Difference between VoIP and IPT
With decreasing costs for broadband technologies, people have begun using data networks to make and receive voice calls. Two terms associated with this relatively new phenomenon are Voice over Internet Protocol (VoIP) and Internet Protocol Telephony (IPT or IP telephony). Though many of the differences between the two terms are semantic, there are some key differences between certain implementation of Internet-based phone calls.
Put simply, VoIP is a component of IP Telephony. IP telephony solutions look to provide the exact same services as a public switch telephone network (PSTN) or internal business telephone network, using internet technologies instead of traditional analog lines. This transition often requires the use of a PSTN line, both to facilitate the use of traditional telephone numbers and to provide the technology a «gateway» through which it can call non IP-based phones. However, when two IP-enabled phones communicate through these networks, there is little or no reason to involve tradition telephone networks. This IP-to-IP communication is often referred to a VoIP.
Many services labeled as VoIP do not actually serve as complete replacement for a telephone line. One of the biggest difference for this is 911 service. Without a local switch programmed to refer to the nearest 911 call center, services like Skype fail to provide a complete telephone replacement solution, even though they can dial other number directly. Many IP Telephony systems, particularly in the business class, will reach a local emergency operator when dialing 911.
Implementing a VoIP or IPT systems can vary greatly in cost and usefulness. Skype, for example, requires little more than a free download on a PC with working speakers and a microphone. Skype users can buy additional compatible equipment to then make the experience more phone-like, and must pay money to call traditional phone numbers. Users can even pay an annual fee to have their Skype username accessible as a regular telephone number. On the higher end, Cisco Systems Unified Communications can cost thousands of dollars in backend equipment alone. Individual handsets can cost over $400, in addition to the PSTN circuit which must be leased in order to gain access to 911 services and a VoIP «gateway» must be purchased in order to convert IP voice packets for travel on a PSTN. Though the terms are used interchangeably, more expensive systems are often referred to as an IP Telephony, while individual solutions like Skype are typically referred to as VoIP.
Advantages of VoIP
With the high cost of IP telephony services, you might wonder why anyone chooses these systems over simpler VoIP or traditional lines. One of the great benefits, however, is the avoidance of long distance charges. While PSTN long distance lines view each connected call as a billable item, broadband providers only require you pay a fixed fee for general internet traffic. Whether you make 20 minutes or 20 hours of long distance calls in a month, the general cost will remain the same on a VoIP or IP system. Furthermore, the calling process can be greatly simplified. Calling a Skype user, for example, places the call with a username instead of a fixed location. Whether the Skype user or number you are calling has is in the U.S. or China, you call will be connected transparently to that person.