| The History of Traditional PSTN | | | | enough to keep up with the new technologies and |
| The traditional PSTN (Public Switched Telephone | | | | customer requirements. Here are some simple |
| Network) has been continuously improving since | | | | explanations. |
| its inception by Alexander Bell. There are valid | | | | 1. Data traffic has overtaken voice traffic. The |
| reasons why PSTN exists in its current state. | | | | current status is: data traffic is actually running on |
| What is Ring-Down | | | | top of networks that were built for voice. |
| At first, Bell developed a ring-down circuit, which | | | | However, data traffic has its own characteristics |
| means no dialing of numbers. Instead, a physical | | | | which makes it simply not efficient running on top |
| wire connected two phone devices. You simply | | | | of a voice network. |
| pick up the phone and the other person is on the | | | | The industry trend is to build networks with a |
| other end directly and there was no ringing at all. | | | | data-centric approach. Then all traffics including |
| Basically this structure fell flat when more and | | | | data, voice and video can all run on this network. |
| more users joined the network. Since based on | | | | 2. PSTN is not capable of keeping up with |
| this concept, you will need a wire between any | | | | customers' new demands. PSTN was designed as |
| two person who wants to have a phone call. With | | | | a one-company show. Only vendors of the PSTN |
| more customers joining in, this became a messed | | | | equipment can develop applications for that |
| up mesh network which was very costly and | | | | equipment. With modern ever changing demands, |
| impossible to construct and manage. | | | | it is simply impossible for any one company to |
| The Inception of Switch | | | | meet all the needs of all the customers. A more |
| That was the time when the concept of a switch | | | | open infrastructure which allows many vendors to |
| came to play. Each user only needed one cable to | | | | provide applications is required. |
| connect to the central office switch, the switch | | | | 3. Current PSTN cannot support Data, Video and |
| can then connect the user to any other users. | | | | Voice altogether. In the backbone of PSTN, the |
| Initially, the switch was manually operated by a | | | | convergence of data, voice and video is has been |
| telephone operator. The operator connected the | | | | happening for fairly long time. However, it still |
| caller to whoever he wanted to call by manually | | | | takes some time to make it to all the homes. |
| connecting the voice path. | | | | With high speed broadband access, such as DSL, |
| Later, the manual labor switch was replaced by | | | | cable or wireless, the convergence of data, video |
| electronic switches which was much faster and | | | | and voice to the home is finally happening. |
| had much more capacity. | | | | 4. PSTN was simply not designed for carrying |
| Limitations of PSTN | | | | data traffic. Because the bearer channels, call |
| PSTN has actually done a pretty job: switching | | | | control and service logic are tightly bound in one |
| voice calls, that is, until now. With more data | | | | closed platform, it is not possible to make minor |
| traffic than voice traffic on the network, the | | | | changes that might improve audio quality. |
| traditional PSTN network just is not flexible | | | | |