If any organization wanting to leverage the enterprise grade PBX functionality offered by Skype for Business, must deploy the on premise environment hybrid mode with O365 solution, Skype for Business Server.So that users Homed in On-Premise SFB can leverage enterprise voice capabilities.
With Current release of CCE you will not required entire Skype for Business environment for PSTN Capability.
What is Skype for Business Cloud Connector Edition ( CCE)
Skype for Business Cloud Connector Edition is a package of virtual machines for deployment within an organization's infrastructure that enables public switched telephone network (PSTN) connections with Microsoft's Cloud PBX service.
"With Cloud Connector Edition, you deploy a set of packaged VMs that contain a minimal Skype for Business Server topology -- consisting of an Edge component, Mediation component, and a Central Management Store (CMS) role. You will also install a domain controller, which is required for the internal functioning of Cloud Connector. These services are configured for hybrid with your Office 365 tenant that includes Skype for Business Online services."
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