Planning Multi-Forest Environments for Hybrid Skype for Business deployments

NADIR KHAN, isn't this covered here?

When Skype for Business Server is deployed in one forest (a resource forest) but provides functionality to users in one or more other forests (account forests), users in other forests must be represented as disabled user objects in the forest where Skype for Business Server is deployed. An identity management product, such as Microsoft Identity Manager, needs to be deployed and configured to provision and synchronize the users from the account forests into the forest where Skype for Business Server is deployed. Users must be synchronized into the forest hosting Skype for Business server as disabled user objects. They cannot be synchronized as Active Directory contact objects, because Azure Active Directory Connect will not properly sync contacts into Azure AD for use with Skype.
Regardless of any multi-forest configuration, the forest hosting Skype for Business server can also provide functionality for any enabled users that exist in the same forest.