Hi

You can T1 getting connected onto your router and have a isdn backup link for redundancy purpose.

The above setup can be used out in remote/branch office and in your main/central office you can make use of dual T1's or multiple T1's based on the concurrent bandwidth usage from the remote locations..

You need to analyze and monitor the scenario first and need to work out the bandwidth capacity..

Based on your analysis you can decide on the redundant bandwidth requirements.

Also you need to make sure that your equipments in both the remote as well as at the central site supports the required bandwidth as well as the cards/modules...

regds