on VoIP see Popular VoIP Phones