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Skype for Business Server 2019 Capacity Planning (Mediation Servers)

Skype for Business Server 2019 Capacity Planning (Mediation Servers)
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Mediation servers in S4B server 2015 supports between 1100 – 1500 users for Mediation server in the pool. Now S4B server 2019 that number is up to 2000 users per Mediation server. So in a Mediation pool that number has increased exponentially from the previous version; approx. 500 users per server now. When planning out deployments that require Mediation server roles such as Enterprise voice or Dial in conferencing, or connecting to your existing telephony equipment such as Avaya or Cisco (forgive me for not naming all the others).

Purpose of the Mediation Server

Before we start digging into the number crunching of the Mediation server role lets review what’s it is used for. Mediation servers translate signals between the Skype for Business’ Enterprise Voice infrastructure, and PSTN components such as Gateways, SBCs, and PBXs via a SIP trunk created in topology builder.


Components of the Mediation Server

1.Signal Translation: You must have a Mediation server for Enterprise Voice for signal translation and codecs translation from silk to G.711.

2.Call Routing: The server coordinates with your gateway of choice to route calls where they need to go. Peer-to-peer inside the network, out to a branch site, or out to a customer three states away on their cellphone.

3.Media Bypass: Not really a component, but a capability. Skype for Business admins can configure a call route to flow AROUND the Mediation Server! The call route would travel directly between a user’s device and a PSTN Gateway.  It can reduce la without traversing the Mediation Server. Media bypass improves call quality by reducing latency, unnecessary translation, possibility of packet loss, and the number of potential points of failure.

Number Crunching Time 

The following user profiles apply to the Mediation server and Enterprise Voice calls:

  • 60% of users are enabled for Enterprise Voice, and 60% of these users are enabled for PSTN calling.
  • Each of these users enabled for PSTN calling makes 4 PSTN calls during the busy hour. Each call duration is 3 minutes.
  • 65% of these PSTN voice calls use media bypass.

When you’re planning, be sure to take into account the media processing requirements for PSTN calls and A/V conferences that don’t support media bypass, as well as the processing needed to handle signaling interactions for the number of busy-hour calls that need to be supported.

This is one of the Server Roles for whom hardware quality matters. The higher the server’s processing capacity & available RAM, the more calls a Mediation Server can handle.

What does this tell us?

The Mediation server in Skype for Business server 2019 needs to be taken into consideration the concurrent call volume increase from the previous edition of Skype for Business 2015.   Increasing the concurrent calls to 500 is a significant increase for either inbound or outbound calls.  When planning for the quantity of Mediation servers the increased capacity should be a plus with regards to planning and the idea of possibly doing collocation or stand alone of the Mediation servers.

Note:  The Microsoft capacity numbers for Skype for Business server 2019 used 64 GB of memory for performance testing.   Servers with 32 GB of memory are supported for stand-alone Mediation servers.

Note:  To improve the performance of Mediation servers, you should enable receive-side scaling (RSS) on the network adapters on the Mediation servers.   RSS enables incoming packets to be handled in parallel by multiple processors on the server.

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