what are the exact requirements for Ipsec vpn over Adsl line by using Cisco Router Is it possible to fix 1701 adsl in the central and 837 at the branches

Hi , i am Abhijith Thulasidharan from Bahrain , Here there are not so big companies , but there are several small companies those having some small vpns and all .They are using some other companies ADSL Router and they dont have static Ip also , So t...