How does SIP work and what is its use in VOIP?
Do I have to have it or can I use a direct plug-in to the computer to use VOIP?
How does SIP work and what is its use in VOIP?
Do I have to have it or can I use a direct plug-in to the computer to use VOIP?
Right, SIP is an application protocol that runs on top of TCP.
There are many different ways to transfer voice over TCP/IP, however SIP is probably the most used and understood in the industry with the maximum compatibility.
If you just want to make calls from your computer, many come with the phone dialer application (not sure if it is included any more in Vista/7), but you should be able to find one online. This uses a standard modem and had nothing to do wit SIP, it is purely POTS (Plane old telephone system).
As Wil said, SIP is an application layer protocol. SIP is used as signaling protocol in VoIP, ie to manage sessions(voice, video or file transfer) between participants. The actual media is transported using different protocols based on the need, voice packets are transferred as RTP once the SIP signalling is successfully done.
A SIP trunk is a direct connection between your organization and an Internet telephony service provider. SIP trunk enables you to extend VoIP telephony beyond your organization’s firewall without the need for an IP-PSTN gateway. This simpler configuration is easier and less expensive to design, operate, maintain, and upgrade. Here is a suggested [blog]: http://www.dovecommunications.com/modern-voip-features-explained-sip-trunking/ where you can read in more details about SIP trunking.
Try http://gizmo5.com which is a VOIP client that suports SIP-based internet calling. You would be able to make calls through your PC with a headset.