Skype for Business Server requirements for Cloud P...

Cloud PBX with on-premises PSTN connectivity allows companies to leverage their existing Skype for Business Server infrastructure to home users in Skype for Business Online while using their local PSTN breakout.

Recently we received several questions around the requirements for Skype for Business Server versions. While this is documented on TechNet in Prerequisites for using Cloud PBX with on-premises PSTN connectivity, we want to use this article to highlight the requirements regarding server versions. Other requirements are not discussed in this blog article but can be found in the same TechNet article.

Please note that this blog article is specific to leverage Cloud PBX with on-premises PSTN connectivity. If you want to enable “just” hybrid without Cloud PBX, the requirements are not as strict. See TechNet Plan hybrid connectivity between Skype for Business Server and Skype for Business Online for more details.


  • The Federation Edge Server pool is the Edge Server pool that is used for your Federation signaling traffic. Even if you don’t have a Federations with other companies, this Edge Server pool is used for the signaling between your on-premises environment and Skype for Business Online. This Edge Server pool must run Skype for Business Server 2015.
  • Skype for Business Server 2015 must run at least the March 2016 update – of course we always recommend to deploy the latest updates.
  • Other Edge Server pools in your environment can run either Lync Server 2013 or Skype for Business Server 2015.
  • The next hop Front End pool of you Federation Edge pool must run Skype for Business Server 2015.
  • Other Front End pools in your environment can run Lync Server 2013 or Skype for Business 2015.
  • You cannot have any Lync Server 2010 or older in your environment.

So, what should I do if I have…

  • Lync Server 2010: upgrade your complete environment to Skype for Business Server 2015.
  • Lync Server 2013: upgrade your Federation Edge pool and the next hop Front End pool to Skype for Business Server 2015.
  • Skype for Business 2015: nothing, you are ready to go (if you have the minimum required hotfix – see above). 😊

Call to action

  1. Check if your environment meets the requirements for Cloud PBX with on-premises PSTN connectivity.
  2. If you must upgrade (parts of) your environment, watch the following readiness session: Upgrading Server.
  3. If you have not established hybrid yet, watch the following readiness session: Hybrid Configuration.
  4. To learn more about Cloud PBX in general and Cloud PBX with PSTN connectivity, watch the following two sessions: Cloud PBX introduction and Cloud PBX with on premises PSTN connectivity.
  5. If you have any questions or comments, please discuss with us in our community!


Regular Visitor

There is no specific mention of the Mediation Server requirements. I'm assuming that these are included in the line;

- Other Front End pools in your environment can run Lync Server 2013 or Skype for Business 2015

Just seeking confirmation as these play a crucial role in providing the on-premises PSTN connectivity capability.

Thank you!


@Andy Smith, you are correct: Mediation Servers can be Lync Server 2013 or Skype for Business Server 2015.

Regular Visitor

If i'm understanding this correctly, the only hard requirement for specific on prem roles being SfB 2015, is the Federation Edge and the next hop F/E pool as used by the Federation Edge.


So, if the above is true, my assumption is that what we're really talking about here is that the signalling traffic between on prem users and SfB Online must specifically route through SfB 2015 servers.


Media however can traverse Lync 2013 servers (Edge or Mediation), right?


This is important as if this is correct, one can simpy deploy a SfB Edge and SfB F/E pool into an existing on prem topology and use this as the Federation route. The new SfB pool does not even need to host any users or even have any conferencing or mediation workloads deployed.


Voice Routing policies will be configured and leverage PSTN Usgae records that direct calls to existing gateways/mediation servers (can be Lync 2013).


Really appreciate any confirmation you can provide that my understanding is correct (or not!). 


@Andy Smith You are correct, only the Federation Edge and its next hop server need to be Skype for Business Server 2015 (on the minimum required CU); other servers can run Lync Servre 2013 -- this includes Mediation Servers, other pools and other Edge Servers (so media might flow via Lync Server 2013).

Occasional Visitor

Can you confirm that one must eliminate Lync 2010 completely from the topology in order to deploy Hybrid Voice? I had in mind deploying separate Skype for Business 2015 edge, front-end and mediation pools to facilitate Hybrid Voice within a topology that also includes Lync 2010 pools. All telephony resources would be connected to Skype 2015 servers. No Lync 2010 users would be enabled for Enterprise Voice. All telephony users would be homed in the cloud. Are you telling me I have to upgrade those Lync 2010 pools to Lync 2013?




@Gregory Williams Cloud PBX with on-premises PSTN connectitivy has not been tested with Lync Server 2010. 

Occasional Visitor

@Thomas Binder Thanks for the quick response.


Do I understand correctly that the scenario I described hasn't been specifically tested, but you aren't aware of any reason it shouldn't work?


Thanks again.


@Gregory Williams, I'm are not aware of any isues. However at the same time, since this is a non-supported combination, I'm not aware of anyone who has tried it. The solution was not designed, build or tested with interoperability with Lync Server 2010 in mind. If you run into any issues in your environment that could be connected to this unsuppoted configuration, support would not even know if this combination is supposed to work -- and you might have to move to a fully supported architecture for troubleshooting your issue. Future hotfixes/changes/improvements will be build without considering Lync Server 2010. Ultimately, since this is an unsupported configuration, no other customers are (or should) run this configuration. As you can see, there is a lot of risk invovled.