Telecom and VoIP for non-specialists. Part 1.

Hello to all!
One of mine friends suggests me to start a series of articles about telecom, PBXes and other stuff I work with. For a non-telecom boys and girls. So, why not?

And I’d like to start with a disclaimer. All you will read here is not «last and final truth». It’s just mine point of view on things I work with. I work mostly with SMB market, so if you come and ask something about large distributed call-centres with tons of queues and agents, and reports… I know basics of telecom and using this knowledge I can answer how to build this. But honestly - I like to be more close to ground. Reason - you speak to people more, than to machines. And all this «bloody enterprise» things make me feel like a hamster in a ball. Endless reports, numbers, conversions… Boring. Much more interesting to work with SMB. And easier, of course. And - no possible to work for something really heavy all alone. That’s may be the real reason. So, back to disclaimer, all here is my own opinion. Can be right, can be wrong, but based on experience. If you think I’m wrong somewhere - you’re welcome to comments :) Also, english - is not my native, so there would be errors, but hope, everybody can catch main idea.

Let’s start than with little dive-in.
History of telecom starts earlier, than history of computers and IT. And for many years computers and telecom industry was close, but really not the same, like nowadays. They have separate standards, separate networks, different ideology.
And ok, let’s narrow a bit our field of view and talk about PBX’es. What PBX is? Normally you see a phone on your work desk or home. You know, if you dial a number, you can talk to person you’ve dialed. But how your phone is connected to other’s? It’s done via PBX.
First PBX’es was actually alive girls who manually switches wires from one jack to another. Actually, «jack» connector is from these times. Later girls were replaced by electrical mechanics. If you are old enough or live in some god’s forgotten place with telephone, you can remember disk phones or when you push buttons on your phones, you can hear «ticks» depends on digit dialed. That is actually commands to PBX mechanism.
Next big era is fully digital. You may heard ISDN abbreviation. That’s it. Still alive and well. But, modern system use 10-20% of this standard. ISDN was designed not only a voice carrying network, but data also. But, for data it was really expensive and data was moved to other networks. That’s why sometimes ISDN is decoded as It Still Does Nothing ;)

That’s it for now. Muse had left me. In next part we will talk about nowadays.