incoming call routing

[xth]

Hello everyone
I’m kind of a newbi about PBX (I hope that I ‘m in the right section of this forum). I m’ working on an PBX Avaya R013x.01.5.642.3
I’m trying to understand how does it work when an user call another user in the company or outside and what happen when someone is called from outside.
I found this schema

http://tech.yanatm.com/wp-content/uploads/2013/06/Call-Routing.png

and it’s really help me understand what happened when someone call someone else. But I have throuble figuring out what happened when you’re called.
Does it exist an ‘incoming call route’ or incoming call come from thrunk then goes directly on the diaplan ?
Could you point at me document where I can find this information or can you explain me ?
Another question is : if in you diaplan you haven’t any line which redirect to uniform-dial plan (udp in “call type) how does your udp table is used ? In another way I have a diplan with no redirection to udp table but my udp table is already configurated and running

 

[lopes1211]

The phone company normally sends digits (often the last 4 of the called number) along with the inbound call. If this matches an extension in your system.....that's where the call goes. If there is no match, it will query the UDP table. If still no matches, it will go to the "unassigned number" destination defined on page 1 of "change system features".

There are also incoming number tables for each trunk where you can change, add, or delete digits coming in on each trunk group. typically "change inc trunk X" where X is the trunk group number.

-CL

 

[xth]

Thanks a lot for your answer.
Could you explain me something ?
In my diaplan i have this line

Dialed Total Call
String Length Type
2 4 ext

And in my uniform diaplan i have
MatchingPattern Len Del Insert Digits Net Conv
2091 4 0 006 aar n

My question is: if digit 2XXX are ext in diaplan how can and this line my uniform diaplan table be use ?

As you can think i'm trying to understand how the phone system was configured in my company