VOIP Blog: SIP 101 - Session Initiation Protocol Explained

« Broadvoice & Asterisk Exceeding my VOIP needs | Main | Random Thought on website hits and weather patterns »

July 29, 2005

SIP 101 - Session Initiation Protocol Explained

For all of us that use it but didn't understand exactly what it was doing... This is an excellent primer on SIP. Now if I could just get my hands on one of those SIP WiFi phones...

Session Initiation Protocol or SIP refers specifically to a language that various computers can communicate to one another in so that they can complete voice calls. It has become vitally important in recent years as it plays a central role in VoIP or Voice Over Internet Protocol. VoIP Is the rapidly growing technology which has millions of Americans throwing out their local and long-distance telephone bills and replacing them with free calls made over the internet.

While Session Initiation Protocol sounds like technobabble, it helps if you can imagine SIP as the common language that new generation operators use to complete calls over the internet. With SIP, however, the operators are no longer hundreds of people in a room somewhere connecting one call to another but simply your computer device connecting to the telephone or computer device of the person you want to talk to. The fact that there is no need for real operators, or even a central board to complete calls through, explains part of why SIP is so revolutionary.

SIP was intended to give ordinary callers like you and me all the familiar functions and features of what we expect from a phone call, such as a dial tone, a ringing sound, etc. So while all the communication from our end seemed exactly the same as before, SIP makes phone calls by communicating directly with the other person’s telephone device. Unlike traditional telephony, which was based on a cog and wheel approach in which the call you placed goes through a central location and then is routed to the person you are trying to call, SIP is based on internet protocol. This means that there is no need for a central cog to run calls through, but rather calls can be made directly from person to person.

The fact that the technology is based on internet protocol (IP) rather than a traditional cog and wheel also means that placing and receiving calls are no longer inhibited by location. To conceive of this more easily it is best to think of something like your e-mail. You can take your laptop and access your e-mail from your home, just as easily as you can plug that laptop into the internet at access your e-mail from anywhere. In the same way, you can plug your SIP phone into any access point in the internet and call a person who can be located anywhere in the world. Similarly you can receive phone calls from anywhere in the world no matter where you are, simply be plugging your SIP phone into the internet.

As you can probably imagine, this ability has some pretty remarkable applications. For companies or businessmen that work out of the office, moving your office phone number is as simple as picking up the phone and carrying it with you. There is nothing else to it. For those often staying in hotels for travel or business, this means always having the direct office line with you wherever and whenever you want. No need to forward calls or even to ever pay for long distance or hotel phone access again!

The SIP technology is already revolutionizing the way in which humans communicate. In recent years, literally millions of Americans have tossed aside their traditional land based phone lines and opted for the freedom and cheapness of VoIP. Empowered with SIP technology it is uniquely able to provide you with virtually free calling, anywhere in the world, anytime in the world, without having to forward calls, change your number, or rely on others to check important messages. It is truly a technology for the future of business as well as the future of communication.

Posted by Sean at July 29, 2005 08:14 AM