Carrier drops can because of many reasons. Modem at rouer lost the Carrier signal because of client modem carrier dropped. This disconnect reason can occur during call setup and data mode.
Carrier lost condition can also occur during normal data mode when the client abruptly drops carrier. The common cause is a non-negotiated or dirty disconnect on the part of the client modem. This can occur if the link is abruptly dropped (that is, network error), the client modem's power is shut off to disconnect the call. This can also occur with cheaper client modems that do not implement the Layer I and/or Layer II clear-down protocols on a DTR drop. For a large number of client modems, this is considered a normal disconnection.
To really troubleshoot what exactly had happened for the call, we need to know the disconnect code that digital modem (if you have it on router/NAS) generates for disconnect. So what kind of modems you have on a router?
