.. _availablity:

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TMC MCCS Leaf Nodes Availability
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1. TMC identifies and acts based on subsystem responsiveness.

2. To determine if a subsystem is responsive, TMC reads the state of subsystem devices from their respective Leaf Nodes.

   a. TMC calls the **state()** method on the Tango device proxy to check the device's current state.

      i. This is a network operation.

      ii. The operation will fail if the device is unreachable.

3. TMC uses this mechanism to collect responsiveness information of an MCCS Subarray/MCCS Master.

   a. The result is stored in the **isSubsystemAvailable** attribute of the TMC MCCS Leaf Node.

      i. **True** if the subsystem is reachable.

      ii. **False** if the subsystem is not reachable.