Intro and Scenario
Some months ago, Microsoft added to its Office 365/Skype Online offer Cloud PBX with PSTN calling (Public Switched Telephone Network is the aggregate of the world's circuit-switched telephone networks).
Cloud PBX gives the capability to connect Skype for Business (S4B) Online users to the PSTN with no existing on-premises deployment.
Your telco, in such a scenario, could be Microsoft itself but this kind of solution involves some interesting downsides.
Microsoft should be able to offer phone numbers in many different countries that have dissimilar regulations and that will have different carriers and providers, each one trying to offer something more interesting than competitors.
The alternative to the aforementioned scenario (and a more down-to-earth solution) is having all Skype for Business workload in the Cloud with minimum footprint on-premises, just to connect S4B users to local PSTN services (using SIP or ISDN).
This is what Microsoft calls Skype for Business Cloud Connector Edition (previously, you may have heard names like MinTop or Minimal Topology).
While I will not deep dive the specifications of this solution, the implications it has must be understood from any customer that is evaluating a Cloud based VOIP system like this one
CCE is a downloadable package from Microsoft. Inside the package, you will have four virtual machines running on Hyper-V that you will have to deploy in your DMZ.
As you can see in the following schema (from the TechNet post Plan for Skype for Business Cloud Connector Edition ( https://technet.microsoft.com/en-us/library/mt605227.aspx) CCE acts as a bridge between your local telco provider and the Microsoft Cloud.
Deploying more than a single CCE on a site will add resiliency and increase the number of supported calls.
Note that, in this kind of scenario, you have purchase PSTN conferencing from Microsoft or from audio conferencing provider (ACP) partner if you want to add dial-in conferencing.
In addition, from a security point of view, the Directory Services inside the CCE have no communication with your production Domain Controllers.
Is CCE useful for My Company?
In the TechNet post Plan your Cloud PBX solution in Skype for Business 2015 or Lync Server 2013 ( https://technet.microsoft.com/en-us/library/mt612869.aspx) Microsoft offers an interesting "block diagram” to help customers selecting the right solution.
CCE is seen as something fit for greenfield deployments, while existing Skype for Business infrastructures are suitable to work with Cloud PBX directly.
Vendors like Audiocodes are already offering support to the CCE onboard of their Gateways and Session Border Controllers (SBCs).
That is interesting because to talk with the local PSTN you usually already have the requirement for a gateway/SBC.
Therefore, CCE will probably add small or no cost to what you already had to spend anyway.
CCE is an interesting proposal to realize an hybrid voice deployment (Cloud services and local telco) with little effort.
Removing the Skype for Business (on-premises) deployment from the requirements to use Cloud PBX with PSTN calling simplifies the whole process of moving Enterprise Voice (VOIP) to the Cloud.
Having CCE integrated with gateways is another help in making the aforementioned Cloud adoption straightforward.