I have a Cisco 3640 core router at headquarters linked to 18 remote sites via point-to-point. The core router is linked to the service provider via ATM and linked to each remote site via point-to-point T1s. One of the remote sites has a Cisco 1751 and is linked to the core router via Frame Relay T1. This particular site keeps dropping the link and I am not sure how to troubleshoot this issue or where to start. The only fact I have is that this site's circuit keeps dropping! Could someone guide as what I should be looking for or what steps to take in order to troubleshoot this issue?