First, check the 'Network' log under maint. Alarm 75's and Evt 330-337 are typically phone company dropping you and then the DS1 syncing up again. If you catch it when it's first down, check the smart jack......that may tell you something ( phone company guy in SAC 2 blocks away tracing wires and yours happens to be loose, .....). Typically, you don't have to reboot the whole system, disabling and re-enabling the card in s/w (maint)is enough. Everything has a threshold and when the DTI card gets overwhelmed with errors, it won't auto-restore. While you may have a problem with on-site eq, keep this in mind: the phone company has 3x-15x the equipment that you do to go bad (repeaters, smartjack, DSX wiring, digital card, potentially miles of cable, Lightspan eq,......). Just check/replace all connections on your side of the smartjack.