Why is VoIP Replacing PSTN (Public Switched Telephone Network)? Fiber Optic Communication Tutorial

The History of Traditional PSTN

The traditional PSTN (Public Switched Telephone Network) has been continuously improving since its inception by Alexander Bell. There are valid reasons why PSTN exists in its current state.

What is Ring-Down

At first, Bell developed a ring-down circuit, which means no dialing of numbers. Instead, a physical wire connected two phone devices. You simply pick up the phone and the other person is on the other end directly and there was no ringing at all.

Basically this structure fell flat when more and more users joined the network. Since based on this concept, you will need a wire between any two person who wants to have a phone call. With more customers joining in, this became a messed up mesh network which was very costly and impossible to construct and manage.

The Inception of Switch

That was the time when the concept of a switch came to play. Each user only needed one cable to connect to the central office switch, the switch can then connect the user to any other users.

Initially, the switch was manually operated by a telephone operator. The operator connected the caller to whoever he wanted to call by manually connecting the voice path.

Later, the manual labor switch was replaced by electronic switches which was much faster and had much more capacity.

Limitations of PSTN

PSTN has actually done a pretty job: switching voice calls, that is, until now. With more data traffic than voice traffic on the network, the traditional PSTN network just is not flexible enough to keep up with the new technologies and customer requirements. Here are some simple explanations.

1. Data traffic has overtaken voice traffic. The current status is: data traffic is actually running on top of networks that were built for voice. However, data traffic has its own characteristics which makes it simply not efficient running on top of a voice network.

The industry trend is to build networks with a data-centric approach. Then all traffics including data, voice and video can all run on this network.

2. PSTN is not capable of keeping up with customers’ new demands. PSTN was designed as a one-company show. Only vendors of the PSTN equipment can develop applications for that equipment. With modern ever changing demands, it is simply impossible for any one company to meet all the needs of all the customers. A more open infrastructure which allows many vendors to provide applications is required.

3. Current PSTN cannot support Data, Video and Voice altogether. In the backbone of PSTN, the convergence of data, voice and video is has been happening for fairly long time. However, it still takes some time to make it to all the homes. With high speed broadband access, such as DSL, cable or wireless, the convergence of data, video and voice to the home is finally happening.

4. PSTN was simply not designed for carrying data traffic. Because the bearer channels, call control and service logic are tightly bound in one closed platform, it is not possible to make minor changes that might improve audio quality.