| IP Telephony is the transport of phone calls through | | | | improved to a great extent, and a vast number of |
| the Internet. IP Telephony services are available | | | | users are opting for VoIP based telephone systems. |
| between computers and telephones. PC-to-PC is | | | | IP telephony applications require firewalls to pass their |
| suitable for users who already have Internet access | | | | Real Time Transport Protocol (RTP) streams. SIP |
| and an audio-equipped computer. Software is available | | | | technology has a better mechanism to tackle this |
| for free. Integration with Internet services such as | | | | problem. SIP server can act as a registrar, proxy or |
| instant messaging and e-mail are provided. PC to | | | | redirect server. It features an application-server |
| telephone uses a gateway for call conversion from | | | | interface, presence support, SMS gateway, simplified |
| digital to analog and analog to digital. | | | | accounting and authorization and server status |
| Telephone-to-telephone requires two gateways, | | | | monitoring. Linux based SIP software supports |
| GSTN-to-Internet, and Internet-to-GSTN. IP Telephony | | | | numerous codes and phonebook. |
| services are either network-centric or | | | | The traditional telecommunication operators have been |
| end-system-centric. Mobility features are included in IP | | | | providing special call services using their existing |
| Telephony. IP Telephony services use either VoIP or | | | | infrastructure that has been accomplished with |
| SIP based services. VoIP systems are more popular, | | | | Intelligent networking architecture. In IP Telephony, |
| and their applications are generally used with a simple | | | | router congestion is the main hindering factor, because |
| microphone and computer speakers. However, IP | | | | the audio quality is not on par with PSTN services. |
| telephones or VoIP boxes can also be used. In recent | | | | Quality wise, IP Telephony services are yet to match |
| years, the quality and reliability of VoIP technology has | | | | their PSTN counterparts. |