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+Requirements from other Projects
+.. <Malla> This scenario could be out of scope in Escalator project, but
+ having the option to support this should be better to align with
+ Doctor requirements.
+The scope of Doctor project also covers maintenance scenario in which
+1. The VIM administrator requests host maintenance to VIM.
+2. VIM will notify it to consumer such as VNFM to trigger application level
+ migration or switching active-standby nodes.
+3. VIM waits response from the consumer for a short while.
+- VIM should send out notification of VM migration to consumer (VNFM)
+ as abstracted message like "maintenance".
+- VIM could wait VM migration until it receives "VM ready to
+ maintenance" message from the owner (VNFM)
+- Escalator upgrade one site should at least not lead to the other site
+ API token validation failed.