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VoIP 101 - Page 1 of 2
Posted: September 07, 2005
Author: Jason Kohrs
Manufacturer: N/A
Source: Geeks.com Tech Tips
More Information: Nortel VoIP
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At this point most people have probably heard of VoIP, and many may have used it, but they may not fully understand the basics of this rapidly expanding technology. This Tech Tip will take a look at some of the basic features, modes of operation, and other background information on one of the latest ways technology can be used to connect people.


The acronym VoIP stands for Voice over Internet Protocol, and the basic concept of the term can be fairly well understood by just looking at the words that make up the acronym. For a more complete definition, VoIP can be described as a means of converting analog audio signals (your voice) into digital data that can be transferred over the Internet.

Getting Setup:

When many people think of VoIP they instantly think of services like Vonage or Packet8 that are in business to become your full feature telephony solution. Although these companies do offer VoIP services, the term can be used to describe something much simpler.

Taking a look at the basic definition again we can see that we only need to be able to capture the audio and transmit it digitally in order to have VoIP. This can be done without subscribing to a service and without a specialized telephone or other equipment. Basic VoIP can be accomplished by an internet connected PC with a soundcard sporting a microphone and speakers. Keeping that in mind, let’s look at the three basic ways people implement VoIP…

The PC to PC version of VoIP is what was described in the previous paragraph. With a fairly typical computer connected to broadband internet, and some kind of software for managing the communications, anyone can be up and running with a basic version of VoIP that may be totally free. Such software is available as a free download, and Skype is one of the more popular applications in use. Skype allows members to make free PC to PC calls, regardless of distance, and for an extra fee they can send/receive calls from standard telephones. As mentioned, you only need a PC with a soundcard, a microphone, and a decent set of speakers, but there are also specialized USB VoIP telephones that make it even more convenient. Using a USB VoIP phone not only makes the communication seem a bit more traditional, but it also frees up the soundcard for typical audio applications (MP3s, games, etc), while the phones circuitry handles all audio processing for phone calls.

Using an ATA, or Analog Telephone Adaptor, may be the most common form of VoIP in use today. With an ATA, a standard telephone can be plugged into the adapter just as you would plug it into a phone jack in the wall. The ATA is then connected to your network, or directly to your broadband internet gateway, in order to convert the analog audio into digital data for transmission over the internet. Vonage and other similar services use ATAs to implement VoIP, as it is a simple approach for people with existing phone equipment that they would like to continue using. In addition, it can allow for a home pre-wired for multiple phone jacks to continue operating as is, with the only new piece of hardware required being the ATA.

IP phones are another way to implement VoIP. An IP Phone may appear to be much like your standard telephone, with the only physical difference being that the (RJ-11) phone jack has been replaced by an (RJ-45) Ethernet connector. Internally there will be some differences in the circuitry in order to allow the conversion from analog to digital to happen right in the phone. An IP phone is then connected directly to your network or broadband internet gateway, with no adaptor required. Packet8 is one service that offers IP phones to their customers, in addition to the more typical ATA VoIP service. The downside to IP phones is that the implementation requires all new telephones designed solely for use with VoIP. Any existing analog equipment can not be used.

VoIP Protocols:

Just as with most other means of communicating data over the Internet, there are a few VOIP protocols that have been developed by various groups and companies. Some of the current protocols include SIP, IAX, H.323, MEGACO, and MGCP. Let’s look at some details of the first three, as they may be the ones you are most likely to encounter.

SIP, or Session Initiation Protocol, is the most commonly used VoIP protocol and was developed by the Internet Engineering Task Force (IETF). One issue with SIP is that it is not particularly NAT (Network Address Translation) friendly. NAT is what allows a local area network to manage one set of IP addresses for internal communications, and a second set of IP addresses for external communications.

IAX, or Inter-Asterisk eXchange, is another VoIP protocol that is used with free Asterisk software for managing a PBX (Private Branch eXchange). IAX (or more recently IAX2) deals better with NAT than SIP, but its implementation is limited to Asterisk servers only. A PBX is private phone network used within an organization that can connect all internal lines to each other, as well as using a central access point for connecting to any outside line.

H.323 was originally developed by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) for use with multimedia conferencing over local area networks (LANs), and was later applied to VoIP applications. This is an older protocol that isn’t commonly used.

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