In any of the groups containing the FAS in the 8, 34 and 140 Mbit/s frames, alarm bits and spare bits are also to be found. These are known as service bits. The A bits (alarm) carry an alarm indication to the remote multiplexing device when certain breakdown conditions are detected in the near end device. The spare bits are designed for national use and must be set to "1" in digital paths that cross international boundaries.