CloudPBX via on-premises PBX

Howdy Folks,

Some interesting functionality has come out of the new Microsoft Office 365 CloudPBX with on-premises PSTN Connectivity in Skype for Business Server 2015. On 7th October 2015 Microsoft rolled out CloudPBX with on-premises PSTN Connectivity in preview with global release.

I have one big concern at this moment in time–Media Bypass.  If Media Bypass is not used in situations where utilising Office 365 with an ExpressRoute, this will result in a trombone effect in the network.  This occurs when the data uses the same path for the outward and return journeys.

Update Nov 11, 2015 – This has confirmed that only the signalling will be passed through Office 365, all media traffic will go via on-premises mediation direct to the gateway.

What is not clear is whether or not the traffic from users will go to their Office 365 tenant or the media traffic will go directly to the required on-premises Skype for Business Pool.

Enterprise Voice feature Supported in Cloud PBX with on-premises PSTN Connectivity?
PSTN incoming and outgoing calls Yes
Call hold/retrieve Yes
Call transfer Yes
Call forwarding Yes
Voicemail Yes
USB peripherals Yes
Delegation (Boss/admin) Yes
Team call Yes
Outside voice: mobile Yes
Integration with on-premises PBX Yes
On-premises configurable dial plan Yes
Dial-out from ad-hoc meetings Yes
Skype for Business Phone Edition devices Yes
Phones Yes, for a list of supported devices see
Network QoS – DSCP Yes
Basic 911 Yes (information assigned to your trunk or PBX is reported to the public safety answering point (PSAP)).
Media bypass No
Response group service No
Call Park No
Voice resiliency No
Private line No
Analog and common area phones No
Integration with on-premises call centre solutions No
Call Via Work and Remote call control (RCC) No
E9-1-1 No


Microsoft’s phone hardware partners have already built some IP phones with support for the Cloud PBX with PSTN Calling feature. It’s currently supported in the following phones if they have updated firmware: Polycom CX600, CX3000 and VVX models, and HP 4120 phone. Microsoft has also promised that new phone support will be arriving “over the next several months.”



The On-Premises environment must be configured in as a Hybrid.  This means a functional Front End Pool either Enterprise or Standard,  Edge Server, and, what isn’t made clear on TechNet, a Revers Proxy configured per the standard Lync, Skype for Business configuration.

Server role Supported versions Notes
Front End Server Skype for Business Server 2015

Lync Server 2013

Lync Server 2010, with October 2012 cumulutive updates or later

The Front End pool must be configured as the next hop to the Edge Server
Edge Server Skype for Business Server 2015

Lync Server 2013

Mediation Server Skype for Business Server 2015

Lync Server 2013

Lync Server 2010, with October 2012 cumulutive updates or later



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