Before that you need to understand the delivery scheduling process.
For example customer requested date is 15.04 2014
Order is created today i.e 28.03.2014.
Here system always does backward scheduling first. If the backward scheduling failed then system does forward scheduling. Backward scheduling failed if the material availability date is going beyond the order creation date. then in that case system does forward scheduling.
Backward scheduling does based on the customer requested date and forward scheduling does based on the order creation date.
when system does forward scheduling it will get two scheduling date in the schedule line tab.
Suppose Pick/Pack time is 1
Loading date is 1
transit time is 1
transportation time is 1
Here system will do the backward scheduling first for calculating the customer requested date
Delivery date minus transit time (Route) = Goods issue date
Goods issue date minus loading time (shipping point) = Loading date
Loading date minus transportation lead time (Route )= Transportation Planning date
Loading date minus pick/pack time (Shipping point) = Material availability date
here material availability date is 12.04.2014. on that date system will check whether material is available or not. If yes, then system will confirmed the quantity. If not then system will again do forward scheduling.
Suppose material available date is 13.04.2014 then system will add the all the above date to material availability date to calculate the actual customer delivery date
So here the customer requested date is 16.04.2014
Transportation lead time & pick/pack run parallely. system will consider the highest between both.