When syncronized OST file by default

Hi,

I saw the below MS article regarding .OST syncronization.

http://office.microsoft.com/en-in/outlook-help/introduction-to-outlook-data-files-pst-and-ost-HA010354876.aspx

They mentioned that You’ll not be aware of these changes on the server until you synchronize.

But I did not see when .ost syncronized and method (diffarencial or incrimental update) 

My enviroment is below:

We have network connection.

Run Outlook as cahced mode.

In this case, I would like to know the syncronization process for .OST

For example .OAB file syncronized every 24 horus, but how about .OST?

Could someone any idea?