How to give author, editor, viewer permissions to room calendars?

On exchange server 2010, Exchange Management Console, mailbox > 'new mailbox' > 'room mailbox' > 'new user' 

On active directory, you will see the new room mailbox, disabled. Enable it. Create a password.

On EMC, 'distribution group' > 'new distribution group', create groups to be given (author, edit, review) permission to the new room mailbox.

Add users to each distribution group.

Log on any computer with the new room user. Open MS Outlook > new room mailbox calendar, grant each group permission to the new room mailbox calendar. (After a user is migrated to Office 365, we then can not add remote user to room calendars)

Room calendar management in Exchange email system

In Exchange Management Console, -
Create a Room Mailbox.
If the room does not have an owner, then we can right-click on the Room mailbox and select 'Manage Full Access Permission'. We can add users or user groups.

If the room has an owner, then it is of no use to change anything within 'Manage Full Access Permission'. We have to go to the owner's Outlook. In Calendar, we right-click on the Room, and select 'Change Sharing Permissions'. Add users or user groups, and change permissions.