-5. The Consumer switches to standby configuration (STBY)
-6. Instructions from Consumer to VIM requesting certain actions to be performed
- (step 6a). After receiving such instructions, the VIM executes the requested
- action in order to empty the physical resources (step 6b) and informs the
- Consumer is about the result of the actions. Note: this step is out of scope
- of Doctor.
-7. Maintenance response from VIM to inform the Administrator that the physical
- machines have been emptied (or the operation resulted in an error state).
-8. The Administrator is coordinating and executing the maintenance
- operation/work on the NFVI. Note: this step is out of scope of Doctor.
+4. Maintenance policies are enforced in the VIM, e.g. affected VM(s) are shut down
+ on the physical server(s), or affected Consumer(s) are notified about the planned
+ maintenance operation (steps 4a/4b).
+
+
+Once the affected Consumer(s) have been notified, they take specific actions (e.g. switch to standby
+(STBY) configuration, request to terminate the virtual resource(s)) to allow the maintenance
+action to be executed. After the physical resources have been emptied, the VIM puts the physical
+resources in "in-maintenance" state and sends a MaintenanceResponse back to the Administrator.
+
+.. figure:: images/figure5b.png
+ :name: figure5b
+ :width: 100%
+
+ Successful NFVI maintenance
+
+The high level message flow for a successful NFVI maintenance is show in :numref:`figure5b`.
+It consists of the following steps:
+
+5. The Consumer C3 switches to standby configuration (STBY).
+6. Instructions from Consumers C2/C3 are shared to VIM requesting certain actions to be performed
+ (steps 6a, 6b). After receiving such instructions, the VIM executes the requested
+ action in order to empty the physical resources (step 6c) and informs the
+ Consumer about the result of the actions (steps 6d, 6e).
+7. The VIM switches the physical resources to "in-maintenance" state
+8. Maintenance response is sent from VIM to inform the Administrator that the physical
+ servers have been emptied.
+9. The Administrator is coordinating and executing the maintenance
+ operation/work on the NFVI. Note: this step is out of scope of Doctor project.
+
+The requested actions to empty the physical resources may not be successful (e.g. migration fails
+or takes too long) and in such a case, the VIM puts the physical resources back to 'enabled' and
+informs the Administrator about the problem.
+
+.. figure:: images/figure5c.png
+ :name: figure5c
+ :width: 100%
+
+ Example of failed NFVI maintenance
+
+An example of a high level message flow to cover the failed NFVI maintenance case is
+shown in :numref:`figure5c`.
+It consists of the following steps:
+
+5. The Consumer C3 switches to standby configuration (STDBY).
+6. Instructions from Consumers C2/C3 are shared to VIM requesting certain actions to be performed (steps 6a, 6b).
+ The VIM executes the requested actions and sends back a NACK to consumer C2 (step 6d) as the
+ migration of the virtual resource(s) is not completed by the given timeout.
+7. The VIM switches the physical resources to "enabled" state.
+8. MaintenanceResponse is sent from VIM to inform the Administrator that the maintenance action cannot start.
+