What is Voice Over IP?

GMartin used Ask the Experts™
Hello and Good Morning Everyone,

          I recently added another phone line to my AT&T setup.  The hardware hookups are as follows:  The telephone/copier/fax machine has a direct telephone line connection to the back of the AT&T Gateway at the port labeled Phone Lines 1 & 2.  Then, I have another telephone line running from the Ext port of the  telephone/copier/fax machine  to the chordless phone.  That said, an AT&T agent explained to me that the  telephone/copier/fax machine with the direct connection to the Gateway will get the new activated number and the other phone, chordless one, will retain the old VoIP number.   Given this information, could someone explain what is meant by VoIP or Voice Over IP?  I did not want to bog down my AT&T agent with too many questions.  So, I decided to submit this one for review here.

            Any shared thoughts and explanations in simple terms with respect to the definition and function of VoIP will be greatly appreciated.

            Thank you

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Software Developer / Linux System Administrator / Managing Director
VOIP, Voice Over Internet Protocol is a means of making phone calls on the Internet. You will commonly hear the term SIP mentioned at the same time, which is related to establishing calls and signalling that a line is ringing, for example. Most public telephone networks are moving over to VOIP as a means of connecting their internal networks and ultimately your phone line will also use it, in due course. There are many providers of VOIP services and generally the cost is lower than making calls on the usual public telephone networks.

Often, if you make a call that starts with a VOIP service and terminates with another VOIP service, the call itself is free of charge. This will depend on the provider, naturally.
I'd modify Martyn's answer slightly.  VoIP is a method of putting voice calls on TCP/IP, not necessarily (though commonly) on the internet.  I've seen uses where VoIP is used internally but connects to a phone controller that gets phone service through a non-VoIP connection (POTs or some other line).
Martyn SpencerSoftware Developer / Linux System Administrator / Managing Director

Thanks for the clarification CompProbSolve. I was deliberately using a term that most people would understand rather than making specific mention of TCP/IP, UDP etc.
nociSoftware Engineer
Distinguished Expert 2018

Other protocol besides SIP can be used for signaling (H.323,  Jingle (XMPP), XMPP, MGCP, SKINNY, ) and besides Signalling also RTP (and possible variants) is used to transport the MEDIA (voice, video...).


Hello and Good Evening Everyone,

          Thank you so much for taking the time to address my question.  While I certainly appreciated everyone's feedback, I have to go with Martyn's input because of its simplicity and clarification of technical terms.  

           Thanks again :-)


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