Call center call routing

One of the call center that I was working with is HSBC call center.This a large call center with latest AVAYA technology,giving priority for customer service.
Before going in to details on contact centers let me get an example,a company like where I got my internship.When a customer call from out side he will hear a ring/music/beep then he will receive a welcome massage like "welcome to ABC company.If you know the extension dial now or wait for operator assistance".In there he can either wait or enter the ext he preferred to call.System will route the call to the given end point.This is a simple route pattern to begin.This roting pattern vary with the company complexity and its business.
To understand the call routing further let's take above example.For a PBX system we have to get number and a preallocated extension block from a service provider(SLT,LANKABELL,SUNTEL..).Let's say I got ext from suntel and lankabell:
Suntel - 4 472200 (200-299)
Lankabel- 5 472200 (200-299)
Direct invert dialing is given to last three digits.Take extension 222 as an example.So when customer wants to call to ext 222 he will dial 4472222 directly.Then the system match this to VDN(Vector Directory Number) after placing 1 before the ext.Calls coming to the trunk,we con figure a option in trunk whether to enter a digit or delete a digit.Always changes will be done to the start of the ext.Here we add 1 to the start od DID ext and create a VDN 1222.Each VDN carries a number of it's vector,measurability,COR,COS and other parameters.Measured parameter have 4 options int/ext/none/both.All of them are defining the source of reports.
For external call handling we need E1 cards.Let's take a example of 8 E1 card PBX system,4 E1 cards for the cal