This is telephone systems. We’re talking about PBXs and telephones.
Now the first thing that we have to talk about when we are talking about telephone systems like Alcatel Systems is we have to talk about what goes on outside of your building. So we will get into the PBX that sits inside your building and the voicemail that sits inside your building, the telephones that sit inside the building, but the first thing to understand with conventional telephones is what goes on outside the building. How does that telephone call get to you or get to your building in the first place?
The first concept you have to understand is the PSTN. PSTN. This is called the Public Switched Telephone Network. So just like you have routers for the internet, the PSTN is basically like the internet for telephones. So this is how telephone calls get routed. So basically what happens on the Public Switched Telephone Network, PSTN, is you have things called central offices. So every area has a central office or a few central offices.
