What You Need to Know About VOIP

By: Chuck Parrish

VOIP (Voice Over Internet Protocol) is the main technology behind Internet Telephones. VOIP, just as the name implies, is a technology that allows voice conversations to be conducted over an IP network. This IP network could be a small company network, a wide-area network or the internet itself. For our purposes, an Internet telephone is the use of VOIP technology to carry voice conversations over the internet.

The Protocol

VOIP is actually a group of protocols that are optimized for establishing a P2P (peer-to-peer or PC to PC) session. Establishing a P2P session allows for a continuous stream of data to be carried over the internet. Voice signals require this type of session because of their continuous nature. There are several VOIP protocols being used by different providers and software developers. SIP (Session Initiation Protocol) and Open Standards Protocol are two that have gained wide acceptance.

The Hardware

There are basically three different types of internet telephones in use. The first is called a PC softphone, and is actually a software application that uses the existing PC sound card, microphone and speakers (or headset) to implement an internet telephone. The second type is a VOIP (or simply IP) handset. This type has more complex hardware and relies on the PC only for processing and routing of the VOIP data. The third type is referred to as an ATA (Analog Telephone Adapter) or simply IP Phone adapter. This is the most complex hardware, and contains a microprocessor that handles all of the necessary VOIP functions to implement an internet telephone. This type does not require the presence of a PC to function but only an active connection to a high-speed internet provider is necessary.

The Software

The software required for each of the three types of internet telephones is also different. PC softphones require the most extensive software applications. They implement a 'virtual telephone' with an on screen telephone keypad and display. PC softphone software must handle the conversion of the analog signals by the PC sound card, the dialing and answering functions and the routing and processing of the VOIP data. The third type of internet telephone, the ATA or IP phone adapter, actually requires no specialized software to function. As mentioned previously, this type of internet telephone equipment does not require the presence of a PC to operate.

The Service Provider

The VOIP service provider is also an important component of an internet telephone system. The service provider handles initiation of the P2P session, associating of phone numbers to IP addresses, and routing of the VOIP data to another PC or to a local PSTN (Public Switched Telephone Network) when a landline or mobile number is involved in the call.

Putting it all together, what happens when I place an internet telephone call using VOIP?

Regardless of the type of hardware and software being used to implement the internet telephone, the process of making a VOIP telephone call is essentially the same. The major differences among the different types of internet telephones is the amount and type of processing being done by hardware as opposed to software.

If you place a call using an ATA or IP phone adapter to a landline number, connected to a regular analog telephone, the process can be simplified as follows: When you dial the number, the ATA converts the analog touch tone signals into digital form. The number information is routed by the ATA to the VOIP service provider, where the number is associated with an IP address and routed to the physical location that you are calling, establishing a connection to the PSTN at that location. This causes the landline phone to ring on the other end.

When the call is answered, the sound of the other persons voice is transmitted via the PSTN to an interface to the VOIP service provider on the internet. This interface translates the analog voice signals from the phone into digital signals that can be handled by the VOIP service provider. The service provider then routes these digital signals back to the ATA on the originating end, where the digital signals are converted back into analog signals that can be understood by the analog telephone. The same process happens in reverse in order to carry the sound of your voice to the landline number.

As you can see, quite a bit happens when you place a call using VOIP. However, internet telephone hardware and software have progressed to the point where most of this is invisible to the user. Placing an internet telephone call is today almost identical to placing a call using a traditional telephone. This ease of use, coupled with the unique advantages of internet telephones, explains the explosive growth in VOIP telephone usage.

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