When it comes to telephone systems, it’s important to understand what happens outside of your building. While PBX and other devices sit inside your building, you need to know how the telephone call actually gets to you. This is where the PSTN, or public switched telephone network, comes in.
The PSTN is like the internet for telephones. It’s the network that routes telephone calls. Every area has one or more central offices, which are responsible for every house that has a telephone line. The wire in your wall goes to the D mark point in the back of your house and then all the way back to the central office.
The PSTN is the network of these central offices. When you make a call, the North American dialing plan comes into play. This plan is like a routing protocol for the telephone system. The system looks at the telephone number and routes the call based on the area code and other factors.
While the PSTN is responsible for everything that happens on the network, the telephone company is only responsible for what happens up to the D mark point on your building. Anything on the building side of the D mark is your responsibility.
In summary, the PSTN is the backbone of the telephone system. All telephone lines lead back to a central office and the North American dialing plan routes calls across the network. It’s important to understand that the telephone company is only responsible for the network up to the D mark point on your building. Anything on the building side of the D mark is your responsibility.