IR/ISO - Significance of 'Item Identifier type' on : Customer>Standard>Order Management (TAB)

Hi,

I would like to know the significance of Item Identifier type on :  Customer>Standard>Order Management (TAB)

I am trying to import internal order with 'Item Identifier type" as 'Customer Item', but Order import program is failing. But, if setup 'Item Identifier type' as 'INTERNAL'

then order import is through & internal order is created.

Our requirement is that we want to import internal sales orders with 'ITEM IDENTIFIER TYPE' as "CUSTOMER ITEM'

I appreciate expert openions

Thanks & regards

Keshav Ingale