SIP - Finding Common Ground
The Spread of VoIP
The world of communications is on a threshold. The Plain Old Telephone System (POTS) which has dominated global connectivity for so long is slowly giving way to the future - VoIP. By allowing users to place calls over the Internet with low bandwidth requirements, it's a technology whose time has come, and not much can be done about it.
According to Metcalfe's law, the value of a communication network increases proportionately to the square of the users. Each new convert to VoIP therefore, grows the value of the system as a whole. Unfortunately, though VoIP is spreading worldwide, for a long time, there were conflicting standards of implementation - one of the banes of new technologies.
Then came along the SIP protocol crafted by the Internet Engineering Task Force (IETF) which aimed to allow developers the freedom to create their own system with their own protocols under an umbrella signalling protocol. And suddenly a few years down the line, SIP is probably the most used protocol and its numbers are growing rapidly.
So far though, there hasn't been a consistent and easy way for people using VoIP to connect to others using VoIP even if the protocol is the same. The reason is the traditional PSTN system which has been both an enabler and a hindrance to the adoption of VoIP. It's an enabler because it allowed VoIP users to communicate with the rest of the world. Without that functionality and interoperability, VoIP's usefulness goes down drastically.
It's been a hindrance because people have now become used to dialing numbers to contact people even when they need to make a VoIP to VoIP call. Unfortunately this has locked people into the PSTN system since there's no easy way to tell if a particular number is linked to a VoIP account or a regular phone. Each and every VoIP call to a number outside the provider's own network has to drop down to the PSTN system for resolution thereby incurring costs and degrading the quality of the VoIP experience. This is true even with mobile hosted phone systems.
SIP and the number directory
One solution to the problem of the phone call dropping down to the PSTN network each time is to have a central registry where each VoIP linked number is referenced along with its "SIP address." The system isn't perfected yet and there are still issues such as who will host the registry etc. in addition to the telcos fighting it tooth and nail because it threatens the very survival of their business.
But it's only a matter of time before this happens and SIP will be able to claim its role as being pivotal in the widespread adoption of VoIP and PBX Hosted Phone Systems.