T1 is 1.544 mbps, while E1 is 2.048 mbps. Which country/continent are you planning to implement this solution. T1 is used in the US, while E1 is used in Europe and Asia.
A 1720 would suit you just fine with two modular slots cable of taking a WIC-1DSU-T1 on each slot. The router also has one fast ethernet (10/100) port on board. This will work fine only for a T1 solution.
If you are looking for E1,you will need a 1721 which has support for VWIC-1MFT-E1 which can be used for voice and data E1 circuits.
Are you sure you have a 2569 ? I can find no reference of a 2569 model. If you have E1 interfaces on both routers you can go the E1 route. If you do not have E1 interfaces you can use synchronous X.21 interfaces and order a nx64k style service from BT or the likes.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...