In case a customer has multiple sites in their on-premises deployment, and if they have deployed just one Skype for Business Server 2015 Edge server/pool, then Search traffic from all sites will go through the single available Edge server.The administrator needs to make sure the pools from all sites can access the deployed Skype for Business Server 2015 Edge server/pool.After you enable Skype Connectivity your Skype for Business users will be able to search for and add Skype users.Skype Directory Search traffic flows through Skype for Business Server Edge servers.In fact, they offer unlimited calls to over 50 countries.
Skype Premium also allows you to call mobile phones and landlines from all parts of the world.
Federation traffic goes through edge configured by the administrator.
For example, the administrator could choose to continue to send federation traffic through Lync Server 2013 Edge servers which would not support Skype Directory Search.
Skype Connectivity is also a feature of Skype for Business Online, which is part of Office 365.
You can enable the Skype Connectivity feature from the Skype for Business Administration Center within the Office 365 portal. If you want to control individual user access to Skype Connectivity, you can do so by editing individual users’ External Communications settings.