SQL Server database backup on Remote site We have 4 different sites and each site has a SQL Server.

Our requirement is to have a SQL Server backup or database (Mdf files) of site 1, 2, 3 in site 4.

In case of disaster on any of the site  we need most recent database of the site.

each of the site is connected in network with very limited bandwidth.
As the database size is more it is not possible to take complete backup every time.

For the above scenario can any one suggest me a better solution?
You can use Deltacopy http://www.aboutmyip.com/AboutMyXApp/DeltaCopy.jsp it's a rsync solution for Windows, it can be used to sync files or folder between servers.