BRI back-to-back is not possible, you'll need an ISDN simulator in between the 801s.
The adapter appears to be an NT1 that is required to make a S/T interface to U interface.
Just FYI, PRI back-to-back is possible. Simply configure "isdn protocol-emulate network" on one side's D channel and use "isdn protocol-emulate user" (the default) on the other side. Will need a T1 x-over cable.
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...