Voice Over Internet Protocol (VOIP) is a technology that allows voice communications over networks that use internet protocol (IP) such as the internet and similar packet-switched networks.  VOIP is also known by other names such as internet telephony, IP telephony, voice over broadband (VOBB), and broadband telephony. 

In VOIP, basic communications services such as voice, fax, and messaging transmissions are sent via the internet, instead of the conventional route through a public switched telephone network (PSTN). During a VOIP call, the analog voice signal is first converted into a digital signal.  This digital signal is then compressed and translated into IP packets that are then transmitted over the internet. Once the IP packets are received at the other end, they are reconstructed back into an analog voice signal that can be heard by the recipient of the call.

Mass-market VOIP services utilizing broadband networks started to gain a foothold in 2004.  Such VOIP services allow the subscriber to make and receive VOIP calls the way they would over a PSTN system.  Many VOIP service providers in the US offer unlimited calling for a flat monthly fee.

Subscribers commonly access the services offered by VOIP service providers by these three methods:

1) by using an analog telephone adapter (ATA)  which is connected between an ordinary telephone jack and the IP network;

2)  by using computer software (known as a softphone) that allows a computer to make the VOIP call; or

3)  by using a stand-alone VOIP phone that connects directly to the IP network using technologies such as the Wi-Fi or the Ethernet.

    

Figure 1.  VOIP phones look just like ordinary phones

            

Benefits offered by VOIP technology include the following:

-  lower operational and infrastructure costs, since both voice and data can be sent over the internet;

-  unification of communications services under a single system that delivers phone calls, faxes, voice and standard email, video conferences, etc.;

-  free special telephony features such as conference calling, call forwarding, caller ID;

-  lower subscriber costs because fees are based on the amount of information sent, not on the time of connection;

-  ease of implementing security for VOIP calls;

-  ease of adding more phone lines using the same connection;

-  wide availability, since it can be used in any place that has an internet connection. 

  

Challenges that still face VOIP technology include:

- vulnerability of the VOIP system to unreliable internet connections;

- vulnerability to internet traffic congestion, which can result in packet loss or delay;

- dependence on the user's main power lines, so the VOIP system can also go down during a power outage;

- difficulty in identifying the actual physical location of a caller, which may pose some problems during emergency calls;

- lack of redundancy,  which may mean that the VOIP service may fail if a failure somewhere in the internet infrastructure occurs.

     

    

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