I have Cisco 4000 in my office and I have Cisco 4500 at our colo. I have tested the configuration back-to-back using DTE and DCE cables and the Cisco's seems to be working fine. They also work fine with having the 2 Larscom Split-T CSU back-to back. But when I put the Larscom Split-T csu on either ends of the T1 loop it doesn't work. I once thought that there is something to do with the clock of the loop. Then I have also tested having Normal Clock at one end and Inverse clock on the other, then too it doesn't work.
Please advice what else can be done to solve this problem.