VoIP is a term that gets bandied about quite frequently, but such liberal use of the term has distorted its meaning. Like when you studied for the SAT and the verbal section focused on fine shades of difference between words, so too is the case with Internet Protocol Telephony (IPT).
Really, IPT is an umbrella term that includes both Internet telephony and VoIP. The second edition of Telecommunications Essentials by Lillian Goleniewski provides definitions for each of these:
IPT, broadly speaking, is the transmission of voice, fax, and related services over packet-switched IP-based networks.
Internet Telephony is a form of IPT where the principal transmission network is the public Internet.
VoIP is another form of IPT in which the principal transmission network or networks are private, managed IP-based networks.
System Structure, or What Components Make up VoIP?
Going down the VoIP rabbit hole means that things can get complicated things quickly.
The VoIP network is actually modeled on the PSTN network, but several different pieces of hardware and software exist to make the packet-switching possible.
These constitute the actual handsets, or similar, used to make a phone call. Legacy phones can connect to a VoIP network with an adapter. Other calling options include an IP phones look like regular phones, but they connect to the network using an Ethernet jack rather than a telephone jack. Computers that have the right software and hardware accessories (microphone, speakers, soundcard, headset, etc.) can also be used to make VoIP phone calls.
ìGateways provide seamless interoperability between circuit-switching and packet-switching network domains.î In other words, the media gateway connects the IP network to the PSTN and allows those two networks to talk to each other. Gateways also handle IP signaling functions and support Local Exchange and Toll switches on the PSTN. On top of all that, gateways can handle a wide variety of traffic types: data, voice, fax, multi-media, etc.
The function of the softswitch is to ìcontrol the voice or data traffic path by signaling between media gateways that transport the traffic.î Softswitches use established protocols and specifications to ensure ìthat a callís or connectionís underlying signaling information gets communicated between gateways.î This information includes things like caller ID, billing info, and other call triggers. Whereas a media gateway is an actual piece of hardware, a softswitch is software, and can be incorporated into a media gateway.
How does a VoIP call work?
Well that depends on whether the called party is on an analog phone or another IP device. There are many different VoIP providers that facilitate VoIP calls.
If youíre calling another IP device the call doesnít need to connect to the PSTN. A caller dials the number and the call is passed from the device to a router. The router passes the call to the internet where it reaches one of the VoIP providerís servers. From there the call gets passed along local internet lines on the other end to the recipientís router and then to their IP device.
The process for calling an analog phone is exactly the same except with one altered step. After the call leaves providerís servers, it goes through a media gateway that translates everything from digital to analog and passes the call to the local PSTN. The call is then carried along the local PSTN as an analog signal to the correct subscriber line.
VoIP has useful applications for everyone from individual subscribers to large enterprises. The future is bright for VoIP as the number of applications and its technological capabilities continue to increase. Session Initiation Protocol (SIP) has emerged as a technology that complements VoIP quite well. Stay tuned for more information on SIP.
Are VoIP calls free?
Now that you know, in broad strokes, how VoIP works, itís worth re-visiting the distinction between VoIP and Internet telephony. The conflation of these two types of IPT has created a belief that VoIP is free. Well that couldnít be further from the truth.
Remember, VoIP relies on private, managed networks. This means that a company leases internet lines directly from a bandwidth provider, which results in better quality of service (Note: an intranet is another type of private network). There are plenty of different VoIP companies, but one that many people are likely familiar with is Vonage. While these providers may offer less expensive options than a traditional phone company, their services certainly arenít free.
On the other hand, internet telephony operates over the public internet. This is the province of ìover-the-topî (OTT) services like Skype, Google Voice, and Appleís Facetime. OTT refers to any service that is delivered using your Internet Service Providerís (ISP) network, but isnít provided directly by the ISP. For example, On-Demand movies that you access through your cable box are not OTT, but Netflix and Skype are.
You may not pay directly to make calls with Skype or Facetime, but because those services work on the public internet they are more susceptible to lag, dropouts, and other errors.